Cisco Press Cisco OSPF Command and Configuration Handbook (CCIE Professional Development)

Cisco Press Cisco OSPF Command and Configuration Handbook (CCIE Professional Development)
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Table of Contents
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Index
Cisco® OSPF Command and Configuration Handbook (CCIE Professional Development)
By William R. Parkhurst Ph.D.
Publisher: Cisco Press
Pub Date: April 19, 2002
ISBN: 1-58705-071-4
Pages: 528
Slots: 2
As one of the most predominantly deployed Interior Gateway Protocols, Open Shortest Path First (OSPF) demands a wealth of knowledge on
the part of internetworking professionals working with it on a daily basis. Unfortunately, publicly available documentation on the OSPF
command set varies from being too thin on coverage to being too demanding on the required equipment needed to test what the
documentation covers.
Cisco OSPF Command and Configuration Handbook is a clear, concise, and complete source of documentation for all Cisco IOS(r) Software
OSPF commands. The way you use this book will depend on your objectives. If you are preparing for the CCIE written and lab exams, then
this book can be used as a laboratory guide to learn the purpose and proper use of every OSPF command. If you are a network designer,
then this book can be used as a ready reference for any OSPF command.
Cisco OSPF Command and Configuration Handbook provides example scenarios that demonstrate the proper use of every OSPF command
that can be implemented on a minimum number of routers. This will enable you to learn each command without requiring an extensive and
expensive lab configuration. The scenarios clearly present the purpose and use of each command. Some of the examples lead you into
common non-working situations in order to reinforce the understanding of the operation of the particular OSPF command.
This book is part of the Cisco CCIE Professional Development Series, which offers expert-level instruction on network design, deployment,
and support methodologies to help networking professionals manage complex networks and prepare for CCIE exams.
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Table of Contents
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Index
Cisco® OSPF Command and Configuration Handbook (CCIE Professional Development)
By William R. Parkhurst Ph.D.
Publisher: Cisco Press
Pub Date: April 19, 2002
ISBN: 1-58705-071-4
Pages: 528
Slots: 2
Copyright
About the Author
About the Technical Reviewers
Acknowledgments
Introduction
Recommended Reading
Icons Used in This Book
Command Syntax Conventions
Chapter 1. OSPF Process Configuration Commands
Section 1-1. router ospf process-id
Section 1-2. router ospf process-id vrf name
Chapter 2. OSPF Area Commands
Section 2-1. area area-id authentication
Section 2-2. area area-id authentication message-digest
Section 2-3. area area-id default-cost cost
Section 2-4. area area-id nssa
Section 2-5. area area-id nssa default-information-originate
Section 2-6. area area-id nssa no-redistribution
Section 2-7. area area-id nssa no-summary
Section 2-8. area area-id range ip-address mask
Section 2-9. area area-id range ip-address mask advertise
Section 2-10. area area-id range ip-address mask not-advertise
Section 2-11. area area-id stub
Section 2-12. area area-id stub no-summary
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Section 2-13. area transit-area-id virtual-link router-id
Section 2-14. area transit-area-id virtual-link router-id authentication authentication-key password
Section 2-15. area transit-area-id virtual-link router-id authentication message-digest
Section 2-16. area transit-area-id virtual-link router-id authentication null
Section 2-17. area transit-area-id virtual-link router-id authentication-key password
Section 2-18. area transit-area-id virtual-link router-id dead-interval seconds
Section 2-19. area transit-area-id virtual-link router-id hello-interval seconds
Section 2-20. area transit-area-id virtual-link router-id message-digest-key key-id md5 password
Section 2-21. area transit-area-id virtual-link router-id retransmit-interval seconds
Section 2-22. area transit-area-id virtual-link router-id transmit-delay seconds
Chapter 3. Auto Cost
Section 3-1. auto-cost reference-bandwidth bandwidth
Troubleshooting
Chapter 4. Default Route Generation
Section 4-1. default-information originate
Section 4-2. default-information originate always
Section 4-3. default-information originate metric cost
Section 4-4. default-information originate always metric cost
Section 4-5. default-information originate metric-type type
Section 4-6. default-information originate always metric-type type
Section 4-7. default-information originate route-map route-map-name
Chapter 5. Setting the Default Metric for Redistributed Protocols
Section 5-1. default-metric cost
Chapter 6. Administrative Distance
Section 6-1. distance administrative-distance
Section 6-2. distance administrative-distance source-ip-address source-ip-mask
Section 6-3. distance administrative-distance source-ip-address source-ip-mask access-list-number
Section 6-4. distance ospf external administrative-distance
Section 6-5. distance ospf inter-area administrative-distance
Section 6-6. distance ospf intra-area administrative-distance
Chapter 7. Filtering Routes with Distribute Lists
Section 7-1. distribute-list access-list-number in
Section 7-2. distribute-list access-list-number in interface-type interface-number
Section 7-3. distribute-list access-list-number out
Section 7-4. distribute-list access-list-number out interface-type interface-number
Section 7-5. distribute-list access-list-number out routing-process
Section 7-6. distribute-list access-list-name in
Section 7-7. distribute-list access-list-name in interface-type interface-number
Section 7-8. distribute-list access-list-name out
Section 7-9. distribute-list access-list-name out interface-type interface-number
Section 7-10. distribute-list access-list-name out routing-process
Section 7-11. distribute-list prefix prefix-list-name in
Section 7-12. distribute-list prefix prefix-list-name in interface-type interface-number
Section 7-13. distribute-list prefix prefix-list-name out
Section 7-14. distribute-list prefix prefix-list-name out interface-type interface-number
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Section 7-15. distribute-list prefix prefix-list-name out routing-process
Chapter 8. Handling of MOSPF LSAs
Section 8-1. ignore lsa mospf
Chapter 9. Logging OSPF Neighbor Changes
Section 9-1. log-adjacency-changes
Section 9-2. log adjacency-changes detail
Chapter 10. Multiple Path Configuration
Section 10-1. maximum-paths number-of-paths
Chapter 11. OSPF neighbor Commands
Section 11-1. neighbor ip-address
Section 11-2. neighbor ip-address cost cost
Section 11-3. neighbor ip-address database-filter all out
Section 11-4. neighbor ip-address poll-interval interval
Section 11-5. neighbor ip-address priority priority
Chapter 12. OSPF network Command
Section 12-1. network ip-address wild-card-mask area area-id
Chapter 13. Passive OSPF Interfaces
Section 13-1. passive-interface interface-name interface-number
Section 13-2. passive-interface default
Chapter 14. Route Redistribution
Section 14-1. redistribute routing-process process-id
Section 14-2. redistribute routing-process process-id metric ospf-metric
Section 14-3. redistribute routing-process process-id metric-type metric-type
Section 14-4. redistribute routing-process process-id subnets
Section 14-5. redistribute routing-process process-id tag tag-value
Section 14-6. redistribute routing-process process-id route-map route-map-name
Chapter 15. Controlling the OSPF Router ID
Section 15-1. router-id ip-address
Chapter 16. Summarizing External Routes
Section 16-1. summary-address ip-address mask
Section 16-2. summary-address ip-address mask not-advertise
Section 16-3. summary-address ip-address mask tag value
Chapter 17. OSPF Timers
Section 17-1. timers lsa-group-pacing seconds
Section 17-2. timers spf delay interval
Chapter 18. Traffic Sharing
Section 18-1. traffic-share min across-interfaces
Chapter 19. Interface Configuration Commands
Section 19-1. ip ospf authentication
Section 19-2. ip ospf authentication authentication-key password
Section 19-3. ip ospf authentication message-digest
Section 19-4. ip ospf authentication null
Section 19-5. ip ospf cost cost
Section 19-6. ip ospf database-filter all out
Section 19-7. ip ospf dead-interval seconds
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Section 19-8. ip ospf demand-circuit
Section 19-9. ip ospf flood-reduction
Section 19-10. ip ospf hello-interval seconds
Section 19-11. ip ospf message-digest-key key-id md5 password
Section 19-12. ip ospf mtu-ignore
Section 19-13. ip ospf network broadcast
Section 19-14. ip ospf network non-broadcast
Section 19-15. ip ospf network point-to-multipoint
Section 19-16. ip ospf network point-to-multipoint non-broadcast
Section 19-17. ip ospf network point-to-point
Section 19-18. ip ospf priority priority
Section 19-19. ip ospf retransmit-interval seconds
Section 19-20. ip ospf transmit-delay seconds
Chapter 20. show Commands
Section 20-1. show ip ospf
Section 20-2. show ip ospf process-id
Section 20-3. show ip ospf border-routers
Section 20-4. show ip ospf process-id border-routers
Section 20-5. show ip ospf database
Section 20-6. show ip ospf process-id database
Section 20-7. show ip ospf database adv-routerrouter-id
Section 20-8. show ip ospf process-id database adv-router router-id
Section 20-9. show ip ospf database asbr-summary
Section 20-10. show ip ospf process-id database asbr-summary
Section 20-11. show ip ospf database asbr-summary asbr-id
Section 20-12. show ip ospf process-id database asbr-summary asbr-id
Section 20-13. show ip ospf database database-summary
Section 20-14. show ip ospf process-id database database-summary
Section 20-15. show ip ospf database external
Section 20-16. show ip ospf process-id database external
Section 20-17. show ip ospf database network
Section 20-18. show ip ospf process-id database network
Section 20-19. show ip ospf database nssa-external
Section 20-20. show ip ospf process-id database nssa-external
Section 20-21. show ip ospf database router
Section 20-22. show ip ospf process-id database router
Section 20-23. show ip ospf database self-originate
Section 20-24. show ip ospf process-id database self-originate
Section 20-25. show ip ospf database summary
Section 20-26. show ip ospf process-id database summary
Section 20-27. show ip ospf flood-list
Section 20-28. show ip ospf process-id flood-list
Section 20-29. show ip ospf flood-list int-name int-number
Section 20-30. show ip ospf process-id flood-list int-name int-number
Section 20-31. show ip ospf interface
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Section 20-32. show ip ospf process-id interface
Section 20-33. show ip ospf interface int-name int-number
Section 20-34. show ip ospf process-id interface int-name int-number
Section 20-35. show ip ospf neighbor
Section 20-36. show ip ospf process-id neighbor
Section 20-37. show ip ospf neighbor neighbor-id
Section 20-38. show ip ospf process-id neighbor neighbor-id
Section 20-39. show ip ospf neighbor int-name int-number
Section 20-40. show ip ospf process-id neighbor int-name int-number
Section 20-41. show ip ospf neighbor detail
Section 20-42. show ip ospf process-id neighbor detail
Section 20-43. show ip ospf neighbor detail neighbor-id
Section 20-44. show ip ospf process-id neighbor detail neighbor-id
Section 20-45. show ip ospf neighbor int-name int-number
Section 20-46. show ip ospf process-id neighbor int-name int-number
Section 20-47. show ip ospf request-list
Section 20-48. show ip ospf process-id request-list
Section 20-49. show ip ospf request-list neighbor-id
Section 20-50. show ip ospf process-id request-list neighbor-id
Section 20-51. show ip ospf request-list int-name int-number
Section 20-52. show ip ospf process-id request-list int-name int-number
Section 20-53. show ip ospf retransmission-list
Section 20-54. show ip ospf process-id retransmission-list
Section 20-55. show ip ospf retransmission neighbor-id
Section 20-56. show ip ospf process-id retransmission neighbor-id
Section 20-57. show ip ospf retransmission int-name int-number
Section 20-58. show ip ospf process-id retransmission int-name int-number
Section 20-59. show ip ospf summary-address
Section 20-60. show ip ospf process-id summary-address
Section 20-61. show ip ospf virtual-links
Section 20-62. show ip ospf process-id virtual-links
Chapter 21. debug Commands
Section 21-1. debug ip ospf adj
Section 21-2. debug ip ospf events
Section 21-3. debug ip ospf flood
Section 21-4. debug ip ospf floodip-access-list-number
Section 21-5. debug ip ospf lsa-generation
Section 21-6. debug ip ospf lsa-generation ip-access-list-number
Section 21-7. debug ip ospf packet
Section 21-8. debug ip ospf retransmission
Section 21-9. debug ip ospf spf
Section 21-10. debug ip ospf spf external
Section 21-11. debug ip ospf spf external access-list-number
Section 21-12. debug ip ospf spf inter
Section 21-13. debug ip ospf spf inter access-list-number
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Section 21-14. debug ip ospf spf intra
Section 21-15. debug ip ospf spf intra access-list-number
Chapter 22. clear Commands
Section 22-1. clear ip ospf counters
Section 22-2. clear ip ospf process-id counters
Section 22-3. clear ip ospf process-id counters neighbor
Section 22-4. clear ip ospf process-id counters neighbor int-name int-number
Section 22-5. clear ip ospf process
Section 22-6. clear ip ospf process-id process
Section 22-7. clear ip ospf redistribution
Section 22-8. clear ip ospf process-id redistribition
Index
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Copyright
Copyright© 2002 Cisco Systems, Inc.
Published by:
Cisco Press
201 West 103rd Street
Indianapolis, IN 46290 USA
All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including
photocopying, recording, or by any information storage and retrieval system, without written permission from the publisher, except for the
inclusion of brief quotations in a review.
Printed in the United States of America 1 2 3 4 5 6 7 8 9 0
First Printing April 2002
Library of Congress Cataloging-in-Publication Number: 2001094058
Warning and Disclaimer
This book is designed to provide information about Cisco IOS Software OSPF commands. Every effort has been made to make this book as
complete and as accurate as possible, but no warranty or fitness is implied.
The information is provided on an "as is" basis. The authors, Cisco Press, and Cisco Systems, Inc., shall have neither liability nor
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The opinions expressed in this book belong to the author and are not necessarily those of Cisco Systems, Inc.
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To my family and friends. In the final analysis, what else is there?
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About the Author
William R. Parkhurst, Ph.D., CCIE #2969, is a program manager with the CCIE group at Cisco Systems. Bill is responsible for the CCIE
Communications and Services exams. Prior to joining the CCIE team, Bill was a Consulting Systems Engineer supporting Sprint. Bill first
became associated with Cisco Systems while he was a Professor of Electrical and Computer Engineering at Wichita State University (WSU).
In conjunction with Cisco Systems, WSU established the first CCIE Preparation Laboratory.
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About the Technical Reviewers
Mike Bass has worked for 22 years in computer networking, the last 17 years at Sprint. Mike's networking experience began with
mini-computer and mainframe networks and now consists of planning and design for distributed and peer-to-peer systems supporting voice,
video, and data services. Mike is currently responsible for the introduction of new networking technologies to support Sprint internal
associates.
Brian Morgan, CCIE #4865, CCSI, is the Director of Data Network Engineering at Allegiance Telecom, Inc. He's been in the networking
industry for over 12 years. Prior to going to Allegiance, Brian was an instructor/consultant teaching ICND, BSCN, BSCI, CATM, CVOICE, and
BCRAN. Brian is a co-author of the Cisco Press Remote Access Exam Certification Guide and technical editor of numerous other Cisco Press
titles.
Bill Wagner works as a Cisco Certified System Instructor for Mentor Technologies. He has 23 years of computer programming and data
communications experience. He has worked for corporations and companies such as Independent Computer Consultants, Numerax, Mc
Graw-Hill/Numerax, and Standard and Poor. His teaching experience started with the Chubb Institute, Protocol Interface Inc, Geotrain, Mentor
Technologies. He is currently teaching at Skyline Computers Corporation.
Robert L. White is an IP Network Design Engineer with Sprint's Long Distance Division internal data network. Robert's design expertise
focuses on routing protocols, external gateway connectivity, and IP address administration on a large multi-protocol network.
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Acknowledgments
I would like to acknowledge the superb effort of all those involved with the development of this handbook. The reviewers of this book, Mike
Bass, Brian Morgan, Bill Wagner, and Robert White, not only found the errors in the book but also contributed suggestions on how to improve
the content and clarity of this handbook. Their efforts are greatly appreciated. I would also like to thank John Kane and Chris Cleveland of
Cisco Press for their guidance and help in bringing this project to a successful completion. Finally, I want to thank my wife, Debbie, for her
encouragement and support during the many evenings and weekends while I was spending more time with routers than with her. She was
also the initial reviewer of this book and found misspellings, grammatical errors, and things that just didn't make sense. Once again she made
me look good in the eyes of my editor.
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Introduction
I have been involved with the world of networking from many directions. My experiences in education, network consulting, service provider
support, and certification have shown me that there is a common thread that frustrates people in all of these arenas. That common thread is
documentation. There are many factors that cause documentation to be frustrating but the most common are amount, clarity, and
completeness. The amount of documentation available, especially in regards to OSPF, can be overwhelming. For a person who is beginning
to learn OSPF, the question is, "Where do I begin?" There are very good books, RFCs, white papers, and command references available, but
it is difficult to know where to start. The clarity of documentation depends on your personal situation. For a seasoned OSPF designer, the
documentation may be clear and concise. To an individual preparing for a professional certification such as the CCIE, the same
documentation may be confusing. Even if the documentation is clear it is sometimes not complete. You may understand the words but be
confused by the application. The purpose of this book is to provide an OSPF handbook that is clear, concise, and complete. This book is not
meant to be read from cover to cover. The way you use this book will depend on your objectives. If you are preparing for the CCIE written and
lab exams, this book can be used as a laboratory guide to learn the purpose and proper use of every OSPF command. If you are a network
designer then this book can be used as a ready reference for any OSPF command. In order to satisfy these varying audiences the structure
of this book is reasonably simple. Each OSPF command is illustrated using the following structure:
Listing of the command structure and syntax
Syntax description for the command with an explanation of all command parameters
The purpose of the command and the situation where the command is used
The first release of the IOS in which the command appeared
One or more configuration examples to demonstrate the proper use of the command
Procedures and examples to verify that the command is working properly
How to troubleshoot the command when things are not working as intended
The example scenarios that demonstrate the proper use of the OSPF commands can be implemented on a minimum number of routers. This
will allow you to learn each command without requiring an extensive and expensive lab configuration. The scenarios are presented so that the
purpose and use of each command can be presented without clouding the issue. Some of the examples lead you into common non-working
situations in order to reinforce the understanding of the operation of the particular OSPF command.
My hope is that this handbook will help you prepare for the CCIE exam, allow you to properly use OSPF in your network, or both.
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Recommended Reading
This book assumes that you have a working knowledge of OSPF theory of operation and OSPF terminology. The following references can be
used to supplement your knowledge of OSPF.
OSPF Network Design Solutions, Thomas M. Thomas II, Cisco Press (second edition will be released December 2002)
Routing TCP/IP Volume 1, Jeff Doyle, Cisco Press
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Icons Used in This Book
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Command Syntax Conventions
The conventions used to present command syntax in this book are the same conventions used in the Cisco IOS Software Command
Reference. The Command Reference describes these conventions as follows:
Vertical bars (|) separate alternative, mutually exclusive elements.
Square brackets [ ] indicate optional elements.
Braces { } indicate a required choice.
Braces within brackets [{ }] indicate a required choice within an optional element.
Boldface indicates commands and keywords that are entered literally as shown. In actual configuration examples and output (not
general command syntax), boldface indicates commands that are manually input by the user (such as a show command).
Italics indicate arguments for which you supply actual values.
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Chapter 1. OSPF Process Configuration Commands
Section 1-1. router ospf process-id
Section 1-2. router ospf process-id vrf name
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1-1 router ospf process-id
Syntax Description:
process-id— The OSPF process ID. The range of values is 1 to 65535.
Purpose: Used to enable one or more OSPF processes on a router. The process ID is only significant on the local router. Use the
no form of
the command to remove an OSPF process.
Initial IOS Software Release: 10.0
Configuration Example: Enabling an OSPF Process
Before you enable an OSPF process, there must be at least one active interface with an assigned IP address. OSPF uses the highest IP
address assigned to an active interface as the OSPF Router ID. If loopback interfaces have been configured, then OSPF will use the highest
loopback address as the Router ID even if the highest loopback IP address is smaller than the IP address of any active physical interface.
Using a loopback interface on an OSPF router is recommended because a loopback interface is never down. A loopback interface will
produce a stable OSPF router ID. The network in Figure 1-1 demonstrates that the OSPF Router ID (RID) is the highest IP address assigned
to an active physical interface. If a loopback interface is used, then OSPF will use the loopback IP address as the OSPF RID.
Figure 1-1. OSPF Router ID Selection
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Start by removing all IP addresses and loopback interfaces from Router B. Now, attempt to configure an OSPF process on Router B.
rtrB#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
rtrB(config)#router ospf 1
OSPF: Could not allocate router id
OSPF cannot be enabled on Router B because OSPF needs a RID and there are no IP addresses assigned on Router B. Configure the serial
interfaces on Routers A and B and then configure an OSPF process on Router B.
Router A
interface Serial0/1
bandwidth 64
ip address 10.1.1.1 255.255.255.252
clockrate 64000
_______________________________________________________________________
Router B
interface Serial0
ip address 10.1.1.2 255.255.255.252
bandwidth 64
router ospf 1
The configuration of the OSPF process on Router B was successful. Examine the OSPF RID on Router B using theshow ip ospf command.
rtrB#show ip ospf
Routing Process "ospf 1" with ID 10.1.1.2
Supports only single TOS(TOS0) routes
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Number of DCbitless external LSA 0
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Number of DoNotAge external LSA 0
Number of areas in this router is 0. 0 normal 0 stub 0 nssa
The only active interface on Router B is Serial0, so OSPF will use the IP address assigned to Serial0 for the router ID. Add a loopback
interface to Router B and then re-examine the OSPF RID on Router B.
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
rtrB#show ip ospf
Routing Process "ospf 1" with ID 10.1.1.2
Supports only single TOS(TOS0) routes
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 0. 0 normal 0 stub 0 nssa
The OSPF RID has not changed. This is a stability feature of OSPF. The router ID will not change unless the OSPF process is restarted or if
the interface used for the RID goes down. Shut down the serial interface on Router B, re-enable the serial interface on Router B, and examine
the effect on the OSPF RID.
Verification
Verify that the OSPF RID on Router B is equal to the IP address assigned to the loopback interface.
rtrB#show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Supports only single TOS(TOS0) routes
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 0. 0 normal 0 stub 0 nssa
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Troubleshooting
Verify that a loopback interface has been configured and an IP address assigned before configuring OSPF. A loopback interface is not
mandatory, but it will add stability to your OSPF network.
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1-2 router ospf process-id vrf name
Syntax Description:
process-id— The OSPF process ID. The range of values is 1 to 65535.
name— VPN Routing/Forwarding Instance (VRF) name. Routes learned by the OSPF process will be placed in the VRF instead
of the global IP routing table.
Purpose: In a Multiprotocol Label Switching (MPLS) virtual private network (VPN) environment, this formof the OSPF router command is
used to transfer VPN customer routes between the service provider and the VPN customer. In an MPLS/VPN environment, there are three
types of routers, as shown in Figure 1-2.
Figure 1-2. General MPLS/VPN Architecture
Provider (P) routers
Customer edge (CE) routers
Provider edge (PE) routers
P routers are routers in the service provider network that have no connections to CE routers. PE routers are the interface routers between the
customer and the service provider. Tag or label switching and an interior gateway protocol (IGP), such as OSPF, are run between P and PE
routers to exchange internal service provider routes. These routes are installed in the global IP routing table on the P and PE routers. The PE
routers have additional IP routing tables, one for each attached VPN customer. These routing tables are called VRF instances. When OSPF
is configured using the vrf option, routes learned from the CE will be placed into the appropriate VRF on the PE router. These VPN routes will
be exchanged between PE routers via multiprotocol IBGP. For a detailed discussion of MPLS and MPLS VPNs, see the Cisco Press book
MPLS and VPN Architectures by Ivan Pepelnjak and Jim Guichard.
Initial IOS Software Release: 12.0
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Chapter 2. OSPF Area Commands
Section 2-1. area area-id authentication
Section 2-2. area area-id authentication message-digest
Section 2-3. area area-id default-cost cost
Section 2-4. area area-id nssa
Section 2-5. area area-id nssa default-information-originate
Section 2-6. area area-id nssa no-redistribution
Section 2-7. area area-id nssa no-summary
Section 2-8. area area-id range ip-address mask
Section 2-9. area area-id range ip-address mask advertise
Section 2-10. area area-id range ip-address mask not-advertise
Section 2-11. area area-id stub
Section 2-12. area area-id stub no-summary
Section 2-13. area transit-area-id virtual-link router-id
Section 2-14. area transit-area-id virtual-link router-id authentication authentication-key password
Section 2-15. area transit-area-id virtual-link router-id authentication message-digest
Section 2-16. area transit-area-id virtual-link router-id authentication null
Section 2-17. area transit-area-id virtual-link router-id authentication-key password
Section 2-18. area transit-area-id virtual-link router-id dead-interval seconds
Section 2-19. area transit-area-id virtual-link router-id hello-interval seconds
Section 2-20. area transit-area-id virtual-link router-id message-digest-key key-id md5 password
Section 2-21. area transit-area-id virtual-link router-id retransmit-interval seconds
Section 2-22. area transit-area-id virtual-link router-id transmit-delay seconds
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2-1 area area-id authentication
NOTE
This command requires the following additional commands:
For a physical interface: ip ospf authentication-key password (see Section 19-2)
For a virtual link if authentication is used in area 0: area transit-area virtual-link router-id authentication-key password
(see Section 2-17)
Syntax Description:
area-id— OSPF area ID. This value can be entered as a decimal number in the range of 0 to 4,294,967,295 or in IP address
format in the range 0.0.0.0 to 255.255.255.255. This command will enable simple password authentication in the indicated OSPF
area. By default, authentication is not enabled.
transit-area— The OSPF area across which the virtual link is configured.
password— Clear-text password to be used for authentication in the selected area on the selected interface or virtual link. The
password is an alphanumeric string from 1 to 8 characters.
router-id— OSPF router ID of the router at the remote end of the virtual link.
Purpose: To enable simple clear-text password authentication in an OSPF area. OSPF simple authentication requires the use of the router
configuration command to enable authentication in an area and the interface or virtual-link command for password configuration. Because this
router configuration command enables authentication in an area, you must configure every interface in the area for authentication if using
Cisco IOS Software Release 11.X or earlier. In Cisco IOS Software Release 12.X, the authentication used on an interface can be different
than the authentication enabled for an area. When using Cisco IOS Software Release 12.X, the authentication method used on different
interfaces in the same area does not need to be the same. You can remove authentication from selected interfaces using the interface
command ip ospf authentication null (see Section 19-1). The password does not need to be the same on every interface in the area, but
both ends of a common link must use the same password. Authentication is enabled by area (Cisco IOS Software Release 11.X and earlier),
so it is possible to employ authentication in one area without using authentication in other areas. The clear-text password is not encrypted, so
it will be possible for someone to intercept OSPF protocol packets and compromise the password.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Simple Password Authentication
For the network in Figure 2-1, start by configuring OSPF without authentication in Area 0.
Figure 2-1. Network Used to Demonstrate OSPF Authentication Configuration and
Troubleshooting
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
ip address 10.1.1.9 255.255.255.252
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clock rate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.15 area 0
_______________________________________________________________________
Router B
interface Loopback0
.
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ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
clock rate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.15 area 0
_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
interface Serial1
ip address 10.1.1.10 255.255.255.252
clock rate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.15 area 0
Verify the OSPF configuration on Routers A, B, and C by displaying the state of each router's OSPF neighbors.
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rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
3.3.3.3
1 FULL/ -
00:00:38
10.1.1.10
Serial0/0
2.2.2.2
1 FULL/ -
00:00:37
10.1.1.2
Serial0/1
_______________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
1.1.1.1
1 FULL/ -
00:00:35
10.1.1.1
Serial0
3.3.3.3
1 FULL/ -
00:00:30
10.1.1.6
Serial1
_______________________________________________________________________
rtrC#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
2.2.2.2
1 FULL/ -
00:00:30
10.1.1.5
Serial0
1.1.1.1
1 FULL/ -
00:00:37
10.1.1.9
Serial1
Verify that OSPF is not using authentication.
rtrA#show ip ospf
Routing Process "ospf 1" with ID 1.1.1.1
Supports only single TOS(TOS0) routes
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
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Number of DoNotAge external LSA 0
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Area BACKBONE(0)
Number of interfaces in this area is 2
Area has no authentication
SPF algorithm executed 6 times
Area ranges are
Number of LSA 3. Checksum Sum 0x25F8D
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Modify the configurations on Routers A, B, and C by adding simple password authentication to Area 0. For this example, you will use the
clear-text password "cisco".
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
ip address 10.1.1.9 255.255.255.252
ip ospf authentication-key cisco
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
ip ospf authentication-key cisco
clock rate 64000
!
router ospf 1
area 0 authentication
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network 10.1.1.0 0.0.0.15 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
ip ospf authentication-key cisco
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
ip ospf authentication-key cisco
clock rate 64000
!
router ospf 1
area 0 authentication
network 10.1.1.0 0.0.0.15 area 0
_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
ip ospf authentication-key cisco
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!
interface Serial1
ip address 10.1.1.10 255.255.255.252
ip ospf authentication-key cisco
clock rate 64000
!
router ospf 1
area 0 authentication
network 10.1.1.0 0.0.0.15 area 0
Verification
Verify that the OSPF neighbor relationships are still active.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
3.3.3.3
1 FULL/ -
00:00:31
10.1.1.10
Serial0/0
2.2.2.2
1 FULL/ -
00:00:30
10.1.1.2
Serial0/1
_______________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
1.1.1.1
1 FULL/ -
00:00:38
10.1.1.1
Serial0
3.3.3.3
1 FULL/ -
00:00:33
10.1.1.6
Serial1
_______________________________________________________________________
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rtrC#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
2.2.2.2
1 FULL/ -
00:00:33
10.1.1.5
Serial0
1.1.1.1
1 FULL/ -
00:00:30
10.1.1.9
Serial1
Verify that simple authentication is enabled for Area 0.
rtrA#show ip ospf
Routing Process "ospf 1" with ID 1.1.1.1
Supports only single TOS(TOS0) routes
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Area BACKBONE(0)
Number of interfaces in this area is 2
Area has simple password authentication
SPF algorithm executed 9 times
Area ranges are
Number of LSA 3. Checksum Sum 0x24F95
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
The password used can be seen by anyone looking at your configuration. For added security, the password in the configuration can be
encrypted using the global configuration command service password-encryption, as shown in the following configuration.
Router A
service password-encryption
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Listing the configuration will show that the password has been encrypted. Although the password is encrypted in the configuration, it will still
be sent in clear text by OSPF.
rtrA#show running-config
Building configuration...
Current configuration:
!
version 12.0
service timestamps debug uptime
service timestamps log uptime
service password-encryption
!
hostname rtrA
!
ip subnet-zero
!
interface Loopback0
ip address 1.1.1.1 255.255.255.255
no ip directed-broadcast
!
interface Serial0/0
ip address 10.1.1.9 255.255.255.252
no ip directed-broadcast
ip ospf authentication-key 7 121A0C041104
no ip mroute-cache
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
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no ip directed-broadcast
ip ospf authentication-key 7 02050D480809
clockrate 64000
Troubleshooting
Step 1. Before enabling authentication in an OSPF area, verify that there is a neighbor relationship among all OSPF routers by
using the show ip ospf neighbor command.
Step 2. Verify that authentication has been enabled for every OSPF router with an interface in the area where authentication is
being deployed.
Step 3. Verify that every interface in an OSPF area that is using authentication is configured with the proper password.
Step 4. If any OSPF neighbor relationships disappear after configuring authentication, then debugging can be used to determine
the problem. For example, change the password on Router A, Interface Serial 0/0, to bosco, as shown here.
Router A
interface Serial0/0
ip address 10.1.1.9 255.255.255.252
ip ospf authentication-key bosco
List the OSPF neighbors for Router A.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/ -
Dead Time Address
00:00:36
10.1.1.2
Interface
Serial0/1
Router A has lost Router C as a neighbor. Enable debugging on Router A to see if the problem can be determined.
rtrA#debug ip ospf events
OSPF events debugging is on
rtrA#
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03:41:09: OSPF: Rcv hello from 2.2.2.2 area 0 from Serial0/1 10.1.1.2
03:41:09: OSPF: End of hello processing
03:41:09: OSPF: Rcv pkt from 10.1.1.10, Serial0/0 : Mismatch Authentication Key
- Clear Text
Be careful when configuring passwords. A space is a valid character, so if you use the passwordcisco<space> then there will be a password
mismatch, but you won't be able to tell by looking at the configuration.
Change the password on Router A, serial 0/0, back to cisco and remove the OSPF router configuration command area 0 authentication.
Router A
interface Serial0/0
ip address 10.1.1.9 255.255.255.252
ip ospf authentication-key cisco
!
router ospf 1
no area 0 authentication
Router A should drop both OSPF neighbors.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
3.3.3.3
1 INIT/ -
00:00:38
10.1.1.10
Serial0/0
2.2.2.2
1 INIT/ -
00:00:39
10.1.1.2
Serial0/1
Now debug the OSPF traffic on Router B or C to determine the problem.
rtrB#debug ip ospf events
OSPF events debugging is on
rtrB#
03:55:35: OSPF: Rcv pkt from 10.1.1.1, Serial0 : Mismatch Authentication type. I
nput packet specified type 0, we use type 1
03:55:40: OSPF: Rcv hello from 3.3.3.3 area 0 from Serial1 10.1.1.6
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03:55:40: OSPF: End of hello processing
Routers B and C are using type 1 authentication (simple password) and Router A is using type 0 authentication (none).
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2-2 area area-id authentication message-digest
NOTE
This command requires the following additional commands:
For a physical interface: ip ospf message-digest-key key-id md5 password (see Section 19-9)
For a virtual link if authentication is used in Area 0: area transit-area virtual-link router-id message-digest-key key-id md5
password (see Section 2-20)
Syntax Description:
area-id— OSPF area ID. This value can be entered as a decimal number in the range of 0 to 4,294,967,295 or in IP address
format in the range 0.0.0.0 to 255.255.255.255. This command will enable simple password authentication in the indicated OSPF
area. By default, authentication is not enabled.
key-id— Key used to encrypt a password. The range of values is 1 to 255. Both ends of a link must use the same key and password.
password— Password to be used for authentication in the selected area on the selected interface or virtual link. The password is
an alphanumeric string from 1 to 8 characters.
transit-area— The OSPF area across which the virtual link is configured.
router-id— OSPF router ID of the router at the remote end of the virtual link.
Purpose: To enable MD5 password authentication in an OSPF area. OSPF MD5 authentication requires the use of the router configuration
command to enable authentication in an area and the interface or virtual link command for key and password configuration. Since this router
configuration command enables authentication in an area, every interface in the area must be configured with an authentication key and
password if using Cisco IOS Software Release 11.X or earlier. In Cisco IOS Software Release 12.X, the authentication used on an interface
can be different from the authentication enabled for an area. When using Cisco IOS Software Release 12.X, the authentication method used
on different interfaces in the same area does not need to be the same. Authentication can be turned off on selected interfaces using the
command ip ospf authentication null (see Section 19-1). The key and password do not need to be the same on every interface, but both
ends of a common link need to use the same key and password. Authentication is enabled by area (Cisco IOS Software Release 11.X and
earlier) so it is possible to employ authentication in one area without using authentication in other areas. The password is encrypted, so it is
extremely difficult for someone to intercept OSPF protocol packets and compromise the password.
Initial Cisco IOS Software Release: 11.0
Configuration Example 1: MD5 Password Authentication
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For the network in Figure 2-2, initially configure OSPF without authentication in Area 0.
Figure 2-2. Network Used to Demonstrate OSPF MD5 Authentication Configuration and
Troubleshooting
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
ip address 10.1.1.9 255.255.255.252
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clock rate 64000
!
.
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router ospf 1
network 10.1.1.0 0.0.0.15 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
clock rate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.15 area 0
_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
interface Serial1
ip address 10.1.1.10 255.255.255.252
.
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clock rate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.15 area 0
Verify the OSPF configuration on Routers A, B, and C by displaying the state of each router's OSPF neighbors.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
3.3.3.3
1 FULL/ -
00:00:38
10.1.1.10
Serial0/0
2.2.2.2
1 FULL/ -
00:00:37
10.1.1.2
Serial0/1
_______________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
1.1.1.1
1 FULL/ -
00:00:35
10.1.1.1
Serial0
3.3.3.3
1 FULL/ -
00:00:30
10.1.1.6
Serial1
_______________________________________________________________________
rtrC#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
2.2.2.2
1 FULL/ -
00:00:30
10.1.1.5
Serial0
1.1.1.1
1 FULL/ -
00:00:37
10.1.1.9
Serial1
Verify that OSPF is not using authentication.
rtrA#show ip ospf
Routing Process "ospf 1" with ID 1.1.1.1
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Supports only single TOS(TOS0) routes
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Area BACKBONE(0)
Number of interfaces in this area is 2
Area has no authentication
SPF algorithm executed 6 times
Area ranges are
Number of LSA 3. Checksum Sum 0x25F8D
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Modify the configurations on Routers A, B, and C by adding MD5 password authentication to area 0. For this example, use the passwords
ciscoab, ciscobc, and ciscoac to demonstrate that multiple passwords can be used in an area.
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
ip address 10.1.1.9 255.255.255.252
ip ospf message-digest-key 1 md5 ciscoac
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
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ip ospf message-digest-key 2 ciscoab
clock rate 64000
!
router ospf 1
area 0 authentication message-digest
network 10.1.1.0 0.0.0.15 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
ip ospf message-digest-key 2 md5 ciscoab
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
ip ospf message-digest-key 3 md5 ciscobc
clock rate 64000
!
router ospf 1
area 0 authentication message-digest
network 10.1.1.0 0.0.0.15 area 0
_______________________________________________________________________
Router C
interface Loopback0
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ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
ip ospf message-digest-key 3 ciscobc
!
interface Serial1
ip address 10.1.1.10 255.255.255.252
ip ospf message-digest-key 1 md5 ciscoac
clock rate 64000
!
router ospf 1
area 0 authentication message-digest
network 10.1.1.0 0.0.0.15 area 0
Verification
Verify that the OSPF neighbor relationships are still active.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
3.3.3.3
1 FULL/ -
00:00:31
10.1.1.10
Serial0/0
2.2.2.2
1 FULL/ -
00:00:30
10.1.1.2
Serial0/1
_______________________________________________________________________
rtrB#show ip ospf neighbor
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Neighbor ID
Pri State
Dead Time Address
Interface
1.1.1.1
1 FULL/ -
00:00:38
10.1.1.1
Serial0
3.3.3.3
1 FULL/ -
00:00:33
10.1.1.6
Serial1
_______________________________________________________________________
rtrC#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
2.2.2.2
1 FULL/ -
00:00:33
10.1.1.5
Serial0
1.1.1.1
1 FULL/ -
00:00:30
10.1.1.9
Serial1
Verify that MD5 authentication is enabled for Area 0.
rtrA#show ip ospf
Routing Process "ospf 1" with ID 1.1.1.1
Supports only single TOS(TOS0) routes
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Area BACKBONE(0)
Number of interfaces in this area is 2
Area has message digest authentication
SPF algorithm executed 2 times
Area ranges are
Number of LSA 3. Checksum Sum 0x14A19
Number of DCbitless LSA 0
Number of indication LSA 0
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Number of DoNotAge LSA 0
The password used can be seen by anyone looking at your configuration. For added security, the password in the configuration can be
encrypted using the global configuration command service password-encryption, as shown in the following configuration.
Router A
service password-encryption
Listing the configuration will show that the password has been encrypted.
rtrA#show running-config
Building configuration...
Current configuration:
!
version 12.0
service timestamps debug uptime
service timestamps log uptime
service password-encryption
!
hostname rtrA
!
ip subnet-zero
!
interface Loopback0
ip address 1.1.1.1 255.255.255.255
no ip directed-broadcast
!
interface Serial0/0
ip address 10.1.1.9 255.255.255.252
no ip directed-broadcast
ip ospf message-digest-key 1 md5 7 02050D4808090E22
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no ip mroute-cache
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
no ip directed-broadcast
ip ospf message-digest-key 2 md5 7 045802150C2E4D4C
clockrate 64000
Configuration Example 2: Changing Keys and Passwords
For additional security, you may choose to periodically change the key and password. With clear-text authentication, changing passwords will
cause a loss of OSPF connectivity from the time you change the password on one interface until you change the password at the other end of
the link. With MD5 authentication, you can configure a new key and password on a link while leaving the old key and password in place. The
old key and password will continue to be used until the new key and password are configured on the other end of the link. Modify the key and
password on the link between Routers A and B. Add a new key and password on Router A in order to observe the behavior when the new
key and password have only been configured on one end of the link.
Router A
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
no ip directed-broadcast
ip ospf message-digest-key 2 md5 ciscoab
ip ospf message-digest-key 4 md5 cisconew
clockrate 64000
Verify that the OSPF neighbor relationship between Routers A and B is still active.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
3.3.3.3
1 FULL/ -
00:00:34
10.1.1.10
Serial0/0
2.2.2.2
1 FULL/ -
00:00:35
10.1.1.2
Serial0/1
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You can determine if Router A is using both keys when communicating with Router B by viewing the interface properties or by enabling
OSPF debugging.
rtrA#show ip ospf interface s0/1
Serial0/1 is up, line protocol is up
Internet Address 10.1.1.1/30, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:08
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2
Suppress hello for 0 neighbor(s)
Message digest authentication enabled
Youngest key id is 4
Rollover in progress, 1 neighbor(s) using the old key(s):
key id 2
rtrA#debug ip ospf events
OSPF events debugging is on
rtrA#
01:30:25: OSPF: Rcv hello from 3.3.3.3 area 0 from Serial0/0 10.1.1.10
01:30:25: OSPF: End of hello processing
01:30:26: OSPF: Rcv hello from 2.2.2.2 area 0 from Serial0/1 10.1.1.2
01:30:26: OSPF: End of hello processing
01:30:30: OSPF: Send with youngest Key 1
01:30:30: OSPF: Send with key 2
01:30:30: OSPF: Send with key 4
Notice that both keys are being used for authentication. Configure the new key and password on Router B while leaving the old key and
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password in place.
Router B
interface Serial0
ip address 10.1.1.2 255.255.255.252
no ip directed-broadcast
ip ospf message-digest-key 2 md5 ciscoab
ip ospf message-digest-key 4 md5 cisconew
Routers A and B will now use the youngest key (the last key configured).
rtrA#show ip ospf interface s0/1
Serial0/1 is up, line protocol is up
Internet Address 10.1.1.1/30, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2
Suppress hello for 0 neighbor(s)
Message digest authentication enabled
Youngest key id is 4
The old key and password can now be removed from routers A and B using the no form of the interface command.
Troubleshooting
Step 1. Before enabling authentication in an OSPF area, verify that there is a neighbor relationship among all OSPF routers by
using the show ip ospf neighbor command.
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Step 2. Verify that authentication has been enabled for every OSPF router with an interface in the area where authentication is
being deployed.
Step 3. Verify that every interface using authentication in an OSPF area has been configured with the proper key and password.
Step 4. If any OSPF neighbor relationships disappear after configuring md5 authentication, debugging can be used to determine
the problem. For example, change the key-id on router B, interface Serial 0, to 5. Use the no form of the command to remove the
original key and password before applying the new key.
Router B
interface Serial0
ip address 10.1.1.2 255.255.255.252
no ip ospf message-digest-key 2 md5 ciscoab
ip ospf message-digest-key 5 md5 ciscoab
List the OSPF neighbors for Router A.
rtrA#show ip ospf neighbor
Neighbor ID
3.3.3.3
Pri State
1 FULL/ -
Dead Time Address
00:00:31
10.1.1.10
Interface
Serial0/0
Router A has lost Router C as a neighbor. Enable debugging on Router A to see if you can determine the problem.
rtrA#debug ip ospf events
OSPF events debugging is on
rtrA#
00:09:34: OSPF: Rcv pkt from 10.1.1.2, Serial0/1 : Mismatch Authentication Key No message digest key 5 on interface
Be careful when configuring passwords. A space is a valid character, so if you use the password cisco<space> then there will be a password
mismatch, but you won't be able to tell by looking at the configuration, especially if the password is encrypted in the configuration.
On Router A, remove the OSPF router configuration command area 0 authentication message-digest. Restore the proper key on Serial0
on Router B.
Router A
interface Serial0/0
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ip address 10.1.1.9 255.255.255.252
ip ospf authentication-key cisco
!
router ospf 1
no area 0 authentication message-digest
_______________________________________________________________________
Router B
interface Serial0
ip address 10.1.1.2 255.255.255.252
no ip ospf message-digest-key 5 md5 ciscoab
ip ospf message-digest-key 2 md5 ciscoab
Router A should drop both OSPF neighbors.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
3.3.3.3
1 INIT/ -
00:00:38
10.1.1.10
Serial0/0
2.2.2.2
1 INIT/ -
00:00:39
10.1.1.2
Serial0/1
Now debug the OSPF traffic on Router B or C to determine the problem.
rtrB#debug ip ospf events
OSPF events debugging is on
rtrB#
21:43:04: OSPF: Rcv hello from 3.3.3.3 area 0 from Serial1 10.1.1.6
21:43:04: OSPF: End of hello processing
21:43:05: OSPF: Send with youngest Key 4
21:43:05: OSPF: Send with youngest Key 3
21:43:08: OSPF: Rcv pkt from 10.1.1.1, Serial0 : Mismatch Authentication type. I
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nput packet specified type 0, we use type 2
Routers B and C are using type 2 authentication (MD5) and Router A is using type 0 authentication (none).
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2-3 area area-id default-cost cost
NOTE
This command requires the following additional commands:
area area-id nssa (see Section 2-4)
or
area area-id stub (see Section 2-11)
Syntax Description:
area-id— OSPF area ID. This value can be entered as a decimal number in the range of 0 to 4,294,967,295 or in IP address form
in the range 0.0.0.0 to 255.255.255.255.
cost— The default cost of an OSPF stub area's advertised external default route metric. The range of values is 0 to 16,777,215.
The default value is 1. The cost value will be added to the cost of reaching the Area Border Router (ABR) that is advertising the
default route.
Purpose: External networks will not be advertised into a stub or totally stubby area. External networks are networks that have been
redistributed into OSPF. External OSPF routes and inter-area OSPF routes are not advertised into a totally stubby area. When an OSPF area
is configured as a stub area, a default route will be generated by the ABR into the stub area in place of the external routes. When an OSPF
area is configured as a totally stubby area, the default route replaces the external and inter-area routes. The purpose of this command is to
set the cost of the default route advertised into a stubby, totally stubby, or not-so-stubby area. If this command is not used, then the cost of
the default route will be 1. When configuring stub areas, all routers with interfaces in the stub area must be configured with the same stub
area type.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Setting the Default Cost for a Stub Area
Initially, the network in Figure 2-3 is configured without a stubby area to compare the differences between the routes advertised into a normal
area with those advertised into a stubby area. You will redistribute the loopback interface on Router C in order to generate an external route
on Routers A and B.
Figure 2-3. External OSPF Routes Are Not Advertised into an OSPF Stub Area. Inter-area and
External Routes Are Not Advertised into a Totally Stubby Area
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clock rate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 1
_______________________________________________________________________
.
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Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
clock rate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 1
network 10.1.1.4 0.0.0.3 area 0
_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router ospf 1
redistribute connected subnnets
network 10.1.1.4 0.0.0.3 area 0
.
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If you examine the IP routing table on Router A, you can see that all OSPF routes are being advertised into Area 1.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O E2
3.3.3.3 [110/20] via 10.1.1.2, 00:00:04, Serial0/1
10.0.0.0/30 is subnetted, 3 subnets
C
O IA
10.1.1.0 is directly connected, Serial0/1
10.1.1.4 [110/128] via 10.1.1.2, 00:00:04, Serial0/1
Modify the configurations on Routers A and B so that Area 1 is a stub area.
Router A
router ospf 1
area 1 stub
network 10.1.1.0 0.0.0.3 area 1
_______________________________________________________________________
Router B
router ospf 1
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area 1 stub
network 10.1.1.0 0.0.0.3 area 1
network 10.1.1.4 0.0.0.3 area 0
Re-examine the IP routing table on Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 10.1.1.2 to network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 3 subnets
C
O IA
10.1.1.0 is directly connected, Serial0/1
10.1.1.4 [110/128] via 10.1.1.2, 00:00:06, Serial0/1
O*IA 0.0.0.0/0 [110/65] via 10.1.1.2, 00:00:06, Serial0/1
Notice that the cost of the default route is 65. This is the sum of the cost to the ABR of 64 and the cost of the default route, which has the
default value of 1. You can verify the default cost by using the command show ip ospf on Router B.
rtrB#show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Supports only single TOS(TOS0) routes
It is an area border router
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
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Number of external LSA 3. Checksum Sum 0x14B45
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 1 normal 1 stub 0 nssa
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 21 times
Area ranges are
Number of LSA 3. Checksum Sum 0x14F55
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Area 1
Number of interfaces in this area is 1
It is a stub area
generates stub default route with cost 1
Area has no authentication
SPF algorithm executed 37 times
Area ranges are
Number of LSA 4. Checksum Sum 0x1E701
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Modify the cost of the default route being generated by Router B.
Router B
router ospf 1
area 1 stub
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area 1 default-cost 15
Network 10.1.1.0 0.0.0.3 area 1
Network 10.1.1.4 0.0.0.3 area 0
Verification
Verify the new cost for the default route on Router A by using the show ip route command or the show ip route 0.0.0.0 command. You can
also verify the cost of the default route on Router B by using the show ip ospf command.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 10.1.1.2 to network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 3 subnets
C
O IA
10.1.1.0 is directly connected, Serial0/1
10.1.1.4 [110/128] via 10.1.1.2, 00:03:39, Serial0/1
O*IA 0.0.0.0/0 [110/79] via 10.1.1.2, 00:00:09, Serial0/1
rtrA#show ip route 0.0.0.0
Routing entry for 0.0.0.0/0, supernet
Known via "ospf 1", distance 110, metric 79, candidate default path, type inte
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r area
Redistributing via ospf 1
Last update from 10.1.1.2 on Serial0/1, 00:01:05 ago
Routing Descriptor Blocks:
* 10.1.1.2, from 2.2.2.2, 00:01:05 ago, via Serial0/1
Route metric is 79, traffic share count is 1
_______________________________________________________________________
rtrB#show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Supports only single TOS(TOS0) routes
It is an area border router
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 3. Checksum Sum 0x14B45
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 1 normal 1 stub 0 nssa
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 21 times
Area ranges are
Number of LSA 3. Checksum Sum 0x14F55
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Area 1
Number of interfaces in this area is 1
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It is a stub area
generates stub default route with cost 15
Area has no authentication
SPF algorithm executed 37 times
Area ranges are
Number of LSA 4. Checksum Sum 0x27068
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
The new cost is now 64 + 15 or 79.
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Verify that the ABR to the stub area and all routers in the stub area have been configured as a stub using the router
configuration command area x stub.
Step 3. Verify that the default-cost command has been configured on the ABR(s) for the stub area. Thedefault-cost command will
only work on the stub area ABR.
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2-4 area area-id nssa
Syntax Description:
area-id— OSPF area ID. This value can be entered as a decimal number in the range of 1 to 4,294,967,295 or in IP address form
in the range 0.0.0.1 to 255.255.255.255. Area 0 can be entered but Area 0 cannot be configured as a not-so-stubby area (NSSA).
Purpose: In a stub or totally stubby area, the ABR to the stub area will prevent OSPF external routes (type 5) from being advertised into the
stub area. This implies that an Autonomous System Boundary Router (ASBR) cannot be part of a stubby or totally stubby area because an
ASBR generates OSPF external type 5 routes. There will be situations where you want to create a stubby or totally stubby area relative to
OSPF and also want to advertise redistributed routes from an ASBR across the area. An OSPF area that has these properties is an NSSA. In
Figure 2-4, you want Router B, the ABR to block OSPF external routes from Area 1. You also want the routes redistributed by Router C, the
ASBR, to be allowed into the area. If you configure Area 1 as an NSSA, then the external OSPF routes that Router B receives from Area 0
will be blocked from Area 1. The redistributed routes from the ASBR will be sent as OSPF type 7 routes. Router B will convert these type 7
routes to OSPF type 5 routes and advertise them into Area 0. Routes are normally redistributed into OSPF as type 5 routes. An ASBR that
has been configured as an NSSA will generate type 7 routes instead of type 5 routes.
Figure 2-4. An OSPF NSSA
Initial Cisco IOS Software Release: 11.2
Configuration Example: Configuring an OSPF NSSA
In Figure 2-4, Routers C and D are running RIP Version 2. Router D is advertising the networks 156.26.32.0/24 and 156.26.33.0/24 to Router
C via RIP. Router C will redistribute the RIP routes, including the 10.1.1.8/30 network, into OSPF. Because Area 1 has been defined as an
NSSA, the redistributed RIP routes will be advertised into Area 1 as OSPF type 7 routes. Initially you will configure Area 1 as a normal OSPF
area in order to see the routes that are advertised.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
redistribute connected subnets
network 10.1.1.0 0.0.0.3 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
lockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
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Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
interface Serial1
ip address 10.1.1.10 255.255.255.252
clockrate 64000
!
router ospf 1
redistribute rip subnets
network 10.1.1.4 0.0.0.3 area 1
!
router rip
version 2
passive-interface Serial0
network 10.0.0.0
_______________________________________________________________________
Router D
interface Loopback0
ip address 156.26.32.1 255.255.255.0
!
interface Loopback1
ip address 156.26.33.1 255.255.255.0
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!
interface Serial0/0
ip address 10.1.1.9 255.255.255.252
!
router rip
version 2
network 10.0.0.0
network 156.26.0.0
no auto-summary
Router A is advertising Loopback 0 as an OSPF type 5 external route because this route was injected into OSPF through redistribution.
Routers A and B are also learning the redistributed RIP routes as external type 5 OSPF routes.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O E2
156.26.32.0 [110/20] via 10.1.1.2, 00:02:25, Serial0/1
O E2
156.26.33.0 [110/20] via 10.1.1.2, 00:02:25, Serial0/1
10.0.0.0/30 is subnetted, 3 subnets
O E2
10.1.1.8 [110/20] via 10.1.1.2, 00:02:25, Serial0/1
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C
10.1.1.0 is directly connected, Serial0/1
O IA
10.1.1.4 [110/128] via 10.1.1.2, 00:02:25, Serial0/1
_______________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O E2
1.1.1.1 [110/20] via 10.1.1.1, 00:04:14, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O E2
156.26.32.0 [110/20] via 10.1.1.6, 00:04:14, Serial1
O E2
156.26.33.0 [110/20] via 10.1.1.6, 00:04:14, Serial1
10.0.0.0/30 is subnetted, 3 subnets
O E2
10.1.1.8 [110/20] via 10.1.1.6, 00:04:14, Serial1
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
Router C is learning the network redistributed by Router A as an OSPF external type 5 route.
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
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N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O E2
1.1.1.1 [110/20] via 10.1.1.5, 00:06:24, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
R
156.26.32.0 [120/1] via 10.1.1.9, 00:00:18, Serial1
R
156.26.33.0 [120/1] via 10.1.1.9, 00:00:18, Serial1
10.0.0.0/30 is subnetted, 3 subnets
C
O IA
C
10.1.1.8 is directly connected, Serial1
10.1.1.0 [110/128] via 10.1.1.5, 00:06:24, Serial0
10.1.1.4 is directly connected, Serial0
Now modify the OSPF configurations on Routers B and C in order to create the NSSA.
Router B
router ospf 1
area 1 nssa
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
Router C
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router ospf 1
area 1 nssa
redistribute rip subnets
network 10.1.1.4 0.0.0.3 area 1
Verification
Verify that Area 1 has been configured as an NSSA.
rtrB#show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Supports only single TOS(TOS0) routes
It is an area border and autonomous system boundary router
Redistributing External Routes from,
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 5. Checksum Sum 0x324D4
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 1 normal 0 stub 1 nssa
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 11 times
Area ranges are
Number of LSA 3. Checksum Sum 0x20790
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
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Area 1
Number of interfaces in this area is 1
It is a NSSA area
Perform type-7/type-5 LSA translation
Area has no authentication
SPF algorithm executed 22 times
Area ranges are
Number of LSA 7. Checksum Sum 0x26D1D
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Now inspect the routing tables on Routers A, B, and C to view the effect of configuring Area 1 as an NSSA.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O E2
1.1.1.1 [110/20] via 10.1.1.1, 00:03:55, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O N2
156.26.32.0 [110/20] via 10.1.1.6, 00:03:55, Serial1
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O N2
156.26.33.0 [110/20] via 10.1.1.6, 00:03:55, Serial1
10.0.0.0/30 is subnetted, 3 subnets
O N2
10.1.1.8 [110/20] via 10.1.1.6, 00:03:55, Serial1
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
The redistributed RIP routes have been converted from OSPF E2 routes to OSPF N2 routes. This means that the redistributed RIP routes
are now being advertised as type 7 routes instead of type 5 routes. On Router A, these routes should still be OSPF type 5 routes because
Router B is converting them from type 7 to type 5.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O E2
156.26.32.0 [110/20] via 10.1.1.2, 00:07:28, Serial0/1
O E2
156.26.33.0 [110/20] via 10.1.1.2, 00:07:28, Serial0/1
10.0.0.0/30 is subnetted, 3 subnets
O E2
C
O IA
10.1.1.8 [110/20] via 10.1.1.2, 00:07:28, Serial0/1
10.1.1.0 is directly connected, Serial0/1
10.1.1.4 [110/128] via 10.1.1.2, 00:08:31, Serial0/1
Finally, inspect the IP routing table on Router C.
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rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
R
156.26.32.0 [120/1] via 10.1.1.9, 00:00:10, Serial1
R
156.26.33.0 [120/1] via 10.1.1.9, 00:00:10, Serial1
10.0.0.0/30 is subnetted, 3 subnets
C
O IA
C
10.1.1.8 is directly connected, Serial1
10.1.1.0 [110/128] via 10.1.1.5, 00:08:58, Serial0
10.1.1.4 is directly connected, Serial0
The 1.1.1.1 route that Router A was advertising as an OSPF external type 5 route has been blocked from entering the NSSA area by Router
B, but the inter-area routes have been permitted. Also notice that unlike a stub or totally stubby area, there is no default route advertised by
the ABR or ASBR.
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Verify that every router in the NSSA has been configured with the commandarea x nssa.
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2-5 area area-id nssa default-information-originate
Syntax Description:
area-id— OSPF area ID. This value can be entered as a decimal number in the range of 1 to 4,294,967,295 or in IP address form
in the range 0.0.0.1 to 255.255.255.255. Area 0 can be entered, but Area 0 cannot be configured as an NSSA.
Purpose: This command is used on an OSPF ABR or an OSPF ASBR to generate an OSPF NSSA external type 2 default route into an
NSSA. A default route does not need to be defined when using this command on an ABR. If this command is configured on an ASBR, then a
default route needs to be configured. In a stub or totally stubby area, the ABR to the stub area will prevent OSPF external routes (type 5) from
being advertised into the stub area. This implies that an ASBR cannot be part of a stubby or totally stubby area since an ASBR generates
OSPF external type 5 routes. Situations arise where you want to create a stubby or totally stubby area relative to OSPF but also want to
advertise redistributed routes from an ASBR across the area. An OSPF area that has these properties is an NSSA. In Figure 2-5, you want
Router B, the ABR, to block OSPF external routes from Area 1 and advertise a default route into the NSSA. You also want the routes
redistributed by Router C, the ASBR, to be allowed into the area. If you configure Area 1 as an NSSA, then the external OSPF routes that
Router B receives from Area 0 will be blocked from Area 1. The redistributed routes from the ASBR will be sent as OSPF type 7 routes.
Router B will convert these type 7 routes to OSPF type 5 routes and advertise them into Area 0. Normally, routes redistributed into OSPF are
type 5 routes. An ASBR that has been configured as an NSSA will generate type 7 routes instead of type 5 routes. By default, an ABR does
not generate a default route into an NSSA.
Figure 2-5. The default-information-originate Command Generates an OSPF NSSA Default Route
into an OSPF NSSA
Initial Cisco IOS Software Release: 11.2
Configuration Example: Advertising an OSPF NSSA Default Route into an OSPF
NSSA
In Figure 2-5, Routers C and D are running RIP Version 2. Router D is advertising the networks 156.26.32.0/24 and 156.26.33.0/24 to Router
C via RIP. Router C will redistribute the RIP routes, including the 10.1.1.8/30 network, into OSPF. Because Area 1 has been defined as an
NSSA, the redistributed RIP routes will be advertised into Area 1 as OSPF type 7 routes. Initially, you will configure Area 1 as a normal OSPF
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area in order to see the routes that are advertised.
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
redistribute connected subnets
network 10.1.1.0 0.0.0.3 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
lockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
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_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
interface Serial1
ip address 10.1.1.10 255.255.255.252
clockrate 64000
!
router ospf 1
redistribute rip subnets
network 10.1.1.4 0.0.0.3 area 1
!
router rip
version 2
passive-interface Serial0
network 10.0.0.0
_______________________________________________________________________
Router D
interface Loopback0
ip address 156.26.32.1 255.255.255.0
!
interface Loopback1
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ip address 156.26.33.1 255.255.255.0
!
interface Serial0/0
ip address 10.1.1.9 255.255.255.252
!
router rip
version 2
network 10.0.0.0
network 156.26.0.0
no auto-summary
Router A is advertising Loopback 0 as an OSPF type 5 external route because this route was injected into OSPF through redistribution.
Routers A and B are also learning the redistributed RIP routes as external type 5 OSPF routes.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O E2
156.26.32.0 [110/20] via 10.1.1.2, 00:02:25, Serial0/1
O E2
156.26.33.0 [110/20] via 10.1.1.2, 00:02:25, Serial0/1
10.0.0.0/30 is subnetted, 3 subnets
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O E2
C
10.1.1.8 [110/20] via 10.1.1.2, 00:02:25, Serial0/1
10.1.1.0 is directly connected, Serial0/1
O IA
10.1.1.4 [110/128] via 10.1.1.2, 00:02:25, Serial0/1
_______________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O E2
1.1.1.1 [110/20] via 10.1.1.1, 00:04:14, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O E2
156.26.32.0 [110/20] via 10.1.1.6, 00:04:14, Serial1
O E2
156.26.33.0 [110/20] via 10.1.1.6, 00:04:14, Serial1
10.0.0.0/30 is subnetted, 3 subnets
O E2
10.1.1.8 [110/20] via 10.1.1.6, 00:04:14, Serial1
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
Router C is learning the network redistributed by Router A as an OSPF external type 5 route.
rtrC#show ip route
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Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O E2
1.1.1.1 [110/20] via 10.1.1.5, 00:06:24, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
R
156.26.32.0 [120/1] via 10.1.1.9, 00:00:18, Serial1
R
156.26.33.0 [120/1] via 10.1.1.9, 00:00:18, Serial1
10.0.0.0/30 is subnetted, 3 subnets
C
O IA
C
10.1.1.8 is directly connected, Serial1
10.1.1.0 [110/128] via 10.1.1.5, 00:06:24, Serial0
10.1.1.4 is directly connected, Serial0
Now modify the OSPF configurations on Routers B and C in order to create the NSSA.
Router B
router ospf 1
area 1 nssa
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
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Router C
router ospf 1
area 1 nssa
redistribute rip subnets
network 10.1.1.4 0.0.0.3 area 1
Verify that Area 1 has been configured as an NSSA.
rtrB#show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Supports only single TOS(TOS0) routes
It is an area border and autonomous system boundary router
Redistributing External Routes from,
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 5. Checksum Sum 0x324D4
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 1 normal 0 stub 1 nssa
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 11 times
Area ranges are
Number of LSA 3. Checksum Sum 0x20790
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Area 1
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Number of interfaces in this area is 1
It is a NSSA area
Perform type-7/type-5 LSA translation
Area has no authentication
SPF algorithm executed 22 times
Area ranges are
Number of LSA 7. Checksum Sum 0x26D1D
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Now inspect the routing tables on Routers A, B, and C to view the effect of configuring Area 1 as an NSSA.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O E2
1.1.1.1 [110/20] via 10.1.1.1, 00:03:55, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O N2
156.26.32.0 [110/20] via 10.1.1.6, 00:03:55, Serial1
O N2
156.26.33.0 [110/20] via 10.1.1.6, 00:03:55, Serial1
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10.0.0.0/30 is subnetted, 3 subnets
O N2
10.1.1.8 [110/20] via 10.1.1.6, 00:03:55, Serial1
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
The redistributed RIP routes have been converted from OSPF E2 routes to OSPF N2 routes. This means that the redistributed RIP routes
are now being advertised as type 7 routes instead of type 5 routes. On Router A, these routes should still be OSPF type 5 routes since
Router B is converting them from type 7 to type 5.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O E2
156.26.32.0 [110/20] via 10.1.1.2, 00:07:28, Serial0/1
O E2
156.26.33.0 [110/20] via 10.1.1.2, 00:07:28, Serial0/1
10.0.0.0/30 is subnetted, 3 subnets
O E2
C
O IA
10.1.1.8 [110/20] via 10.1.1.2, 00:07:28, Serial0/1
10.1.1.0 is directly connected, Serial0/1
10.1.1.4 [110/128] via 10.1.1.2, 00:08:31, Serial0/1
Finally, inspect the IP routing table on Router C.
rtrC#show ip route
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Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
R
156.26.32.0 [120/1] via 10.1.1.9, 00:00:10, Serial1
R
156.26.33.0 [120/1] via 10.1.1.9, 00:00:10, Serial1
10.0.0.0/30 is subnetted, 3 subnets
C
O IA
C
10.1.1.8 is directly connected, Serial1
10.1.1.0 [110/128] via 10.1.1.5, 00:08:58, Serial0
10.1.1.4 is directly connected, Serial0
The 1.1.1.1 route that Router A was advertising as an OSPF external type 5 route has been blocked from entering the NSSA area by Router
B but the inter-area routes have been permitted. Also notice that unlike a stub or totally stubby area, there is no default route advertised by
the ABR or ASBR.
Modify the configuration on Router B in order to generate an OSPF NSSA default route into the NSSA.
Router B
router ospf 1
area 1 nssa defalt-information-originate
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
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Verification
Verify that a default route is being advertised into the NSSA by inspecting the routing table on Router C.
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 10.1.1.5 to network 0.0.0.0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
R
156.26.32.0 [120/1] via 10.1.1.9, 00:00:23, Serial1
R
156.26.33.0 [120/1] via 10.1.1.9, 00:00:23, Serial1
10.0.0.0/30 is subnetted, 3 subnets
C
O IA
C
10.1.1.8 is directly connected, Serial1
10.1.1.0 [110/128] via 10.1.1.5, 00:14:39, Serial0
10.1.1.4 is directly connected, Serial0
O*N2 0.0.0.0/0 [110/1] via 10.1.1.5, 00:14:39, Serial0
Troubleshooting
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Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Verify that every router in the NSSA has been configured with the command area x nssa.
Step 3. The command option default-information-originate can only be used on the NSSA ABR or ASBR. Ensure that this
command has been configured on either the ABR or ASBR.
< Free Open Study >
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< Free Open Study >
2-6 area area-id nssa no-redistribution
Syntax Description:
area-id— OSPF area ID. This value can be entered as a decimal number in the range of 1 to 4,294,967,295 or in IP address form
in the range 0.0.0.1 to 255.255.255.255. Area 0 can be entered but Area 0 cannot be configured as an NSSA.
Purpose: In a stub or totally stubby area, the ABR to the stub area will prevent OSPF external routes (type 5) from being advertised into the
stub area. This implies that an ASBR cannot be part of a stubby or totally stubby area because an ASBR generates OSPF external type 5
routes. Situations arise where you want to create a stubby or totally stubby area relative to OSPF but also want to advertise redistributed
routes from an ASBR across the area. An OSPF area that has these properties is an NSSA. In Figure 2-6, you want Router B, the ABR, to
block OSPF external routes from Area 1. You also want the routes redistributed by Router C, the ASBR, to be allowed into the area.
Additionally, Router B is an ASBR for the EIGRP routes received from Router E. You want the EIGRP routes to be redistributed into Area 0
but you do not want them advertised into Area 1, the NSSA. If you configure Area 1 as an NSSA, then the external OSPF routes that Router
B receives from Area 0 will be blocked from Area 1. The redistributed routes from the ASBR (Router C) will be sent as OSPF type 7 routes.
Router B will convert these type 7 routes to OSPF type 5 routes and advertise them into Area 0. If you use the no-redistribute keyword on
Router B, then the EIGRP routes will not be converted to OSPF type 7 routes. This will prevent them from entering Area 1 but will allow them
to be advertised into Area 0. Normally, routes redistributed into OSPF are type 5 routes. An ASBR that has been configured as an NSSA will
generate type 7 routes instead of type 5 routes.
Figure 2-6. An OSPF ABR/ASBR Can Control the Redistribution of Routes into an NSSA
Initial Cisco IOS Software Release: 11.2
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Configuration Example: Preventing Redistributed Routes from Entering an OSPF
NSSA
In Figure 2-6, Routers C and D are running RIP Version 2. Router D is advertising the networks 156.26.32.0/24 and 156.26.33.0/24 to Router
C via RIP. Router C will redistribute the RIP routes, including the 10.1.1.8/30 network, into OSPF. Routers B and E are running EIGRP.
Router B will redistribute the EIGRP routes into OSPF. Since Area 1 has been defined as an NSSA, the redistributed RIP and EIGRP routes
will be advertised into Area 1 as OSPF type 7 routes. Initially, you will configure Area 1 as a normal OSPF area in order to see the routes that
are advertised.
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
redistribute connected subnets
network 10.1.1.0 0.0.0.3 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.1 255.255.255.0
!
interface Serial0
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ip address 10.1.1.2 255.255.255.252
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
lockrate 64000
!
router eigrp 1
network 172.16.0.0
!
router ospf 1
redistribute eigrp 1 subnets
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
interface Serial1
ip address 10.1.1.10 255.255.255.252
clockrate 64000
!
router ospf 1
redistribute rip subnets
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network 10.1.1.4 0.0.0.3 area 1
!
router rip
version 2
passive-interface Serial0
network 10.0.0.0
_______________________________________________________________________
Router D
interface Loopback0
ip address 156.26.32.1 255.255.255.0
!
interface Loopback1
ip address 156.26.33.1 255.255.255.0
!
interface Serial0/0
ip address 10.1.1.9 255.255.255.252
!
router rip
version 2
network 10.0.0.0
network 156.26.0.0
no auto-summary
_______________________________________________________________________
Router E
interface Loopback0
ip address 142.1.4.4 255.255.255.255
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!
interface Ethernet0/0
ip address 172.16.1.2 255.255.255.0
!
router eigrp 1
network 142.1.0.0
network 172.16.0.0
no-auto-summary
Router A is advertising Loopback0 as an OSPF type 5 external route since this route was injected into OSPF through redistribution. Routers A
and B are also learning the redistributed RIP routes as external type 5 OSPF routes. Routers A and C are learning the EIGRP routes that
were redistributed by Router B.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O E2
156.26.32.0 [110/20] via 10.1.1.2, 00:02:29, Serial0/1
O E2
156.26.33.0 [110/20] via 10.1.1.2, 00:02:29, Serial0/1
172.16.0.0/24 is subnetted, 1 subnets
O E2
172.16.1.0 [110/20] via 10.1.1.2, 00:01:28, Serial0/1
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142.1.0.0/32 is subnetted, 1 subnets
O E2
142.1.4.4 [110/20] via 10.1.1.2, 00:01:28, Serial0/1
10.0.0.0/30 is subnetted, 3 subnets
O E2
C
10.1.1.8 [110/20] via 10.1.1.2, 00:02:29, Serial0/1
10.1.1.0 is directly connected, Serial0/1
O IA
10.1.1.4 [110/128] via 10.1.1.2, 00:02:30, Serial0/1
_______________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O E2
1.1.1.1 [110/20] via 10.1.1.1, 00:09:03, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O E2
156.26.32.0 [110/20] via 10.1.1.6, 00:09:03, Serial1
O E2
156.26.33.0 [110/20] via 10.1.1.6, 00:09:03, Serial1
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
142.1.0.0/32 is subnetted, 1 subnets
D
142.1.4.4 [90/409600] via 172.16.1.2, 00:09:41, Ethernet0
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10.0.0.0/30 is subnetted, 3 subnets
O E2
10.1.1.8 [110/20] via 10.1.1.6, 00:09:03, Serial1
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
Router C is learning the networks redistributed by Routers A and B as an OSPF external type 5 route.
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O E2
1.1.1.1 [110/20] via 10.1.1.5, 00:12:02, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
R
156.26.32.0 [120/1] via 10.1.1.9, 00:00:27, Serial1
R
156.26.33.0 [120/1] via 10.1.1.9, 00:00:27, Serial1
172.16.0.0/24 is subnetted, 1 subnets
O E2
172.16.1.0 [110/20] via 10.1.1.5, 00:10:43, Serial0
142.1.0.0/32 is subnetted, 1 subnets
O E2
142.1.4.4 [110/20] via 10.1.1.5, 00:10:43, Serial0
10.0.0.0/30 is subnetted, 3 subnets
C
10.1.1.8 is directly connected, Serial1
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O IA
C
10.1.1.0 [110/128] via 10.1.1.5, 00:12:03, Serial0
10.1.1.4 is directly connected, Serial0
Now modify the OSPF configurations on Routers B and C in order to create the NSSA.
Router B
router ospf 1
area 1 nssa
redistribute eigrp 1 subnets
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
Router C
router ospf 1
area 1 nssa
redistribute rip subnets
network 10.1.1.4 0.0.0.3 area 1
Verification
Verify that Area 1 has been configured as an NSSA.
rtrB#show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Supports only single TOS(TOS0) routes
It is an area border and autonomous system boundary router
Redistributing External Routes from,
eigrp 1, includes subnets in redistribution
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
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Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 7. Checksum Sum 0x3F1B4
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 1 normal 0 stub 1 nssa
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 10 times
Area ranges are
Number of LSA 3. Checksum Sum 0x275D9
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Area 1
Number of interfaces in this area is 1
It is a NSSA area
Perform type-7/type-5 LSA translation
Area has no authentication
SPF algorithm executed 23 times
Area ranges are
Number of LSA 9. Checksum Sum 0x4AE6A
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Now inspect the routing tables on Routers A, B, and C to view the effect of configuring Area 1 as an NSSA.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
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D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O E2
1.1.1.1 [110/20] via 10.1.1.1, 00:02:19, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O N2
156.26.32.0 [110/20] via 10.1.1.6, 00:02:20, Serial1
O N2
156.26.33.0 [110/20] via 10.1.1.6, 00:02:20, Serial1
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
142.1.0.0/32 is subnetted, 1 subnets
D
142.1.4.4 [90/409600] via 172.16.1.2, 00:18:28, Ethernet0
10.0.0.0/30 is subnetted, 3 subnets
O N2
10.1.1.8 [110/20] via 10.1.1.6, 00:02:20, Serial1
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
_______________________________________________________________________
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
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E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
R
156.26.32.0 [120/1] via 10.1.1.9, 00:00:06, Serial1
R
156.26.33.0 [120/1] via 10.1.1.9, 00:00:06, Serial1
172.16.0.0/24 is subnetted, 1 subnets
O N2
172.16.1.0 [110/20] via 10.1.1.5, 00:04:52, Serial0
142.1.0.0/32 is subnetted, 1 subnets
O N2
142.1.4.4 [110/20] via 10.1.1.5, 00:04:53, Serial0
10.0.0.0/30 is subnetted, 3 subnets
C
10.1.1.8 is directly connected, Serial1
O IA
C
10.1.1.0 [110/128] via 10.1.1.5, 00:04:53, Serial0
10.1.1.4 is directly connected, Serial0
The redistributed RIP and EIGRP routes have been converted from OSPF E2 routes to OSPF N2 routes. This means that the redistributed
RIP and EIGRP routes are now being advertised as type 7 routes instead of type 5 routes. On Router A, these routes should still be OSPF
type 5 routes. Router B is converting the external routes learned via Router C from type 7 to type 5. Router B is also advertising the
redistributed EIGRP routes as type 5 into Area 0 and type 7 into Area 1.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
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U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O E2
156.26.32.0 [110/20] via 10.1.1.2, 00:06:14, Serial0/1
O E2
156.26.33.0 [110/20] via 10.1.1.2, 00:06:14, Serial0/1
172.16.0.0/24 is subnetted, 1 subnets
O E2
172.16.1.0 [110/20] via 10.1.1.2, 00:06:46, Serial0/1
142.1.0.0/32 is subnetted, 1 subnets
O E2
142.1.4.4 [110/20] via 10.1.1.2, 00:06:46, Serial0/1
10.0.0.0/30 is subnetted, 3 subnets
O E2
C
10.1.1.8 [110/20] via 10.1.1.2, 00:06:14, Serial0/1
10.1.1.0 is directly connected, Serial0/1
The 1.1.1.1 route that Router A was advertising as an OSPF external type 5 route has been blocked from entering the NSSA area by Router
B, but the inter-area routes have been permitted. Also, notice that unlike a stub or totally stubby area there is no default route advertised by
the ABR or ASBR.
Finally, modify the configuration on Router B to prevent the redistributed EIGRP routes from being advertised into Area 1, but still allow them
to be advertised into Area 0.
Router B
router ospf 1
area 1 nssa no-redistribution
redistribute eigrp 1 subnets
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
Verify that Router B is no longer advertising the redistributed EIGRP routes into Area 1.
rtrB#show ip ospf
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Routing Process "ospf 1" with ID 2.2.2.2
Supports only single TOS(TOS0) routes
It is an area border and autonomous system boundary router
Redistributing External Routes from,
eigrp 1, includes subnets in redistribution
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 7. Checksum Sum 0x3EFB5
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 1 normal 0 stub 1 nssa
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 11 times
Area ranges are
Number of LSA 3. Checksum Sum 0x26FDC
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Area 1
Number of interfaces in this area is 1
It is a NSSA area, no redistribution into this area
Perform type-7/type-5 LSA translation
Area has no authentication
SPF algorithm executed 26 times
Area ranges are
Number of LSA 7. Checksum Sum 0x31A46
Number of DCbitless LSA 0
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Number of indication LSA 0
Number of DoNotAge LSA 0
_______________________________________________________________________
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
R
156.26.32.0 [120/1] via 10.1.1.9, 00:00:02, Serial1
R
156.26.33.0 [120/1] via 10.1.1.9, 00:00:02, Serial1
10.0.0.0/30 is subnetted, 3 subnets
C
10.1.1.8 is directly connected, Serial1
O IA
C
10.1.1.0 [110/128] via 10.1.1.5, 00:04:37, Serial0
10.1.1.4 is directly connected, Serial0
Verify that the redistributed EIGRP routes are being advertised into Area 0.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
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E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O E2
156.26.32.0 [110/20] via 10.1.1.2, 00:02:45, Serial0/1
O E2
156.26.33.0 [110/20] via 10.1.1.2, 00:02:45, Serial0/1
172.16.0.0/24 is subnetted, 1 subnets
O E2
172.16.1.0 [110/20] via 10.1.1.2, 00:14:41, Serial0/1
142.1.0.0/32 is subnetted, 1 subnets
O E2
142.1.4.4 [110/20] via 10.1.1.2, 00:14:41, Serial0/1
10.0.0.0/30 is subnetted, 3 subnets
O E2
C
O IA
10.1.1.8 [110/20] via 10.1.1.2, 00:02:45, Serial0/1
10.1.1.0 is directly connected, Serial0/1
10.1.1.4 [110/128] via 10.1.1.2, 00:14:42, Serial0/1
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Verify that every router in the NSSA has been configured with the commandarea x nssa.
Step 3. The no-redistribute keyword should only be used on the ASBR performing the route redistribution.
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2-7 area area-id nssa no-summary
Syntax Description:
area-id— OSPF area ID. This value can be entered as a decimal number in the range of 1 to 4,294,967,295 or in IP address form
in the range 0.0.0.1 to 255.255.255.255. Area 0 can be entered, but Area 0 cannot be configured as an NSSA.
Purpose: This command is used on an OSPF ABR to block OSPF inter-area routes from entering an NSSA. This command will also
generate an OSPF inter-area default route into the NSSA. This will make the NSSA a totally stubby area. In a stub or totally stubby area, the
ABR to the stub area will prevent OSPF external routes (type 5) from being advertised into the stub area. This implies that an ASBR cannot
be part of a stubby or totally stubby area because an ASBR generates OSPF external type 5 routes. Situations arise where you want to
create a stubby or totally stubby area relative to OSPF but also want to advertise redistributed routes from an ASBR across the area. An
OSPF area that has these properties is an NSSA. In Figure 2-7, you want Router B, the ABR, to block OSPF external routes and OSPF
inter-area routes from Area 1 and advertise a default route into the NSSA. You also want the routes redistributed by Router C, the ASBR, to
be allowed into the area. If you configure Area 1 as an NSSA, then the external OSPF routes that Router B receives from Area 0 will be
blocked from Area 1. The redistributed routes from the ASBR will be sent as OSPF type 7 routes. Router B will convert these type 7 routes to
OSPF type 5 routes and advertise them into Area 0. Normally, routes redistributed into OSPF are type 5 routes. An ASBR that has been
configured as an NSSA will generate type 7 routes instead of type 5 routes. By default, an ABR does not generate a default route into an
NSSA.
Figure 2-7. A Totally Stubby NSSA
Initial Cisco IOS Software Release: 11.2
Configuration Example: Creating a Totally Stubby NSSA
In Figure 2-7, Routers C and D are running RIP version 2. Router D is advertising the networks 156.26.32.0/24 and 156.26.33.0/24 to Router
C via RIP. Router C will redistribute the RIP routes, including the 10.1.1.8/30 network, into OSPF. Because Area 1 has been defined as an
NSSA, the redistributed RIP routes will be advertised into Area 1 as OSPF type 7 routes. Initially we will configure Area 1 as a normal OSPF
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area in order to see the routes that are advertised.
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
redistribute connected subnets
network 10.1.1.0 0.0.0.3 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
lockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
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_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
interface Serial1
ip address 10.1.1.10 255.255.255.252
clockrate 64000
!
router ospf 1
redistribute rip subnets
network 10.1.1.4 0.0.0.3 area 1
!
router rip
version 2
passive-interface Serial0
network 10.0.0.0
_______________________________________________________________________
Router D
interface Loopback0
ip address 156.26.32.1 255.255.255.0
!
interface Loopback1
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ip address 156.26.33.1 255.255.255.0
!
interface Serial0/0
ip address 10.1.1.9 255.255.255.252
!
router rip
version 2
network 10.0.0.0
network 156.26.0.0
no auto-summary
Router A is advertising Loopback0 as an OSPF type 5 external route because this route was injected into OSPF through redistribution.
Routers A and B are also learning the redistributed RIP routes as external type 5 OSPF routes.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O E2
156.26.32.0 [110/20] via 10.1.1.2, 00:02:25, Serial0/1
O E2
156.26.33.0 [110/20] via 10.1.1.2, 00:02:25, Serial0/1
10.0.0.0/30 is subnetted, 3 subnets
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O E2
C
10.1.1.8 [110/20] via 10.1.1.2, 00:02:25, Serial0/1
10.1.1.0 is directly connected, Serial0/1
O IA
10.1.1.4 [110/128] via 10.1.1.2, 00:02:25, Serial0/1
_______________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O E2
1.1.1.1 [110/20] via 10.1.1.1, 00:04:14, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O E2
156.26.32.0 [110/20] via 10.1.1.6, 00:04:14, Serial1
O E2
156.26.33.0 [110/20] via 10.1.1.6, 00:04:14, Serial1
10.0.0.0/30 is subnetted, 3 subnets
O E2
10.1.1.8 [110/20] via 10.1.1.6, 00:04:14, Serial1
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
Router C is learning the network redistributed by Router A as an OSPF external type 5 route.
rtrC#show ip route
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Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O E2
1.1.1.1 [110/20] via 10.1.1.5, 00:06:24, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
R
156.26.32.0 [120/1] via 10.1.1.9, 00:00:18, Serial1
R
156.26.33.0 [120/1] via 10.1.1.9, 00:00:18, Serial1
10.0.0.0/30 is subnetted, 3 subnets
C
O IA
C
10.1.1.8 is directly connected, Serial1
10.1.1.0 [110/128] via 10.1.1.5, 00:06:24, Serial0
10.1.1.4 is directly connected, Serial0
Now modify the OSPF configurations on Routers B and C in order to create the NSSA.
Router B
router ospf 1
area 1 nssa
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
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Router C
router ospf 1
area 1 nssa
redistribute rip subnets
network 10.1.1.4 0.0.0.3 area 1
Verify that Area 1 has been configured as an NSSA.
rtrB#show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Supports only single TOS(TOS0) routes
It is an area border and autonomous system boundary router
Redistributing External Routes from,
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 5. Checksum Sum 0x324D4
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 1 normal 0 stub 1 nssa
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 11 times
Area ranges are
Number of LSA 3. Checksum Sum 0x20790
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Area 1
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Number of interfaces in this area is 1
It is a NSSA area
Perform type-7/type-5 LSA translation
Area has no authentication
SPF algorithm executed 22 times
Area ranges are
Number of LSA 7. Checksum Sum 0x26D1D
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Now inspect the routing tables on Routers A, B, and C to view the effect of configuring Area 1 as an NSSA.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O E2
1.1.1.1 [110/20] via 10.1.1.1, 00:03:55, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O N2
156.26.32.0 [110/20] via 10.1.1.6, 00:03:55, Serial1
O N2
156.26.33.0 [110/20] via 10.1.1.6, 00:03:55, Serial1
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10.0.0.0/30 is subnetted, 3 subnets
O N2
10.1.1.8 [110/20] via 10.1.1.6, 00:03:55, Serial1
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
The redistributed RIP routes have been converted from OSPF E2 routes to OSPF N2 routes. This means that the redistributed RIP routes
are now being advertised as type 7 routes instead of type 5 routes. On Router A, these routes should still be OSPF type 5 routes because
Router B is converting them from type 7 to type 5.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
O E2
156.26.32.0 [110/20] via 10.1.1.2, 00:07:28, Serial0/1
O E2
156.26.33.0 [110/20] via 10.1.1.2, 00:07:28, Serial0/1
10.0.0.0/30 is subnetted, 3 subnets
O E2
C
O IA
10.1.1.8 [110/20] via 10.1.1.2, 00:07:28, Serial0/1
10.1.1.0 is directly connected, Serial0/1
10.1.1.4 [110/128] via 10.1.1.2, 00:08:31, Serial0/1
Finally, inspect the IP routing table on Router C.
rtrC#show ip route
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Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
R
156.26.32.0 [120/1] via 10.1.1.9, 00:00:10, Serial1
R
156.26.33.0 [120/1] via 10.1.1.9, 00:00:10, Serial1
10.0.0.0/30 is subnetted, 3 subnets
C
O IA
C
10.1.1.8 is directly connected, Serial1
10.1.1.0 [110/128] via 10.1.1.5, 00:08:58, Serial0
10.1.1.4 is directly connected, Serial0
The 1.1.1.1 route that Router A was advertising as an OSPF external type 5 route has been blocked from entering the NSSA area by Router
B, but the inter-area routes have been permitted. Also notice that unlike a stub or totally stubby area, there is no default route advertised by
the ABR or ASBR.
Modify the configuration on Router B in order to generate a default route into the NSSA and to block OSPF inter-area routes.
Router B
router ospf 1
area 1 nssa no-summary
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
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Verification
Verify that a default route is being advertised into the NSSA and that OSPF inter-area routes are being blocked by the ABR by inspecting the
routing table on Router C.
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 10.1.1.5 to network 0.0.0.0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
156.26.0.0/24 is subnetted, 2 subnets
R
156.26.32.0 [120/1] via 10.1.1.9, 00:00:25, Serial1
R
156.26.33.0 [120/1] via 10.1.1.9, 00:00:25, Serial1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.8 is directly connected, Serial1
C
10.1.1.4 is directly connected, Serial0
O*IA 0.0.0.0/0 [110/65] via 10.1.1.5, 00:00:03, Serial0
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
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Step 2. Verify that every router in the NSSA has been configured with the commandarea x nssa.
Step 3. The command option no-summary can only be used on the NSSA ABR. Ensure that this command has been configured
on the ABR.
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2-8 area area-id range ip-address mask
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2-9 area area-id range ip-address mask advertise
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2-10 area area-id range ip-address mask not-advertise
Syntax Description:
area-id— OSPF area ID. This value can be entered as a decimal number in the range of 0 to 4,294,967,295 or in IP address form
in the range 0.0.0.0 to 255.255.255.255.
ip-address— IP address of the summary route.
mask— Subnet mask used to generate the summary.
Purpose: OSPF can summarize OSPF routes from the backbone or Area 0 into a non-zero OSPF area or from a non-zero area into the
backbone. OSPF route summarization can only occur on an ABR. An ABR is a router than has at least one interface in Area 0 and at least
one interface in a non-zero OSPF area. Commands 2-8 and 2-9 are equivalent. Using the keyword not-advertise will suppress the
advertisement of the summary route by the ABR.
Initial Cisco IOS Software Release: 10.0
Configuration Example 1: Summarizing OSPF Routes from a Non-zero OSPF Area
into the Backbone
In Figure 2-8, Router B will summarize the four Area 1 routes into Area 0. This example simulates four networks on Router B using loopback
interfaces. These four networks will then be summarized into the backbone using the area range command.
Figure 2-8. An ABR Can Summarize OSPF Routes from a Non-zero Area into the Backbone or
Area 0
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Loopback1
ip address 156.26.32.1 255.255.255.240
!
interface Loopback2
ip address 156.26.32.17 255.255.255.240
!
interface Loopback3
ip address 156.26.32.33 255.255.255.240
!
interface Loopback4
.
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ip address 156.26.32.49 255.255.255.240
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 156.26.32.0 0.0.0.63 area 1
Before summarizing the routes, inspect the IP routing table on Router A to verify that the four networks are being advertised.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
156.26.0.0/32 is subnetted, 4 subnets
O IA
156.26.32.33 [110/65] via 10.1.1.2, 00:06:57, Serial0/1
O IA
156.26.32.49 [110/65] via 10.1.1.2, 00:06:57, Serial0/1
O IA
156.26.32.1 [110/65] via 10.1.1.2, 00:06:57, Serial0/1
O IA
156.26.32.17 [110/65] via 10.1.1.2, 00:06:57, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
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A 26-bit subnet mask is required to summarize the four loopback addresses being advertised by Router B. Modify the configuration on Router
B in order to summarize the four loopback addresses.
Router B
router ospf 1
area 1 range 156.26.32.0 255.255.255.192
network 10.1.1.0 0.0.0.3 area 0
network 156.26.32.0 0.0.0.63 area 1
There are two important components to notice in the area range command. The first is the area ID. This is the area where the routes
originated. In this example, the originating area is Area 1. The second component is the mask that is used with the area range command.
The format of the mask is the opposite of the format used with the OSPF network command.
Verification
Verify that the four loopback networks have been summarized by Router B by inspecting the IP routing table on Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
156.26.0.0/26 is subnetted, 1 subnets
O IA
156.26.32.0 [110/65] via 10.1.1.2, 00:04:57, Serial0/1
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10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.8 is directly connected, Serial0/0
C
10.1.1.0 is directly connected, Serial0/1
Configuration Example 2: Summarizing OSPF Routes from Area 0 into a Non-zero
OSPF Area
In Figure 2-9, Router B will summarize the four Area 0 routes into Area 1. This example simulates four networks on Router B using loopback
interfaces. These four networks will then be summarized into Area 1 from Area 0 using the area range command. The configuration changes
from the previous example are highlighted in the following listing.
Figure 2-9. An ABR Can Summarize OSPF Routes from the Backbone or Area 0 into a Non-Zero
Area
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
.
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!
router ospf 1
network 10.1.1.0 0.0.0.3 area 1
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Loopback1
ip address 156.26.32.1 255.255.255.240
!
interface Loopback2
ip address 156.26.32.17 255.255.255.240
!
interface Loopback3
ip address 156.26.32.33 255.255.255.240
!
interface Loopback4
ip address 156.26.32.49 255.255.255.240
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 1
network 156.26.32.0 0.0.0.63 area 0
.
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Before summarizing the routes, inspect the IP routing table on Router A to verify that the four networks are being advertised.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
156.26.0.0/32 is subnetted, 4 subnets
O IA
156.26.32.33 [110/65] via 10.1.1.2, 00:06:29, Serial0/1
O IA
156.26.32.49 [110/65] via 10.1.1.2, 00:06:29, Serial0/1
O IA
156.26.32.1 [110/65] via 10.1.1.2, 00:06:29, Serial0/1
O IA
156.26.32.17 [110/65] via 10.1.1.2, 00:06:29, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.8 is directly connected, Serial0/0
C
10.1.1.0 is directly connected, Serial0/1
A 26-bit subnet mask is required to summarize the four loopback addresses being advertised by Router B. Modify the configuration on
Router B in order to summarize the four loopback addresses.
Router B
router ospf 1
area 0 range 156.26.32.0 255.255.255.192
network 10.1.1.0 0.0.0.3 area 1
network 156.26.32.0 0.0.0.63 area 0
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Verification
Verify that the four loopback networks have been summarized by Router B by inspecting the IP routing table on Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
156.26.0.0/26 is subnetted, 1 subnets
O IA
156.26.32.0 [110/65] via 10.1.1.2, 00:04:57, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.8 is directly connected, Serial0/0
C
10.1.1.0 is directly connected, Serial0/1
Configuration Example 3: Using a Static Route to Null 0 for the Summary Address
If the ABR has a default static route pointing to the router that is receiving the summary for the four loopback addresses, then this could
create a forwarding loop. In Figure 2-10, the network 156.26.32.0/28 is down. Also, Router B has a default static route pointing to Router A.
Router A is receiving a summary from Router B that contains the network 156.26.32.0/28.
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Figure 2-10. A Forwarding Loop Can Be Created If the Router Advertising the Summary Has a
Default Static Route
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 1
______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
.
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interface Loopback1
ip address 156.26.32.1 255.255.255.240
shutdown
!
interface Loopback2
ip address 156.26.32.17 255.255.255.240
!
interface Loopback3
ip address 156.26.32.33 255.255.255.240
!
interface Loopback4
ip address 156.26.32.49 255.255.255.240
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
no ip directed-broadcast
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 1
network 156.26.32.0 0.0.0.63 area 0
!
ip route 0.0.0.0 0.0.0.0 Serial0
When Router A sends traffic to Router B for host 156.26.32.1, Router B will not find this specific network in the IP routing table. Router B will
then use the default route and send the traffic back to Router A as seen in the following ping trace.
rtrA#trace 156.26.32.1
Type escape sequence to abort.
Tracing the route to 156.26.32.1
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1 10.1.1.2 16 msec 16 msec 16 msec
2 10.1.1.1 28 msec 28 msec 28 msec
To prevent this situation, create a static route to Null0 for every summary that the ABR is advertising. In IOS 12.X, OSPF will automatically
create the route to Null0 for the summary.
Router B
ip route 0.0.0.0 0.0.0.0 Serial0
ip route 156.26.32.0 255.255.255.192 Null0
Even if the ABR does not have a default route, it is always a good idea to create a static route to Null0 for every summary that the ABR is
advertising. If you now perform a ping trace from Router A you can see that Router B is discarding the traffic since the specific route for
156.26.32.1 is no longer in the IP routing table. Router B will look up the best match for the route, which is now Null0. The traffic will be
discarded.
rtrA#trace 156.26.32.1
Type escape sequence to abort.
Tracing the route to 156.26.32.1
1 10.1.1.2 16 msec 16 msec 16 msec
2 10.1.1.2 !H !H *
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. The area area-id range command will only work on an OSPF ABR.
Step 3. Verify that you are using the proper area ID in thearea area-id range command.
Step 4. Verify that you are using the correct IP address and mask with the
area range command.
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2-11 area area-id stub
Syntax Description:
area-id— OSPF area ID. This value can be entered as a decimal number in the range of 0 to 4,294,967,295 or in IP address form
in the range 0.0.0.0 to 255.255.255.255.
Purpose: In Figure 2-11, Area 1 has one exit point. Routers in Area 1 do not need to know the specific external routes that are being
redistributed into OSPF by the ASBR. Therefore, Area 1 can be configured as a stub area and the ABR will advertise a default route into Area
1.
Figure 2-11. An OSPF Stub Area with One Exit
In Figure 2-12, Area 1 has two exit points. If routing to the external networks that have been redistributed into OSPF by the ASBR can be
sub-optimal, then Area 1 can be configured as a stub area. The routers in Area 1 will be receiving a default route advertisement from both
ABRs. All routers in a stub area, including the ABR, must be configured with the command area area-id stub. Inter-area OSPF routes will be
advertised into a stub area but external OSPF routes will be blocked. The ABR for the stub area will inject a default route into the stub area.
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The backbone or Area 0 cannot be configured as a stub area. An ASBR cannot be part of a stub area since the purpose of an ASBR is to
inject external routes into OSPF. A stub area cannot be used as the transit area for a virtual link.
Figure 2-12. An OSPF Stub Area with Multiple Exits
Initial Cisco IOS Software Release: 10.0
Configuration Example: Configuring an OSPF Stub Area
In Figure 2-13, Router C is redistributing connected interfaces into OSPF. These redistributed routes are OSPF external routes.
Figure 2-13. An OSPF Stub Area
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 1
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
clock rate 64000
!
.
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router ospf 1
network 10.1.1.4 0.0.0.3 area 0
network 10.1.1.0 0.0.0.3 area 1
_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router ospf 1
redistribute connected subnets
network 10.1.1.4 0.0.0.15 area 0
Before configuring Area 1 as a stub area, verify that the redistributed routes are being advertised as OSPF external routes.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
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C
1.1.1.1 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O E2
3.3.3.3 [110/20] via 10.1.1.2, 00:00:25, Serial0/1
10.0.0.0/30 is subnetted, 3 subnets
C
10.1.1.8 is directly connected, Serial0/0
C
10.1.1.0 is directly connected, Serial0/1
O IA
10.1.1.4 [110/128] via 10.1.1.2, 00:00:25, Serial0/1
There is one OSPF external route and one OSPF inter-area route in the routing table on Router A. Configure Area 1 as a stub area by
modifying the configurations on Routers A and B as shown in the following listing.
Router A
router ospf 1
area 1 stub
network 10.1.1.0 0.0.0.3 area 1
_______________________________________________________________________
Router B
router ospf 1
area 1 stub
network 10.1.1.0 0.0.0.3 area 1
network 10.1.1.4 0.0.0.3 area 0
Verification
Verify that OSPF inter-area routes are being advertised into the stub area. Also, verify that external OSPF routes have been blocked from
being advertised into the stub area and that the ABR is injecting a default route into the stub area.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
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N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 10.1.1.2 to network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 3 subnets
C
10.1.1.8 is directly connected, Serial0/0
C
10.1.1.0 is directly connected, Serial0/1
O IA
10.1.1.4 [110/128] via 10.1.1.2, 00:00:04, Serial0/1
O*IA 0.0.0.0/0 [110/65] via 10.1.1.2, 00:00:04, Serial0/1
Verify that Area 1 is a stub area by using the command show ip ospf on Routers A and B.
rtrA#show ip ospf
Routing Process "ospf 1" with ID 1.1.1.1
Supports only single TOS(TOS0) routes
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 1 normal 1 stub 0 nssa
Area BACKBONE(0) (Inactive)
Number of interfaces in this area is 0
Area has no authentication
SPF algorithm executed 2 times
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Area ranges are
Number of LSA 1. Checksum Sum 0x51E9
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Area 1
Number of interfaces in this area is 1
It is a stub area
Area has no authentication
SPF algorithm executed 6 times
Area ranges are
Number of LSA 9. Checksum Sum 0x38619
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
______________________________________________________________________
rtrB#show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Supports only single TOS(TOS0) routes
It is an area border router
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 3. Checksum Sum 0x14F43
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 3
Number of areas in this router is 2. 1 normal 1 stub 0 nssa
Area BACKBONE(0)
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Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 15 times
Area ranges are
Number of LSA 4. Checksum Sum 0x20ABC
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Area 1
Number of interfaces in this area is 1
It is a stub area
generates stub default route with cost 1
Area has no authentication
SPF algorithm executed 18 times
Area ranges are
Number of LSA 8. Checksum Sum 0x34E69
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Ensure that every router in the stub area and the ABR to the stub area have the area configured as a stub using the router
configuration command area area-id stub.
Step 3. An ASBR should not be part of a stub area.
Step 4. A stub area cannot be used as the transit area for a virtual link.
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2-12 area area-id stub no-summary
Syntax Description:
area-id— OSPF area ID. This value can be entered as a decimal number in the range of 0 to 4,294,967,295 or in IP address form
in the range 0.0.0.0 to 255.255.255.255.
Purpose: Use of the no-summary keyword on the stub area's ABR creates a totally stubby area. In a totally stubby area, both external and
inter-area OSPF routes are blocked from being advertised into the area. The backbone or Area 0 cannot be configured as a totally stubby
area. An ASBR cannot be part of a totally stubby area, since the purpose of an ASBR is to inject external routes into OSPF. A totally stubby
area cannot be used as the transit area for a virtual link.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Configuring an OSPF Totally Stubby Area
In Figure 2-14, Router C is redistributing connected interfaces into OSPF. These redistributed routes are OSPF external routes.
Figure 2-14. An OSPF Totally Stubby Area
Router A
interface Loopback0
.
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ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 1
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
clock rate 64000
!
router ospf 1
network 10.1.1.4 0.0.0.3 area 0
network 10.1.1.0 0.0.0.3 area 1
_______________________________________________________________________
Router C
interface Loopback0
.
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ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router ospf 1
redistribute connected subnets
network 10.1.1.4 0.0.0.15 area 0
Before configuring Area 1 as a totally stubby area, verify that the redistributed routes and OSPF inter-area routes are being advertised into
Area 1.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O E2
3.3.3.3 [110/20] via 10.1.1.2, 00:00:02, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
O IA
10.1.1.0 is directly connected, Serial0/1
10.1.1.4 [110/128] via 10.1.1.2, 00:00:02, Serial0/1
There is one OSPF external route and one OSPF inter-area route in the routing table on Router A. Configure Area 1 as a stub area by
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modifying the configurations on Routers A and B as shown in the following listing.
Router A
router ospf 1
area 1 stub
network 10.1.1.0 0.0.0.3 area 1
_______________________________________________________________________
Router B
router ospf 1
area 1 stub
network 10.1.1.4 0.0.0.3 area 0
network 10.1.1.0 0.0.0.3 area 1
Verification
Verify that the external OSPF routes have been blocked from being advertised into the stub area. Also verify that the ABR is injecting a
default route into the stub area.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 10.1.1.2 to network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
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C
1.1.1.1 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial1
O IA
10.1.1.4 [110/128] via 10.1.1.2, 00:00:09, Serial0/1
O*IA 0.0.0.0/0 [110/65] via 10.1.1.2, 00:00:09, Serial0/1
Modify the configuration on Router B, the ABR, to create a totally stubby area.
Router B
router ospf 1
area 1 stub no-summary
network 10.1.1.4 0.0.0.3 area 0
network 10.1.1.0 0.0.0.3 area 1
Verify that the OSPF inter-area routes are no longer being advertised by the ABR into the stub area.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 10.1.1.2 to network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
O*IA 0.0.0.0/0 [110/65] via 10.1.1.2, 00:00:17, Serial0/1
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You can also verify that Router B is blocking OSPF inter-area routes or summary LSAs by using the command show ip ospf.
rtrB#show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Supports only single TOS(TOS0) routes
It is an area border router
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 3. Checksum Sum 0x14946
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 1 normal 1 stub 0 nssa
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 17 times
Area ranges are
Number of LSA 4. Checksum Sum 0x204BF
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Area 1
Number of interfaces in this area is 1
It is a stub area, no summary LSA in this area
generates stub default route with cost 1
Area has no authentication
SPF algorithm executed 25 times
Area ranges are
Number of LSA 7. Checksum Sum 0x424A1
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Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Ensure that every router in the stub area and the ABR to the stub area have the area configured as a stub by using the
router configuration command area area-id stub.
Step 3. When creating a totally stubby area, verify that the keywordno-summary has been used on the ABR to the stub area.
Step 4. An ASBR should not be part of a totally stubby area.
Step 5. A totally stubby area cannot be used as the transit area for a virtual link.
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2-13 area transit-area-id virtual-link router-id
Syntax Description:
transit-area-id— The OSPF area ID of the area connecting the two ABRs that the virtual link will cross. This value can be entered
as a decimal number in the range of 0 to 4,294,967,295 or in IP address form in the range 0.0.0.0 to 255.255.255.255.
router-id— OSPF router ID of the router at the remote end of the virtual link.
Purpose: All non-zero OSPF areas must have a connection to the backbone or Area 0 and Area 0 must be contiguous. A virtual link is used
to repair a segmented backbone or to connect a non-zero area that has been disconnected from Area 0. The transit area cannot be a stub
area. Virtual links are used to repair a discontiguous backbone or to temporarily attach a disconnected non-zero area to the backbone. A
virtual link should not be part of an initial OSPF design.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Creating an OSPF Virtual Link
In Figure 2-15, Area 2 does not have a direct connection to Area 0. A virtual link is needed to repair this situation. Initially, you will configure
the routers in Figure 2-15 without using a virtual link.
Figure 2-15. OSPF Virtual Link
Router A
.
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interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 1.1.1.1 0.0.0.0 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
.
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Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router ospf 1
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
If you inspect the IP routing table on Router B, you will see that the 3.3.3.3 network from Router C is not present.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O IA
1.1.1.1 [110/65] via 10.1.1.1, 00:01:01, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
.
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C
10.1.1.4 is directly connected, Serial1
Area 2 on Router C does not have a direct connection to Area 0. A virtual link needs to be configured to correct this situation. The transit
area in this case is Area 1. You also need the router IDs of the two ABRs to be able to construct the virtual link. The first method to determine
the router ID is to use the show ip ospf neighbor command. This will display the router ID of the remote end of the virtual link.
rtrB#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
1.1.1.1
1 FULL/ -
00:00:32
10.1.1.1
Serial0
3.3.3.3
1 FULL/ -
00:00:36
10.1.1.6
Serial1
_______________________________________________________________________
rtrC#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/ -
Dead Time Address
00:00:35
10.1.1.5
Interface
Serial0
Router B has an ID of 2.2.2.2 and Router C has an ID of 3.3.3.3. The local router ID can be found by using the show ip ospf command.
rtrB#show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Supports only single TOS(TOS0) routes
It is an area border router
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 2 normal 0 stub 0 nssa
Area BACKBONE(0)
Number of interfaces in this area is 2
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Area has no authentication
SPF algorithm executed 3 times
Area ranges are
Number of LSA 3. Checksum Sum 0x1FD00
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Area 1
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 2 times
Area ranges are
Number of LSA 5. Checksum Sum 0x2B171
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
_______________________________________________________________________
rtrC#show ip ospf
Routing Process "ospf 1" with ID 3.3.3.3
Supports only single TOS(TOS0) routes
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 2 normal 0 stub 0 nssa
Area 1
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Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 12 times
Area ranges are
Number of LSA 5. Checksum Sum 0x2B171
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Area 2
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 1 times
Area ranges are
Number of LSA 1. Checksum Sum 0xDDE0
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
We now have the information we need to configure the virtual link. On Router B, the form of the command is:
area transit-area-id virtual-link router-C-ID
And on Router C the command takes the form:
area transit-area-id virtual-link router-B-ID
Modify the configurations on Routers B and C to construct the virtual link.
Router B
router ospf 1
area 1 virtual-link 3.3.3.3
network 2.2.2.2 0.0.0.0 area 0
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network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
Router C
router ospf 1
area 1 virtual-link 2.2.2.2
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Verification
Verify that Router C has a connection to Area 0.
rtrC#show ip ospf
Routing Process "ospf 1" with ID 3.3.3.3
Supports only single TOS(TOS0) routes
It is an area border router
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 3. 3 normal 0 stub 0 nssa
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 3 times
Area ranges are
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Number of LSA 6. Checksum Sum 0x45CF4
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 3
Area 1
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 14 times
Area ranges are
Number of LSA 10. Checksum Sum 0x4A8BD
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Area 2
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 3 times
Area ranges are
Number of LSA 5. Checksum Sum 0x2B425
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Router C now has an interface in Area 0 and this interface is the virtual link. Verify that the virtual link is active on Routers B and C.
rtrB#show ip ospf virtual-links
Virtual Link OSPF_VL0 to router 3.3.3.3 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial1, Cost of using 64
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Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:09
Adjacency State FULL (Hello suppressed)
_______________________________________________________________________
rtrC#show ip ospf virtual-links
Virtual Link OSPF_VL0 to router 2.2.2.2 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:00
Adjacency State FULL (Hello suppressed)
Finally, verify that the loopback interfaces for Routers A, B, and C are being advertised to all OSPF neighbors.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
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2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.2, 00:09:04, Serial0/1
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/129] via 10.1.1.2, 00:09:04, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
O IA
10.1.1.4 [110/128] via 10.1.1.2, 00:09:04, Serial0/1
_______________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/65] via 10.1.1.1, 00:10:19, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/65] via 10.1.1.6, 00:10:20, Serial1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
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_______________________________________________________________________
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/129] via 10.1.1.5, 00:11:10, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.5, 00:11:11, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
O
10.1.1.0 [110/128] via 10.1.1.5, 00:11:11, Serial0
C
10.1.1.4 is directly connected, Serial0
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers using the show ip ospf neighbor command.
Step 2. Verify that the transit area ID used in thearea virtual-link command is the proper area.
Step 3. Verify that the router IDs used in thearea virtual-link are correct.
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< Free Open Study >
2-14 area transit-area-id virtual-link router-id authentication
authentication-key password
< Free Open Study >
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< Free Open Study >
2-15 area transit-area-id virtual-link router-id authentication
message-digest
< Free Open Study >
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< Free Open Study >
2-16 area transit-area-id virtual-link router-id authentication null
NOTE
Command 2-15 requires the use of the area transit-area-id virtual-link router-id message-digest-key key-id md5 password
command (see Section 2-20).
Syntax Description:
transit-area-id— The OSPF area ID of the area connecting the two ABRs that the virtual link will cross. This value can be entered
as a decimal number in the range of 0 to 4,294,967,295 or in IP address form in the range 0.0.0.0 to 255.255.255.255. The transit
area cannot be a stub area.
router-id— OSPF router ID of the router at the remote end of the virtual link.
key-id— Key to use to encrypt a password. The range of values is 1 to 255. Both ends of a virtual link must use the same key and
password.
password— Password to be used for authentication in the selected area on the selected interface or virtual link. The password is
an alphanumeric string from 1 to 8 characters.
Purpose: In Cisco IOS Software Releases prior to 12.0, if authentication was enabled in Area 0, then all virtual links had to be configured
with the same authentication type. This command allows the configuration of authentication over a virtual link that is different from the
authentication type being used in Area 0. If authentication is used, then both ends of the virtual link must be configured with the same
authentication method. Also, the same password or key and password must be configured on both ends of the virtual link.
Initial Cisco IOS Software Release: 12.0
Configuration Example 1: Simple Password Authentication Over a Virtual Link
In Figure 2-16, Area 2 does not have a direct connection to Area 0. A virtual link is needed to repair this situation. Start by configuring the
routers in Figure 2-16 without using authentication over the virtual link.
Figure 2-16. The Authentication Type Used on an OSPF Virtual Link Can Be Different from the
Type Used in Area 0
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 1.1.1.1 0.0.0.0 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
.
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ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router ospf 1
area 1 virtual-link 3.3.3.3
network 10.1.1.0 0.0.0.3 area 0
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.4 0.0.0.3 area 1
________________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router ospf 1
area 1 virtual-link 2.2.2.2
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Area 2 on Router C does not have a direct connection to Area 0. A virtual link needs to be configured to correct this situation. The transit
area in this case is Area 1. You also need the router IDs of the two ABRs to be able to construct the virtual link. The first method to determine
the router ID is to use the show ip ospf neighbor command. This will display the router ID of the remote end of the virtual link.
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/ -
Dead Time Address
00:00:32
10.1.1.1
Interface
Serial0
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3.3.3.3
1 FULL/ -
00:00:36
10.1.1.6
Serial1
_______________________________________________________________________
rtrC#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/ -
Dead Time Address
00:00:35
10.1.1.5
Interface
Serial0
Router B has an ID of 2.2.2.2 and Router C has an ID of 3.3.3.3. The local router ID can be found by using the show ip ospf command.
rtrB#show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Supports only single TOS(TOS0) routes
It is an area border router
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 2 normal 0 stub 0 nssa
Area BACKBONE(0)
Number of interfaces in this area is 2
Area has no authentication
SPF algorithm executed 3 times
Area ranges are
Number of LSA 3. Checksum Sum 0x1FD00
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Area 1
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Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 2 times
Area ranges are
Number of LSA 5. Checksum Sum 0x2B171
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
_______________________________________________________________________
rtrC#show ip ospf
Routing Process "ospf 1" with ID 3.3.3.3
Supports only single TOS(TOS0) routes
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 2 normal 0 stub 0 nssa
Area 1
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 12 times
Area ranges are
Number of LSA 5. Checksum Sum 0x2B171
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
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Area 2
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 1 times
Area ranges are
Number of LSA 1. Checksum Sum 0xDDE0
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
You want to add simple password authentication to the virtual link but you do not want to configure authentication over any other link in Area
0. Modify the configurations on Routers B and C to enable simple password authentication over the virtual link using the password cisco.
Router B
router ospf 1
area 1 virtual-link 3.3.3.3 authentication authentication-key cisco
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
Router C
router ospf 1
area 1 virtual-link 2.2.2.2 authentication authentication-key cisco
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Verification
Router C now has an interface in Area 0 and this interface is the virtual link. Verify that the virtual link is active on Routers B and C.
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rtrB#show ip ospf virtual-links
Virtual Link OSPF_VL0 to router 3.3.3.3 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial1, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:09
Adjacency State FULL (Hello suppressed)
_______________________________________________________________________
rtrC#show ip ospf virtual-links
Virtual Link OSPF_VL1 to router 2.2.2.2 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:06
Adjacency State FULL (Hello suppressed)
Also, verify that the loopback interfaces for Routers A, B, and C are being advertised to all OSPF neighbors.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
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U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.2, 00:09:04, Serial0/1
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/129] via 10.1.1.2, 00:09:04, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
O IA
10.1.1.4 [110/128] via 10.1.1.2, 00:09:04, Serial0/1
_______________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/65] via 10.1.1.1, 00:10:19, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
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3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/65] via 10.1.1.6, 00:10:20, Serial1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
_______________________________________________________________________
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/129] via 10.1.1.5, 00:11:10, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.5, 00:11:11, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
O
10.1.1.0 [110/128] via 10.1.1.5, 00:11:11, Serial0
C
10.1.1.4 is directly connected, Serial0
Configuration Example 2: MD5 Authentication Over a Virtual Link
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Modify the configurations on Routers B and C by adding MD5 password authentication to the virtual link. For this example, use the password
cisco.
Router B
router ospf 1
area 1 virtual-link 3.3.3.3 authentication message-digest
area 1 virtual-link 3.3.3.3 message-digest-key 1 md5 cisco
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
Router C
router ospf 1
area 1 virtual-link 2.2.2.2 authentication message-digest
area 1 virtual-link 2.2.2.2 message-digest-key 1 md5 cisco
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Verification
Verify that the virtual link is still active and that MD5 authentication is enabled.
rtrB#show ip ospf virtual-links
Virtual Link OSPF_VL3 to router 3.3.3.3 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial1, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
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Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:01
Adjacency State FULL (Hello suppressed)
Message digest authentication enabled
Youngest key id is 1
rtrC#show ip ospf virtual-links
Virtual Link OSPF_VL4 to router 2.2.2.2 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Adjacency State FULL (Hello suppressed)
Message digest authentication enabled
Youngest key id is 1
Also, verify that the loopback interfaces for Routers A, B, and C are being advertised to all OSPF neighbors.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
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1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.2, 00:09:04, Serial0/1
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/129] via 10.1.1.2, 00:09:04, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
O IA
10.1.1.4 [110/128] via 10.1.1.2, 00:09:04, Serial0/1
_______________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/65] via 10.1.1.1, 00:10:19, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/65] via 10.1.1.6, 00:10:20, Serial1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
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C
10.1.1.4 is directly connected, Serial1
_______________________________________________________________________
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/129] via 10.1.1.5, 00:11:10, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.5, 00:11:11, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
O
10.1.1.0 [110/128] via 10.1.1.5, 00:11:11, Serial0
C
10.1.1.4 is directly connected, Serial0
Configuration Example 3: Changing Keys and Passwords
For additional security you may choose to periodically change the key and password. With clear-text authentication, when you change
passwords there will be a loss of OSPF connectivity from the time you change the password on one end of the virtual link until you change
the password at the other end of the virtual link. With MD5 authentication, you can configure a new key and password on a virtual link while
leaving the old key and password in place. The old key and password will continue to be used until the new key and password are configured
on the other end of the virtual link. Modify the key and password on the virtual link between Routers B and C. First add a new key and
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password to Router B in order to observe the behavior when the new key and password have been configured on only one end of the virtual
link.
Router B
router ospf 1
area 1 virtual-link 3.3.3.3 authentication message-digest
area 1 virtual-link 3.3.3.3 message-digest-key 1 md5 cisco
area 1 virtual-link 3.3.3.3 message-digest-key 2 md5 bosco
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
Examine the effect of adding a new key and password on only one end of the virtual link.
rtrB#show ip ospf virtual-links
Virtual Link OSPF_VL3 to router 3.3.3.3 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial1, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:08
Adjacency State FULL (Hello suppressed)
Message digest authentication enabled
Youngest key id is 2
Rollover in progress, 1 neighbor(s) using the old key(s):
key id 1
Notice that both keys are being used for authentication. Configure the new key and password on Router C while leaving the old key and
password in place.
Router C
router ospf 1
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area 1 virtual-link 2.2.2.2 authentication message-digest
area 1 virtual-link 2.2.2.2 message-digest-key 1 md5 cisco
area 1 virtual-link 2.2.2.2 message-digest-key 2 md5 bosco
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Verify that Router C is now using the new key and password.
rtrC#show ip ospf virtual-links
Virtual Link OSPF_VL4 to router 2.2.2.2 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:09
Adjacency State FULL (Hello suppressed)
Message digest authentication enabled
Youngest key id is 2
Rollover in progress, 1 neighbor(s) using the old key(s):
key id 1
You can now remove the old key and password from Routers B and C.
Router B
router ospf 1
no area 1 virtual-link 3.3.3.3 message-digest-key 1
_______________________________________________________________________
Router C
router ospf 1
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no area 1 virtual-link 2.2.2.2 message-digest-key 1
Verification
Verify that Routers B and C are using the new key and password.
rtrB#show ip ospf virtual-links
Virtual Link OSPF_VL3 to router 3.3.3.3 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial1, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:04
Adjacency State INIT (Hello suppressed)
Message digest authentication enabled
Youngest key id is 2
_______________________________________________________________________
rtrC#show ip ospf virtual-links
Virtual Link OSPF_VL4 to router 2.2.2.2 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:08
Adjacency State FULL (Hello suppressed)
Message digest authentication enabled
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Youngest key id is 2
Configuration Example 4: Null Authentication
If authentication, either clear text or md5, is configured for Area 0, then authentication must be enabled on all virtual links. If authentication is
not required on a virtual link, then NULL authentication can be employed to override the authentication that has been configured for Area 0.
Configure the routers in Figure 2-16 with simple password authentication on Area 0.
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
ip ospf authentication-key cisco
clockrate 64000
!
router ospf 1
area 0 authentication
network 1.1.1.1 0.0.0.0 area 0
network 10.1.1.0 0.0.0.3 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
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ip ospf authentication-key cisco
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router ospf 1
area 0 authentication
area 1 virtual-link 3.3.3.3
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router ospf 1
area 1 virtual-link 2.2.2.2
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
When authentication is enabled for Area 0, then the same authentication type is automatically enabled for the virtual link. Because the virtual
link is not using authentication, routing updates will not be accepted over the virtual link. This can be seen by enabling OSPF debugging on
either Router B or C.
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rtrB#debug ip ospf adj
OSPF adjacency events debugging is on
rtrB#
23:13:13: OSPF: Rcv pkt from 10.1.1.6, Serial1 : Mismatch Authentication type. I
nput packet specified type 0, we use type 1
This situation can be fixed by either configuring the same authentication type on the virtual link (seeSections 2-17 and 2-20) or by explicitly
configuring the virtual link to use NULL authentication. Modify the configurations on routers B and C to use NULL authentication on the virtual
link.
Router B
router ospf 1
area 0 authentication
area 1 virtual-link 3.3.3.3 authentication null
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
Router C
router ospf 1
area 1 virtual-link 2.2.2.2 authentication null
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Verification
Verify that all OSPF routes are being advertised.
rtrA#show ip route
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Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.2, 00:03:46, Serial0/1
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/129] via 10.1.1.2, 00:03:46, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
O IA
10.1.1.4 [110/128] via 10.1.1.2, 00:03:46, Serial0/1
_______________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
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Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/65] via 10.1.1.1, 00:04:48, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/65] via 10.1.1.6, 00:04:49, Serial1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
_______________________________________________________________________
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/129] via 10.1.1.5, 00:05:33, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.5, 00:05:33, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
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10.0.0.0/30 is subnetted, 2 subnets
O
10.1.1.0 [110/128] via 10.1.1.5, 00:05:34, Serial0
C
10.1.1.4 is directly connected, Serial0
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Verify that the transit area ID used in thearea virtual-link command is proper.
Step 3. Verify that the router IDs used in thearea virtual-link are correct.
Step 4. If using simple password authentication, verify that the same password is being used on each side of the virtual link.
Step 5. If using MD5 authentication, verify that the same key and password are being used on each side of the virtual link.
< Free Open Study >
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< Free Open Study >
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2-17 area transit-area-id virtual-link router-id authentication-key password
Syntax Description:
transit-area-id— The OSPF area ID of the area connecting the two ABRs that the virtual link will cross. This value can be entered
as a decimal number in the range of 0 to 4,294,967,295 or in IP address form in the range 0.0.0.0 to 255.255.255.255. The transit
area cannot be a stub area.
router-id— OSPF router ID of the router at the remote end of the virtual link.
password— Password to be used for authentication in the selected area on the selected interface or virtual link. The password is
an alphanumeric string from 1 to 8 characters.
Purpose: If simple password authentication is enabled in Area 0, then all virtual links need to be configured with the same authentication
type. This command is used to configure simple password authentication over a virtual link. In Cisco IOS Software Release 12.0 and later,
virtual link authentication can be configured independently of Area 0 (see Section 2-14).
Initial Cisco IOS Software Release: 10.0
Configuration Example 1: Simple Password Authentication Over a Virtual Link
In Figure 2-17, simple password authentication has been enabled for Area 0. Initially, authentication is not enabled over the virtual link so you
can see the effect of enabling authentication in Area 0 but not over the virtual link.
Figure 2-17. Prior to Cisco IOS Software Release 12.0, if Authentication Is Enabled in Area 0 Then
the Same Authentication Must Be Enabled Over the Virtual Link
Router A
.
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interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
ip ospf authentication-key cisco
clockrate 64000
!
router ospf 1
area 0 authentication
network 10.1.1.0 0.0.0.3 area 0
network 1.1.1.1 0.0.0.0 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
ip ospf authentication-key cisco
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router ospf 1
.
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area 0 authentication
area 1 virtual-link 3.3.3.3
network 10.1.1.0 0.0.0.3 area 0
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router ospf 1
area 1 virtual-link 2.2.2.2
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Verify that authentication has been enabled for Area 0.
rtrA#show ip ospf
Routing Process "ospf 1" with ID 1.1.1.1
Supports only single TOS(TOS0) routes
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
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Area BACKBONE(0)
Number of interfaces in this area is 2
Area has simple password authentication
SPF algorithm executed 2 times
Area ranges are
Number of LSA 6. Checksum Sum 0x3B837
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 3
_______________________________________________________________________
rtrB#show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Supports only single TOS(TOS0) routes
It is an area border router
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 2 normal 0 stub 0 nssa
Area BACKBONE(0)
Number of interfaces in this area is 3
Area has simple password authentication
SPF algorithm executed 8 times
Area ranges are
Number of LSA 6. Checksum Sum 0x3B837
Number of DCbitless LSA 0
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Number of indication LSA 0
Number of DoNotAge LSA 3
Area 1
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 4 times
Area ranges are
Number of LSA 6. Checksum Sum 0x364E1
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
When authentication is enabled in Area 0, then this authentication type will be applied to all interfaces in Area 0, including virtual links. Any
routing updates from neighbors in Area 0 will be rejected if the authentication type and password do not match. Because a virtual link is
considered to be in Area 0, routing updates passing over the virtual link will be rejected. This can be verified by examining the IP routing table
on Router B.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/65] via 10.1.1.1, 00:06:34, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
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C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
Router B has learned the routes being advertised by Router A but not the routes advertised by Router C. Simple password authentication
needs to be enabled on the virtual link so that routing updates can be exchanged between routers B and C. You can also use a different
authentication type on the virtual link using command 2-14, 2-15, or 2-16. In this case, configure the same authentication type that is being
used in Area 0. Change the password over the virtual link to demonstrate that the passwords for different interfaces do not need to be the
same. Remember that the password for a common link must be the same at both ends of the link. Modify the configurations on Routers B and
C to enable simple password authentication over the virtual link using the password bosco.
Router B
router ospf 1
area 0 authentication
area 1 virtual-link 3.3.3.3 authentication-key bosco
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
Router C
router ospf 1
area 0 authentication
area 1 virtual-link 2.2.2.2 authentication-key bosco
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Notice that the command area 0 authentication was used on Router C because the virtual link is in Area 0.
Verification
Verify that authentication has been enabled over the virtual link.
rtrC#show ip ospf
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Routing Process "ospf 1" with ID 3.3.3.3
Supports only single TOS(TOS0) routes
It is an area border router
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 3. 3 normal 0 stub 0 nssa
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has simple password authentication
SPF algorithm executed 4 times
Area ranges are
Number of LSA 6. Checksum Sum 0x3CFAD
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 3
Area 1
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 22 times
Area ranges are
Number of LSA 10. Checksum Sum 0x4ACBB
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Area 2
Number of interfaces in this area is 1
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Area has no authentication
SPF algorithm executed 18 times
Area ranges are
Number of LSA 5. Checksum Sum 0x238E3
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Verify that all OSPF routes are now being exchanged.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.2, 00:09:04, Serial0/1
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/129] via 10.1.1.2, 00:09:04, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
O IA
10.1.1.0 is directly connected, Serial0/1
10.1.1.4 [110/128] via 10.1.1.2, 00:09:04, Serial0/1
_______________________________________________________________________
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rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/65] via 10.1.1.1, 00:10:19, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/65] via 10.1.1.6, 00:10:20, Serial1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
_______________________________________________________________________
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
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U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/129] via 10.1.1.5, 00:11:10, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.5, 00:11:11, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
O
10.1.1.0 [110/128] via 10.1.1.5, 00:11:11, Serial0
C
10.1.1.4 is directly connected, Serial0
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers using theshow ip ospf neighbor command.
Step 2. Verify that the transit area ID used in thearea virtual-link command is proper.
Step 3. Verify that the router IDs used in thearea virtual-link are correct.
Step 4. Verify that the same password is being used on each side of the virtual link.
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2-18 area transit-area-id virtual-link router-id dead-interval seconds
Syntax Description:
transit-area-id— The OSPF area ID of the area connecting the two ABRs that the virtual link will cross. This value can be entered
as a decimal number in the range of 0 to 4,294,967,295 or in IP address form in the range 0.0.0.0 to 255.255.255.255. The transit
area cannot be a stub area.
router-id— OSPF router ID of the router at the remote end of the virtual link.
seconds— If Hello packets from a neighbor are not received during a period of time equal to the dead interval, then the neighbor
will be declared down. The range of values is 1–8192 seconds. The default value is 40 seconds.
Purpose: When an OSPF router receives a Hello packet from an OSPF neighbor, the receiving router assumes that the neighbor is active.
The dead interval is used to determine when an OSPF neighbor has become inactive. If a Hello packet has not been received during the time
set for the dead interval, then the neighbor will be declared down. By default, the dead interval is four times the Hello interval. The dead
interval should always be greater than the Hello interval.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Modifying the Dead Interval Over a Virtual Link
Configure the network in Figure 2-18 to observe the default timer values over the virtual link. You will then experiment with adjusting the
values of the dead interval.
Figure 2-18. The Dead Interval Must Be Configured with the Same Value at Both Ends of an OSPF
Virtual Link
Router A
.
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interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 1.1.1.1 0.0.0.0 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router ospf 1
area 1 virtual-link 3.3.3.3
network 10.1.1.0 0.0.0.3 area 0
network 2.2.2.2 0.0.0.0 area 0
.
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network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router ospf 1
area 1 virtual-link 2.2.2.2
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Verify that the virtual link is active and that all OSPF routes are being exchanged.
rtrB#show ip ospf virtual-links
Virtual Link OSPF_VL0 to router 3.3.3.3 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial1, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:03
Adjacency State FULL (Hello suppressed)
_______________________________________________________________________
rtrC#show ip ospf virtual-links
Virtual Link OSPF_VL7 to router 2.2.2.2 is up
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Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:06
Adjacency State FULL (Hello suppressed)
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/129] via 10.1.1.5, 00:02:25, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.5, 00:02:26, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
O
10.1.1.0 [110/128] via 10.1.1.5, 00:02:26, Serial0
C
10.1.1.4 is directly connected, Serial0
Notice that the default Hello interval is 10 seconds and the default dead interval is 40 seconds. Modify the configuration on Router B to
change the dead interval to 41 seconds while leaving the value for the dead interval on Router C set to the default of 40 seconds.
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Router B
router ospf 1
area 1 virtual-link 3.3.3.3 dead-interval 41
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
Is the virtual link still active?
rtrB#show ip ospf virtual-links
Virtual Link OSPF_VL0 to router 3.3.3.3 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial1, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 41, Wait 40, Retransmit 5
Hello due in 00:00:07
The virtual link is up. Now check to see if the OSPF routes are being exchanged.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
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1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/65] via 10.1.1.1, 00:07:49, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
Router B has learned the routes being advertised by Router A but not the routes advertised by Router C. Because the dead interval time on
Router B does not match the dead inter- val on Router C, routes will not be exchanged over the virtual link. Modify the dead interval time on
Router C to match the dead interval time on Router B.
Router C
router ospf 1
router ospf 1
area 1 virtual-link 2.2.2.2 dead-interval 41
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Verification
Verify that the dead interval on Router C matches the dead interval on Router B.
rtrC#show ip ospf virtual-links
Virtual Link OSPF_VL7 to router 2.2.2.2 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 41, Wait 40, Retransmit 5
Hello due in 00:00:00
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Adjacency State FULL (Hello suppressed)
Verify that all OSPF routes are now being exchanged.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.2, 00:09:04, Serial0/1
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/129] via 10.1.1.2, 00:09:04, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
O IA
10.1.1.4 [110/128] via 10.1.1.2, 00:09:04, Serial0/1
_______________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
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i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/65] via 10.1.1.1, 00:10:19, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/65] via 10.1.1.6, 00:10:20, Serial1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
_______________________________________________________________________
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/129] via 10.1.1.5, 00:11:10, Serial0
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2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.5, 00:11:11, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
O
10.1.1.0 [110/128] via 10.1.1.5, 00:11:11, Serial0
C
10.1.1.4 is directly connected, Serial0
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers using the show ip ospf neighbor command.
Step 2. Verify that the transit area ID used in thearea virtual-link command is the proper area.
Step 3. Verify that the router IDs used in thearea virtual-link are correct.
Step 4. Verify that the dead interval is being used on both ends of the virtual link.
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2-19 area transit-area-id virtual-link router-id hello-interval seconds
Syntax Description:
transit-area-id— The OSPF area ID of the area connecting the two ABRs that the virtual link will cross. This value can be entered
as a decimal number in the range of 0 to 4,294,967,295 or in IP address form in the range 0.0.0.0 to 255.255.255.255. The transit
area cannot be a stub area.
router-id— OSPF router ID of the router at the remote end of the virtual link.
seconds— The time in seconds between sending Hello packets over the virtual link. The range of values is 1–8192 seconds. The
default value is 10 seconds (30 seconds on a nonbroadcast multiaccess [NBMA] network).
Purpose: OSPF Hello packets are used to initially establish the neighbor relationship. Once the neighbor relationship is established, the
packets are used as a keepalive mechanism to determine if the neighbor at the other end of the virtual link is still active. The Hello interval
should be less than the dead interval (see Command 2-18).
Initial Cisco IOS Software Release: 10.0
Configuration Example: Modifying the Hello Interval Over a Virtual Link
Configure the network in Figure 2-19 to observe the default timer values over the virtual link. You will then experiment with adjusting the
values of the Hello interval.
Figure 2-19. The Hello Interval Must Be Configured with the Same Value at Both Ends of an OSPF
Virtual Link
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 1.1.1.1 0.0.0.0 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router ospf 1
area 1 virtual-link 3.3.3.3
network 10.1.1.0 0.0.0.3 area 0
.
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network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router ospf 1
area 1 virtual-link 2.2.2.2
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Verify that the virtual link is active and that all OSPF routes are being exchanged.
rtrB#show ip ospf virtual-links
Virtual Link OSPF_VL0 to router 3.3.3.3 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial1, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:03
Adjacency State FULL (Hello suppressed)
_______________________________________________________________________
rtrC#show ip ospf virtual-links
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Virtual Link OSPF_VL7 to router 2.2.2.2 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:06
Adjacency State FULL (Hello suppressed)
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/129] via 10.1.1.5, 00:02:25, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.5, 00:02:26, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
O
10.1.1.0 [110/128] via 10.1.1.5, 00:02:26, Serial0
C
10.1.1.4 is directly connected, Serial0
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Notice that the default Hello interval is 10 seconds and the default dead interval is 40 seconds. Modify the configuration on Router B to
change the Hello interval to 11 seconds while leaving the value for the Hello interval on Router C set to the default of 10 seconds.
Router B
router ospf 1
area 1 virtual-link 3.3.3.3 hello-interval 11
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
Is the virtual link still active?
rtrB#show ip ospf virtual-links
Virtual Link OSPF_VL0 to router 3.3.3.3 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial1, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 11, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:07
The virtual link is up. Now check to see if the OSPF routes are being exchanged.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
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1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/65] via 10.1.1.1, 00:07:49, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
Router B has learned the routes being advertised by Router A but not the routes advertised by Router C. Because the Hello interval time on
Router B does not match the Hello interval on Router C, routes will not be exchanged over the virtual link. Modify the Hello interval time on
Router C to match the Hello interval time on Router B.
Router C
router ospf 1
router ospf 1
area 1 virtual-link 2.2.2.2 hello-interval 11
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Verification
Verify that the Hello interval on Router C matches the dead interval on Router B.
rtrC#show ip ospf virtual-links
Virtual Link OSPF_VL7 to router 2.2.2.2 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
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Timer intervals configured, Hello 11, Dead 41, Wait 40, Retransmit 5
Hello due in 00:00:00
Adjacency State FULL (Hello suppressed)
Verify that all OSPF routes are now being exchanged.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.2, 00:09:04, Serial0/1
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/129] via 10.1.1.2, 00:09:04, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
O IA
10.1.1.4 [110/128] via 10.1.1.2, 00:09:04, Serial0/1
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
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N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/65] via 10.1.1.1, 00:10:19, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/65] via 10.1.1.6, 00:10:20, Serial1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
_______________________________________________________________________
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
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O
1.1.1.1 [110/129] via 10.1.1.5, 00:11:10, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.5, 00:11:11, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
O
10.1.1.0 [110/128] via 10.1.1.5, 00:11:11, Serial0
C
10.1.1.4 is directly connected, Serial0
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Verify that the transit area ID used in the area virtual-link command is the proper area.
Step 3. Verify that the router IDs used in thearea virtual-link are correct.
Step 4. Verify that the Hello interval is being used on both ends of the virtual link.
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2-20 area transit-area-id virtual-link router-id message-digest-key key-id
md5 password
Syntax Description:
transit-area-id— The OSPF area ID of the area connecting the two ABRs that the virtual link will cross. This value can be entered
as a decimal number in the range of 0 to 4,294,967,295 or in IP address form in the range 0.0.0.0 to 255.255.255.255. The transit
area cannot be a stub area.
router-id— OSPF router ID of the router at the remote end of the virtual link.
key-id— Key to use to encrypt a password. The range of values is 1 to 255. Both ends of a virtual link must use the same key and
password.
password— Password to be used for authentication in the selected area on the selected interface or virtual link. The password is
an alphanumeric string from 1 to 8 characters.
Purpose: If message digest authentication is enabled in Area 0, then all virtual links need to be configured with the same authentication type.
This command is used to configure message digest authentication over a virtual link. In Cisco IOS Software Release 12.0 and later, virtual
link authentication can be configured independent of Area 0 (see Section 2-15).
Initial Cisco IOS Software Release: 11.0
Configuration Example 1: Message Digest Authentication Over a Virtual Link
In Figure 2-20, message authentication has been enabled for Area 0. Initially, authentication is not enabled over the virtual link so you can
see the effect of enabling authentication in Area 0 but not over the virtual link.
Figure 2-20. Prior to Cisco IOS Software Release 12.0, if Message Digest Authentication Is
Enabled in Area 0 Then Message Digest Authentication Must Be Enabled Over the Virtual Link
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
ip ospf message-digest-key 1 md5 cisco
clockrate 64000
!
router ospf 1
area 0 authentication-message digest
network 10.1.1.0 0.0.0.3 area 0
network 1.1.1.1 0.0.0.0 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
ip ospf message-digest-key 1 md5 cisco
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
.
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clockrate 64000
!
router ospf 1
area 0 authentication message-digest
area 1 virtual-link 3.3.3.3
network 10.1.1.0 0.0.0.3 area 0
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router ospf 1
area 1 virtual-link 2.2.2.2
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Verify that authentication has been enabled for Area 0.
rtrA#show ip ospf
Routing Process "ospf 1" with ID 1.1.1.1
Supports only single TOS(TOS0) routes
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
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Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Area BACKBONE(0)
Number of interfaces in this area is 2
Area has message digest authentication
SPF algorithm executed 8 times
Area ranges are
Number of LSA 6. Checksum Sum 0x4AC3C
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 3
_______________________________________________________________________
rtrB#show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Supports only single TOS(TOS0) routes
It is an area border router
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 2 normal 0 stub 0 nssa
Area BACKBONE(0)
Number of interfaces in this area is 3
Area has message digest authentication
SPF algorithm executed 14 times
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Area ranges are
Number of LSA 6. Checksum Sum 0x4AC3C
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 3
Area 1
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 4 times
Area ranges are
Number of LSA 8. Checksum Sum 0x4AED7
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
When authentication is enabled in Area 0, then this authentication type will be applied to all interfaces in Area 0, including virtual links. Any
routing updates from neighbors in Area 0 will be rejected if the authentication type and password do not match. Because a virtual link is
considered to be in Area 0, routing updates passing over the virtual link will be rejected. This can be verified by examining the IP routing table
on Router B.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
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O
1.1.1.1 [110/65] via 10.1.1.1, 00:06:34, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
Router B has learned the routes being advertised by Router A, but not the routes advertised by Router C. You must enable message digest
authentication on the virtual link so that routing updates can be exchanged between Routers B and C. You can also use a different
authentication type on the virtual link using command 2-14, 2-15, or 2-16. In this case, you will configure the same authentication type that is
being used in Area 0. Change the key and password used over the virtual link to demonstrate that the keys and passwords for different
interfaces do not need to be the same. Remember that the key and password for a common link must be the same at both ends of the link.
Modify the configurations on Routers B and C to enable message digest authentication over the virtual link using a key of 2 and the password
bosco.
Router B
router ospf 1
area 0 authentication
area 1 virtual-link 3.3.3.3 message-digest-key 2 md5 bosco
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
Router C
router ospf 1
area 0 authentication
area 1 virtual-link 2.2.2.2 message-digest-key 2 md5 bosco
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Notice that the command area 0 authentication message-digest was used on Router C because the virtual link is in Area 0.
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Verification
Verify that message digest authentication has been enabled over the virtual link.
rtrC#show ip ospf virtual-links
Virtual Link OSPF_VL7 to router 2.2.2.2 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:06
Adjacency State FULL (Hello suppressed)
Message digest authentication enabled
Youngest key id is 2
Verify that all OSPF routes are now being exchanged.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
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2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.2, 00:09:04, Serial0/1
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/129] via 10.1.1.2, 00:09:04, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
O IA
10.1.1.4 [110/128] via 10.1.1.2, 00:09:04, Serial0/1
_______________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/65] via 10.1.1.1, 00:10:19, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/65] via 10.1.1.6, 00:10:20, Serial1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
_______________________________________________________________________
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rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/129] via 10.1.1.5, 00:11:10, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.5, 00:11:11, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
O
10.1.1.0 [110/128] via 10.1.1.5, 00:11:11, Serial0
C
10.1.1.4 is directly connected, Serial0
Configuration Example 2: Changing Keys and Passwords
For additional security you may choose to periodically change the key and password. With clear-text authentication, when you change
passwords there will be a loss of OSPF connectivity from the time you change the password on one end of the virtual link until you change
the password at the other end of the virtual link. With MD5 authentication you can configure a new key and password on a virtual link while
leaving the old key and password in place. The old key and password will continue to be used until the new key and password are configured
on the other end of the virtual link. Modify the key and password on the virtual link between Routers B and C. First, add a new key and
password to Router B in order to observe the behavior when the new key and password have only been configured on one end of the virtual
link.
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Router B
router ospf 1
area 0 authentication message-digest
area 1 virtual-link 3.3.3.3 message-digest-key 2 md5 bosco
area 1 virtual-link 3.3.3.3 message-digest-key 3 md5 newton
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
Examine the effect of adding a new key and password on only one end of the virtual link.
rtrB#show ip ospf virtual-links
Virtual Link OSPF_VL1 to router 3.3.3.3 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial1, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:03
Adjacency State FULL (Hello suppressed)
Message digest authentication enabled
Youngest key id is 3
Rollover in progress, 1 neighbor(s) using the old key(s):
key id 2
Notice that both keys are being used for authentication. Configure the new key and password on Router C while leaving the old key and
password in place.
Router C
router ospf 1
area 0 authentication message-digest
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area 1 virtual-link 2.2.2.2 message-digest-key 2 md5 bosco
area 1 virtual-link 2.2.2.2 message-digest-key 3 md5 newton
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Verify that Router C is now using the new key and password.
rtrC#show ip ospf virtual-links
Virtual Link OSPF_VL7 to router 2.2.2.2 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:04
Adjacency State FULL (Hello suppressed)
Message digest authentication enabled
Youngest key id is 3
Rollover in progress, 1 neighbor(s) using the old key(s):
key id 2
You can now remove the old key and password from Routers B and C.
Router B
router ospf 1
no area 1 virtual-link 3.3.3.3 message-digest-key 2
_______________________________________________________________________
Router C
router ospf 1
no area 1 virtual-link 2.2.2.2 message-digest-key 2
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Verification
Verify that only the new key and password are being used over the virtual link.
rtrB#show ip ospf virtual-links
Virtual Link OSPF_VL0 to router 3.3.3.3 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial1, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:01
Adjacency State INIT (Hello suppressed)
Message digest authentication enabled
Youngest key id is 3
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers using the show ip ospf neighbor command.
Step 2. Verify that the transit area ID used in thearea virtual-link command is the proper area.
Step 3. Verify that the router IDs used in thearea virtual-link are correct.
Step 4. Verify that the same key and password are being used on each side of the virtual link.
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2-21 area transit-area-id virtual-link router-id retransmit-interval seconds
Syntax Description:
transit-area-id— The OSPF area ID of the area connecting the two ABRs that the virtual link will cross. This value can be entered
as a decimal number in the range of 0 to 4,294,967,295 or in IP address form in the range 0.0.0.0 to 255.255.255.255. The transit
area cannot be a stub area.
router-id— OSPF router ID of the router at the remote end of the virtual link.
seconds— The range of values is 1–8192 seconds. The default value is 5 seconds.
Purpose: When a router advertises a link-state advertisement (LSA) over a virtual link, the LSA is added to a retransmission list for the virtual
link. The LSA will be retransmitted until the LSA is acknowledged. The number of seconds between the advertisements is called the
retransmit interval.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Modifying the Retransmit Interval Over a Virtual Link
Configure the network in Figure 2-21 to observe the default timer values over the virtual link. You will then experiment with adjusting the
values of the retransmit interval.
Figure 2-21. The Retransmit Interval Is the Time Between Resending Unacknowledged LSAs
Router A
.
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interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 1.1.1.1 0.0.0.0 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router ospf 1
area 1 virtual-link 3.3.3.3
network 10.1.1.0 0.0.0.3 area 0
network 2.2.2.2 0.0.0.0 area 0
.
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network 10.1.1.4 0.0.0.3 area 1
_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router ospf 1
area 1 virtual-link 2.2.2.2
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Verify that the virtual link is active and that all OSPF routes are being exchanged.
rtrB#show ip ospf virtual-links
Virtual Link OSPF_VL0 to router 3.3.3.3 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial1, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:03
Adjacency State FULL (Hello suppressed)
_______________________________________________________________________
rtrC#show ip ospf virtual-links
Virtual Link OSPF_VL7 to router 2.2.2.2 is up
.
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Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:06
Adjacency State FULL (Hello suppressed)
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/129] via 10.1.1.5, 00:02:25, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.5, 00:02:26, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
O
10.1.1.0 [110/128] via 10.1.1.5, 00:02:26, Serial0
C
10.1.1.4 is directly connected, Serial0
Notice that the default retransmit interval is 5 seconds. Modify the configuration on Router B to change the retransmit interval to 6 seconds
while leaving the value for the retransmit interval on Router C set to the default of 5 seconds.
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Router B
router ospf 1
area 1 virtual-link 3.3.3.3 retransmit-interval 6
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 1
Is the virtual link still active?
rtrB#show ip ospf virtual-links
Virtual Link OSPF_VL0 to router 3.3.3.3 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial1, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 6
Hello due in 00:00:07
The virtual link is up. Now check to see if the OSPF routes are being exchanged.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
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1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/65] via 10.1.1.1, 00:03:53, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/65] via 10.1.1.6, 00:03:54, Serial1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
Router B has learned the routes being advertised by Router A and the routes advertised by Router C. Unlike the Hello interval (see
Section
2-19) and the dead interval (see Section 2-18), the virtual link does not need to have the same retransmit interval configured on both ends of
the link.
Verification
Verify that the new retransmit interval has been configured on Router C.
rtrC#show ip ospf virtual-links
Virtual Link OSPF_VL7 to router 2.2.2.2 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 6
Hello due in 00:00:00
Adjacency State FULL (Hello suppressed)
Verify that all OSPF routes are now being exchanged.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
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D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.2, 00:09:04, Serial0/1
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/129] via 10.1.1.2, 00:09:04, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
O IA
10.1.1.4 [110/128] via 10.1.1.2, 00:09:04, Serial0/1
_______________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
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1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/65] via 10.1.1.1, 00:10:19, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/65] via 10.1.1.6, 00:10:20, Serial1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
_______________________________________________________________________
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/129] via 10.1.1.5, 00:11:10, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.5, 00:11:11, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
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O
10.1.1.0 [110/128] via 10.1.1.5, 00:11:11, Serial0
C
10.1.1.4 is directly connected, Serial0
Verification
The retransmit interval can be verified by using the show ip ospf virtual-links command.
rtrC#show ip ospf virtual-links
Virtual Link OSPF_VL7 to router 2.2.2.2 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:04
Adjacency State FULL (Hello suppressed)
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers using the show ip ospf neighbors command.
Step 2. Verify that the transit area ID used in thearea virtual-link command is the proper area.
Step 3. Verify that the router IDs used in thearea virtual-link are correct.
Step 4. Verify that the desired retransmit interval has been configured by using the commandshow ip ospf virtual-links.
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< Free Open Study >
2-22 area transit-area-id virtual-link router-id transmit-delay seconds
Syntax Description:
transit-area-id— The OSPF area ID of the area connecting the two ABRs that the virtual link will cross. This value can beentered
as a decimal number in the range of 0 to 4,294,967,295 or in IP address form in the range 0.0.0.0 to 255.255.255.255. The transit
area cannot be a stub area.
router-id— OSPF router ID of the router at the remote end of the virtual link.
seconds— The range of values is 1–8192 seconds. The default value is 1 second.
Purpose: When an LSA is created, the router will set the LS age field to 0. The transmit delay value is added to the age field of the LSA. This
initial value represents the time delay of propagating the LSA over the virtual link.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Modifying the Transmit Delay Value for a Virtual Link
Configure the network in Figure 2-22 and set the transmit delay value to 2 seconds.
Figure 2-22. Transmit Delay Represents the LSA Propagation Delay Over a Virtual Link
Router A
.
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interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 1.1.1.1 0.0.0.0 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router ospf 1
area 1 virtual-link 3.3.3.3 transmit-delay 2
network 10.1.1.0 0.0.0.3 area 0
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.4 0.0.0.3 area 1
.
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_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router ospf 1
area 1 virtual-link 2.2.2.2 transmit-delay 2
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 1
Verification
Verify that the transmit delay value has been modified, that the virtual link is active, and that all OSPF routes are being exchanged.
rtrB#show ip ospf virtual-links
Virtual Link OSPF_VL0 to router 3.3.3.3 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial1, Cost of using 64
Transmit Delay is 2 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 6
Hello due in 00:00:01
Adjacency State FULL (Hello suppressed)
_______________________________________________________________________
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rtrC#show ip ospf virtual-links
Virtual Link OSPF_VL7 to router 2.2.2.2 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0, Cost of using 64
Transmit Delay is 2 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:03
Adjacency State FULL (Hello suppressed)
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/129] via 10.1.1.5, 00:02:25, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/65] via 10.1.1.5, 00:02:26, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
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O
10.1.1.0 [110/128] via 10.1.1.5, 00:02:26, Serial0
C
10.1.1.4 is directly connected, Serial0
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Verify that the transit area ID used in thearea virtual-link command is the proper area.
Step 3. Verify that the router IDs used in thearea virtual-link are correct.
Step 4. Verify that the desired transmit delay value has been configured by using the commandshow ip ospf virtual-links.
< Free Open Study >
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< Free Open Study >
Chapter 3. Auto Cost
Section 3-1. auto-cost reference-bandwidth bandwidth
Troubleshooting
< Free Open Study >
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< Free Open Study >
3-1 auto-cost reference-bandwidth bandwidth
Syntax Description:
bandwidth— Value to use as the reference bandwidth when calculating the cost of an OSPF route. Range of values is 1 to
4,294,967 Mbps. The default value is 100 Mbps.
Purpose: By default, OSPF calculates the cost of an interface by dividing the bandwidth of the interface into 100,000,000.Table 3-1 lists the
costs for various interface types. Using the default value when your network has interfaces with a bandwidth greater than 100,000,000 is not
recommended. OSPF will not be able to differentiate between a 100-Mbps interface and any interface with a bandwidth greater than 100
Mbps. This command allows you to change the OSPF reference value globally so the calculated cost for every interface is updated. The cost
for individual interfaces can be adjusted using the interface command ip ospf cost (see Section 19-5). The use of the ip ospf cost interface
command is not recommended.
Table 3-1. Default OSPF Cost for Selected Interfaces
Interface Type
Interface Bandwidth
OSPF Cost
Loopback
8,000,000,000
1
Serial
56,000
1785
T1
1,544,000
64
Ethernet
10,000,000
10
Fast Ethernet
100,000,000
1
Gigabit Ethernet
1,000,000,000
1
OC48
2,500,000,000
1
Initial Cisco IOS Software Release: 11.2
Configuration Example: Globally Modifying OSPF Interface Costs
Configure the routers in Figure 3-1 using the default reference value of 100,000,000 to investigate the costs of the various interfaces.
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Figure 3-1. OSPF Cost Is Based on the Interface Bandwidth
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
.
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interface Serial1
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.4 0.0.0.3 area 1
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router ospf 1
network 3.3.3.3 0.0.0.0 area 1
network 10.1.1.4 0.0.0.3 area 1
Verify that Routers A, B, and C have established OSPF neighbor relationships.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/BDR
Dead Time Address
00:00:30
172.16.1.2
Interface
Ethernet0/0
________________________________________________________________________________
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rtrB#show ip ospf neighbor
Neighbor ID
Pri State
1.1.1.1
1 FULL/DR
3.3.3.3
1 FULL/ -
Dead Time Address
00:00:38
00:00:38
172.16.1.1
10.1.1.6
Interface
Ethernet0
Serial1
________________________________________________________________________________
rtrC#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/ -
Dead Time Address
00:00:34
10.1.1.5
Interface
Serial0
Now inspect the routing tables on Routers A, B, and C to determine the OSPF cost of the routes.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/11] via 172.16.1.2, 00:49:20, Ethernet0/0
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/75] via 172.16.1.2, 00:49:20, Ethernet0/0
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172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
10.0.0.0/30 is subnetted, 1 subnets
O IA
10.1.1.4 [110/74] via 172.16.1.2, 00:49:20, Ethernet0/0
________________________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/11] via 172.16.1.1, 01:06:18, Ethernet0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O
3.3.3.3 [110/65] via 10.1.1.6, 01:06:48, Serial1
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial1
________________________________________________________________________________
rtrC#show ip route
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Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O IA
1.1.1.1 [110/75] via 10.1.1.5, 01:07:11, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/65] via 10.1.1.5, 01:07:22, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
172.16.0.0/24 is subnetted, 1 subnets
O IA
172.16.1.0 [110/74] via 10.1.1.5, 01:07:41, Serial0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial0
For each OSPF route in the IP routing tables, there are two numbers that represent the cost of the route. For example, in the IP routing table
on Router C the entry for network 1.1.1.1 is:
O IA
1.1.1.1 [110/75] via 10.1.1.5, 01:07:11, Serial0.
The first number, 110, represents the administrative distance for an OSPF route. The administrative distance is used if the router is learning
about the same route from more than one IP routing protocol. The route with the lowest administrative distance will be considered the best
route. The second number, 75, is the cost for Router C to reach network 1.1.1.1 on Router A. This figure consists of the cost to traverse the
serial link between Routers B and C plus the cost to traverse the Ethernet link between Routers A and B plus the cost of the loopback
interface on Router A. You can determine these individual costs by examining the interfaces on each router. First, view the cost associated
with the serial interface between Routers B and C, as shown here:
rtrC#show ip ospf interface serial 0
Serial0 is up, line protocol is up
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Internet Address 10.1.1.6/30, Area 1
Process ID 1, Router ID 3.3.3.3, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:00
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2
Suppress hello for 0 neighbor(s)
The cost of the first link is 64. Now view the cost associated with the Ethernet network between Routers A and B.
rtrB#show ip ospf interface e0
Ethernet0 is up, line protocol is up
Internet Address 172.16.1.2/24, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State BDR, Priority 1
Designated Router (ID) 1.1.1.1, Interface address 172.16.1.1
Backup Designated router (ID) 2.2.2.2, Interface address 172.16.1.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:07
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1 (Designated Router)
Suppress hello for 0 neighbor(s)
Finally, view the cost of the loopback interface on Router A.
rtrA#show ip ospf interface loopback0
Loopback0 is up, line protocol is up
Internet Address 1.1.1.1/32, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type LOOPBACK, Cost: 1
Loopback interface is treated as a stub Host
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The three costs are 64, 10, and 1, for a total cost of 75.
Because the default reference is 100,000,000, the cost of the Ethernet link is 100,000,000/10,000,000 = 10. By definition, the cost of a
loopback interface is 1. The question is, why is the cost of the Serial interface 64? The clock rate on the Serial link is 64,000, so shouldn't the
cost be 100,000,000/64,000 = 1562? Even though we have set a clock rate on the interface, the bandwidth is not 64,000, as can be seen by
inspecting the interface properties.
rtrB#show interfaces serial 1
Serial1 is up, line protocol is up
Hardware is HD64570
Internet address is 10.1.1.5/30
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255
Encapsulation HDLC, loopback not set, keepalive set (10 sec)
Last input 00:00:07, output 00:00:08, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0 (size/max/drops); Total output drops: 0
Queueing strategy: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/1/256 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
2559 packets input, 168890 bytes, 0 no buffer
Received 1338 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
2589 packets output, 173462 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
0 output buffer failures, 0 output buffers swapped out
2 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up
The bandwidth is T1 or 1,544,000 bps. Therefore, the OSPF cost is 100,000,000/1,544,000 = 64. We can modify the cost of the serial
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interface by using the bandwidth command on Routers B and C.
Router B
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
________________________________________________________________________________
Router C
interface Serial0
bandwidth 64
ip address 10.1.1.6 255.255.255.252
no ip directed-broadcast
Re-examine the bandwidth of the serial link on Router B.
rtrB#show interfaces serial 1
Serial1 is up, line protocol is up
Hardware is HD64570
Internet address is 10.1.1.5/30
MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec, rely 255/255, load 1/255
Encapsulation HDLC, loopback not set, keepalive set (10 sec)
Last input 00:00:08, output 00:00:09, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0 (size/max/drops); Total output drops: 0
Queueing strategy: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/1/256 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
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5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
2599 packets input, 171490 bytes, 0 no buffer
Received 1359 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
2630 packets output, 176116 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
0 output buffer failures, 0 output buffers swapped out
2 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up
Inspect the routing table on Router C to see if the OSPF costs have been updated.
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O IA
1.1.1.1 [110/1573] via 10.1.1.5, 00:02:04, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/1563] via 10.1.1.5, 00:02:05, Serial0
3.0.0.0/24 is subnetted, 1 subnets
C
3.3.3.0 is directly connected, Loopback0
172.16.0.0/24 is subnetted, 1 subnets
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O IA
172.16.1.0 [110/1572] via 10.1.1.5, 00:02:05, Serial0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial0
Now change the default OSPF cost reference so that an Ethernet network has a cost of 50. The cost equation is:
Rearranging, we get this equation:
So we want to change the OSPF cost reference to 500 Mbps.
Router A
router ospf 1
auto-cost reference-bandwidth 500
network 1.1.1.1 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router B
router ospf 1
auto-cost reference-bandwidth 500
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.4 0.0.0.3 area 1
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router C
router ospf 1
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auto-cost reference-bandwidth 500
network 3.3.3.3 0.0.0.0 area 1
network 10.1.1.4 0.0.0.3 area 1
When you configure the new cost reference, the router will give you a friendly reminder, as shown here:
rtrC(config-router)#auto-cost reference-bandwidth 500
% OSPF: Reference bandwidth is changed.
Please ensure reference bandwidth is consistent across all routers.
Verification
Verify that the new cost reference is being used to calculate OSPF costs.
rtrA#show ip ospf interface ethernet 0/0
Ethernet0/0 is up, line protocol is up
Internet Address 172.16.1.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 50
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 1.1.1.1, Interface address 172.16.1.1
Backup Designated router (ID) 2.2.2.2, Interface address 172.16.1.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:03
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2 (Backup Designated Router)
Suppress hello for 0 neighbor(s)
rtrA#show ip ospf interface loopback 0
Loopback0 is up, line protocol is up
Internet Address 1.1.1.1/32, Area 0
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Process ID 1, Router ID 1.1.1.1, Network Type LOOPBACK, Cost: 1
Loopback interface is treated as a stub Host
______________________________________________________________________________________
rtrC#show ip ospf interface serial 0
Serial0 is up, line protocol is up
Internet Address 10.1.1.6/30, Area 1
Process ID 1, Router ID 3.3.3.3, Network Type POINT_TO_POINT, Cost: 7812
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:01
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2
Suppress hello for 0 neighbor(s)
Notice that the cost of the loopback interfaces remains 1.
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Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers using the show ip ospf neighbors command.
Step 2. Verify that the same reference bandwidth has been configured on all OSPF routers in the same domain. Two different
OSPF domains can use a different reference bandwidth.
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Chapter 4. Default Route Generation
Section 4-1. default-information originate
Section 4-2. default-information originate always
Section 4-3. default-information originate metric cost
Section 4-4. default-information originate always metric cost
Section 4-5. default-information originate metric-type type
Section 4-6. default-information originate always metric-type type
Section 4-7. default-information originate route-map route-map-name
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4-1 default-information originate
Syntax Description:
This form of the command has no arguments.
Purpose: To enable OSPF to advertise the default route 0.0.0.0 into the OSPF domain. This form of the command will only advertise the
default route if the route exists in the local IP routing table.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Advertising a Default Route into the OSPF Domain
Configure the routers in Figure 4-1 as shown in the following code.
Figure 4-1. When OSPF Advertises a Default Route the Advertising Router Becomes an
Autonomous System Border Router (ASBR)
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
.
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ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
Verify that Routers A and B have established an OSPF neighbor relationship, as shown here:
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/BDR
Dead Time Address
00:00:30
172.16.1.2
Interface
Ethernet0/0
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________________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:00:38
172.16.1.1
Interface
Ethernet0
Modify the configuration on Router B so that OSPF will advertise a default route into the OSPF domain.
Router B
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
default-information originate
Inspect the routing table on Router A to see if the default route is being advertised.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/11] via 172.16.1.2, 00:05:30, Ethernet0/0
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172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
Router B is not advertising the default route because there is not a default route in the routing table on Router B. Configure a static default
route on Router B. Once the static route is configured, then Router B should advertise the default route to Router A.
Router B
ip route 0.0.0.0 0.0.0.0 Serial1
Verification
Verify that the default route is in the IP routing table on Router B.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 0.0.0.0 to network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/11] via 172.16.1.1, 00:09:15, Ethernet0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
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C
10.1.1.4 is directly connected, Serial1
S* 0.0.0.0/0 is directly connected, Serial1
Verify that the default route is being advertised to Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 172.16.1.2 to network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/11] via 172.16.1.2, 00:10:27, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
O*E2 0.0.0.0/0 [110/1] via 172.16.1.2, 00:01:17, Ethernet0/0
Troubleshooting:
Step 1. Verify that there is a neighbor relationship between the OSPF routers using theshow ip ospf neighbors command.
Step 2. Verify that the router that is to advertise the default route has a default route in the IP routing table.
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4-2 default-information originate always
Syntax Description:
This form of the command has no arguments.
Purpose: To enable OSPF to advertise the default route 0.0.0.0 into the OSPF domain. This form of the command will advertise the default
route even if the route does not exist in the local IP routing table. If the always keyword is not used and the default route is flapping, then
OSPF needs to send an update into the OSPF domain every time the route flaps. Using the always keyword will minimize OSPF database
activity if the default route is flapping.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Unconditionally Advertising a Default Route into the OSPF
Domain
Configure the routers in Figure 4-2 as shown in the following code.
Figure 4-2. When OSPF Advertises a Default Route, the Advertising Router Becomes an ASBR.
The default-information-originate always Command Will Unconditionally Advertise a Default Route
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
.
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!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
______________________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
Verify that Routers A and B have established an OSPF neighbor relationship, as shown here.
rtrA#show ip ospf neighbor
.
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Neighbor ID
2.2.2.2
Pri State
1 FULL/BDR
Dead Time Address
00:00:30
172.16.1.2
Interface
Ethernet0/0
________________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:00:38
172.16.1.1
Interface
Ethernet0
Modify the configuration on Router B so that OSPF will unconditionally advertise a default route into the OSPF domain.
Router B
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
default-information originate always
Verification
Verify that the default route is in the IP routing table on Router B.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
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1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/11] via 172.16.1.1, 16:23:59, Ethernet0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial1
Router B does not have a default route in the IP routing table. Verify that a default route is being advertised to Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 172.16.1.2 to network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/11] via 172.16.1.2, 00:10:27, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
O*E2 0.0.0.0/0 [110/1] via 172.16.1.2, 00:01:17, Ethernet0/0
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Troubleshooting
If there is an OSPF relationship between the OSPF routers, then this command should work as expected.
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4-3 default-information originate metric cost
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4-4 default-information originate always metric cost
Syntax Description:
cost— The cost of the advertised external default route metric. The range of values is 0 to 16,777,214. The default value is 1.
Purpose: To set the external cost of the default route advertised into the OSPF domain. The first form of the command will advertise the
default route only if the route exists in the local IP routing table. The second form will unconditionally advertise the default route. If more than
one OSPF router is advertising a default route, the metric can be used to select the preferred default route. The default route with the lowest
metric is considered the best route.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Unconditionally Advertising a Default Route into the OSPF
Domain
Configure the routers in Figure 4-3 as shown in the following listing.
Figure 4-3. When OSPF Advertises a Default Route, the Advertising Router Becomes an ASBR.
The Default Cost of the Default Route is 1
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
.
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!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
Verify that Routers A and B have established an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
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Neighbor ID
2.2.2.2
Pri State
1 FULL/BDR
Dead Time Address
00:00:30
Interface
172.16.1.2
Ethernet0/0
________________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:00:38
172.16.1.1
Interface
Ethernet0
Modify the configuration on Router B so that OSPF will unconditionally advertise a default route into the OSPF domain.
Router B
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
default-information originate always
Verify that the default route is in the IP routing table on Router B.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/11] via 172.16.1.1, 16:23:59, Ethernet0
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2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial1
Router B does not have a default route in the IP routing table. Verify that a default route is being advertised to Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 172.16.1.2 to network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/11] via 172.16.1.2, 00:10:27, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
O*E2 0.0.0.0/0 [110/1] via 172.16.1.2, 00:01:17, Ethernet0/0
Notice that the default cost of the default route is 1. Modify the configuration on Router B to give the default route a cost of 15.
Router B
router ospf 1
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network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
default-information originate always metric 15
Verification
Verify that the cost of the default route has been modified.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 172.16.1.2 to network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/11] via 172.16.1.2, 00:15:49, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
O*E2 0.0.0.0/0 [110/15] via 172.16.1.2, 00:01:56, Ethernet0/0
rtrA#show ip route 0.0.0.0
Routing entry for 0.0.0.0/0, supernet
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Known via "ospf 1", distance 110, metric 15, candidate default path
Tag 1, type extern 2, forward metric 10
Redistributing via ospf 1
Last update from 172.16.1.2 on Ethernet0/0, 00:02:33 ago
Routing Descriptor Blocks:
* 172.16.1.2, from 2.2.2.2, 00:02:33 ago, via Ethernet0/0
Route metric is 15, traffic share count is 1
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers using theshow ip ospf neighbors command.
Step 2. If using the always form of the command, then this command should work as expected.
Step 3. If you are not using thealways form of the command, then verify that the advertising router has a default route in the IP
routing table.
< Free Open Study >
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< Free Open Study >
4-5 default-information originate metric-type type
< Free Open Study >
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< Free Open Study >
4-6 default-information originate always metric-type type
Syntax Description:
type— The type can be set to 1 or 2. The cost of a type 1 route includes both the external cost of the redistributed route and the
OSPF cost. The cost of a type 2 route only includes the external cost. The default is type 2.
Purpose: When a route is redistributed into OSPF, the route is assigned a metric that represents the cost of reaching that route from the
ASBR. In Figure 4-4, the external cost of the default route is 1. This is the value the ASBR would assign to the default route (seeSections 4-3
and 4-4). If the default route is advertised as a type 2 route (the default case), then the cost of the default route should be 1 on every router in
the OSPF domain. If the default route is advertised as a type 1 route, then the cost of the default route would include the internal cost of
reaching the ASBR and the external cost of the route that was set by the ASBR. If multiple paths exist to reach the ASBR across the OSPF
domain, all routes would have an equal cost if advertised as type 2 routes. If the default route is advertised as a type 1 route, then OSPF can
determine the best path to the ASBR.
Figure 4-4. When OSPF Advertises a Default Route the Advertising Router Becomes an ASBR. A
Type 1 Route Includes Both the Internal and External Cost of Reaching the Route. A Type 2 Route
Only Includes the External Cost
Initial Cisco IOS Software Release: 10.0
Configuration Example: Setting the OSPF Metric Type for a Default Route
Configure the routers in Figure 4-4 as shown in the following listing.
Router A
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interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
Verify that Routers A and B have established an OSPF neighbor relationship, as shown here.
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rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/BDR
Dead Time Address
00:00:30
172.16.1.2
Interface
Ethernet0/0
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:00:38
172.16.1.1
Interface
Ethernet0
Modify the configuration on Router B so that OSPF will unconditionally advertise a default route into the OSPF domain.
Router B
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
default-information originate always
Verify that the default route is in the IP routing table on Router B.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
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O
1.1.1.1 [110/11] via 172.16.1.1, 16:23:59, Ethernet0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial1
Router B does not have a default route in the IP routing table. Verify that a default route is being advertised to Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 172.16.1.2 to network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/11] via 172.16.1.2, 00:10:27, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
O*E2 0.0.0.0/0 [110/1] via 172.16.1.2, 00:01:17, Ethernet0/0
rtrA#show ip route 0.0.0.0
Routing entry for 0.0.0.0/0, supernet
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Known via "ospf 1", distance 110, metric 1, candidate default path
Tag 1, type extern 2, forward metric 10
Redistributing via ospf 1
Last update from 172.16.1.2 on Ethernet0/0, 00:00:09 ago
Routing Descriptor Blocks:
* 172.16.1.2, from 2.2.2.2, 00:00:09 ago, via Ethernet0/0
Route metric is 1, traffic share count is 1
Notice that the default cost of the default route is 1 and the route type is type 2 (the default). The type 2 route does not include the cost of
reaching the ASBR over the Ethernet link. Modify the configuration on Router B to advertise the default route as a type 1 route.
Router B
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
default-information originate always metric-type 1
Verification
Verify that the metric type of the default route has been modified.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 172.16.1.2 to network 0.0.0.0
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1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/11] via 172.16.1.2, 00:02:09, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
O*E1 0.0.0.0/0 [110/11] via 172.16.1.2, 00:00:22, Ethernet0/0
rtrA#show ip route 0.0.0.0
Routing entry for 0.0.0.0/0, supernet
Known via "ospf 1", distance 110, metric 11, candidate default path
Tag 1, type extern 1
Redistributing via ospf 1
Last update from 172.16.1.2 on Ethernet0/0, 00:00:57 ago
Routing Descriptor Blocks:
* 172.16.1.2, from 2.2.2.2, 00:00:57 ago, via Ethernet0/0
Route metric is 11, traffic share count is 1
The cost of the default route now includes the external cost (1) and the internal OSPF cost (10) for a total of 11.
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers using theshow ip ospf neighbors command.
Step 2. If using the always form of the command, then this command should work as expected.
Step 3. If you are not using thealways form of the command, then verify that the advertising router has a default route in the IP
routing table.
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< Free Open Study >
4-7 default-information originate route-map route-map-name
Syntax Description:
route-map-name— OSPF will generate a default route only if the conditions of the route map are satisfied. If the keywordalways is
used, the default route will be advertised regardless of the conditions in the route map.
Purpose: The advertisement of a default route can be made conditional using a route map. If the conditions of the route map are satisfied,
then the default route will be advertised into the OSPF domain.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Using a Route Map for Conditional Default Route
Advertisement
In Figure 4-5, Router B is receiving the route 3.3.3.0/30 from Router C via EIGRP. This network will carry all default traffic from the OPSF
domain. If this network is down then you don't want the traffic from the OSPF domain to be sent to Router C. A route map can be used on
Router B to make a conditional advertisement of a default route. For this example, the condition will be the existence of the 3.3.3.0/30 in the IP
routing table on Router B.
Figure 4-5. When OSPF Advertises a Default Route, the Advertising Router Becomes an ASBR.
The Advertisement of a Default Route Can Be Made Conditional Using a Route Map
Router A
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interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router eigrp 1
network 10.0.0.0
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
.
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network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router C
interface Loopback0
description Simulate the network 3.3.3.0/30
ip address 3.3.3.1 255.255.255.252
!
interface Serial0
bandwidth 64
ip address 10.1.1.6 255.255.255.252
!
router eigrp 1
network 3.0.0.0
network 10.0.0.0
no auto-summary
Verify that Routers A and B have established an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/BDR
Dead Time Address
00:00:30
172.16.1.2
Interface
Ethernet0/0
________________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:00:38
172.16.1.1
Interface
Ethernet0
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Verify that Routers B and C have formed an EIGRP relationship.
rtrB#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H Address
Interface Hold Uptime SRTT RTO Q Seq
(sec)
0 10.1.1.6
Se1
(ms)
Cnt Num
10 00:13:27 399 2394 0 4
________________________________________________________________________________
rtrC#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H Address
Interface Hold Uptime SRTT RTO Q Seq
(sec)
0 10.1.1.5
Se0
(ms)
Cnt Num
11 00:13:53 28 2280 0 6
Verify that Router B is receiving the 3.3.3.0/30 network from Router C.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/11] via 172.16.1.1, 00:13:37, Ethernet0
2.0.0.0/32 is subnetted, 1 subnets
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C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/30 is subnetted, 1 subnets
D
3.3.3.0 [90/40640000] via 10.1.1.6, 00:13:38, Serial1
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial1
Modify the configuration on router B so that OSPF will conditionally advertise a default route into the OSPF domain based on the existence of
the 3.3.3.0/30 network.
Router B
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
default-information originate route-map exist
!
access-list 1 permit 3.3.3.0 0.0.0.3
!
route-map exist permit 10
match ip address 1
Verification
Verify that the default route is in the IP routing table on Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
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E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 172.16.1.2 to network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/11] via 172.16.1.2, 00:15:57, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
O*E2 0.0.0.0/0 [110/1] via 172.16.1.2, 00:15:57, Ethernet0/0
Test the route map by shutting down the loopback0 interface on Router C so the 3.3.3.0/30 will no longer be advertised by EIGRP. This
should prevent Router B from advertising the default route.
Router C
interface Loopback0
shutdown
Verify that the 3.3.3.0/30 network is not in the IP routing table on Router B.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
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1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/11] via 172.16.1.1, 00:19:58, Ethernet0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial1
Verify that the default route is not being advertised to Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/11] via 172.16.1.2, 00:20:13, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
Reenable the loopback interface on Router C and verify that the default route is being advertised.
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Router C
interface Loopback0
no shutdown
________________________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/11] via 172.16.1.1, 00:22:27, Ethernet0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/30 is subnetted, 1 subnets
D
3.3.3.0 [90/40640000] via 10.1.1.6, 00:00:05, Serial1
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial1
________________________________________________________________________________
rtrA#show ip route
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Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 172.16.1.2 to network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/11] via 172.16.1.2, 00:22:44, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
O*E2 0.0.0.0/0 [110/1] via 172.16.1.2, 00:01:00, Ethernet0/0
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers using the show ip ospf neighbors command.
Step 2. Verify the syntax and conditions of the route map.
Step 3. If you are using thealways form of the command, then the default route will be advertised regardless of the conditions in
the route map.
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Chapter 5. Setting the Default Metric for Redistributed
Protocols
Section 5-1. default-metric cost
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5-1 default-metric cost
Syntax Description:
cost— External cost assigned to routes redistributed into OSPF. The range of values is 1 to 4,294,967,295. The default metric for
redistributed BGP routes is 1. The default metric for all other redistributed protocols is 20.
Purpose: Used to assign a cost to routes redistributed into OSPF that have not been assigned a metric by theredistribute command. Using
the default-metric command will not affect routes that have been assigned a metric by theredistribute command.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Setting the Default Cost for Redistributed Routes
In Figure 5-1, Router B is receiving the routes 3.3.3.0/24 and 10.1.1.4/30 from Router C via EIGRP. These EIGRP routes will be initially
redistributed into OSPF using the default metric of 20. SeeChapter 14, "Route Redistribution," for the use of theredistribute command.
Figure 5-1. The Default Metric for redistributed BGP Routes Is 1 and the Default Metric for Other
redistributed
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
.
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interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router eigrp 1
network 10.0.0.0
router ospf 1
redistribute eigrp 1 subnets
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
______________________________________________________________________
.
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Router C
interface Loopback0
description Simulate the network 3.3.3.0/24
ip address 3.3.3.3 255.255.255.0
!
interface Serial0
bandwidth 64
ip address 10.1.1.6 255.255.255.252
!
router eigrp 1
network 3.0.0.0
network 10.0.0.0
no auto-summary
Verify that Routers A and B have established an OSPF neighbor relationship, as shown here:
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/BDR
Dead Time Address
00:00:30
172.16.1.2
Interface
Ethernet0/0
_______________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:00:38
172.16.1.1
Interface
Ethernet0
Verify that Routers B and C have formed an EIGRP relationship.
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rtrB#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H Address
Interface Hold Uptime SRTT RTO Q Seq
(sec)
0 10.1.1.6
Se1
(ms)
Cnt Num
10 00:13:27 399 2394 0 4
______________________________________________________________________________________
rtrC#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H Address
Interface Hold Uptime SRTT RTO Q Seq
(sec)
0 10.1.1.5
Se0
(ms)
Cnt Num
11 00:13:53 28 2280 0 6
Verify that Router B is receiving the 3.3.3.0/24 network from Router C.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/11] via 172.16.1.1, 00:13:37, Ethernet0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/24 is subnetted, 1 subnets
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D
3.3.3.0 [90/40640000] via 10.1.1.6, 00:13:38, Serial1
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial1
Inspect the routing table on Router A to verify the default cost of the redistributed route.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/11] via 172.16.1.2, 00:27:10, Ethernet0/0
3.0.0.0/24 is subnetted, 1 subnets
O E2
3.3.3.0 [110/20] via 172.16.1.2, 00:01:58, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
10.0.0.0/30 is subnetted, 1 subnets
O E2
10.1.1.4 [110/20] via 172.16.1.2, 00:01:58, Ethernet0/0
The redistributed EIGRP routes have a cost or metric of 20. These routes were redistributed as type 2 routes (the default) so the cost of
crossing the Ethernet network is not included. Modify the configuration on Router B so the redistributed EIGRP routes are assigned a cost of
55.
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Router B
router ospf 1
redistribute eigrp 1 subnets
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
default-metric 55
Verification
Verify that the redistributed EIGRP routes have been assigned a cost of 55.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O
2.2.2.2 [110/11] via 172.16.1.2, 00:00:06, Ethernet0/0
3.0.0.0/24 is subnetted, 1 subnets
O E2
3.3.3.0 [110/55] via 172.16.1.2, 00:00:06, Ethernet0/0
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172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
10.0.0.0/30 is subnetted, 1 subnets
O E2
10.1.1.4 [110/55] via 172.16.1.2, 00:00:06, Ethernet0/0
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers using the show ip ospf neighbors command.
Step 2. Verify that the routes to be redistributed are in the IP routing table.
Step 3. Verify that you have used the desired metric with thedefault-metric command.
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Chapter 6. Administrative Distance
Section 6-1. distance administrative-distance
Section 6-2. distance administrative-distance source-ip-address source-ip-mask
Section 6-3. distance administrative-distance source-ip-address source-ip-mask access-list-number
Section 6-4. distance ospf external administrative-distance
Section 6-5. distance ospf inter-area administrative-distance
Section 6-6. distance ospf intra-area administrative-distance
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6-1 distance administrative-distance
Syntax Description:
administrative-distance— The supplied value will be applied to the administrative distance of all OSPF routes in the local routing
table. The default administrative distance for OSPF routes is 110.
Purpose: If a router has learned about a network from more than one routing protocol, then the administrative distance is used to select the
best route. The best route is the route that will be installed in the IP routing table. It is the route with the lowest administrative distance. The
default administrative distances for the IP routing protocols are as follows:
connected— 0
static— 1
EBGP— 20
EIGRP— 90
IGRP— 100
OSPF— 110
IS-IS— 115
RIP— 120
IBGP— 200
Initial Cisco IOS Software Release: 10.0
Configuration Example: Adjusting the Administrative Distance to Influence Route
Selection
In Figure 6-1, Router B is receiving the route 3.3.3.0/24 from Router A via OSPF and Router C via EIGRP. Because EIGRP has a lower
administrative distance than OSPF, the EIGRP route will be installed in the routing table on Router B. A loopback address on Routers A and
C is used to simulate the network that is being propagated by OSPF and EIGRP. The ip ospf network point-to-point interface command
(see Section 19-17) on Router A is used so the loopback is advertised as a /24 network and not a /32 network.
Figure 6-1. When a Router Learns the Same Route via Two Different Routing Protocols, the
Administrative Distance Is Used to Select the Best Route
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Loopback1 description Simulate the network 3.3.3.0/24
ip address 3.3.3.3 255.255.255.0
ip ospf network point-to-point
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
router-id 1.1.1.1
network 1.1.1.1 0.0.0.0 area 0
network 3.3.3.0 0.0.0.255 area 0
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
.
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!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router eigrp 1
network 10.0.0.0
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router C
interface Loopback0
description Simulate the network 3.3.3.0/24
ip address 3.3.3.3 255.255.255.0
!
interface Serial0
bandwidth 64
ip address 10.1.1.6 255.255.255.252
!
router eigrp 1
network 3.0.0.0
.
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network 10.0.0.0
no auto-summary
Verify that Routers A and B have established an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
Dead Time Address
1 FULL/BDR
00:00:30
172.16.1.2
Interface
Ethernet0/0
________________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
Dead Time Address
1 FULL/DR
00:00:38
172.16.1.1
Interface
Ethernet0
Verify that Routers B and C have formed an EIGRP relationship.
rtrB#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H Address
Interface Hold Uptime SRTT RTO Q Seq
(sec)
0 10.1.1.6
Se1
(ms)
Cnt Num
10 00:13:27 399 2394 0 4
________________________________________________________________________________
rtrC#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H Address
Interface Hold Uptime SRTT RTO Q Seq
(sec)
0 10.1.1.5
Se0
(ms)
Cnt Num
11 00:13:53 28 2280 0 6
Verify that Router B is installing the 3.3.3.0/24 network learned via EIGRP from Router C.
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rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/11] via 172.16.1.1, 00:13:37, Ethernet0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/24 is subnetted, 1 subnets
D
3.3.3.0 [90/40640000] via 10.1.1.6, 00:13:38, Serial1
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial1
Modify the configuration on Router B to set the administrative distance of all OSPF routes to 80. Because this value is less than the
administrative distance for EIGRP (90), the OSPF route for 3.3.3.0/24 should be installed in the IP routing table on Router B.
Router B
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
distance 80
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Verification
Verify that the OSPF route for 3.3.3.0/24 has been installed in the routing table on Router B.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [80/11] via 172.16.1.1, 00:01:22, Ethernet0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/24 is subnetted, 1 subnets
O
3.3.3.0 [80/11] via 172.16.1.1, 00:01:23, Ethernet0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial1
Troubleshooting
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Step 1. Verify that there is a neighbor relationship between the OSPF routers using the show ip ospf neighbors command.
Step 2. Verify that the correct administrative distance is being used with thedistance command.
Step 3. Verify the administrative distance of the OSPF routes using theshow ip route command.
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6-2 distance administrative-distance source-ip-address source-ip-mask
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6-3 distance administrative-distance source-ip-address source-ip-mask
access-list-number
Syntax Description:
administrative-distance— The supplied value will be applied to the administrative distance of selected OSPF routes in the local
routing table. The default administrative distance for OSPF routes is 110.
source-ip-address— IP address of the source of the OSPF routes. For OSPF, the source address is the OSPF router ID.
source-ip-mask— IP mask for the source of the OSPF routes.
access-list-number— Standard IP access number used to determine which routes learned from the source will have their
administrative distance modified. The range of access list numbers is 1–99 and 1300–1999.
Purpose: If a router has learned about a network from more than one routing protocol, then the administrative distance is used to select the
best route. The best route is the route that will be installed in the IP routing table, the route with the lowest administrative distance. The default
administrative distances for the IP routing protocols are as follows:
connected— 0
static— 1
EBGP— 20
EIGRP— 90
IGRP— 100
OSPF— 110
IS-IS— 115
RIP— 120
IBGP— 200
Command 6-2 is used to modify the administrative distance of all routes learned from sources that match the source IP address/mask pair.
Command 6-3 is used to modify the administrative distance of selected routes learned from sources that match the IP address/mask pair by
using an IP access list.
Initial Cisco IOS Software Release: 10.0
Configuration Example 1: Adjusting the Administrative Distance of All Routes
Learned from a Particular OSPF Neighbor
In Figure 6-2, Router B is receiving the route 3.3.3.0/24 from Router A via OSPF and Router C via EIGRP. Because EIGRP hasa lower
administrative distance than OSPF, the EIGRP route will be installed in the routing table on Router B. A loopback address on Routers A and
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C is used to simulate the network that is being propagated by OSPF and EIGRP. The ip ospf network point-to-point interface command
(see Section 19-7) on Router A is used so the loopback is advertised as a /24 network and not a /32 network.
Figure 6-2. The Administrative Distance of OSPF Routes Can Be Modified Based on the Neighbor
Router's OSPF ID
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Loopback1
description Simulate the network 3.3.3.0/24
ip address 3.3.3.3 255.255.255.0
ip ospf network point-to-point
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
router-id 1.1.1.1
network 1.1.1.1 0.0.0.0 area 0
network 3.3.3.0 0.0.0.255 area 0
network 172.16.1.0 0.0.0.255 area 0
.
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________________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router eigrp 1
network 10.0.0.0
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router C
interface Loopback0
description Simulate the network 3.3.3.0/24
ip address 3.3.3.3 255.255.255.0
!
interface Serial0
.
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bandwidth 64
ip address 10.1.1.6 255.255.255.252
!
router eigrp 1
network 3.0.0.0
network 10.0.0.0
no auto-summary
Verify that Routers A and B have established an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
Dead Time Address
1 FULL/BDR
00:00:30
172.16.1.2
Interface
Ethernet0/0
________________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
Dead Time Address
1 FULL/DR
00:00:38
172.16.1.1
Interface
Ethernet0
Verify that Routers B and C have formed an EIGRP relationship.
rtrB#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H Address
Interface Hold Uptime SRTT RTO Q Seq
(sec)
0 10.1.1.6
Se1
(ms)
Cnt Num
10 00:13:27 399 2394 0 4
________________________________________________________________________________
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rtrC#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H Address
Interface Hold Uptime SRTT RTO Q Seq
(sec)
0 10.1.1.5
Se0
(ms)
Cnt Num
11 00:13:53 28 2280 0 6
Verify that Router B is installing the 3.3.3.0/24 network learned via EIGRP from Router C.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/11] via 172.16.1.1, 00:13:37, Ethernet0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/24 is subnetted, 1 subnets
D
3.3.3.0 [90/40640000] via 10.1.1.6, 00:13:38, Serial1
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial1
Modify the configuration on Router B to set the administrative distance of all OSPF routes learned from neighbor 172.16.1.1 to 80. Because
this value is less than the administrative distance for EIGRP (90), the OSPF route for 3.3.3.0/24 should be installed in the IP routing table on
Router B. When using the distance command with OSPF, the source address is the OSPF router ID. The source mask is an inverse mask.
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Therefore, to set the administrative distance of OSPF routes learned from Router A, use the source address/mask pair 1.1.1.1/0.0.0.0.
Router B
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
distance 80 1.1.1.1 0.0.0.0
Verification
Verify that the OSPF route for 3.3.3.0/24 has been installed in the routing table on Router B.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [80/11] via 172.16.1.1, 00:01:22, Ethernet0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/24 is subnetted, 1 subnets
O
3.3.3.0 [80/11] via 172.16.1.1, 00:01:23, Ethernet0
172.16.0.0/24 is subnetted, 1 subnets
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C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial1
Configuration Example 2: Adjusting the Administrative Distance of Selected
Routes Learned from a Particular OSPF Neighbor
Modify the configuration on Router B to modify only the administrative distance of the network 3.3.3.0/24. The network 1.1.1.1/32 should
maintain the default OSPF administrative distance of 110. The OSPF router ID of Router A can be found by using the show ip ospf
command.
rtrA#show ip ospf
Routing Process "ospf 1" with ID 1.1.1.1
Supports only single TOS(TOS0) routes
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Area BACKBONE(0)
Number of interfaces in this area is 3
Area has no authentication
SPF algorithm executed 32 times
Area ranges are
Number of LSA 3. Checksum Sum 0x15E77
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
________________________________________________________________________________
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Router B
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
distance 80 1.1.1.1 0.0.0.0 1
!
access-list 1 permit 3.3.3.0 0.0.0.255
Verification
Verify that the administrative distance for the 3.3.3.0/24 network has been modified while the 1.1.1.1 network remains unchanged.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O
1.1.1.1 [110/11] via 172.16.1.1, 00:03:51, Ethernet0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/24 is subnetted, 1 subnets
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O
3.3.3.0 [80/11] via 172.16.1.1, 00:03:52, Ethernet0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial1
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers using the show ip ospf neighbors command.
Step 2. Verify that the correct administrative distance is being used with thedistance command.
Step 3. The source address for OSPF is the OSPF router ID. Ensure that the proper OSPF router ID is being used.
Step 4. Ensure that the source mask is an inverse mask.
Step 5. Verify the syntax of the access-list and make sure the distance command is referencing the correct access list.
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6-4 distance ospf external administrative-distance
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6-5 distance ospf inter-area administrative-distance
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6-6 distance ospf intra-area administrative-distance
Syntax Description:
administrative-distance— The supplied value will be applied to the administrative distance of either the external, inter-area, or
intra-area OSPF routes in the local routing table. The default administrative distance for these OSPF routes is 110.
Purpose: If a router has learned about a network from more than one routing protocol, then the administrative distance is used to select the
best route. The best route is the route that will be installed in the IP routing table, the route with the lowest administrative distance. The default
administrative distances for the IP routing protocols are:
connected— 0
static— 1
EBGP— 20
EIGRP— 90
IGRP— 100
OSPF— 110
IS-IS— 115
RIP— 120
IBGP— 200
There are three types of OSPF routes. These types are external (either type 1 or 2), inter-area, and intra-area. External routes are those that
have been redistributed into OSPF. A route to an area directly connected to the router is an intra-area route and a route to an area that is not
directly connected to the router is an inter-area route. These commands are used to modify the administrative distance of all routes belonging
to one of the three types of OSPF routes.
Initial Cisco IOS Software Release: 11.1
Configuration Example: Adjusting the Administrative Distance Based on the Type
of OSPF Route
In Figure 6-3, Router A is receiving two OSPF external routes from the redistribution of EIGRP on Router B. Router A is also receiving an
OSPF inter-area route and an OSPF intra-area route from Router B.
Figure 6-3. The Three Types of OSPF Routes Are Inter-area, Intra-area, and External
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Loopback1
ip address 51.51.51.51 255.255.255.0
!
.
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interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router eigrp 1
network 10.0.0.0
!
router ospf 1
router-id 2.2.2.2
redistribute eigrp 1 subnets
network 2.2.2.2 0.0.0.0 area 2
network 51.51.51.51 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.0
!
interface Serial0
bandwidth 64
ip address 10.1.1.6 255.255.255.252
!
router eigrp 1
.
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network 3.0.0.0
network 10.0.0.0
no auto-summary
Verify that Routers A and B have established an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
Dead Time Address
1 FULL/BDR
00:00:30
172.16.1.2
Interface
Ethernet0/0
________________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
Dead Time Address
1 FULL/DR
00:00:38
172.16.1.1
Interface
Ethernet0
Verify that Routers B and C have formed an EIGRP relationship.
rtrB#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H Address
Interface Hold Uptime SRTT RTO Q Seq
(sec)
0 10.1.1.6
Se1
(ms)
Cnt Num
10 00:13:27 399 2394 0 4
________________________________________________________________________________
rtrC#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H Address
Interface Hold Uptime SRTT RTO Q Seq
(sec)
0 10.1.1.5
Se0
(ms)
Cnt Num
11 00:13:53 28 2280 0 6
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Verify that Router A is learning each type of OSPF route.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
51.0.0.0/32 is subnetted, 1 subnets
O
51.51.51.51 [110/11] via 172.16.1.2, 00:21:44, Ethernet0/0
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/11] via 172.16.1.2, 00:21:44, Ethernet0/0
3.0.0.0/24 is subnetted, 1 subnets
O E2
3.3.3.0 [110/20] via 172.16.1.2, 00:21:44, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
10.0.0.0/30 is subnetted, 1 subnets
O E2
10.1.1.4 [110/20] via 172.16.1.2, 00:21:44, Ethernet0/0
Modify the configuration on Router A to set the administrative distance of OSPF inter-area routes to 60, intra-area routes to 70, and external
routes to 50.
Router A
router ospf 1
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network 1.1.1.1 0.0.0.0 area 1
network 3.3.3.0 0.0.0.255 area 0
network 172.16.1.0 0.0.0.255 area 0
distance ospf intra-area 70 inter-area 60 external 50
Verification
Verify that the different OSPF route types have been configured with the proper administrative distance.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
51.0.0.0/32 is subnetted, 1 subnets
O
51.51.51.51 [70/11] via 172.16.1.2, 00:02:04, Ethernet0/0
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [60/11] via 172.16.1.2, 00:02:04, Ethernet0/0
3.0.0.0/24 is subnetted, 1 subnets
O E2
3.3.3.0 [50/20] via 172.16.1.2, 00:02:04, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
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10.0.0.0/30 is subnetted, 1 subnets
O E2
10.1.1.4 [50/20] via 172.16.1.2, 00:02:04, Ethernet0/0
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers using the show ip ospf neighbors command.
Step 2. Verify that the correct administrative distance is being used with thedistance ospf command and that the distance is being
applied to the correct OSPF route type.
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Chapter 7. Filtering Routes with Distribute Lists
Section 7-1. distribute-list access-list-number in
Section 7-2. distribute-list access-list-number in interface-type interface-number
Section 7-3. distribute-list access-list-number out
Section 7-4. distribute-list access-list-number out interface-type interface-number
Section 7-5. distribute-list access-list-number out routing-process
Section 7-6. distribute-list access-list-name in
Section 7-7. distribute-list access-list-name in interface-type interface-number
Section 7-8. distribute-list access-list-name out
Section 7-9. distribute-list access-list-name out interface-type interface-number
Section 7-10. distribute-list access-list-name out routing-process
Section 7-11. distribute-list prefix prefix-list-name in
Section 7-12. distribute-list prefix prefix-list-name in interface-type interface-number
Section 7-13. distribute-list prefix prefix-list-name out
Section 7-14. distribute-list prefix prefix-list-name out interface-type interface-number
Section 7-15. distribute-list prefix prefix-list-name out routing-process
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7-1 distribute-list access-list-number in
Syntax Description:
access-list-number— Standard IP access number used to determine which routes learned via OSPF will be prevented from being
installed in the IP routing table. The range of access list numbers is 1–99 and 1300–2699.
Purpose: To prevent OSPF learned routes from being installed in the IP routing table. Even though an OSPF route may be prevented from
being installed in the IP routing table, the route will still be in the OSPF database and advertised to OSPF neighbors. If you want to block a
particular route or group of routes from entering the IP routing table, use a distribute list on all OSPF routers.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Preventing OSPF Learned Routes from Being Installed in
the IP Routing Table
In Figure 7-1, Router A is receiving the OSPF routes 2.2.2.2, 3.3.3.3, and 4.4.4.4 from Router B. Start by configuring Routers A and B as
shown in the listing that follows.
Figure 7-1. A Distribute List/Access List Controls Which OSPF Routes Are Transferred from the
OSPF Database into the IP Routing Table
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Loopback1
ip address 3.3.3.3 255.255.255.255
!
interface Loopback2
ip address 4.4.4.4 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
.
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router ospf 1
router-id 2.2.2.2
network 2.2.2.2 0.0.0.0 area 2
network 3.3.3.3 0.0.0.0 area 0
network 4.4.4.4 0.0.0.0 area 4
network 172.16.1.2 0.0.0.0 area 0
Verify that Routers A and B have established a FULL OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/BDR
Dead Time Address
00:00:30
172.16.1.2
Interface
Ethernet0/0
________________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:00:38
172.16.1.1
Interface
Ethernet0
Verify that Router A is receiving the routes 2.2.2.2, 3.3.3.3, and 4.4.4.4 from Router B.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
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Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/11] via 172.16.1.2, 00:04:28, Ethernet0/0
3.0.0.0/32 is subnetted, 1 subnets
O
3.3.3.3 [110/11] via 172.16.1.2, 00:04:28, Ethernet0/0
4.0.0.0/32 is subnetted, 1 subnets
O IA
4.4.4.4 [110/11] via 172.16.1.2, 00:04:28, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
For illustrative purposes, verify that these three routes are in the OSPF database on Router A.
rtrA#show ip ospf database
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum Link count
1.1.1.1
1.1.1.1
493
0x800000A5 0x8F6F 1
2.2.2.2
2.2.2.2
489
0x80000030 0x7ECF 2
Net Link States (Area 0)
Link ID
172.16.1.1
ADV Router
1.1.1.1
Age
496
Seq#
Checksum
0x80000001 0x6DFD
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Summary Net Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum
1.1.1.1
1.1.1.1
714
0x80000033 0xE21F
2.2.2.2
2.2.2.2
487
0x80000049 0x6A79
4.4.4.4
2.2.2.2
490
0x80000001 0x9E85
Router Link States (Area 1)
Link ID
ADV Router
1.1.1.1
1.1.1.1
Age
726
Seq#
Checksum Link count
0x80000001 0xD351 1
Summary Net Link States (Area 1)
Link ID
ADV Router
2.2.2.2
1.1.1.1
492
0x80000001 0x7DA8
3.3.3.3
1.1.1.1
492
0x80000001 0x4FD2
4.4.4.4
1.1.1.1
492
0x80000001 0x21FC
172.16.1.0
1.1.1.1
Age
496
Seq#
Checksum
0x80000003 0x3B34
Modify the configuration on Router A to prevent the OSPF routes 2.2.2.2 and 3.3.3.3 from being installed in the IP routing table.
Router A
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
distribute-list 1 in
!
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access-list 1 deny 2.2.2.0 0.0.0.255
access-list 1 deny 3.3.3.0 0.0.0.255
access-list 1 permit any
Verification
Verify that the OSPF routes 2.2.2.2 and 3.3.3.3 have been blocked from entering the IP routing table on Router A. They should be absent
from the IP routing table.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
4.0.0.0/32 is subnetted, 1 subnets
O IA
4.4.4.4 [110/11] via 172.16.1.2, 00:03:39, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
Verify that the routes 2.2.2.2 and 3.3.3.3 are still in the OSPF database on Router A.
rtrA#show ip ospf database
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OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum Link count
1.1.1.1
1.1.1.1
951
0x800000A5 0x8F6F 1
2.2.2.2
2.2.2.2
947
0x80000030 0x7ECF 2
Net Link States (Area 0)
Link ID
ADV Router
172.16.1.1
1.1.1.1
Age
954
Seq#
Checksum
0x80000001 0x6DFD
Summary Net Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum
1.1.1.1
1.1.1.1
1172
0x80000033 0xE21F
2.2.2.2
2.2.2.2
945
0x80000049 0x6A79
4.4.4.4
2.2.2.2
948
0x80000001 0x9E85
Router Link States (Area 1)
Link ID
ADV Router
1.1.1.1
1.1.1.1
Age
1184
Seq#
Checksum Link count
0x80000001 0xD351 1
Summary Net Link States (Area 1)
Link ID
ADV Router
Age
Seq#
Checksum
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3.3.3.3
1.1.1.1
946
0x80000001 0x4FD2
4.4.4.4
1.1.1.1
946
0x80000001 0x21FC
172.16.1.0
1.1.1.1
950
0x80000003 0x3B34
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Verify that the distribute-list command is referencing the correct access list number.
Step 3. Verify the syntax of the access list.
Step 4. Verify that the access list has been referenced by using the command show ip access-lists access-list-number. For
example, for the preceding configuration, the output should be:
rtrA#show ip access-lists 1
Standard IP access list 1
deny 2.2.2.0, wildcard bits 0.0.0.255 (1 match) check=4
deny 3.3.3.0, wildcard bits 0.0.0.255 (1 match) check=3
permit any (3 matches)
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7-2 distribute-list access-list-number in interface-type interface-number
Syntax Description:
access-list-number— Standard IP access number used to determine which routes learned via OSPF will be prevented from being
installed in the IP routing table. The range of access list numbers is 1–99 and 1300–2699.
interface-type— Optional parameter, along with the interface-number, used to apply the distribute list to OSPF routes learned
through a particular interface.
interface-number— Number of the interface type.
Purpose: To prevent OSPF routes learned over a specific interface from being installed in the IP routing table. Even though an OSPF route
may be prevented from being installed in the IP routing table, the route will still be in the OSPF database. Because the filtered route will still
be in the OSPF database, it is possible for the route to be received from another OSPF interface.
Initial Cisco IOS Software Release: 10.0. The interface-type and interface-number parameters were added in 11.2.
Configuration Example: Preventing Routes Learned via OSPF Over a Specific
Interface from Being Installed in the IP Routing Table
In Figure 7-2, Router A is receiving the OSPF routes 2.2.2.2, 3.3.3.3, and 4.4.4.4 from Router B over two serial interfaces. Start by
configuring Routers A and B as shown in the listing below the figure.
Figure 7-2. A Distribute List/Access List Controls Which OSPF Routes, Learned Over a Specific
Interface, Are Transferred from the OSPF Database into the IP Routing Table
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
ip address 10.1.1.6 255.255.255.252
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 0
________________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
.
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!
interface Loopback1
ip address 3.3.3.3 255.255.255.255
!
interface Loopback2
ip address 4.4.4.4 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router ospf 1
router-id 2.2.2.2
network 2.2.2.2 0.0.0.0 area 2
network 3.3.3.3 0.0.0.0 area 0
network 4.4.4.4 0.0.0.0 area 4
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 0
Verify that Routers A and B have established a FULL OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/ -
Dead Time Address
00:00:33
10.1.1.5
Interface
Serial0/0
.
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2.2.2.2
1 FULL/ -
00:00:37
10.1.1.2
Serial0/1
________________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
1.1.1.1
1 FULL/ -
00:00:38
10.1.1.1
Serial0
1.1.1.1
1 FULL/ -
00:00:36
10.1.1.6
Serial1
Verify that Router A is receiving the routes 2.2.2.2, 3.3.3.3, and 4.4.4.4 from Router B.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/65] via 10.1.1.5, 00:00:10, Serial0/0
[110/65] via 10.1.1.2, 00:00:10, Serial0/1
3.0.0.0/32 is subnetted, 1 subnets
O
3.3.3.3 [110/65] via 10.1.1.5, 00:00:10, Serial0/0
[110/65] via 10.1.1.2, 00:00:10, Serial0/1
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4.0.0.0/32 is subnetted, 1 subnets
O IA
4.4.4.4 [110/65] via 10.1.1.5, 00:00:10, Serial0/0
[110/65] via 10.1.1.2, 00:00:11, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
C
10.1.1.4 is directly connected, Serial0/0
For illustrative purposes, verify that these three routes are in the OSPF database on Router A.
rtrA#show ip ospf database
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 0)
1.1.1.1
1.1.1.1
1423
0x800000C1 0xE80E 4
2.2.2.2
2.2.2.2
1451
0x80000050 0xA7E3 5
Summary Net Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum
1.1.1.1
1.1.1.1
165
0x80000044 0xC030
2.2.2.2
2.2.2.2
707
0x80000057 0x4E87
4.4.4.4
2.2.2.2
707
0x8000000F 0x8293
Router Link States (Area 1)
Link ID
ADV Router
1.1.1.1
1.1.1.1
Age
1666
Seq#
Checksum Link count
0x80000008 0xC558 1
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Summary Net Link States (Area 1)
Link ID
ADV Router
Age
Seq#
Checksum
2.2.2.2
1.1.1.1
1423
0x80000006 0x9159
3.3.3.3
1.1.1.1
1669
0x80000009 0x5D86
4.4.4.4
1.1.1.1
1669
0x80000009 0x2FB0
10.1.1.0
1.1.1.1
168
0x80000007 0x36B3
10.1.1.4
1.1.1.1
1425
0x80000008 0xCD8
Modify the configuration on Router A to prevent the OSPF routes 2.2.2.2 and 3.3.3.3 received over interface Serial 0/0 and the routes
3.3.3.3 and 4.4.4.4 received over Serial 0/1 from being installed in the IP routing table.
Router A
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
distribute-list 1 in Serial0/0
distribute-list 2 in Serial0/1
!
access-list 1 deny 2.2.2.0 0.0.0.255
access-list 1 deny 3.3.3.0 0.0.0.255
access-list 1 permit any
access-list 2 deny 3.3.3.0 0.0.0.255
access-list 2 deny 4.4.4.0 0.0.0.255
access-list 2 permit any
Verification
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Determine the routes that have been filtered from reaching the IP routing table on Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/65] via 10.1.1.2, 00:01:15, Serial0/1
4.0.0.0/32 is subnetted, 1 subnets
O IA
4.4.4.4 [110/65] via 10.1.1.5, 00:01:15, Serial0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
C
10.1.1.4 is directly connected, Serial0/0
Access list 1 on Router A allows network 4.4.4.0. Access list 2 on Router A allows network 2.2.2.0. The only network that is filtered by both
access lists is 3.3.3.0. Verify that routes 2.2.2.2, 3.3.3.3, and 4.4.4.4 are still in the OSPF database on Router A.
rtrA#show ip ospf database
OSPF Router with ID (1.1.1.1) (Process ID 1)
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Router Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum Link count
1.1.1.1
1.1.1.1
1815
0x800000C1 0xE80E 4
2.2.2.2
2.2.2.2
1843
0x80000050 0xA7E3 5
Summary Net Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum
1.1.1.1
1.1.1.1
557
0x80000044 0xC030
2.2.2.2
2.2.2.2
1099
0x80000057 0x4E87
4.4.4.4
2.2.2.2
1099
0x8000000F 0x8293
Router Link States (Area 1)
Link ID
ADV Router
1.1.1.1
1.1.1.1
Age
43
Seq#
Checksum Link count
0x80000009 0xC359 1
Summary Net Link States (Area 1)
Link ID
ADV Router
Age
Seq#
Checksum
2.2.2.2
1.1.1.1
1815
3.3.3.3
1.1.1.1
45
0x8000000A 0x5B87
4.4.4.4
1.1.1.1
45
0x8000000A 0x2DB1
10.1.1.0
1.1.1.1
559
0x80000007 0x36B3
10.1.1.4
1.1.1.1
1816
0x80000008 0xCD8
0x80000006 0x9159
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Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Verify that the distribute-list command is referencing the correct access list number and interface.
Step 3. Verify the syntax of the access list.
Step 4. Verify that the access list has been referenced by using the commandshow ip access-lists access-list-number. For
example, for the preceding configuration, the output would be the following:
rtrA#show ip access-lists 1
Standard IP access list 1
deny 2.2.2.0, wildcard bits 0.0.0.255 (5 matches) check=15
deny 3.3.3.0, wildcard bits 0.0.0.255 (5 matches) check=10
permit any (10 matches)
Standard IP access list 2
deny 3.3.3.0, wildcard bits 0.0.0.255 (4 matches) check=12
deny 4.4.4.0, wildcard bits 0.0.0.255 (4 matches) check=8
permit any (8 matches)
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7-3 distribute-list access-list-number out
Syntax Description:
access-list-number— Standard IP access number used to determine which routes learned via OSPF will be prevented from being
installed in the IP routing table. The range of access list numbers is 1–99 and 1300–2699.
Purpose: For distance vector protocols (RIP, IGRP, EIGRP), this command prevents routes selected by the access list from being
advertised to a neighbor. OSPF is a link-state protocol and does not advertise routes to a neighbor but advertises a link-state database. The
neighbor determines the routes from the information in the link-state database. Therefore, this command has no effect when used with OSPF.
Initial Cisco IOS Software Release: 10.0. The interface-type and interface-number parameters were added in 11.2.
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< Free Open Study >
7-4 distribute-list access-list-number out interface-type interface-number
Syntax Description:
access-list-number— Standard IP access number used to determine which routes learned via OSPF will be prevented from being
installed in the IP routing table. The range of access list numbers is 1–99 and 1300–2699.
interface-type— Optional parameter, along with the interface-number, used to apply the distribute list to OSPF routes learned
through a particular interface.
interface-number— Number of the interface type.
Purpose: For distance vector protocols (RIP, IGRP, EIGRP), this command prevents routes selected by the access list from being advertised
to a neighbor. OSPF is a link-state protocol and does not advertise routes to a neighbor but advertises a link-state database. The neighbor
determines the routes from the information in the link-state database. Therefore, this command has no effect when used with OSPF.
Initial Cisco IOS Software Release: 10.0. The interface-type and interface-number parameters were added in 11.2.
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7-5 distribute-list access-list-number out routing-process
Syntax Description:
access-list-number— Standard IP access number used to determine which routes redistributed into OSPF will be prevented from
being installed in the OSPF database. This has the effect of preventing the blocked redistributed routes from being advertised to
OSPF neighbors. The range of access list numbers is 1–99 and 1300–2699.
routing-process— The routing process that has been redistributed into OSPF (RIP, IGRP, EIGRP, OSPF, BGP, EGP, static, or
connected).
Purpose: To prevent routes that were redistributed into OSPF from another routing process from being installed in the OSPF database. This
command can be used to filter OSPF routes by using two OSPF processes and to redistribute the routes between the OSPF processes.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Preventing Routes Redistributed into OSPF from Being
Installed in the IP Routing Table
In Figure 7-3, Router B is receiving the EIGRP routes 10.1.1.4/30, 3.3.3.0/24, and 4.4.4.0/24 from Router C. Router B is redistributing EIGRP
into OSPF, and these routes will be advertised to Router A as OSPF external type two routes. Start by configuring Routers A, B, and C as
shown in the listing that follows the figure.
Figure 7-3. A Distribute List/Access List Prevents Redistributed Routes from Being Installed in the
OSPF Database
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router eigrp 1
network 10.0.0.0
.
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router ospf 1
redistribute eigrp 1 subnets
network 2.2.2.2 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.0
!
interface Loopback1
ip address 4.4.4.4 255.255.255.0
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router eigrp 1
network 3.0.0.0
network 4.0.0.0
network 10.0.0.0
no auto-summary
Verify that Routers A and B have established a FULL OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
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2.2.2.2
1 FULL/BDR
00:00:30
172.16.1.2
Ethernet0/0
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:00:38
172.16.1.1
Interface
Ethernet0
Verify that Router B is receiving the routes 3.3.3.0/24 and 4.4.4.0/24 from Router C via EIGRP.
rtrB# show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/24 is subnetted, 1 subnets
D
3.3.3.0 [90/40640000] via 10.1.1.6, 00:38:45, Serial1
4.0.0.0/24 is subnetted, 1 subnets
D
4.4.4.0 [90/40640000] via 10.1.1.6, 00:38:45, Serial1
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial1
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Verify that Router A is receiving the routes 10.1.1.4/30, 3.3.3.0/24, and 4.4.4.0/24 from Router B as OSPF external type 2 routes.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/11] via 172.16.1.2, 00:27:48, Ethernet0/0
3.0.0.0/24 is subnetted, 1 subnets
O E2
3.3.3.0 [110/20] via 172.16.1.2, 00:05:41, Ethernet0/0
4.0.0.0/24 is subnetted, 1 subnets
O E2
4.4.4.0 [110/20] via 172.16.1.2, 00:27:48, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
10.0.0.0/30 is subnetted, 1 subnets
O E2
10.1.1.4 [110/20] via 172.16.1.2, 00:05:42, Ethernet0/0
For illustrative purposes, verify that these three routes are in the OSPF database on Router B.
rtrB#show ip ospf database external
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OSPF Router with ID (2.2.2.2) (Process ID 1)
Type-5 AS External Link States
LS age: 441
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 3.3.3.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000001
Checksum: 0x3F50
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
LS age: 1788
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 4.4.4.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000003
Checksum: 0x1773
Length: 36
Network Mask: /24
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Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
LS age: 459
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 10.1.1.4 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000001
Checksum: 0xD7B3
Length: 36
Network Mask: /30
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
Modify the configuration on Router B to allow only the installation of EIGRP route 4.4.4.0/24 into the OSPF database.
Router B
router ospf 1
redistribute eigrp 1 subnets
network 2.2.2.2 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
distribute-list 1 out eigrp 1
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access-list 1 permit 4.4.4.0 0.0.0.255
Verification
Verify that the EIGRP routes 10.1.1.4/30 and 3.3.3.0/24 have been blocked from entering the OSPF database on Router B.
rtrB#show ip ospf database external
OSPF Router with ID (2.2.2.2) (Process ID 1)
Type-5 AS External Link States
LS age: 419
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 4.4.4.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000004
Checksum: 0x1574
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
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Verify that Router A is receiving only one external type 2 route from Router B.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/11] via 172.16.1.2, 00:38:45, Ethernet0/0
4.0.0.0/24 is subnetted, 1 subnets
O E2
4.4.4.0 [110/20] via 172.16.1.2, 00:38:45, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Verify that the distribute-list command is referencing the correct access list number and routing process.
Step 3. Verify the syntax of the access list.
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Step 4. Verify that the intended routes are in the OSPF database using the command show ip ospf database external.
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7-6 distribute-list access-list-name in
Syntax Description:
access-list-name— Named IP access list that is used to determine which routes learned via OSPF will be prevented from being
installed in the IP routing table.
Purpose: To prevent OSPF learned routes from being installed in the IP routing table. Even though an OSPF route may be prevented from
being installed in the IP routing table, the route will still be in the OSPF database.
Initial Cisco IOS Software Release: 11.2
Configuration Example: Preventing OSPF Learned Routes from Being Installed in
the IP Routing Table
In Figure 7-4, Router A is receiving the OSPF routes 2.2.2.2, 3.3.3.3, and 4.4.4.4 from Router B. Start by configuring Routers A and B as
shown in the listing that follows the figure.
Figure 7-4. A Distribute List/Named Access List Controls Which OSPF Routes Are Transferred
from the OSPF Database Into the IP Routing Table
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Loopback1
ip address 3.3.3.3 255.255.255.255
!
interface Loopback2
ip address 4.4.4.4 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
.
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router ospf 1
router-id 2.2.2.2
network 2.2.2.2 0.0.0.0 area 2
network 3.3.3.3 0.0.0.0 area 0
network 4.4.4.4 0.0.0.0 area 4
network 172.16.1.2 0.0.0.0 area 0
Verify that Routers A and B have established a FULL OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/BDR
Dead Time Address
00:00:30
172.16.1.2
Interface
Ethernet0/0
________________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:00:38
172.16.1.1
Interface
Ethernet0
Verify that Router A is receiving the routes 2.2.2.2, 3.3.3.3, and 4.4.4.4 from Router B.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
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Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/11] via 172.16.1.2, 00:04:28, Ethernet0/0
3.0.0.0/32 is subnetted, 1 subnets
O
3.3.3.3 [110/11] via 172.16.1.2, 00:04:28, Ethernet0/0
4.0.0.0/32 is subnetted, 1 subnets
O IA
4.4.4.4 [110/11] via 172.16.1.2, 00:04:28, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
For illustrative purposes, verify that these three routes are in the OSPF database on Router A.
rtrA#show ip ospf database
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum Link count
1.1.1.1
1.1.1.1
493
0x800000A5 0x8F6F 1
2.2.2.2
2.2.2.2
489
0x80000030 0x7ECF 2
Net Link States (Area 0)
Link ID
172.16.1.1
ADV Router
1.1.1.1
Age
496
Seq#
Checksum
0x80000001 0x6DFD
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Summary Net Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum
1.1.1.1
1.1.1.1
714
0x80000033 0xE21F
2.2.2.2
2.2.2.2
487
0x80000049 0x6A79
4.4.4.4
2.2.2.2
490
0x80000001 0x9E85
Router Link States (Area 1)
Link ID
ADV Router
1.1.1.1
1.1.1.1
Age
726
Seq#
Checksum Link count
0x80000001 0xD351 1
Summary Net Link States (Area 1)
Link ID
ADV Router
2.2.2.2
1.1.1.1
492
0x80000001 0x7DA8
3.3.3.3
1.1.1.1
492
0x80000001 0x4FD2
4.4.4.4
1.1.1.1
492
0x80000001 0x21FC
172.16.1.0
1.1.1.1
Age
496
Seq#
Checksum
0x80000003 0x3B34
Modify the configuration on Router A to prevent the OSPF routes 2.2.2.2 and 3.3.3.3 from being installed in the IP routing table.
Router A
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
distribute-list filter-ospf in
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ip access-list standard filter-ospf
deny 2.2.2.0 0.0.0.255
deny 3.3.3.0 0.0.0.255
permit any
Verification
Verify that the OSPF routes 2.2.2.2 and 3.3.3.3 have been blocked from entering the IP routing table on Router A. They should be absent
from the IP routing table.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
4.0.0.0/32 is subnetted, 1 subnets
O IA
4.4.4.4 [110/11] via 172.16.1.2, 00:03:39, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
Verify that routes 2.2.2.2 and 3.3.3.3 are still in the OSPF database on Router A.
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rtrA#show ip ospf database
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum Link count
1.1.1.1
1.1.1.1
951
0x800000A5 0x8F6F 1
2.2.2.2
2.2.2.2
947
0x80000030 0x7ECF 2
Net Link States (Area 0)
Link ID
ADV Router
172.16.1.1
1.1.1.1
Age
954
Seq#
Checksum
0x80000001 0x6DFD
Summary Net Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum
1.1.1.1
1.1.1.1
1172
0x80000033 0xE21F
2.2.2.2
2.2.2.2
945
0x80000049 0x6A79
4.4.4.4
2.2.2.2
948
0x80000001 0x9E85
Router Link States (Area 1)
Link ID
ADV Router
1.1.1.1
1.1.1.1
Age
1184
Seq#
Checksum Link count
0x80000001 0xD351 1
Summary Net Link States (Area 1)
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Link ID
ADV Router
3.3.3.3
1.1.1.1
946
0x80000001 0x4FD2
4.4.4.4
1.1.1.1
946
0x80000001 0x21FC
172.16.1.0
1.1.1.1
Age
950
Seq#
Checksum
0x80000003 0x3B34
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Verify that the distribute-list command is referencing the correct named access list.
Step 3. Verify the syntax of the named access list.
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7-7 distribute-list access-list-name in interface-type interface-number
Syntax Description:
access-list-name— Named IP access used to determine which routes learned via OSPF will be prevented from being installed in
the IP routing table.
interface-type— Optional parameter, along with the interface-number, used to apply the distribute list to OSPF routes learned
through a particular interface.
interface-number— Number of the interface type.
Purpose: To prevent OSPF routes learned over a specific interface from being installed in the IP routing table. Even though an OSPF route
may be prevented from being installed in the IP routing table, the route will still be in the OSPF database. The route could be learned via
another OSPF interface and would therefore appear in the IP routing table.
Initial Cisco IOS Software Release: 10.0. The interface-type and interface-number parameters were added in Release 11.2.
Configuration Example: Preventing Routes Learned via OSPF Over a Specific
Interface from Being Installed in the IP Routing Table
In Figure 7-5, Router A is receiving the OSPF routes 2.2.2.2, 3.3.3.3, and 4.4.4.4 from Router B over two serial interfaces. Start by
configuring routes A and B as shown in the listing that follows the figure.
Figure 7-5. A Distribute List/Named Access List Is Used to Control Which OSPF Routes, Learned
Over a Specific Interface, Are Transferred from the OSPF Database into the IP Routing Table
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
ip address 10.1.1.6 255.255.255.252
no ip mroute-cache
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 0
________________________________________________________________________________
Router B
interface Loopback0
.
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ip address 2.2.2.2 255.255.255.255
!
interface Loopback1
ip address 3.3.3.3 255.255.255.255
!
interface Loopback2
ip address 4.4.4.4 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router ospf 1
router-id 2.2.2.2
network 2.2.2.2 0.0.0.0 area 2
network 3.3.3.3 0.0.0.0 area 0
network 4.4.4.4 0.0.0.0 area 4
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 0
Verify that Routers A and B have established a FULL OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
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2.2.2.2
1 FULL/ -
00:00:34
10.1.1.5
Serial0/0
2.2.2.2
1 FULL/ -
00:00:38
10.1.1.2
Serial0/1
rtrB#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
1.1.1.1
1 FULL/ -
00:00:32
10.1.1.1
Serial0
1.1.1.1
1 FULL/ -
00:00:30
10.1.1.6
Serial1
Verify that Router A is receiving the routes 2.2.2.2, 3.3.3.3, and 4.4.4.4 from Router B.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/65] via 10.1.1.5, 00:00:10, Serial0/0
[110/65] via 10.1.1.2, 00:00:10, Serial0/1
3.0.0.0/32 is subnetted, 1 subnets
O
3.3.3.3 [110/65] via 10.1.1.5, 00:00:10, Serial0/0
[110/65] via 10.1.1.2, 00:00:10, Serial0/1
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4.0.0.0/32 is subnetted, 1 subnets
O IA
4.4.4.4 [110/65] via 10.1.1.5, 00:00:10, Serial0/0
[110/65] via 10.1.1.2, 00:00:11, Serial0/1
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
C
10.1.1.4 is directly connected, Serial0/0
For illustrative purposes, verify that these three routes are in the OSPF database on Router A.
rtrA#show ip ospf database
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 0)
1.1.1.1
1.1.1.1
1423
0x800000C1 0xE80E 4
2.2.2.2
2.2.2.2
1451
0x80000050 0xA7E3 5
Summary Net Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum
1.1.1.1
1.1.1.1
165
0x80000044 0xC030
2.2.2.2
2.2.2.2
707
0x80000057 0x4E87
4.4.4.4
2.2.2.2
707
0x8000000F 0x8293
Router Link States (Area 1)
Link ID
ADV Router
Age
Seq#
Checksum Link count
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1.1.1.1
1.1.1.1
1666
0x80000008 0xC558 1
Summary Net Link States (Area 1)
Link ID
ADV Router
Age
Seq#
Checksum
2.2.2.2
1.1.1.1
1423
0x80000006 0x9159
3.3.3.3
1.1.1.1
1669
0x80000009 0x5D86
4.4.4.4
1.1.1.1
1669
0x80000009 0x2FB0
10.1.1.0
1.1.1.1
168
0x80000007 0x36B3
10.1.1.4
1.1.1.1
1425
0x80000008 0xCD8
Modify the configuration on Router A to prevent the OSPF routes 2.2.2.2 and 3.3.3.3, received over interface Serial 0/0, and the routes
3.3.3.3 and 4.4.4.4, received over Serial 0/1, from being installed in the IP routing table.
Router A
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
distribute-list filter-ospf1 in Serial0/0
distribute-list filter-ospf2 in Serial0/1
!
ip access-list standard filter-ospf1
deny 2.2.2.0 0.0.0.255
deny 3.3.3.0 0.0.0.255
permit any
ip access-list standard filter-ospf2
deny 3.3.3.0 0.0.0.255
deny 4.4.4.0 0.0.0.255
permit any
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Verification
Determine which routes have been prevented from reaching the IP routing table on Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/65] via 10.1.1.2, 00:01:15, Serial0/1
4.0.0.0/32 is subnetted, 1 subnets
O IA
4.4.4.4 [110/65] via 10.1.1.5, 00:01:15, Serial0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
C
10.1.1.4 is directly connected, Serial0/0
Named access list filter-ospf1 denies networks 2.2.2.0 and 3.3.3.0. Named access listfilter-ospf2 denies networks 3.3.3.0 and 4.4.4.0. The
only network that is filtered by both access lists is 3.3.3.0. Verify that routes 2.2.2.2, 3.3.3.3, and 4.4.4.4 are still in the OSPF database on
Router A.
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rtrA#show ip ospf database
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum Link count
1.1.1.1
1.1.1.1
1815
0x800000C1 0xE80E 4
2.2.2.2
2.2.2.2
1843
0x80000050 0xA7E3 5
Summary Net Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum
1.1.1.1
1.1.1.1
557
0x80000044 0xC030
2.2.2.2
2.2.2.2
1099
0x80000057 0x4E87
4.4.4.4
2.2.2.2
1099
0x8000000F 0x8293
Router Link States (Area 1)
Link ID
ADV Router
1.1.1.1
1.1.1.1
Age
43
Seq#
Checksum Link count
0x80000009 0xC359 1
Summary Net Link States (Area 1)
Link ID
ADV Router
Age
Seq#
Checksum
2.2.2.2
1.1.1.1
1815
3.3.3.3
1.1.1.1
45
0x8000000A 0x5B87
4.4.4.4
1.1.1.1
45
0x8000000A 0x2DB1
0x80000006 0x9159
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10.1.1.0
1.1.1.1
559
0x80000007 0x36B3
10.1.1.4
1.1.1.1
1816
0x80000008 0xCD8
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Verify that the distribute-list command is referencing the correctly named access list and interface.
Step 3. Verify the syntax of the named access list.
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< Free Open Study >
7-8 distribute-list access-list-name out
Syntax Description:
access-list-name— Standard named IP access list that determines which routes learned via OSPF will be prevented from being
installed in the IP routing table.
Purpose: For distance vector protocols (RIP, IGRP, EIGRP) this command prevents routes selected by the named access list from being
advertised to a neighbor. OSPF is a link-state protocol and does not advertise routes to a neighbor but advertises a link-state database. The
neighbor determines the routes from the information in the link-state database. Therefore, this command has no effect when used with OSPF.
Initial Cisco IOS Software Release: 11.2
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7-9 distribute-list access-list-name out interface-type interface-number
Syntax Description:
access-list-name— Named IP access list that determines which routes learned via OSPF will be prevented from being installed in
the IP routing table.
interface-type— Optional parameter, along with the interface-number, used to apply the distribute list to OSPF routes learned
through a particular interface.
interface-number— Number of the interface-type.
Purpose: For distance vector protocols (RIP, IGRP, EIGRP) this command prevents routes selected by the named access list from being
advertised to a neighbor. OSPF is a link-state protocol and does not advertise routes to a neighbor, but advertises a link-state database. The
neighbor determines the routes from the information in the link-state database. Therefore, this command has no effect when used with OSPF.
Initial Cisco IOS Software Release: 11.2.
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< Free Open Study >
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7-10 distribute-list access-list-name out routing-process
Syntax Description:
access-list-name:— Standard IP access list name that determines which routes redistributed into OSPF will be prevented from
being installed in the OSPF database. This has the effect of preventing the blocked redistributed routes from being advertised to
OSPF neighbors.
routing-process— The routing process that has been redistributed into OSPF (RIP, IGRP, EIGRP, OSPF, BGP, EGP, static, or
connected).
Purpose: To prevent routes, redistributed into OSPF from another routing rocess, from being installed in the OSPF database.
Initial Cisco IOS Software Release: 11.2
Configuration Example: Preventing Routes Redistributed into OSPF from Being
Installed in the OSPF Database
In Figure 7-6, Router B is receiving the EIGRP routes 10.1.1.4/30, 3.3.3.0/24, and 4.4.4.0/24 from Router C. Router B is redistributing EIGRP
into OSPF and these routes will be advertised to Router A as OSPF external type 2 routes. Start by configuring Routers A, B, and C as
shown in the listing that follows the figure.
Figure 7-6. A Distribute List/Named Access List Prevents Redistributed Routes from Being
Installed in the OSPF Database
Router A
.
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interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router eigrp 1
network 10.0.0.0
!
router ospf 1
.
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redistribute eigrp 1 subnets
network 2.2.2.2 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.0
!
interface Loopback1
ip address 4.4.4.4 255.255.255.0
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router eigrp 1
network 3.0.0.0
network 4.0.0.0
network 10.0.0.0
no auto-summary
Verify that Routers A and B have established a FULL OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/BDR
Dead Time Address
00:00:30
172.16.1.2
Interface
Ethernet0/0
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rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:00:38
172.16.1.1
Interface
Ethernet0
Verify that Router B is receiving routes 3.3.3.0/24 and 4.4.4.0/24 from Router C via EIGRP.
rtrB# show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/24 is subnetted, 1 subnets
D
3.3.3.0 [90/40640000] via 10.1.1.6, 00:38:45, Serial1
4.0.0.0/24 is subnetted, 1 subnets
D
4.4.4.0 [90/40640000] via 10.1.1.6, 00:38:45, Serial1
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial1
Verify that Router A is receiving routes 10.1.1.4/30, 3.3.3.0/24, and 4.4.4.0/24 from Router B as OSPF external type 2 routes.
rtrA#show ip route
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Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/11] via 172.16.1.2, 00:27:48, Ethernet0/0
3.0.0.0/24 is subnetted, 1 subnets
O E2
3.3.3.0 [110/20] via 172.16.1.2, 00:05:41, Ethernet0/0
4.0.0.0/24 is subnetted, 1 subnets
O E2
4.4.4.0 [110/20] via 172.16.1.2, 00:27:48, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
10.0.0.0/30 is subnetted, 1 subnets
O E2
10.1.1.4 [110/20] via 172.16.1.2, 00:05:42, Ethernet0/0
For illustrative purposes, verify that these three routes are in the OSPF database on Router B.
rtrB#show ip ospf database external
OSPF Router with ID (2.2.2.2) (Process ID 1)
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Type-5 AS External Link States
LS age: 441
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 3.3.3.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000001
Checksum: 0x3F50
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
LS age: 1788
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 4.4.4.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000003
Checksum: 0x1773
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
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Forward Address: 0.0.0.0
External Route Tag: 0
LS age: 459
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 10.1.1.4 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000001
Checksum: 0xD7B3
Length: 36
Network Mask: /30
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
Modify the configuration on Router B to allow only the installation of the EIGRP route 4.4.4.0/24 into the OSPF database using a named
access list.
Router B
router ospf 1
redistribute eigrp 1 subnets
network 2.2.2.2 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
distribute-list filter-eigrp out eigrp 1
!
ip access-list standard filter-eigrp
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permit 4.4.4.0 0.0.0.255
Verification
Verify that the EIGRP routes 10.1.1.4/30 and 3.3.3.0/24 have been blocked from entering the OSPF database on Router B.
rtrB#show ip ospf database external
OSPF Router with ID (2.2.2.2) (Process ID 1)
Type-5 AS External Link States
LS age: 419
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 4.4.4.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000004
Checksum: 0x1574
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
Verify that Router A is receiving only one external type 2 route from Router B.
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rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/11] via 172.16.1.2, 00:38:45, Ethernet0/0
4.0.0.0/24 is subnetted, 1 subnets
O E2
4.4.4.0 [110/20] via 172.16.1.2, 00:38:45, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers using the show ip ospf neighbor command.
Step 2. Verify that the distribute-list command is referencing the correct access list name and routing process.
Step 3. Verify the syntax of the named access list.
Step 4. Verify that the intended routes are in the OSPF database using the command show ip ospf database external.
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< Free Open Study >
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< Free Open Study >
7-11 distribute-list prefix prefix-list-name in
Syntax Description:
prefix-list-name— IP prefix list that determines which routes learned via OSPF will be prevented from being installed in the IP
routing table.
Purpose: To prevent OSPF learned routes from being installed in the IP routing table. Even though an OSPF route may be prevented from
being installed in the IP routing table, the route will still be in the OSPF database and advertised to OSPF neighbors. Therefore, the
distribute command should be used with other routing protocols such as RIP, IGRP, EIGRP, and BGP.
Initial Cisco IOS Software Release: 12.0
Configuration Example: Preventing OSPF Learned Routes from Being Installed in
the IP Routing Table
In Figure 7-7, Router A is receiving the OSPF routes 2.2.2.2, 3.3.3.3, and 4.4.4.4 from Router B. Start by configuring Routers A and B as
shown in the listing that follows the figure.
Figure 7-7. A Distribute List/Prefix List Controls Which OSPF Routes Are Transferred from the
OSPF Database into the IP Routing Table
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Loopback1
ip address 3.3.3.3 255.255.255.255
!
interface Loopback2
ip address 4.4.4.4 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
.
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!
router ospf 1
router-id 2.2.2.2
network 2.2.2.2 0.0.0.0 area 2
network 3.3.3.3 0.0.0.0 area 0
network 4.4.4.4 0.0.0.0 area 4
network 172.16.1.2 0.0.0.255 area 0
Verify that Routers A and B have established a FULL OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/BDR
Dead Time Address
00:00:30
172.16.1.2
Interface
Ethernet0/0
__________________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:00:38
172.16.1.1
Interface
Ethernet0
Verify that Router A is receiving routes 2.2.2.2, 3.3.3.3, and 4.4.4.4 from Router B.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
.
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* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/11] via 172.16.1.2, 00:04:28, Ethernet0/0
3.0.0.0/32 is subnetted, 1 subnets
O
3.3.3.3 [110/11] via 172.16.1.2, 00:04:28, Ethernet0/0
4.0.0.0/32 is subnetted, 1 subnets
O IA
4.4.4.4 [110/11] via 172.16.1.2, 00:04:28, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
For illustrative purposes, verify that these three routes are in the OSPF database on Router A.
rtrA#show ip ospf database
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 0)
Link ID
ADV Router
Age
1.1.1.1
1.1.1.1
493
0x800000A5 0x8F6F 1
2.2.2.2
2.2.2.2
489
0x80000030 0x7ECF 2
Net Link States (Area 0)
Seq#
Checksum Link count
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Link ID
ADV Router
172.16.1.1
1.1.1.1
Age
496
Seq#
Checksum
0x80000001 0x6DFD
Summary Net Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum
1.1.1.1
1.1.1.1
714
0x80000033 0xE21F
2.2.2.2
2.2.2.2
487
0x80000049 0x6A79
4.4.4.4
2.2.2.2
490
0x80000001 0x9E85
Router Link States (Area 1)
Link ID
ADV Router
1.1.1.1
1.1.1.1
Age
726
Seq#
Checksum Link count
0x80000001 0xD351 1
Summary Net Link States (Area 1)
Link ID
ADV Router
2.2.2.2
1.1.1.1
492
0x80000001 0x7DA8
3.3.3.3
1.1.1.1
492
0x80000001 0x4FD2
4.4.4.4
1.1.1.1
492
0x80000001 0x21FC
172.16.1.0
1.1.1.1
Age
496
Seq#
Checksum
0x80000003 0x3B34
Modify the configuration on Router A to prevent the OSPF routes 2.2.2.2 and 3.3.3.3 from being installed in the IP routing table. A 32-bit
mask is needed in the prefix list because OSPF is advertising the loopback interfaces as host routes.
Router A
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
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distribute-list prefix filter-ospf in
!
ip prefix-list filter-ospf seq 5 deny 2.2.2.2/32
ip prefix-list filter-ospf seq 10 deny 3.3.3.3/32
ip prefix-list filter-ospf seq 15 permit 0.0.0.0/0
Verification
Verify that the OSPF routes 2.2.2.2 and 3.3.3.3 have been blocked from entering the IP routing table on Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
4.0.0.0/32 is subnetted, 1 subnets
O IA
4.4.4.4 [110/11] via 172.16.1.2, 00:03:39, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
Verify that routes 2.2.2.2 and 3.3.3.3 are still in the OSPF database on Router A.
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rtrA#show ip ospf database
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum Link count
1.1.1.1
1.1.1.1
951
0x800000A5 0x8F6F 1
2.2.2.2
2.2.2.2
947
0x80000030 0x7ECF 2
Net Link States (Area 0)
Link ID
ADV Router
172.16.1.1
1.1.1.1
Age
954
Seq#
Checksum
0x80000001 0x6DFD
Summary Net Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum
1.1.1.1
1.1.1.1
1172
0x80000033 0xE21F
2.2.2.2
2.2.2.2
945
0x80000049 0x6A79
4.4.4.4
2.2.2.2
948
0x80000001 0x9E85
Router Link States (Area 1)
Link ID
ADV Router
1.1.1.1
1.1.1.1
Age
1184
Seq#
Checksum Link count
0x80000001 0xD351 1
Summary Net Link States (Area 1)
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Link ID
ADV Router
3.3.3.3
1.1.1.1
946
0x80000001 0x4FD2
4.4.4.4
1.1.1.1
946
0x80000001 0x21FC
172.16.1.0
1.1.1.1
Age
950
Seq#
Checksum
0x80000003 0x3B34
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Verify that the distribute-list command is referencing the correct IP prefix list.
Step 3. Verify the syntax of the prefix list.
< Free Open Study >
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< Free Open Study >
7-12 distribute-list prefix prefix-list-name in interface-type interface-number
Syntax Description:
prefix-list-name— Named IP prefix list that determines which routes learned via OSPF will be prevented from being installed in
the IP routing table.
interface-type— Optional parameter, along with the interface-number, used to apply the distribute list to OSPF routes learned
through a particular interface.
interface-number— Number of the interface-type.
Purpose: To prevent OSPF routes learned over a specific interface from being installed in the IP routing table. Even though an OSPF route
may be prevented from being installed in the IP routing table, the route will still be in the OSPF database. The filtered routes may be learned
via another OSPF interface and installed in the IP routing table.
Initial Cisco IOS Software Release: 10.0. The interface-type and interface-number parameters were added in Release 11.2.
Configuration Example: Preventing Routes Learned via OSPF Over a Specific
Interface from Being Installed in the IP Routing Table
In Figure 7-8, Router A is receiving the OSPF routes 2.2.2.2, 3.3.3.3, and 4.4.4.4 from Router B over two serial interfaces. Start by
configuring Routers A and B as shown in the listing that follows the figure.
Figure 7-8. A Distribute List/Prefix List Controls Which OSPF Routes, Learned Over a Specific
Interface, Are Transferred from the OSPF Database into the IP Routing Table
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
ip address 10.1.1.6 255.255.255.252
no ip mroute-cache
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 0
________________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
.
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!
interface Loopback1
ip address 3.3.3.3 255.255.255.255
!
interface Loopback2
ip address 4.4.4.4 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router ospf 1
router-id 2.2.2.2
network 2.2.2.2 0.0.0.0 area 2
network 3.3.3.3 0.0.0.0 area 0
network 4.4.4.4 0.0.0.0 area 4
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 0
Verify that Routers A and B have established a FULL OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/ -
Dead Time Address
00:00:34
10.1.1.5
Interface
Serial0/0
.
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2.2.2.2
1 FULL/ -
00:00:38
10.1.1.2
Serial0/1
rtrB#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
1.1.1.1
1 FULL/ -
00:00:32
10.1.1.1
Serial0
1.1.1.1
1 FULL/ -
00:00:30
10.1.1.6
Serial1
Verify that Router A is receiving routes 2.2.2.2, 3.3.3.3, and 4.4.4.4 from Router B.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/65] via 10.1.1.5, 00:00:10, Serial0/0
[110/65] via 10.1.1.2, 00:00:10, Serial0/1
3.0.0.0/32 is subnetted, 1 subnets
O
3.3.3.3 [110/65] via 10.1.1.5, 00:00:10, Serial0/0
[110/65] via 10.1.1.2, 00:00:10, Serial0/1
4.0.0.0/32 is subnetted, 1 subnets
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O IA
4.4.4.4 [110/65] via 10.1.1.5, 00:00:10, Serial0/0
[110/65] via 10.1.1.2, 00:00:11, Serial0/1
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
C
10.1.1.4 is directly connected, Serial0/0
For illustrative purposes, verify that these three routes are in the OSPF database on Router A.
rtrA#show ip ospf database
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 0)
1.1.1.1
1.1.1.1
1423
0x800000C1 0xE80E 4
2.2.2.2
2.2.2.2
1451
0x80000050 0xA7E3 5
Summary Net Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum
1.1.1.1
1.1.1.1
165
0x80000044 0xC030
2.2.2.2
2.2.2.2
707
0x80000057 0x4E87
4.4.4.4
2.2.2.2
707
0x8000000F 0x8293
Router Link States (Area 1)
Link ID
ADV Router
1.1.1.1
1.1.1.1
Age
1666
Seq#
Checksum Link count
0x80000008 0xC558 1
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Summary Net Link States (Area 1)
Link ID
ADV Router
Age
Seq#
Checksum
2.2.2.2
1.1.1.1
1423
0x80000006 0x9159
3.3.3.3
1.1.1.1
1669
0x80000009 0x5D86
4.4.4.4
1.1.1.1
1669
0x80000009 0x2FB0
10.1.1.0
1.1.1.1
168
0x80000007 0x36B3
10.1.1.4
1.1.1.1
1425
0x80000008 0xCD8
Modify the configuration on Router A to prevent the OSPF routes 2.2.2.2 and 3.3.3.3, received over interface Serial 0/0, and the routes
3.3.3.3 and 4.4.4.4, received over Serial 0/1, from being installed in the IP routing table.
Router A
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
distribute-list prefix filter-ospf1 in Serial0/0
distribute-list prefix filter-ospf2 in Serial0/1
!
ip prefix-list filter-ospf1 seq 5 deny 2.2.2.2/32
ip prefix-list filter-ospf1 seq 10 deny 3.3.3.3/32
ip prefix-list filter-ospf1 seq 15 permit 0.0.0.0/0
!
ip prefix-list filter-ospf2 seq 5 deny 3.3.3.3/32
ip prefix-list filter-ospf2 seq 10 deny 4.4.4.4/32
ip prefix-list filter-ospf2 seq 15 permit 0.0.0.0/0
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Verification
Determine the routes that have been filtered from reaching the IP routing table on Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/65] via 10.1.1.2, 00:01:15, Serial0/1
4.0.0.0/32 is subnetted, 1 subnets
O IA
4.4.4.4 [110/65] via 10.1.1.5, 00:01:15, Serial0/0
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
C
10.1.1.4 is directly connected, Serial0/0
ip prefix-list filter-ospf1 denies networks 2.2.2.2 and 3.3.3.3. ip prefix-list filter-ospf2 denies networks 3.3.3.3 and 4.4.4.4. The only
network that is denied by both prefix lists is 3.3.3.3. Verify that routes 2.2.2.2, 3.3.3.3, and 4.4.4.4 are still in the OSPF database on Router A.
rtrA#show ip ospf database
OSPF Router with ID (1.1.1.1) (Process ID 1)
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Router Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum Link count
1.1.1.1
1.1.1.1
1815
0x800000C1 0xE80E 4
2.2.2.2
2.2.2.2
1843
0x80000050 0xA7E3 5
Summary Net Link States (Area 0)
Link ID
ADV Router
Age
Seq#
Checksum
1.1.1.1
1.1.1.1
557
0x80000044 0xC030
2.2.2.2
2.2.2.2
1099
0x80000057 0x4E87
4.4.4.4
2.2.2.2
1099
0x8000000F 0x8293
Router Link States (Area 1)
Link ID
ADV Router
1.1.1.1
1.1.1.1
Age
43
Seq#
Checksum Link count
0x80000009 0xC359 1
Summary Net Link States (Area 1)
Link ID
ADV Router
Age
Seq#
Checksum
2.2.2.2
1.1.1.1
1815
3.3.3.3
1.1.1.1
45
0x8000000A 0x5B87
4.4.4.4
1.1.1.1
45
0x8000000A 0x2DB1
10.1.1.0
1.1.1.1
559
0x80000007 0x36B3
10.1.1.4
1.1.1.1
1816
0x80000008 0xCD8
0x80000006 0x9159
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Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Verify that the distribute-list command is referencing the correct IP prefix list and interface.
Step 3. Verify the syntax of the prefix list.
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7-13 distribute-list prefix prefix-list-name out
Syntax Description:
prefix-list-name— Standard named IP prefix list that determines which routes learned via OSPF will be prevented from being
installed in the IP routing table.
Purpose: For distance vector protocols (RIP, IGRP, EIGRP) this command prevents routes selected by the named prefix list from being
advertised to a neighbor. OSPF is a link-state protocol and does not advertise routes to a neighbor but advertises a link-state database. The
neighbor determines the routes from the information in the link-state database. Therefore, this command has no effect when used with OSPF.
Initial Cisco IOS Software Release: 11.2
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7-14 distribute-list prefix prefix-list-name out interface-type
interface-number
Syntax Description:
prefix-list-name— Named IP prefix list that determines which routes learned via OSPF will be prevented from being installed in the
IP routing table.
interface-type— Optional parameter, along with the interface-number, used to apply the distribute list to OSPF routes learned
through a particular interface.
interface-number— Number of the interface-type.
Purpose: For distance vector protocols (RIP, IGRP, EIGRP) this command prevents routes selected by the named prefix list from being
advertised to a neighbor. OSPF is a link-state protocol and does not advertise routes to a neighbor, but advertises a link-state database. The
neighbor determines the routes from the information in the link-state database. Therefore, this command has no effect when used with OSPF.
Initial Cisco IOS Software Release: 12.0.
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7-15 distribute-list prefix prefix-list-name out routing-process
Syntax Description:
prefix-list-name— IP prefix list name that determines which routes redistributed into OSPF will be prevented from being installed
in the OSPF database. This has the effect of preventing the blocked redistributed routes from being advertised to OSPF
neighbors.
routing-process— The routing process that has been redistributed into OSPF (RIP, IGRP, EIGRP, OSPF, BGP, EGP, static, or
connected).
Purpose: To prevent routes that were redistributed into OSPF from another routing process from being installed in the OSPF database.
Initial Cisco IOS Software Release: 11.2
Configuration Example: Preventing Routes Redistributed into OSPF from Being
Installed in the OSPF Database
In Figure 7-9, Router B is receiving the EIGRP routes 10.1.1.4/30, 3.3.3.0/24, and 4.4.4.0/24 from Router C. Router B is redistributing EIGRP
into OSPF, and these routes will be advertised to Router A as OSPF external type 2 routes. Start by configuring Routers A, B, and C as
shown in the listing that follows the figure.
Figure 7-9. A Distribute List/Prefix List Prevents Redistributed Routes from Being Installed in the
OSPF Database
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
router eigrp 1
network 10.0.0.0
.
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!
router ospf 1
redistribute eigrp 1 subnets
network 2.2.2.2 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
________________________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.0
!
interface Loopback1
ip address 4.4.4.4 255.255.255.0
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router eigrp 1
network 3.0.0.0
network 4.0.0.0
network 10.0.0.0
no auto-summary
Verify that Routers A and B have established a FULL OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
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2.2.2.2
1 FULL/BDR
00:00:30
172.16.1.2
Ethernet0/0
________________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:00:38
172.16.1.1
Interface
Ethernet0
Verify that Router B is receiving routes 3.3.3.0/24 and 4.4.4.0/24 from Router C via EIGRP.
rtrB# show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/24 is subnetted, 1 subnets
D
3.3.3.0 [90/40640000] via 10.1.1.6, 00:38:45, Serial1
4.0.0.0/24 is subnetted, 1 subnets
D
4.4.4.0 [90/40640000] via 10.1.1.6, 00:38:45, Serial1
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.4 is directly connected, Serial1
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Verify that Router A is receiving routes 10.1.1.4/30, 3.3.3.0/24, and 4.4.4.0/24 from Router B as OSPF external type 2 routes.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/11] via 172.16.1.2, 00:27:48, Ethernet0/0
3.0.0.0/24 is subnetted, 1 subnets
O E2
3.3.3.0 [110/20] via 172.16.1.2, 00:05:41, Ethernet0/0
4.0.0.0/24 is subnetted, 1 subnets
O E2
4.4.4.0 [110/20] via 172.16.1.2, 00:27:48, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
10.0.0.0/30 is subnetted, 1 subnets
O E2
10.1.1.4 [110/20] via 172.16.1.2, 00:05:42, Ethernet0/0
For illustrative purposes, verify that these three routes are in the OSPF database on Router B.
rtrB#show ip ospf database external
OSPF Router with ID (2.2.2.2) (Process ID 1)
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Type-5 AS External Link States
LS age: 441
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 3.3.3.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000001
Checksum: 0x3F50
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
LS age: 1788
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 4.4.4.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000003
Checksum: 0x1773
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
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TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
LS age: 459
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 10.1.1.4 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000001
Checksum: 0xD7B3
Length: 36
Network Mask: /30
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
Modify the configuration on Router B to allow only the installation of the EIGRP route 4.4.4.0/24 into the OSPF database using an IP prefix
list.
Router B
router ospf 1
redistribute eigrp 1 subnets
network 2.2.2.2 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
distribute-list prefix filter-eigrp out eigrp 1
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ip prefix-list filter-eigrp seq 5 permit 4.4.4.0/24
Verification
Verify that the EIGRP routes 10.1.1.4/30 and 3.3.3.0/24 have been blocked from entering the OSPF database on Router B.
rtrB#show ip ospf database external
OSPF Router with ID (2.2.2.2) (Process ID 1)
Type-5 AS External Link States
LS age: 419
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 4.4.4.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000004
Checksum: 0x1574
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
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Verify that Router A is receiving only one external type 2 route from Router B.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/11] via 172.16.1.2, 00:38:45, Ethernet0/0
4.0.0.0/24 is subnetted, 1 subnets
O E2
4.4.4.0 [110/20] via 172.16.1.2, 00:38:45, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Verify that the distribute-list command is referencing the correct prefix list name and routing process.
Step 3. Verify the syntax of the prefix list.
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Step 4. Verify that the intended routes are in the OSPF database by using the command show ip ospf database external.
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Chapter 8. Handling of MOSPF LSAs
Section 8-1. ignore lsa mospf
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8-1 ignore lsa mospf
Syntax Description:
This command has no arguments.
Purpose: Cisco routers do not support Multicast OSPF (MOSPF). By default, if a type 6 MOSPF LSA is received, the router generates a
syslog message. This command prevents the generation of a syslog message when a type 6 LSA is received.
Initial Cisco IOS Software Release: 11.1
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Chapter 9. Logging OSPF Neighbor Changes
Section 9-1. log-adjacency-changes
Section 9-2. log adjacency-changes detail
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9-1 log-adjacency-changes
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9-2 log adjacency-changes detail
Syntax Description:
This command has no arguments.
Purpose: To enable the logging of changes in an OSPF neighbor's status. If the UNIX syslog facility is enabled, messages can be sent to a
UNIX host running the syslog daemon. If you are not using the UNIX syslog facility, then the status change messages are stored in the
router's internal buffer. This command is an excellent tool for troubleshooting OSPF.
Initial Cisco IOS Software Release: 11.2. The detail keyword was added in 12.1.
Configuration Example 1: Enabling OSPF Neighbor Status-Change Logging to the
Console
To enable the display of OSPF neighbor status-change events on the console, use the following configuration.
router ospf 1
log-adjacency-changes
Verification
When the state of an OSPF neighbor changes, the events are displayed on the console. For example, if you execute the commandclear ip
ospf process on an OSPF neighbor, the following output should be displayed.
rtrA#clear ip ospf process
Reset ALL OSPF processes? [no]: y
rtrA#
00:52:14: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from FULL to DOW
N, Neighbor Down: Interface down or detached
00:52:23: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from LOADING to
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FULL, Loading Done
If the keyword detail is used, then complete information regarding the neighbor status will be logged.
router ospf 1
log-adjacency-changes detail
rtrA#clear ip ospf process
Reset ALL OSPF processes? [no]: yes
rtrA#
00:50:12: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from FULL to DOW
N, Neighbor Down: Interface down or detached
00:50:13: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from DOWN to INI
T, Received Hello
00:50:13: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from INIT to 2WA
Y, 2-Way Received
00:50:13: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from 2WAY to EXS
TART, AdjOK?
00:50:13: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from EXSTART to
EXCHANGE, Negotiation Done
00:50:13: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from EXCHANGE to
LOADING, Exchange Done
00:50:13: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from LOADING to
FULL, Loading Done
Configuration Example 2: Enabling OSPF Neighbor Status-Change Logging to
Memory
Use the following configuration to enable the logging of OSPF neighbor status-change events to memory.
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logging buffered 4096 debugging
!
router ospf 1
log-adjacency-changes detail
The parameters 4096 and debugging are default values and are supplied by the router when you use the commandlogging buffered. The
default values vary by platform.
Verification
The show logging command displays the status of buffered logging. If logging is enabled, then the contents of the buffer will be displayed.
rtrA#show logging
Syslog logging: enabled (0 messages dropped, 0 messages rate-limited, 0 flushes,
0 overruns)
Console logging: level debugging, 67 messages logged
Monitor logging: level debugging, 0 messages logged
Buffer logging: level debugging, 8 messages logged
Logging Exception size (4096 bytes)
Trap logging: level informational, 71 message lines logged
Log Buffer (4096 bytes):
00:56:38: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from FULL to DOW
N, Neighbor Down: Interface down or detached
00:56:43: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from DOWN to INI
T, Received Hello
00:56:43: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from INIT to 2WA
Y, 2-Way Received
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00:56:43: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from 2WAY to EXS
TART, AdjOK?
00:56:43: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from EXSTART to
EXCHANGE, Negotiation Done
00:56:43: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from EXCHANGE to
LOADING, Exchange Done
00:56:43: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from LOADING to
FULL, Loading Done
Troubleshooting
Step 1. Verify that the OSPF neighbors have established a relationship.
Step 2. Verify that buffered logging is enabled using the show logging command.
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Chapter 10. Multiple Path Configuration
Section 10-1. maximum-paths number-of-paths
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10-1 maximum-paths number-of-paths
Syntax Description:
number-of-paths— Determines the number of parallel equal-cost paths to the same destination that OSPF will install in the IP
routing table. The range of values is 1 to 6. The default is 4 paths.
Purpose: To configure the number of equal-cost parallel paths that OSPF will install in the IP routing table.
Initial Cisco IOS Software Release: 11.2
Configuration Example: Setting the Maximum Number of Equal-Cost Paths That
OSPF Will Install in the IP Routing Table
In Figure 10-1, Router A has two parallel equal-cost paths to the loopback network on Router B. By default, OSPF will install both paths in the
IP routing table. Configure Routers A and B as shown in the following lines of code.
Figure 10-1. OSPF Can Install Up to Six Parallel Equal-Cost Paths in the IP Routing Table
Router A
interface Serial0/0
bandwidth 64
ip address 10.1.1.6 255.255.255.252
.
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!
interface Serial0/1
bandwidth 64
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 0
______________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
bandwidth 64
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 0
network 2.2.2.2 0.0.0.0 area 2
Verify that OSPF on Router A has installed the two paths to network 2.2.2.2 on Router B.
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rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/1563] via 10.1.1.5, 00:00:36, Serial0/0
[110/1563] via 10.1.1.2, 00:00:36, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
C
10.1.1.4 is directly connected, Serial0/0
To prove that the paths must have equal cost, change the bandwidth on Serial 0/1 on Router A to 63.
Router A
interface Serial0/0
bandwidth 63
ip address 10.1.1.6 255.255.255.252
The OSPF cost for Serial 0/0 is now 100,000,000/63,000 = 1587. The OSPF cost of Serial 0/1 is 100,000,000/64,000 = 1562. Display the
routing table on Router A to determine the effect of changing the cost of interface Serial 0/0.
rtrA#show ip route
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Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/1563] via 10.1.1.2, 00:04:27, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
C
10.1.1.4 is directly connected, Serial0/0
The cost of the two paths to reach 2.2.2.2 on Router B is no longer equal, so OSPF will install the route with the lowest cost.
What happens if OSPF has more equal-cost paths to a destination than are allowed by themaximum-paths command? In Figure 10-1 there
are two equal-cost paths to network 2.2.2.2 (if we reset the bandwidth on Serial 0/0 to 64). If we set the maximum paths variable to 1, which
path will be installed in the IP routing table? Modify the configuration on Router A so Serial 0/0 has a bandwidth of 64 and the
maximum-paths variable is set to 1.
Router A
interface Serial0/0
bandwidth 64
ip address 10.1.1.6 255.255.255.252
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
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network 10.1.1.4 0.0.0.3 area 0
maximum-paths 1
Verification
Verify that OSPF has installed only one route to 2.2.2.2 on Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/1563] via 10.1.1.2, 00:02:00, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
C
10.1.1.4 is directly connected, Serial0/0
Troubleshooting
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Nothing should go wrong with this command if configured correctly (famous last words?).
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Chapter 11. OSPF neighbor Commands
Section 11-1. neighbor ip-address
Section 11-2. neighbor ip-address cost cost
Section 11-3. neighbor ip-address database-filter all out
Section 11-4. neighbor ip-address poll-interval interval
Section 11-5. neighbor ip-address priority priority
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11-1 neighbor ip-address
Syntax Description:
ip-address— IP address of the OSPF neighbor. If a secondary address is used on the interface, then the primary address must be
used with this command.
Purpose: To configure OSPF neighbors over a nonbroadcast multiaccess (NBMA) network such as Frame Relay or X.25.
Initial Cisco IOS Software Release: 10.0 (12.0 for multipoint networks)
Configuration Example 1: Using the neighbor Command to Enable OSPF on an
NBMA
OSPF treats an NBMA network like any other broadcast network such as Ethernet. Because of this, OSPF thinks the network has broadcast
capabilities even though it does not. This lack of a broadcast capability necessitates the use of the neighbor command to establish an OSPF
neighbor. Prior to the introduction of the ip ospf network interface commands (see Sections 19-11 through 19-14) the neighbor command
was used to configure OSPF neighbors over NBMA networks such as X.25 and Frame Relay. The ip ospf network interface commands
have removed the necessity of using the neighbor command, but an understanding of the use of the neighbor command will reinforce the
concepts covered in Sections 19-11 through 19-14. Figure 11-1 shows the topology that is used in this chapter to demonstrate the use of the
OSPF neighbor command. A Cisco router has been configured as a Frame Relay switch in order to demonstrate the behavior of OSPF over
an NBMA network. The configuration for the Frame Relay switch is shown in the listing that follows the figure. The four interfaces on the
Frame Relay switch are fully meshed with the DLCIs shown in Figure 11-1.
Figure 11-1. Fully Meshed Frame Relay Switch Used to Demonstrate the Use of the OSPF neighbor
Command
.
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Frame Switch
hostname frame-relay
!
frame-relay switching
!
interface Serial1/0
no ip address
no ip directed-broadcast
encapsulation frame-relay
no ip mroute-cache
no fair-queue
clockrate 2015232
frame-relay lmi-type ansi
frame-relay intf-type dce
frame-relay route 101 interface Serial1/1 110
frame-relay route 102 interface Serial1/2 120
frame-relay route 103 interface Serial1/3 130
!
interface Serial1/1
no ip address
no ip directed-broadcast
encapsulation frame-relay
clockrate 2015232
.
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frame-relay lmi-type ansi
frame-relay intf-type dce
frame-relay route 110 interface Serial1/0 101
frame-relay route 112 interface Serial1/2 121
frame-relay route 113 interface Serial1/3 131
!
interface Serial1/2
no ip address
no ip directed-broadcast
encapsulation frame-relay
clockrate 2015232
frame-relay lmi-type ansi
frame-relay intf-type dce
frame-relay route 120 interface Serial1/0 102
frame-relay route 121 interface Serial1/1 112
frame-relay route 123 interface Serial1/3 132
!
interface Serial1/3
no ip address
no ip directed-broadcast
encapsulation frame-relay
clockrate 2015232
frame-relay lmi-type ansi
frame-relay intf-type dce
frame-relay route 130 interface Serial1/0 103
frame-relay route 131 interface Serial1/1 113
frame-relay route 132 interface Serial1/2 123
.
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For the first configuration example, an OSPF neighbor relationship will be established over Frame Relay between two OSPF routers as
shown in Figure 11-2. The initial configurations for Routers A and B are shown in thelisting that follows. The routers will learn the local DLCI
numbers through inverse ARP so the DLCIs do not need to be explicitly configured.
Figure 11-2. If the ip ospf network Command Is Not Used on an NBMA Network, then the OSPF
neighbor Command Must Be Configured on One End of the Frame Relay Link
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
ip address 10.1.1.1 255.255.255.252
encapsulation frame-relay
frame-relay lmi-type ansi
.
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!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
encapsulation frame-relay
frame-relay lmi-type ansi
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
Verify that Routers A and B have IP connectivity by using the ping command.
rtrA#ping 10.1.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms
List the Frame Relay DLCIs that the routers are using.
rtrB#show frame-relay map
Serial0 (up): ip 0.0.0.0 dlci 113(0x71,0x1C10)
.
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broadcast,
CISCO, status defined, inactive
Serial0 (up): ip 0.0.0.0 dlci 112(0x70,0x1C00)
broadcast,
CISCO, status defined, inactive
Serial0 (up): ip 0.0.0.0 dlci 110(0x6E,0x18E0)
broadcast,
CISCO, status defined, active
Serial0 (up): ip 10.1.1.1 dlci 110(0x6E,0x18E0), dynamic,
broadcast,, status defined, active
Because the Frame Relay switch is fully meshed, the routers are learning all the DLCIs for their particular interface via inverse ARP. Disable
inverse ARP and map the appropriate IP address to its corresponding DLCI on Routers A and B.
Router A
interface Serial0/0
ip address 10.1.1.1 255.255.255.252
encapsulation frame-relay
frame-relay map ip 10.1.1.2 101 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
____________________________________________________________________________
Router B
interface Serial0
ip address 10.1.1.2 255.255.255.252
encapsulation frame-relay
frame-relay map ip 10.1.1.1 110 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
.
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Verify that Routers A and B are using the assigned DLCI.
rtrA#show frame-relay map
Serial0/0 (up): ip 10.1.1.2 dlci 101(0x65,0x1850), static,
broadcast,
CISCO, status defined, active
________________________________________________________________
rtrB#show frame map
Serial0 (up): ip 10.1.1.1 dlci 110(0x6E,0x18E0), static,
broadcast,
CISCO, status defined, active
View the state of the OSPF neighbor relationship between Routers A and B.
rtrA#show ip ospf neighbor
<no output>
An OSPF neighbor relationship has not been established. The neighbor command can be used in order to establish OSPF neighbors over
Frame Relay. Modify the configuration on Router A using the neighbor command.
Router A
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
neighbor 10.1.1.2
Verification
Verify that an OSPF neighbor relationship has been established between Routers A and B.
rtrA#show ip ospf neighbor
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Neighbor ID
2.2.2.2
Pri State
1 FULL/DR
Dead Time Address
00:01:53
10.1.1.2
Interface
Serial0/0
The neighbor relationship has been established even though the neighbor command was configured on only one end of the link. Why was a
Designated Router (DR) elected? OSPF thinks that this point-to-point link is a broadcast network, and DRs are always elected on broadcast
networks.
Configuration Example 2: Configuring OSPF Neighbors on a Hub and Spoke
Topology with the Neighbors on the Same IP Subnet
In Figure 11-3, Routers A, B, and C are configured for a hub and spoke topology on a common IP subnet. For this topology, Router must
A
be
elected as the DR because Router A has a direct connection to Router B and Router C. Routers B or C should never be elected as the DR.
To prevent Routers B and C from becoming the DR on the Frame Relay subnet, set the OSPF priority to 0 on both of their interfaces.
Configure Routers A, B, and C as shown in the listing that follows.
Figure 11-3. In a Hub and Spoke Topology, the Hub Router Must Be Elected the OSPF DR if the
Spokes Are on the Same IP Subnet
Router A
interface Loopback0
.
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ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
ip address 10.1.1.1 255.255.255.248
encapsulation frame-relay
frame-relay map ip 10.1.1.2 101 broadcast
frame-relay map ip 10.1.1.3 102 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.7 area 0
neighbor 10.1.1.3
neighbor 10.1.1.2
________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.248
encapsulation frame-relay
ip ospf priority 0
frame-relay map ip 10.1.1.1 110 broadcast
frame-relay map ip 10.1.1.3 110 broadcast
no frame-relay inverse-arp
.
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frame-relay lmi-type ansi
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.7 area 0
________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.3 255.255.255.248
encapsulation frame-relay
ip ospf priority 0
frame-relay map ip 10.1.1.1 120 broadcast
frame-relay map ip 10.1.1.2 120 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
!
router ospf 1
network 3.3.3.3 0.0.0.0 area 0
network 10.1.1.0 0.0.0.7 area 0
On Routers B and C, there are two frame-relay map statements. These are needed because Router B receives routes from Router C with a
next hop of 10.1.1.3 and Router C receives routes from Router B with a next hop of 10.1.1.2. Because Routers B and C are not directly
connected, the frame-relay map statements are required to direct traffic between Routers B and C to go through Router A.
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Verification
Verify that Router A has an OSPF relationship with Routers B and C. Verify that all OSPF routes are being exchanged and are reachable.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
3.3.3.3
0 FULL/DROTHER
00:01:49
10.1.1.3
Serial0/0
2.2.2.2
0 FULL/DROTHER
00:01:58
10.1.1.2
Serial0/0
_____________________________________________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:01:52
10.1.1.1
Interface
Serial0
___________________________________________________________________________________________________________
rtrC#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:01:32
10.1.1.1
Interface
Serial0
_____________________________________________________________________________________________________________
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
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* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/49] via 10.1.1.2, 00:20:27, Serial0/0
3.0.0.0/32 is subnetted, 1 subnets
O
3.3.3.3 [110/49] via 10.1.1.3, 00:20:27, Serial0/0
10.0.0.0/29 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0/0
__________________________________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O IA
1.1.1.1 [110/65] via 10.1.1.1, 00:21:19, Serial0
2.0.0.0/32 is subnetted, 1 subnets
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C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O
3.3.3.3 [110/65] via 10.1.1.3, 00:21:20, Serial0
172.16.0.0/24 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0
___________________________________________________________________________________________
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O IA
1.1.1.1 [110/65] via 10.1.1.1, 00:22:18, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/65] via 10.1.1.2, 00:22:19, Serial0
3.0.0.0/32 is subnetted, 1 subnets
C
3.3.3.3 is directly connected, Loopback0
10.0.0.0/29 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0
________________________________________________________________________________
rtrA#ping 2.2.2.2
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Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms
rtrA#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms
________________________________________________________________________
rtrB#ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms
rtrB#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/8/8 ms
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rtrC#ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms
rtrC#ping 2.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/9/12 ms
Configuration Example 3: Configuring OSPF Neighbors on a Hub and Spoke
Topology with the Neighbors on Different IP Subnets
In Figure 11-4, the Frame Relay links between Routers A and B and Routers A and C are on different IP subnets. This topology requires the
use of subinterfaces on the Serial 0/0 interface on Router A. Configure Routers A, B, and C as shown in the listing that follows the figure.
Figure 11-4. In a Hub and Spoke Topology, Subinterfaces Are Required on the Hub Router if the
Spokes Are in Different IP Subnets
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
no ip address
encapsulation frame-relay
frame-relay lmi-type ansi
!
interface Serial0/0.1 point-to-point
ip address 10.1.1.1 255.255.255.252
frame-relay interface-dlci 101
!
interface Serial0/0.2 point-to-point
ip address 10.1.1.5 255.255.255.252
frame-relay interface-dlci 102
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
.
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network 10.1.1.4 0.0.0.3 area 0
________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
encapsulation frame-relay
frame-relay map ip 10.1.1.1 110 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.3 area 0
neighbor 10.1.1.1
________________________________________________________________
Router C
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
.
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interface Serial0
ip address 10.1.1.2 255.255.255.252
encapsulation frame-relay
frame-relay map ip 10.1.1.1 120 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.3 area 0
neighbor 10.1.1.1
Notice that the OSPF neighbor statements have been moved to Routers B and C. The neighbor statement cannot be used on a Frame
Relay point-to-point subinterface. If you try to use this command on Router A, the router will notify you that this is unacceptable.
rtrA(config-router)#neighbor 10.1.1.2
OSPF: Neighbor command is allowed only on NBMA and point-to-multipoint networks
rtrA(config-router)#
Verification
Verify that Router A has formed an OSPF neighbor relationship with Routers B and C.
rtrA#show ip ospf neighbor
<no output>
Something is wrong. Enable OSPF debugging to see if you can determine the problem.
rtrA#debug ip ospf events
OSPF events debugging is on
rtrA#
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00:16:18: OSPF: Rcv hello from 2.2.2.2 area 0 from Serial0/0.1 10.1.1.2
00:16:18: OSPF: Mismatched hello parameters from 10.1.1.2
00:16:52: OSPF: Rcv hello from 3.3.3.3 area 0 from Serial0/0.2 10.1.1.6
00:16:52: OSPF: Mismatched hello parameters from 10.1.1.6
00:16:52: Dead R 120 C 40, Hello R 30 C 10
If there is a mismatch of Hello parameters, then OSPF will not form a neighbor relationship. Inspect the Hello parameters on Router A and
compare them to the Hello parameters on Routers B and C.
rtrA#show ip ospf interface s0/0.1
Serial0/0.1 is up, line protocol is up
Internet Address 10.1.1.1/30, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 48
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:18
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2
Suppress hello for 0 neighbor(s)
________________________________________________________________
rtrB#show ip ospf interface s0
Serial0 is up, line protocol is up
Internet Address 10.1.1.2/30, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type NON_BROADCAST, Cost: 64
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 2.2.2.2, Interface address 10.1.1.2
Backup Designated router (ID) 1.1.1.1, Interface address 10.1.1.1
Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
Hello due in 00:00:04
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Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1 (Backup Designated Router)
Suppress hello for 0 neighbor(s)
Modify the configuration on Router A so that the Hello parameters match those being used on Routers B and C.
Router A
interface Serial0/0
no ip address
encapsulation frame-relay
frame-relay lmi-type ansi
!
interface Serial0/0.1 point-to-point
ip address 10.1.1.1 255.255.255.252
ip ospf hello-interval 30
frame-relay interface-dlci 101
!
interface Serial0/0.2 point-to-point
ip address 10.1.1.5 255.255.255.252
ip ospf hello-interval 30
frame-relay interface-dlci 102
By default, the OSPF dead interval is four times the Hello interval, so the dead interval does not need to be reconfigured on Router A. When
the Hello interval is set to 30, the dead interval will automatically be set to 120. Verify that Router A has established a FULL OSPF neighbor
relationship with Routers B and C.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
2.2.2.2
1 FULL/ -
00:01:58
10.1.1.2
Serial0/0.1
3.3.3.3
0 FULL/ -
00:01:57
10.1.1.6
Serial0/0.2
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Troubleshooting
Step 1. Verify IP connectivity over the NBMA network by pinging the other end of the link. If the ping is unsuccessful, there is a
problem with the interface configuration. Check the interface for the correct encapsulation, lmi-type, IP address, and DLCI
mapping.
Step 2. Verify that the neighbor command has been used on at least one end of the NBMA link.
Step 3. Verify that both ends of the link are using the same values for the Hello and dead intervals.
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11-2 neighbor ip-address cost cost
Syntax Description:
ip-address— IP address of the OSPF neighbor. If a secondary address is used on the interface, then the primary address must be
used with this command.
cost— The cost to reach the OSPF neighbor. The range of values is 1 to 65535.
Purpose: To configure the cost of an OSPF neighbor on a point-to-multipoint network.
Initial Cisco IOS Software Release: 11.3
Configuration Example: Modifying the Cost of an OSPF Neighbor on a
Point-to-Multipoint Interface
The cost to reach an OSPF neighbor is, by default, the bandwidth of the network connecting the two neighbors divided into 100,000,000. In
Figure 11-5, the bandwidth of the Frame Relay link is 2048 kbps. Therefore, the OSPF cost of the Frame Relay interfaces is 48
(100,000,000/2,048,000). The cost option of the neighbor command can be used to change the cost to reach the neighbor. The interface
command ip ospf cost (see Section 19-3) can also be used to change this cost. The neighbor cost command can only be used on
point-to-multipoint interfaces. The listing that follows the figure shows the configurations of the Frame Relay switch and Routers A and B.
Figure 11-5. The Default Cost of an OSPF Interface Is 100,000,000/(Interface Bandwidth in bps).
The neighbor cost Command Can Be Used to Modify the Interface Cost
.
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Frame Switch
hostname frame-relay
!
frame-relay switching
!
interface Serial1/0
no ip address
no ip directed-broadcast
encapsulation frame-relay
no ip mroute-cache
no fair-queue
clockrate 2015232
frame-relay lmi-type ansi
frame-relay intf-type dce
frame-relay route 101 interface Serial1/1 110
frame-relay route 102 interface Serial1/2 120
frame-relay route 103 interface Serial1/3 130
!
interface Serial1/1
no ip address
no ip directed-broadcast
.
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encapsulation frame-relay
clockrate 2015232
frame-relay lmi-type ansi
frame-relay intf-type dce
frame-relay route 110 interface Serial1/0 101
frame-relay route 112 interface Serial1/2 121
frame-relay route 113 interface Serial1/3 131
________________________________________________________________________
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
bandwidth 2048
ip address 10.1.1.1 255.255.255.252
encapsulation frame-relay
ip ospf network point-to-multipoint
frame-relay map ip 10.1.1.2 101 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
________________________________________________________________
Router B
.
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interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
bandwidth 2048
ip address 10.1.1.2 255.255.255.252
encapsulation frame-relay
ip ospf network point-to-multipoint
frame-relay map ip 10.1.1.1 110 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.3 area 0
The interface command ip ospf network point-to-multipoint (see Section 19-15) is used because the neighbor cost command will work
only on a point-to-multipoint interface. Display the IP routing table on Router B to see the cost of reaching the loopback network on Router A.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
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O IA
1.1.1.1 [110/49] via 10.1.1.1, 00:22:11, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C
10.1.1.0/30 is directly connected, Serial0
O
10.1.1.1/32 [110/10] via 10.1.1.1, 00:22:11, Serial0
The cost is the sum of the cost of the loopback interface (1) and the cost of the Frame Relay link (48) for a total cost of 49. Modify the
configuration on Router B to change the cost of the Frame Relay link to 10.
Router B
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.3 area 0
neighbor 10.1.1.1 cost 10
Verification
Verify that the cost of the Frame Relay interface, as seen by Router B, has changed to 10.
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
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Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O IA
1.1.1.1 [110/11] via 10.1.1.1, 00:01:49, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C
10.1.1.0/30 is directly connected, Serial0
O
10.1.1.1/32 [110/10] via 10.1.1.1, 00:01:49, Serial0
Troubleshooting
Step 1. Verify IP connectivity over the NBMA network by pinging the other end of the link. If the ping is unsuccessful, there is a
problem with the interface configuration. Check the interface for the correct encapsulation, lmi-type, IP address, and DLCI
mapping.
Step 2. Verify that the OSPF routers have established a FULL adjacency over the NBMA network.
Step 3. If the OSPF neighbors have a FULL adjacency, then the command neighbor cost should work. Remember that this
command can be used only on a point-to-multipoint interface.
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< Free Open Study >
11-3 neighbor ip-address database-filter all out
Syntax Description:
ip-address— IP address of the OSPF neighbor. If a secondary address is used on the interface, then the primary address must be
used with this command because OSPF will only form an adjacency using the primary address.
Purpose: To prevent the flooding of link-state advertisements (LSAs) to the indicated neighbor. Many Internet service providers (ISPs)
employ redundant links between OSPF neighbors. When an OSPF router receives an LSA, the LSA is flooded on all OSPF inter-faces except
for the interface on which the LSA was received. This command allows an ISP to choose between flooding overhead and flooding reliability.
For example, if there are two links between OSPF neighbors, this command can be used to prevent the flooding of LSAs on one of the links.
This command can be used only on a multipoint interface or an NBMA interface.
Initial Cisco IOS Software Release: 12.0
Configuration Example: Reducing the Flooding of LSAs on a Redundant OSPF Link
In Figure 11-6, there are two parallel links between Routers A and B. To reduce LSA flooding, overhead LSA flooding is prevented on link 2
using the database-filter option of the neighbor command. This reduction of LSA flooding can also be achieved by using the interface
command ip ospf database-filter all out (see Section 19-4). Configure Routers A and B as shown in the listing that follows the figure. The
point-to-multipoint network type is used on Router A's Serial 0/1 interface and Router B's Serial 0 interface so the database filter can be
applied to the interface.
Figure 11-6. Reducing LSA Flooding Overhead by Preventing LSA Flooding on One of the Parallel
Links Using the neighbor database-filter all out Command
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
bandwidth 64
ip address 10.1.1.1 255.255.255.252
!
interface Serial0/1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
ip ospf network point-to-multipoint
clockrate 64000
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 0
neighbor 10.1.1.6 database-filter all out
_________________________________________________________________________________________
.
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Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
bandwidth 64
ip ospf network point-to-multipoint
!
interface Serial1
bandwidth 64
ip address 10.1.1.2 255.255.255.252
clockrate 64000
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 0
Verification
Verify that the database filter has been applied to interface Serial 0/1 on Router A.
rtrA#show ip ospf neighbor detail
Neighbor 2.2.2.2, interface address 10.1.1.2
In the area 0 via interface Serial0/0
Neighbor priority is 1, State is FULL, 6 state changes
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DR is 0.0.0.0 BDR is 0.0.0.0
Options 2
Dead timer due in 00:00:33
Neighbor 2.2.2.2, interface address 10.1.1.6
In the area 0 via interface Serial0/1
Neighbor priority is 1, State is FULL, 6 state changes
Database-filter all out
DR is 0.0.0.0 BDR is 0.0.0.0
Options 2
Dead timer due in 00:01:55
Troubleshooting
Step 1. The database-filter all out command can be applied only to a point-to-multipoint or NBMA interface.
Step 2. Verify that the OSPF routers have established a FULL adjacency.
Step 3. If the OSPF neighbors have a FULL adjacency, then the command database-filter all out should work.
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< Free Open Study >
11-4 neighbor ip-address poll-interval interval
Syntax Description:
ip-address— IP address of the OSPF neighbor. If a secondary address is used on the interface, then the primary address must be
used with this command because OSPF will only form an adjacency using the primary address.
interval— Poll interval in seconds. The range of values is from 0–4,294,967,295.
Purpose: If a Hello packet has not been received from a neighbor during the dead interval, the neighbor is declared down. Hello packets will
be sent to the neighbor at the rate specified by the poll interval when the neighbor is down. This option does not apply to point-to-multipoint
interfaces.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Setting the Poll Interval on an NBMA Network
In Figure 11-7, Routers A and B have formed an OSPF adjacency over the NBMA network. Hello packets will be sent by both routers
periodically. The time between Hello packets is determined by the Hello interval. If Router A does not receive a Hello packet from Router B
during a period of time determined by the dead interval, Router A will declare Router B down. Router A will continue to send Hello packets to
Router B, but at a reduced rate. This reduced rate is the poll interval. The configuration for the routers in Figure 11-7 is shown in the listing
that follows.
Figure 11-7. When a Neighbor on an NBMA Network Is Declared Down, Hello Packets Will Be Sent
at a Reduced Rate Determined by the Poll Interval
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
bandwidth 64
ip address 10.1.1.1 255.255.255.252
encapsulation frame-relay
frame-relay lmi-type ansi
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
neighbor 10.1.1.2
________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
no ip directed-broadcast
encapsulation frame-relay
no ip mroute-cache
frame-relay lmi-type ansi
.
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!
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.3 area 0
The value of the poll interval can be viewed using the show ip ospf neighbor detail command.
rtrA#show ip ospf neighbor detail
Neighbor 2.2.2.2, interface address 10.1.1.2
In the area 0 via interface Serial0/0
Neighbor priority is 1, State is FULL, 16 state changes
DR is 10.1.1.2 BDR is 10.1.1.1
Poll interval 60
Options 2
Dead timer due in 00:01:42
Modify the configuration on Router A to change the poll interval to 90.
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
neighbor 10.1.1.2 poll-interval 90
Verification
Verify that Router A is now using a poll interval of 90.
rtrA#show ip ospf neighbor detail
Neighbor 2.2.2.2, interface address 10.1.1.2
In the area 0 via interface Serial0/0
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Neighbor priority is 0, State is FULL, 17 state changes
DR is 10.1.1.2 BDR is 10.1.1.1
Poll interval 90
Options 2
Dead timer due in 00:01:31
Troubleshooting
Step 1. The poll-interval option can be applied only to NBMA networks. This option is not allowed on a point-to-multipoint
interface.
Step 2. Verify that the OSPF routers have established a FULL adjacency.
Step 3. If the OSPF neighbors have a FULL adjacency, the command poll-interval should work.
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< Free Open Study >
11-5 neighbor ip-address priority priority
Syntax Description:
ip-address— IP address of the OSPF neighbor. If a secondary address is used on the interface, then the primary address must be
used with this command because OSPF will only form an adjacency using the primary address.
priority— The OSPF priority of the neighbor with the given IP address. The range of values is 0 to 255. The router with the lowest
OSPF priority on a network will be elected the DR for the network. A priority of zero means that the router is not eligible to be
elected the DR or Backup Designated Router (BDR). The default priority is 1.
Purpose: To influence the election of the DR. The router with the lowest non-zero priority will be elected the DR. In a hub and spoke
topology, the hub router should be elected as the DR.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Setting the Priority of an OSPF Neighbor
Configure the routers in Figure 11-8 as shown in the listing that follows.
Figure 11-8. The Election of the DR Can Be Influenced by Using the priority Option with the
neighbor Router Configuration Command
Router A
interface Loopback0
.
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ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
bandwidth 64
ip address 10.1.1.1 255.255.255.252
encapsulation frame-relay
frame-relay map ip 10.1.1.2 101 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
encapsulation frame-relay
bandwidth 64
frame-relay map ip 10.1.1.1 110 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
!
router ospf 1
.
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network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.3 area 0
neighbor 10.1.1.1 priority 1
Examine the state of the OSPF neighbors to determine which router has been elected the DR.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/BDR
Dead Time Address
00:01:45
10.1.1.2
Interface
Serial0/0
______________________________________________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:01:37
10.1.1.1
Interface
Serial0
Router A is the DR because it has a lower OSPF router ID. Modify the configuration on Router B so that it will be elected the DR. This can be
accomplished by either setting the priority to 0 or larger than 1 in the neighbor statement.
Router B
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.3 area 0
neighbor 10.1.1.1 priority 2
OSPF will not immediately elect a new DR. For stability reasons, OSPF will elect a new DR only if the current DR is down. Force the
re-election of the DR by clearing the OSPF process on Router A.
rtrA#clear ip ospf process
Reset ALL OSPF processes? [no]: y
rtrA#
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Verification
Verify that Router B has been elected as the DR.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/DR
Dead Time Address
00:01:45
10.1.1.2
Interface
Serial0/0
_____________________________________________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/BDR
Dead Time Address
00:01:44
10.1.1.1
Interface
Serial0
Troubleshooting
Step 1. The configured priority value will not take effect until the current DR is down and a new election takes place.
Step 2. Verify that the desired priority value has been used with the OSPFneighbor command.
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Chapter 12. OSPF network Command
Section 12-1. network ip-address wild-card-mask area area-id
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12-1 network ip-address wild-card-mask area area-id
Syntax Description:
ip-address— The ip-address in conjunction with the wild-card-mask defines a block of IP addresses. An interface with an IP
address that is contained within the defined block is configured to run OSPF in the indicated area.
wild-card-mask— Inverse IP address mask used to determine a range of IP addresses.
area-id— OSPF area ID. The value can be entered as a decimal number in the range of 0 to 4,294,967,295 or in IP address
format in the range 0.0.0.0 to 255.255.255.255.
Purpose: The network command is used to define the interfaces that will run OSPF and the OSPF area of the interface. One or more
interfaces can be selected with a single network command. If the IP address assigned to an interface is part of the address block the
ip-address/wild-card-mask pair defines, the interface will be enabled for OSPF in the indicated area.
Initial Cisco IOS Software Release: 10.0
Configuration Example 1: Using a Host Address to Enable OSPF on an Interface
In Figure 12-1, host addresses are initially used to configure the interfaces to run OSPF. A host address consists of an IP address and a
32-bit mask in the form
Figure 12-1. Network Used to Illustrate the Use of the OSPF network Command
A.B.C.D 0.0.0.0
.
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This address/mask pair defines an IP address block that contains one address. Therefore, this form can be used to enable only one interface
per network statement for OSPF.
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 172.16.1.1 0.0.0.0 area 0
________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 172.16.1.2 0.0.0.0 area 0
Verification
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Verify that the proper interfaces have been configured for OSPF.
rtrA#show ip ospf interface
Ethernet0/0 is up, line protocol is up
Internet Address 172.16.1.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 1.1.1.1, Interface address 172.16.1.1
Backup Designated router (ID) 2.2.2.2, Interface address 172.16.1.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Index 1/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 2, maximum is 2
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2 (Backup Designated Router)
Suppress hello for 0 neighbor(s)
Loopback0 is up, line protocol is up
Internet Address 1.1.1.1/32, Area 1
Process ID 1, Router ID 1.1.1.1, Network Type LOOPBACK, Cost: 1
Loopback interface is treated as a stub Host
________________________________________________________________
rtrB#show ip ospf interface
Ethernet0 is up, line protocol is up
Internet Address 172.16.1.2/24, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State BDR, Priority 1
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Designated Router (ID) 1.1.1.1, Interface address 172.16.1.1
Backup Designated router (ID) 2.2.2.2, Interface address 172.16.1.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:00
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1 (Designated Router)
Suppress hello for 0 neighbor(s)
Loopback0 is up, line protocol is up
Internet Address 2.2.2.2/32, Area 2
Process ID 1, Router ID 2.2.2.2, Network Type LOOPBACK, Cost: 1
Loopback interface is treated as a stub Host
Configuration Example 2: Using the Same Network/Mask Pair in the OSPF network
Statement That Is Used for the Interface
One problem that can arise when using a host address in the network statement is if the IP address of the interface changes. If you change
the IP address of the Ethernet interface on Router A from 172.16.1.1 to 172.16.1.3, then the interface will no longer be enabled for OSPF.
You need to delete the network statement containing the host route 172.16.1.1 and re-enter thenetwork statement using the host route
172.16.1.3. If you change the IP address on the Ethernet interface on Router A, you should see the following output:
rtrA#conf t
Enter configuration commands, one per line. End with CNTL/Z.
rtrA(config)#int e0/0
rtrA(config-if)# ip add 172.16.1.3 255.255.255.0
rtrA(config-if)# ^Z
rtrA#
05:23:52: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet0/0 from FULL to DOW
N, Neighbor Down: Interface down or detached
You have broken the OSPF network and Routers A and B are no longer talking to OSPF. If you had used the same address (almost) and
mask (reverse) that was assigned to the interface in the network command then this problem would have gone away.
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Router A
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 172.16.1.1 0.0.0.255 area 0
The new address/mask pair defines the IP address block 172.16.1.0–172.16.1.255. If any IP address in this range is used, the Ethernet
interface will still be activated for OSPF.
Verification
Verify that OSPF is active on the Ethernet interface on Router A.
rtrA#show ip ospf interface ethernet 0/0
Ethernet0/0 is up, line protocol is up
Internet Address 172.16.1.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State WAITING, Priority 1
No designated router on this network
No backup designated router on this network
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:04
Wait time before Designated router selection 00:00:34
Index 1/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 2
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
Changing the IP address on an active OSPF interface will cause OSPF to go inactive on the interface until the router determines that the
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new IP address falls within the range of one of the network commands. If it does, OSPF will be reactivated on the interface.
Configuration Example 3: Using a Shorter Mask to Enable OSPF on Multiple
Interfaces
In Figure 12-2, the routers in Area 1 use IP addresses assigned from the IP address block 10.1.0.0/16, and the routers in Area 2 use the
address block 10.2.0.0/16. For this case, only one network statement is needed on the routers in Areas 1 and 2 and two network statements
are needed on the Area Border Routers (ABRs). Assume there are 20 routers in Area 1 and each router has five interfaces. If we use the
methods from configuration example 1 or 2, we would need to configure five network statements per router. If an interface is added to a
router, then a new OSPF network statement needs to be configured on that router. This would work well, but it could become
administratively intensive. If one network statement is used, then no additional OSPF configuration would be necessary when a new
interface is added to a router. The configurations for the routers are shown in the listing that follows the figure.
Figure 12-2. If All Interfaces on a Router Have Been Assigned to a Common IP Address Block and
OSPF Area, Then One network Statement Can Be Used To Enable the Interfaces for OSPF
Router A
router ospf 1
network 172.16.1.0 0.0.0.255 area 0
network 10.1.0.0 0.0.255.255 area 1
________________________________________________________________
Router B
router ospf 1
network 172.16.1.0 0.0.0.255 area 0
network 10.2.0.0 0.0.255.255 area 2
.
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________________________________________________________________
Area 1 Router
router ospf 1
network 10.1.0.0 0.0.255.255 area 1
________________________________________________________________
Area 2 Router
router ospf 1
network 10.2.0.0 0.0.255.255 area 2
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbors command.
Step 2. Verify that you are using the proper IP address/wild-card maskin the network statement.
Step 3. Use the show ip ospf interface command to verify that the interfaces are in the intended OSPF area.
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Chapter 13. Passive OSPF Interfaces
Section 13-1. passive-interface interface-name interface-number
Section 13-2. passive-interface default
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13-1 passive-interface interface-name interface-number
Syntax Description:
interface-name— Name of the interface.
interface-number— Number of the interface.
Purpose: To prevent OSPF packets from being sent on the specified interface.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Using a Passive Interface to Reduce Protocol Traffic
In Figure 13-1, Router B has a BGP neighbor relationship with Router C. The BGP routes learned by Router B from Router C are
redistributed into OSPF. The network between Routers B and C needs to be advertised by OSPF to Router A so there is IP connectivity
between Routers A and C. There is no need to send OSPF protocol packets to Router C. Therefore, the Serial 1 interface on Router B can be
made passive under OSPF. The network between Routers B and C could also be advertised by redistributing connected routes on Router B.
The redistributed networks would be advertised as OSPF external routes.
Figure 13-1. OSPF Will Advertise the Network Assigned to an Interface if the Interface Is Included
in One of the OSPF network Statements. If the Interface Does Not Have Any OSPF Neighbors, then
the Interface Can Be Made Passive
Router A
.
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interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
bandwidth 64
ip address 10.1.1.1 255.255.255.252
clock rate 64000
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial1
ip address 10.1.1.5 255.255.255.252
clock rate 64000
!
router ospf 1
redistribute bgp 1 subnets
passive-interface Serial1
network 2.2.2.2 0.0.0.0 area 2
.
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network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 0
!
router bgp 1
neighbor 10.1.1.6 remote-as 2
________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router bgp 2
network 3.3.3.3 mask 255.255.255.255
neighbor 10.1.1.5 remote-as 1
!
ip route 0.0.0.0 0.0.0.0 Serial0
The OSPF configuration on Router B contains the following statement:
network 10.1.1.4 0.0.0.3 area 0
This statement enables OSPF on the Serial 1 interface on Router B and causes OSPF to advertise the network 10.1.1.4. OSPF protocol
packets will be sent from the Serial 1 interface on Router B. Router C is not running OSPF, so there is no need to send protocol packets over
this network. The passive-interface command prevents the OSPF packets from being sent while allowing the network to be advertised into
OSPF. The redistribution of BGP into OSPF on Router B allows Router A to reach the 3.3.3.3 network on Router C. The static default route
on Router C allows Router C to reach the 1.1.1.1 network on Router A.
Verification
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Verify that the Serial 1 interface is a passive OSPF interface.
rtrB#show ip ospf interface serial 1
Serial1 is up, line protocol is up
Internet Address 10.1.1.5/30, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
No Hellos (Passive interface)
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
Verify that the 10.1.1.4 network is being advertised to Router A via OSPF.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/1563] via 10.1.1.2, 03:30:49, Serial0/1
3.0.0.0/32 is subnetted, 1 subnets
O E2
3.3.3.3 [110/1] via 10.1.1.2, 03:30:49, Serial0/1
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172.16.0.0/24 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0/1
O
10.1.1.4 [110/3124] via 10.1.1.2, 03:30:49, Serial0/1
Verify that Routers A and C can reach each other's attached networks.
rtrA#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 56/58/60 ms
________________________________________________________________
rtrC#ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 56/57/60 ms
Troubleshooting
Step 1. Verify that the intended interface has been made passive. A common mistake is to make the wrong OSPF interface
passive.
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13-2 passive-interface default
Syntax Description:
This form of the command has no arguments.
Purpose: To make all OSPF interfaces passive.
Initial Cisco IOS Software Release: 12.0
Configuration Example: Many Interfaces, Few Neighbors
In Figure 13-2, Router A has one OSPF neighbor and connections to five non-OSPF routers. Router A wants to advertise all connected
networks to Router B via OSPF, but does not want to transmit OSPF traffic on the interfaces connecting to non-OSPF routers. In addition,
Router A wants to advertise the connected networks as OSPF routes. This condition means that redistributing connected routes on Router A
is not an option, because these routes would be advertised as external routes.
Figure 13-2. All OSPF Interfaces Can Be Made Passive Using the Command passive-interface
default. The no Form of the Command Can Then Be Used to Enable Selected Interfaces
.
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For the moment, assume that the default option is not available with thepassive-interface command. The configuration for Router A would
require five passive-interface commands.
Router A
router ospf 1
passive-interface Serial1/0
passive-interface Serial1/1
passive-interface Serial1/2
passive-interface Serial1/3
passive-interface Serial1/4
network 10.1.0.0 0.0.255.255 area 0
The OSPF configuration for Router A is not very complicated. But assume that you have a core router with over 100 interfaces to non-OSPF
routers. The configuration would become rather cumbersome. There would be over 100 passive-interface statements in the OSPF
configuration. Therefore, the default option is an option of convenience. Start by using the commandpassive-interface default to make all
OSPF interfaces passive. Then activate the interfaces that have OSPF neighbors, using the no passive-interface form of the command. The
previous configuration would become
router ospf 1
passive-interface default
no passive-interface Serial0/1
network 10.1.0.0 0.0.255.255 area 0
Verification
Verify that the Serial 1 interface is a passive OSPF interface.
rtrB#show ip ospf interface
Loopback0 is up, line protocol is up
Internet Address 2.2.2.2/32, Area 2
Process ID 1, Router ID 2.2.2.2, Network Type LOOPBACK, Cost: 1
Loopback interface is treated as a stub Host
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Serial0/1 is up, line protocol is up
Internet Address 10.1.1.2/30, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1
Suppress hello for 0 neighbor(s)
Serial1/0 is up, line protocol is up
Internet Address 10.1.1.5/30, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
No Hellos (Passive interface)
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
...
Troubleshooting
Step 1. When using the default option, make sure that interfaces with OSPF neighbors have been made active using theno
passive-interface command.
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Chapter 14. Route Redistribution
Section 14-1. redistribute routing-process process-id
Section 14-2. redistribute routing-process process-id metric ospf-metric
Section 14-3. redistribute routing-process process-id metric-type metric-type
Section 14-4. redistribute routing-process process-id subnets
Section 14-5. redistribute routing-process process-id tag tag-value
Section 14-6. redistribute routing-process process-id route-map route-map-name
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14-1 redistribute routing-process process-id
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14-2 redistribute routing-process process-id metric ospf-metric
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14-3 redistribute routing-process process-id metric-type metric-type
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14-4 redistribute routing-process process-id subnets
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14-5 redistribute routing-process process-id tag tag-value
Syntax Description:
routing-process— Routing process to redistribute into OSPF. The routing process can be BGP, Connected, EGP, EIGRP, IGRP,
ISIS, ISO-IGRP, Mobile, ODR, OSPF, RIP, or Static.
process-id— The process ID of the routing process (if applicable).
ospf-metric— The metric or cost to assign to the redistributed routes. If this option is not used, a default metric of 1 will be used for
redistributed BGP routes and a default metric of 20 will be used for all other protocols. The range of values is 0–16,777,214.
metric-type— Routes are redistributed into OSPF as either type 1 or type 2 routes. The default is type 2.
tag-value— A 32-bit value that is attached to the redistributed routes. The route tag is not used by OSPF but can be referenced in
a route map for making policy decisions. One possible use is to base the decision to redistribute a route based on the route tag
(see Section 14-6). The default tag value is 0. The range of values for the tag is 0–4,294,967,295.
Purpose: To redistribute routes learned from another routing process into OSPF. Redis-tributed routes become OSPF external type 2 routes
by default. The default cost or metric of a redistributed route is 1 for BGP and 20 for all other protocols. This command will redistribute
classful routes into OSPF only if the subnets keyword is not used. There are three general types of classful routes:
A Class A address with an 8-bit subnet mask
A Class B address with a 16-bit subnet mask
A Class C address with a 24-bit subnet mask
Initial Cisco IOS Software Release: 10.0
Configuration Example: 1 Redistributing Classful Routes into OSPF with the
Default Type and Metric
In Figure 14-1, Router B is receiving six routes from Router C via EIGRP. Three of the EIGRP routes are classful (5.0.0.0/8, 145.5.0.0/16,
205.5.5.0/24) and three are classless (6.0.0.0/12, 146.6.0.0/20, 206.6.6.0/28). Before redistributing the EIGRP routes into OSPF on Router B,
configure the routers as shown in the listing that follows.
Figure 14-1. By Default, OSPF Will Redistribute Only Classful Routes
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial 1
ip address 10.1.1.5 255.255.255.252
.
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!
router eigrp 1
network 10.0.0.0
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Loopback1
ip address 5.5.5.5 255.0.0.0
!
interface Loopback2
ip address 6.6.6.6 255.240.0.0
!
interface Loopback3
ip address 145.5.5.5 255.255.0.0
!
interface Loopback4
ip address 146.6.6.6 255.255.240.0
!
interface Loopback5
ip address 205.5.5.5 255.255.255.0
!
interface Loopback6
.
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ip address 206.6.6.6 255.255.255.240
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router eigrp 1
network 5.0.0.0
network 6.0.0.0
network 10.0.0.0
network 145.5.0.0
network 146.6.0.0
network 205.5.5.0
network 206.6.6.0
no auto-summary
Verify that Routers A and B have established an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
Dead Time Address
1 FULL/ -
00:00:36
10.1.1.2
Interface
Serial0/1
Verify that Routers B and C have formed an EIGRP neighbor relationship.
rtrB#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H Address
Interface Hold Uptime SRTT RTO Q Seq
(sec)
0 10.1.1.6
Se1
(ms)
Cnt Num
11 00:25:42 308 2280 0 4
Verify that Router B is receiving the six EIGRP routes from Router C.
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rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
2.0.0.0/32 is subnetted, 1 subnets
C
D
2.2.2.2 is directly connected, Loopback0
205.5.5.0/24 [90/40640000] via 10.1.1.6, 00:26:25, Serial1
206.6.6.0/28 is subnetted, 1 subnets
D
D
206.6.6.0 [90/40640000] via 10.1.1.6, 00:26:25, Serial1
5.0.0.0/8 [90/40640000] via 10.1.1.6, 00:26:25, Serial1
6.0.0.0/12 is subnetted, 1 subnets
D
D
6.0.0.0 [90/40640000] via 10.1.1.6, 00:26:25, Serial1
145.5.0.0/16 [90/40640000] via 10.1.1.6, 00:26:25, Serial1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
146.6.0.0/20 is subnetted, 1 subnets
D
146.6.0.0 [90/40640000] via 10.1.1.6, 00:26:27, Serial1
Modify the configuration on Router B to redistribute the classful EIGRP routes into OSPF.
router ospf 1
redistribute eigrp 1
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When the command redistribute eigrp 1 is entered, the router will give you the following friendly reminder:
rtrB(config-router)#redistribute eigrp 1
% Only classful networks will be redistributed
Verification
Determine the routes that have been redistributed by examining the IP routing table on Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
O E2 205.5.5.0/24 [110/20] via 10.1.1.2, 00:33:23, Serial0/1
O E2 5.0.0.0/8 [110/20] via 10.1.1.2, 00:33:23, Serial0/1
O E2 145.5.0.0/16 [110/20] via 10.1.1.2, 00:33:23, Serial0/1
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0/1
Only the EIGRP classful routes were redistributed into OSPF. As you can see in the routing table on Router A, EIGRP routes were
redistributed as external type 2 with a cost or metric of 20. This information can also be found by inspecting the OSPF database on Router B.
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rtrB#show ip ospf database external
OSPF Router with ID (2.2.2.2) (Process ID 1)
Type-5 AS External Link States
LS age: 410
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 5.0.0.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000004
Checksum: 0x642C
Length: 36
Network Mask: /8
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
LS age: 419
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 145.5.0.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000004
Checksum: 0x5F9
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Length: 36
Network Mask: /16
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
LS age: 435
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 205.5.5.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000004
Checksum: 0xBEFE
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
Configuration Example: 2 Redistributing Classful Routes into OSPF with the
Default Type and Specific Metric
In the first configuration example for Figure 14-1, the EIGRP routes were redistributed into OSPF with a default metric of 20. For this
example, modify the configuration on Router B to change the metric of all the redistributed EIGRP routes to 66.
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Router B
router ospf 1
redistribute eigrp 1 metric 66
Verification
Verify that the new metric has been applied to the redistributed EIGRP routes. On Router A you can look at the IP routing table and on
Router B you can inspect the OSPF database.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
O E2 205.5.5.0/24 [110/66] via 10.1.1.2, 00:00:16, Serial0/1
O E2 5.0.0.0/8 [110/66] via 10.1.1.2, 00:00:16, Serial0/1
O E2 145.5.0.0/16 [110/66] via 10.1.1.2, 00:00:16, Serial0/1
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0/1
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Configuration Example: 3 Redistributing Classful Routes into OSPF as Type 1
Routes Using a Specific Metric
Routes are redistributed in OSPF as either type 1 (E1) routes or type 2 (E2) routes, with type 2 being the default. A type 1 route has a metric
that is the sum of the internal OSPF cost and the external redistributed cost. A type 2 route has a metric equal only to the redistributed cost,
as shown in Figure 14-2. If routes are redistributed into OSPF as type 2 then every router in the OSPF domain will see the same cost to reach
the external networks. If routes are redistributed into OSPF as type 1, then the cost to reach the external networks could vary from router to
router.
Figure 14-2. OSPF Routes Are Redistributed as Either Type 1 or Type 2 Routes
Modify the configuration on Router B so that the EIGRP routes are redistributed as type 1 routes.
Router B
router ospf 1
redistribute eigrp 1 metric 66 metric-type 1
Verification
Verify that the EIGRP routes have been redistributed into OSPF as type 1 routes with a metric of 66.
rtrB#show ip ospf database external
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OSPF Router with ID (2.2.2.2) (Process ID 1)
Type-5 AS External Link States
LS age: 149
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 5.0.0.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000008
Checksum: 0xA638
Length: 36
Network Mask: /8
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 66
Forward Address: 0.0.0.0
External Route Tag: 0
LS age: 158
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 145.5.0.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000008
Checksum: 0x4706
Length: 36
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Network Mask: /16
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 66
Forward Address: 0.0.0.0
External Route Tag: 0
LS age: 168
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 205.5.5.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000008
Checksum: 0x10B
Length: 36
Network Mask: /24
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 66
Forward Address: 0.0.0.0
External Route Tag: 0
Verify that the cost of these routes as seen by Router A is the sum of the redistributed metric and the OSPF cost to reach Router B.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
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P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
O E1 205.5.5.0/24 [110/1628] via 10.1.1.2, 00:05:36, Serial0/1
O E1 5.0.0.0/8 [110/1628] via 10.1.1.2, 00:05:36, Serial0/1
O E1 145.5.0.0/16 [110/1628] via 10.1.1.2, 00:05:36, Serial0/1
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0/1
Configuration Example: 4 Redistributing Subnet Routes into OSPF as Type 1
Routes Using a Specific Metric
The previous configuration examples redistributed only the classful EIGRP routes into OSPF. Modify the configuration on Router B to
redistribute all the EIGRP routes.
Router B
router ospf 1
redistribute eigrp 1 metric 66 metric-type 1 subnets
Verification
Verify that the classless EIGRP routes have been redistributed into OSPF on Router B by inspecting the IP routing table on Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
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N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
O E1 205.5.5.0/24 [110/1628] via 10.1.1.2, 00:22:36, Serial0/1
206.6.6.0/28 is subnetted, 1 subnets
O E1
206.6.6.0 [110/1628] via 10.1.1.2, 00:02:37, Serial0/1
O E1 5.0.0.0/8 [110/1628] via 10.1.1.2, 00:22:36, Serial0/1
6.0.0.0/12 is subnetted, 1 subnets
O E1
6.0.0.0 [110/1628] via 10.1.1.2, 00:02:37, Serial0/1
O E1 145.5.0.0/16 [110/1628] via 10.1.1.2, 00:22:37, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
O E1
10.1.1.4 [110/1628] via 10.1.1.2, 00:02:40, Serial0/1
146.6.0.0/20 is subnetted, 1 subnets
O E1
6.0.0.0 [110/1628] via 10.1.1.2, 00:02:37, Serial0/1
Configuration Example: 5 Redistributing Subnet Routes into OSPF as Type 1
Routes Using a Specific Metric and Route Tag
A route tag is a 32-bit value that is attached to the redistributed routes. Every route that is redistributed will be assigned the same route tag
unless a route map is used (see Section 14-6). OSPF itself does not use the route tag, but you can use the tag value to implement policy
decisions. For example, in Section 14-6, the tag value is used to determine which routes will be redistributed into OSPF based on their tag
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values. This example presents only the mechanics of assigning the tag. Modify the configuration on Router B to redistribute the EIGRP routes
with a tag value of 555.
Router B
router ospf 1
redistribute eigrp 1 metric 66 metric-type 1 subnets tag 555
Verification
The tag value can be verified by examining a particular route in the IP routing table on Router A.
rtrA#show ip route 5.0.0.0
Routing entry for 5.0.0.0/8
Known via "ospf 1", distance 110, metric 1628
Tag 555, type extern 1
Last update from 10.1.1.2 on Serial0/1, 00:03:57 ago
Routing Descriptor Blocks:
* 10.1.1.2, from 2.2.2.2, 00:03:57 ago, via Serial0/1
Route metric is 1628, traffic share count is 1
The tag value can also be verified by inspecting the external routes in the OSPF database on either Router A or B.
rtrA#show ip ospf database external 5.0.0.0
OSPF Router with ID (1.1.1.1) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 313
Options: (No TOS-capability, DC)
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LS Type: AS External Link
Link State ID: 5.0.0.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 8000002A
Checksum: 0x8D02
Length: 36
Network Mask: /8
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 66
Forward Address: 0.0.0.0
External Route Tag: 555
_______________________________________________________________________
rtrB#show ip ospf database external 145.5.0.0
OSPF Router with ID (2.2.2.2) (Process ID 1)
Type-5 AS External Link States
LS age: 373
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 145.5.0.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 8000002A
Checksum: 0x2ECF
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Length: 36
Network Mask: /16
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 66
Forward Address: 0.0.0.0
External Route Tag: 555
Troubleshooting
Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbors command.
Step 1. Verify that the redistribute command is referencing the correct routing process and process number (if applicable).
Step 2. Remember the defaults: metric = 20 (1 for BGP), metric type = 2, tag = 0.
To avoid problems associated with mutual redistribution, either use a distribute list (see Sections 7-5, 7-10, and 7-15) or a route map (see
Section 14-6) to allow only routes that originated in the routing process domain.
For example, if on the same router, EIGRP is redistributed into OSPF and OSPF is redistributed into EIGRP, then OSPF routes will be
redistributed back into OSPF from EIGRP and EIGRP routes will be redistributed back into EIGRP from OSPF. Use a route map or distribute
list to prevent this from occurring.
< Free Open Study >
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< Free Open Study >
14-6 redistribute routing-process process-id route-map route-map-name
Syntax Description:
routing-process— Routing process to redistribute into OSPF. The routing process can be BGP, Connected, EGP, EIGRP, IGRP,
ISIS, ISO-IGRP, Mobile, ODR, OSPF, RIP, or Static.
process-id— The process ID of the routing process (if applicable).
route-map-name— Name of the route map used to control which routes are redistributed or to set the parameters of the
redistributed routes (metric, metric-type, or tag).
Purpose: To control the redistribution of routes learned from another routing process into OSPF. Redistributed routes become OSPF external
type 2 routes by default. The default cost or metric of a redistributed route is 1 for BGP and 20 for all other protocols. This command will
redistribute classful routes into OSPF only if the subnets keyword is not used. There are three general types of classful routes:
A Class A address with an 8-bit mask
A Class B address with a 16-bit mask
A Class C address with a 24-bit mask
You can use the subnets keyword to redistribute all routes. You can also use themetric, metric-type, and tag keywords. These values can
also be set in the route map as shown in the examples covered in this section.
Initial Cisco IOS Software Release: 10.0
Configuration Example: 1 Controlling the Routes to Be Redistributed Based on IP
Address
In Figure 14-3, Router B is receiving six routes from Router C via EIGRP. Three of the EIGRP routes are classful (5.0.0.0/8, 145.5.0.0/16,
205.5.5.0/24) and three are classless (6.0.0.0/12, 146.6.0.0/20, 206.6.6.0/28). For this example, only the classless routes will be redistributed.
Before redistributing the EIGRP routes into OSPF on Router B, configure the routers as shown in the listing that follows.
Figure 14-3. A Route Map Is Needed to Control Which Routes Are Redistributed into OSPF from
EIGRP
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
interface Serial 1
ip address 10.1.1.5 255.255.255.252
!
.
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router eigrp 1
network 10.0.0.0
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Loopback1
ip address 5.5.5.5 255.0.0.0
!
interface Loopback2
ip address 6.6.6.6 255.240.0.0
!
interface Loopback3
ip address 145.5.5.5 255.255.0.0
!
interface Loopback4
ip address 146.6.6.6 255.255.240.0
!
interface Loopback5
ip address 205.5.5.5 255.255.255.0
!
interface Loopback6
.
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ip address 206.6.6.6 255.255.255.240
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
!
router eigrp 1
network 5.0.0.0
network 6.0.0.0
network 10.0.0.0
network 145.5.0.0
network 146.6.0.0
network 205.5.5.0
network 206.6.6.0
no auto-summary
Verify that Routers A and B have established an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
Dead Time Address
1 FULL/ -
00:00:36
10.1.1.2
Interface
Serial0/1
Verify that Routers B and C have formed an EIGRP neighbor relationship.
rtrB#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H Address
Interface Hold Uptime SRTT RTO Q Seq
(sec)
0 10.1.1.6
Se1
(ms)
Cnt Num
11 00:25:42 308 2280 0 4
Verify that Router B is receiving the six EIGRP routes from Router C.
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rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
2.0.0.0/32 is subnetted, 1 subnets
C
D
2.2.2.2 is directly connected, Loopback0
205.5.5.0/24 [90/40640000] via 10.1.1.6, 00:26:25, Serial1
206.6.6.0/28 is subnetted, 1 subnets
D
D
206.6.6.0 [90/40640000] via 10.1.1.6, 00:26:25, Serial1
5.0.0.0/8 [90/40640000] via 10.1.1.6, 00:26:25, Serial1
6.0.0.0/12 is subnetted, 1 subnets
D
D
6.0.0.0 [90/40640000] via 10.1.1.6, 00:26:25, Serial1
145.5.0.0/16 [90/40640000] via 10.1.1.6, 00:26:25, Serial1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
C
10.1.1.4 is directly connected, Serial1
146.6.0.0/20 is subnetted, 1 subnets
D
146.6.0.0 [90/40640000] via 10.1.1.6, 00:26:27, Serial1
Modify the configuration on Router B to redistribute only the classless EIGRP routes into OSPF.
Router B
router ospf 1
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redistribute eigrp 1 subnets route-map control-eigrp
!
access-list 1 permit 6.0.0.0 0.15.255.255
access-list 1 permit 146.6.0.0 0.0.15.255
access-list 1 permit 206.6.6.0 0.0.0.15
access-list 1 permit 10.1.1.4 0.0.0.3
route-map control-eigrp permit 10
match ip address 1
Verification
Verify that only the classless EIGRP routes have been redistributed into OSPF.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
206.6.6.0/28 is subnetted, 1 subnets
O E2
206.6.6.0 [110/20] via 10.1.1.2, 00:02:05, Serial0/1
6.0.0.0/12 is subnetted, 1 subnets
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O E2
6.0.0.0 [110/20] via 10.1.1.2, 00:02:05, Serial0/1
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0/1
146.6.0.0/20 is subnetted, 1 subnets
O E2
146.6.0.0 [110/20] via 10.1.1.2, 00:02:06, Serial0/1
O E2
10.1.1.4 [110/200] via 10.1.1.2, 00:02:06, Serial0/1
Configuration Example: 2 Modifying the Metric of Redistributed Routes Using a
Route Map
In the first configuration example for Figure 14-3, the EIGRP routes were redistributed into OSPF with a default metric of 20. For this
example, modify the configuration on Router B to change the metric of the classful routes to 100 and the metric of the classless routes to 200.
Router B
router ospf 1
redistribute eigrp 1 subnets route-map control-eigrp
!
access-list 1 permit 6.0.0.0 0.15.255.255
access-list 1 permit 146.6.0.0 0.0.15.255
access-list 1 permit 206.6.6.0 0.0.0.15
access-list 1 permit 10.1.1.4 0.0.0.3
route-map control-eigrp permit 10
match ip address 1
set metric 200
!
route-map control-eigrp permit 20
set metric 100
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Verification
Verify that the new metric has been applied to the redistributed EIGRP routes. On Router A you can look at the IP routing table and the
OSPF database.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
O E2 205.5.5.0/24 [110/100] via 10.1.1.2, 00:01:53, Serial0/1
206.6.6.0/28 is subnetted, 1 subnets
O E2
206.6.6.0 [110/200] via 10.1.1.2, 00:01:53, Serial0/1
O E2 5.0.0.0/8 [110/100] via 10.1.1.2, 00:01:53, Serial0/1
6.0.0.0/12 is subnetted, 1 subnets
O E2
6.0.0.0 [110/200] via 10.1.1.2, 00:01:53, Serial0/1
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
O E2 145.5.0.0/16 [110/100] via 10.1.1.2, 00:01:54, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
O E2
10.1.1.0 is directly connected, Serial0/1
10.1.1.4 [110/200] via 10.1.1.2, 00:01:55, Serial0/1
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146.6.0.0/20 is subnetted, 1 subnets
O E2
146.6.0.0 [110/200] via 10.1.1.2, 00:01:55, Serial0/1
rtrA#show ip ospf database external 5.0.0.0
OSPF Router with ID (1.1.1.1) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 254
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 5.0.0.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000002
Checksum: 0x8BB6
Length: 36
Network Mask: /8
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 100
Forward Address: 0.0.0.0
External Route Tag: 0
rtrA#show ip ospf database external 206.6.6.0
OSPF Router with ID (1.1.1.1) (Process ID 1)
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Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 297
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 206.6.6.0 (External Network Number )
Advertising Router: 2.2.2.2
LS Seq Number: 80000003
Checksum: 0x51C4
Length: 36
Network Mask: /28
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 200
Forward Address: 0.0.0.0
External Route Tag: 0
Configuration Example: 3 Modifying the Metric Type of Redistributed Routes Using
a Route Map
In Figure 14-3, configuration example 1 for the redistribute route-map command, the EIGRP routes were redistributed into OSPF with a
default metric type of 2. For this example, modify the configuration on Router B to change the metric type of the classful routes to type 1.
Router B
router ospf 1
redistribute eigrp 1 subnets route-map control-eigrp
network 10.1.1.0 0.0.0.3 area 0
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!
access-list 1 permit 6.0.0.0 0.15.255.255
access-list 1 permit 146.6.0.0 0.0.15.255
access-list 1 permit 206.6.6.0 0.0.0.15
access-list 1 permit
route-map control-eigrp permit 10
match ip address 1
set metric 200
!
route-map control-eigrp permit 20
set metric 100
set metric-type type-1
Verification
Verify that the classful EIGRP routes have been redistributed into OSPF as metric type 1 routes.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
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1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
O E1 205.5.5.0/24 [110/1662] via 10.1.1.2, 00:01:38, Serial0/1
206.6.6.0/28 is subnetted, 1 subnets
O E2
206.6.6.0 [110/200] via 10.1.1.2, 00:01:38, Serial0/1
O E1 5.0.0.0/8 [110/1662] via 10.1.1.2, 00:01:38, Serial0/1
6.0.0.0/12 is subnetted, 1 subnets
O E2
6.0.0.0 [110/200] via 10.1.1.2, 00:01:38, Serial0/1
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
O E1 145.5.0.0/16 [110/1662] via 10.1.1.2, 00:01:39, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
O E2
10.1.1.4 [110/200] via 10.1.1.2, 00:01:41, Serial0/1
146.6.0.0/20 is subnetted, 1 subnets
O E2
146.6.0.0 [110/200] via 10.1.1.2, 00:01:41, Serial0/1
Configuration Example: 4 Modifying the Tag Value of Redistributed Routes Using a
Route Map
Modify the configuration on Router B (see Figure 14-3) to set the tag value for the classless routes to 1 and the classful routes to 2.
Router B
router ospf 1
redistribute eigrp 1 subnets route-map control-eigrp
network 10.1.1.0 0.0.0.3 area 0
!
access-list 1 permit 6.0.0.0 0.15.255.255
access-list 1 permit 146.6.0.0 0.0.15.255
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access-list 1 permit 206.6.6.0 0.0.0.15
access-list 1 permit 10.1.1.4 0.0.0.3
route-map control-eigrp permit 10
match ip address 1
set metric 200
set tag 1
!
route-map control-eigrp permit 20
set metric 100
set metric-type type-1
set tag 2
Verification
Verify that the tags have been set on the redistributed EIGRP routes.
rtrB#show ip ospf database external 5.0.0.0
OSPF Router with ID (2.2.2.2) (Process ID 1)
Type-5 AS External Link States
LS age: 164
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 5.0.0.0 (External Network Number )
Advertising Router: 2.2.2.2
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LS Seq Number: 80000007
Checksum: 0x2299
Length: 36
Network Mask: /8
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 100
Forward Address: 0.0.0.0
External Route Tag: 2
_______________________________________________________________________
rtrA#show ip route 206.6.6.0 255.255.255.240
Routing entry for 206.6.6.0/28
Known via "ospf 1", distance 110, metric 200
Tag 1, type extern 2, forward metric 1562
Last update from 10.1.1.2 on Serial0/1, 00:04:40 ago
Routing Descriptor Blocks:
* 10.1.1.2, from 2.2.2.2, 00:04:40 ago, via Serial0/1
Route metric is 200, traffic share count is 1
Configuration Example: 5 Controlling Route Redistribution Based on Tag Values
In Figure 14-4, Router B is learning six routes via EIGRP. The EIGRP routes are redistributed into OSPF with the classful routes assigned a
tag of 2 and the classless routes a tag of 1. Router A is redistributing the OSPF external routes into RIP-2. The policy is to redistribute only
the classless routes into RIP-2. This can be accomplished using a route map and an IP access list. Because the external routes have been
tagged, a route map can be used that redistributes only routes with a tag value equal to 1. Configure the routers as shown in the listing that
follows the figure. Initially, all OSPF routes will be redistributed into RIP-2 on Router A.
Figure 14-4. A Route Map Can Be Used to Control Route Redistribution Based on the Tag Value
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
bandwidth 64
ip address 10.1.1.9 255.255.255.252
no ip mroute-cache
!
interface Serial0/1
bandwidth 64
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
!
router rip
version 2
.
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redistribute ospf 1 metric 1
passive-interface Serial0/1
network 10.0.0.0
no auto-summary
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
bandwidth 64
ip address 10.1.1.2 255.255.255.252
no ip directed-broadcast
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
!
router eigrp 1
network 10.0.0.0
!
router ospf 1
redistribute eigrp 1 subnets route-map set-tags
network 10.1.1.0 0.0.0.3 area 0
!
.
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access-list 1 permit 6.0.0.0 0.15.255.255
access-list 1 permit 146.6.0.0 0.0.15.255
access-list 1 permit 206.6.6.0 0.0.0.15
access-list 1 permit 10.1.1.4 0.0.0.3
route-map set-tags permit 10
match ip address 1
set tag 1
!
route-map set-tags permit 20
set tag 2
_______________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Loopback1
ip address 5.5.5.5 255.0.0.0
!
interface Loopback2
ip address 6.6.6.6 255.240.0.0
!
interface Loopback3
ip address 145.5.5.5 255.255.0.0
!
interface Loopback4
ip address 146.6.6.6 255.255.240.0
.
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!
interface Loopback5
ip address 205.5.5.5 255.255.255.0
!
interface Loopback6
ip address 206.6.6.6 255.255.255.240
!
interface Serial0
bandwidth 64
ip address 10.1.1.6 255.255.255.252
no ip directed-broadcast
!
router eigrp 1
network 5.0.0.0
network 6.0.0.0
network 10.0.0.0
network 145.5.0.0
network 146.6.0.0
network 205.5.5.0
network 206.6.6.0
no auto-summary
_______________________________________________________________________
Router D
interface Serial0/1
ip address 10.1.1.10 255.255.255.252
clockrate 64000
!
.
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router rip
version 2
network 10.0.0.0
Verify that Router D is receiving the redistributed OSPF routes from Router A.
rtrD#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
R
205.5.5.0/24 [120/1] via 10.1.1.9, 00:00:01, Serial0/1
206.6.6.0/28 is subnetted, 1 subnets
R
R
206.6.6.0 [120/1] via 10.1.1.9, 00:00:02, Serial0/1
5.0.0.0/8 [120/1] via 10.1.1.9, 00:00:02, Serial0/1
6.0.0.0/12 is subnetted, 1 subnets
R
6.0.0.0 [120/1] via 10.1.1.9, 00:00:02, Serial0/1
172.16.0.0/24 is subnetted, 1 subnets
R
172.16.1.0 [120/1] via 10.1.1.9, 00:00:02, Serial0/1
R
145.5.0.0/16 [120/1] via 10.1.1.9, 00:00:02, Serial0/1
10.0.0.0/30 is subnetted, 3 subnets
C
10.1.1.8 is directly connected, Serial0/1
R
10.1.1.0 [120/1] via 10.1.1.9, 00:00:02, Serial0/1
R
10.1.1.4 [120/1] via 10.1.1.9, 00:00:02, Serial0/1
146.6.0.0/20 is subnetted, 1 subnets
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R
146.6.0.0 [120/1] via 10.1.1.9, 00:00:05, Serial0/1
Modify the configuration on Router A so that only OSPF routes with a tag value of 1 get redistributed into RIP.
Router A
router rip
version 2
redistribute ospf 1 metric 1 route-map check-tags
passive-interface Serial0/1
network 10.0.0.0
no auto-summary
!
route-map check-tags permit 10
match tag 1
Verification
Verify that the only OSPF routes redistributed into RIP on Router A are those routes with a tag value of 1.
rtrD#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
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206.6.6.0/28 is subnetted, 1 subnets
R
206.6.6.0 [120/1] via 10.1.1.9, 00:00:01, Serial0/1
6.0.0.0/12 is subnetted, 1 subnets
R
6.0.0.0 [120/1] via 10.1.1.9, 00:00:02, Serial0/1
10.0.0.0/30 is subnetted, 3 subnets
C
10.1.1.8 is directly connected, Serial0/1
R
10.1.1.0 [120/1] via 10.1.1.9, 00:00:02, Serial0/1
R
10.1.1.4 [120/1] via 10.1.1.9, 00:00:02, Serial0/1
146.6.0.0/20 is subnetted, 1 subnets
R
146.6.0.0 [120/1] via 10.1.1.9, 00:00:02, Serial0/1
Troubleshooting
Step 1. Verify that the routes have been assigned the proper tags by using the commandshow ip ospf database external or the
command show ip route ip-address mask.
Step 2. Verify that the redistribute command is referencing the correct routing process and process number (if applicable).
Step 3. Verify that the redistribute command is referencing the correct route map name.
Step 4. Verify the syntax and logic of the route map.
To avoid problems associated with mutual redistribution, use a distribute list (see Sections 7-5, 7-10, and 7-15) or a route map to allow only
routes that have originated in the routing process domain. For example, if EIGRP is redistributed into OSPF and OSPF is redistributed into
EIGRP on the same router, then OSPF routes will be redistributed back into OSPF from EIGRP and EIGRP routes will be redistributed back
into EIGRP from OSPF. Using a route map or distribute list will prevent this from occurring.
< Free Open Study >
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< Free Open Study >
Chapter 15. Controlling the OSPF Router ID
Section 15-1. router-id ip-address
< Free Open Study >
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< Free Open Study >
15-1 router-id ip-address
Syntax Description:
ip-address— The IP address that is to be used as the OSPF router ID.
Purpose: To configure the OSPF router ID. The default OSPF router ID is the numerically highest IP address of any loopback interface that
has been configured on the router. If no loopback interfaces have been configured, then the OSPF router ID is the numerically highest IP
address of any active interface. The router ID is a component of every OSPF exchange, including Hello packets and link-state advertisements
(LSAs). For multiaccess networks, the OSPF router ID is used in the election of the Designated Router (DR). It is desirable to have an OSPF
router ID that does not change. If loopback interfaces are not configured on an OSPF router, then the command router-id should be used to
establish a stable OSPF router ID
Initial Cisco IOS Software Release: 12.0(1)T
Configuration Example: OSPF Router ID Selection
In Figure 15-1, Routers A and B are OSPF neighbors. Router A has two physical interfaces configured, Ethernet 0/0 and Serial 0/1. Initially,
interface Ethernet 0/0 is in the shutdown state, so OSPF will choose the router ID as the IP address assigned to Serial 0/1 because it is the
only remaining active interface. Configure Routers A and B as shown in the listing that follows the figure.
Figure 15-1. OSPF Router ID
.
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Router A
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
shutdown
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
.
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!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
To determine the OSPF router ID of Router A, use the show ip ospf command on Router A or theshow ip ospf neighbor command on
Router B.
rtrA#show ip ospf
Routing Process "ospf 1" with ID 10.1.1.1 and Domain ID 0.0.0.1
Supports only single TOS(TOS0) routes
Supports opaque LSA
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 8. Checksum Sum 0x3BAD0
Number of opaque AS LSA 0. Checksum Sum 0x0
Number of DCbitless external and opaque AS LSA 0
Number of DoNotAge external and opaque AS LSA 0
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
External flood list length 0
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Area BACKBONE(0)
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 2 times
Area ranges are
Number of LSA 3. Checksum Sum 0x23124
Number of opaque link LSA 0. Checksum Sum 0x0
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
10.1.1.1
Pri State
1 FULL/ -
Dead Time Address
00:00:34
10.1.1.1
Interface
Serial0
Enable the Ethernet 0/0 interface on Router A and observe the effect on the OSPF router ID.
Router A
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
no shutdown
Verify that interface E0/0 is up.
rtrA#show ip interface brief
Interface
Ethernet0/0
IP-Address
172.16.1.1
OK? Method Status
YES NVRAM up
Protocol
up
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Serial0/0
unassigned
Ethernet0/1
Serial0/1
YES manual administratively down down
unassigned
10.1.1.1
YES NVRAM administratively down down
YES NVRAM up
up
View the OSPF router ID on Router A.
rtrA#show ip ospf
Routing Process "ospf 1" with ID 10.1.1.1 and Domain ID 0.0.0.1
Supports only single TOS(TOS0) routes
Supports opaque LSA
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 8. Checksum Sum 0x3AED6
Number of opaque AS LSA 0. Checksum Sum 0x0
Number of DCbitless external and opaque AS LSA 0
Number of DoNotAge external and opaque AS LSA 0
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
External flood list length 0
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 2 times
Area ranges are
Number of LSA 3. Checksum Sum 0x23124
Number of opaque link LSA 0. Checksum Sum 0x0
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
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Flood list length 0
The OSPF router ID has not changed, even though the IP address on Ethernet 0/0 is higher than the IP address on Serial 0/1. This is a
stability feature of OSPF. The router ID will not change until you reload the router or remove the OSPF configuration and then reconfigure
OSPF. Remove the OSPF process on Router A using the command no router ospf 1 in configuration mode. Reconfigure the OSPF process
on Router A using the previous listing. Has the OSPF router ID changed?
rtrA#show ip ospf
Routing Process "ospf 1" with ID 172.16.1.1 and Domain ID 0.0.0.1
Supports only single TOS(TOS0) routes
Supports opaque LSA
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 8. Checksum Sum 0x3AED6
Number of opaque AS LSA 0. Checksum Sum 0x0
Number of DCbitless external and opaque AS LSA 0
Number of DoNotAge external and opaque AS LSA 0
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
External flood list length 0
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 1 times
Area ranges are
Number of LSA 4. Checksum Sum 0x27A6A
Number of opaque link LSA 0. Checksum Sum 0x0
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
The OSPF router ID has changed. Now add a loopback interface on Router A with an IP address of 1.1.1.1/32. Even though this IP address
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is lower than the IP address assigned to Ethernet 0/0 and Serial 0/1, OSPF will use the loopback IP address as the router ID. Of course,
OSPF will use the loopback address as the router ID only if the router is reloaded and the OSPF process is cleared or if the OSPF process is
removed and then reconfigured. So remove and reconfigure the OSPF process on Router A and display the OSPF router ID.
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
Now that the loopback interface has been added, remove and re-apply the OSPF configuration, clear the OSPF process, or simply save and
reload the router.
rtrA#show ip ospf
Routing Process "ospf 1" with ID 1.1.1.1 and Domain ID 0.0.0.1
Supports only single TOS(TOS0) routes
Supports opaque LSA
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 8. Checksum Sum 0x3AED6
Number of opaque AS LSA 0. Checksum Sum 0x0
Number of DCbitless external and opaque AS LSA 0
Number of DoNotAge external and opaque AS LSA 0
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
External flood list length 0
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 2 times
Area ranges are
Number of LSA 4. Checksum Sum 0x1FF72
Number of opaque link LSA 0. Checksum Sum 0x0
Number of DCbitless LSA 0
Number of indication LSA 0
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Number of DoNotAge LSA 0
Flood list length 0
Finally, use the router-id command to change the OSPF router ID on Router A to 1.2.3.4.
Router A
router ospf 1
router-id 1.2.3.4
network 10.1.1.0 0.0.0.3 area 0
When the command router-id is entered, you should observe the router giving you some friendly advice:
rtrA(config-router)#router-id 1.2.3.4
Reload or use "clear ip ospf process" command, for this to take effect
Heed the router's advice and clear the OSPF process on Router A.
Verification
Verify that the OSPF process ID on Router A has been changed to 1.2.3.4.
rtrA#clear ip ospf process 1
rtrA#rtrA# show ip ospf
Routing Process "ospf 1" with ID 1.2.3.4 and Domain ID 0.0.0.1
Supports only single TOS(TOS0) routes
Supports opaque LSA
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 16. Checksum Sum 0x75DAC
Number of opaque AS LSA 0. Checksum Sum 0x0
Number of DCbitless external and opaque AS LSA 0
Number of DoNotAge external and opaque AS LSA 0
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Number of areas in this router is 1. 1 normal 0 stub 0 nssa
External flood list length 0
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 4 times
Area ranges are
Number of LSA 7. Checksum Sum 0x3BFF9
Number of opaque link LSA 0. Checksum Sum 0x0
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
Troubleshooting
Step 1. The only thing that can go wrong with this command is forgetting to clear the OSPF process using the EXEC command
clear ip ospf process.
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Chapter 16. Summarizing External Routes
Section 16-1. summary-address ip-address mask
Section 16-2. summary-address ip-address mask not-advertise
Section 16-3. summary-address ip-address mask tag value
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16-1 summary-address ip-address mask
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16-2 summary-address ip-address mask not-advertise
Syntax Description:
ip-address— IP address of the summary route.
mask— Subnet mask used to generate the summary.
Purpose: OSPF can summarize routes that have been redistributed into OSPF. The summary can be applied to routes redistributed from a
dynamic routing protocol, static routes, and connected routes. The router performing the redistribution is called an Autonomous System
Boundary Router (ASBR). The summary-address command can be used on an ASBR or an Area Border Router (ABR). When used on an
ABR, only external OSPF routes can be summarized. Using the not-advertise keyword suppresses the advertisement of the summary route
by the ASBR or ABR.
Initial Cisco IOS Software Release: 10.0
Configuration Example 1: Summarizing Routes Redistributed into OSPF
In Figure 16-1, Router B will summarize the four networks that are being redistributed into OSPF. For this example we will simulate four
networks on Router B using loopback interfaces. These four networks will then be redistributed into OSPF. The router performing the
redistribution is an ASBR.
Figure 16-1. An ASBR Can Summarize Redistributed Routes into OSPF
Router A
.
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interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Loopback1
ip address 156.26.32.1 255.255.255.240
!
interface Loopback2
ip address 156.26.32.17 255.255.255.240
no ip directed-broadcast
!
interface Loopback3
ip address 156.26.32.33 255.255.255.240
!
interface Loopback4
ip address 156.26.32.49 255.255.255.240
.
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!
interface Serial0
ip address 10.1.1.2 255.255.255.252
no ip directed-broadcast
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
redistribute connected subnets
Before summarizing the routes, inspect the IP routing table on Router A to verify that the four networks are being advertised.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O E2
2.2.2.2 [110/20] via 10.1.1.2, 00:03:17, Serial0/1
156.26.0.0/28 is subnetted, 4 subnets
O E2
156.26.32.32 [110/20] via 10.1.1.2, 00:03:17, Serial0/1
O E2
156.26.32.48 [110/20] via 10.1.1.2, 00:03:17, Serial0/1
O E2
156.26.32.0 [110/20] via 10.1.1.2, 00:02:52, Serial0/1
O E2
156.26.32.16 [110/20] via 10.1.1.2, 00:03:17, Serial0/1
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10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0/1
A 26-bit subnet mask is required to summarize the four loopback addresses being advertised by Router B. Modify the configuration on Router
B in order to summarize the four loopback addresses.
Router B
router ospf 1
summary-address 156.26.32.0 255.255.255.192
network 10.1.1.0 0.0.0.3 area 0
Verification
Verify that the four loopback networks have been summarized by Router B by inspecting the IP routing table on Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O E2
2.2.2.2 [110/20] via 10.1.1.2, 00:05:36, Serial0/1
156.26.0.0/26 is subnetted, 1 subnets
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O E2
156.26.32.0 [110/20] via 10.1.1.2, 00:00:21, Serial0/1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/1
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. The summary-address command will only work on an OSPF ASBR.
Step 3. Verify that you are using the correct IP address and mask with the
summary-address command.
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16-3 summary-address ip-address mask tag value
Syntax Description:
ip-address— IP address of the summary route.
mask— Subnet mask used to generate the summary.
tag— The summary route will be tagged with this value. The range of values is 0 to 4,294,967,295.
Purpose: OSPF can summarize routes that have been redistributed into OSPF. The summary can be applied to routes redistributed from a
dynamic routing protocol, static, or connected routes. The router performing the redistribution is an ASBR. The summary-address command
can only be used on an ASBR. Using the not-advertise keyword will suppress the advertisement of the summary route by the ASBR. Using a
tag allows routing policies to be based on the tag value instead of the IP address.
Initial Cisco IOS Software Release: 10.0
Configuration Example 1: Attaching a Tag to Summarized Routes Created on an
ASBR
In Figure 16-2, Router B will summarize the four networks that are being redistributed into OSPF into two summaries. Each summary will be
given a different tag value. This example simulates four networks on Router B using loopback interfaces. These four networks will then be
redistributed into OSPF. The router performing the redistribution is an ASBR.
Figure 16-2. Tagging Redistributed Routes
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 1
_______________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Loopback1
ip address 156.26.32.1 255.255.255.240
!
interface Loopback2
ip address 156.26.32.17 255.255.255.240
no ip directed-broadcast
!
interface Loopback3
ip address 156.26.32.33 255.255.255.240
!
interface Loopback4
.
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ip address 156.26.32.49 255.255.255.240
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
no ip directed-broadcast
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 1
redistribute connected subnets
Before summarizing the routes, inspect the IP routing table on Router A to verify that the four networks are being advertised.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O E2
2.2.2.2 [110/20] via 10.1.1.2, 00:03:17, Serial0/1
156.26.0.0/28 is subnetted, 4 subnets
O E2
156.26.32.32 [110/20] via 10.1.1.2, 00:03:17, Serial0/1
O E2
156.26.32.48 [110/20] via 10.1.1.2, 00:03:17, Serial0/1
O E2
156.26.32.0 [110/20] via 10.1.1.2, 00:02:52, Serial0/1
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O E2
156.26.32.16 [110/20] via 10.1.1.2, 00:03:17, Serial0/1
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0/1
A 27-bit subnet mask will be used to summarize the four loopback addresses being advertised by Router B into two summaries. Modify the
configuration on Router B in order to summarize the four loopback addresses into two summaries.
Router B
router ospf 1
summary-address 156.26.32.0 255.255.255.224 tag 88
summary-address 156.26.32.32 255.255.255.224 tag 42
network 10.1.1.0 0.0.0.3 area 1
Verification
Verify that Router B has summarized the four loopback networks into two summaries by inspecting the IP routing table on Router A.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
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O E2
2.2.2.2 [110/20] via 10.1.1.2, 00:36:53, Serial0/1
156.26.0.0/27 is subnetted, 2 subnets
O E2
156.26.32.32 [110/20] via 10.1.1.2, 00:01:04, Serial0/1
O E2
156.26.32.0 [110/20] via 10.1.1.2, 00:01:09, Serial0/1
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0/1
Verify that the summaries have been tagged with the proper values.
rtrA#show ip route 156.26.32.0
Routing entry for 156.26.32.0/27
Known via "ospf 1", distance 110, metric 20
Tag 88, type extern 2, forward metric 64
Redistributing via ospf 1
Last update from 10.1.1.2 on Serial0/1, 00:02:43 ago
Routing Descriptor Blocks:
* 10.1.1.2, from 2.2.2.2, 00:02:43 ago, via Serial0/1
Route metric is 20, traffic share count is 1
rtrA#show ip route 156.26.32.32
Routing entry for 156.26.32.32/27
Known via "ospf 1", distance 110, metric 20
Tag 42, type extern 2, forward metric 64
Redistributing via ospf 1
Last update from 10.1.1.2 on Serial0/1, 00:02:46 ago
Routing Descriptor Blocks:
* 10.1.1.2, from 2.2.2.2, 00:02:46 ago, via Serial0/1
Route metric is 20, traffic share count is 1
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Configuration Example 2: Using the Tag Value to Control Route Redistribution
In Figure 16-2, Routers A and C are running RIP Version 2. Redistribute OSPF into RIP on Router A, but allow only those routes with a tag
value of 88 to be redistributed. Add the configuration for Router C and modify the configuration for Router A as follows:
Router A
interface Serial0/0
ip address 10.1.1.9 255.255.255.252
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 1
!
router rip
version 2
redistribute ospf 1 metric 1 route-map checktags
passive-interface Serial0/1
network 10.0.0.0
no auto-summary
!
route-map checktags permit 10
match tag 88
_______________________________________________________________________
Router C
interface Serial1
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ip address 10.1.1.10 255.255.255.252
clockrate 64000
!
router rip
version 2
network 10.0.0.0
Verification
Verify that the only routes that were redistributed into RIP on Router A are routes with a tag value of 88.
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
156.26.0.0/27 is subnetted, 1 subnets
R
156.26.32.0 [120/1] via 10.1.1.9, 00:00:25, Serial1
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.8 is directly connected, Serial1
R
10.1.1.0 [120/1] via 10.1.1.9, 00:00:25, Serial1
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Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. The summary-address command will only work on an OSPF ASBR.
Step 3. Verify that you are using the correct IP address and mask with the summary-address command.
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Chapter 17. OSPF Timers
Section 17-1. timers lsa-group-pacing seconds
Section 17-2. timers spf delay interval
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17-1 timers lsa-group-pacing seconds
Syntax Description:
seconds— The minimum time between sending groups of timer-expired link-state advertisements (LSAs). The range of values is
10 to 1800 seconds. The default time is 240 seconds.
Purpose: Each OSPF LSA has an age parameter indicating if it is still valid. When the age of an LSA is equal to the maximum age (1 hour),
the LSA is discarded. In order to refresh LSAs, the originating router will send the LSAs every 30 minutes. This periodic refresh process
prevents the LSAs from reaching the maximum age and therefore prevents the LSAs from being discarded. LSA refreshing occurs even if the
LSA has not changed. In addition, a checksum is performed on all LSAs every 10 minutes. If an LSA is discarded, this means that the
information it contained is no longer in the OSPF database. Routes based on the discarded LSA will be removed from the IP routing table.
Before the LSA group-pacing feature was available, refreshing was performed using a single timer. Another timer was used for the checksum
and aging function. Every 30 minutes an OSPF router would scan the entire database and refresh every LSA that was originated by the
router. This process was CPU intensive because every LSA, after being refreshed, would have identical age timers. After the LSA age timers
were refreshed, the router would transmit the LSAs to neighboring OSPF routers. This resulted in periodically high network usage for large
OSPF networks. LSA pacing was developed to solve the problem of periodic high CPU usage and network utilization.
Each LSA now has its own timers and LSAs are refreshed independently of other LSAs at random intervals. This paces the refreshing and
transmitting of LSAs, which spreads out the CPU and network loads. For most situations the default pacing interval is sufficient. Decreasing
the pacing interval may be of benefit for large OSPF networks.
Initial Cisco IOS Software Release: 11.3 (AA)
Configuration Example: Modifying the LSA Group Pacing
LSA group pacing can be modified with the timers lsa-group-pacing router configuration command as shown in the following listing.
Router A
router ospf 1
log-adjacency-changes
timers lsa-group-pacing 180
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
Verification
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The LSA pacing interval can be verified with the show ip ospf timer lsa-groupcommand.
rtrA#show ip ospf timer lsa-group
OSPF Router with ID (1.1.1.1) (Process ID 1)
Group size 6, Head 0, Search Index 4, Interval 180 sec
Next update due in 00:00:22
Current time 134571
Index 0 Timestamp 134593
Index 1 Timestamp 134777
Index 2 Timestamp 134971
Index 3 Timestamp 135153
Index 4 Timestamp 135351
Index 5 Timestamp 135544
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17-2 timers spf delay interval
Syntax Description:
delay— The delay, in seconds, between when a topology change is received and theshortest path first (SPF) calculation begins.
The range of values is 0 to 4,294,967,295 seconds. The default time is 5 seconds.
interval— The interval, in seconds, between successive SPF calculations. The range of values is 0 to 4,294,967,295 seconds. The
default time is 10 seconds.
Purpose: When a change in the OSPF topology occurs, the OSPF process will run an SPF calculation. Thedelay parameter of this command
sets the delay time between receipt of an OSPF topology change and the start of the SPF calculation. The interval parameter is the wait time
between two SPF calculations. If the SPF calculation is being executed fre-quently, there may be a flapping interface in the network, causing
OSPF to send frequent topology changes.
Initial Cisco IOS Software Release: 10.3
Configuration Example: Modifying the LSA Group Pacing
The SPF timers can be modified with the timers spf router configuration command, as shown in the following listing.
Router A
router ospf 1
log-adjacency-changes
timers spf 8 16
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
Verification
The SPF timer values can be verified with the show ip ospf command.
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rtrA#show ip ospf
Routing Process "ospf 1" with ID 1.1.1.1 and Domain ID 0.0.0.1
Supports only single TOS(TOS0) routes
Supports opaque LSA
It is an area border router
SPF schedule delay 8 secs, Hold time between two SPFs 16 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of opaque AS LSA 0. Checksum Sum 0x0
Number of DCbitless external and opaque AS LSA 0
Number of DoNotAge external and opaque AS LSA 0
Number of areas in this router is 2. 2 normal 0 stub 0 nssa
External flood list length 0
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 24 times
Area ranges are
Number of LSA 16. Checksum Sum 0x8759C
Number of opaque link LSA 0. Checksum Sum 0x0
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
Area 1
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 12 times
Area ranges are
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Number of LSA 3. Checksum Sum 0x14E8B
Number of opaque link LSA 0. Checksum Sum 0x0
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
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Chapter 18. Traffic Sharing
Section 18-1. traffic-share min across-interfaces
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18-1 traffic-share min across-interfaces
Syntax Description:
This command has no arguments.
Purpose: This command is used with IGRP and EIGRP to support unequal-cost load balancing. This command appears as an option under
OSPF but the command does not apply to OSPF.
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Chapter 19. Interface Configuration Commands
Section 19-1. ip ospf authentication
Section 19-2. ip ospf authentication authentication-key password
Section 19-3. ip ospf authentication message-digest
Section 19-4. ip ospf authentication null
Section 19-5. ip ospf cost cost
Section 19-6. ip ospf database-filter all out
Section 19-7. ip ospf dead-interval seconds
Section 19-8. ip ospf demand-circuit
Section 19-9. ip ospf flood-reduction
Section 19-10. ip ospf hello-interval seconds
Section 19-11. ip ospf message-digest-key key-id md5 password
Section 19-12. ip ospf mtu-ignore
Section 19-13. ip ospf network broadcast
Section 19-14. ip ospf network non-broadcast
Section 19-15. ip ospf network point-to-multipoint
Section 19-16. ip ospf network point-to-multipoint non-broadcast
Section 19-17. ip ospf network point-to-point
Section 19-18. ip ospf priority priority
Section 19-19. ip ospf retransmit-interval seconds
Section 19-20. ip ospf transmit-delay seconds
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19-1 ip ospf authentication
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19-2 ip ospf authentication authentication-key password
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19-3 ip ospf authentication message-digest
Command 19-3 requires the use of command 19-11 (ip ospf message-digest-key key-id md5 password).
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19-4 ip ospf authentication null
Syntax Description:
key-id— Key used to identify the password. Range of values is 1 to 255. Both ends of a link must use the same key and password.
password— Password to be used for authentication in the selected area on the selected interface. The password is an
alphanumeric string from 1 to 8 characters.
Purpose: In IOS versions before 12.0, if authentication was enabled for an OSPF area, then all interfaces in the area had to be configured
with the same authentication type. This command allows the configuration of authentication on an interface that is different from the
authentication type being used in the area.
Initial Cisco IOS Software Release: 12.0
Configuration Example 1: Simple Password Authentication on an OSPF Network
In Figure 19-1, the serial link in Area 0 is not using authentication, but simple password authentication is employed on the Ethernet network.
Start by configuring Routers A and B as shown in the following listing.
Figure 19-1. OSPF Authentication Can Be Configured on Individual Networks
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 172.16.1.0 0.0.0.255 area 0
network 1.1.1.1 0.0.0.0 area 1
_________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
.
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router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 172.16.1.0 0.0.0.255 area 0
network 2.2.2.2 0.0.0.0 area 2
Verify that Routers A and B have established a FULL OSPF neighbor relationship over the serial and Ethernet networks.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
2.2.2.2
1 FULL/BDR
2.2.2.2
1 FULL/ -
Dead Time Address
00:00:32
00:00:35
Interface
172.16.1.2
10.1.1.2
Ethernet0/0
Serial0/1
Verify that authentication is not being used in Area 0.
rtrA#show ip ospf
Routing Process "ospf 1" with ID 1.1.1.1
Supports only single TOS(TOS0) routes
It is an area border router
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 2 normal 0 stub 0 nssa
Area BACKBONE(0)
Number of interfaces in this area is 2
Area has no authentication
SPF algorithm executed 8 times
Area ranges are
Number of LSA 5. Checksum Sum 0x23C8C
.
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Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Area 1
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 5 times
Area ranges are
Number of LSA 4. Checksum Sum 0x22672
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Modify the configurations on Routers A and B so that simple password authentication is used on the Ethernet network. Use the clear-text
password laura.
Router A
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
ip ospf authentication
ip ospf authentication-key laura
_________________________________________________________________
Router B
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
ip ospf authentication
ip ospf authentication-key laura
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Verification
Verify that Routers A and B have a FULL OSPF neighbor relationship over both the serial and Ethernet networks.
rtrB#show ip ospf neighbor
Neighbor ID
Pri State
1.1.1.1
1 FULL/BDR
1.1.1.1
1 FULL/ -
Dead Time Address
00:00:36
00:00:30
Interface
172.16.1.1
10.1.1.1
Ethernet0
Serial0
Configuration Example 2: MD5 Authentication on an OSPF Network
Change the authentication type on the Ethernet network to MD5. Use the passwordlaura and a key ID of1.
Router A
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 laura
_________________________________________________________________
Router B
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 laura
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Verification
Verify that message digest authentication is being used on the Ethernet network.
rtrA#show ip ospf interface Ethernet0/0
Ethernet0/0 is up, line protocol is up
Internet Address 172.16.1.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State BDR, Priority 1
Designated Router (ID) 2.2.2.2, Interface address 172.16.1.2
Backup Designated router (ID) 1.1.1.1, Interface address 172.16.1.1
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2 (Designated Router)
Suppress hello for 0 neighbor(s)
Message digest authentication enabled
Youngest key id is 1
Also, verify that Routers A and B have established FULL OSPF neighbor relationships over the serial and Ethernet networks.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
2.2.2.2
1 FULL/DR
2.2.2.2
1 FULL/ -
Dead Time Address
00:00:39
00:00:32
172.16.1.2
10.1.1.2
Interface
Ethernet0/0
Serial0/1
Configuration Example 3: Changing Keys and Passwords
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For additional security, you may choose to periodically change the key and password. With clear-text authentication, when you change
passwords there will be a loss of OSPF connectivity from the time you change the password on one router's interface until you change the
password on the remaining interfaces attached to the network. With MD5 authentication, you can configure a new key and password on an
interface while leaving the old key and password in place. The old key and password will continue to be used until the new key and password
are configured on the other interfaces attached to the network. Modify the key and password on the Ethernet network between Routers A and
B. First add a new key and password to Router A in order to observe the behavior when the new key and password have been configured on
only one interface.
Router A
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 laura
ip ospf message-digest-key 2 md5 elvis
Examine the effect of adding a new key and password on only one interface.
rtrA#show ip ospf interface e0/0
Ethernet0/0 is up, line protocol is up
Internet Address 172.16.1.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State BDR, Priority 1
Designated Router (ID) 2.2.2.2, Interface address 172.16.1.2
Backup Designated router (ID) 1.1.1.1, Interface address 172.16.1.1
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:07
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2 (Designated Router)
Suppress hello for 0 neighbor(s)
Message digest authentication enabled
Youngest key id is 2
Rollover in progress, 1 neighbor(s) using the old key(s):
key id 1
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Notice that both keys are being used for authentication. Configure the new key and password on Router B while leaving the old key and
password in place.
Router B
interface Ethernet0/0
ip address 172.16.1.2 255.255.255.0
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 laura
ip ospf message-digest-key 2 md5 elvis
Verification
Verify that Router B is now using the new key and password.
rtrB#show ip ospf interface ethernet 0
Ethernet0 is up, line protocol is up
Internet Address 172.16.1.2/24, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 2.2.2.2, Interface address 172.16.1.2
Backup Designated router (ID) 1.1.1.1, Interface address 172.16.1.1
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:05
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1 (Backup Designated Router)
Suppress hello for 0 neighbor(s)
Message digest authentication enabled
Youngest key id is 2
You can now remove the old key and password from Routers A and B.
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Router A
interface Ethernet0/0
no ip ospf message-digest-key 1
_________________________________________________________________
Router B
interface Ethernet0
no ip ospf message-digest-key 1
Configuration Example 4: Null Authentication
Prior to Cisco IOS Software Release 12.0, if authentication was configured for an OSPF area then the same authentication type had to be
enabled on all interfaces in the area. In Cisco IOS Software Release 12.0 and later, if authentication is not required on an interface, NULL
authentication can be employed to override the authentication that has been con-figured for the area. Configure the routers in Figure 19-1
with simple password authentication in Area 0 and on the Ethernet network. Do not configure authentication on the serial link.
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
ip ospf authentication-key laura
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
ip ospf authentication null
clockrate 64000
!
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router ospf 1
area 0 authentication
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
network 172.16.1.0 0.0.0.255 area 0
_________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
ip add 172.16.1.2 255.255.255.0
ip ospf authentication-key laura
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
ip ospf authentication null
!
router ospf 1
area 0 authentication
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.3 area 0
network 172.16.1.0 0.0.0.255 area 0
Verification
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Verify that Routers A and B have formed FULL OSPF neighbor relationships over the Ethernet and serial networks.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
2.2.2.2
1 FULL/DR
2.2.2.2
1 FULL/ -
Dead Time Address
00:00:31
00:00:35
Interface
172.16.1.2
10.1.1.2
Ethernet0/0
Serial0/1
Troubleshooting
Step 1. If using simple password authentication, verify that the same password is being used on every interface attached to the
network.
Step 2. If using MD5 authentication, verify that the same key and password are being used on every interface attached to the
network.
Step 3. Mismatched keys and passwords can be found by enabling OSPF debugging. A sample session is shown in the following
output where simple password authentication is used and the passwords assigned to the interfaces do not match.
rtrA#debug ip ospf adj
OSPF adjacency events debugging is on
rtrA#
00:47:55: OSPF: Rcv pkt from 172.16.1.2, Ethernet0/0 :
Mismatch Authentication Key - Clear Text
00:47:55: OSPF: Rcv hello from 2.2.2.2 area 0 from Serial0/1 10.1.1.2
00:47:55: OSPF: End of hello processing
The following output is for message digest authentication when the keys match but the passwords do not.
rtrB#debug ip ospf adj
OSPF adjacency events debugging is on
rtrB#
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00:51:37: OSPF: Rcv pkt from 10.1.1.1, Serial0 : Mismatch Authentication Key –
Message Digest Key 1
The final debug output is for message digest authentication with a key mismatch. One interface has been configured with a key ID of 1 and
the other interface has a key ID of 2.
rtrA#debug ip ospf adj
OSPF adjacency events debugging is on
rtrA#
00:53:31: OSPF: Send with youngest Key 1
00:53:36: OSPF: Rcv pkt from 10.1.1.2, Serial0/1 : Mismatch Authentication Key No message digest key 2 on interface
00:53:41: OSPF: Send with youngest Key 1
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19-5 ip ospf cost cost
Syntax Description:
cost— OSPF metric to use for the interface. The range of values is 1 to 65535.
Purpose: By default OSPF calculates the cost of an interface by dividing the bandwidth of the interface into 100 million.Table 19-1 lists the
costs for various interface types. Using the default value when your network has interfaces with a bandwidth greater than 100,000,000 bps is
not recommended. OSPF will not be able to differentiate between a 100-Mbps interface and an interface with a bandwidth greater than 100
Mbps. The ip ospf cost command enables you to change the OSPF cost for an interface. The default reference value used to calculate the
OSPF cost of an interface can be modified using the command auto-cost reference-bandwidth (see Section 3-1).
Table 19-1. Default OSPF Cost for Selected Interfaces
Interface Type
Interface Bandwidth in Bits per Second (bps)
OSPF Cost
Serial
56,000
1785
T1
1,544,000
64
Ethernet
10,000,000
10
Fast Ethernet
100,000,000
1
Gigabit Ethernet
1,000,000,000
1
OC48
2,500,000,000
1
Initial Cisco IOS Software Release: 10.0
Configuration Example: Modifying the OSPF Cost of an Interface
In Figure 19-2, the Ethernet network has an OSPF cost of 10. Configure Routers A and B as shown and verify the OSPF cost of the interface.
Figure 19-2. The Default Cost of an OSPF Interface Is 100,000,000 Divided by the Interface
Bandwidth
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 172.16.1.0 0.0.0.255 area 0
network 1.1.1.1 0.0.0.0 area 1
_______________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0
.
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ip address 172.16.1.2 255.255.255.0
!
router ospf 1
network 172.16.1.0 0.0.0.255 area 0
network 2.2.2.2 0.0.0.0 area 2
The OSPF cost of an interface can be found by using the show ip ospf interface command.
rtrA#show ip ospf interface Ethernet0/0
Ethernet0/0 is up, line protocol is up
Internet Address 172.16.1.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 1.1.1.1, Interface address 172.16.1.1
No backup designated router on this network
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:06
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
The cost to reach the loopback interface is the cost of the Ethernet interface plus the cost of the loopback interface, as shown here.
rtrA#show ip ospf interface loopback 0
Loopback0 is up, line protocol is up
Internet Address 1.1.1.1/32, Area 1
Process ID 1, Router ID 1.1.1.1, Network Type LOOPBACK, Cost: 1
Loopback interface is treated as a stub Host
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
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N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/11] via 172.16.1.2, 00:02:43, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0/1
Modify the configuration on Routers A and B to change the cost of the Ethernet network to 100.
Router A
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
ip ospf cost 100
_________________________________________________________________
Router B
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
ip ospf cost 100
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Verification
Verify that the cost of the Ethernet interface is 100.
rtrA#show ip ospf interface ethernet 0/0
Ethernet0/0 is up, line protocol is up
Internet Address 172.16.1.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 100
Transmit Delay is 1 sec, State BDR, Priority 1
Designated Router (ID) 2.2.2.2, Interface address 172.16.1.2
Backup Designated router (ID) 1.1.1.1, Interface address 172.16.1.1
Flush timer for old DR LSA due in 00:02:45
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:09
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2 (Designated Router)
Suppress hello for 0 neighbor(s)
Verify that the cost to reach the loopback network is now 101 (100 + 1).
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
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1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/101] via 172.16.1.2, 00:02:43, Ethernet0/0
172.16.0.0/24 is subnetted, 1 subnets
C
172.16.1.0 is directly connected, Ethernet0/0
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0/1
Troubleshooting
Step 1. Verify that the correct cost has been used in the ip ospf cost interface command.
Step 2. For consistency, use the same cost for every interface attached to the same network.
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19-6 ip ospf database-filter all out
Syntax Description:
This command has no arguments.
Purpose: To prevent the flooding of link-state advertisements (LSAs) on an interface. Many Internet service providers employ redundant
links between OSPF neighbors. When an OSPF router receives an LSA, the LSA is flooded on all OSPF interfaces except for the interface
on which the LSA was received. The ip ospf database-filter all out command enables an ISP to choose between flooding overhead and
flooding reliability. For example, if there are two links between OSPF neighbors, this command can be used to prevent the flooding of LSAs
on one of the links.
Initial Cisco IOS Software Release: 12.0
Configuration Example: Reducing the Flooding of LSAs on a Redundant OSPF Link
Figure 19-3 shows two parallel links between Routers A and B. To reduce the LSA flooding overhead, LSA flooding is prevented on link 2
using the database-filter option of the ip ospf interface command. This reduction of LSA flooding can also be achieved by using the router
configuration command neighbor ospf database-filter all out (see Section 11-3). Configure Routers A and B as shown in the lines following
the figure:
Figure 19-3. LSA Flooding Overhead Can Be Reduced by Preventing LSA Flooding on One of the
Parallel Links
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
bandwidth 64
ip address 10.1.1.1 255.255.255.252
!
interface Serial0/1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
ip ospf database-filter all out
clockrate 64000
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 0
_________________________________________________________________
Router B
interface Loopback0
.
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ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.6 255.255.255.252
bandwidth 64
!
interface Serial1
bandwidth 64
ip address 10.1.1.2 255.255.255.252
clockrate 64000
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 0
Verification
Verify that the database filter has been applied to interface Serial 0/1 on Router A.
rtrA#show ip ospf neighbor detail
Neighbor 2.2.2.2, interface address 10.1.1.2
In the area 0 via interface Serial0/0
Neighbor priority is 1, State is FULL, 6 state changes
DR is 0.0.0.0 BDR is 0.0.0.0
Options 2
Dead timer due in 00:00:33
Neighbor 2.2.2.2, interface address 10.1.1.6
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In the area 0 via interface Serial0/1
Neighbor priority is 1, State is FULL, 6 state changes
Database-filter all out
DR is 0.0.0.0 BDR is 0.0.0.0
Options 2
Dead timer due in 00:01:55
Troubleshooting
Step 1. If the OSPF neighbors have a FULL adjacency, then the interface commandip ospf database-filter all out should work.
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19-7 ip ospf dead-interval seconds
Syntax Description:
seconds— If Hello packets from a neighbor are not received during a period of time equal to the dead interval, the neighbor will be
declared down. The range of values is 1–8192 seconds. The default value is four times the Hello interval.
Purpose: When an OSPF router receives a Hello packet from an OSPF neighbor, the receiving router assumes that the neighbor is active.
The dead interval is used to determine when an OSPF neighbor has become inactive. If a Hello packet has not been received during the time
set for the dead interval, then the neighbor will be declared down. By default, the dead interval is four times the Hello interval. The dead
interval should always be greater than the Hello interval.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Modifying the Interface Dead Interval
Configure the network in Figure 19-4 so you can observe the default timer values on an OSPF interface. You will then experiment with
adjusting the values of the dead interval.
Figure 19-4. The Dead Interval Must Be Configured with the Same Value on All Interfaces Attached
to a Common Network
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
.
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network 1.1.1.1 0.0.0.0 area 1
_________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 2.2.2.2 0.0.0.0 area 2
Inspect the dead interval on the serial interface by using the command show ip ospf interface.
rtrA#show ip ospf interface serial 0/1
Serial0/1 is up, line protocol is up
Internet Address 10.1.1.1/30, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:05
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2
Suppress hello for 0 neighbor(s)
Notice that the default Hello interval is 10 seconds and the default dead interval is 40 seconds. Modify the configuration on Router A to
change the dead interval to 41 seconds while leaving the value for the dead interval on Router B set to the default of 40 seconds.
Router A
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interface Serial0/1
bandwidth 64
ip address 10.1.1.1 255.255.255.252
ip ospf dead-interval 41
clockrate 64000
Verify that Routers A and B have formed an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
(no output)
Because the dead interval on Router A does not match the dead interval on Router B, the routers will not form an OSPF neighbor
relationship. OSPF neighbors must agree on the Hello and dead intervals and the authentication method used must be the same on both
ends of a link. Enable OSPF debugging to verify the problem.
rtrA#debug ip ospf adj
OSPF adjacency events debugging is on
rtrA#
02:17:31: OSPF: Rcv hello from 2.2.2.2 area 0 from Serial0/1 10.1.1.2
02:17:31: OSPF: Mismatched hello parameters from 10.1.1.2
02:17:31: Dead R 40 C 41, Hello R 10 C 10
Modify the dead interval of the serial interface on Router B.
Router B
interface Serial0
ip address 10.1.1.2 255.255.255.252
ip ospf dead-interval 41
Verification
Verify that the dead interval on Router B matches the dead interval on Router A.
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rtrB#show ip ospf interface serial 0
Serial0 is up, line protocol is up
Internet Address 10.1.1.2/30, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 41, Wait 41, Retransmit 5
Hello due in 00:00:04
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1
Suppress hello for 0 neighbor(s)
Verify that Routers A and B have established an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/ -
Dead Time Address
00:00:35
10.1.1.2
Interface
Serial0/1
Troubleshooting
Step 1. Verify that the same dead interval is being used on all interfaces attached to a common network.
Step 2. Verify that the dead interval is greater than the Hello interval.
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19-8 ip ospf demand-circuit
Syntax Description:
This command has no arguments.
Purpose: On an OSPF demand circuit, periodic Hello messages are suppressed and periodic refreshes of LSAs do not flood the demand
circuit. The ip ospf demand-circuit command allows the underlying data link layer to be closed when the topology is stable. In a
point-to-multipoint topology, only the multipoint end must be configured with this command. This command is normally used on a tariff link
such as ISDN. A tariff link is one that incurs a financial charge for every packet that is sent on the link. Configuring the link as a demand
circuit will suppress periodic OSPF packets, reducing the line charges.
Initial Cisco IOS Software Release: 11.2
Configuration Example: Configuring a Point-to-Point Link as an OSPF Demand
Circuit
Configure the serial network in Figure 19-5 as an OSPF demand circuit.
Figure 19-5. Configuring a Link as an OSPF Demand Circuit Will Suppress Hello Packets and
Periodic Refreshing of LSAs
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
ip ospf demand-circuit
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 1.1.1.1 0.0.0.0 area 1
_________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 2.2.2.2 0.0.0.0 area 2
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Verification
Verify that the serial interface has been configured as an OSPF demand circuit.
rtrA#show ip ospf interface serial 0/1
Serial0 is up, line protocol is up
Internet Address 10.1.1.1/30, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 64
Configured as demand circuit.
Run as demand circuit.
DoNotAge LSA allowed. Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 41, Retransmit 5
Hello due in 00:00:04
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2 (Hello suppressed)
Suppress hello for 1 neighbor(s)
Verify that the other end of the serial link is configured as a demand circuit even though the command ip ospf demand-circuit was not used
on Router B.
rtrB#show ip ospf interface serial 0
Serial0 is up, line protocol is up
Internet Address 10.1.1.2/30, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 64
Configured as demand circuit.
Run as demand circuit.
DoNotAge LSA allowed. Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 41, Retransmit 5
Hello due in 00:00:04
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1 (Hello suppressed)
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Suppress hello for 1 neighbor(s)
Verify that Routers A and B have established an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/ -
Dead Time Address
00:00:35
10.1.1.2
Interface
Serial0/1
Troubleshooting
Step 1. The ip ospf demand-circuit command will work if there are no errors in the configuration. Before using this command,
ensure that the routers have established an OSPF neighbor relationship over the link that is to be configured as a demand circuit.
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19-9 ip ospf flood-reduction
Syntax Description:
This command has no arguments.
Purpose: An OSPF LSA, by default, is refreshed every 30 minutes even if there has been no change to the LSA. If the LSAs are not
changing, then this indicates a stable network topology. For large networks, the periodic flooding of LSAs in a stable network is unnecessary.
The ip ospf flood-reduction interface command causes LSAs to be sent with the DoNotAge bit set, which has the effect of disabling the
periodic refresh of LSAs. If there is a change in the network topology, the LSAs will be flooded regardless of whether or not this command is
used. When flood reduction is enabled on an interface, the OSPF neighbor relationship on the interface will be reset.
Initial Cisco IOS Software Release: 12.1
Configuration Example: Configuring OSPF Flood Reduction on an Interface
Configure the routers in Figure 19-6 without using flood reduction in order to investigate the changes in the OSPF database once flood
reduction is enabled.
Figure 19-6. Network Used to Demonstrate the Changes in the OSPF Database when Flood
Reduction Is Enabled
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
.
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ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 1.1.1.1 0.0.0.0 area 1
_________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 2.2.2.2 0.0.0.0 area 2
Inspect the OSPF database on Router B for network 1.1.1.1.
rtrB#show ip ospf database router 1.1.1.1
OSPF Router with ID (2.2.2.2) (Process ID 1)
Router Link States (Area 0)
Routing Bit Set on this LSA
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LS age: 113
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 1.1.1.1
Advertising Router: 1.1.1.1
LS Seq Number: 80000041
Checksum: 0xDD9F
Length: 48
Area Border Router
Number of Links: 2
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 2.2.2.2
(Link Data) Router Interface address: 10.1.1.1
Number of TOS metrics: 0
TOS 0 Metrics: 1562
Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.1.1.0
(Link Data) Network Mask: 255.255.255.252
Number of TOS metrics: 0
TOS 0 Metrics: 1562
Modify the configuration on Router A to enable OSPF flood reduction on the serial interface.
Router A
interface Serial0/1
bandwidth 64
ip address 10.1.1.1 255.255.255.252
ip ospf flood-reduction
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clockrate 64000
Verification
Verify that flood reduction is enabled on Router A by checking the OSPF database on Router B.
rtrB#show ip ospf database router 1.1.1.1
OSPF Router with ID (2.2.2.2) (Process ID 1)
Router Link States (Area 0)
Routing Bit Set on this LSA
LS age: 5 (DoNotAge)
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 1.1.1.1
Advertising Router: 1.1.1.1
LS Seq Number: 80000043
Checksum: 0xD9A1
Length: 48
Area Border Router
Number of Links: 2
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 2.2.2.2
(Link Data) Router Interface address: 10.1.1.1
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Number of TOS metrics: 0
TOS 0 Metrics: 1562
Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.1.1.0
(Link Data) Network Mask: 255.255.255.252
Number of TOS metrics: 0
TOS 0 Metrics: 1562
Troubleshooting
Step 1. If there is an OSPF neighbor on an interface then the command ip ospf flood-reduction should work.
Step 2. The routers receiving the LSAs tagged as DoNotAge should be running Cisco IOS Software Release 11.2 or later.
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19-10 ip ospf hello-interval seconds
Syntax Description:
seconds— The time in seconds between sending Hello packets over a link. The range of values is 1–8192 seconds. The default
value is 10 seconds (30 seconds on a nonbroadcast multiaccess [NBMA] network).
Purpose: OSPF Hello packets are used to initially establish the neighbor relationship. Once the neighbor relationship is established, the
packets are used as a keepalive mechanism to determine if OSPF neighbors are active. The Hello interval should be less than the dead
interval. All interfaces on a common network must have the same Hello interval or an OSPF neighbor relationship will not be established.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Modifying the Interface Hello Interval
Configure the network in Figure 19-7 so you can observe the default timer values on an OSPF interface link. You will then experiment with
adjusting the values of the Hello interval.
Figure 19-7. The Hello Interval Must Be Configured with the Same Value on All Interfaces Attached
to a Common Network
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 1.1.1.1 0.0.0.0 area 1
_________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
!
router ospf 1
network 10.1.1.0 0.0.0.3 area 0
network 2.2.2.2 0.0.0.0 area 2
View the timer values for the serial interface on Routers A and B.
.
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rtrA#show ip ospf interface s0/1
Serial0/1 is up, line protocol is up
Internet Address 10.1.1.1/30, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:09
Index 1/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 2
Last flood scan time is 0 msec, maximum is 4 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2
Suppress hello for 0 neighbor(s)
_________________________________________________________________
rtrB#show ip ospf interface serial 0
Serial0 is up, line protocol is up
Internet Address 10.1.1.2/30, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:09
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1
Suppress hello for 0 neighbor(s)
Notice that the default Hello interval is 10 seconds and the default dead interval is 40 seconds. Modify the configuration on Router A to
change the Hello interval to 11 seconds while leaving the value for the Hello interval on Router B set to the default of 10 seconds.
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Router A
interface Serial0/1
bandwidth 64
ip address 10.1.1.1 255.255.255.252
ip ospf hello-interval 11
clockrate 64000
Inspect the OSPF interface timers for serial 0/1 on Router A.
rtrA#show ip ospf interface serial 0/1
Serial0/1 is up, line protocol is up
Internet Address 10.1.1.1/30, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 11, Dead 44, Wait 44, Retransmit 5
Hello due in 00:00:05
Index 1/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 0, maximum is 2
Last flood scan time is 0 msec, maximum is 4 msec
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
The dead timer has been automatically set to four times the Hello interval.
Verify that Routers A and B have an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
(no output)
Because the Hello interval time on Router A does not match the Hello interval on Router B, an OSPF neighbor relationship will notbe
established. This can be seen by enabling OSPF debugging on Router B.
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rtrB#debug ip ospf adj
OSPF adjacency events debugging is on
rtrB#
17:03:20: OSPF: Rcv hello from 1.1.1.1 area 0 from Serial0 10.1.1.1
17:03:20: OSPF: Mismatched hello parameters from 10.1.1.1
17:03:20: Dead R 44 C 40, Hello R 11 C 10
Modify the Hello interval on Router B to match the Hello interval on Router A.
Router B
interface Serial0
ip address 10.1.1.2 255.255.255.252
ip ospf hello-interval 11
Verification
Verify that the Hello interval on Router A matches the Hello interval on Router B.
rtrB#show ip ospf interface serial 0
Serial0 is up, line protocol is up
Internet Address 10.1.1.2/30, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 11, Dead 44, Wait 44, Retransmit 5
Hello due in 00:00:07
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1
Suppress hello for 0 neighbor(s)
Verify that the OSPF neighbor relationship has been re-established.
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rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/ -
Dead Time Address
00:00:42
10.1.1.1
Interface
Serial0
Troubleshooting
Step 1. Verify that all interfaces attached to a common network are using the same value for the Hello interval.
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19-11 ip ospf message-digest-key key-id md5 password
Syntax Description:
key-id— Key used to identify the password. The range of values is 1 to 255. All interfaces attached to a common network must
use the same key and password.
password— Password to be used for authentication on the interface. The password is an alphanumeric string from 1 to 16
characters.
Purpose: If message digest authentication is enabled in Area 0 then all interfaces in the area need to be configured with the same
authentication type. This command is used to configure message digest authentication on an OSPF interface. In Cisco IOS Software Release
12.0 and later, interface authentication can be configured independent of the authentication applied to an area (see Sections 19-1 to 19-4).
Initial Cisco IOS Software Release: 11.0
Configuration Example 1: Message Digest Authentication on an OSPF Interface
In Figure 19-8, message authentication has been enabled for Area 0. The serial interfaces in Area 0 are configured with message digest
authentication using a key ID of 1 and a password of cisco.
Figure 19-8. Prior to Cisco IOS Software Release 12.0, if Message Digest Authentication Is
Enabled in an OSPF Area, Then Message Digest Authentication Must Be Enabled on All Interfaces
in the Area
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
ip ospf message-digest-key 1 md5 cisco
clockrate 64000
!
router ospf 1
area 0 authentication-message digest
network 10.1.1.0 0.0.0.3 area 0
network 1.1.1.1 0.0.0.0 area 1
_________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
.
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ip ospf message-digest-key 1 md5 cisco
!
router ospf 1
area 0 authentication message-digest
network 10.1.1.0 0.0.0.3 area 0
network 2.2.2.2 0.0.0.0 area 2
Verification
Verify that authentication has been enabled for Area 0.
rtrA#show ip ospf
Routing Process "ospf 1" with ID 1.1.1.1 and Domain ID 0.0.0.1
Supports only single TOS(TOS0) routes
Supports opaque LSA
It is an area border router
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of opaque AS LSA 0. Checksum Sum 0x0
Number of DCbitless external and opaque AS LSA 0
Number of DoNotAge external and opaque AS LSA 0
Number of areas in this router is 2. 2 normal 0 stub 0 nssa
External flood list length 0
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has message digest authentication
SPF algorithm executed 41 times
Area ranges are
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Number of LSA 8. Checksum Sum 0x404DC
Number of opaque link LSA 0. Checksum Sum 0x0
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
Area 1
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 18 times
Area ranges are
Number of LSA 2. Checksum Sum 0x1A57A
Number of opaque link LSA 0. Checksum Sum 0x0
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
_________________________________________________________________
rtrB#show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Supports only single TOS(TOS0) routes
It is an area border router
Summary Link update interval is 00:30:00 and the update due in 00:21:19
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 2. 2 normal 0 stub 0 nssa
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Area BACKBONE(0)
Number of interfaces in this area is 1
Area has message digest authentication
SPF algorithm executed 4 times
Area ranges are
Link State Update Interval is 00:30:00 and due in 00:21:19
Link State Age Interval is 00:20:00 and due in 00:11:18
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Area 2
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 2 times
Area ranges are
Link State Update Interval is 00:30:00 and due in 00:21:16
Link State Age Interval is 00:20:00 and due in 00:11:16
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Verify that message digest authentication is enabled on the serial interfaces.
rtrA#show ip ospf interface serial 0/1
Serial0/1 is up, line protocol is up
Internet Address 10.1.1.1/30, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
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Index 1/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 2
Last flood scan time is 0 msec, maximum is 4 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2
Suppress hello for 0 neighbor(s)
Message digest authentication enabled
Youngest key id is 1
_________________________________________________________________
rtrB#show ip ospf interface serial 0
Serial0 is up, line protocol is up
Internet Address 10.1.1.2/30, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:07
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1
Suppress hello for 0 neighbor(s)
Message digest authentication enabled
Youngest key id is 1
Verify that Routers A and B have established an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/ -
Dead Time Address
00:00:37
10.1.1.2
Interface
Serial0/1
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Configuration Example 2: Changing Keys and Passwords
For additional security, you may choose to periodically change your key and password. With clear-text authentication, when you change
passwords there will be a loss of OSPF connectivity from the time you change the password on one end interface until you change the
password on the other interfaces in the area. With MD5 authentication, you can configure a new key and password on an OSPF interface
while leaving the old key and password in place. The old key and password will continue to be used until the new key and password are
configured on the other interface. Modify the key and password on the serial interfaces on Routers A and B. First, add a new key and
password to Router A in order to observe the behavior when the new key and password have only been configured on one end of the serial
network.
Router A
interface Serial0/1
ip address 10.1.1.1 255.255.255.252
ip ospf message-digest-key 1 md5 cisco
ip ospf message-digest-key 2 md5 budman
clockrate 64000
Examine the effect of adding a new key and password on only one end of the serial link.
rtrA#show ip ospf interface serial 0/1
Serial0/1 is up, line protocol is up
Internet Address 10.1.1.1/30, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:04
Index 1/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 2
Last flood scan time is 0 msec, maximum is 4 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2
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Suppress hello for 0 neighbor(s)
Message digest authentication enabled
Youngest key id is 2
Rollover in progress, 1 neighbor(s) using the old key(s):
key id 1
Notice that both keys are being used for authentication. Configure the new key and password on Router B while leaving the old key and
password in place.
Router B
interface Serial0
ip address 10.1.1.2 255.255.255.252
ip ospf message-digest-key 1 md5 cisco
ip ospf message-digest-key 2 md5 budman
Verification
Verify that Router B is now using the new key and password.
rtrB#show ip ospf interface serial 0
Serial0 is up, line protocol is up
Internet Address 10.1.1.2/30, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:00
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1
Suppress hello for 0 neighbor(s)
Message digest authentication enabled
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Youngest key id is 2
You can now remove the old key and password from Routers A and B.
Router A
interface Serial0/1
no ip ospf message-digest-key 1 md5 cisco
_________________________________________________________________
Router B
interface Serial0
no ip ospf message-digest-key 1 md5 cisco
Troubleshooting
Step 1. Verify that the same key and password are being used on all interfaces attached to a common network.
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19-12 ip ospf mtu-ignore
Syntax Description:
This command has no arguments.
Purpose: If there is a maximum transmission unit (MTU) mismatch between neighboring OSPF routers, then the routers will not form an
OSPF adjacency.
Initial Cisco IOS Software Release: 12.0 (3)
Configuration Example: OSPF Adjacency and MTU Mismatch
In Figure 19-9, Routers A and B have an MTU of 1500 on their serial interfaces and Router C has an MTU of 1490. When Routers A and C
reach the EXSTART state in the forming of the adjacency, they will attempt to exchange their OSPF database description packets. An OSPF
router will ignore a database description packet if there is an MTU mismatch. When there is a mismatch, the database description packet will
not be acknowledged and the sending router will continue to send the packets until they are acknowledged. The acknowledgement will never
come and the routers will be stuck in the EXSTART state. To demonstrate this, Router C has been configured with an MTU of 1490 as shown
in the following configurations.
Figure 19-9. OSPF Will Not Form a Neighbor Relationship if There Is an MTU Mismatch Between
the Interfaces Connecting the Routers
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
bandwidth 64
no ip address
encapsulation frame-relay
frame-relay lmi-type ansi
!
interface Serial0/0.1 point-to-point
ip address 10.1.1.1 255.255.255.252
frame-relay interface-dlci 101
!
interface Serial0/0.2 point-to-point
ip address 10.1.1.5 255.255.255.252
frame-relay interface-dlci 102
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.4 0.0.0.3 area 0
_________________________________________________________________
Router B
interface Loopback0
.
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ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
encapsulation frame-relay
ip ospf network point-to-point
no ip mroute-cache
bandwidth 64
frame-relay map ip 10.1.1.1 110 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.3 area 0
_________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
mtu 1490
bandwidth 64
no ip address
encapsulation frame-relay
no ip mroute-cache
.
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!
interface Serial0.1 point-to-point
ip address 10.1.1.6 255.255.255.252
frame-relay interface-dlci 120
!
router ospf 1
network 3.3.3.3 0.0.0.0 area 3
network 10.1.1.4 0.0.0.3 area 0
Enable OSPF debugging on Router A and then reset the OSPF process on Router A.
rtrA#debug ip ospf events
OSPF events debugging is on
rtrA#clear ip ospf process
Reset ALL OSPF processes? [no]: y
rtrA#
.
.
.
05:37:58: OSPF: Rcv DBD from 3.3.3.3 on Serial0/0.2 seq 0xF91 opt 0x2 flag 0x7 l
en 32 mtu 1490 state EXCHANGE
05:37:58: OSPF: Send DBD to 3.3.3.3 on Serial0/0.2 seq 0xF91 opt 0x42 flag 0x2 l
en 152
05:38:03: OSPF: Rcv hello from 3.3.3.3 area 0 from Serial0/0.2 10.1.1.6
05:38:03: OSPF: End of hello processing
05:38:03: OSPF: Rcv DBD from 3.3.3.3 on Serial0/0.2 seq 0xF91 opt 0x2 flag 0x7 l
en 32 mtu 1490 state EXCHANGE
05:38:03: OSPF: Send DBD to 3.3.3.3 on Serial0/0.2 seq 0xF91 opt 0x42 flag 0x2 l
en 152
.
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.
.
You can see from the debug output on Router A that Routers A and C are stuck in the EXSTART state. This can also be seen by examining
the OSPF neighbors as seen by Routers A and C.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
3.3.3.3
1 EXCHANGE/ -
2.2.2.2
1 FULL/ -
00:00:35
00:00:38
10.1.1.6
10.1.1.2
Interface
Serial0/0.2
Serial0/0.1
_________________________________________________________________
rtrC#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 EXSTART/ -
Dead Time Address
00:00:38
10.1.1.5
Interface
Serial0.1
This problem can be fixed by configuring the MTU to be the same on all of the serial interfaces. Cisco does not support the configuration of
the MTU on Ethernet or Token Ring interfaces, so the only option is to use the ip ospf mtu-ignore interface command if a mismatch occurs
on these network types. For this example, configure Routers A and C to ignore the MTU mismatch.
Router A
interface Serial0/0
bandwidth 64
no ip address
encapsulation frame-relay
frame-relay lmi-type ansi
!
interface Serial0/0.1 point-to-point
ip address 10.1.1.1 255.255.255.252
frame-relay interface-dlci 101
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interface Serial0/0.2 point-to-point
ip address 10.1.1.5 255.255.255.252
ip ospf mtu-ignore
frame-relay interface-dlci 102
_________________________________________________________________
Router C
interface Serial0
mtu 1490
bandwidth 64
no ip address
no ip directed-broadcast
encapsulation frame-relay
!
interface Serial0.1 point-to-point
ip address 10.1.1.6 255.255.255.252
no ip directed-broadcast
ip ospf mtu-ignore
frame-relay interface-dlci 120
Verification
Verify that Routers A and C have formed an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
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3.3.3.3
1 FULL/ -
00:00:36
10.1.1.6
Serial0/0.2
2.2.2.2
1 FULL/ -
00:00:36
10.1.1.2
Serial0/0.1
Troubleshooting
Step 1. Verify the IP address and netmask assignments used on the network interfaces.
Step 2. Verify that the proper DLCIs and IP addresses are used in theframe relay map ip statements. These can be checked
using the show frame-relay map command, as shown here.
rtrA#show frame-relay map
Serial0/0 (up): ip 10.1.1.2 dlci 101(0x65,0x1850), static,
broadcast,
CISCO, status defined, active
Serial0/0 (up): ip 10.1.1.3 dlci 102(0x66,0x1860), static,
broadcast,
CISCO, status defined, active
Step 3. Before configuring OSPF, check IP connectivity by pinging the other end of the link.
Step 4. If you are mixing network types (multipoint and point-to-point) verify that the Hello intervals match on all routers.
Step 5. If there is an MTU mismatch, either modify the MTU on one end of the link to match the other end or use the
ip ospf
mtu-ignore interface command.
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< Free Open Study >
19-13 ip ospf network broadcast
Syntax Description:
This command has no arguments.
Purpose: Used to configure an NBMA network as a broadcast network.
Initial Cisco IOS Software Release: 10.0
Configuration Example 1: Fully-meshed OSPF Neighbors on an NBMA Network
OSPF views networks as being of one of three types:
A broadcast multiaccess network— On a broadcast multiaccess network, all routers attached to the network have a direct
communication link with all other routers on the network. Examples of a broadcast multiaccess network are Ethernet, Token Ring,
and FDDI. When OSPF sends a protocol packet onto a broadcast multiaccess network, all OSPF routers on the network will
receive the packet.
A point-to-point network— On a point-to-point network, only two routers exist on the network, one at each end of the
point-to-point link. Examples of a point-to-point network are High-Level Data Link Control (HDLC) and Point-to-Point Protocol
(PPP).
An NBMA network— Examples of an NBMA network are Frame Relay and X.25. On an NBMA network, all OSPF routers could
possibly have connections to all other OSPF routers on the network, but all the connections are logical point-to-point links so an
OSPF protocol packet sent on one link will not reach all OSPF neighbors. NBMA networks can be configured, from an OSPF point
of view, as broadcast, point-to-point, or multipoint.
This example will investigate configuring Frame Relay as an OSPF broadcast network.
In Figure 19-10, three OSPF routers are fully meshed over a Frame Relay network. Every OSPF router has a connection to every other
OSPF router. For this case, the Frame Relay network can be made to behave like a multiaccess network by configuring the network type as
broadcast. As with all OSPF broadcast networks, a Designated Router (DR) and Backup Designated Router (BDR) will be elected for the
network. Initially, the routers in Figure 19-10 are configured without specifying a network type in order to observe the OSPF behavior on an
NBMA network.
Figure 19-10. An NBMA Network Is Typically Configured as a Broadcast Network when the OSPF
Routers Are Fully Meshed and the PVCs Are on the Same IP Subnet
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
bandwidth 64
ip address 10.1.1.1 255.255.255.248
encapsulation frame-relay
frame-relay map ip 10.1.1.2 101 broadcast
frame-relay map ip 10.1.1.3 102 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.7 area 0
_________________________________________________________________
.
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Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.248
encapsulation frame-relay
frame-relay map ip 10.1.1.1 110 broadcast
frame-relay map ip 10.1.1.3 112 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.7 area 0
_________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.3 255.255.255.248
encapsulation frame-relay
frame-relay map ip 10.1.1.1 120 broadcast
frame-relay map ip 10.1.1.2 121 broadcast
.
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no frame-relay inverse-arp
!
router ospf 1
network 3.3.3.3 0.0.0.0 area 3
network 10.1.1.0 0.0.0.7 area 0
Frame Relay inverse ARP is disabled on Routers A, B, and C and staticframe-relay map statements are used to map remote IP addresses
to the proper Frame Relay DLCI. This is not necessary for the operation of OSPF over Frame Relay but only prevents the routers from
leaning DLCIs that are not used. Chapter 11 shows how the OSPF neighbor command is used to configure OSPF over an NBMA network.
For this example, the OSPF interface command ip ospf network broadcast is used to have OSPF treat the Frame Relay network as a
broadcast network. Without the neighbor command or the ip ospf network broadcast command, OSPF does not know how to treat the
NBMA network so OSPF neighbor relationships will not be formed, as shown in the output of the show ip ospf neighbor command.
rtrA#show ip ospf neighbor
(no output)
OSPF is not sending any protocol packets to the NBMA network. Modify the configurations on Routers A, B, and C to configure the NBMA
network as a broadcast network.
Router A
interface Serial0/0
bandwidth 64
ip address 10.1.1.1 255.255.255.248
encapsulation frame-relay
ip ospf network broadcast
frame-relay map ip 10.1.1.2 101 broadcast
frame-relay map ip 10.1.1.3 102 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
_________________________________________________________________
Router B
interface Serial0
ip address 10.1.1.2 255.255.255.248
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encapsulation frame-relay
ip ospf network broadcast
frame-relay map ip 10.1.1.1 110 broadcast
frame-relay map ip 10.1.1.3 112 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
_________________________________________________________________
Router C
interface Serial0
ip address 10.1.1.3 255.255.255.248
encapsulation frame-relay
ip ospf network broadcast
frame-relay map ip 10.1.1.1 120 broadcast
frame-relay map ip 10.1.1.2 121 broadcast
no frame-relay inverse-arp
Verification
Verify that OSPF is treating the Frame Relay network as a broadcast network.
rtrA#show ip ospf interface serial 0/0
Serial0/0 is up, line protocol is up
Internet Address 10.1.1.1/29, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 1562
Transmit Delay is 1 sec, State DROTHER, Priority 1
Designated Router (ID) 3.3.3.3, Interface address 10.1.1.3
Backup Designated router (ID) 2.2.2.2, Interface address 10.1.1.2
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Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:01
Index 1/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 0, maximum is 2
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 2, Adjacent neighbor count is 2
Adjacent with neighbor 3.3.3.3 (Designated Router)
Adjacent with neighbor 2.2.2.2 (Backup Designated Router)
Suppress hello for 0 neighbor(s)
Verify that Routers A, B, and C have formed a FULL OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
3.3.3.3
1 FULL/DR
2.2.2.2
1 FULL/BDR
Dead Time Address
00:00:35
00:00:36
10.1.1.3
10.1.1.2
Interface
Serial0/0
Serial0/0
Router C has been elected the DR and Router B has been elected the BDR. For a fully meshed configuration, the router selected as the DR
is not important as long as all PVCs remain active and the full mesh is maintained. In the next example, the selection of the DR becomes an
important issue if the routers are not fully meshed.
Configuration Example 2: Partially-meshed OSPF Neighbors on an NBMA Network
There is a scaling problem with a fully meshed broadcast network. The number of PVCs required grows exponentially with the number of
routers in the mesh. The formula to determine the number of PVCs based on the number of routers (n) is given by this equation:
Therefore, five routers require 10 PVCs and 10 routers require 45 PVCs. As you can see, this can become expensive not only in terms of
cost but also in terms of management complexity. If you add one router to a 10-router mesh, then an additional 11 PVCs need to be
purchased and configured. The number of PVCs can be reduced if a hub-and-spoke topology is used as shown in Figure 19-11. Router A is
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the hub router and Routers B and C are spoke routers. Spoke routers only have a connection or PVC to the hub router. A broadcast network
can be used with a partial mesh, but there are a number of concerns that need to be addressed as will be pointed out in this example.
Remove the PVC between Routers B and C (see Figure 19-10) to produce the topology in Figure 19-11.
Figure 19-11. An NBMA Network Can Be Configured as a Broadcast Network Using a Partial Mesh
Configuration. The Hub Router Should Always Be the DR
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
bandwidth 64
ip address 10.1.1.1 255.255.255.248
encapsulation frame-relay
ip ospf network broadcast
frame-relay map ip 10.1.1.2 101 broadcast
frame-relay map ip 10.1.1.3 102 broadcast
no frame-relay inverse-arp
.
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frame-relay lmi-type ansi
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.7 area 0
_________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.248
encapsulation frame-relay
ip ospf network broadcast
frame-relay map ip 10.1.1.1 110 broadcast
no frame-relay map ip 10.1.1.3 112 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.7 area 0
_________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
.
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interface Serial0
ip address 10.1.1.3 255.255.255.248
encapsulation frame-relay
ip ospf network broadcast
frame-relay map ip 10.1.1.1 120 broadcast
no frame-relay map ip 10.1.1.2 121 broadcast
no frame-relay inverse-arp
!
router ospf 1
network 3.3.3.3 0.0.0.0 area 3
network 10.1.1.0 0.0.0.7 area 0
Use the command clear ip ospf process on Router A to reset OSPF. Check the status of the OSPF neighbors on Router A.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
3.3.3.3
1 FULL/DR
00:00:35
2.2.2.2
1 FULL/DROTHER
10.1.1.3
00:00:34
10.1.1.2
Interface
Serial0/0
Serial0/0
The first concern with a partial mesh broadcast network is the election of the DR. Router C was elected as the DR because it has the highest
router ID. All routers on a broadcast network need to become adjacent with the DR. Router B cannot become adjacent with the DR because
there is not a direct connection between Routers B and C. The solution is to ensure that the hub router, Router A, is elected as the DR. If
Router A fails, then it does not make any difference if either Router B or C is the BDR because they will no longer have an IP path between
them. Router A needs to be configured so it is always elected the DR. One way to accomplish this is to set the interface priority on Routers B
and C to zero. Setting the OSPF priority to zero makes the router ineligible to become the DR on the network. The default interface priority is
1, so Router A will always be elected the DR.
Another way is to ensure that the router that you want to become DR has the highest OSPF router ID.
Router B
interface Serial0
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ip address 10.1.1.2 255.255.255.248
encapsulation frame-relay
ip ospf network broadcast
ip ospf priority 0
frame-relay map ip 10.1.1.1 110 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
_________________________________________________________________
Router C
interface Serial0
ip address 10.1.1.3 255.255.255.248
encapsulation frame-relay
ip ospf network broadcast
ip ospf priority 0
frame-relay map ip 10.1.1.1 120 broadcast
no frame-relay inverse-arp
Reset the OSPF process on Router A.
rtrA#clear ip ospf process
Reset ALL OSPF processes? [no]: y
Verify that Router A is now the DR and that neither router B nor C is the BDR.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
3.3.3.3
0 FULL/DROTHER
00:00:32
10.1.1.3
Serial0/0
2.2.2.2
0 FULL/DROTHER
00:00:32
10.1.1.2
Serial0/0
_________________________________________________________________
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rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:00:39
10.1.1.1
Interface
Serial0
_________________________________________________________________
rtrC#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:00:35
10.1.1.1
Interface
Serial0
Each router is advertising its loopback network into OSPF. Check the routing tables on Routers A, B, and C to determine if the routes are
being advertised to all routers.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/1563] via 10.1.1.2, 00:01:06, Serial0/0
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3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/1563] via 10.1.1.3, 00:01:06, Serial0/0
10.0.0.0/29 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0/0
_________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O IA
1.1.1.1 [110/65] via 10.1.1.1, 00:03:23, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O IA
C
3.3.3.3 [110/65] via 10.1.1.3, 00:03:23, Serial0
169.254.0.0/16 is directly connected, Ethernet0
10.0.0.0/29 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0
_________________________________________________________________
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
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D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O IA
1.1.1.1 [110/65] via 10.1.1.1, 00:03:43, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/65] via 10.1.1.2, 00:03:44, Serial0
3.0.0.0/32 is subnetted, 1 subnets
C
3.3.3.3 is directly connected, Loopback0
10.0.0.0/29 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0
The routes are being advertised, but can all routers reach them?
rtrA#ping 2.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms
rtrA#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
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!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms
_________________________________________________________________
rtrB#ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/6/8 ms
rtrB#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
_________________________________________________________________
rtrC#ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms
rtrC#ping 2.2.2.2
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Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
Router A can ping Routers B and C because they are directly connected. Router B can ping A but not C and Router C can ping A but not B.
The problem is that Routers B and C think they are directly connected because they are on the same IP subnet and the network type is
broadcast. This line was highlighted previously in the routing table on Router B.
O IA 3.3.3.3 [110/65] via 10.1.1.3, 00:03:23, Serial0
For Router B to reach network 3.3.3.3 on Router C, it must send the packet to 10.1.1.3. Router B is not directly connected to Router C so the
packet must first be sent to Router A. This is accomplished by an additional frame-relay map statement on Routers B and C.
Router B
interface Serial0
ip address 10.1.1.2 255.255.255.248
encapsulation frame-relay
ip ospf network broadcast
ip ospf priority 0
frame-relay map ip 10.1.1.1 110 broadcast
frame-relay map ip 10.1.1.3 110 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
_________________________________________________________________
Router C
interface Serial0
ip address 10.1.1.3 255.255.255.248
encapsulation frame-relay
ip ospf network broadcast
ip ospf priority 0
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frame-relay map ip 10.1.1.1 120 broadcast
frame-relay map ip 10.1.1.2 120 broadcast
no frame-relay inverse-arp
19-2 Verification
Verify that all routers can ping the loopback interfaces on the other routers.
rtrA#ping 2.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms
rtrA#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/6/8 ms
_________________________________________________________________
rtrB#ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms
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rtrB#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/8/12 ms
_________________________________________________________________
rtrC#ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms
rtrC#ping 2.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/9/12 ms
Troubleshooting
Step 1. Verify the IP address and netmask assignments used on the NBMA network interfaces.
Step 2. Verify that the proper DLCIs and IP addresses are used in theframe-relay map ip statements. These can be checked
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using the show frame-relay map command, as shown here:
rtrA#show frame-relay map
Serial0/0 (up): ip 10.1.1.2 dlci 101(0x65,0x1850), static,
broadcast,
CISCO, status defined, active
Serial0/0 (up): ip 10.1.1.3 dlci 102(0x66,0x1860), static,
broadcast,
CISCO, status defined, active
Step 3. Before configuring OSPF, check IP connectivity by pinging the other end of each Frame Relay link.
Step 4. If using a partial mesh with a broadcast network, ensure that the hub router is elected DR.
Step 5. If using a partial mesh with a broadcast network, ensure that the spoke routers have been configured withframe
a
relay
map command to each spoke through the hub router.
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< Free Open Study >
19-14 ip ospf network non-broadcast
Syntax Description:
This command has no arguments.
Purpose: OSPF sends Hello packets and other protocol packets as multicast. If the network does not support multicast or you want OSPF to
communicate with neighbors using unicast, use this command. The neighbor command is required if the network is configured as
non-broadcast. See Chapter 11 for configuration examples.
Initial Cisco IOS Software Release: 10.0
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< Free Open Study >
19-15 ip ospf network point-to-multipoint
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< Free Open Study >
19-16 ip ospf network point-to-multipoint non-broadcast
Syntax Description:
This command has no arguments.
Purpose: Used to configure an NBMA network as a multipoint network. OSPF uses multicast to send Hello and other protocol packets over
a point-to-multipoint network. On some networks, such as ATM, the connections are dynamic and the Hello packets will be sent only over
established connections. Therefore, the non-broadcast option needs to be used in conjunction with theneighbor command (see Chapter 11)
if running OSPF over an ATM multipoint network.
Initial Cisco IOS Software Release: 10.3. The non-broadcast keyword was added in 11.3.
Configuration Example 1: Multipoint Hub with Point-to-Point Spokes
OSPF views networks as being of one of three types:
A broadcast multiaccess network— On a broadcast multiaccess network, all routers attached to the network have a direct
communication link with all other routers on the network. Examples of a broadcast multiaccess network are Ethernet, Token Ring,
and FDDI. When OSPF sends a protocol packet onto a broadcast multiaccess network, all OSPF routers on the network will
receive the packet.
A point-to-point network— On a point-to-point network, only two routers exist on the network, one at each end of the
point-to-point link. Examples of a point-to-point network are HDLC and PPP.
An NBMA network— Examples of an NBMA network are Frame Relay and X.25. On an NBMA network, all OSPF routers could
possibly have connections to all other OSPF routers on the network but all the connections are logical point-to-point links, so an
OSPF protocol packet sent on one link will not reach all OSPF neighbors. NBMA networks can be configured, from an OSPF point
of view, as broadcast, point-to-point, or multipoint.
This example investigates configuring Frame Relay as an OSPF multipoint network.
In Figure 19-12, three OSPF routers are partially meshed over a Frame Relay network. Router A is the hub and Routers B and C are spokes.
The two PVCs are configured on the same IP subnet. Initially, the routers in Figure 19-12 are configured without specifying a network type in
order to observe the OSPF behavior on an NBMA network.
Figure 19-12. An OSPF Multipoint Network Is Used when There Is a Partial Mesh Between the
Routers and the Routers Are on the Same IP Subnet
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/0
bandwidth 64
ip address 10.1.1.1 255.255.255.248
encapsulation frame-relay
frame-relay map ip 10.1.1.2 101 broadcast
frame-relay map ip 10.1.1.3 102 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.7 area 0
______________________________________________________________________________
.
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Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.248
encapsulation frame-relay
frame-relay map ip 10.1.1.1 110 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.7 area 0
______________________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
ip address 10.1.1.3 255.255.255.248
encapsulation frame-relay
frame-relay map ip 10.1.1.1 120 broadcast
no frame-relay inverse-arp
!
router ospf 1
.
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network 3.3.3.3 0.0.0.0 area 3
network 10.1.1.0 0.0.0.7 area 0
Frame Relay inverse ARP is disabled on Routers A, B, and C and static frame-relay map statements are used to map remote IP addresses
to the proper Frame Relay DLCI. This is not necessary for the operation of OSPF over Frame Relay, but only prevents the routers from
learning DLCIs that are not used. In Chapter 11, the OSPF neighbor command was used to configure OSPF over an NBMA network. For this
example, the OSPF interface command ip ospf network point-to-multipoint forces OSPF to treat the Frame Relay network as a multipoint
network. Without the neighbor command or the ip ospf network command, OSPF does not know how to treat the NBMA network, so OSPF
neighbor relationships will not be formed. This is shown in the output of the show ip ospf neighbor command shown here.
rtrA#show ip ospf neighbor
(no output)
OSPF is not sending any protocol packets onto the NBMA network. Modify the configurations on Routers A, B, and C to configure the NBMA
network as a multipoint network. For this example use the network type point-to-multipoint on Router A and point-to-point on Routers B
and C.
Router A
interface Serial0/0
bandwidth 64
ip address 10.1.1.1 255.255.255.248
encapsulation frame-relay
ip ospf network point-to-multipoint
frame-relay map ip 10.1.1.2 101 broadcast
frame-relay map ip 10.1.1.3 102 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
______________________________________________________________________________
Router B
interface Serial0
bandwidth 64
ip address 10.1.1.2 255.255.255.248
encapsulation frame-relay
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ip ospf network point-to-point
frame-relay map ip 10.1.1.1 110 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
______________________________________________________________________________
Router C
interface Serial0
bandwidth 64
ip address 10.1.1.3 255.255.255.248
encapsulation frame-relay
ip ospf network point-to-point
frame-relay map ip 10.1.1.1 120 broadcast
no frame-relay inverse-arp
Verification
Verify that OSPF is treating the Frame Relay network as a multipoint network on Router A and as a point-to-point network on Routers B and
C.
rtrA#show ip ospf interface serial 0/0
Serial0/0 is up, line protocol is up
Internet Address 10.1.1.1/29, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_MULTIPOINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_MULTIPOINT,
Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
Hello due in 00:00:16
Index 1/2, flood queue length 0
Next 0x0(0)/0x0(0)
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Last flood scan length is 1, maximum is 4
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 2, Adjacent neighbor count is 2
Adjacent with neighbor 3.3.3.3
Adjacent with neighbor 2.2.2.2
Suppress hello for 0 neighbor(s)
______________________________________________________________________________
rtrB#show ip ospf interface serial 0
Serial0 is up, line protocol is up
Internet Address 10.1.1.2/29, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:18
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1
Suppress hello for 0 neighbor(s)
______________________________________________________________________________
rtrC#show ip ospf interface serial 0
Serial0 is up, line protocol is up
Internet Address 10.1.1.3/29, Area 0
Process ID 1, Router ID 3.3.3.3, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:14
Neighbor Count is 1, Adjacent neighbor count is 1
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Adjacent with neighbor 1.1.1.1
Suppress hello for 0 neighbor(s)
Verify that Routers A, B, and C have formed an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
(no neighbors)
Router A has not formed a neighbor relationship with either Router B or C. Enable OSPF debugging to determine the problem.
rtrA#debug ip ospf events
OSPF events debugging is on
rtrA#
23:42:12: OSPF: Rcv hello from 3.3.3.3 area 0 from Serial0/0 10.1.1.3
23:42:12: OSPF: Mismatched hello parameters from 10.1.1.3
23:42:12: OSPF: Dead R 40 C 120, Hello R 10 C 30
23:42:16: OSPF: Rcv hello from 2.2.2.2 area 0 from Serial0/0 10.1.1.2
23:42:16: OSPF: Mismatched hello parameters from 10.1.1.2
23:42:16: OSPF: Dead R 40 C 120, Hello R 10 C 30
There is a mismatch in the Hello parameters between Router A and Routers B and C. Router A is configured as a multipoint network and the
Hello time is 30 seconds. Routers B and C are configured as point-to-point networks and the Hello time is 10 seconds. OSPF will not form an
adjacency if the Hello intervals do not match. Change the Hello interval on Routers B and C to 30 seconds.
Router B
interface Serial0
ip address 10.1.1.2 255.255.255.248
encapsulation frame-relay
ip ospf network point-to-point
ip ospf hello-interval 30
bandwidth 64
frame-relay map ip 10.1.1.1 110 broadcast
no frame-relay inverse-arp
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frame-relay lmi-type ansi
______________________________________________________________________________
Router C
interface Serial0
bandwidth 64
ip address 10.1.1.3 255.255.255.248
encapsulation frame-relay
ip ospf network point-to-point
ip ospf hello-interval 30
no ip mroute-cache
frame-relay map ip 10.1.1.1 120 broadcast
no frame-relay inverse-arp
Verify that the OSPF neighbor relationships are established.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
3.3.3.3
1 FULL/ -
00:01:39
10.1.1.3
Serial0/0
2.2.2.2
1 FULL/ -
00:01:58
10.1.1.2
Serial0/0
Each router is advertising its loopback network into OSPF. Check the routing tables on Routers A, B, and C to determine if the routes are
being advertised to all routers.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
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* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/1563] via 10.1.1.2, 00:01:06, Serial0/0
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/1563] via 10.1.1.3, 00:01:06, Serial0/0
10.0.0.0/29 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0/0
______________________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O IA
1.1.1.1 [110/65] via 10.1.1.1, 00:03:23, Serial0
2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
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3.0.0.0/32 is subnetted, 1 subnets
O IA
C
3.3.3.3 [110/65] via 10.1.1.1, 00:03:23, Serial0
169.254.0.0/16 is directly connected, Ethernet0
10.0.0.0/29 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0
______________________________________________________________________________
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O IA
1.1.1.1 [110/65] via 10.1.1.1, 00:03:43, Serial0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/65] via 10.1.1.1, 00:03:44, Serial0
3.0.0.0/32 is subnetted, 1 subnets
C
3.3.3.3 is directly connected, Loopback0
10.0.0.0/29 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0
The routes are being advertised, but can all routers reach them?
rtrA#ping 2.2.2.2
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Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms
rtrA#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms
______________________________________________________________________________
rtrB#ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms
rtrB#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/8/12 ms
______________________________________________________________________________
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rtrC#ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms
rtrC#ping 2.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/8/12 ms
Configuration Example 2: Partially Meshed Hub and Spoke Using a Multipoint
Network
Change the network type on Routers B and C to point-to-multipoint. This will automatically set the Hello interval to 30 seconds.
Router B
interface Serial0
ip address 10.1.1.2 255.255.255.248
encapsulation frame-relay
ip ospf network point-to-multipoint
bandwidth 64
frame-relay map ip 10.1.1.1 110 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
_________________________________________________________________
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Router C
interface Serial0
bandwidth 64
ip address 10.1.1.3 255.255.255.248
encapsulation frame-relay
ip ospf network point-to-multipoint
frame-relay map ip 10.1.1.1 120 broadcast
no frame-relay inverse-arp
Verification
Verify that all routers can ping the loopback interfaces on the other routers.
rtrA#ping 2.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms
rtrA#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/6/8 ms
______________________________________________________________________________
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rtrB#ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms
rtrB#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/8/12 ms
_____________________________________________________________________________
rtrC#ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms
rtrC#ping 2.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/9/12 ms
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Troubleshooting
Step 1. Verify the IP address and netmask assignments used on the NBMA network interfaces.
Step 2. Verify that the proper DLCIs and IP addresses are used in theframe-relay map ip statements. These can be checked
using the show frame-relay map command, as shown here.
rtrA#show frame-relay map
Serial0/0 (up): ip 10.1.1.2 dlci 101(0x65,0x1850), static,
broadcast,
CISCO, status defined, active
Serial0/0 (up): ip 10.1.1.3 dlci 102(0x66,0x1860), static,
broadcast,
CISCO, status defined, active
Step 3. Before configuring OSPF, check IP connectivity by pinging the other end of each Frame Relay link.
Step 4. If you are mixing network types (multipoint and point-to-point) verify that the Hello intervals match on all routers.
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19-17 ip ospf network point-to-point
Syntax Description:
This command has no arguments.
Purpose: Used to configure an NBMA network as a point-to-point network.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Point-to-Point Partially Meshed OSPF Neighbors
OSPF views networks as being of one of three types:
A broadcast multiaccess network— On a broadcast multiaccess network, all routers attached to the network have a direct
communication link with all other routers on the network. Examples of a broadcast multiaccess network are Ethernet, Token Ring,
and FDDI. When OSPF sends a protocol packet onto a broadcast multiaccess network, all OSPF routers on the network will
receive the packet.
A point-to-point network— On a point-to-point network, only two routers exist on the network, one at each end of the
point-to-point link. Examples of a point-to-point network are HDLC and PPP.
An NBMA network— Examples of an NBMA network are Frame Relay and X.25. On an NBMA network, all OSPF routers could
possibly have connections to all other OSPF routers on the network but all the connections are logical point-to-point links, so an
OSPF protocol packet sent on one link will not reach all OSPF neighbors. NBMA networks can be configured, from an OSPF point
of view, as broadcast, point-to-point, or multipoint.
This example investigates configuring Frame Relay as an OSPF point-to-point network.
In Figure 19-13, three OSPF routers are partially meshed over a Frame Relay network. Router A is the hub and routers B and C are spokes.
The two PVCs are configured on different IP subnets; therefore, the hub router needs two logical interfaces, one for each IP subnet. Initially
the routers in Figure 19-13 are configured without specifying a network type in order to observe the OSPF behavior on an NBMA network.
Router C uses a subinterface and Router B uses a major interface to illustrate the configuration differences.
Figure 19-13. A Point-to-Point NBMA Network
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
interface Serial0/0
bandwidth 64
no ip address
encapsulation frame-relay
frame-relay lmi-type ansi
!
interface Serial0/0.1 point-to-point
ip address 10.1.1.1 255.255.255.252
frame-relay interface-dlci 101
!
interface Serial0/0.2 point-to-point
ip address 10.1.1.5 255.255.255.252
frame-relay interface-dlci 102
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
.
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network 10.1.1.4 0.0.0.3 area 0
_______________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
encapsulation frame-relay
bandwidth 64
frame-relay map ip 10.1.1.1 110 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.3 area 0
____________________________________________________________________________
Router C
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial0
bandwidth 64
no ip address
encapsulation frame-relay
.
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no frame-relay inverse-arp
!
interface Serial0.1 point-to-point
ip address 10.1.1.6 255.255.255.252
frame-relay interface-dlci 120
!
router ospf 1
network 3.3.3.3 0.0.0.0 area 3
network 10.1.1.4 0.0.0.3 area 0
Frame Relay inverse ARP has been disabled on Router B to prevent Router B from learning about DLCIs that are not being used.
Subinterfaces are used on Routers A and C so Frame Relay inverse ARP is automatically disabled. Chapter 11 demonstrates how to use the
OSPF neighbor command to configure OSPF over an NBMA network. For this example, the OSPF interface commandip ospf network
point-to-point has not been used on any of the routers. Determine if any OSPF neighbor relationships have been formed with Router A.
rtrA#show ip ospf neighbor
Neighbor ID
3.3.3.3
Pri State
1 FULL/ -
Dead Time Address
00:00:38
10.1.1.6
Interface
Serial0/0.2
An OSPF neighbor relationship has been established between Routers A and C, but not Routers A and B. To understand why, you need to
look at the OSPF network type that is being used on the Frame Relay interfaces.
rtrA#show ip ospf int s0/0.1
Serial0/0.1 is up, line protocol is up
Internet Address 10.1.1.1/30, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:07
Index 1/1, flood queue length 0
Next 0x0(0)/0x0(0)
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Last flood scan length is 1, maximum is 6
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
rtrA#show ip ospf int s0/0.2
Serial0/0.2 is up, line protocol is up
Internet Address 10.1.1.5/30, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:07
Index 2/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 2
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 3.3.3.3
Suppress hello for 0 neighbor(s)
____________________________________________________________________________
rtrC#show ip ospf int s0.1
Serial0.1 is up, line protocol is up
Internet Address 10.1.1.6/30, Area 0
Process ID 1, Router ID 3.3.3.3, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:06
Neighbor Count is 1, Adjacent neighbor count is 1
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Adjacent with neighbor 1.1.1.1
Suppress hello for 0 neighbor(s)
When the subinterfaces were created on Routers A and C, the type was set to point-to-point; therefore, the interface commandip ospf
network point-to-point is not needed. Router B is not using a subinterface and the default OSPF network type is nonbroadcast.
rtrB#show ip ospf interface serial 0
Serial0 is up, line protocol is up
Internet Address 10.1.1.2/30, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type NON_BROADCAST, Cost: 1562
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 2.2.2.2, Interface address 10.1.1.2
No backup designated router on this network
Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
Hello due in 00:00:16
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
The neighbor command (Chapter 11) or the ip ospf network point-to-point command can be used on Router B to enable OSPF over the
Frame Relay link. Modify Router B using the ip ospf network command.
Router B
interface Serial0
ip address 10.1.1.2 255.255.255.252
encapsulation frame-relay
ip ospf network point-to-point
bandwidth 64
frame-relay map ip 10.1.1.1 110 broadcast
no frame-relay inverse-arp
frame-relay lmi-type ansi
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Verification
Verify that OSPF is treating the Frame Relay network as a point-to-point network on Router B.
rtrB#show ip ospf interface serial 0
Serial0 is up, line protocol is up
Internet Address 10.1.1.2/30, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1
Suppress hello for 0 neighbor(s)
Verify that the OSPF neighbor relationships are established.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
3.3.3.3
1 FULL/ -
00:00:31
10.1.1.6
Serial0/0.2
2.2.2.2
1 FULL/ -
00:00:36
10.1.1.2
Serial0/0.1
Each router is advertising its loopback network into OSPF. Check the routing tables on Routers A, B, and C to determine if the routes are
being advertised to all routers.
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
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* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/1563] via 10.1.1.2, 00:45:57, Serial0/0.1
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/1563] via 10.1.1.6, 00:45:57, Serial0/0.2
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0/0.1
C
10.1.1.4 is directly connected, Serial0/0.2
___________________________________________________________________________________
rtrB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O IA
1.1.1.1 [110/1563] via 10.1.1.1, 00:46:46, Serial0
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2.0.0.0/32 is subnetted, 1 subnets
C
2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O IA
3.3.3.3 [110/3125] via 10.1.1.1, 00:46:46, Serial0
10.0.0.0/30 is subnetted, 2 subnets
C
10.1.1.0 is directly connected, Serial0
O
10.1.1.4 [110/3124] via 10.1.1.1, 00:46:46, Serial0
_________________________________________________________________
rtrC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
O IA
1.1.1.1 [110/1563] via 10.1.1.5, 00:47:13, Serial0.1
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/3125] via 10.1.1.5, 00:47:13, Serial0.1
3.0.0.0/32 is subnetted, 1 subnets
C
3.3.3.3 is directly connected, Loopback0
10.0.0.0/30 is subnetted, 2 subnets
O
10.1.1.0 [110/3124] via 10.1.1.5, 00:47:14, Serial0.1
C
10.1.1.4 is directly connected, Serial0.1
Even though the routes are being advertised, they may not be reachable. Use the ping command to see if the routes can be reached.
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rtrA#ping 2.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms
rtrA#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms
______________________________________________________________________________
rtrB#ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms
rtrB#ping 3.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 3.3.3.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/8/12 ms
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______________________________________________________________________________
rtrC#ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms
rtrC#ping 2.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/8/12 ms
Troubleshooting
Step 1. Verify the IP address and netmask assignments used on the NBMA network interfaces.
Step 2. Verify that the proper DLCIs and IP addresses arebeing used. These can be checked using theshow frame-relay map
command.
rtrA#show frame-relay map
Serial0/0.2 (up): point-to-point dlci, dlci 102(0x66,0x1860), broadcast
status defined, active
Serial0/0.1 (up): point-to-point dlci, dlci 101(0x65,0x1850), broadcast
status defined, active
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Step 3. Before configuring OSPF, check IP connectivity by pinging the other end of each Frame Relay link.
Step 4. If you are mixing network types (multipoint and point-to-point), verify that the Hello intervals match on all routers.
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19-18 ip ospf priority priority
Syntax Description:
priority— The OSPF priority value for the interface. The range of values is 0 to 255. The default value is 1.
Purpose: On a multiaccess network such as Ethernet, the router with the highest priority will be elected the DR. If all interface priorities are
equal, then the router with the highest router ID will be elected the DR. The ip ospf priority command is used to influence the selection of the
DR on a multiaccess network. If the priority is 0, then the router will not be elected the DR or BDR.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Influencing the Election of the Designated Router
In Figure 19-14, Router B will be elected the DR on the Ethernet network because Router B has a higher router ID than Router A and their
OSPF priorities on the Ethernet network are equal.
Figure 19-14. Router B Is the DR on the Ethernet Network Because Its Router ID Is Higher than the
Router ID for Router A
Router A
.
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interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
ip address 172.16.1.1 255.255.255.0
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 0
______________________________________________________________________________
Router B
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
!
router ospf 1
network 172.16.1.0 0.0.0.255 area 0
Verify that Routers A and B have formed an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
172.16.1.2
1 FULL/DR
Dead Time Address
00:00:36
172.16.1.2
Interface
Ethernet0/0
______________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/BDR
Dead Time Address
00:00:39
172.16.1.1
Interface
Ethernet0
.
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Router B has been elected the DR because it has a higher router ID and the OSPF priorities for Routers A and B are both 1.
rtrA#show ip ospf interface ethernet 0/0
Ethernet0/0 is up, line protocol is up
Internet Address 172.16.1.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State BDR, Priority 1
Designated Router (ID) 172.16.1.2, Interface address 172.16.1.2
Backup Designated router (ID) 1.1.1.1, Interface address 172.16.1.1
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:09
Index 1/1, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 3
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 172.16.1.2 (Designated Router)
Suppress hello for 0 neighbor(s)
Modify the OSPF priority for the Ethernet interface on Router B so the value is 2.
Router B
interface Ethernet0
ip address 172.16.1.2 255.255.255.0
ip ospf priority 2
Verification
Verify that the new priority has been configured on Router B.
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rtrB#show ip ospf interface ethernet 0
Ethernet0 is up, line protocol is up
Internet Address 172.16.1.2/24, Area 0
Process ID 1, Router ID 172.16.1.2, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State DR, Priority 2
Designated Router (ID) 1.1.1.1, Interface address 172.16.1.1
Backup Designated router (ID) 172.16.1.2, Interface address 172.16.1.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1 (Designated Router)
Suppress hello for 0 neighbor(s)
Router A is still the BDR. For stability, OSPF will not elect another router as DR unless the current DR goes down. Shut down the Ethernet
interface on Router B and wait until the dead time has expired on Router A. After the dead time has expired on Router A, reenable the
Ethernet interface on Router B. Verify that Router A is now the DR.
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
172.16.1.2
2 FULL/BDR
Dead Time Address
00:00:39
172.16.1.2
Interface
Ethernet0/0
______________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
1.1.1.1
Pri State
1 FULL/DR
Dead Time Address
00:00:34
172.16.1.1
Interface
Ethernet0
Modify the priority on Router B so Router B is not eligible to be elected DRR or BDR.
Router B
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interface Ethernet0
ip address 172.16.1.2 255.255.255.0
ip ospf priority 0
Shut down the Ethernet interface on Router B and wait for the dead time to expire. After the dead time has expired, reenable the Ethernet
interface on Router B. Then check the status of the OSPF neighbor relationship.
rtrB#show ip ospf interface ethernet 0
Ethernet0 is up, line protocol is up
Internet Address 172.16.1.2/24, Area 0
Process ID 1, Router ID 172.16.1.2, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State DROTHER, Priority 0
Designated Router (ID) 1.1.1.1, Interface address 172.16.1.1
No backup designated router on this network
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:09
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1 (Designated Router)
Suppress hello for 0 neighbor(s)
______________________________________________________________________________
rtrA#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
172.16.1.2
0 FULL/DROTHER
00:00:31
Interface
172.16.1.2
Ethernet0/0
______________________________________________________________________________
rtrB#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
Interface
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1.1.1.1
1 FULL/DR
00:00:32
172.16.1.1
Ethernet0
Router B now has the status DROTHER because it cannot be the DR or BDR.
Troubleshooting
Step 1. Changing the priority value will not automatically cause OSPF to elect a new DR. If your design calls for a specific router
to become the DR on a multiaccess network, configure the interface priority before enabling the OSPF process.
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19-19 ip ospf retransmit-interval seconds
Syntax Description:
seconds— The range of values is 1 to 8192 seconds. The default value is 5 seconds.
Purpose: When a router advertises an LSA over an interface, the LSA is added to a retransmission list for the interface. The LSA will be
retransmitted until it is acknowledged. The number of seconds between the advertisements is called the retransmit interval.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Modifying the Retransmit Interval
Configure the network in Figure 19-15 so you can observe the default timer values over the serial link. You will then experiment by adjusting
the values of the retransmit interval.
Figure 19-15. The Retransmit Interval Is the Time Between Resending Unacknowledged LSAs
.
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Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
bandwidth 64
ip address 10.1.1.1 255.255.255.252
clockrate 64000
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
______________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
bandwidth 64
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.3 area 0
.
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Verify that Routers A and B have formed an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/ -
Dead Time Address
00:00:31
10.1.1.2
Interface
Serial0/1
Examine the default retransmission interval by inspecting the OSPF interface properties on Routers A and B.
rtrA#show ip ospf int serial 0/1
Serial0/1 is up, line protocol is up
Internet Address 10.1.1.1/30, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:07
Index 1/1, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2
Suppress hello for 0 neighbor(s)
____________________________________________________________________________
rtrB#show ip ospf interface serial 0
Serial0 is up, line protocol is up
Internet Address 10.1.1.2/30, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
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Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:05
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1
Suppress hello for 0 neighbor(s)
Change the retransmission interval on Router A to 10 seconds.
Router A
interface Serial0/1
bandwidth 64
ip address 10.1.1.1 255.255.255.252
ip ospf retransmit-interval 10
clockrate 64000
Unlike the Hello interval (discussed in Section 9-10) and the dead interval (discussed in Section 19-7), the retransmit interval does not have to
be the same on every interface attached to a common network.
Verification
Verify that the new retransmit interval has been configured on Router A.
rtrA#show ip ospf interface serial 0/1
Serial0/1 is up, line protocol is up
Internet Address 10.1.1.1/30, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 10
Hello due in 00:00:04
Index 1/1, flood queue length 0
Next 0x0(0)/0x0(0)
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Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2
Suppress hello for 0 neighbor(s)
Verify that Routers A and B have an OSPF neighbor relationship.
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/ -
Dead Time Address
00:00:37
10.1.1.2
Interface
Serial0/1
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using the show ip ospf neighbor command.
Step 2. Verify that the desired retransmit interval has been configured by using the commandshow ip ospf interface.
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19-20 ip ospf transmit-delay seconds
Syntax Description:
seconds— The range of values is 1 to 8192 seconds. The default value is 1 second.
Purpose: When an LSA is created, the router sets the LS age field to 0. The transmit delay value is added to the age field of the LSA. This
initial value represents the time delay of propagating the LSA over the interface.
Initial Cisco IOS Software Release: 10.0
Configuration Example: Modifying the Transmit Delay Value for an OSPF Interface
Configure the network in Figure 19-16 and set the transmit delay value on Router A to 2 seconds.
Figure 19-16. Transmit Delay Represents the LSA Propagation Delay Over an OSPF Interface
Router A
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial0/1
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bandwidth 64
ip address 10.1.1.1 255.255.255.252
ip ospf transmit-delay 2
clockrate 64000
!
router ospf 1
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 0
____________________________________________________________________________
Router B
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial0
ip address 10.1.1.2 255.255.255.252
bandwidth 64
!
router ospf 1
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.3 area 0
Verification
Verify that the transmit delay value has been modified, that the OSPF neighbor relationship is active, and that all OSPF routes are being
exchanged.
rtrA#show ip ospf interface serial 0/1
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Serial0/1 is up, line protocol is up
Internet Address 10.1.1.1/30, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 1562
Transmit Delay is 2 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:00
Index 1/1, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 2, maximum is 2
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2
Suppress hello for 0 neighbor(s)
rtrA#show ip ospf neighbor
Neighbor ID
2.2.2.2
Pri State
1 FULL/ -
Dead Time Address
00:00:36
10.1.1.2
Interface
Serial0/1
rtrA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
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1.0.0.0/32 is subnetted, 1 subnets
C
1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O IA
2.2.2.2 [110/1563] via 10.1.1.2, 00:40:39, Serial0/1
10.0.0.0/30 is subnetted, 1 subnets
C
10.1.1.0 is directly connected, Serial0/1
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using theshow ip ospf neighbor command.
Step 2. Verify that the desired transmit delay value has been configured by using the OSPF interface commandip ospf
transmit-delay.
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Chapter 20. show Commands
Section 20-1. show ip ospf
Section 20-2. show ip ospf process-id
Section 20-3. show ip ospf border-routers
Section 20-4. show ip ospf process-id border-routers
Section 20-5. show ip ospf database
Section 20-6. show ip ospf process-id database
Section 20-7. show ip ospf database adv-routerrouter-id
Section 20-8. show ip ospf process-id database adv-router router-id
Section 20-9. show ip ospf database asbr-summary
Section 20-10. show ip ospf process-id database asbr-summary
Section 20-11. show ip ospf database asbr-summary asbr-id
Section 20-12. show ip ospf process-id database asbr-summary asbr-id
Section 20-13. show ip ospf database database-summary
Section 20-14. show ip ospf process-id database database-summary
Section 20-15. show ip ospf database external
Section 20-16. show ip ospf process-id database external
Section 20-17. show ip ospf database network
Section 20-18. show ip ospf process-id database network
Section 20-19. show ip ospf database nssa-external
Section 20-20. show ip ospf process-id database nssa-external
Section 20-21. show ip ospf database router
Section 20-22. show ip ospf process-id database router
Section 20-23. show ip ospf database self-originate
Section 20-24. show ip ospf process-id database self-originate
Section 20-25. show ip ospf database summary
Section 20-26. show ip ospf process-id database summary
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Section 20-27. show ip ospf flood-list
Section 20-28. show ip ospf process-id flood-list
Section 20-29. show ip ospf flood-list int-name int-number
Section 20-30. show ip ospf process-id flood-list int-name int-number
Section 20-31. show ip ospf interface
Section 20-32. show ip ospf process-id interface
Section 20-33. show ip ospf interface int-name int-number
Section 20-34. show ip ospf process-id interface int-name int-number
Section 20-35. show ip ospf neighbor
Section 20-36. show ip ospf process-id neighbor
Section 20-37. show ip ospf neighbor neighbor-id
Section 20-38. show ip ospf process-id neighbor neighbor-id
Section 20-39. show ip ospf neighbor int-name int-number
Section 20-40. show ip ospf process-id neighbor int-name int-number
Section 20-41. show ip ospf neighbor detail
Section 20-42. show ip ospf process-id neighbor detail
Section 20-43. show ip ospf neighbor detail neighbor-id
Section 20-44. show ip ospf process-id neighbor detail neighbor-id
Section 20-45. show ip ospf neighbor int-name int-number
Section 20-46. show ip ospf process-id neighbor int-name int-number
Section 20-47. show ip ospf request-list
Section 20-48. show ip ospf process-id request-list
Section 20-49. show ip ospf request-list neighbor-id
Section 20-50. show ip ospf process-id request-list neighbor-id
Section 20-51. show ip ospf request-list int-name int-number
Section 20-52. show ip ospf process-id request-list int-name int-number
Section 20-53. show ip ospf retransmission-list
Section 20-54. show ip ospf process-id retransmission-list
Section 20-55. show ip ospf retransmission neighbor-id
Section 20-56. show ip ospf process-id retransmission neighbor-id
Section 20-57. show ip ospf retransmission int-name int-number
Section 20-58. show ip ospf process-id retransmission int-name int-number
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Section 20-59. show ip ospf summary-address
Section 20-60. show ip ospf process-id summary-address
Section 20-61. show ip ospf virtual-links
Section 20-62. show ip ospf process-id virtual-links
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20-1 show ip ospf
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20-2 show ip ospf process-id
Syntax Description:
process-id— The OSPF process ID. The range of values is 1 to 4,294,967,295.
Purpose: To display information and parameters for one or more OSPF processes. The output of this command can be filtered, using regular
expressions, by one of the following forms:
show ip ospf | begin regular-expression
show ip ospf | exclude regular-expression
show ip ospf | include regular-expression
Cisco IOS Software Initial Release: 10.0
Example: Displaying OSPF Process Information
The following is a representative output from the show ip ospf EXEC command.
r2#show ip ospf
Routing Process "ospf 1" with ID 2.2.2.2
Supports only single TOS(TOS0) routes
Supports opaque LSA
It is an area border router
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 1. Checksum Sum 0xAB1F
Number of opaque AS LSA 0. Checksum Sum 0x0
Number of DCbitless external and opaque AS LSA 0
Number of DoNotAge external and opaque AS LSA 0
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Number of areas in this router is 4. 4 normal 0 stub 0 nssa
External flood list length 0
Area BACKBONE(0)
Number of interfaces in this area is 3
Area has no authentication
SPF algorithm executed 19 times
Area ranges are
Number of LSA 15. Checksum Sum 0x7A630
Number of opaque link LSA 0. Checksum Sum 0x0
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 5
Flood list length 0
Area 1
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 10 times
Area ranges are
Number of LSA 22. Checksum Sum 0xD15F3
Number of opaque link LSA 0. Checksum Sum 0x0
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
Area 2
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm executed 2 times
Area ranges are
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Number of LSA 12. Checksum Sum 0x7AB94
Number of opaque link LSA 0. Checksum Sum 0x0
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
Area 9
Number of interfaces in this area is 2
Area has no authentication
SPF algorithm executed 3 times
Area ranges are
8.8.8.0/27 Active(1) Advertise
Number of LSA 12. Checksum Sum 0x6FB7C
Number of opaque link LSA 0. Checksum Sum 0x0
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
Table 20-1 provides an explanation for the significant lines in the preceding output.
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Table 20-1. Significant Output from show ip ospf
Line
Content Description
Routing Process "ospf 1" with ID
2.2.2.2
The local OSPF process ID and OSPF router ID.
It is an area border router
OSPF router type. Possible types are Area Border Router (ABR),
Autonomous System Border Router (ASBR), or internal.
SPF schedule delay 5 secs, Hold time
between two SPFs 10 secs
The hold time between Shortest Path First (SPF) calculations is 10
seconds. If there is a flapping interface or a duplicate IP address in the
OSPF domain, an SPF calculation will be triggered every time the router
receives an update. If the number of SPF calculations (see lines 16, 27,
38, and 49) is incrementing every 10 seconds, then there is probably a
flapping interface or a misconfiguration somewhere in the OSPF
domain.
Number and types of OSPF areas configured on the local router.
Number of areas in this router is 4. 4
normal 0 stub 0 nssa
Area BACKBONE(0)
Indicates the start of the output containing information for a specific
OSPF area.
Area 1
Area 2
Area 9
Number of interfaces in this area is 3
Number of interfaces, either physical or loopback, that have been
configured to run OSPF. The network command determines the
interfaces that will be active.
Area has no authentication
Type of authentication configured for the area.
SPF algorithm executed 19 times
Number of times the SPF calculation has been run.
Area ranges are
Indicates if OSPF routes are being summarized using the area range
command.
or
Area ranges are
8.8.8.0/27 Active(1) Advertise
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20-3 show ip ospf border-routers
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20-4 show ip ospf process-id border-routers
Syntax Description:
process-id— The OSPF process ID . Range of values is 1 to 4,294,967,295.
Purpose: To display the OSPF routing table entries to ABRs and ASBRs. The output of this command can be filtered, using regular
expressions, by one of the following forms:
show ip ospf border-routers | begin regular-expression
show ip ospf border-routers | exclude regular-expression
show ip ospf border-routers | include regular-expression
Initial Cisco IOS Software Release: 10.0
Example: Displaying OSPF Border Router Information
The following is a representative output from the show ip ospf border-routers EXEC command.
r6#show ip ospf border-routers
OSPF Process 1 internal Routing Table
Codes: i - Intra-area route, I - Inter-area route
I 4.4.4.4 [122] via 10.1.1.18, Serial0/1, ASBR, Area 7, SPF 5
i 1.1.1.1 [48] via 10.1.1.18, Serial0/1, ABR, Area 7, SPF 5
Table 20-2 provides an explanation for the highlighted line in the preceding output.
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Table 20-2. Significant Output from the show ip ospf border-routers Command
Field
Description
I
Indicates the type of route to the ABR or ASBR. Possible values are I for an inter-area route
and i for an intra-area route.
4.4.4.4
Indicates the router ID of the ABR or ASBR.
[122]
Indicates the OSPF cost of the route to the ABR or ASBR.
via
10.1.1.18
Indicates the next hop toward the ABR or ASBR.
Serial0/1
Indicates the interface used to reach the next hop.
ASBR
Indicates the border router type (ABR or ASBR).
Area 7
Indicates the area from which the route to the border router was learned.
SPF 5
The number of the SPF calculations that calculated this route.
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20-5 show ip ospf database
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20-6 show ip ospf process-id database
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20-7 show ip ospf database adv-router router-id
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20-8 show ip ospf process-id database adv-router router-id
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20-9 show ip ospf database asbr-summary
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20-10 show ip ospf process-id database asbr-summary
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20-11 show ip ospf database asbr-summary asbr-id
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20-12 show ip ospf process-id database asbr-summary asbr-id
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20-13 show ip ospf database database-summary
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20-14 show ip ospf process-id database database-summary
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20-15 show ip ospf database external
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20-16 show ip ospf process-id database external
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20-17 show ip ospf database network
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20-18 show ip ospf process-id database network
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20-19 show ip ospf database nssa-external
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20-20 show ip ospf process-id database nssa-external
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20-21 show ip ospf database router
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20-22 show ip ospf process-id database router
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20-23 show ip ospf database self-originate
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20-24 show ip ospf process-id database self-originate
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20-25 show ip ospf database summary
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20-26 show ip ospf process-id database summary
Syntax Description:
process-id— The OSPF process ID. The range of values is 1 to 4,294,967,295.
router-id— The OSPF router ID of the advertising router.
asbr-id— The OSPF router ID of the ASBR.
Purpose: To display information contained in the OSPF database. An OSPF process ID can be used if more than one OSPF process is
active, using the form show ip ospf process-id database. The output of this command can be filtered, using regular expressions, by one of
the following forms:
show ip ospf database | begin regular-expression
show ip ospf database | exclude regular-expression
show ip ospf database | include regular-expression
Initial Cisco IOS Software Release: 10.0. The database-summary option was added in Release 11.0 and theadv-router and self-originate
options were added in Release 12.0.
Example 1: Displaying OSPF Database Information from a Specific OSPF Router
The following is a representative output from the show ip ospf database adv-router EXEC command.
r6#show ip ospf database adv-router 1.1.1.1
OSPF Router with ID (6.6.6.6) (Process ID 1)
Router Link States (Area 7)
Link ID
ADV Router
1.1.1.1
1.1.1.1
Age
431
Seq#
Checksum Link count
0x80000012 0x2714 2
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Summary Net Link States (Area 7)
Link ID
ADV Router
Age
Seq#
Checksum
1.1.1.1
1.1.1.1
431
0x80000010 0x29FB
2.2.2.2
1.1.1.1
431
0x80000010 0x7D63
4.4.4.4
1.1.1.1
431
0x80000010 0x8549
8.8.8.0
1.1.1.1
431
0x80000003 0x18E4
10.1.1.0
1.1.1.1
431
0x80000010 0x24BC
10.1.1.4
1.1.1.1
431
0x80000010 0x3785
10.1.1.12
1.1.1.1
431
0x80000010 0xF1A8
172.16.1.0
1.1.1.1
1198
0x80000013 0x213
172.16.2.0
1.1.1.1
431
0x80000010 0x9888
Summary ASB Link States (Area 7)
Link ID
ADV Router
4.4.4.4
1.1.1.1
Age
431
Seq#
Checksum
0x80000010 0x6D61
Table 20-3 provides an explanation for the highlighted line in the preceding output.
Table 20-3. Significant Output from the show ip ospf database adv-router Command
Field
Description
10.1.1.12
Indicates the route advertised by the advertising router.
1.1.1.1
Indicates the OSPF router ID of the advertising router.
431
Indicates the age of the LSA for this route.
0x80000010
Indicates the LSA sequence number used to detect old or duplicate LSAs.
0xF1A8
Indicates the LSA checksum.
.
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Example 2: Displaying OSPF Database Information from an OSPF ASBR Router
The following is representative output from the show ip ospf database asbr-summary EXEC command.
r6#show ip ospf database asbr-summary
OSPF Router with ID (6.6.6.6) (Process ID 1)
Summary ASB Link States (Area 7)
Routing Bit Set on this LSA
LS age: 1124
Options: (No TOS-capability, DC, Upward)
LS Type: Summary Links(AS Boundary Router)
Link State ID: 4.4.4.4 (AS Boundary Router address)
Advertising Router: 1.1.1.1
LS Seq Number: 80000010
Checksum: 0x6D61
Length: 28
Network Mask: /0
TOS: 0 Metric: 74
Table 20-4 provides an explanation for the highlighted lines in the preceding output.
Table 20-4. Significant Output from the show ip ospf database asbr-summary Command
Field
Description
OSPF router ID of the ASBR.
Link State ID: 4.4.4.4
(AS Boundary Router address)
.
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Field
Advertising Router: 1.1.1.1
Description
OSPF router ID of the router advertising the LSA.
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20-27 show ip ospf flood-list
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20-28 show ip ospf process-id flood-list
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20-29 show ip ospf flood-list int-name int-number
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20-30 show ip ospf process-id flood-list int-name int-number
Syntax Description:
process-id— The OSPF process ID. The range of values is 1 to 4,294,967,295.
int-name— Interface name.
int-number— Interface number.
Purpose: To display LSAs that are queued for flooding. An OSPF process ID can be used if more than one OSPF process is active using the
form show ip ospf process-id flood-list. The output of this command can be filtered, using regular expressions, by one of the following forms:
show ip ospf flood-list | begin regular-expression
show ip ospf flood-list | exclude regular-expression
show ip ospf flood-list | include regular-expression
Initial Cisco IOS Software Release: 12.0 (1)T
Example: Displaying All OSPF Floodlist Information
The following is a representative output from the show ip ospf flood-list EXEC command.
r4#show ip ospf flood-list
OSPF Router with ID (4.4.4.4) (Process ID 1)
Interface Serial0/0, Queue length 0
Interface Ethernet1/0, Queue length 0
Interface Ethernet0/0, Queue length 0
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Interface Loopback0, Queue length 0
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20-31 show ip ospf interface
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20-32 show ip ospf process-id interface
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20-33 show ip ospf interface int-name int-number
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20-34 show ip ospf process-id interface int-name int-number
Syntax Description:
process-id— The OSPF process ID. The range of values is 1 to 4,294,967,295.
int-name— Interface name.
int-number— Interface number.
Purpose: To display information regarding OSPF-enabled interfaces. An OSPF process ID can be used if more than one OSPF process is
active using the form show ip ospf process-id interface. The output of this command can be filtered, using regular expressions, by one of the
following forms:
show ip ospf interface | begin regular-expression
show ip ospf interface | exclude regular-expression
show ip ospf interface | include regular-expression
Initial Cisco IOS Software Release: 10.0
Example 1: Displaying Information for an OSPF-Enabled Interface
The following is a representative output from the show ip ospf interface EXEC command. This command can be used to verify that an
interface is enabled for OSPF, verify that the interface is in the proper OSPF area, and inspect the OSPF parameters that have been
configured such as priority, Hello interval, and dead interval.
r4#show ip ospf 1 interface ethernet 1/0
Ethernet1/0 is up, line protocol is up
Internet Address 172.16.2.2/24, Area 0
Process ID 1, Router ID 4.4.4.4, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 4.4.4.4, Interface address 172.16.2.2
Backup Designated router (ID) 2.2.2.2, Interface address 172.16.2.1
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Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:08
Index 2/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 3, maximum is 3
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2 (Backup Designated Router)
Suppress hello for 0 neighbor(s)
Table 20-5 provides an explanation for the significant lines in the preceding output.
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Table 20-5. Significant Output from show ip ospf interface
Line
Content Description
Ethernet1/0 is up, line protocol is up
Link and protocol status.
Internet Address 172.16.2.2/24, Area 0
Interface IP address, prefix length, and assigned OSPF area.
OSPF process ID and local OSPF router ID.
Process ID 1, Router ID 4.4.4.4,
OSPF network type and link cost.
Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State DR,
This router is the DR for the Ethernet network and has an OSPF
priority of 1.
Priority 1
Router ID and IP address of the BDR for this network.
Backup Designated router (ID) 2.2.2.2,
Interface address 172.16.2.1
OSPF timer values for this interface.
Timer intervals configured, Hello 10,
Dead 40, Wait 40, Retransmit 5
There is one neighbor on this interface and that neighbor is the BDR.
Neighbor Count is 1, Adjacent neighbor
count is 1
Adjacent with neighbor 2.2.2.2
(Backup Designated Router)
Example 2: Displaying OSPF Timer Information for an OSPF-enabled Interface
The following example demonstrates how to use a regular expression to limit the amount of information displayed by the show ip ospf
interface command. A regular expression will be used to display only information regarding the OSPF timer values for a specific OSPF
interface.
r4#show ip ospf interface ethernet 1/0 | include Timer
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
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20-35 show ip ospf neighbor
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20-36 show ip ospf process-id neighbor
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20-37 show ip ospf neighbor neighbor-id
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20-38 show ip ospf process-id neighbor neighbor-id
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20-39 show ip ospf neighbor int-name int-number
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20-40 show ip ospf process-id neighbor int-name int-number
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20-41 show ip ospf neighbor detail
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20-42 show ip ospf process-id neighbor detail
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20-43 show ip ospf neighbor detail neighbor-id
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20-44 show ip ospf process-id neighbor detail neighbor-id
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20-45 show ip ospf neighbor int-name int-number
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20-46 show ip ospf process-id neighbor int-name int-number
Syntax Description:
neighbor-id— OSPF router ID.
int-name— Interface name.
int-number— Interface number.
Purpose: To display information regarding OSPF-enabled interfaces. An OSPF process ID can be used if more than one OSPF process is
active using the form show ip ospf process-id neighbor. The output of this command can be filtered, using regular expressions, by one of
the following forms:
show ip ospf neighbor | begin regular-expression
show ip ospf neighbor | exclude regular-expression
show ip ospf neighbor | include regular-expression
Initial Cisco IOS Software Release: 10.0
Example 1: Displaying Information for All OSPF Neighbors
The following is a representative output from the show ip ospf neighbor EXEC command.
r2#show ip ospf neighbor
Neighbor ID
Pri State
Dead Time Address
00:00:35
172.16.2.2
Interface
4.4.4.4
1 FULL/DR
Ethernet0/0
3.3.3.3
1 FULL/ -
00:00:38
10.1.1.6
Serial0/1
1.1.1.1
1 FULL/ -
00:00:38
10.1.1.1
Serial0/0
A regular expression can be used to display information about a specific neighbor.
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r2#show ip ospf neighbor | include 4.4.4.4
4.4.4.4
1 FULL/DR
00:00:35
172.16.2.2
Ethernet0/0
Example 2: Displaying Detailed Information for a Specific OSPF Neighbor
r2#show ip ospf neighbor detail 1.1.1.1
Neighbor 1.1.1.1, interface address 10.1.1.1
In the area 1 via interface Serial0/0
Neighbor priority is 1, State is FULL, 12 state changes
DR is 0.0.0.0 BDR is 0.0.0.0
Options is 0x2
Dead timer due in 00:00:38
Neighbor is up for 4d02h
Index 1/1, retransmission queue length 0, number of retransmission 1
First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0)
Last retransmission scan length is 1, maximum is 1
Last retransmission scan time is 0 msec, maximum is 0 msec
Table 20-6 provides an explanation for the significant lines in the preceding output.
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Table 20-6. Significant Output from show ip ospf neighbor detail
Line
Content Description
Neighbor's router ID and address on this network.
Neighbor 1.1.1.1, interface address
10.1.1.1
In the area 1 via interface Serial0/0
Neighbor priority is 1, State is
The neighbor is in Area 1 and reachable via interface Serial0/0.
The neighbor's OSPF priority, the state of the neighbor relationship, and
number of state changes for the neighbor relationship.
FULL, 12 state changes
DR is 0.0.0.0 BDR is 0.0.0.0
This is a serial link, so there is no DR or BDR.
Options is 0x2
0x00 indicates that the area is a stub area. 0x2 indicates that the area is
not a stub area.
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20-47 show ip ospf request-list
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20-48 show ip ospf process-id request-list
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20-49 show ip ospf request-list neighbor-id
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20-50 show ip ospf process-id request-list neighbor-id
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20-51 show ip ospf request-list int-name int-number
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20-52 show ip ospf process-id request-list int-name int-number
Syntax Description:
process-id— The OSPF process ID. The range of values is 1 to 4,294,967,295.
neighbor-id— Neighbor's OSPF router ID.
int-name— Interface name.
int-number— Interface number.
Purpose: To display all link-state information requested by a router. An OSPF process ID can be used if more than one OSPF process is
active using the form show ip ospf process-id request-list. The output of this command can be filtered, using regular expressions, by one of
the following forms:
show ip ospf request-list | begin regular-expression
show ip ospf request-list | exclude regular-expression
show ip ospf request-list | include regular-expression
Initial Cisco IOS Software Release: 10.2
Example: Displaying Request List Information for a Particular OSPF Neighbor
The following is a representative output from the show ip ospf request-list EXEC command.
r2#show ip ospf request-list 3.3.3.3
OSPF Router with ID (2.2.2.2) (Process ID 1)
Neighbor 3.3.3.3, interface Serial0/1 address 10.1.1.6
Type LS ID
ADV RTR
Seq NO
Age
Checksum
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1 3.3.3.3
3.3.3.3
0x8000020C 9
0x6572
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20-53 show ip ospf retransmission-list
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20-54 show ip ospf process-id retransmission-list
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20-55 show ip ospf retransmission neighbor-id
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20-56 show ip ospf process-id retransmission neighbor-id
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20-57 show ip ospf retransmission int-name int-number
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20-58 show ip ospf process-id retransmission int-name int-number
Syntax Description:
process-id— The OSPF process ID. The range of values is 1 to 4,294,967,295.
neighbor-id— Neighbor's OSPF router ID.
int-name— Interface name.
int-number— Interface number.
Purpose: To display a list of LSAs waiting to be re-sent. An OSPF process ID can be used if more than one OSPF process is active using the
form show ip ospf process-id retransmission-list. The output of this command can be filtered, using regular expressions, by one of the
following forms:
show ip ospf retransmission-list | begin regular-expression
show ip ospf retransmission-list | exclude regular-expression
show ip ospf retransmission-list | include regular-expression
Initial Cisco IOS Software Release: 10.2
Example: Displaying the List of LSAs Waiting to Be Re-sent on a Particular Interface
The following is a representative output from the show ip ospf retransmission-list EXEC command.
r2#show ip ospf retransmission-list serial 0/0
OSPF Router with ID (2.2.2.2) (Process ID 1)
Neighbor 1.1.1.1, interface Serial0/0 address 10.1.1.1
Link state retransmission due in 2969 msec, Queue length 2
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Type LS ID
1 2.2.2.2
ADV RTR
2.2.2.2
Seq NO
0x80000219
Age
0
Checksum
0xB123
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20-59 show ip ospf summary-address
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20-60 show ip ospf process-id summary-address
Syntax Description:
process-id— The OSPF process ID. The range of values is 1 to 4,294,967,295.
Purpose: To display a list of summary addresses that have been configured on the router. An OSPF process ID can be used if more than one
OSPF process is active using the form show ip ospf process-id summary-address. The output of this command can be filtered, using
regular expressions, by one of the following forms:
show ip ospf summary-address | begin regular-expression
show ip ospf summary-address | exclude regular-expression
show ip ospf summary-address | include regular-expression
Initial Cisco IOS Software Release: 10.0
Example: Displaying the List of Summary Addresses Configured on a Router
The following is a representative output from the show ip ospf summary-address EXEC command.
r4#show ip ospf summary-address
OSPF Process 1, Summary-address
169.254.0.0/255.254.0.0 Metric 10, Type 2, Tag 0
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20-61 show ip ospf virtual-links
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20-62 show ip ospf process-id virtual-links
Syntax Description:
process-id— The OSPF process ID. The range of values is 1 to 4,294,967,295.
Purpose: To display the status and information regarding any virtual links that have been configured on the router. An OSPF process ID can
be used if more than one OSPF process is active using the form show ip ospf process-id virtual-links. The output of this command can be
filtered, using regular expressions, by one of the following forms:
show ip ospf virtual-links | begin regular-expression
show ip ospf virtual-links | exclude regular-expression
show ip ospf virtual-links | include regular-expression
Initial Cisco IOS Software Release: 10.0
Example: Displaying the Status of All Virtual Links Configured on the Local Router
The following is a representative output from the show ip ospf virtual-links EXEC command.
r1#show ip ospf virtual-links
Virtual Link OSPF_VL0 to router 2.2.2.2 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Serial0/0, Cost of using 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:01
Adjacency State FULL (Hello suppressed)
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Chapter 21. debug Commands
Section 21-1. debug ip ospf adj
Section 21-2. debug ip ospf events
Section 21-3. debug ip ospf flood
Section 21-4. debug ip ospf floodip-access-list-number
Section 21-5. debug ip ospf lsa-generation
Section 21-6. debug ip ospf lsa-generation ip-access-list-number
Section 21-7. debug ip ospf packet
Section 21-8. debug ip ospf retransmission
Section 21-9. debug ip ospf spf
Section 21-10. debug ip ospf spf external
Section 21-11. debug ip ospf spf external access-list-number
Section 21-12. debug ip ospf spf inter
Section 21-13. debug ip ospf spf inter access-list-number
Section 21-14. debug ip ospf spf intra
Section 21-15. debug ip ospf spf intra access-list-number
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21-1 debug ip ospf adj
Syntax Description:
This command has no arguments.
Purpose: To display information regarding the formation of an OSPF neighbor relationship. If an OSPF neighbor relationship is not being
formed between two routers, this command can be used to determine the problem.
Example 1: Displaying the Successful Formation of an OSPF Adjacency
The following is representative output from the debug ip ospf adj EXEC command for a successful configuration. The EXEC commandclear
ip ospf process is used to clear the existing adjacency.
r6#debug ip ospf adj
OSPF adjacency events debugging is on
r6#clear ip ospf process
Reset ALL OSPF processes? [no]: yes
r6#
6w3d: OSPF: Interface Loopback0 going Down
6w3d: OSPF: 6.6.6.6 address 6.6.6.6 on Loopback0 is dead, state DOWN
6w3d: OSPF: Interface Serial0/1 going Down
6w3d: OSPF: 6.6.6.6 address 10.1.1.17 on Serial0/1 is dead, state DOWN
6w3d: OSPF: 1.1.1.1 address 10.1.1.18 on Serial0/1 is dead, state DOWN
6w3d: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on Serial0/1 from FULL to DOWN,
Neighbor Down: Interface down or detached
6w3d: OSPF: Interface Loopback0 going Up
6w3d: OSPF: Interface Serial0/1 going Up
6w3d: OSPF: Build router LSA for area 7, router ID 6.6.6.6, seq 0x80000001
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6w3d: OSPF: 2 Way Communication to 1.1.1.1 on Serial0/1, state 2WAY
6w3d: OSPF: Send DBD to 1.1.1.1 on Serial0/1 seq 0x12F4 opt 0x42 flag 0x7 len 32
6w3d: OSPF: Rcv DBD from 1.1.1.1 on Serial0/1 seq 0x2071 opt 0x2 flag 0x7 len 32
mtu 1500 state EXSTART
6w3d: OSPF: First DBD and we are not SLAVE
6w3d: OSPF: Rcv DBD from 1.1.1.1 on Serial0/1 seq 0x12F4 opt 0x2 flag 0x2 len 27
2 mtu 1500 state EXSTART
6w3d: OSPF: NBR Negotiation Done. We are the MASTER
6w3d: OSPF: Send DBD to 1.1.1.1 on Serial0/1 seq 0x12F5 opt 0x42 flag 0x3 len 52
6w3d: OSPF: Database request to 1.1.1.1
6w3d: OSPF: sent LS REQ packet to 10.1.1.18, length 144
6w3d: OSPF: Rcv DBD from 1.1.1.1 on Serial0/1 seq 0x12F5 opt 0x2 flag 0x0 len 32
mtu 1500 state EXCHANGE
6w3d: OSPF: Send DBD to 1.1.1.1 on Serial0/1 seq 0x12F6 opt 0x42 flag 0x1 len 32
6w3d: OSPF: Rcv DBD from 1.1.1.1 on Serial0/1 seq 0x12F6 opt 0x2 flag 0x0 len 32
mtu 1500 state EXCHANGE
6w3d: OSPF: Exchange Done with 1.1.1.1 on Serial0/1
6w3d: OSPF: Synchronized with 1.1.1.1 on Serial0/1, state FULL
6w3d: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on Serial0/1 from LOADING to FULL,
Loading Done
Example 2: Displaying the Attempted Formation of an OSPF Adjacency when There
Is an Area Mismatch
The following is representative output from the debug ip ospf adj EXEC command when one end of a serial link has been configured in the
wrong OSPF area. The EXEC command clear ip ospf process is used to clear the existing adjacency.
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r6#debug ip ospf adj
OSPF adjacency events debugging is on
r6#clear ip ospf process
Reset ALL OSPF processes? [no]: yes
r6#
6w3d: OSPF: Interface Loopback0 going Down
6w3d: OSPF: 6.6.6.6 address 6.6.6.6 on Loopback0 is dead, state DOWN
6w3d: OSPF: Interface Serial0/1 going Down
6w3d: OSPF: 6.6.6.6 address 10.1.1.17 on Serial0/1 is dead, state DOWN
6w3d: OSPF: Interface Loopback0 going Up
6w3d: OSPF: Interface Serial0/1 going Up
6w3d: OSPF: Build router LSA for area 7, router ID 6.6.6.6, seq 0x80000001
6w3d: OSPF: Build router LSA for area 17, router ID 6.6.6.6, seq 0x80000001
6w3d: OSPF: Rcv pkt from 10.1.1.18, Serial0/1, area 0.0.0.17
mismatch area 0.0.0.7 in the header
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21-2 debug ip ospf events
Syntax Description:
This command has no arguments.
Purpose: To display information regarding OSPF events such as the forming of adjacencies, Hello packets, LSA flooding, Designated Router
(DR) selection, and shortest path first (SPF) calculations. If an OSPF neighbor relationship is not being formed between two routers, then this
command can be used to determine the problem.
Example 1: Displaying the Successful Formation of an OSPF Adjacency
The following is representative output from the debug ip ospf events EXEC command for a successful configuration. The EXEC command
clear ip ospf process is used to clear the existing adjacency.
r6#debug ip ospf events
OSPF events debugging is on
r6#clear ip ospf process
Reset ALL OSPF processes? [no]: yes
r6#
6w4d: OSPF: Rcv hello from 1.1.1.1 area 7 from Serial0/1 10.1.1.18
6w4d: OSPF: 2 Way Communication to 1.1.1.1 on Serial0/1, state 2WAY
6w4d: OSPF: Send DBD to 1.1.1.1 on Serial0/1 seq 0x22BC opt 0x42 flag 0x7 len 32
6w4d: OSPF: End of hello processing
6w4d: OSPF: Rcv DBD from 1.1.1.1 on Serial0/1 seq 0x1D6E opt 0x2 flag 0x7 len 32
mtu 1500 state EXSTART
6w4d: OSPF: First DBD and we are not SLAVE
6w4d: OSPF: Rcv DBD from 1.1.1.1 on Serial0/1 seq 0x22BC opt 0x2 flag 0x2 len 27
2 mtu 1500 state EXSTART
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6w4d: OSPF: NBR Negotiation Done. We are the MASTER
6w4d: OSPF: Send DBD to 1.1.1.1 on Serial0/1 seq 0x22BD opt 0x42 flag 0x3 len 52
6w4d: OSPF: Database request to 1.1.1.1
6w4d: OSPF: sent LS REQ packet to 10.1.1.18, length 144
6w4d: OSPF: Rcv DBD from 1.1.1.1 on Serial0/1 seq 0x22BD opt 0x2 flag 0x0 len 32
mtu 1500 state EXCHANGE
6w4d: OSPF: Send DBD to 1.1.1.1 on Serial0/1 seq 0x22BE opt 0x42 flag 0x1 len 32
6w4d: OSPF: Rcv DBD from 1.1.1.1 on Serial0/1 seq 0x22BE opt 0x2 flag 0x0 len 32
mtu 1500 state EXCHANGE
6w4d: OSPF: Exchange Done with 1.1.1.1 on Serial0/1
6w4d: OSPF: Synchronized with 1.1.1.1 on Serial0/1, state FULL
6w4d: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on Serial0/1 from LOADING to FULL,
Loading Done
Example 2: Debugging an OSPF Adjacency Problem
The following is representative output from the debug ip ospf events EXEC command when there is a mismatch in the dead interval.
r6#debug ip ospf events
OSPF events debugging is onr6#
6w4d: OSPF: Rcv hello from 1.1.1.1 area 7 from Serial0/1 10.1.1.18
6w4d: OSPF: Mismatched hello parameters from 10.1.1.18
6w4d: OSPF: Dead R 40 C 123, Hello R 10 C 10
R is the received dead interval time and C is the dead interval time configured on the local router.
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21-3 debug ip ospf flood
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21-4 debug ip ospf flood ip-access-list-number
Syntax Description:
ip-access-list-number— Number of the IP access list used to filter the output of the flood command. Valid ranges are 1 to 99 and
1300 to 1999.
Purpose: To enable the display of events generated by the OSPF flooding protocol. Thedebug ip ospf flood command generates
information about flooding, which includes the sending and receiving of update and acknowledgement packets.
Example 1: Displaying All Output from the OSPF Flooding Protocol
Debugging the OSPF flooding protocol will generate an enormous amount of information on its operation, as shown in the following output.
r6#debug ip ospf flood
OSPF flooding debugging is on
r6#clear ip ospf process
Reset ALL OSPF processes? [no]: yes
r6#
6w4d: Inc retrans unit nbr count index 1 (0/1) to 1/1
6w4d: Set Nbr 1.1.1.1 1 first flood info from 0 (0) to 623AA2D8 (300)
6w4d: Init Nbr 1.1.1.1 1 next flood info to 623AA2D8
6w4d: OSPF: Add Type 1 LSA ID 6.6.6.6 Adv rtr 6.6.6.6 Seq 80000125 to Serial0/1
1.1.1.1 retransmission list
6w4d: OSPF: Start Serial0/1 1.1.1.1 retrans timer
6w4d: Set idb next flood info from 0 (0) to 623AA2D8 (300)
6w4d: OSPF: Add Type 1 LSA ID 6.6.6.6 Adv rtr 6.6.6.6 Seq 80000125 to Serial0/1
flood list
6w4d: OSPF: Start Serial0/1 pacing timer
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6w4d: OSPF: Flooding update on Serial0/1 to 224.0.0.5 Area 7
6w4d: OSPF: Send Type 1, LSID 6.6.6.6, Adv rtr 6.6.6.6, age 3600, seq 0x80000125
(0)
6w4d: Create retrans unit 0x623B71A8/0x623C5DE8 1 (0/1) 1
6w4d: OSPF: Set nbr 1 (0/1) retrans to 4560 count to 1
6w4d: Set idb next flood info from 623AA2D8 (300) to 0 (0)
6w4d: OSPF: Remove Type 1 LSA ID 6.6.6.6 Adv rtr 6.6.6.6 Seq 80000125 from
Serial0/1 flood list
6w4d: OSPF: Stop Serial0/1 flood timer
6w4d: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on Serial0/1 from FULL to DOWN,
Neighbor Down: Interface down or detached
6w4d: Dec retrans unit nbr count index 1 (0/1) to 0/0
6w4d: Free nbr retrans unit 0x623B71A8/0x623C5DE8 0 total 0. Also Free nbr
retrans block
6w4d: Set Nbr 1.1.1.1 1 first flood info from 623AA2D8 (300) to 0 (0)
6w4d: Adjust Nbr 1.1.1.1 1 next flood info to 0
6w4d: OSPF: Remove Type 1 LSA ID 6.6.6.6 Adv rtr 6.6.6.6 Seq 80000125 from 1.1.1
.1 retransmission list
6w4d: OSPF: Stop nbr 1.1.1.1 retransmission timer
6w4d: OSPF: Build router LSA for area 7, router ID 6.6.6.6, seq 0x80000001
6w4d: OSPF: received update from 1.1.1.1, Serial0/1
6w4d: OSPF: Rcv Update Type 1, LSID 1.1.1.1, Adv rtr 1.1.1.1, age 5, seq 0x80000
130
6w4d: OSPF: Rcv Update Type 3, LSID 172.16.2.0, Adv rtr 1.1.1.1, age 107, seq 0x
80000001
6w4d:
Mask /24
6w4d: OSPF: Rcv Update Type 3, LSID 172.16.1.0, Adv rtr 1.1.1.1, age 107, seq 0x
80000001
6w4d:
Mask /24
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6w4d: OSPF: Rcv Update Type 3, LSID 10.1.1.12, Adv rtr 1.1.1.1, age 107, seq 0x8
0000001
6w4d:
Mask /30
6w4d: OSPF: Rcv Update Type 3, LSID 10.1.1.4, Adv rtr 1.1.1.1, age 107, seq 0x80
000001
6w4d:
Mask /30
6w4d: OSPF: Rcv Update Type 3, LSID 10.1.1.0, Adv rtr 1.1.1.1, age 353, seq 0x80
000110
6w4d:
Mask /30
6w4d: OSPF: Rcv Update Type 3, LSID 8.8.8.0, Adv rtr 1.1.1.1, age 107, seq 0x800
00001
6w4d:
Mask /27
6w4d: OSPF: Rcv Update Type 3, LSID 4.4.4.4, Adv rtr 1.1.1.1, age 107, seq 0x800
00001
6w4d:
Mask /32
6w4d: OSPF: Rcv Update Type 3, LSID 2.2.2.2, Adv rtr 1.1.1.1, age 107, seq 0x800
00001
6w4d:
Mask /32
6w4d: OSPF: Rcv Update Type 3, LSID 1.1.1.1, Adv rtr 1.1.1.1, age 353, seq 0x800
00110
6w4d:
Mask /32
6w4d: OSPF: Rcv Update Type 4, LSID 4.4.4.4, Adv rtr 1.1.1.1, age 107, seq 0x800
00001
6w4d:
Mask /0
6w4d: OSPF: Rcv Update Type 5, LSID 169.254.0.0, Adv rtr 4.4.4.4, age 989, seq 0
x80000090
6w4d:
Mask /15
6w4d: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on Serial0/1 from LOADING to FULL,
Loading Done
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... (many more pages of output!!!)
Example 2: Selective Display of OSPF Protocol Debugging Output
For this example, only flooding protocol information for LSAs with an ID of 172.16.1.0/24 will be displayed.
access-list 1 permit 172.16.1.0 0.0.0.255
r6#debug ip ospf flood 1
OSPF flooding debugging is on for access list 1
r6#clear ip ospf process
Reset ALL OSPF processes? [no]: yes
r6#
6w4d: Inc retrans unit nbr count index 1 (0/1) to 1/1
6w4d: Set Nbr 1.1.1.1 1 first flood info from 0 (0) to 623AA408 (303)
6w4d: Init Nbr 1.1.1.1 1 next flood info to 623AA408
6w4d: OSPF: Start Serial0/1 1.1.1.1 retrans timer
6w4d: Set idb next flood info from 0 (0) to 623AA408 (303)
6w4d: OSPF: Start Serial0/1 pacing timer
6w4d: Create retrans unit 0x623B71A8/0x623C5DE8 1 (0/1) 1
6w4d: OSPF: Set nbr 1 (0/1) retrans to 4504 count to 1
6w4d: Set idb next flood info from 623AA408 (303) to 0 (0)
6w4d: OSPF: Stop Serial0/1 flood timer
6w4d: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on Serial0/1 from FULL to DOWN,
Neighbor Down: Interface down or detached
6w4d: Dec retrans unit nbr count index 1 (0/1) to 0/0
6w4d: Free nbr retrans unit 0x623B71A8/0x623C5DE8 0 total 0. Also Free nbr
retrans block
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6w4d: Set Nbr 1.1.1.1 1 first flood info from 623AA408 (303) to 0 (0)
6w4d: Adjust Nbr 1.1.1.1 1 next flood info to 0
6w4d: OSPF: Stop nbr 1.1.1.1 retransmission timer
6w4d: OSPF: Build router LSA for area 7, router ID 6.6.6.6, seq 0x80000001
6w4d: OSPF: received update from 1.1.1.1, Serial0/1
6w4d: OSPF: Rcv Update Type 3, LSID 172.16.1.0, Adv rtr 1.1.1.1, age 287, seq 0x
80000001
6w4d:
Mask /24
6w4d: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on Serial0/1 from LOADING to FULL,
Loading Done
6w4d: Inc retrans unit nbr count index 1 (0/1) to 1/1
6w4d: Set Nbr 1.1.1.1 1 first flood info from 0 (0) to 623AA324 (304)
6w4d: Init Nbr 1.1.1.1 1 next flood info to 623AA324
6w4d: OSPF: Start Serial0/1 1.1.1.1 retrans timer
6w4d: Set idb next flood info from 0 (0) to 623AA324 (304)
6w4d: OSPF: Start Serial0/1 pacing timer
6w4d: OSPF: Build router LSA for area 7, router ID 6.6.6.6, seq 0x80000002
6w4d: Create retrans unit 0x623B71A8/0x623C5DE8 1 (0/1) 1
6w4d: OSPF: Set nbr 1 (0/1) retrans to 4568 count to 1
6w4d: Set idb next flood info from 623AA324 (304) to 0 (0)
6w4d: OSPF: Stop Serial0/1 flood timer
6w4d: Update router LSA 6.6.6.6 6.6.6.6 1 80000126
6w4d: OSPF: Rate limit LSA generation for 6.6.6.6 6.6.6.6 1
6w4d: OSPF: Sending delayed ACK on Serial0/1
6w4d: OSPF: Ack Type 3, LSID 172.16.1.0, Adv rtr 1.1.1.1, age 287, seq 0x8000000
1
6w4d: OSPF: Set nbr 1 (0/1) retrans to 4960 count to 2
6w4d: Set Nbr 1.1.1.1 1 next flood info from 623AA324 (304) to 623AA324 (304)
6w4d: Dec retrans unit nbr count index 1 (0/1) to 0/0
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6w4d: Free nbr retrans unit 0x623B71A8/0x623C5DE8 0 total 0. Also Free nbr
retrans block
ns block
6w4d: Adjust Nbr 1.1.1.1 1 next flood info to 0
6w4d: OSPF: Stop nbr 1.1.1.1 retransmission timer
6w4d: Inc retrans unit nbr count index 1 (0/1) to 1/1
6w4d: Set Nbr 1.1.1.1 1 first flood info from 0 (0) to 623AA324 (305)
6w4d: Init Nbr 1.1.1.1 1 next flood info to 623AA324
6w4d: OSPF: Start Serial0/1 1.1.1.1 retrans timer
6w4d: Set idb next flood info from 0 (0) to 623AA324 (305)
6w4d: OSPF: Start Serial0/1 pacing timer
6w4d: OSPF: Build router LSA for area 7, router ID 6.6.6.6, seq 0x80000127
6w4d: Create retrans unit 0x623B71A8/0x623C5DE8 1 (0/1) 1
6w4d: OSPF: Set nbr 1 (0/1) retrans to 4576 count to 1
6w4d: Set idb next flood info from 623AA324 (305) to 0 (0)
6w4d: OSPF: Stop Serial0/1 flood timer
6w4d: OSPF: Set nbr 1 (0/1) retrans to 4596 count to 2
6w4d: Set Nbr 1.1.1.1 1 next flood info from 623AA324 (305) to 623AA324 (305)
6w4d: Dec retrans unit nbr count index 1 (0/1) to 0/0
6w4d: Free nbr retrans unit 0x623B71A8/0x623C5DE8 0 total 0. Also Free nbr retra
ns block
6w4d: Set Nbr 1.1.1.1 1 first flood info from 623AA324 (305) to 0 (0)
6w4d: Adjust Nbr 1.1.1.1 1 next flood info to 0
6w4d: OSPF: Stop nbr 1.1.1.1 retransmission timer
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21-5 debug ip ospf lsa-generation
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21-6 debug ip ospf lsa-generation ip-access-list-number
Syntax Description:
ip-access-list-number— Number of the IP access list used to filter the output of the flood command. Valid ranges are 1 to 99 and
1300 to 1999.
Purpose: To display information regarding the generation and flooding of summary LSAs.
Example: Displaying the Successful Formation of an OSPF Adjacency
The following is representative output from the debug ip ospf lsa-generation EXEC command on a router that is redistributing EIGRP
routes into OSPF.
r4#debug ip ospf lsa-generation
OSPF summary lsa generation debugging is on
r4#clear ip ospf process
Reset ALL OSPF processes? [no]: yes
r4#
6w4d: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet1/0 from FULL to DOWN,
Neighbor Down: Interface down or detached
6w4d: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on Ethernet0/0 from FULL to DOWN,
Neighbor Down: Interface down or detached
6w4d: OSPF: Start redist-scanning
6w4d: OSPF: Scan the RIB for both redistribution and translation
6w4d: OSPF: net 169.254.0.0 up, new metric decreases: old 16777215, new 10
6w4d: OSPF: Generate external LSA 169.254.0.0, mask 255.254.0.0, type 5, age 0,
metric 10, tag 0, metric-type 2, seq 0x80000001
6w4d: OSPF: generate external LSA for summary 169.254.0.0 255.254.0.0, metric 10
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6w4d: OSPF: End scanning, Elapsed time 4ms
6w4d: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on Ethernet0/0 from LOADING to FULL
, Loading Done
6w4d: OSPF: Generate external LSA 169.254.0.0, mask 255.254.0.0, type 5, age 0,
metric 10, tag 0, metric-type 2, seq 0x80000091
6w4d: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Ethernet1/0 from LOADING to FULL
, Loading Done
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21-7 debug ip ospf packet
Syntax Description:
This command has no arguments.
Purpose: To display OSPF packet information.
Example: Displaying OSPF Packet Information
The following is representative output from the debug ip ospf packet EXEC command.
r6#debug ip ospf packet
OSPF packet debugging is on
r6#
6w4d: OSPF: rcv. v:2 t:1 l:48 rid:1.1.1.1
aid:0.0.0.7 chk:0 aut:2 keyid:8 seq:0xC from Serial0/1
Table 21-1 provides a description for the highlighted lines of output as follows:
Table 21-1. Explanation for debug ip ospf packet Output
Field
What It Represents
v:
OSPF version
t:
Packet type:
1 – Hello
2 – Database Description
3 – Link-State Request
4 – Link-State Update
5 – Link-State Acknowledgement
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Field
What It Represents
l:
Packet length in bytes
rid:
OSPF router ID
aid:
OSPF area ID
aut:
Authentication used:
0 – None
1 – Simple password
2 – MD5
keyid:
MD5 authentication key
seq:
Sequence number
From
Interface that received the packet
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21-8 debug ip ospf retransmission
Syntax Description:
The command has no parameters.
Purpose: To display OSPF LSA retransmission events. The link-state retransmission list is a list of LSAs that have been flooded but not
acknowledged by an OSPF neighbor. The unacknowledged LSAs will be retransmitted at intervals until they are acknowledged, or until the
adjacency with the neighbor is removed.
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21-9 debug ip ospf spf
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21-10 debug ip ospf spf external
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21-11 debug ip ospf spf external access-list-number
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21-12 debug ip ospf spf inter
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21-13 debug ip ospf spf inter access-list-number
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21-14 debug ip ospf spf intra
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21-15 debug ip ospf spf intra access-list-number
Syntax Description:
ip-access-list-number— Number of the IP access list used to filter the output of thedebug ip ospf spf command. Valid ranges are
1 to 99 and 1300 to 1999.
Purpose: To display OSPF shortest path first (SPF) calculations.
Example: Displaying SPF Output for External OSPF Routes
The following is representative output from the debug ip ospf spf external EXEC command.
r4#debug ip ospf spf external
OSPF spf external events debugging is on
r6#
6w4d: OSPF: Started Building Type 5 External Routes
6w4d: OSPF: Start processing Type 5 External LSA 169.254.0.0, mask 255.254.0.0,
adv 4.4.4.4, age 39, seq 0x80000095, metric 10, metric-type 2
6w4d: OSPF: Did not find route to ASBR 4.4.4.4
6w4d: OSPF: ex_delete_old_routes
6w4d: OSPF: Started Building Type 7 External Routes
6w4d: OSPF: ex_delete_old_routes
6w4d: OSPF: Started Building Type 5 External Routes
6w4d: OSPF: Start processing Type 5 External LSA 169.254.0.0, mask 255.254.0.0,
adv 4.4.4.4, age 49, seq 0x80000095, metric 10, metric-type 2
6w4d:
Add better path to LSA ID 169.254.0.0, gateway 10.1.1.18, dist 10
6w4d:
Add path: next-hop 10.1.1.18, interface Serial0/1
6w4d:
Add External Route to 169.254.0.0. Metric: 10, Next Hop: 10.1.1.18
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6w4d: OSPF: insert route list LS ID 169.254.0.0, type 5, adv rtr 4.4.4.4
6w4d: OSPF: ex_delete_old_routes
6w4d: OSPF: Started Building Type 7 External Routes
6w4d: OSPF: ex_delete_old_routes
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Chapter 22. clear Commands
Section 22-1. clear ip ospf counters
Section 22-2. clear ip ospf process-id counters
Section 22-3. clear ip ospf process-id counters neighbor
Section 22-4. clear ip ospf process-id counters neighbor int-name int-number
Section 22-5. clear ip ospf process
Section 22-6. clear ip ospf process-id process
Section 22-7. clear ip ospf redistribution
Section 22-8. clear ip ospf process-id redistribition
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22-1 clear ip ospf counters
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22-2 clear ip ospf process-id counters
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22-3 clear ip ospf process-id counters neighbor
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22-4 clear ip ospf process-id counters neighbor int-name int-number
Syntax Description:
process-id— The OSPF process ID. The range of values is from 1 to 4,294,967,295.
int-name— Interface name.
int-number— Interface number.
Purpose: To reset neighbor state transition counters.
Initial Cisco IOS Software Release: 11.1
Example: Viewing and Clearing OSPF Neighbor State Transition Counters
The show ip ospf neighbor detail command is used to display the neighbor state transition counter.
r4#show ip ospf neighbor detail
Neighbor 2.2.2.2, interface address 172.16.2.1
In the area 0 via interface Ethernet1/0
Neighbor priority is 1, State is FULL, 6 state changes
DR is 172.16.2.2 BDR is 172.16.2.1
Options is 0x42
Dead timer due in 00:00:38
Neighbor is up for 01:06:06
Index 2/2, retransmission queue length 0, number of retransmission 1
First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0)
Last retransmission scan length is 1, maximum is 1
Last retransmission scan time is 0 msec, maximum is 0 msec
The clear ip ospf counters command will reset the state transition counter to 0.
r4#clear ip ospf counters
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r4#show ip ospf neighbor detail
Neighbor 2.2.2.2, interface address 172.16.2.1
In the area 0 via interface Ethernet1/0
Neighbor priority is 1, State is FULL, 0 state changes
DR is 172.16.2.2 BDR is 172.16.2.1
Options is 0x42
Dead timer due in 00:00:33
Neighbor is up for 01:11:01
Index 2/2, retransmission queue length 0, number of retransmission 1
First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0)
Last retransmission scan length is 1, maximum is 1
Last retransmission scan time is 0 msec, maximum is 0 msec
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22-5 clear ip ospf process
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22-6 clear ip ospf process-id process
Syntax Description:
process-id— The OSPF process ID. The range of values is from 1 to 4,294,967,295.
Purpose: To reset and restart all OSPF processes or a specific OSPF process on the local router. Be aware that routes learned via OSPF
will be cleared until the OSPF routing process re-establishes adjacencies with neighbor routers.
Initial Cisco IOS Software Release: 11.1
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22-7 clear ip ospf redistribution
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22-8 clear ip ospf process-id redistribition
Syntax Description:
process-id— The OSPF process ID. The range of values is from 1 to 4,294,967,295.
Purpose: To clear routes that have been redistributed into OSPF.
Initial Cisco IOS Software Release: 11.1
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ABR:NSSA:route redistribution
ASBR:NSSA:route redistribution
addresses:IP.
NBMA (non-broadcast multiaccess) networks
non-broadcast multiaccess networks. See NBMA;access:NBMA. See NBMA [See also IP]
adjacency:MTU mismatches
MTU:mismatches
mismatches:MTU;databases:MTU:mismatches;packets:MTU:mismatches 2nd 3rd 4th
administration:distance:installing
installation:administrative distance
protocols:administrative distance:installing;IP:administrative distance:installing;multiple protocol 2nd 3rd 4th 5th 6th 7th 8th
administration:distance:modifying types
modification:administrative distance:types
protocols:administrative distance:modifying types;EIGRP:administrative distance:modifying types;type 2nd 3rd
area 0 authentication command
commands:area 0 authentication 2nd
area 0 authentication message-digest command
commands:area 0 authentication message-digest 2nd
area commands:area area-id authentication
commands:area:area area-id authentication
authentication:area-area-id authentication command 2nd 3rd 4th 5th
area commands:area area-id authentication message-digest
commands:area:area area-id authentication message-digest
authentication:area-area-id authentication message-digest command 2nd 3rd 4th 5th 6th 7th
area commands:area area-id default-cost cost
commands:area:area area-id default-cost cost
configuration:stubby areas;areas:stubby:configuration;costs:ABR;ABR (Area Border Router):costs;route 2nd 3rd 4th 5th
area commands:area area-id no-summary
commands:area:area area-id no-summary
ABR:stub areas:creating;stub areas:creating 2nd 3rd 4th
ABR:stub areas:creating;stub areas:creating;troubleshooting:stub areas;stub areas:troubleshooting
area commands:area area-id nssa
commands:area:area area-id nssa
configuration:stubby areas:NSSA;areas:stubby:NSSA;NSSA (not-so-stubby area);ABR:NSSA 2nd 3rd 4th
area commands:area area-id nssa default-information-originate
commands:area:area area-id nssa default-information-originate
configuration:stubby areas:NSSA;areas:stubby:NSSA;NSSA (not-so-stubby area);ABR:NSSA 2nd 3rd 4th 5th 6th 7th
area commands:area area-id nssa no-redistribution
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commands:area:area area-id nssa no-redistribution
redistribution:NSSA;areas:stubby:redistribution;NSSA (not-so-stubby area):redistribution 2nd 3rd 4th 5th 6th 7th
area commands:area area-id nssa no-summary
commands:area:area area-id nssa no-summary
summaries:NSSA;areas:stubby:summaries;NSSA (not-so-stubby area):summaries;routes:blocking;blocking:r 2nd 3rd 4th 5th 6th 7th
8th
area commands:area area-id nssat
commands:area:area area-id nssa
configuration:stubby areas:NSSA;areas:stubby:NSSA;NSSA (not-so-stubby area);ABR:NSSA 2nd
area commands:area area-id range ip-address mask
commands:area:area area-id ip-address mask
area commands:area area-id range ip-address mask advertise
commands:area:area area-id ip-address mask advertise
area commands:area area-id range ip-address not-mask
commands:area:area area-id ip-address not-mask
summaries:routes;routes:summaries;ABR:routes:summaries
summaries:routes;routes:summaries;ABR:routes:summaries;backbone:routes:summarization 2nd 3rd
summaries:routes;routes:summaries;ABR:routes:summaries;loopback interfaces:routes:summarization;inte 2nd 3rd
summaries:routes;routes:summaries;ABR:routes:summaries;static routes:summarization;static routes:sum 2nd 3rd
area commands:area area-id stub
commands:area:area area-id stub
ABR:stub areas:configuration;configuration:stub areas;stub areas:configuration 2nd 3rd 4th 5th
area commands:area transit-area-id virtual-link router-id
commands:area:area transit-area-id virtual-link router-id
virtual links;backbones:virtual links;troubleshooting:backbones:virtual links;connections:backbones 2nd 3rd 4th
area commands:area transit-area-id virtual-link router-id authentication authentication-key password
commands:area:area transit-area-id virtual-link router-id authentication authentication-key password
area commands:area transit-area-id virtual-link router-id authentication message-digest
commands:area:area transit-area-id virtual-link router-id authentication message-digest
area commands:area transit-area-id virtual-link router-id authentication null
commands:area:area transit-area-id virtual-link router-id authentication null
authentication:virtual links;virtual links:authentication;configuration:virtual links 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th 12th
area commands:area transit-area-id virtual-link router-id authentication-key password
commands:area:area transit-area-id virtual-link router-id authentication-key password
authentication:virtual links:configuration;configuration:virtual links 2nd 3rd 4th 5th 6th 7th 8th 9th 10th
area commands:area transit-area-id virtual-link router-id hello-interval seconds
commands:area:area transit-area-id virtual-link router-id hello-interval seconds
intervals:Hello:configuration;Hello interval:configuration;configuration:Hello interval 2nd 3rd 4th 5th 6th
area commands:area transit-area-id virtual-link router-id message-digest-key key-id md5 password
commands:area:area transit-area-id virtual-link router-id message-digest-key key-id md5 password2nd 3rd 4th 5th 6th 7th 8th
area commands:area transit-area-id virtual-link router-id retransmit-interval seconds
commands:area:area transit-area-id virtual-link router-id retransmit-interval seconds 2nd 3rd 4th 5th
area commands:area transit-area-id virtual-link router-id transmit-delay seconds
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commands:area:area transit-area-id virtual-link router-id transmit-delay seconds 2nd 3rd 4th
area range command
commands:area range
network command;commands:network
ASBR
routers:ASBR
ASBR (Autonomous System Border Router)
routers:ASBR
ASBR (Autonomous System Boundary Router)
routers:ASBR
attachments:tags:summarized routes
tags:summarized routes:attaching
ASBR:summarized routes:attaching 2nd
ASBR:summarized routes:attaching;values:tags:controlling router redistribution 2nd 3rd
auto-cost reference-bandwidth bandwidth command
commands
auto-cost reference-bandwidth bandwidth
auto-cost reference-bandwidth bandwidth;interfaces;costs;costs;interfaces;configuration:routers;inte 2nd 3rd 4th 5th 6th 7th
auto-cost reference-bandwidth command
commands:auto-cost reference-bandwidth
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Backup Designated Router (BDR)
BDR (Backup Designated Router)
routers:BDR
bandwidth command
commands:bandwidth
bandwidth:costs:calculation
calculation:costs:bandwidth
dividing bandwidth;modifcation:bandwidth:calculating costs 2nd 3rd 4th 5th 6th 7th
dividing bandwidth;modifcation:bandwidth:calculating costs;verification:costs;costs:verification
broadcase multiaccess networks
networks:broadcast multiaccess
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clear ip ospf process command
commands:clear ip ospf process
clearing:commands:clear ip ospf counters
commands:clear ip ospf counters
clearing:commands:clear ip ospf process
commands:clear ip ospf process
clearing:commands:clear ip ospf process-id counters
commands:clear ip ospf process-id counters
clearing:commands:clear ip ospf process-id counters neighbor
commands:clear ip ospf process-id counters neighbor
clearing:commands:clear ip ospf process-id counters neighbor int-name int-number
commands:clear ip ospf process-id counters neighbor int-name int-number 2nd
clearing:commands:clear ip ospf process-id process
commands:clear ip ospf process-id process
clearing:commands:clear ip ospf process-id redistribution
commands:clear ip ospf process-id redistribution
clearing:commands:clear ip ospf redistribution
commands:clear ip ospf redistribution
commands:show:show ip ospf neighbor detail neighbor-id
show commands:show ip ospf neighbor detail neighbor-id
commands:show:show ip ospf neighbor int-name int-number
show commands:show ip ospf neighbor int-name int-number
commands:show:show ip ospf process-id neighbor detail neighbor-id
show commands:show ip ospf process-id neighbor detail neighbor-id
commands:show:show ip ospf process-id neighbor int-name int-number
show commands:show ip ospf process-id neighbor int-name int-number
interfaces:viewing;viewing:interfaces 2nd
commands:show:show ip ospf process-id request-list
show commands:show ip ospf process-id request-list
commands:show:show ip ospf process-id request-list int-name int-number
show commands:show ip ospf process-id request-list int-name int-number
commands:show:show ip ospf process-id request-list neighbor-id
show commands:show ip ospf process-id request-list neighbor-id
commands:show:show ip ospf request-list
show commands:show ip ospf request-list
commands:show:show ip ospf request-list int-name int-number
show commands:show ip ospf request-list int-name int-number
commands:show:show ip ospf request-list neighbor-id
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show commands:show ip ospf request-list neighbor-id
configuration
interfaces
ip ospf authentication authentication-key password
ip ospf message-digest-key key-id md5 password command 2nd 3rd 4th 5th
configuration:interfaces:ip ospf network point-to-multipoint non-broadcast command
NBMA networks:multipoint networks:configuring
networks:NBMA:mulitpoint networks;multicasting 2nd 3rd 4th 5th 6th 7th
configuration:loopback interfaces
loopback interfaces:configuration
interfaces:loopback:configuration;stability:loopback interfaces:configuration
configuration:metrics:redistributed protocols
defaults:metrics:redistributed protocols
metrics:defaults:redistributed protocols;redistributed protocols:default metrics:configuring;protoco 2nd 3rd 4th
configuration:networks
authentication:networks
troubleshooting:networks;networks:authentication;networks:configuration;networks:troubleshooting
configuration:point-to-point links:demand circuits
point-to-point links:demand circuits:configuring
demand ciruits:point-to-point links:configuring;circuits:point-to-point links:configuring;serial net 2nd 3rd
configuration:routers:metric types
metrics:types:configuring
types:metric:configuring;routers:metric types:configuring 2nd 3rd 4th
configuration:routes:summarizing redistribution
networks:redistribution 2nd 3rd
controlling:routes:redistribution
redistribution:tags:controling
tags:values:controlling redistribution;values:tags:controlling redistribution 2nd 3rd 4th
customer routes:VPN:transferring
P (provider) routers
routers:P;CE (customer edge) routers;routers:CE;PE (provider edge) routers;routers:PE
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debugging:debug ip ospf adj command
commands:debug ip ospf adj
adjacency:debugging;clearing:adjacency 2nd
debugging:debug ip ospf events command
commands:debug ip ospf events
events:debugging
events:debugging;adjacency:clearing;clearing:adjacency 2nd
debugging:debug ip ospf flood command
commands:debug ip ospf flood
debugging:debug ip ospf flood ip-access-list-number command
commands:debug ip ospf flood ip-access-list-number
IP:flooding:debugging;flooding:IP access:debugging;access:IP:debugging
debugging:debug ip ospf inter access-list-number command
commands:debug ip ospf inter access-list-number
debugging:debug ip ospf inter command
commands:debug ip ospf inter
debugging:debug ip ospf intra access-list-number command
commands:debug ip ospf intra access-list-number 2nd
debugging:debug ip ospf intra command
commands:debug ip ospf intra
debugging:debug ip ospf lsa-generation command
commands:debug ip ospf lsa-generation
debugging:debug ip ospf lsa-generation ip-access-list-number command
commands:debug ip ospf lsa-generation ip-access-list-number
flooding:LSAs;LSA:flooding;summary LSAs:flooding
debugging:debug ip ospf packet command
commands:debug ip ospf packet
packets:debugging
debugging:debug ip ospf retransmission command
commands:debug ip ospf retransmission
LSA:retransmission;retransmission:LSA;events:LSA:retransmission
debugging:debug ip ospf spf command
commands:debug ip ospf spf
debugging:debug ip ospf spf external access-list-number command
commands:debug ip ospf spf external access-list-number
debugging:debug ip ospf spf external command
commands:debug ip ospf spf external
default-information originate always command
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commands:default-information originate always
routes:defaults:advertising;advertising:default routes;configuration:routes:advertising defaults;alw 2nd 3rd 4th
default-information originate always metric cost command
commands:default-information originate always metric cost
costs:external:configuring;external costs:configuring;configuration:costs:external;routes:costs:exte 2nd 3rd 4th
default-information originate always metric-type type command
commands:default-information originate always metric-type type
ASBR:routes:assigning;routes:ASBR:assigning;assignment:routes:ASBR;routes:ASBR:assigning;costs:route 2nd 3rd 4th 5th
default-information originate command
commands:default-information originate
routes:defaults:advertising;advertising:default routes;configuration:routes:advertising defaults 2nd 3rd
default-information originate metric cost command
commands:default-information originate metric cost
default-information originate metric-type type command
commands:default-information originate metric-type type
default-information originate route-map route-map-name command
commands:default-information originate route-map route-map-name
routes:maps:configuring;maps:routes:maps:configuring;configuraiton:routes:maps 2nd 3rd 4th 5th
default-metric cost command
commands:default-metric cost
costs:redistributed routes:configuring;routes:redistributed:configuring costs;assignments:costs:redi 2nd 3rd 4th 5th
defaults
interfaces
costs
defaults:routes:generating
routers:defaults:generating
generation:default routes
Designated Router (DR)
DR (Designated Router)
routers:DR
designated routers:electing
routers:designated:electing
election:designated routers 2nd 3rd
displaying. [See viewing]
distance administrative-distance command
commands:distance administrative-distance
administration:distance:selecting;selection:administrative distance;protocols:administrative distanc 2nd 3rd 4th
distance administrative-distance source-ip-address source-ip mask access-list-number command
commands:distance administrative-distance source-ip-address source-ip-mask access-list-number 2nd 3rd 4th 5th 6th 7th
distance administrative-distance source-ip-address source-ip mask command
commands:distance administrative-distance source-ip-address source-ip-mask
distance ospf external administrative-distance command
commands:distance ospf external administrative-distance
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distance ospf inter-area administrative-distance command
commands:distance ospf inter-area administrative-distance
distance ospf intra-area administrative-distance command
commands:distance ospf intra-area administrative-distance 2nd 3rd 4th
distribute lists:distribute-list access-list-number in interface-type interface-number
routes:distribute-list access-list-number in interface-type interface-number 2nd 3rd 4th 5th
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[A] [B] [C] [D] [E] [F] [H] [I] [L] [M] [N] [P] [R] [S] [T] [U] [V] [W]
EIGRP
redistributed routes
configuring costs
EIGRP:relationships
relationships:EIGRP
EIGRP:routes:blocking
blocking:routes:EIGRP
verification:EIGRP:blocking
EIGRP:routes:redistribution
routes:redistribution:EIGRP
redistribution:routes:EIGRP 2nd 3rd 4th 5th
enabling:interfaces:shorter masks
interfaces:shorter masks:enabling
shorter masks:enabling;masks:shorter:enabling 2nd
enabling:NBMA:neighbors
NBMA:neighbors:enabling
neighbors:NBMA:enabling;configuration:neighbors:NBMA;broadcasting:neighbors:enabling on NBMA network 2nd 3rd 4th 5th
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filters
databases
filters:distribute-list access-list-name in command
commands:distribute-list access-list-name in
distribute lists:distribute-list access-list-name in;routes:distribute-list access-list-name in 2nd 3rd 4th 5th
filters:distribute-list access-list-name in interface-type interface-number command
commands:distribute-list access-list-name in interface-type interface-number
distribute lists:distribute-list access-list-name in interface-type interface-number 2nd 3rd 4th 5th
filters:distribute-list access-list-name out command
commands:distribute-list access-list-name out
distribute lists:distribute-list access-list-name out;routes:distribute-list access-list-name out 2nd
filters:distribute-list access-list-name out interface-type interface-number command
commands:distribute-list access-list-name out interface-type interface-number
distribute lists:distribute-list access-list-name out interface-type interface-number
filters:distribute-list access-list-name out routing-process command
commands:distribute-list access-list-name out routing-process
distribute lists:distribute-list access-list-name out routing-process 2nd 3rd 4th 5th 6th
filters:distribute-list access-list-number in command
commands:distribute-list access-list-number-in
distribute lists:distribute-list access-list-number in;routes:filters:distribute-list access-list-nu 2nd 3rd 4th 5th
filters:distribute-list access-list-number in interface-type interface-number command
commands:distribute-list access-list-number in interface-type interface-number 2nd 3rd 4th 5th
filters:distribute-list access-list-number out command
commands:distribute-list access-list-number out
distribute lists:distribute-list access-list number out;routes:distribute-list access-list-number ou
filters:distribute-list access-list-number out interface-type interface-number command
commands:distribute-list access-list-number out interface-type interface-number
distribute lists:distribute-list access-list number out interface-type interface-number
filters:distribute-list access-list-number out routing-processcommand
commands:distribute-list access-list-number out routing-process
distribute lists:distribute-list access-list number out routing-process 2nd 3rd 4th 5th 6th
filters:distribute-list prefix prefix-list-name in command
commands:distribute-list prefix prefix-list-name in
distribute lists:distribute-list prefix prefix-list-name in;routes:distribute-list prefix prefix-lis 2nd 3rd 4th 5th
filters:distribute-list prefix prefix-list-name in interface-type interface-numbercommand
commands:distribute-list prefix prefix-list-name in interface-type interface-number 2nd 3rd 4th 5th 6th
filters:distribute-list prefix prefix-list-name out command
commands:distribute-list prefix prefix-list-name out
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routes:distribute-list prefix prefix-list-name out;distributed lists:distribute-list prefix-list-nam
filters:distribute-list prefix prefix-list-name out interface-type interface-number command
commands:distribute-list prefix prefix-list-name out interface-type interface-number
filters:distribute-list prefix prefix-list-name out routing-process command
commands:distribute-list prefix prefix-list-name out routing process 2nd 3rd 4th 5th 6th
Frame Relay:configuring
switches:Frame Relay:configuring
configuration:Frame Relay
fully-meshed neighbors:NBMA networks:configuring
neighbors:fully-meshed:configuring NBMA networks
NBMA networks:fully-meshed neighbors:configuring;network:NBMA:fully-meshed neighbors 2nd 3rd 4th
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Hello intervals:verification
verification:Hello intervals
High-Level Data Link Control (HDLC)
HDLC (High-Level Data Link Control)
hosts:addresses:enabling interfaces
addresses:hosts:enabling interfaces
enabling:interfaces:host addresses;interfaces:host addresses:enabling 2nd
hubs:neighbors:configuring
spokes:neighbors:configuring
configuration:neighbors:hubs/spokes;IP:subnets:configuring neighbors;subnets:neighbors:configuring 2nd 3rd 4th 5th 6th
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interfaces
Frame Relay
learned routes
preventing installation 2nd 3rd 4th
interfaces:commands:ip ospf authentication
commands:interfaces:ip ospf authentication
ip ospf authentication command;configuration:interfaces:ip ospf authentication
interfaces:commands:ip ospf authentication authentication-key password
commands:interfaces:ip ospf authentication authentication-key password
ip ospf authentication authentication-key password command
interfaces:commands:ip ospf authentication message-digest
commands:interfaces:ip ospf authentication message-digest
ip ospf authentication message-digest command;configuration:interfaces:ip ospf authentication messag
interfaces:commands:ip ospf authentication null
commands:interfaces:ip ospf authentication null
ip ospf authentication null command;configuration:interfaces:ip ospf authentication null 2nd 3rd 4th 5th 6th 7th 8th
interfaces:commands:ip ospf cost cost
commands:interfaces:ip ospf cost cost
ip ospf cost cost command;configuration:interfaces:ip ospf cost cost;costs:interfaces;bandwidth:inte 2nd 3rd 4th
interfaces:commands:ip ospf database-filter all out
commands:interfaces:ip ospf database-filter all out
ip ospf database-filter all out command;configuration:interfaces:ip ospf database-filter all out 2nd 3rd
interfaces:commands:ip ospf dead-interval seconds
commands:interfaces:ip ospf dead-interval seconds
ip ospf dead-interval seconds command;configuration:interfaces:ip ospf dead-interval seconds 2nd 3rd 4th
interfaces:commands:ip ospf demand-circuit
commands:interfaces:ip ospf demand-circuit
ip ospf demand-circuit command;configuration:interfaces:ip ospf demand-circuit 2nd 3rd
interfaces:commands:ip ospf flood-reduction
commands:interfaces:ip ospf flood reduction
ip ospf flood-reduction command;configuration:interfaces:ip ospf flood-reduction 2nd 3rd
interfaces:commands:ip ospf hello-interval seconds
commands:interfaces:ip ospf hello-interval seconds
ip ospf hello-interval seconds command;configuration:interfaces:ip ospf hello-interval seconds 2nd 3rd 4th
interfaces:commands:ip ospf message-digest-key key-id md5 password
commands:interfaces:ip ospf message-digest-key key-id md5 password
ip ospf message-digest-key key-id md5 password command 2nd 3rd 4th 5th
interfaces:commands:ip ospf mtu-ignore
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commands:interfaces:ip ospf mtu-ignore
ip ospf mtu-ignore command;configuration:interfaces:ip ospf mtu-ignore command 2nd 3rd 4th
interfaces:commands:ip ospf network broadcast
commands:interfaces:ip ospf network broadcast
ip ospf network broadcast command;configuration:interfaces:ip ospf network broadcast command 2nd 3rd 4th 5th 6th 7th 8th 9th
interfaces:commands:ip ospf network non-broadcast
commands:interfaces:ip ospf network non-broadcast
ip ospf network non-broadcast command;configuration:interfaces:ip ospf network non-broadcast command
interfaces:commands:ip ospf network point-to-multipoint
commands:interfaces:ip ospf networkpoint-to-multipoint
ip ospf network point-to-multipoint command;configuration:interfaces:ip ospf network point-to-multip
interfaces:commands:ip ospf network point-to-multipoint non-broadcast
commands:interfaces:ip ospf network point-to-multipoint non-broadcast
ip ospf network point-to-multipoint non-broadcast command 2nd 3rd 4th 5th 6th
interfaces:commands:ip ospf network point-to-point
commands:interfaces:ip ospf network point-to-point
ip ospf network point-to-point command;configuration:interfaces:ip ospf network point-to-point comma 2nd 3rd 4th 5th 6th 7th
interfaces:commands:ip ospf priority priority
commands:interfaces:ip ospf priority priority
ip ospf priority priority command;configuration:interfaces:ip ospf priority priority command 2nd 3rd 4th
interfaces:commands:ip ospf retransmit-interval seconds
commands:interfaces:ip ospf retransmit-interval seconds
ip ospf retransmit-interval seconds command;configuration:interfaces:ip ospf retransmit-interval sec 2nd 3rd
interfaces:commands:ip ospf transmit-delay seconds
commands:interfaces:ip ospf transmit-delay seconds
ip ospf transmit-delay seconds command;configuration:interfaces:ip ospf transmit-delay seconds comma 2nd 3rd
interior gateway protocol.
IGP (interior gateway protocol)
protocols:IGP (interior gateway protocol);instances;VFR;options;vrf [See IGP]
ip ospf authentication null command
commands:ip ospf authentication null 2nd
ip ospf cost command
commands:ip ospf cost
ip ospf network command
commands:ip ospf network
ip ospf network point-to-multipoint command
commands:ip ospf network point-to-multipoint
ip ospf network point-to-point interface command
commands:ip ospf network point-to-point interface
ip prefix-list filter-ospf1 command
commands:ip prefix-list filter ospf1
ip prefix-list filter-ospf2 command
commands:ip prefix-list filter ospf2
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IP:addresses:controlling route reditribution
addresses:IP:controlling route redistribution
redistribution:IP addresses:controlling with;controlling:routes:IP addresses 2nd 3rd
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learned routes:installation:preventing
installation:learned routes:preventing
prevention:learned routes;IP:learned routes:preventing installation;routing:tables:preventing learne 2nd 3rd 4th 5th 6th 7th 8th 9th
10th 11th 12th 13th 14th 15th 16th 17th 18th 19th
link-state advertisement (LSA)
LSA (link-state advertisement)
advertisements:LSA;retransmit intervals:modification;intervals:retransmit:modification;modification: 2nd 3rd 4th 5th
link-state databases:advertisements
advertisements:link-state databases
databases:link-state:advertisements
links
virtual links. [See virtual links]
log-adjacency-changes command
commands:log-adjacency
log-adjacency-changes detail command
commands:log-adjacency detail
logging:neighbors:status;neighbors:status:logging;status:neighbors:logging;modification:status:loggi 2nd 3rd 4th
logging buffered command
commands:logging buffered
show logging command;commands:show logging;buffers:logging:viewing status;logging:buffers:viewing;vi
loopback interfaces
costs
LSA:flooding:reducing
flodding:LSA:reducing
reduction:flooding:LSAs;databases:LSAs:reducing flooding 2nd 3rd
flooding:LSAs:reducing
reduction:flooding:LSAs;filters:LSA flooding;redundant links:LSA flooding:reducing;links:LSA floodin 2nd 3rd
LSA:MOSPF
MOSPF (Multicast OSPF)
messages:MOSPF;ignore lsa mospf command;commands:ignore lsa mospf;syslog:messages:preventing;prevent
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maximum-paths number-of-paths command
commands:maximum-paths number-of-paths
costs:paths:configuring maximums;installation:paths:IP routing tables;IP:paths:installing;routing:ta 2nd 3rd 4th
MD5:authentication
authentication:MD5
;networks:MD5:authentication 2nd
MD5:configuration
MD5:troubleshooting;authentication:MD5;configuration:MD5;troubleshooting:MD5;passwords:MD5:authentic
MD5:authentication:enabling
authentication:MD5:enabling
enabling:authentication:MD5
MD5:modification
modification:MD5
keys:modification;modification:keys;modification:passwords;passwords:modification;links:keys/passwor
MD5:virtual links:adding passwords
adding:passwords:MD5 virtual links
passwords:MD5:adding 2nd
MD5:virtual links:authentication
virtual links:MD5:authentication
authentication:MD5:virtual links;configuration:MD5:authentication 2nd 3rd 4th 5th
MD5:virtual links:modification
virtual links:MD5:modification
modification:MD5:virtual links;configuration:MD5:modification;keys:MD5:modification;passwords:MD5:mo 2nd 3rd
message digests:authentication
authentication:message digests 2nd
verification:authentication:message digests
message digests:authentication:modifying
authentication:message digests:modifying
modification:message digests:authentication;passwords:message digest:modifying;keys:message digests: 2nd
metrics
types:route maps
diverting:traffic;traffic:diverting;types:metrics:route maps;conditional advertisemnts:default route 2nd 3rd 4th 5th
metrics:modifying
modification:metrics
routes:maps:modifying metrics;maps:routes:modifying metrics;redistribution:metrics:modifying
routes:maps:modifying metrics;maps:routes:modifying metrics;redistribution:metrics:modifying;tags:va
routes:maps:modifying metrics;maps:routes:modifying metrics;redistribution:metrics:modifying;types:m
modification
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interfaces
costs 2nd 3rd
modification:administrative distance
routes:administrative distance:modifying
EIGRP:administrative distance:modifying 2nd 3rd 4th
modification:interfaces:dead intervals
dead intervals:modifying
intervals:dead:modifying;timers:dead intervals:modifying;values:dead intervals:modifying 2nd 3rd
modification:LSA:group pacing
pacing:LSA groups
intervals:LSA group pacing:modifying;configuration:LSA:group pacing 2nd 3rd
modification:neighbors:costs
costs:neighbors:modifying
point-to-multipoint interfaces:neighbors:modifying costs;interfaces:neighbors:modifying costs 2nd 3rd 4th
modification:networks:statements
networks:statements:modifiying
statements:networks:modifying;interfaces:network statements:modifying;masks:network statements:modif 2nd
multiple paths:configuring
paths:multiple:configuring
configuration:multiple paths 2nd 3rd 4th
multipoint hubs
hubs:multipoint
connections:multipoint networks 2nd 3rd 4th
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NBMA:poll intervals:configuring
configuration:poll intervals
poll intervals:configuring;intervals:poll:configuring;adjacency:poll intervals:configuring 2nd 3rd
neighbors:administrative distance:modifying
modification:administrative distance:neighbors
installation:routes:EIGRP;EIGRP:routes:installing;routes:EIGRP:installing;configuration:administrati 2nd 3rd 4th 5th
neighbors:neighbor ip-address command
commands:neighbors:neighbor-ip address
IP:addresses:neighbor ip-address command 2nd 3rd 4th 5th 6th 7th 8th
neighbors:neighbor ip-address cost cost command
commands:neighbors:neighbor-ip address cost cost
IP:addresses:neighbor ip-address cost cost command 2nd 3rd 4th 5th
neighbors:neighbor ip-address database-filter all out command
commands:neighbors:neighbor-ip address database-filter all out
IP:addresses:neighbor ip-address database-filter all out command 2nd 3rd
neighbors:neighbor ip-address poll-interval interval command
commands:neighbors:neighbor-ip address poll-interval interval
IP:addresses:neighbor ip-address poll-interval interval command 2nd 3rd
neighbors:neighbor ip-address priority priority command
commands:neighbors:neighbor-ip address priority priority
IP:addresses:neighbor ip-address priority priority command 2nd 3rd
neighbors:point-to-point partially-meshed
point-to-point partially meshed neighbors
NBMA networks:configuring;networks:NBMA:configuring 2nd 3rd 4th 5th 6th
neighbors:state transition counters
states:neighbor transition counters
transitions:neighbor state counters;counters:neighbor state transitions 2nd
neighbors:statements
statements:neighbors
networks:commands:network ip-address wild-card-mask area area-id
commands:network ip-address wild-card-mask area area-id 2nd 3rd 4th 5th
no passive-interface command
commands:no passive-interface
no router ospf 1 command
commands:no router ospf 1
NSSA:troubleshooting
troubleshooting:NSSA
null authentication
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authentication:null 2nd
verification:null authentication
Null authentication
configuration:Null authentication
authentication:Null;MD5:Null authentication;clear text authentication:Null authentication 2nd 3rd 4th
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parallel equal cost paths, installing
partially-meshed hubs
hubs:partially-meshed
mulitpoint networks:partially-meshed hubs;networks:multipoint:partially-meshed hubs 2nd 3rd 4th
partially-meshed neighbors:NBMA networks:configuring
neighbors:partially-meshed:configuring NBMA networks
NBMA networks:partially-meshed;neighbors:configuring;network:NBMA:partially-meshed neighbors 2nd 3rd 4th
passive interfaces:passive-interface default command
commands:passive-interface default
neighbors:interfaces;interfaces:neighbors 2nd
passive interfaces:passive-interface interface-name interface-number command
commands:passive-interface interface-name interface-number
traffic:reducing;reduction:trffic;protocols:traffic:reducing 2nd 3rd
passive interfaces:statements
statements:passive interfaces
passwords. [See also authentication]
passwords:authentication
authentication:passwords
simple password authentication;networks:passwords:authentication 2nd 3rd
passwords:encryption:MD5
encryption:passwords:MD5
passwords:modifying
keys:modifying
modifcation:passwords;modification:keys;authentication:passwords:modifying 2nd 3rd
passwords:virtual links:modification
keys:virtual links:modification
modification:passwords:virtual links;modification:keys:virtual links 2nd 3rd
passwords:virtual links:verification
keys:virtual links:verification
verification:passwords:virtual links;verification:keys:virtual links
paths:troubleshooting
troubleshooting:paths
point-to-point networks
networks:point-to-point
PPP
protocols:PPP
prevention:flooding:LSAs
flooding:LSAs:preventing
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LSA:flodding:preventing;links:LSA;preventing flooding 2nd
LSA:flodding:preventing;links:LSA;preventing flooding;verification:databases:filters
processes:configuration commands:router ospf process-id
configuration
router ospf process-id;commands;router ospf process-id;router ospf process-id command;enabling:proce 2nd 3rd
processes:configuration commands:router ospf process-id vrf name
configuration
router ospf process-id vrf name;commands;router ospf process-id vfr name;router ospf process-id vrf
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[A] [B] [C] [D] [E] [F] [H] [I] [L] [M] [N] [P] [R] [S] [T] [U] [V] [W]
redistribute command
commands:redistribute
redistribution:classful routes
classful routes:redistribution
type:classful routes:redistribution;metrcis:classful routes:redistribution 2nd 3rd 4th 5th 6th
redistribution:subnet routes
subnet routes:redistribution
type:subnet routes:redistribution;metrcis:subet routes:redistribution 2nd
type:subnet routes:redistribution;metrcis:subet routes:redistribution;tags:routes:redistribution 2nd 3rd
reditribution:routes:clearing
redistribution:routes:clearing
regular expressions. [See also expressions]
resetting
state transition counters
resetting:processes
processes:resetting
restrating:processes;processes:restarting
retransmit intervals:modifying
intervals:retransmit:modifying
modification:retransmit intervals;timers:retransmit intervals:modifying 2nd 3rd
RIP:redistribution
EIGRP:redistribution
redistribution:RIP;redistribution:EIGRP
Router ID (RID)
RID (Router ID)
ID:RID
routers:priority:configuring
priority:configuring
configuration:priority 2nd 3rd
routers:router-id ip-address command
commands:router-id ip-address
selection:routers:ID;ID:routers:selecting;configuration:routers:selecting ID 2nd 3rd 4th 5th
routes
distribute-list access-list-name in interface-type interface-number command 2nd 3rd 4th 5th
distribute-list access-list-name out interface-type interface-number command
distribute-list access-list-name out routing-process command 2nd 3rd 4th 5th 6th
distribute-list access-list-number out interface-type interface-number
NSSA
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redsitribution
routes:costs:verification
costs:routes:verification
verification:costs:routes
routes:distribute-list access-list-number out routing-process
redistribution:routes:preventing
prevention:routes:redistribution;databases:routes:preventing redistribution;processes:routing:preven 2nd 3rd 4th 5th 6th
routes:distribute-list prefix prefix-list-name in interface-type interface-number command
distribute lists:distribute-list prefix prefix-list-name in interface-type interface-number
IP:prefix lists 2nd 3rd 4th 5th 6th
routes:distribute-list prefix prefix-list-name out interface-type interface-number
distribute lists:distribute-list prefix-list-name out interface-type interface-number
routes:distribute-list prefix prefix-list-name out routing-process
distribute lists:distribute-list prefix-list-name out routing-process 2nd 3rd 4th 5th 6th
routes:redistribution.
redistribution. See also distribution [See also redistribution]
routes:redistribution:redistribute routing-process process-id
commands:redistribute routing-process process-id
routes:redistribution:redistribute routing-process process-id metric ospf-metric
commands:redistribute routing-process process-id metric ospf-metric
routes:redistribution:redistribute routing-process process-id metric-type metric-type
commands:redistribute routing-process process-id metric-type metric-type
routes:redistribution:redistribute routing-process process-id route-map route-map-name
commands:redistribute routing-process process-id route-map route-map-name 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th
routes:redistribution:redistribute routing-process process-id subnets
commands:redistribute routing-process process-id subnets
routes:redistribution:redistribute routing-process process-id tag tag-value
commands:redistribute routing-process process-id tag tag-value 2nd 3rd 4th 5th 6th 7th 8th 9th 10th
routes:types:modifying administrative distance
inter-area routes:modifying
intra-area routes:modifying;external routes:modifying 2nd 3rd 4th
routes:VPN:transferring
VPN (virtual private network):routes:transferring
transferring:routes:VPN;virtual private network. [See VPN;VRF (VPN Routing/Forwarding Instance) names;names:VRF;MPLS
(Multiprotocol Label Switching);switches:MPLS;labels:MPLS]
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selection
RID
service password-encryption command
commands:service password encryption
encryption:passwords;passwords:encryption
commands:service password-encryption
shortest path first (SPF)
SPF (shortest path first)
show commands:show ip ospf
commands:show:show ip ospf
show commands:show ip ospf database
commands:show:show ip ospf database
show commands:show ip ospf database adv-router router-id
commands:show:show ip ospf database adv-router router-id
show commands:show ip ospf database asbr-summary
commands:show:show ip ospf database asbr-summary
show commands:show ip ospf database asbr-summary asbr-id
commands:show:show ip ospf database asbr-summary asbr-id
show commands:show ip ospf database database-summary
commands:show:show ip ospf database database-summary
show commands:show ip ospf database external
commands:show:show ip ospf database external
show commands:show ip ospf database network
commands:show:show ip ospf database network
show commands:show ip ospf database nssa-external
commands:show:show ip ospf database nssa-external
show commands:show ip ospf database router
commands:show:show ip ospf database router
show commands:show ip ospf database self-originate
commands:show:show ip ospf database self-originate
show commands:show ip ospf database summary
commands:show:show ip ospf database summary
show commands:show ip ospf flood-list
commands:show:show ip ospf flood-list
show commands:show ip ospf flood-list int-name int-number
commands:show:show ip ospf flood-list int-name int-number
show commands:show ip ospf interface
commands:show:show ip ospf interface
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show commands:show ip ospf interface int-name int-number
commands:show:show ip ospf interface int-name int-number
show commands:show ip ospf neighbor
commands:show:show ip ospf neighbor
show commands:show ip ospf neighbor detail
commands:show:show ip ospf neighbor detail
show commands:show ip ospf neighbor int-name int-number
commands:show:show ip ospf neighbor int-name int-number
show commands:show ip ospf neighbor neighbor-id
commands:show:show ip ospf neighbor neighbor-id
show commands:show ip ospf process-id
commands:show:show ip ospf process-id
processes:viewing;viewing:processes;parameters:processes:viewing;regular expressions:processes:viewi 2nd
show commands:show ip ospf process-id border-routers
commands:show:show ip ospf process-id border-routers
viewing:routing tables;routing:tables:viewing;tables:routing:viewing;entries:routing tables:viewing 2nd
show commands:show ip ospf process-id database
commands:show:show ip ospf process-id database
show commands:show ip ospf process-id database adv-router router-id
commands:show:show ip ospf process-id database adv-router router-id
show commands:show ip ospf process-id database asbr-summary
commands:show:show ip ospf process-id database asbr-summary
show commands:show ip ospf process-id database asbr-summary asbr-id
commands:show:show ip ospf process-id database asbr-summary asbr-id
show commands:show ip ospf process-id database database-summary
commands:show:show ip ospf process-id database database-summary
show commands:show ip ospf process-id database external
commands:show:show ip ospf process-id database external
show commands:show ip ospf process-id database network
commands:show:show ip ospf process-id database network
show commands:show ip ospf process-id database nssa-external
commands:show:show ip ospf process-id database nssa-external
show commands:show ip ospf process-id database router
commands:show:show ip ospf process-id database router
show commands:show ip ospf process-id database self-originate
commands:show:show ip ospf process-id database self-originate
show commands:show ip ospf process-id database summary
commands:show:show ip ospf process-id database summary
databases:viewing;viewing:databases 2nd
show commands:show ip ospf process-id flood-list
commands:show:show ip ospf process-id flood-list
show commands:show ip ospf process-id flood-list int-name int-number
commands:show:show ip ospf process-id flood-list int-name int-number 2nd
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show commands:show ip ospf process-id interface
commands:show:show ip ospf process-id interface
show commands:show ip ospf process-id interface int-name int-number
commands:show:show ip ospf process-id interface int-name int-number
viewing;interfaces;interfaces-viewing 2nd
show commands:show ip ospf process-id neighbor
commands:show:show ip process-id ospf neighbor
show commands:show ip ospf process-id neighbor detail
commands:show:show ip ospf process-id neighbor detail
show commands:show ip ospf process-id neighbor int-name int-number
commands:show:show ip process-id ospf neighbor int-name int-number
show commands:show ip ospf process-id neighbor neighbor-id
commands:show:show ip ospf process-id neighbor neighbor-id
show commands:show ip ospf process-id retransmission int-name int-numbert
commands:show:show ip ospf process-id retransmission int-name int-number
LSA;viewing;viewing:LSAs;resending:LSAs:viewing 2nd
show commands:show ip ospf process-id retransmission neighbor-id
commands:show:show ip ospf process-id retransmission neighbor-id
show commands:show ip ospf process-id summary-address
commands:show:show ip ospf process-id summary-address
summaries:addresses:viewing;addresses:summaries:viewing;viewing:summary addresses;routers:summary ad
show commands:show ip ospf process-id virtual-links
commands:show:show ip ospf process-id virtual-links
viewing:virtual links;virtual links:viewing;status:virtual links:viewing;routers:virtual links:viewi
show commands:show ip ospf process-list retransmission-list
commands:show:show ip ospf process-id retransmission-list
show commands:show ip ospf retransmission int-name int-numbert
commands:show:show ip ospf retransmission int-name int-number
show commands:show ip ospf retransmission-list
commands:show:show ip ospf retransmission-list
show commands:show ip ospf retransmission-list neighbor-id
commands:show:show ip ospf retransmission-list neighbor-id
show commands:show ip ospf summary-addres
commands:show:show ip ospf summarty-address
show commands:show ip ospf virtual-links
commands:show:show ip ospf virtual-links
show frame-relay map command
commands:show frame-relay map
show ip access-lists access-list-number command
commands:show ip access-lists access-list-number
show ip ospf command
commands:show ip ospf 2nd
show ip ospf neighbor command
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commands:show ip ospf neighbor
show ip ospf timer lsa-group command
commands:show ip ospf timer las-group
show ip route 0.0.0.0 command
commands:show ip route 0.0.0.0
SPF:output:external routes
output:SPF:exteranl routes
external routes:SPF:output
summaries
change to summarization
summarization:external routes
external routers:summarizing
routers:external:summarizing 2nd 3rd 4th 5th 6th 7th 8th
summary-address ip-address mask command
commands:summary-address ip-address mask
summary-address ip-address mask not-advertise command
commands:summary-address ip-address mask not-advertise
redistribution:routers:summarizing;ASBR:redistribution:summarizing;adverstisement:summary routes 2nd 3rd
summary-address ip-address masktag-value command
commands:summary-address ip-address tag-value
redistribution:routers:summarizing;ASBR:redistribution:summarizing;adverstisement:summary routes 2nd 3rd 4th 5th 6th
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tables:routing.
lists:distribute. See distribute lists [See also routing]
timers lsa-group-pacing seconds command
commands:timers lsa-group-pacing seconds
LSA:timers;groups:LSA:timers;routers:timers;refreshing:timers;datbases:timers 2nd
timers:Hello intervals:modifying
Hello intervals:modifying
modifcation:Hello intervals;intervals:hello:modifying;values:Hello intervals:modifying;links:Hello i 2nd 3rd
traffic:sharing
sharing:traffic
commands:traffic-share min across-interfaces;IGRP;traffic:sharing;EIGRP:traffic:sharing;unequal-cost
transmit delay values:modifying
delay:transmit values:modifying
values:transmit delay:modifying;modification:transmit delay values 2nd
troubleshooting
access lists
administrative distance
neighbors
databases
filters
dead intervals
demand circuits
flood reduction
Hello intervals
interfaces
costs
distribute lists
multipoint networks
NBMA networks
neighbors
costs
poll intervals
priority
networks
summarizing
passive interfaces 2nd
prefix lists
retransmit intervals
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routers
ID
priorities
routes
defaults
distribute lists
redistribution 2nd 3rd
tag values
transmit delay values
wild-card masks
troubleshooting:ABR
ABR:troubleshooting
routers:ABR:troubleshooting
troubleshooting:administrative distance
distance:administrative. [See also administration]
troubleshooting:administrative distance:route types
routes:types:troubleshooting
types:routes:troubleshooting
troubleshooting:bandwidth
bandwidth:troubleshooting
troubleshooting:dead intervals
dead intervals:troubleshooting
troubleshooting:inter-area routes
inter-area routes:troubleshooting
routes:troubleshooting;blocking;routes:troubleshooting
troubleshooting:keys
keys:troubleshooting
passwords:troubleshooting:passwords;passwords:troubleshooting
troubleshooting:MD5
MD5:troubleshooting
troubleshooting:metrics:types
metrics:types:troubleshooting
types:metrics:troubleshooting 2nd
troubleshooting:neighbor relationships
neighbors:relationships:troubleshooting
relationships:neighbors:troubleshooting
troubleshooting:neighbors:IP connectivity
connectivity:IP:troubleshooting
IP:connectivity:troubleshooting
troubleshooting:neighbors:logging buffers
neighbors:logging:troubleshooting
logging:neighbors:troubleshooting;buffers:troubleshooting
troubleshooting:NSSA
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NSSA:troubleshooting
troubleshooting:passwords
passwords:troubleshooting
authentication:troubleshooting;troubleshootng:authentication
troubleshooting:prefix lists
prefix lists.
lists:prefix. See also distribute lists [See also distribute lists]
troubleshooting:redistribution
redistribution:troubleshooting
routes:redistribution:troubleshooting
troubleshooting:retransmit intervals
retransmit intervals:troubleshooting
troubleshooting:RID
RID:troubleshooting
ID:RID:troubleshooting
troubleshooting:routers:relationshsips
routers:relationships:troubleshooting
relationships:routers:troubleshooting
troubleshooting:routes:EIGRP
show ip ospf database external command
commands:show ip ospf database external
troubleshooting:routes:maps
routes:maps:troubleshooting
maps:routes:troubleshooting
troubleshooting:routes:metrics
routes:metrics:troubleshooting
metrics:routes:troubleshooting
troubleshooting:stub areas
stub areas:troubleshooting
troubleshooting:summarization
summarization:troubleshooting
troubleshooting:transmit delays
transmit delays:troubleshooting
troubleshooting:virtual links
virtual links:troubleshooting 2nd
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unconditional advertising default routes
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values:transmit delays:modification
transmit delays:modification
modification:transmit delays;delays:trasnsmit:modifictaion;virtual links:transmit delays:modificatio 2nd 3rd 4th
vector protocols:routes:preventing advertisement
protocols:vector:preventing advertisement
prevention:advertisement:vector protocols;advertisement:vector protocols:preventing;neighbors:advert
verifcation
SPF timer values
verifcation:MD5 authentication
MD5:verification
verification
administrative distance
modifying
route types
authentication
broadcast networks
classful EIGRP routes
classless EIGRP routes
dead intervals
demand circuits
flood reduction
Hello intervals
interfaces
costs
enabling with host addresses
modifying network statements
passive interfaces
logging
buffers
loopback interfaces
pinging
LSA pacing intervals
MD5
authenticaiton
metrics 2nd 3rd
multipoint networks
neighbors
enabling on NBMA networks
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poll intervals
passive interfaces
retransmit intervals
routers
ID
priorities
routes
defaults 2nd
EIGRP
exchanges
filtering
installation
installing
maps
preventing
redistribution 2nd
routing processes
tags 2nd
transmit delay values
verification:classless EIGRP routes
routes:EIGRP:classless
classless EIGRP routes
verification:connections
connections:verification
verification:costs:modifying
costs:modifying
modification:costs
verification:Frame Relay:costs
Frame Relay:costs
costs:Frame Relay
verification:inter-area routes
inter-area routes:verification
routes:verification;blocking;routes:verification
verification:keys
verification:passwords
verification:loopback networks:summarizing
loopback networks:summarizing:verification
verification:metric types:modifying
modification:metrics:types
verification:MTU
troubleshooting:MTU
verification:neighbor relationships
neighbors:relationships:verification
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relationships:neighbors:verification
verification:neighbors:modifying status
clear ip ospf process command
commands:clear ip ospf process
verification:neighbors:priority
election:DR
DR:electing
verification:networks:summarizng
loopback networks:summarizing:verification
verification:NSSA
NSSA:verification
inspection:routing tables;routing:tables:inspection;tables:routing:inspection
verification:passwords
verification:keys
verification:redistribution
routes:redistribution:verification
redistribution:routes:verification
verification:retransmit intervals
retransmit intervals:verification
verification:RID
RID:verification
ID:RID:verification;Router ID. [See RID]
verification:routes:blocking
routes:blocking
blocking:routes
verification:routes:installing
routes:installing:verifying
installation:routes:installing
verification:stub areas
stub areas:verification 2nd
verification:summarization
summarization:verification 2nd
verification:transmit delays
transmit delays:verification
verification:virtual links:interfaces
virtual links:interfaces:verification
interfaces:virtual links:verification
verification:VSSA
VSSA:verification
verificaton
routes
tag values
veritication
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routes
IP routing tables
virtual links:dead intervals:modification
dead intervals:virtual links:modification
modificiation:dead intervals:virtual links;intervals. [See also dead intervals]2nd [See also dead intervals]3rd [See also dead intervals]4th
[See also dead intervals]5th [See also dead intervals]
virtual links:Hello intervals
packets:Hello:virtual links
neighbors:relationships:Hello intervals;relationships:neighbors:Hello intervals
neighbors:relationships:Hello intervals;relationships:neighbors:Hello intervals;modification:Hello i 2nd 3rd 4th 5th
VPN:architecture
MPLS:architecture
architecture:MPLS/VPN
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wil-card masks
masks:wild-card 2nd 3rd 4th 5th
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