Cisco | Nexus 3000 Series | Specifications | Cisco Nexus 3000 Series Specifications

Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Cisco Nexus 3000 Series NX-OS Unicast
Routing Configuration Guide, Release
5.0(3)U2(2)
November 2011
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OL-25782-02
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Cisco Nexus 3000 Series NX-OS Unicast Routing Configuration Guide, Release 5.0(3)U2(2)
©2011 Cisco Systems, Inc. All rights reserved.
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
CONTENTS
New and Changed Information
Preface
xix
xxi
Audience
xxi
Supported Switches xxi
Cisco Nexus 3000 Platform Switches
Organization
xxi
xxii
Document Conventions
xxiii
Related Documentation
xxiv
Obtaining Documentation and Submitting a Service Request
xxiv
xxv
CHAPTER
1
Overview
1-1
Information About Layer 3 Unicast Routing 1-1
Routing Fundamentals 1-2
Packet Switching 1-2
Routing Metrics 1-3
Path Length 1-4
Reliability 1-4
Routing Delay 1-4
Bandwidth 1-4
Load 1-4
Communication Cost 1-4
Router IDs 1-5
Autonomous Systems 1-5
Convergence 1-6
Load Balancing and Equal Cost Multipath 1-6
Route Redistribution 1-6
Administrative Distance 1-7
Stub Routing 1-7
Routing Algorithms 1-8
Static Routes and Dynamic Routing Protocols
Interior and Exterior Gateway Protocols 1-8
Distance Vector Protocols 1-9
1-8
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Link-State Protocols
Layer 3 Virtualization
1-9
1-10
Cisco NX-OS Fowarding Architecture 1-10
Unicast RIB 1-10
Adjacency Manager 1-11
Unicast Forwarding Distribution Module
FIB 1-11
Hardware Forwarding 1-12
Software Forwarding 1-12
Summary of Layer 3 Unicast Routing Features
IPv4 1-12
OSPF 1-13
EIGRP 1-13
BGP 1-13
RIP 1-13
Static Routing 1-13
Layer 3 Virtualization 1-13
Route Policy Manager 1-14
First-Hop Redundancy Protocols 1-14
Object Tracking 1-14
Related Topics
1-11
1-12
1-14
IP
CHAPTER
2
Configuring IPv4
2-1
Information About IPv4 2-1
Multiple IPv4 Addresses 2-2
Address Resolution Protocol 2-2
ARP Caching 2-3
Static and Dynamic Entries in the ARP Cache
Devices that Do Not Use ARP 2-4
Reverse ARP 2-4
Proxy ARP 2-5
Local Proxy ARP 2-5
Gratuitous ARP 2-5
Glean Throttling 2-5
ICMP 2-6
Virtualization Support 2-6
Licensing Requirements for IPv4
2-3
2-6
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Prerequisites for IPv4
2-6
Guidelines and Limitations
Default Settings
2-6
2-7
Configuring IPv4 2-7
Configuring IPv4 Addressing 2-7
Configuring Multiple IP Addresses 2-9
Configuring a Static ARP Entry 2-9
Configuring Proxy ARP 2-10
Configuring Local Proxy ARP 2-11
Configuring Gratuitous ARP 2-12
Configuring IP Directed Broadcasts 2-13
Configuring IP Glean Throttling 2-14
Configuring the Hardware IP Glean Throttle Maximum 2-15
Configuring a Hardware IP Glean Throttle Timeout 2-16
Configuring the Hardware IP Glean Throttle Syslog 2-17
Verifying the IPv4 Configuration
2-18
Configuration Examples for IPv4
2-18
Additional References 2-19
Related Documents 2-19
Standards 2-19
Feature History for IP
2-19
Routing
CHAPTER
3
Configuring OSPFv2
3-1
Information About OSPFv2 3-1
Hello Packet 3-2
Neighbors 3-2
Adjacency 3-3
Designated Routers 3-3
Areas 3-4
Link-State Advertisements 3-5
LSA Types 3-5
Link Cost 3-6
Flooding and LSA Group Pacing
Link-State Database 3-7
Opaque LSAs 3-7
OSPFv2 and the Unicast RIB 3-7
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Authentication 3-7
Simple Password Authentication 3-8
MD5 Authentication 3-8
Advanced Features 3-8
Stub Area 3-8
Not-So-Stubby Area 3-9
Virtual Links 3-9
Route Redistribution 3-10
Route Summarization 3-10
OSPFv2 Stub Router Advertisements 3-11
Multiple OSPFv2 Instances 3-11
SPF Optimization 3-11
Virtualization Support 3-11
Licensing Requirements for OSPFv2
Prerequisites for OSPFv2
3-12
Guidelines and Limitations
Default Settings
3-11
3-12
3-12
Configuring Basic OSPFv2 3-13
Enabling the OSPFv2 Feature 3-13
Creating an OSPFv2 Instance 3-14
Configuring Optional Parameters on an OSPFv2 Instance
Configuring Networks in OSPFv2 3-16
Configuring Authentication for an Area 3-18
Configuring Authentication for an Interface 3-20
3-15
Configuring Advanced OSPFv2 3-22
Configuring Filter Lists for Border Routers 3-23
Configuring Stub Areas 3-24
Configuring a Totally Stubby Area 3-25
Configuring NSSA 3-26
Configuring Virtual Links 3-28
Configuring Redistribution 3-30
Limiting the Number of Redistributed Routes 3-32
Configuring Route Summarization 3-34
Configuring Stub Route Advertisements 3-35
Modifying the Default Timers 3-36
Restarting an OSPFv2 Instance 3-39
Configuring OSPFv2 with Virtualization 3-39
Verifying the OSPFv2 Configuration
Displaying OSPFv2 Statistics
3-41
3-42
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Configuration Examples for OSPFv2
3-42
Additional References 3-43
Related Documents 3-43
MIBs 3-43
Feature History for OSPFv2
CHAPTER
4
Configuring EIGRP
3-43
4-1
Information About EIGRP 4-1
EIGRP Components 4-2
Reliable Transport Protocol 4-2
Neighbor Discovery and Recovery
Diffusing Update Algorithm 4-3
EIGRP Route Updates 4-3
Internal Route Metrics 4-3
External Route Metrics 4-4
EIGRP and the Unicast RIB 4-4
Advanced EIGRP 4-4
Address Families 4-5
Authentication 4-5
Stub Routers 4-5
Route Summarization 4-6
Route Redistribution 4-6
Load Balancing 4-6
Split Horizon 4-6
Virtualization Support 4-7
Licensing Requirements for EIGRP
Prerequisites for EIGRP
4-7
4-7
Guidelines and Limitations
Default Settings
4-2
4-7
4-8
Configuring Basic EIGRP 4-9
Enabling the EIGRP Feature 4-9
Creating an EIGRP Instance 4-10
Restarting an EIGRP Instance 4-12
Shutting Down an EIGRP Instance 4-13
Configuring a Passive Interface for EIGRP 4-13
Shutting Down EIGRP on an Interface 4-13
Configuring Advanced EIGRP 4-13
Configuring Authentication in EIGRP 4-14
Configuring EIGRP Stub Routing 4-16
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Configuring a Summary Address for EIGRP 4-17
Redistributing Routes into EIGRP 4-17
Limiting the Number of Redistributed Routes 4-19
Configuring Load Balancing in EIGRP 4-21
Adjusting the Interval Between Hello Packets and the Hold Time
Disabling Split Horizon 4-23
Tuning EIGRP 4-23
Configuring Virtualization for EIGRP
Verifying the EIGRP Configuration
Displaying EIGRP Statistics
4-25
4-27
4-27
Configuration Examples for EIGRP
Related Topics
4-22
4-28
4-28
Additional References 4-28
Related Documents 4-29
MIBs 4-29
Feature History for EIGRP
CHAPTER
5
Configuring Basic BGP
4-29
5-1
Information About Basic BGP 5-1
BGP Autonomous Systems 5-2
4-Byte AS Number Support 5-2
Administrative Distance 5-2
BGP Peers 5-3
BGP Sessions 5-3
Dynamic AS Numbers for Prefix Peers 5-3
BGP Router Identifier 5-4
BGP Path Selection 5-4
Step 1—Comparing Pairs of Paths 5-5
Step 2—Determining the Order of Comparisons 5-6
Step 3—Determining the Best-Path Change Suppression
BGP and the Unicast RIB 5-7
BGP Virtualization 5-7
Licensing Requirements for Basic BGP
Prerequisites for BGP
5-6
5-7
5-7
Guidelines and Limitations for BGP
5-8
CLI Configuration Modes 5-8
Global Configuration Mode 5-9
Address Family Configuration Mode
5-9
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Neighbor Configuration Mode 5-9
Neighbor Address Family Configuration Mode
Default Settings
5-10
5-10
Configuring Basic BGP 5-10
Enabling the BGP Feature 5-11
Creating a BGP Instance 5-12
Restarting a BGP Instance 5-13
Shutting Down BGP 5-14
Configuring BGP Peers 5-14
Configuring Dynamic AS Numbers for Prefix Peers
Clearing BGP Information 5-18
Verifying the Basic BGP Configuration
Displaying BGP Statistics
5-21
5-23
Configuration Examples for Basic BGP
Related Topics
5-16
5-23
5-23
Where to Go Next
5-23
Additional References 5-23
Related Documents 5-24
MIBs 5-24
Feature History for BGP
CHAPTER
6
Configuring Advanced BGP
5-24
6-1
Information About Advanced BGP 6-1
Peer Templates 6-2
Authentication 6-2
Route Policies and Resetting BGP Sessions
eBGP 6-3
iBGP 6-3
AS Confederations 6-4
Route Reflector 6-5
Capabilities Negotiation 6-5
Route Dampening 6-6
Load Sharing and Multipath 6-6
Route Aggregation 6-7
BGP Conditional Advertisement 6-7
BGP Next-Hop Address Tracking 6-7
Route Redistribution 6-8
BFD 6-8
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Tuning BGP 6-8
BGP Timers 6-9
Tuning the Best-Path Algorithm
Multiprotocol BGP 6-9
Virtualization Support 6-9
Licensing Requirements for Advanced BGP
Prerequisites for BGP
6-9
6-10
Guidelines and Limitations for BGP
Default Settings
6-9
6-10
6-10
Configuring Advanced BGP 6-11
Configuring BGP Session Templates 6-12
Configuring BGP Peer-Policy Templates 6-14
Configuring BGP Peer Templates 6-16
Configuring Prefix Peering 6-19
Configuring BGP Authentication 6-20
Resetting a BGP Session 6-20
Modifying the Next-Hop Address 6-21
Configuring BGP Next-Hop Address Tracking 6-21
Configuring Next-Hop Filtering 6-22
Disabling Capabilities Negotiation 6-22
Configuring eBGP 6-22
Disabling eBGP Single-Hop Checking 6-22
Configuring eBGP Multihop 6-23
Disabling a Fast External Failover 6-23
Limiting the AS-path Attribute 6-24
Configuring Local AS Support 6-24
Configuring AS Confederations 6-25
Configuring Route Reflector 6-25
Configuring Route Dampening 6-27
Configuring Load Sharing and ECMP 6-28
Configuring Maximum Prefixes 6-28
Configuring Dynamic Capability 6-28
Configuring Aggregate Addresses 6-29
Configuring BGP Conditional Advertisement 6-29
Configuring Route Redistribution 6-31
Configuring Multiprotocol BGP 6-33
Tuning BGP 6-34
Configuring Virtualization 6-37
Verifying the Advanced BGP Configuration
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Displaying BGP Statistics
Related Topics
6-40
6-40
Additional References 6-41
Related Documents 6-41
MIBs 6-41
Feature History for BGP
CHAPTER
7
6-41
Configuring Bidirectional Forwarding Detection for BGP
7-1
Information About BFD 7-1
Asynchronous Mode 7-2
BFD Detection of Failures 7-2
BFD Echo Function 7-2
Security 7-3
Virtualization Support 7-3
Licensing Requirements for BFD
Prerequisites for BFD
7-3
Guidelines and Limitations
Default Settings
7-3
7-3
7-4
Configuring BFD 7-5
Configuration Hierarchy 7-5
Task Flow for Configuring BFD 7-5
Enabling the BFD Feature 7-6
Configuring Global BFD Parameters 7-6
Configuring BFD on an Interface 7-8
Configuring BFD on a Port Channel 7-9
Configuring BFD Echo Function 7-10
Optimizing BFD on Subinterfaces 7-11
Configuring BFD on BGP 7-13
Verifying the BFD Configuration
Monitoring BFD
7-14
Feature History for BFD
CHAPTER
8
7-14
7-15
Configuring ECMP for Host Routes
8-1
Information About ECMP for Host Routes
8-1
Licensing Requirements for ECMP for Host Routes
Prerequisites for ECMP for Host Routes
Default Settings
8-1
8-2
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Configuring ECMP for Host Routes 8-2
Enabling the EMCP for Host Routes Feature 8-2
Disabling the EMCP for Host Routes Feature 8-3
Verifying the ECMP for Host Routes Configuration
8-4
Configuration Examples for ECMP for Host Routes
8-4
Additional References 8-4
Related Documents 8-5
Feature History for ECMP for Host Routes
CHAPTER
9
Configuring RIP
8-5
9-1
Information About RIP 9-1
RIP Overview 9-2
RIPv2 Authentication 9-2
Split Horizon 9-2
Route Filtering 9-3
Route Summarization 9-3
Route Redistribution 9-3
Load Balancing 9-3
Virtualization Support 9-4
Licensing Requirements for RIP
Prerequisites for RIP
9-4
Guidelines and Limitations
Default Settings
9-4
9-4
9-4
Configuring RIP 9-5
Enabling the RIP Feature 9-5
Creating a RIP Instance 9-6
Restarting a RIP Instance 9-8
Configuring RIP on an Interface 9-8
Configuring RIP Authentication 9-9
Configuring a Passive Interface 9-11
Configuring Split Horizon with Poison Reverse
Configuring Route Summarization 9-11
Configuring Route Redistribution 9-12
Configuring Virtualization 9-13
Tuning RIP 9-16
Verifying the RIP Configuration
Displaying RIP Statistics
9-11
9-17
9-17
Configuration Examples for RIP
9-18
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Related Topics
9-18
Additional References 9-18
Related Documents 9-19
Standards 9-19
Feature History for RIP
CHAPTER
10
9-19
Configuring Static Routing
10-1
Information About Static Routing 10-1
Administrative Distance 10-2
Directly Connected Static Routes 10-2
Fully Specified Static Routes 10-2
Floating Static Routes 10-2
Remote Next Hops for Static Routes 10-3
Virtualization Support 10-3
Licensing Requirements for Static Routing
Prerequisites for Static Routing
Guidelines and Limitations
Default Settings
10-3
10-3
10-3
10-3
Configuring Static Routing 10-4
Configuring a Static Route 10-4
Configuring Virtualization 10-5
Verifying the Static Routing Configuration
10-6
Configuration Examples for Static Routing
10-6
Additional References 10-6
Related Documents 10-7
CHAPTER
11
Feature History for Static Routing
10-7
Configuring Layer 3 Virtualization
11-1
Layer 3 Virtualization 11-1
Overview of Layer 3 Virtualization 11-1
VRF and Routing 11-2
VRF-Lite 11-2
VRF-Aware Services 11-3
Reachability 11-3
Filtering 11-4
Combining Reachability and Filtering
Licensing Requirements for VRFs
Guidelines and Limitations
11-4
11-5
11-5
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Default Settings
11-6
Configuring VRFs 11-6
Creating a VRF 11-6
Assigning VRF Membership to an Interface 11-8
Configuring VRF Parameters for a Routing Protocol
Configuring a VRF-Aware Service 11-11
Setting the VRF Scope 11-12
Verifying the VRF Configuration
11-13
Configuration Examples for VRF
11-13
Related Topics
11-9
11-14
Additional References 11-14
Related Documents 11-14
Standards 11-14
Feature History for VRF
CHAPTER
12
11-14
Managing the Unicast RIB and FIB
12-1
Information About the Unicast RIB and FIB
Layer 3 Consistency Checker 12-2
FIB Tables 12-2
Virtualization Support 12-2
12-1
Licensing Requirements for the Unicast RIB and FIB
12-3
Managing the Unicast RIB and FIB 12-3
Displaying Module FIB Information 12-3
Configuring Load Sharing in the Unicast FIB 12-4
Configuring Per-Packet Load Sharing 12-5
Displaying Routing and Adjacency Information 12-6
Triggering the Layer 3 Consistency Checker 12-7
Clearing Forwarding Information in the FIB 12-8
Estimating Memory Requirements for Routes 12-9
Clearing Routes in the Unicast RIB 12-9
Verifying the Unicast RIB and FIB Configuration
12-10
Additional References 12-10
Related Documents 12-10
Feature History for Unicast RIB and FIB
CHAPTER
13
Configuring Route Policy Manager
12-10
13-1
Information About Route Policy Manager
Prefix Lists 13-2
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MAC Lists 13-2
Route Maps 13-2
Match Criteria 13-3
Set Changes 13-3
Access Lists 13-3
AS Numbers for BGP 13-3
AS-path Lists for BGP 13-4
Community Lists for BGP 13-4
Extended Community Lists for BGP 13-4
Route Redistribution and Route Maps 13-5
Licensing Requirements for Route Policy Manager
Guidelines and Limitations
Default Settings
13-5
13-5
13-5
Configuring Route Policy Manager 13-6
Configuring IP Prefix Lists 13-6
Configuring MAC Lists 13-7
Configuring AS-path Lists 13-8
Configuring Community Lists 13-9
Configuring Extended Community Lists
Configuring Route Maps 13-12
13-11
Verifying the Route Policy Manager Configuration
13-17
Configuration Examples for Route Policy Manager
13-17
Related Topics
13-18
Additional References 13-18
Related Documents 13-18
Standards 13-18
Feature History for Route Policy Manager
13-18
First-Hop Redundancy Protocols
CHAPTER
14
Configuring HSRP
14-1
Information About HSRP 14-1
HSRP Overview 14-2
HSRP for IPv4 14-3
HSRP Versions 14-4
HSRP Authentication 14-4
HSRP Messages 14-4
HSRP Load Sharing 14-4
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Object Tracking and HSRP 14-5
Virtualization Support 14-5
Licensing Requirements for HSRP
Prerequisites for HSRP
14-6
Guidelines and Limitations
Default Settings
14-6
14-6
14-6
Configuring HSRP 14-7
Enabling the HSRP Feature 14-7
Configuring the HSRP Version 14-8
Configuring an HSRP Group for IPv4 14-8
Configuring the HSRP Virtual MAC Address
Authenticating HSRP 14-10
Configuring HSRP Object Tracking 14-12
Configuring the HSRP Priority 14-14
Customizing HSRP 14-14
Verifying the HSRP Configuration
14-16
Configuration Examples for HSRP
14-16
14-10
Additional References 14-16
Related Documents 14-17
MIBs 14-17
Feature History for HSRP
CHAPTER
15
Configuring VRRP
14-17
15-1
Information About VRRP 15-1
VRRP Operation 15-2
VRRP Benefits 15-3
Multiple VRRP Groups 15-3
VRRP Router Priority and Preemption
VRRP Advertisements 15-5
VRRP Authentication 15-5
VRRP Tracking 15-5
Virtualization Support 15-5
Licensing Requirements for VRRP
Guidelines and Limitations
Default Settings
15-4
15-6
15-6
15-6
Configuring VRRP 15-7
Enabling the VRRP Feature 15-7
Configuring VRRP Groups 15-8
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Configuring VRRP Priority 15-9
Configuring VRRP Authentication 15-11
Configuring Time Intervals for Advertisement Packets
Disabling Preemption 15-14
Configuring VRRP Interface State Tracking 15-15
Verifying the VRRP Configuration
Displaying VRRP Statistics
15-12
15-17
15-17
Configuration Examples for VRRP
15-18
Additional References 15-19
Related Documents 15-19
Feature History for VRRP
CHAPTER
16
Configuring Object Tracking
15-19
16-1
Information About Object Tracking 16-1
Object Tracking Overview 16-1
Object Track List 16-2
Virtualization Support 16-2
Licensing Requirements for Object Tracking
Guidelines and Limitations
Default Settings
16-3
16-3
16-3
Configuring Object Tracking 16-3
Configuring Object Tracking for an Interface 16-4
Configuring Object Tracking for Route Reachability 16-5
Configuring an Object Track List with a Boolean Expression 16-6
Configuring an Object Track List with a Percentage Threshold 16-7
Configuring an Object Track List with a Weight Threshold 16-8
Configuring an Object Tracking Delay 16-10
Configuring Object Tracking for a Nondefault VRF 16-12
Verifying the Object Tracking Configuration
16-13
Configuration Examples for Object Tracking
16-13
Related Topics
16-13
Additional References 16-13
Related Documents 16-14
Standards 16-14
Feature History for Object Tracking
APPENDIX
A
IETF RFCs A-1
BGP RFCs
16-14
A-1
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First-Hop Redundancy Protocols RFCs
IP Services RFCs A-2
OSPF RFCs A-2
RIP RFCs A-2
A-2
GLOSSARY
INDEX
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New and Changed Information
This chapter provides release-specific information for each new and changed feature in the Cisco Nexus
3000 Series NX-OS Unicast Routing Configuration Guide, Release 5.0(3)U2(2). The latest version of
this document is available at the following Cisco website:
http://www.cisco.com/en/US/products/ps11541/products_installation_and_configuration_guides_list.h
tml
To check for additional information, see the Cisco Nexus 7000 Series NX-OS Release Notes, Release 5.x
available at the following Cisco website:
http://www.cisco.com/en/US/products/ps11541/prod_release_notes_list.html
Table 1 summarizes the new and changed features for the Cisco Nexus 3000 Series NX-OS Unicast
Routing Configuration Guide, Release 5.0(3)U2(2), and tells you where they are documented.
Table 1
New and Changed Features for 5.0(3)
Feature
Description
IPv4
Added information to configure the glean
throttling feature.
Changed in
Release
Where Documented
5.0(3)U2(1)
Chapter 2, “Configuring IPv4”
Bidirectional forwarding Added information on how to configure BFD 5.0(3)U2(2)
detection (BFD) for BGP for BGP.
Chapter 7, “Configuring
Bidirectional Forwarding
Detection for BGP”
Equal-cost multipathing Added information on how to configure
(ECMP) protocol for host ECMP for host routes.
routes
5.0(3)U2(2)
Chapter 8, “Configuring ECMP
for Host Routes”
BGP
Added support for Local AS.
5.0(3)U2(2a) Configuring Local AS Support,
page 6-24
BFD for BGP
Added guidelines and limitations for LACP
configuration, and for BFD echo and URFP.
5.0(3)U2(2a) Guidelines and Limitations,
page 7-3
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Preface
This document describes the configuration details for Cisco NX-OS unicast routing in Cisco NX-OS
switches.
This chapter includes the following sections:
•
Audience, page -xxi
•
Supported Switches, page -xxi
•
Organization, page -xxii
•
Document Conventions, page -xxiii
•
Related Documentation, page -xxiv
•
Obtaining Documentation and Submitting a Service Request, page -xxiv
Audience
To use this guide, you must be familiar with IP and routing technology.
Supported Switches
This section includes the following topics:
•
Cisco Nexus 3000 Platform Switches, page -xxi
Cisco Nexus 3000 Platform Switches
Table 1 describes the Cisco Nexus 3000 Series switch:
Note
For more information on these switches, see the Cisco Nexus 3000 Series Hardware Installation Guide
available at the following URL:
http://www.cisco.com/en/US/products/ps9670/tsd_products_support_series_home.html
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Table 1
Supported Cisco Nexus 3000 Platform Switches
Switch
Description
Cisco Nexus 3064PQ Switch
The Cisco Nexus 3064UP switch is a high-performance,
high-density, ultra-low-latency Ethernet switch that is part of the
new Cisco Nexus 3000 Series Switches. This compact one-rack-unit
(1RU) form factor 1 and 10 Gigabit Ethernet switch provides
line-rate Layer 2 and 3 switching. The switch runs the
industry-leading Cisco NX-OS Software operating system,
providing customers with robust features and functionality that are
widely deployed globally. The Cisco Nexus 3064UP is well suited
for financial co-location deployments that require support for robust
unicast and multicast routing protocol features at ultra-low
latencies.
Organization
This document is organized into the following chapters:
Title
Description
Chapter 1, “Overview”
Presents an overview of unicast routing and brief
descriptions of each feature.
Chapter 2, “Configuring IPv4”
Describes how to configure and manage IPv4, including
ARP and ICMP.
Chapter 3, “Configuring OSPFv2”
Describes how to configure the OSPFv2 routing protocol
for IPv4 networks.
Chapter 4, “Configuring EIGRP”
Describes how to configure the Cisco EIGRP routing
protocol for IPv4 networks.
Chapter 5, “Configuring Basic BGP”
Describes how to configure basic features for the BGP
routing protocol for IPv4 networks.
Chapter 6, “Configuring Advanced BGP”
Describes how to configure advanced features for the
BGP routing protocol for IPv4 networks, including route
redistribution and route aggregation.
Chapter 7, “Configuring Bidirectional
Forwarding Detection for BGP”
Describes how to configure Bidirectional Forwarding
Detection (BFD) for BGP.
Chapter 8, “Configuring ECMP for Host
Routes”
Describes how to configure the equal-cost multipathing
(ECMP) protocol for host routes
Chapter 9, “Configuring RIP”
Describes how to configure the RIP routing protocols for
IPv4 networks.
Chapter 10, “Configuring Static Routing”
Describes how to configure static routing for IPv4
networks.
Chapter 11, “Configuring Layer 3
Virtualization”
Describes how to configure Layer 3 virtualization.
Chapter 12, “Managing the Unicast RIB
and FIB”
Describes how to view and modify the unicast RIB and
FIB.
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Title
Description
Chapter 13, “Configuring Route Policy
Manager”
Describes how to configure the Route Policy Manager,
including IP prefix lists and route maps for filtering and
redistribution.
Chapter 14, “Configuring HSRP”
Describes how to configure the Hot Standby Routing
Protocol.
Chapter 15, “Configuring VRRP”
Describes how to configure the Virtual Router
Redundancy Protocol.
Chapter 16, “Configuring Object
Tracking”
Describes how to configure object tracking.
Appendix A, “IETF RFCs”
Lists IETF RFCs supported by Cisco NX-OS.
Document Conventions
Command descriptions use these conventions:
Convention
Description
boldface font
Commands and keywords are in boldface.
italic font
Arguments for which you supply values are in italics.
[ ]
Elements in square brackets are optional.
[x|y|z]
Optional alternative keywords are grouped in brackets and separated by vertical
bars.
string
A nonquoted set of characters. Do not use quotation marks around the string or
the string will include the quotation marks.
Screen examples use these conventions:
screen font
Terminal sessions and information that the switch displays are in screen font.
boldface screen
font
Information that you must enter is in boldface screen font.
italic screen font
Arguments for which you supply values are in italic screen font.
< >
Nonprinting characters, such as passwords, are in angle brackets.
[ ]
Default responses to system prompts are in square brackets.
!, #
An exclamation point (!) or a pound sign (#) at the beginning of a line of code
indicates a comment line.
This document uses the following conventions:
Note
Means reader take note. Notes contain helpful suggestions or references to material not covered in the
manual.
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Caution
Means reader be careful. In this situation, you might do something that could result in equipment
damage or loss of data.
Related Documentation
Documentation for the Cisco Nexus 3000 Series Switch is available at the following URL:
http://www.cisco.com/en/US/products/ps11541/tsd_products_support_series_home.html
The documentation set is divided into the following categories:
Release Notes
The release notes are available at the follwing URL:
http://www.cisco.com/en/US/products/ps11541/prod_release_notes_list.html
Installation and Upgrade Guides
The installation and upgrade guides are available at the following URL:
http://www.cisco.com/en/US/products/ps11541/prod_installation_guides_list.html
Command References
The command references are available at the following URL:
http://www.cisco.com/en/US/products/ps11541/prod_command_reference_list.html
Technical References
The technical references are available at the following URL:
http://www.cisco.com/en/US/products/ps11541/prod_technical_reference_list.html
Configuration Guides
The configuration guides are available at the following URL:
http://www.cisco.com/en/US/products/ps11541/products_installation_and_configuration_guides_list.h
tml
Error and System Messages
The system message reference guide is available at the following URL:
http://www.cisco.com/en/US/products/ps11541/products_system_message_guides_list.html
Obtaining Documentation and Submitting a Service Request
For information on obtaining documentation, submitting a service request, and gathering additional
information, see the monthly What’s New in Cisco Product Documentation, which also lists all new and
revised Cisco technical documentation, at:
http://www.cisco.com/en/US/docs/general/whatsnew/whatsnew.html
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delivered directly to your desktop using a reader application. The RSS feeds are a free service. Cisco currently
supports RSS Version 2.0.
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CH A P T E R
1
Overview
This chapter introduces the underlying concepts for Layer 3 unicast routing protocols in Cisco NX-OS.
This chapter includes the following sections:
•
Information About Layer 3 Unicast Routing, page 1-1
•
Routing Algorithms, page 1-8
•
Layer 3 Virtualization, page 1-10
•
Cisco NX-OS Fowarding Architecture, page 1-10
•
Summary of Layer 3 Unicast Routing Features, page 1-12
•
Related Topics, page 1-14
Information About Layer 3 Unicast Routing
Layer 3 unicast routing involves two basic activities: determining optimal routing paths and packet
switching. You can use routing algorithms to calculate the optimal path from the router to a destination.
This calculation depends on the algorithm selected, route metrics, and other considerations such as load
balancing and alternate path discovery.
This section includes the following topics:
•
Routing Fundamentals, page 1-2
•
Packet Switching, page 1-2
•
Routing Metrics, page 1-3
•
Router IDs, page 1-5
•
Autonomous Systems, page 1-5
•
Convergence, page 1-6
•
Load Balancing and Equal Cost Multipath, page 1-6
•
Route Redistribution, page 1-6
•
Administrative Distance, page 1-7
•
Stub Routing, page 1-7
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Routing Fundamentals
Routing protocols use a metric to evaluate the best path to the destination. A metric is a standard of
measurement, such as a path bandwidth, that routing algorithms use to determine the optimal path to a
destination. To aid path determination, routing algorithms initialize and maintain routing tables, that
contain route information such as the IP destination address and the address of the next router or next
hop. Destination and next-hop associations tell a router that an IP destination can be reached optimally
by sending the packet to a particular router that represents the next hop on the way to the final
destination. When a router receives an incoming packet, it checks the destination address and attempts
to associate this address with the next hop. See the “Unicast RIB” section on page 1-10 for more
information about the route table.
Routing tables can contain other information, such as the data about the desirability of a path. Routers
compare metrics to determine optimal routes, and these metrics differ depending on the design of the
routing algorithm used. See the “Routing Metrics” section on page 1-3.
Routers communicate with one another and maintain their routing tables by transmitting a variety of
messages. The routing update message is one such message that consists of all or a portion of a routing
table. By analyzing routing updates from all other routers, a router can build a detailed picture of the
network topology. A link-state advertisement, another example of a message sent between routers,
informs other routers of the link state of the sending router. You can also use link information to enable
routers to determine optimal routes to network destinations. For more information, see the “Routing
Algorithms” section on page 1-8.
Packet Switching
In packet switching, a host determines that it must send a packet to another host. Having acquired a
router address by some means, the source host sends a packet addressed specifically to the router
physical (Media Access Control [MAC]-layer) address but with the IP (network layer) address of the
destination host.
The router examines the destination IP address and tries to find the IP address in the routing table. If the
router does not know how to forward the packet, it typically drops the packet. If the router knows how
to forward the packet, it changes the destination MAC address to the MAC address of the next hop router
and transmits the packet.
The next hop might be the ultimate destination host or another router that executes the same switching
decision process. As the packet moves through the internetwork, its physical address changes, but its
protocol address remains constant (see Figure 1-1).
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Figure 1-1
Packet Header Updates Through a Network
Source host
PC
Packet
To: Destination host
Router 1
(Protocol address)
(Physical address)
Packet
Router 1
To: Destination host
Router 2
(Protocol address)
(Physical address)
Router 2
To: Destination host (Protocol address)
Router 3
(Physical address)
Router 3
Packet
To: Destination host (Protocol address)
Destination host (Physical address)
Packet
182978
Destination host
PC
Routing Metrics
Routing algorithms use many different metrics to determine the best route. Sophisticated routing
algorithms can base route selection on multiple metrics.
This section includes the following metrics:
•
Path Length, page 1-4
•
Reliability, page 1-4
•
Routing Delay, page 1-4
•
Bandwidth, page 1-4
•
Load, page 1-4
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•
Communication Cost, page 1-4
Path Length
The path length is the most common routing metric. Some routing protocols allow you to assign arbitrary
costs to each network link. In this case, the path length is the sum of the costs associated with each link
traversed. Other routing protocols define hop count, a metric that specifies the number of passes through
internetworking products, such as routers, that a packet must take from a source to a destination.
Reliability
The reliability, in the context of routing algorithms, is the dependability (in terms of the bit-error rate)
of each network link. Some network links might go down more often than others. After a network fails,
certain network links might be repaired more easily or more quickly than other links. The reliability
factors that you can take into account when assigning the reliability rating are arbitrary numeric values
that you usually assign to network links.
Routing Delay
The routing delay is the length of time required to move a packet from a source to a destination through
the internetwork. The delay depends on many factors, including the bandwidth of intermediate network
links, the port queues at each router along the way, the network congestion on all intermediate network
links, and the physical distance that the packet needs to travel. Because the routing delay is a
combination of several important variables, it is a common and useful metric.
Bandwidth
The bandwidth is the available traffic capacity of a link. For example, a 10-Gigabit Ethernet link would
be preferable to a 1-Gigabit Ethernet link. Although the bandwidth is the maximum attainable
throughput on a link, routes through links with greater bandwidth do not necessarily provide better
routes than routes through slower links. For example, if a faster link is busier, the actual time required
to send a packet to the destination could be greater.
Load
The load is the degree to which a network resource, such as a router, is busy. You can calculate the load
in a variety of ways, including CPU utilization and packets processed per second. Monitoring these
parameters on a continual basis can be resource intensive.
Communication Cost
The communication cost is a measure of the operating cost to route over a link. The communication cost
is another important metric, especially if you do not care about performance as much as operating
expenditures. For example, the line delay for a private line might be longer than a public line, but you
can send packets over your private line rather than through the public lines that cost money for usage
time.
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Router IDs
Each routing process has an associated router ID. You can configure the router ID to any interface in
the system. If you do not configure the router ID, Cisco NX-OS selects the router ID based on the
following criteria:
•
Cisco NX-OS prefers loopback0 over any other interface. If loopback0 does not exist, then Cisco
NX-OS prefers the first loopback interface over any other interface type.
•
If you have not configured no loopback interfaces, Cisco NX-OS uses the first interface in the
configuration file as the router ID. If you configure any loopback interface after Cisco NX-OS
selects the router ID, the loopback interface becomes the router ID. If the loopback interface is not
loopback0 and you configure loopback0 later with an IP address, the router ID changes to the IP
address of loopback0.
•
If the interface that the router ID is based on changes, that new IP address becomes the router ID. If
any other interface changes its IP address, there is no router ID change.
Autonomous Systems
An autonomous system (AS) is a network controlled by a single technical administration entity.
Autonomous systems divide global external networks into individual routing domains, where local
routing policies are applied. This organization simplifies routing domain administration and simplifies
consistent policy configuration.
Each autonomous system can support multiple interior routing protocols that dynamically exchange
routing information through route redistribution. The Regional Internet Registries assign a unique
number to each public autonomous system that directly connects to the Internet. This autonomous
system number (AS number) identifies both the routing process and the autonomous system.
Cisco NX-OS supports 4-byte AS numbers. Table 1-1 lists the AS number ranges.
Table 1-1
AS Numbers
4-Byte Numbers in
2-Byte Numbers AS.dot Notation
4-Byte Numbers in
plaintext Notation
Purpose
1 to 64511
0.1 to 0.64511
1 to 64511
Public AS (assigned by RIR)1
64512 to 65534
0.64512 to 0.65534 64512 to 65534
Private AS (assigned by local
administrator)
65535
0.65535
Reserved
N/A
1.0 to 65535.65535 65536 to
4294967295
65535
Public AS (assigned by RIR)
1. RIR=Regional Internet Registries
Private autonomous system numbers are used for internal routing domains but must be translated by the
router for traffic that is routed out to the Internet. You should not configure routing protocols to advertise
private autonomous system numbers to external networks. By default, Cisco NX-OS does not remove
private autonomous system numbers from routing updates.
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Note
The autonomous system number assignment for public and private networks is governed by the Internet
Assigned Number Authority (IANA). For information about autonomous system numbers, including the
reserved number assignment, or to apply to register an autonomous system number, refer to the following
URL:
http://www.iana.org/
Convergence
A key aspect to measure for any routing algorithm is how much time a router takes to react to network
topology changes. When a part of the network changes for any reason, such as a link failure, the routing
information in different routers might not match. Some routers will have updated information about the
changed topology, other routers will still have the old information. The convergence is the amount of
time before all routers in the network have updated, matching routing information. The convergence
time varies depending on the routing algorithm. Fast convergence minimizes the chance of lost packets
caused by inaccurate routing information.
Load Balancing and Equal Cost Multipath
Routing protocols can use load balancing or equal cost multipath (ECMP) to share traffic across
multiple paths.When a router learns multiple routes to a specific network, it installs the route with the
lowest administrative distance in the routing table. If the router receives and installs multiple paths with
the same administrative distance and cost to a destination, load balancing can occur. Load balancing
distributes the traffic across all the paths, sharing the load. The number of paths used is limited by the
number of entries that the routing protocol puts in the routing table. Cisco NX-OS supports up to 16
paths to a destination.
The Enhanced Interior Gateway Routing Protocol (EIGRP) also supports unequal cost load balancing.
For more information, see Chapter 4, “Configuring EIGRP.”
Route Redistribution
If you have multiple routing protocols configured in your network, you can configure these protocols to
share routing information by configuring route redistribution in each protocol. For example, you can
configure Open Shortest Path First (OSPF) to advertise routes learned from the Border Gateway Protocol
(BGP). You can also redistribute static routes into any dynamic routing protocol. The router that is
redistributing routes from another protocol sets a fixed route metric for those redistributed routes. This
avoids the problem of incompatible route metrics between the different routing protocols. For example,
routes redistributed from EIGRP into OSPF are assigned a fixed link cost metric that OSPF understands.
Route redistribution also uses an administrative distance (see the “Administrative Distance” section on
page 1-7) to distinguish between routes learned from two different routing protocols. The preferred
routing protocol is given a lower administrative distance so that its routes are picked over routes from
another protocol with a higher administrative distance assigned.
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Administrative Distance
An administrative distance is a rating of the trustworthiness of a routing information source. The higher
the value, the lower the trust rating. Typically, a route can be learned through more than one protocol.
Administrative distance is used to discriminate between routes learned from more than one protocol. The
route with the lowest administrative distance is installed in the IP routing table.
Stub Routing
You can use stub routing in a hub-and-spoke network topology, where one or more end (stub) networks
are connected to a remote router (the spoke) that is connected to one or more distribution routers (the
hub). The remote router is adjacent only to one or more distribution routers. The only route for IP traffic
to follow into the remote router is through a distribution router. This type of configuration is commonly
used in WAN topologies in which the distribution router is directly connected to a WAN. The distribution
router can be connected to many more remote routers. Often, the distribution router is connected to 100
or more remote routers. In a hub-and-spoke topology, the remote router must forward all nonlocal traffic
to a distribution router, so it becomes unnecessary for the remote router to hold a complete routing table.
Generally, the distribution router sends only a default route to the remote router.
Only specified routes are propagated from the remote (stub) router. The stub router responds to all
queries for summaries, connected routes, redistributed static routes, external routes, and internal routes
with the message “inaccessible.” A router that is configured as a stub sends a special peer information
packet to all neighboring routers to report its status as a stub router.
Any neighbor that receives a packet informing it of the stub status does not query the stub router for any
routes, and a router that has a stub peer does not query that peer. The stub router depends on the
distribution router to send the proper updates to all peers.
Figure 1-2 shows a simple hub-and-spoke configuration.
Figure 1-2
Simple Hub-and-Spoke Network
Stub routing does not prevent routes from being advertised to the remote router. Figure 1-2 shows that
the remote router can access the corporate network and the Internet through the distribution router only.
A full route table on the remote router, in this example, serves no functional purpose because the path to
the corporate network and the Internet would always be through the distribution router. A larger route
table would reduce only the amount of memory required by the remote router. The bandwidth and
memory used can be lessened by summarizing and filtering routes in the distribution router. In this
network topology, the remote router does not need to receive routes that have been learned from other
networks because the remote router must send all nonlocal traffic, regardless of its destination, to the
distribution router. To configure a true stub network, you should configure the distribution router to send
only a default route to the remote router.
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OSPF supports stub areas and EIGRP supports stub routers.
Routing Algorithms
Routing algorithms determine how a router gathers and reports reachability information, how it deals
with topology changes, and how it determines the optimal route to a destination. Various types of routing
algorithms exist, and each algorithm has a different impact on network and router resources. Routing
algorithms use a variety of metrics that affect calculation of optimal routes. You can classify routing
algorithms by type, such as static or dynamic, and interior or exterior.
This section includes the following topics:
•
Static Routes and Dynamic Routing Protocols, page 1-8
•
Interior and Exterior Gateway Protocols, page 1-8
•
Distance Vector Protocols, page 1-9
•
Link-State Protocols, page 1-9
Static Routes and Dynamic Routing Protocols
Static routes are route table entries that you manually configure. These static routes do not change unless
you reconfigure them. Static routes are simple to design and work well in environments where network
traffic is relatively predictable and where network design is relatively simple.
Because static routing systems cannot react to network changes, you should not uses them for today’s
large, constantly changing networks. Most routing protocols today use dynamic routing algorithms,
which adjust to changing network circumstances by analyzing incoming routing update messages. If the
message indicates that a network change has occurred, the routing software recalculates routes and sends
out new routing update messages. These messages permeate the network, triggering routers to rerun their
algorithms and change their routing tables accordingly.
You can supplement dynamic routing algorithms with static routes where appropriate. For example, you
should configure each subnetwork with a static route to the IP default gateway or router of last resort (a
router to which all unrouteable packets are sent).
Interior and Exterior Gateway Protocols
You can separate networks into unique routing domains or autonomous systems. An autonomous system
is a portion of an internetwork under common administrative authority that is regulated by a particular
set of administrative guidelines. Routing protocols that route between autonomous systems are called
exterior gateway protocols or interdomain protocols. BGP is an example of an exterior gateway protocol.
Routing protocols used within an autonomous system are called interior gateway protocols or
intradomain protocols. EIGRP and OSPF are examples of interior gateway protocols.
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Distance Vector Protocols
Distance vector protocols use distance vector algorithms (also known as Bellman-Ford algorithms) that
call for each router to send all or some portion of its routing table to its neighbors. Distance vector
algorithms define routes by distance (for example, the number of hops to the destination) and direction
(for example, the next-hop router). These routes are then broadcast to the directly connected neighbor
routers. Each router uses these updates to verify and update the routing tables.
To prevent routing loops, most distance vector algorithms use split horizon with poison reverse which
means that the routes learned from an interface are set as unreachable and advertised back along the
interface that they were learned on during the next periodic update. This feature prevents the router from
seeing its own route updates coming back.
Distance vector algorithms send updates at fixed intervals but can also send updates in response to
changes in route metric values. These triggered updates can speed up the route convergence time. The
Routing Information Protocol (RIP) is a distance vector protocol.
Link-State Protocols
The link-state protocols, also known as shortest path first (SPF), share information with neighboring
routers. Each router builds a link-state advertisement (LSA), which contains information about each link
and directly connected neighbor router.
Each LSA has a sequence number. When a router receives and LSA and updates its link-state database,
the LSA is flooded to all adjacent neighbors. If a router receives two LSAs with the same sequence
number (from the same router), the router does not flood the last LSA received to its neighbors to prevent
an LSA update loop. Because the router floods the LSAs immediately after they receive them,
convergence time for link-state protocols is minimized.
Discovering neighbors and establishing adjacency is an important part of a link state protocol. Neighbors
are discovered using special Hello packets that also serve as keepalive notifications to each neighbor
router. Adjacency is the establishment of a common set of operating parameters for the link-state
protocol between neighbor routers.
The LSAs received by a router are added to its link-state database. Each entry consists of the following
parameters:
•
Router ID (for the router that originated the LSA)
•
Neighbor ID
•
Link cost
•
Sequence number of the LSA
•
Age of the LSA entry
The router runs the SPF algorithm on the link-state database, building the shortest path tree for that
router. This SPF tree is used to populate the routing table.
In link-state algorithms, each router builds a picture of the entire network in its routing tables. The
link-state algorithms send small updates everywhere, while distance vector algorithms send larger
updates only to neighboring routers.
Because they converge more quickly, link-state algorithms are somewhat less prone to routing loops than
distance vector algorithms. However, link-state algorithms require more CPU power and memory than
distance vector algorithms. Link-state algorithms can be more expensive to implement and support.
Link-state protocols are generally more scalable than distance vector protocols.
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Layer 3 Virtualization
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OSPF is an example of a link-state protocol.
Layer 3 Virtualization
Cisco NX-OS supports multiple Virtual Routing and Forwarding Instances (VRFs) and multiple routing
information bases (RIBs) to support multiple address domains. Each VRF is associated with a routing
information base (RIB) and this information is collected by the Forwarding Information Base (FIB). A
VRF represents a Layer 3 addressing domain. Each Layer 3 interface (logical or physical) belongs to one
VRF. For more information, see Chapter 11, “Configuring Layer 3 Virtualization.”
Cisco NX-OS Fowarding Architecture
The Cisco NX-OS forwarding architecture is responsible for processing all routing updates and
populating the forwarding information on the switch.
This section includes the following topics:
•
Unicast RIB, page 1-10
•
Adjacency Manager, page 1-11
•
Unicast Forwarding Distribution Module, page 1-11
•
FIB, page 1-11
•
Hardware Forwarding, page 1-12
•
Software Forwarding, page 1-12
Unicast RIB
The Cisco NX-OS forwarding architecture consists of multiple components, as shown in Figure 1-3.
Figure 1-3
Cisco NX-OS Forwarding Architecture
EIGRP
Switch components
BGP
OSPF
URIB
ARP
Adjacency Manager (AM)
Unicast Forwarding Information Base (UFIB)
239086
Unicast FIB Distribution Module (uFDM)
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The unicast RIB maintains the routing table with directly connected routes, static routes, and routes
learned from dynamic unicast routing protocols. The unicast RIB also collects adjacency information
from sources such as the Address Resolution Protocol (ARP). The unicast RIB determines the best
next-hop for a given route and populates the unicast forwarding information base (FIB) by using the
services of unicast FIB distribution module (FDM).
Each dynamic routing protocol must update the unicast RIB for any route that has timed out. The unicast
RIB then deletes that route and recalculates the best next-hop for that route (if an alternate path is
available).
Adjacency Manager
The adjacency manager maintains adjacency information for different protocols including ARP, Open
Shortest Path First version 2 (OSPFv2), Neighbor Discovery Protocol (NDP), and static configuration.
The most basic adjacency information is the Layer 3 to Layer 2 address mapping discovered by these
protocols. Outgoing Layer 2 packets use the adjacency information to complete the Layer 2 header.
The adjacency manager can trigger ARP requests to find a particular Layer 3 to Layer 2 mapping. The
new mapping becomes available when the corresponding ARP reply is received and processed.
Unicast Forwarding Distribution Module
The unicast forwarding distribution module distributes the forwarding path information from the unicast
RIB and other sources. The unicast RIB generates forwarding information which the unicast FIB
programs into the hardware forwarding tables. The unicast forwarding distribution module also
downloads the FIB information to newly inserted modules.
The unicast forwarding distribution module gathers adjacency information, rewrite information, and
other platform-dependent information when updating routes in the unicast FIB. The adjacency and
rewrite information consists of interface, next-hop, and Layer 3 to Layer 2 mapping information. The
interface and next-hop information is received in route updates from the unicast RIB. The Layer 3 to
Layer 2 mapping is received from the adjacency manager.
FIB
The unicast FIB builds the information used for the hardware forwarding engine. The unicast FIB
receives route updates from the unicast forwarding distribution module and sends the information along
to be programmed in the hardware forwarding engine. The unicast FIB controls the addition, deletion,
and modification of routes, paths, and adjacencies.
The unicast FIBs are maintained on a per-VRF and per-address-family basis. Based on route update
messages, the unicast FIB maintains a per-VRF prefix and next-hop adjacency information database. The
next-hop adjacency data structure contains the next-hop IP address and the Layer 2 rewrite information.
Multiple prefixes could share a next-hop adjacency information structure.
The unicast FIB also enables and disables unicast reverse path forwarding (RPF) checks per interface.
The Cisco Nexus 3000 Series supports the following two RPF modes that can be configured on each
ingress interface:
•
RPF Strict Check—Packets that do not have a verifiable source address in the routers forwarding
table or do not arrive on any of the return paths to the source are dropped.
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•
RPF Loose Check—Packets have a verifiable source address in the routers forwarding table and the
source is reachable through a physical interface. The ingress interface that receives the packet need
not match any of the interfaces in the FIB.
Hardware Forwarding
Cisco NX-OS supports distributed packet forwarding. The ingress port takes relevant information from
the packet header and passes the information to the local switching engine. The local switching engine
does the Layer 3 lookup and uses this information to rewrite the packet header. The ingress module
forwards the packet to the egress port. If the egress port is on a different module, the packet is forwarded
using the switch fabric to the egress module. The egress module does not participate in the Layer 3
forwarding decision.
You also use the show platform fib or show platform forwarding commands to display details on
hardware forwarding.
Software Forwarding
The software forwarding path in Cisco NX-OS is used mainly to handle features that are not supported
in hardware or to handle errors encountered during hardware processing. Typically, packets with IP
options or packets that need fragmentation are passed to the CPU. The unicast RIB and the adjacency
manager makes the forwarding decisions based on the packets that should be switched in software or
terminated.
Software forwarding is controlled by control plane policies and rate limiters.
Summary of Layer 3 Unicast Routing Features
This section provides a brief introduction to the Layer 3 unicast features and protocols supported in
Cisco NX-OS.
This section includes the following topics:
•
IPv4, page 1-12
•
OSPF, page 1-13
•
EIGRP, page 1-13
•
BGP, page 1-13
•
RIP, page 1-13
•
Static Routing, page 1-13
•
Layer 3 Virtualization, page 1-13
•
Route Policy Manager, page 1-14
•
First-Hop Redundancy Protocols, page 1-14
•
Object Tracking, page 1-14
IPv4
Layer 3 uses the IPv4 protocol. For more information, see Chapter 2, “Configuring IPv4.”
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OSPF
The OSPF protocol is a link-state routing protocol used to exchange network reachability information
within an autonomous system. Each OSPF router advertises information about its active links to its
neighbor routers. Link information consists of the link type, the link metric, and the neighbor router
connected to the link. The advertisements that contain this link information are called link-state
advertisements. For more information, see Chapter 3, “Configuring OSPFv2.”
EIGRP
The EIGRP protocol is a unicast routing protocol that has the characteristics of both distance vector and
link-state routing protocols. It is an improved version of IGRP, which is a Cisco proprietary routing
protocol. EIGRP relies on its neighbors to provide the routes, typical to a distance vector routing
protocol. It constructs the network topology from the routes advertised by its neighbors, similar to a
link-state protocol, and uses this information to select loop-free paths to destinations. For more
information, see Chapter 4, “Configuring EIGRP.”
BGP
The Border Gateway Protocol (BGP) is an inter-autonomous system routing protocol. A BGP router
advertises network reachability information to other BGP routers using Transmission Control Protocol
(TCP) as its reliable transport mechanism. The network reachability information includes the destination
network prefix, a list of autonomous systems that needs to be traversed to reach the destination, and the
next-hop router. Reachability information contains additional path attributes such as preference to a
route, origin of the route, community and others. For more information, see Chapter 5, “Configuring
Basic BGP” and Chapter 6, “Configuring Advanced BGP.”
RIP
The Routing Information Protocol (RIP) is a distance-vector protocol that uses a hop count as its metric.
RIP is widely used for routing traffic in the global Internet and is an Interior Gateway Protocol (IGP),
which means that it performs routing within a single autonomous system. For more information, see
Chapter 9, “Configuring RIP.”
Static Routing
Static routing allows you to enter a fixed route to a destination. This feature is useful for small networks
where the topology is simple. Static routing is also used with other routing protocols to control default
routes and route distribution. For more information, see Chapter 10, “Configuring Static Routing.”
Layer 3 Virtualization
Virtualization allows you to share physical resources across separate management domains.
Cisco NX-OS supports Layer 3 virtualization with VPN Routing and Forwarding (VRF). A VRF
provides a separate address domain for configuring Layer 3 routing protocols. For more information, see
Chapter 11, “Configuring Layer 3 Virtualization.”
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Route Policy Manager
The Route Policy Manager provides a route filtering capability in Cisco NX-OS. It uses route maps to
filter routes distributed across various routing protocols and between different entities within a given
routing protocol. Filtering is based on specific match criteria, which is similar to packet filtering by
access control lists. For more information, see Chapter 13, “Configuring Route Policy Manager.”
First-Hop Redundancy Protocols
A first-hop redundancy protocol (FHRP) allows you to provide redundant connections to your hosts. In
the event that an active first-hop router fails, the FHRP automatically selects a standby router to take
over. You do not need to update the hosts with new IP addresses because the address is virtual and shared
between each router in the FHRP group. For more information on the Hot Standby Router Protocol
(HSRP), see Chapter 14, “Configuring HSRP.” For more information on the Virtual Router Redundancy
Protocol (VRRP), see Chapter 15, “Configuring VRRP.”
Object Tracking
Object tracking allows you to track specific objects on the network, such as the interface line protocol
state, IP routing, and route reachability, and take action when the tracked object’s state changes. This
feature allows you to increase the availability of the network and shorten recovery time if an object state
goes down. For more information, see Chapter 16, “Configuring Object Tracking.”
Related Topics
The following Cisco documents are related to the Layer 3 features:
•
Cisco Nexus 7000 Series NX-OS Multicast Routing Configuration Guide, Release 5.x
•
Exploring Autonomous System Numbers:
http://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_9-1/autonomous_system_numb
ers.html
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PA R T
IP
1
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
CH A P T E R
2
Configuring IPv4
This chapter describes how to configure Internet Protocol version 4 (IPv4), which includes addressing,
Address Resolution Protocol (ARP), and Internet Control Message Protocol (ICMP), on the Cisco
NX-OS switch.
This chapter includes the following sections:
•
Information About IPv4, page 2-1
•
Licensing Requirements for IPv4, page 2-6
•
Prerequisites for IPv4, page 2-6
•
Guidelines and Limitations, page 2-6
•
Default Settings, page 2-7
•
Configuring IPv4, page 2-7
•
Configuring IP Directed Broadcasts, page 2-13
•
Configuration Examples for IPv4, page 2-18
•
Additional References, page 2-19
•
Feature History for IP, page 2-19
Information About IPv4
You can configure IP on the switch to assign IP addresses to network interfaces. When you assign IP
addresses, you enable the interfaces and allow communication with the hosts on those interfaces.
You can configure an IP address as primary or secondary on a switch. An interface can have one primary
IP address and multiple secondary addresses. All networking switches on an interface should share the
same primary IP address because the packets that are generated by the switch always use the primary
IPv4 address. Each IPv4 packet is based on the information from a source or destination IP address. See
the “Multiple IPv4 Addresses” section on page 2-2.
You can use a subnet to mask the IP addresses. A mask is used to determine what subnet an IP address
belongs to. An IP address contains the network address and the host address. A mask identifies the bits
that denote the network number in an IP address. When you use the mask to subnet a network, the mask
is then referred to as a subnet mask. Subnet masks are 32-bit values that allow the recipient of IP packets
to distinguish the network ID portion of the IP address from the host ID portion of the IP address.
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Configuring IPv4
Information About IPv4
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The IP feature in the Cisco NX-OS system is responsible for handling IPv4 packets, as well as
forwarding of IPv4 packets, which includes IPv4 unicast/multicast route lookup, reverse path forwarding
(RPF) checks, and software access control list (ACL) forwarding. The IP feature also manages the
network interface IP address configuration, duplicate address checks, static routes, and packet
send/receive interface for IP clients.
This section includes the following topics:
•
Multiple IPv4 Addresses, page 2-2
•
Address Resolution Protocol, page 2-2
•
ARP Caching, page 2-3
•
Static and Dynamic Entries in the ARP Cache, page 2-3
•
Devices that Do Not Use ARP, page 2-4
•
Reverse ARP, page 2-4
•
Proxy ARP, page 2-5
•
Local Proxy ARP, page 2-5
•
ICMP, page 2-6
•
Virtualization Support, page 2-6
Multiple IPv4 Addresses
The Cisco NX-OS system supports multiple IP addresses per interface. You can specify an unlimited
number of secondary addresses for a variety of situations. The most common situations are as follows:
Note
•
When there are not enough host IP addresses for a particular network interface. For example, if your
subnet allows up to 254 hosts per logical subnet, but on one physical subnet you must have 300 host
addresses, then you can use secondary IP addresses on the routers or access servers to allow you to
have two logical subnets using one physical subnet.
•
Two subnets of a single network might otherwise be separated by another network. You can create
a single network from subnets that are physically separated by another network by using a secondary
address. In these instances, the first network is extended, or layered on top of the second network.
A subnet cannot appear on more than one active interface of the router at a time.
If any switch on a network segment uses a secondary IPv4 address, all other switches on that same
network interface must also use a secondary address from the same network or subnet. The inconsistent
use of secondary addresses on a network segment can quickly cause routing loops.
Address Resolution Protocol
Networking switches and Layer 3 switches use Address Resolution Protocol (ARP) to map IP (network
layer) addresses to (Media Access Control [MAC]-layer) addresses to enable IP packets to be sent across
networks. Before a switch sends a packet to another switch, it looks in its own ARP cache to see if there
is a MAC address and corresponding IP address for the destination switch. If there is no entry, the source
switch sends a broadcast message to every switch on the network.
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Each switch compares the IP address to its own. Only the switch with the matching IP address replies to
the switch that sends the data with a packet that contains the MAC address for the switch. The source
switch adds the destination switch MAC address to its ARP table for future reference, creates a data-link
header and trailer that encapsulates the packet, and proceeds to transfer the data. Figure 2-1 shows the
ARP broadcast and response process.
Figure 2-1
ARP Process
Barney
135075
Fred
I need the address of 10.1.1.2.
I heard that broadcast. The message is for me.
Here is my MAC address: 00:1D:7E:1D:00:01.
When the destination switch lies on a remote network which is beyond another switch, the process is the
same except that the switch that sends the data sends an ARP request for the MAC address of the default
gateway. After the address is resolved and the default gateway receives the packet, the default gateway
broadcasts the destination IP address over the networks connected to it. The switch on the destination
switch network uses ARP to obtain the MAC address of the destination switch and delivers the packet.
ARP is enabled by default.
The default system-defined CoPP policy rate-limits ARP broadcast packets. The default system-defined
CoPP policy prevents an ARP broadcast storm from affecting the control plane traffic but does not affect
bridged packets.
ARP Caching
ARP caching minimizes broadcasts and limits wasteful use of network resources. The mapping of IP
addresses to MAC addresses occurs at each hop (switch) on the network for every packet sent over an
internetwork, which may affect network performance.
ARP caching stores network addresses and the associated data-link addresses in memory for a period of
time, which minimizes the use of valuable network resources to broadcast for the same address each time
a packet is sent. You must maintain the cache entries since the cache entries are set to expire periodically
because the information might become outdated. Every switch on a network updates its tables as
addresses are broadcast.
Static and Dynamic Entries in the ARP Cache
You must manually configure the IP addresses, subnet masks, gateways, and corresponding MAC
addresses for each interface of each switch when using static routes. Static routing enables more control
but requires more work to maintain the route table. You must update the table each time you add or
change routes.
Dynamic routing uses protocols that enable the switches in a network to exchange routing table
information with each other. Dynamic routing is more efficient than static routing because the route table
is automatically updated unless you add a time limit to the cache. The default time limit is 25 minutes
but you can modify the time limit if the network has many routes that are added and deleted from the
cache.
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Information About IPv4
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Devices that Do Not Use ARP
When a network is divided into two segments, a bridge joins the segments and filters traffic to each
segment based on MAC addresses. The bridge builds its own address table, which uses MAC addresses
only, as opposed to a switch, which has an ARP cache that contains both IP addresses and the
corresponding MAC addresses.
Passive hubs are central-connection switches that physically connect other switches in a network. They
send messages out on all their ports to the switches and operate at Layer 1 but do not maintain an address
table.
Layer 2 switches determine which port is connected to a device to which the message is addressed and
send only to that port, unlike a hub, which sends the message out all its ports. However, Layer 3 switches
are switches that build an ARP cache (table).
Reverse ARP
Reverse ARP (RARP) as defined by RFC 903 works the same way as ARP, except that the RARP request
packet requests an IP address instead of a MAC address. RARP often is used by diskless workstations
because this type of device has no way to store IP addresses to use when they boot. The only address that
is known is the MAC address because it is burned into the hardware.
Use of RARP requires an RARP server on the same network segment as the router interface. Figure 2-2
illustrates how RARP works.
Reverse ARP
Device A
I am device A and sending
a broadcast that uses my
hardware address.
Can somone on the network
tell me what my IP address is?
RARP server
Okay, your hardware address
is 00:1D:7E:1D:00:01 and
your IP address is 10.0.0.2
135218
Figure 2-2
There are several limitations of RARP. Because of these limitations, most businesses use DHCP to assign
IP addresses dynamically. DHCP is cost effective and requires less maintenance than RARP. The
following are the most important limitations:
•
Since RARP uses hardware addresses, if the internetwork is large with many physical networks, a
RARP server must be on every segment with an additional server for redundancy. Maintaining two
servers for every segment is costly.
•
Each server must be configured with a table of static mappings between the hardware addresses and
IP addresses. Maintenance of the IP addresses is difficult.
•
RARP only provides IP addresses of the hosts and not subnet masks or default gateways.
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Proxy ARP
Proxy ARP enables a switch that is physically located on one network appear to be logically part of a
different physical network connected to the same switch or firewall. Proxy ARP allows you to hide a
switch with a public IP address on a private network behind a router and still have the switch appear to
be on the public network in front of the router. By hiding its identity, the router accepts responsibility
for routing packets to the real destination. Proxy ARP can help switches on a subnet reach remote
subnets without configuring routing or a default gateway.
When switches are not in the same data link layer network but in the same IP network, they try to
transmit data to each other as if they are on the local network. However, the router that separates the
switches does not send a broadcast message because routers do not pass hardware-layer broadcasts and
the addresses cannot be resolved.
When you enable Proxy ARP on the switch and it receives an ARP request, it identifies the request as a
request for a system that is not on the local LAN. The switch responds as if it is the remote destination
for which the broadcast is addressed, with an ARP response that associates the MAC address of the
switch with the IP address of the remote destination. The local switch believes that it is directly
connected to the destination, while in reality its packets are being forwarded from the local subnetwork
toward the destination subnetwork by their local switch. By default, Proxy ARP is disabled.
Local Proxy ARP
You can use local Proxy ARP to enable a switch to respond to ARP requests for IP addresses within a
subnet where normally no routing is required. When you enable local Proxy ARP, ARP responds to all
ARP requests for IP addresses within the subnet and forwards all traffic between hosts in the subnet. Use
this feature only on subnets where hosts are intentionally prevented from communicating directly by the
configuration on the switch to which they are connected.
Gratuitous ARP
Gratuitous ARP sends a request with identical source IP address and destination IP address to detect
duplicate IP addresses. Cisco NX-OS Release 5.0(3) support enabling or disabling gratuitous ARP
requests or ARP cache updates.
Glean Throttling
When forwarding an incoming IP packet in a line card, if the Address Resolution Protocol (ARP) request
for the next hop is not resolved, the line card forwards the packets to the supervisor (glean throttling).
The supervisor resolves the MAC address for the next hop and programs the hardware.
The Cisco Nexus 7000 Series device hardware has glean rate limiters to protect the supervisor from the
glean traffic. If the maximum number of entries is exceeded, the packets for which the ARP request is
not resolved continues to be processed in the software instead of getting dropped in the hardware.
When an ARP request is sent, the software adds a /32 drop adjacency in the hardware to prevent the
packets to the same next-hop IP address to be forwarded to the supervisor. When the ARP is resolved,
the hardware entry is updated with the correct MAC address. If the ARP entry is not resolved before a
timeout period, the entry is removed from the hardware.
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Licensing Requirements for IPv4
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
ICMP
You can use ICMP to provide message packets that report errors and other information that is relevant
to IP processing. ICMP generates error messages, such as ICMP destination unreachable messages,
ICMP Echo Requests (which send a packet on a round trip between two hosts) and Echo Reply messages.
ICMP also provides many diagnostic functions and can send and redirect error packets to the host. By
default, ICMP is enabled.
Some of the ICMP message types are as follows:
Note
•
Network error messages
•
Network congestion messages
•
Troubleshooting information
•
Timeout announcements
ICMP redirects are disabled on interfaces where the local proxy ARP feature is enabled.
Virtualization Support
IPv4 supports Virtual Routing and Forwarding instances (VRFs). By default, Cisco NX-OS places you
in the default VRF unless you specifically configure another VRF. For more information, see
Chapter 11, “Configuring Layer 3 Virtualization.”
Licensing Requirements for IPv4
The following table shows the licensing requirements for this feature:
Product
License Requirement
Cisco NX-OS
IPv4 requires no license. Any feature not included in a license package is bundled with the Cisco NX-OS
system images and is provided at no extra charge to you. For a complete explanation of the Cisco NX-OS
licensing scheme, see the Cisco NX-OS Licensing Guide.
Prerequisites for IPv4
IPv4 has the following prerequisites:
•
IPv4 can only be configured on Layer 3 interfaces.
Guidelines and Limitations
IPv4 has the following configuration guidelines and limitations:
•
You can configure a secondary IP address only after you configure the primary IP address.
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Default Settings
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
•
If the Cisco Nexus 3000 switch is used as a Layer 2 or Layer 3 termination switch, Cisco
recommends that you set the mac-address-table-aging-time to 1800 (higher than the default ARP
aging time of 1500 seconds) on all VLANs.
•
The Cisco Nexus 3000 switch does not support per-VLAN cam aging timers.
Default Settings
Table 2-1 lists the default settings for IP parameters.
Table 2-1
Default IP Parameters
Parameters
Default
ARP timeout
1500 seconds
proxy ARP
disabled
Configuring IPv4
This section includes the following topics:
Note
•
Configuring IPv4 Addressing, page 2-7
•
Configuring Multiple IP Addresses, page 2-9
•
Configuring a Static ARP Entry, page 2-9
•
Configuring Proxy ARP, page 2-10
•
Configuring Local Proxy ARP, page 2-11
•
Configuring IP Directed Broadcasts, page 2-13
•
Configuring IP Glean Throttling, page 2-14
•
Configuring the Hardware IP Glean Throttle Maximum, page 2-15
•
Configuring a Hardware IP Glean Throttle Timeout, page 2-16
•
Configuring the Hardware IP Glean Throttle Syslog, page 2-17
If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature
might differ from the Cisco IOS commands that you would use.
Configuring IPv4 Addressing
You can assign a primary IP address for a network interface.
SUMMARY STEPS
1.
configure terminal
2.
interface ethernet number
3.
no switchport
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4.
ip address ip-address/length [secondary]
5.
(Optional) show ip interface
6.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface ethernet number
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 2/3
switch(config-if)#
Step 3
no switchport
Configures the interface as a Layer 3 routed interface.
Example:
switch(config-if)# no switchport
Step 4
ip address ip-address/length
[secondary]
Example:
switch(config-if)# ip address 192.2.1.1
255.0.0.0
Step 5
show ip interface
Specifies a primary or secondary IPv4 address for an
interface.
•
The network mask can be a four-part dotted
decimal address. For example, 255.0.0.0 indicates
that each bit equal to 1 means the corresponding
address bit belongs to the network address.
•
The network mask can be indicated as a slash (/)
and a number - a prefix length. The prefix length
is a decimal value that indicates how many of the
high-order contiguous bits of the address
comprise the prefix (the network portion of the
address). A slash must precede the decimal value
and there is no space between the IP address and
the slash.
(Optional) Displays interfaces configured for IPv4.
Example:
switch(config-if)# show ip interface
Step 6
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-if)# copy running-config
startup-config
This example shows how to assign an IPv4 address:
switch# configure terminal
switch(config)# interface ethernet 2/3
switch(config-if)# no switchport
switch(config-if)# ip address 192.2.1.1 255.0.0.0
switch(config-if)# copy running-config startup-config
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Configuring Multiple IP Addresses
You can only add secondary IP addresses after you configure primary IP addresses.
SUMMARY STEPS
1.
configure terminal
2.
interface ethernet number
3.
no switchport
4.
ip address ip-address/length [secondary]
5.
(Optional) show ip interface
6.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface ethernet number
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 2/3
switch(config-if)#
Step 3
Configures the interface as a Layer 3 routed interface.
no switchport
Example:
switch(config-if)# no switchport
Step 4
ip address ip-address/length
[secondary]
Specifies the configured address as a secondary IPv4
address.
Example:
switch(config-if)# ip address 192.2.1.1
255.0.0.0 secondary
Step 5
(Optional) Displays interfaces configured for IPv4.
show ip interface
Example:
switch(config-if)# show ip interface
Step 6
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-if)# copy running-config
startup-config
Configuring a Static ARP Entry
You can configure a static ARP entry on the switch to map IP addresses to MAC hardware addresses,
including static multicast MAC addresses.
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SUMMARY STEPS
1.
configure terminal
2.
interface ethernet number
3.
no switchport
4.
ip arp ipaddr mac_addr
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface ethernet number
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 2/3
switch(config-if)#
Step 3
no switchport
Configures the interface as a Layer 3 routed interface.
Example:
switch(config-if)# no switchport
Step 4
ip arp ipaddr mac_addr
Example:
switch(config-if)# ip arp 192.2.1.1
0019.076c.1a78
Step 5
copy running-config startup-config
Associates an IP address with a MAC address as a
static entry.
(Optional) Saves this configuration change.
Example:
switch(config-if)# copy running-config
startup-config
This example shows how to configure a static ARP entry:
switch# configure terminal
switch(config)# interface ethernet 2/3
switch(config-if)# no switchport
switch(config-if)# ip arp 192.2.1.1 0019.076c.1a78
switch(config-if)# copy running-config startup-config
Configuring Proxy ARP
You can configure Proxy ARP on the switch to determine the media addresses of hosts on other networks
or subnets.
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SUMMARY STEPS
1.
configure terminal
2.
interface ethernet number
3.
no switchport
4.
ip proxy-arp
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface ethernet number
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 2/3
switch(config-if)#
Step 3
Configures the interface as a Layer 3 routed interface.
no switchport
Example:
switch(config-if)# no switchport
Step 4
Enables Proxy ARP on the interface.
ip proxy-arp
Example:
switch(config-if)# ip proxy-arp
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-if)# copy running-config
startup-config
This example shows how to configure Proxy ARP:
switch# configure terminal
switch(config)# interface ethernet 2/3
switch(config-if)# no switchport
switch(config-if)# ip proxy-arp
switch(config-if)# copy running-config startup-config
Configuring Local Proxy ARP
You can configure Local Proxy ARP on the switch.
SUMMARY STEPS
1.
configure terminal
2.
interface ethernet number
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3.
no switchport
4.
ip local-proxy-arp
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface ethernet number
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 2/3
switch(config-if)#
Step 3
no switchport
Configures the interface as a Layer 3 routed interface.
Example:
switch(config-if)# no switchport
Step 4
ip local-proxy-arp
Enables Local Proxy ARP on the interface.
Example:
switch(config-if)# ip local-proxy-arp
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-if)# copy running-config
startup-config
This example shows how to configure Local Proxy ARP:
switch# configure terminal
switch(config)# interface ethernet 2/3
switch(config-if)# no switchport
switch(config-if)# ip local-proxy-arp
switch(config-if)# copy running-config startup-config
Configuring Gratuitous ARP
You can configure gratuitous ARP on an interface.
SUMMARY STEPS
1.
configure terminal
2.
interface ethernet number
3.
no switchport
4.
ip arp gratuitous {request | update}
5.
(Optional) copy running-config startup-config
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DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface ethernet number
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 2/3
switch(config-if)#
Step 3
Configures the interface as a Layer 3 routed interface.
no switchport
Example:
switch(config-if)# no switchport
Step 4
ip arp gratuitous {request | update}
Example:
switch(config-if)# ip arp gratuitous
request
Step 5
copy running-config startup-config
Enables gratuitous ARP on the interface. Default is
enabled.
(Optional) Saves this configuration change.
Example:
switch(config-if)# copy running-config
startup-config
This example shows how to disable gratuitous ARP requests:
switch# configure terminal
switch(config)# interface ethernet 2/3
switch(config-if)# no switchport
switch(config-if)# no ip arp gratuitous request
switch(config-if)# copy running-config startup-config
Configuring IP Directed Broadcasts
An IP directed broadcast is an IP packet whose destination address is a valid broadcast address for some
IP subnet, but which originates from a node that is not itself part of that destination subnet.
A switch that is not directly connected to its destination subnet forwards an IP directed broadcast in the
same way it would forward unicast IP packets destined to a host on that subnet. When a directed
broadcast packet reaches a switch that is directly connected to its destination subnet, that packet is
"exploded" as a broadcast on the destination subnet. The destination address in the IP header of the
packet is rewritten to the configured IP broadcast address for the subnet, and the packet is sent as a
link-layer broadcast.
If directed broadcast is enabled for an interface, incoming IP packets whose addresses identify them as
directed broadcasts intended for the subnet to which that interface is attached will be exploded as
broadcasts on that subnet.
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To enable IP directed broadcasts, use the following command in interface configuration mode:
Command
Purpose
ip directed-broadcast
Enables the translation of a directed broadcast to physical
broadcasts
Configuring IP Glean Throttling
Cisco NX-OS software supports glean throttling rate limiters to protect the supervisor from the glean
traffic.
You can enable IP glean throttling.
Note
We recommend that you configure the IP glean throttle feature by using the hardware ip glean throttle
command to filter the unnecessary glean packets that are sent to the supervisor for ARP resolution for
the next hops that are not reachable or do not exist. IP glean throttling boosts software performance and
helps to manage traffic more efficiently.
BEFORE YOU BEGIN
Ensure that you are in the correct VDC (or use the switchto vdc command).
SUMMARY STEPS
1.
configure terminal
2.
hardware ip glean throttle
3.
no hardware ip glean throttle
4.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
hardware ip glean throttle
Enables ARP throttling.
Example:
switch(config)# hardware ip glean
throttle
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Step 3
Command
Purpose
no hardware ip glean throttle
Disables ARP throttling.
Example:
switch(config)# no hardware ip glean
throttle
Step 4
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
This example shows how to enable IP glean throttling:
switch# configure terminal
switch(config)# hardware ip glean throttle
switch(config-if)# copy running-config startup-config
Configuring the Hardware IP Glean Throttle Maximum
You can limit the maximum number of drop adjacencies that are installed in the Forwarding Information
Base (FIB).
BEFORE YOU BEGIN
Ensure that you are in the correct VDC (or use the switchto vdc command).
SUMMARY STEPS
1.
configure terminal
2.
hardware ip glean throttle maximum count
3.
no hardware ip glean throttle maximum count
4.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
hardware ip glean throttle maximum count
Example:
switch(config)# hardware ip glean
throttle maximum 2134
Configures the number of drop adjacencies that are
installed in the FIB.
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Step 3
Command
Purpose
no hardware ip glean throttle maximum
count
Applies the default limits.
Example:
switch(config)# no hardware ip glean
throttle maximum 2134
Step 4
copy running-config startup-config
The default value is 1000. The range is from 0 to
16,383 entries.
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
This example shows how to limit the maximum number of drop adjacencies that are installed in the FIB:
switch# configure terminal
switch(config)# hardware ip glean throttle maximum 2134
switch(config-if)# copy running-config startup-config
Configuring a Hardware IP Glean Throttle Timeout
You can configure a timeout for the installed drop adjacencies to remain in the FIB.
BEFORE YOU BEGIN
Ensure that you are in the correct VDC (or use the switchto vdc command).
SUMMARY STEPS
1.
configure terminal
2.
hardware ip glean throttle maximum timeout timeout-in-sec
3.
no hardware ip glean throttle maximum timeout timeout-in-sec
4.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
hardware ip glean throttle maximum
timeout timeout-in-sec
Configures the timeout for the installed drop
adjacencies to remain in the FIB.
Example:
switch(config)# hardware ip glean
throttle maximum timeout 300
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Step 3
Command
Purpose
no hardware ip glean throttle maximum
timeout timeout-in-sec
Applies the default limits.
Example:
switch(config)# no hardware ip glean
throttle maximum timeout 300
Step 4
copy running-config startup-config
The timeout value is in seconds. The range is from 300
seconds (5 minutes) to 1800 seconds (30 minutes).
Note
After the timeout period is exceeded, the drop
adjacencies are removed from the FIB.
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
This example shows how to configure a timeout for the drop adjacencies that are installed.
switch# configure terminal
switch(config)# hardware ip glean throttle maximum timeout 300
switch(config-if)# copy running-config startup-config
Configuring the Hardware IP Glean Throttle Syslog
You can generate a syslog if the number of packets that get dropped for a specific flow exceeds the
configured packet count.
BEFORE YOU BEGIN
Ensure that you are in the correct VDC (or use the switchto vdc command).
SUMMARY STEPS
1.
configure terminal
2.
hardware ip glean throttle syslog pck-count
3.
no hardware ip glean throttle syslog pck-count
4.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
hardware ip glean throttle syslog
pck-count
Example:
switch(config)# hardware ip glean
throttle syslog 1030
Generates a syslog if the number of packets that get
dropped for a specific flow exceed the configured
packet count.
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Verifying the IPv4 Configuration
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Step 3
Command
Purpose
no hardware ip glean throttle syslog
pck-count
Applies the default limits.
Example:
switch(config)# no hardware ip glean
throttle syslog 1030
Step 4
copy running-config startup-config
The default is 10000 packets. The range is from 0 to
65535 packets.
Note
After the timeout period is exceeded, the drop
adjacencies are removed from the FIB.
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
This example shows how to generate a syslog if the number of packets that get dropped for a specific
flow exceeds the configured packet count:
switch# configure terminal
switch(config)# hardware ip glean throttle syslog 1030
switch(config-if)# copy running-config startup-config
Verifying the IPv4 Configuration
To display the IPv4 configuration, perform one of the following tasks:
Command
Purpose
show hardware forwarding ip verify
Displays the IP packet verification configuration.
show ip adjacency
Displays the adjacency table.
show ip arp
Displays the ARP table.
show ip interface
Displays IP related interface information.
show ip arp statistics [vrf vrf-name]
Displays the ARP statistics.
show ip adjacency summary
Displays the summary of number of throttle adjacencies.
show ip arp summary
Displays the summary of the number of throttle
adjacencies.
show ip adjacency throttle statistics
Displays only the throttled adjacencies.
Configuration Examples for IPv4
This example shows how to configure an IPv4 address:
configure terminal
interface ethernet 1/2
no switchport
ip address 192.2.1.1/16
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Additional References
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Additional References
For additional information related to implementing IP, see the following sections:
•
Related Documents, page 2-19
•
Standards, page 2-19
Related Documents
Related Topic
Document Title
IP CLI commands
Cisco Nexus 3000 Series Command Reference,
Standards
Standards
Title
No new or modified standards are supported by this
—
feature, and support for existing standards has not been
modified by this feature.
Feature History for IP
Table 2-1 lists the release history for this feature.
Table 2-2
Feature History for IP
Feature Name
Releases
Feature Information
IP
5.0(3)U1(1)
This feature was introduced.
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Feature History for IP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
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PA R T
Routing
2
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
CH A P T E R
3
Configuring OSPFv2
This chapter describes how to configure Open Shortest Path First version 2 (OSPFv2) for IPv4 networks.
This chapter includes the following sections:
•
Information About OSPFv2, page 3-1
•
Licensing Requirements for OSPFv2, page 3-11
•
Prerequisites for OSPFv2, page 3-12
•
Default Settings, page 3-12
•
Guidelines and Limitations, page 3-12
•
Configuring Basic OSPFv2, page 3-13
•
Configuring Advanced OSPFv2, page 3-22
•
Verifying the OSPFv2 Configuration, page 3-41
•
Displaying OSPFv2 Statistics, page 3-42
•
Configuration Examples for OSPFv2, page 3-42
•
Additional References, page 3-43
•
Feature History for OSPFv2, page 3-43
Information About OSPFv2
OSPFv2 is an IETF link-state protocol (see the “Link-State Protocols” section on page 1-9) for IPv4
networks. An OSPFv2 router sends a special message, called a hello packet, out each OSPF-enabled
interface to discover other OSPFv2 neighbor routers. Once a neighbor is discovered, the two routers
compare information in the Hello packet to determine if the routers have compatible configurations. The
neighbor routers attempt to establish adjacency, which means that the routers synchronize their
link-state databases to ensure that they have identical OSPFv2 routing information. Adjacent routers
share link-state advertisements (LSAs) that include information about the operational state of each link,
the cost of the link, and any other neighbor information. The routers then flood these received LSAs out
every OSPF-enabled interface so that all OSPFv2 routers eventually have identical link-state databases.
When all OSPFv2 routers have identical link-state databases, the network is converged (see the
“Convergence” section on page 1-6). Each router then uses Dijkstra’s Shortest Path First (SPF)
algorithm to build its route table.
You can divide OSPFv2 networks into areas. Routers send most LSAs only within one area, which
reduces the CPU and memory requirements for an OSPF-enabled router.
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OSPFv2 supports IPv4.
This section includes the following topics:
•
Hello Packet, page 3-2
•
Neighbors, page 3-2
•
Adjacency, page 3-3
•
Designated Routers, page 3-3
•
Areas, page 3-4
•
Link-State Advertisements, page 3-5
•
OSPFv2 and the Unicast RIB, page 3-7
•
Authentication, page 3-7
•
Advanced Features, page 3-8
Hello Packet
OSPFv2 routers periodically send Hello packets on every OSPF-enabled interface. The hello interval
determines how frequently the router sends these Hello packets and is configured per interface. OSPFv2
uses Hello packets for the following tasks:
•
Neighbor discovery
•
Keepalives
•
Designated router election (see the “Designated Routers” section on page 3-3)
The Hello packet contains information about the originating OSPFv2 interface and router, including the
assigned OSPFv2 cost of the link, the hello interval, and optional capabilities of the originating router.
An OSPFv2 interface that receives these Hello packets determines if the settings are compatible with the
receiving interface settings. Compatible interfaces are considered neighbors and are added to the
neighbor table (see the “Neighbors” section on page 3-2).
Hello packets also include a list of router IDs for the routers that the originating interface has
communicated with. If the receiving interface sees its own router ID in this list, then bidirectional
communication has been established between the two interfaces.
OSPFv2 uses Hello packets as a keepalive message to determine if a neighbor is still communicating. If
a router does not receive a Hello packet by the configured dead interval (usually a multiple of the hello
interval), then the neighbor is removed from the local neighbor table.
Neighbors
An OSPFv2 interface must have a compatible configuration with a remote interface before the two can
be considered neighbors. The two OSPFv2 interfaces must match the following criteria:
•
Hello interval
•
Dead interval
•
Area ID (see the “Areas” section on page 3-4)
•
Authentication
•
Optional capabilities
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If there is a match, the following information is entered into the neighbor table:
•
Neighbor ID—The router ID of the neighbor.
•
Priority—Priority of the neighbor. The priority is used for designated router election (see the
“Designated Routers” section on page 3-3).
•
State—Indication of whether the neighbor has just been heard from, is in the process of setting up
bidirectional communications, is sharing the link-state information, or has achieved full adjacency.
•
Dead time—Indication of the time since the last Hello packet was received from this neighbor.
•
IP Address—The IP address of the neighbor.
•
Designated Router—Indication of whether the neighbor has been declared as the designated router
or as the backup designated router (see the “Designated Routers” section on page 3-3).
•
Local interface—The local interface that received the Hello packet for this neighbor.
Adjacency
Not all neighbors establish adjacency. Depending on the network type and designated router
establishment, some neighbors become fully adjacent and share LSAs with all their neighbors, while
other neighbors do not. For more information, see the “Designated Routers” section on page 3-3.
Adjacency is established using Database Description packets, Link State Request packets, and Link
State Update packets in OSPF. The Database Description packet includes just the LSA headers from the
link-state database of the neighbor (see the “Link-State Database” section on page 3-7). The local router
compares these headers with its own link-state database and determines which LSAs are new or updated.
The local router sends a Link State Request packet for each LSA that it needs new or updated information
on. The neighbor responds with a Link State Update packet. This exchange continues until both routers
have the same link-state information.
Designated Routers
Networks with multiple routers present a unique situation for OSPF. If every router floods the network
with LSAs, the same link-state information will be sent from multiple sources. Depending on the type
of network, OSPFv2 might use a single router, the designated router (DR), to control the LSA floods
and represent the network to the rest of the OSPFv2 area (see the “Areas” section on page 3-4). If the
DR fails, OSPFv2 selects a backup designated router (BDR). If the DR fails, OSPFv2 uses the BDR.
Network types are as follows:
•
Point-to-point—A network that exists only between two routers. All neighbors on a point-to-point
network establish adjacency and there is no DR.
•
Broadcast—A network with multiple routers that can communicate over a shared medium that
allows broadcast traffic, such as Ethernet. OSPFv2 routers establish a DR and BDR that controls
LSA flooding on the network. OSPFv2 uses the well-known IPv4 multicast addresses 224.0.0.5 and
a MAC address of 0100.5300.0005 to communicate with neighbors.
The DR and BDR are selected based on the information in the Hello packet. When an interface sends a
Hello packet, it sets the priority field and the DR and BDR field if it knows who the DR and BDR are.
The routers follow an election procedure based on which routers declare themselves in the DR and BDR
fields and the priority field in the Hello packet. As a final tie breaker, OSPFv2 chooses the highest router
IDs as the DR and BDR.
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All other routers establish adjacency with the DR and the BDR and use the IPv4 multicast address
224.0.0.6 to send LSA updates to the DR and BDR. Figure 3-1 shows this adjacency relationship
between all routers and the DR.
DRs are based on a router interface. A router might be the DR for one network and not for another
network on a different interface.
DR in Multi-Access Network
Router A
Router B
Router D
or DR
Router C
Router E
= Multi-access network
= Logical connectivity to Designated Router for OSPF
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Figure 3-1
Areas
You can limit the CPU and memory requirements that OSPFv2 puts on the routers by dividing an
OSPFv2 network into areas. An area is a logical division of routers and links within an OSPFv2 domain
that creates separate subdomains. LSA flooding is contained within an area, and the link-state database
is limited to links within the area. You can assign an area ID to the interfaces within the defined area.
The Area ID is a 32-bit value that you can enter as a number or in dotted decimal notation, such as
10.2.3.1.
Cisco NX-OS always displays the area in dotted decimal notation.
If you define more than one area in an OSPFv2 network, you must also define the backbone area, which
has the reserved area ID of 0. If you have more than one area, then one or more routers become area
border routers (ABRs). An ABR connects to both the backbone area and at least one other defined area
(see Figure 3-2).
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Figure 3-2
OSPFv2 Areas
ABR1
Area 3
Area 0
ABR2
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Area 5
The ABR has a separate link-state database for each area to which it connects. The ABR sends Network
Summary (type 3) LSAs (see the “Route Summarization” section on page 3-10) from one connected area
to the backbone area. The backbone area sends summarized information about one area to another area.
In Figure 3-2, Area 0 sends summarized information about Area 5 to Area 3.
OSPFv2 defines one other router type: the autonomous system boundary router (ASBR). This router
connects an OSPFv2 area to another autonomous system. An autonomous system is a network controlled
by a single technical administration entity. OSPFv2 can redistribute its routing information into another
autonomous system or receive redistributed routes from another autonomous system. For more
information, see “Advanced Features” section on page 3-8.)
Link-State Advertisements
OSPFv2 uses link-state advertisements (LSAs) to build its routing table.
This section includes the following topics:
•
LSA Types, page 3-5
•
Link Cost, page 3-6
•
Flooding and LSA Group Pacing, page 3-6
•
Link-State Database, page 3-7
•
Opaque LSAs, page 3-7
LSA Types
Table 3-1 shows the LSA types supported by Cisco NX-OS.
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Table 3-1
LSA Types
Type
Name
Description
1
Router LSA
LSA sent by every router. This LSA includes the state and the cost of all
links and a list of all OSPFv2 neighbors on the link. Router LSAs trigger an
SPF recalculation. Router LSAs are flooded to local OSPFv2 area.
2
Network LSA
LSA sent by the DR. This LSA lists all routers in the multi-access network.
Network LSAs trigger an SPF recalculation. See the “Designated Routers”
section on page 3-3.
3
Network
Summary LSA
LSA sent by the area border router to an external area for each destination
in the local area. This LSA includes the link cost from the area border router
to the local destination. See the “Areas” section on page 3-4.
4
ASBR Summary LSA sent by the area border router to an external area. This LSA advertises
LSA
the link cost to the ASBR only. See the “Areas” section on page 3-4.
5
AS External
LSA
LSA generated by the ASBR. This LSA includes the link cost to an external
autonomous system destination. AS External LSAs are flooded throughout
the autonomous system. See the “Areas” section on page 3-4.
7
NSSA External
LSA
LSA generated by the ASBR within a not-so-stubby area (NSSA). This LSA
includes the link cost to an external autonomous system destination. NSSA
External LSAs are flooded only within the local NSSA. See the “Areas”
section on page 3-4.
9–11
Opaque LSAs
LSA used to extend OSPF. See the “Opaque LSAs” section on page 3-7.
Link Cost
Each OSPFv2 interface is assigned a link cost. The cost is an arbitrary number. By default, Cisco NX-OS
assigns a cost that is the configured reference bandwidth divided by the interface bandwidth. By default,
the reference bandwidth is 40 Gb/s. The link cost is carried in the LSA updates for each link.
Flooding and LSA Group Pacing
When an OSPFv2 router receives an LSA, it forwards that LSA out every OSPF-enabled interface,
flooding the OSPFv2 area with this information. This LSA flooding guarantees that all routers in the
network have identical routing information. LSA flooding depends on the OSPFv2 area configuration
(see the “Areas” section on page 3-4). The LSAs are flooded based on the link-state refresh time (every
30 minutes by default). Each LSA has its own link-state refresh time.
You can control the flooding rate of LSA updates in your network by using the LSA group pacing
feature. LSA group pacing can reduce high CPU or buffer utilization. This feature groups LSAs with
similar link-state refresh times to allow OSPFv2 to pack multiple LSAs into an OSPFv2 Update
message.
By default, LSAs with link-state refresh times within four minutes of each other are grouped together.
You should lower this value for large link-state databases or raise it for smaller databases to optimize the
OSPFv2 load on your network.
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Link-State Database
Each router maintains a link-state database for the OSPFv2 network. This database contains all the
collected LSAs, and includes information on all the routes through the network. OSPFv2 uses this
information to calculate the bast path to each destination and populates the routing table with these best
paths.
LSAs are removed from the link-state database if no LSA update has been received within a set interval,
called the MaxAge. Routers flood a repeat of the LSA every 30 minutes to prevent accurate link-state
information from being aged out. Cisco NX-OS supports the LSA grouping feature to prevent all LSAs
from refreshing at the same time. For more information, see the “Flooding and LSA Group Pacing”
section on page 3-6.
Opaque LSAs
Opaque LSAs allow you to extend OSPF functionality. Opaque LSAs consist of a standard LSA header
followed by application-specific information. This information might be used by OSPFv2 or by other
applications. Three Opaque LSA types are defined as follows:
•
LSA type 9—Flooded to the local network.
•
LSA type 10—Flooded to the local area.
•
LSA type 11—Flooded to the local autonomous system.
OSPFv2 and the Unicast RIB
OSPFv2 runs the Dijkstra shortest path first algorithm on the link-state database. This algorithm selects
the best path to each destination based on the sum of all the link costs for each link in the path. The
resultant shortest path for each destination is then put in the OSPFv2 route table. When the OSPFv2
network is converged, this route table feeds into the unicast RIB. OSPFv2 communicates with the unicast
RIB to do the following:
•
Add or remove routes
•
Handle route redistribution from other protocols
•
Provide convergence updates to remove stale OSPFv2 routes and for stub router advertisements (see
the “OSPFv2 Stub Router Advertisements” section on page 3-11)
OSPFv2 also runs a modified Dijkstra algorithm for fast recalculation for summary and external (type
3, 4, 5, and 7) LSA changes.
Authentication
You can configure authentication on OSPFv2 messages to prevent unauthorized or invalid routing
updates in your network. Cisco NX-OS supports two authentication methods:
•
Simple password authentication
•
MD5 authentication digest
You can configure the OSPFv2 authentication for an OSPFv2 area or per interface.
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Simple Password Authentication
Simple password authentication uses a simple clear-text password that is sent as part of the OSPFv2
message. The receiving OSPFv2 router must be configured with the same clear-text password to accept
the OSPFv2 message as a valid route update. Because the password is in clear text, anyone who can
watch traffic on the network can learn the password.
MD5 Authentication
You should use MD5 authentication to authenticate OSPFv2 messages. You configure a password that is
shared at the local router and all remote OSPFv2 neighbors. For each OSPFv2 message, Cisco NX-OS
creates an MD5 one-way message digest based on the message itself and the encrypted password. The
interface sends this digest with the OSPFv2 message. The receiving OSPFv2 neighbor validates the
digest using the same encrypted password. If the message has not changed, the digest calculation is
identical and the OSPFv2 message is considered valid.
MD5 authentication includes a sequence number with each OSPFv2 message to ensure that no message
is replayed in the network.
Advanced Features
Cisco NX-OS supports a number of advanced OSPFv2 features that enhance the usability and scalability
of OSPFv2 in the network. This section includes the following topics:
•
Stub Area, page 3-8
•
Not-So-Stubby Area, page 3-9
•
Virtual Links, page 3-9
•
Route Redistribution, page 3-10
•
Route Summarization, page 3-10
•
OSPFv2 Stub Router Advertisements, page 3-11
•
Multiple OSPFv2 Instances, page 3-11
•
SPF Optimization, page 3-11
•
Virtualization Support, page 3-11
Stub Area
You can limit the amount of external routing information that floods an area by making it a stub area.
A stub area is an area that does not allow AS External (type 5) LSAs (see the “Link-State
Advertisements” section on page 3-5). These LSAs are usually flooded throughout the local autonomous
system to propagate external route information. Stub areas have the following requirements:
•
All routers in the stub area are stub routers. See the “Stub Routing” section on page 1-7.
•
No ASBR routers exist in the stub area.
•
You cannot configure virtual links in the stub area.
Figure 3-3 shows an example of an OSPFv2 autonomous system where all routers in area 0.0.0.10 have
to go through the ABR to reach external autonomous systems. area 0.0.0.10 can be configured as a stub
area.
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Figure 3-3
Stub Area
ABR
Backbone
Area 10
ASBR
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Stub area
Stub areas use a default route for all traffic that needs to go through the backbone area to the external
autonomous system. The default route is 0.0.0.0 for IPv4.
Not-So-Stubby Area
A Not-so-Stubby Area (NSSA) is similar to a stub area, except that an NSSA allows you to import
autonomous system external routes within an NSSA using redistribution. The NSSA ASBR redistributes
these routes and generates NSSA External (type 7) LSAs that it floods throughout the NSSA. You can
optionally configure the ABR that connects the NSSA to other areas to translate this NSSA External LSA
to AS External (type 5) LSAs. The ABR then floods these AS External LSAs throughout the OSPFv2
autonomous system. Summarization and filtering are supported during the translation. See the
“Link-State Advertisements” section on page 3-5 for details on NSSA External LSAs.
You can, for example, use NSSA to simplify administration if you are connecting a central site using
OSPFv2 to a remote site that is using a different routing protocol. Before NSSA, the connection between
the corporate site border router and a remote router could not be run as an OSPFv2 stub area because
routes for the remote site could not be redistributed into a stub area. With NSSA, you can extend OSPFv2
to cover the remote connection by defining the area between the corporate router and remote router as
an NSSA (see the “Configuring NSSA” section on page 3-26).
The backbone Area 0 cannot be an NSSA.
Virtual Links
Virtual links allow you to connect an OSPFv2 area ABR to a backbone area ABR when a direct physical
connection is not available. Figure 3-4 shows a virtual link that connects Area 3 to the backbone area
through Area 5.
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Figure 3-4
Virtual Links
Area 0
ABR2
ABR1
Area 3
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Area 5
You can also use virtual links to temporarily recover from a partitioned area, which occurs when a link
within the area fails, isolating part of the area from reaching the designated ABR to the backbone area.
Route Redistribution
OSPFv2 can learn routes from other routing protocols by using route redistribution. See the “Route
Redistribution” section on page 1-6. You configure OSPFv2 to assign a link cost for these redistributed
routes or a default link cost for all redistributed routes.
Route redistribution uses route maps to control which external routes are redistributed. See Chapter 13,
“Configuring Route Policy Manager,” for details on configuring route maps. You can use route maps to
modify parameters in the AS External (type 5) and NSSA External (type 7) LSAs before these external
routes are advertised in the local OSPFv2 autonomous system.
Route Summarization
Because OSPFv2 shares all learned routes with every OSPF-enabled router, you might want to use route
summarization to reduce the number of unique routes that are flooded to every OSPF-enabled router.
Route summarization simplifies route tables by replacing more-specific addresses with an address that
represents all the specific addresses. For example, you can replace 10.1.1.0/24, 10.1.2.0/24, and
10.1.3.0/24 with one summary address, 10.1.0.0/16.
Typically, you would summarize at the boundaries of area border routers (ABRs). Although you could
configure summarization between any two areas, it is better to summarize in the direction of the
backbone so that the backbone receives all the aggregate addresses and injects them, already
summarized, into other areas. The two types of summarization are as follows:
•
Inter-area route summarization
•
External route summarization
You configure inter-area route summarization on ABRs, summarizing routes between areas in the
autonomous system. To take advantage of summarization, you should assign network numbers in areas
in a contiguous way to be able to lump these addresses into one range.
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External route summarization is specific to external routes that are injected into OSPFv2 using route
redistribution. You should make sure that external ranges that are being summarized are contiguous.
Summarizing overlapping ranges from two different routers could cause packets to be sent to the wrong
destination. Configure external route summarization on ASBRs that are redistributing routes into OSPF.
When you configure a summary address, Cisco NX-OS automatically configures a discard route for the
summary address to prevent routing black holes and route loops.
OSPFv2 Stub Router Advertisements
You can configure an OSPFv2 interface to act as a stub router using the OSPFv2 Stub Router
Advertisements feature. Use this feature when you want to limit the OSPFv2 traffic through this router,
such as when you want to introduce a new router to the network in a controlled manner or limit the load
on a router that is already overloaded. You might also want to use this feature for various administrative
or traffic engineering reasons.
OSPFv2 stub router advertisements do not remove the OSPFv2 router from the network topology, but
they do prevent other OSPFv2 routers from using this router to route traffic to other parts of the network.
Only the traffic that is destined for this router or directly connected to this router is sent.
OSPFv2 stub router advertisements mark all stub links (directly connected to the local router) to the cost
of the local OSPFv2 interface. All remote links are marked with the maximum cost (0xFFFF).
Multiple OSPFv2 Instances
Cisco NX-OS supports multiple instances of the OSPFv2 protocol that run on the same node. You cannot
configure multiple instances over the same interface. By default, every instance uses the same system
router ID. You must manually configure the router ID for each instance if the instances are in the same
OSPFv2 autonomous system.
SPF Optimization
Cisco NX-OS optimizes the SPF algorithm in the following ways:
•
Partial SPF for Network (type 2) LSAs, Network Summary (type 3) LSAs, and AS External (type
5) LSAs—When there is a change on any of these LSAs, Cisco NX-OS performs a faster partial
calculation rather than running the whole SPF calculation.
•
SPF timers—You can configure different timers for controlling SPF calculations. These timers
include exponential backoff for subsequent SPF calculations. The exponential backoff limits the
CPU load of multiple SPF calculations.
Virtualization Support
OSPFv2 supports Virtual Routing and Forwarding instances (VRFs). By default, Cisco NX-OS places
you in the default VRF unless you specifically configure another VRF. Each OSPFv2 instance can
support multiple VRFs, up to the system limit. For more information, see Chapter 11, “Configuring
Layer 3 Virtualization.”
Licensing Requirements for OSPFv2
The following table shows the licensing requirements for this feature:
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Product
License Requirement
Cisco NX-OS
OSPFv2 requires a LAN Base Services license. For over 256 routes, OSPFv2 requires an Enterprise services
license. For a complete explanation of the Cisco NX-OS licensing scheme and how to obtain and apply
licenses, see the Cisco NX-OS Licensing Guide.
Prerequisites for OSPFv2
OSPFv2 has the following prerequisites:
•
You must be familiar with routing fundamentals to configure OSPF.
•
You are logged on to the switch.
•
You have configured at least one interface for IPv4 that is capable of communicating with a remote
OSPFv2 neighbor.
•
You have installed the LAN Base Services license.
•
You have completed the OSPFv2 network strategy and planning for your network. For example, you
must decide whether multiple areas are required.
•
You have enabled the OSPF feature (see the “Enabling the OSPFv2 Feature” section on page 3-13).
Guidelines and Limitations
OSPFv2 has the following configuration guidelines and limitations:
•
Note
Cisco NX-OS displays areas in dotted decimal notation regardless of whether you enter the area in
decimal or dotted decimal notation.
If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature
might differ from the Cisco IOS commands that you would use.
Default Settings
Table 3-2 lists the default settings for OSPFv2 parameters.
Table 3-2
Default OSPFv2 Parameters
Parameters
Default
Hello interval
10 seconds
Dead interval
40 seconds
OSPFv2 feature
Disabled
Stub router advertisement announce time
600 seconds
Reference bandwidth for link cost calculation
40 Gb/s
LSA minimal arrival time
1000 milliseconds
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Table 3-2
Default OSPFv2 Parameters (continued)
Parameters
Default
LSA group pacing
240 seconds
SPF calculation initial delay time
0 milliseconds
SPF calculation hold time
5000 milliseconds
SPF calculation initial delay time
0 milliseconds
Configuring Basic OSPFv2
Configure OSPFv2 after you have designed your OSPFv2 network.
This section includes the following topics:
•
Enabling the OSPFv2 Feature, page 3-13
•
Creating an OSPFv2 Instance, page 3-14
•
Configuring Optional Parameters on an OSPFv2 Instance, page 3-15
•
Configuring Optional Parameters on an OSPFv2 Instance, page 3-15
•
Configuring Networks in OSPFv2, page 3-16
•
Configuring Authentication for an Area, page 3-18
•
Configuring Authentication for an Interface, page 3-20
Enabling the OSPFv2 Feature
You must enable the OSPFv2 feature before you can configure OSPFv2.
SUMMARY STEPS
1.
configure terminal
2.
feature ospf
3.
(Optional) show feature
4.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
Enables the OSPFv2 feature.
feature ospf
Example:
switch(config)# feature ospf
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Step 3
Command
Purpose
show feature
(Optional) Displays enabled and disabled features.
Example:
switch(config)# show feature
Step 4
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
Use the no feature ospf command to disable the OSPFv2 feature and remove all associated
configuration.
Command
Purpose
no feature ospf
Disables the OSPFv2 feature and removes all
associated configuration.
Example:
switch(config)# no feature ospf
Creating an OSPFv2 Instance
The first step in configuring OSPFv2 is to create an OSPFv2 instance. You assign a unique instance tag
for this OSPFv2 instance. The instance tag can be any string.
For more information about OSPFv2 instance parameters, see the “Configuring Advanced OSPFv2”
section on page 3-22.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the “Enabling the OSPFv2 Feature” section on
page 3-13).
Use the show ip ospf instance-tag command to verify that the instance tag is not in use.
OSPFv2 must be able to obtain a router identifier (for example, a configured loopback address) or you
must configure the router ID option.
SUMMARY STEPS
1.
configure terminal
2.
router ospf instance-tag
3.
(Optional) router-id ip-address
4.
(Optional) show ip ospf instance-tag
5.
(Optional) copy running-config startup-config
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DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router ospf instance-tag
Example:
switch(config)# router ospf 201
switch(config-router)#
Step 3
router-id ip-address
Example:
switch(config-router)# router-id
192.0.2.1
Step 4
show ip ospf instance-tag
Creates a new OSPFv2 instance with the configured
instance tag.
(Optional) Configures the OSPFv2 router ID. This IP
address identifies this OSPFv2 instance and must exist
on a configured interface in the system.
(Optional) Displays OSPF information.
Example:
switch(config-router)# show ip ospf 201
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
Use the no router ospf command to remove the OSPFv2 instance and all associated configuration.
Command
Purpose
no router ospf instance-tag
Deletes the OSPF instance and the associated
configuration.
Example:
switch(config)# no router ospf 201
Note
This command does not remove OSPF configuration in interface mode. You must manually remove any
OSPFv2 commands configured in interface mode.
Configuring Optional Parameters on an OSPFv2 Instance
You can configure optional parameters for OSPF.
For more information about OSPFv2 instance parameters, see the “Configuring Advanced OSPFv2”
section on page 3-22.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the “Enabling the OSPFv2 Feature” section on
page 3-13).
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OSPFv2 must be able to obtain a router identifier (for example, a configured loopback address) or you
must configure the router ID option.
DETAILED STEPS
You can configure the following optional parameters for OSPFv2 in router configuration mode:
Command
Purpose
distance number
Configures the administrative distance for this
OSPFv2 instance. The range is from 1 to 255. The
default is 110.
Example:
switch(config-router)# distance 25
log-adjacency-changes [detail]
Example:
switch(config-router)#
log-adjacency-changes
maximum-paths path-number
Example:
switch(config-router)# maximum-paths 4
Generates a system message whenever a neighbor
changes state.
Configures the maximum number of equal OSPFv2
paths to a destination in the route table. This
command is used for load balancing. The range is
from 1 to 16. The default is 8.
This example shows how to create an OSPFv2 instance:
switch# configure terminal
switch(config)# router ospf 201
switch(config-router)# copy running-config startup-config
Configuring Networks in OSPFv2
You can configure a network to OSPFv2 by associating it through the interface that the router uses to
connect to that network (see the “Neighbors” section on page 3-2). You can add all networks to the
default backbone area (Area 0), or you can create new areas using any decimal number or an IP address.
Note
All areas must connect to the backbone area either directly or through a virtual link.
Note
OSPF is not enabled on an interface until you configure a valid IP address for that interface.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the “Enabling the OSPFv2 Feature” section on
page 3-13).
SUMMARY STEPS
1.
configure terminal
2.
interface interface-type slot/port
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3.
no switchport
4.
ip address ip-prefix/length
5.
ip router ospf instance-tag area area-id [secondaries none]
6.
(Optional) show ip ospf instance-tag interface interface-type slot/port
7.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface interface-type slot/port
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 1/2
switch(config-if)#
Step 3
Configures the interface as a Layer 3 routed interface.
no switchport
Example:
switch(config-if)# no switchport
Step 4
ip address ip-prefix/length
Example:
switch(config-if)# ip address
192.0.2.1/16
Step 5
ip router ospf instance-tag area area-id
[secondaries none]
Assigns an IP address and subnet mask to this
interface.
Adds the interface to the OSPFv2 instance and area.
Example:
switch(config-if)# ip router ospf 201
area 0.0.0.15
Step 6
show ip ospf instance-tag interface
interface-type slot/port
(Optional) Displays OSPF information.
Example:
switch(config-if)# show ip ospf 201
interface ethernet 1/2
Step 7
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
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Configuring Basic OSPFv2
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You can configure the following optional parameters for OSPFv2 in interface configuration mode:
Command
Purpose
ip ospf cost number
Configures the OSPFv2 cost metric for this
interface. The default is to calculate cost metric,
based on reference bandwidth and interface
bandwidth. The range is from 1 to 65535.
Example:
switch(config-if)# ip ospf cost 25
ip ospf dead-interval seconds
Example:
switch(config-if)# ip ospf dead-interval
50
ip ospf hello-interval seconds
Example:
switch(config-if)# ip ospf hello-interval
25
ip ospf mtu-ignore
Example:
switch(config-if)# ip ospf mtu-ignore
ip ospf passive-interface
Configures the OSPFv2 dead interval, in seconds.
The range is from 1 to 65535. The default is four
times the hello interval, in seconds.
Configures the OSPFv2 hello interval, in seconds.
The range is from 1 to 65535. The default is 10
seconds.
Configures OSPFv2 to ignore any IP MTU
mismatch with a neighbor. The default is to not
establish adjacency if the neighbor MTU does not
match the local interface MTU.
Suppresses routing updates on the interface.
Example:
switch(config-if)# ip ospf
passive-interface
ip ospf priority number
Example:
switch(config-if)# ip ospf priority 25
ip ospf shutdown
Configures the OSPFv2 priority, used to determine
the DR for an area. The range is from 0 to 255. The
default is 1. See the “Designated Routers” section
on page 3-3.
Shuts down the OSPFv2 instance on this interface.
Example:
switch(config-if)# ip ospf shutdown
This example shows how to add a network area 0.0.0.10 in OSPFv2 instance 201:
switch# configure terminal
switch(config)# interface ethernet 1/2
switch(config-if)# no switchport
switch(config-if)# ip address 192.0.2.1/16
switch(config-if)# ip router ospf 201 area 0.0.0.10
switch(config-if)# copy running-config startup-config
Use the show ip ospf interface command to verify the interface configuration. Use the show ip ospf
neighbor command to see the neighbors for this interface.
Configuring Authentication for an Area
You can configure authentication for all networks in an area or for individual interfaces in the area.
Interface authentication configuration overrides area authentication.
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S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the “Enabling the OSPFv2 Feature” section on
page 3-13).
Ensure that all neighbors on an interface share the same authentication configuration, including the
shared authentication key.
Create the key-chain for this authentication configuration. See the Cisco Nexus 7000 Series NX-OS
Security Configuration Guide, Release 5.x.
SUMMARY STEPS
1.
configure terminal
2.
router ospf instance-tag
3.
area area-id authentication [message-digest]
4.
interface interface-type slot/port
5.
no switchport
6.
(Optional) ip ospf authentication-key [0 | 3] key
or
(Optional) ip ospf message-digest-key key-id md5 [0 | 3] key
7.
(Optional) show ip ospf instance-tag interface interface-type slot/port
8.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router ospf instance-tag
Example:
switch(config)# router ospf 201
switch(config-router)#
Step 3
area area-id authentication
[message-digest]
Creates a new OSPFv2 instance with the configured
instance tag.
Configures the authentication mode for an area.
Example:
switch(config-router)# area 0.0.0.10
authentication
Step 4
interface interface-type slot/port
Enters interface configuration mode.
Example:
switch(config-router)# interface
ethernet 1/2
switch(config-if)#
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Step 5
Command
Purpose
no switchport
Configures the interface as a Layer 3 routed interface.
Example:
switch(config-if)# no switchport
Step 6
ip ospf authentication-key [0 | 3] key
Example:
switch(config-if)# ip ospf
authentication-key 0 mypass
ip ospf message-digest-key key-id md5 [0
| 3] key
Example:
switch(config-if)# ip ospf
message-digest-key 21 md5 0 mypass
Step 7
show ip ospf instance-tag interface
interface-type slot/port
(Optional) Configures simple password authentication
for this interface. Use this command if the
authentication is not set to key-chain or
message-digest. 0 configures the password in clear
text. 3 configures the password as 3DES encrypted.
(Optional) Configures message digest authentication
for this interface. Use this command if the
authentication is set to message-digest. The key-id
range is from 1 to 255. The MD5 option 0 configures
the password in clear text and 3 configures the pass key
as 3DES encrypted.
(Optional) Displays OSPF information.
Example:
switch(config-if)# show ip ospf 201
interface ethernet 1/2
Step 8
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
Configuring Authentication for an Interface
You can configure authentication for individual interfaces in the area. Interface authentication
configuration overrides area authentication.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the “Enabling the OSPFv2 Feature” section on
page 3-13).
Ensure that all neighbors on an interface share the same authentication configuration, including the
shared authentication key.
Create the key-chain for this authentication configuration. See the Cisco Nexus 7000 Series NX-OS
Security Configuration Guide, Release 5.x.
SUMMARY STEPS
1.
configure terminal
2.
interface interface-type slot/port
3.
no switchport
4.
ip ospf authentication [message-digest]
5.
(Optional) ip ospf authentication key-chain key-id
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6.
(Optional) ip ospf authentication-key [0 | 3] key
7.
(Optional) ip ospf message-digest-key key-id md5 [0 | 3] key
8.
(Optional) show ip ospf instance-tag interface interface-type slot/port
9.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface interface-type slot/port
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 1/2
switch(config-if)#
Step 3
Configures the interface as a Layer 3 routed interface.
no switchport
Example:
switch(config-if)# no switchport
Step 4
ip ospf authentication [message-digest]
Example:
switch(config-if)# ip ospf
authentication
Step 5
ip ospf authentication key-chain
key-name
Example:
switch(config-if)# ip ospf
authentication key-chain Test1
Step 6
ip ospf authentication-key [0 | 3 | 7]
key
Example:
switch(config-if)# ip ospf
authentication-key 0 mypass
Step 7
ip ospf message-digest-key key-id md5 [0
| 3 | 7] key
Example:
switch(config-if)# ip ospf
message-digest-key 21 md5 0 mypass
Enables interface authentication mode for OSPFv2 for
either cleartext or message-digest type. Overrides
area-based authentication for this interface. All
neighbors must share this authentication type.
(Optional) Configures interface authentication to use
key chains for OSPFv2. See the Cisco Nexus 7000
Series NX-OS Security Configuration Guide, Release
5.x, for details on key chains.
(Optional) Configures simple password authentication
for this interface. Use this command if the
authentication is not set to key-chain or
message-digest.
The options are as follows:
•
0—configures the password in clear text.
•
3—configures the pass key as 3DES encrypted.
•
7—configures the key as Cisco type 7 encrypted.
(Optional) Configures message digest authentication
for this interface. Use this command if the
authentication is set to message-digest.The key-id
range is from 1 to 255. The MD5 options are as
follows:
•
0—configures the password in clear text.
•
3—configures the pass key as 3DES encrypted.
•
7—configures the key as Cisco type 7 encrypted.
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Step 8
Command
Purpose
show ip ospf instance-tag interface
interface-type slot/port
(Optional) Displays OSPF information.
Example:
switch(config-if)# show ip ospf 201
interface ethernet 1/2
Step 9
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
This example shows how to set an interface for simple, unencrypted passwords and set the password for
Ethernet interface 1/2:
switch# configure terminal
switch(config)# router ospf 201
switch(config-router)# exit
switch(config)# interface ethernet 1/2
switch(config-if)# no switchport
switch(config-if)# ip router ospf 201 area 0.0.0.10
switch(config-if)# ip ospf authentication
switch(config-if)# ip ospf authentication-key 0 mypass
switch(config-if)# copy running-config startup-config
Configuring Advanced OSPFv2
Configure OSPFv2 after you have designed your OSPFv2 network.
This section includes the following topics:
•
Configuring Filter Lists for Border Routers, page 3-23
•
Configuring Stub Areas, page 3-24
•
Configuring a Totally Stubby Area, page 3-25
•
Configuring NSSA, page 3-26
•
Configuring Virtual Links, page 3-28
•
Configuring Redistribution, page 3-30
•
Limiting the Number of Redistributed Routes, page 3-32
•
Configuring Route Summarization, page 3-34
•
Configuring Stub Route Advertisements, page 3-35
•
Modifying the Default Timers, page 3-36
•
Restarting an OSPFv2 Instance, page 3-39
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S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Configuring Filter Lists for Border Routers
You can separate your OSPFv2 domain into a series of areas that contain related networks. All areas
must connect to the backbone area through an area border router (ABR). OSPFv2 domains can connect
to external domains as well, through an autonomous system border router (ASBR). See the “Areas”
section on page 3-4.
ABRs have the following optional configuration parameters:
•
Area range—Configures route summarization between areas.
•
Filter list—Filters the Network Summary (type 3) LSAs on an ABR that are allowed in from an
external area.
ASBRs also support filter lists.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the “Enabling the OSPFv2 Feature” section on
page 3-13).
Create the route map that the filter list uses to filter IP prefixes in incoming or outgoing Network
Summary (type 3) LSAs. See Chapter 13, “Configuring Route Policy Manager.”
SUMMARY STEPS
1.
configure terminal
2.
router ospf instance-tag
3.
area area-id filter-list route-map map-name {in | out}
4.
(Optional) show ip ospf policy statistics
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router ospf instance-tag
Example:
switch(config)# router ospf 201
switch(config-router)#
Step 3
area area-id filter-list route-map
map-name {in | out}
Creates a new OSPFv2 instance with the configured
instance tag.
Filters incoming or outgoing Network Summary (type
3) LSAs on an ABR.
Example:
switch(config-router)# area 0.0.0.10
filter-list route-map FilterLSAs in
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Step 4
Command
Purpose
show ip ospf policy statistics area id
filter-list {in | out}
(Optional) Displays OSPF policy information.
Example:
switch(config-if)# show ip ospf policy
statistics area 0.0.0.10 filter-list in
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
This example shows how to configure a filter list in area 0.0.0.10:
switch# configure terminal
switch(config)# router ospf 201
switch(config-router)# area 0.0.0.10 filter-list route-map FilterLSAs in
switch(config-router)# copy running-config startup-config
Configuring Stub Areas
You can configure a stub area for part of an OSPFv2 domain where external traffic is not necessary. Stub
areas block AS External (type 5) LSAs, limiting unnecessary routing to and from selected networks. See
the “Stub Area” section on page 3-8. You can optionally block all summary routes from going into the
stub area.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the “Enabling the OSPFv2 Feature” section on
page 3-13).
Ensure that there are no virtual links or ASBRs in the proposed stub area.
SUMMARY STEPS
1.
configure terminal
2.
router ospf instance-tag
3.
area area-id stub
4.
(Optional) area area-id default-cost cost
5.
(Optional) show ip ospf instance-tag
6.
(Optional) copy running-config startup-config
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Configuring Advanced OSPFv2
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router ospf instance-tag
Example:
switch(config)# router ospf 201
switch(config-router)#
Step 3
Creates a new OSPFv2 instance with the configured
instance tag.
Creates this area as a stub area.
area area-id stub
Example:
switch(config-router)# area 0.0.0.10
stub
Step 4
area area-id default-cost cost
Example:
switch(config-router)# area 0.0.0.10
default-cost 25
Step 5
show ip ospf instance-tag
(Optional) Sets the cost metric for the default summary
route sent into this stub area. The range is from 0 to
16777215. The default is 1.
(Optional) Displays OSPF information.
Example:
switch(config-if)# show ip ospf 201
Step 6
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
This example shows how to create a stub area:
switch# configure terminal
switch(config)# router ospf 201
switch(config-router)# area 0.0.0.10 stub
switch(config-router)# copy running-config startup-config
Configuring a Totally Stubby Area
You can create a totally stubby area and prevent all summary route updates from going into the stub area.
To create a totally stubby area, use the following command in router configuration mode:
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Configuring Advanced OSPFv2
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Command
Purpose
area area-id stub no-summary
Creates this area as a totally stubby area.
Example:
switch(config-router)# area 20 stub
no-summary
Configuring NSSA
You can configure an NSSA for part of an OSPFv2 domain where limited external traffic is required. See
the “Not-So-Stubby Area” section on page 3-9. You can optionally translate this external traffic to an
AS External (type 5) LSA and flood the OSPFv2 domain with this routing information. An NSSA can
be configured with the following optional parameters:
•
No redistribution—Redistributed routes bypass the NSSA and are redistributed to other areas in the
OSPFv2 autonomous system. Use this option when the NSSA ASBR is also an ABR.
•
Default information originate—Generates an NSSA External (type 7) LSA for a default route to the
external autonomous system. Use this option on an NSSA ASBR if the ASBR contains the default
route in the routing table. This option can be used on an NSSA ABR whether or not the ABR
contains the default route in the routing table.
•
Route map—Filters the external routes so that only those routes that you want are flooded
throughout the NSSA and other areas.
•
Translate—Translates NSSA External LSAs to AS External LSAs for areas outside the NSSA. Use
this command on an NSSA ABR to flood the redistributed routes throughout the OSPFv2
autonomous system. You can optionally suppress the forwarding address in these AS External LSAs.
If you choose this option, the forwarding address is set to 0.0.0.0.
•
No summary—Blocks all summary routes from flooding the NSSA. Use this option on the NSSA
ABR.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the “Enabling the OSPFv2 Feature” section on
page 3-13).
Ensure that there are no virtual links in the proposed NSSA and that it is not the backbone area.
SUMMARY STEPS
1.
configure terminal
2.
router ospf instance-tag
3.
area area-id nssa [no-redistribution] [default-information-originate [route-map map-name]]
[no-summary] [translate type7 {always | never} [suppress-fa]]
4.
(Optional) area area-id default-cost cost
5.
(Optional) show ip ospf instance-tag
6.
(Optional) copy running-config startup-config
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Configuring OSPFv2
Configuring Advanced OSPFv2
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router ospf instance-tag
Example:
switch(config)# router ospf 201
switch(config-router)#
Step 3
area area-id nssa [no-redistribution]
[default-information-originate]
[route-map map-name]] [no-summary]
[translate type7 {always | never}
[suppress-fa]]
Creates a new OSPFv2 instance with the configured
instance tag.
Creates this area as an NSSA.
Example:
switch(config-router)# area 0.0.0.10
nssa
Step 4
area area-id default-cost cost
Example:
switch(config-router)# area 0.0.0.10
default-cost 25
Step 5
show ip ospf instance-tag
(Optional) Sets the cost metric for the default summary
route sent into this NSSA.
(Optional) Displays OSPF information.
Example:
switch(config-if)# show ip ospf 201
Step 6
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
This example shows how to create an NSSA that blocks all summary route updates:
switch# configure terminal
switch(config)# router ospf 201
switch(config-router)# area 0.0.0.10 nssa no-summary
switch(config-router)# copy running-config startup-config
This example shows how to create an NSSA that generates a default route:
switch# configure terminal
switch(config)# router ospf 201
switch(config-router)# area 0.0.0.10 nssa default-info-originate
switch(config-router)# copy running-config startup-config
This example shows how to create an NSSA that filters external routes and blocks all summary route
updates:
switch# configure terminal
switch(config)# router ospf 201
switch(config-router)# area 0.0.0.10 nssa route-map ExternalFilter no-summary
switch(config-router)# copy running-config startup-config
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This example shows how to create an NSSA that always translates NSSA External (type 5) LSAs to AS
External (type 7) LSAs:
switch# configure terminal
switch(config)# router ospf 201
switch(config-router)# area 0.0.0.10 nssa translate type 7 always
switch(config-router)# copy running-config startup-config
Configuring Virtual Links
A virtual link connects an isolated area to the backbone area through an intermediate area. See the
“Virtual Links” section on page 3-9. You can configure the following optional parameters for a virtual
link:
Note
•
Authentication—Sets a simple password or MD5 message digest authentication and associated keys.
•
Dead interval—Sets the time that a neighbor waits for a Hello packet before declaring the local
router as dead and tearing down adjacencies.
•
Hello interval—Sets the time between successive Hello packets.
•
Retransmit interval—Sets the estimated time between successive LSAs.
•
Transmit delay—Sets the estimated time to transmit an LSA to a neighbor.
You must configure the virtual link on both routers involved before the link becomes active.
You cannot add a virtual link to a stub area.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the “Enabling the OSPFv2 Feature” section on
page 3-13).
SUMMARY STEPS
1.
configure terminal
2.
router ospf instance-tag
3.
area area-id virtual-link router-id
4.
(Optional) show ip ospf virtual-link [brief]
5.
(Optional) copy running-config startup-config
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Configuring Advanced OSPFv2
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
Creates a new OSPFv2 instance with the configured
instance tag.
router ospf instance-tag
Example:
switch(config)# router ospf 201
switch(config-router)#
Step 3
Creates one end of a virtual link to a remote router.
You must create the virtual link on that remote router
to complete the link.
area area-id virtual-link router-id
Example:
switch(config-router)# area 0.0.0.10
virtual-link 10.1.2.3
switch(config-router-vlink)#
Step 4
(Optional) Displays OSPF virtual link information.
show ip ospf virtual-link [brief]
Example:
switch(config-router-vlink)# show ip ospf
virtual-link
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router-vlink)# copy
running-config startup-config
You can configure the following optional commands in virtual link configuration mode:
Command or Action
Purpose
authentication [key-chain key-id |
message-digest | null]
(Optional) Overrides area-based authentication for this
virtual link.
Example:
switch(config-router-vlink)#
authentication message-digest
authentication-key [0 | 3] key
Example:
switch(config-router-vlink)#
authentication-key 0 mypass
dead-interval seconds
Example:
switch(config-router-vlink)#
dead-interval 50
hello-interval seconds
Example:
switch(config-router-vlink)#
hello-interval 25
(Optional) Configures a simple password for this virtual
link. Use this command if the authentication is not set to
key-chain or message-digest. 0 configures the password
in clear text. 3 configures the password as 3DES
encrypted.
(Optional) Configures the OSPFv2 dead interval, in
seconds. The range is from 1 to 65535. The default is four
times the hello interval, in seconds.
(Optional) Configures the OSPFv2 hello interval, in
seconds. The range is from 1 to 65535. The default is 10
seconds.
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Configuring Advanced OSPFv2
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Command or Action
Purpose
message-digest-key key-id md5 [0 | 3]
key
(Optional) Configures message digest authentication for
this virtual link. Use this command if the authentication
is set to message-digest. 0 configures the password in
cleartext. 3 configures the pass key as 3DES encrypted.
Example:
switch(config-router-vlink)#
message-digest-key 21 md5 0 mypass
retransmit-interval seconds
Example:
switch(config-router-vlink)#
retransmit-interval 50
transmit-delay seconds
Example:
switch(config-router-vlink)#
transmit-delay 2
(Optional) Configures the OSPFv2 retransmit interval, in
seconds. The range is from 1 to 65535. The default is 5.
(Optional) Configures the OSPFv2 transmit-delay, in
seconds. The range is from 1 to 450. The default is 1.
This example shows how to create a simple virtual link between two ABRs.
The configuration for ABR 1 (router ID 27.0.0.55) is as follows:
switch# configure terminal
switch(config)# router ospf 201
switch(config-router)# area 0.0.0.10 virtual-link 10.1.2.3
switch(config-router-vlink)# copy running-config startup-config
The configuration for ABR 2 (Router ID 10.1.2.3) is as follows:
switch# configure terminal
switch(config)# router ospf 101
switch(config-router)# area 0.0.0.10 virtual-link 27.0.0.55
switch(config-router-vlink)# copy running-config startup-config
Configuring Redistribution
You can redistribute routes learned from other routing protocols into an OSPFv2 autonomous system
through the ASBR.
You can configure the following optional parameters for route redistribution in OSPF:
•
Note
•
Note
Default information originate—Generates an AS External (type 5) LSA for a default route to the
external autonomous system.
Default information originate ignores match statements in the optional route map.
Default metric—Sets all redistributed routes to the same cost metric.
If you redistribute static routes, Cisco NX-OS also redistributes the default static route.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the “Enabling the OSPFv2 Feature” section on
page 3-13).
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Configuring Advanced OSPFv2
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Create the necessary route maps used for redistribution.
SUMMARY STEPS
1.
configure terminal
2.
router ospf instance-tag
3.
redistribute {bgp id | direct | eigrp id | ospf id | rip id | static} route-map map-name
4.
default-information originate [always] [route-map map-name]
5.
default-metric cost
6.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router ospf instance-tag
Example:
switch(config)# router ospf 201
switch(config-router)#
Step 3
redistribute {bgp id | direct | eigrp id
| ospf id | rip id | static} route-map
map-name
Creates a new OSPFv2 instance with the configured
instance tag.
Redistributes the selected protocol into OSPF through
the configured route map.
Note
Example:
switch(config-router)# redistribute bgp
64496 route-map FilterExternalBGP
Step 4
default-information originate [always]
[route-map map-name]
Example:
switch(config-router)#
default-information-originate route-map
DefaultRouteFilter
Creates a default route into this OSPF domain if the
default route exists in the RIB. Use the following
optional keywords:
•
always —Always generate the default route of
0.0.0. even if the route does not exist in the RIB.
•
route-map—Generate the default route if the
route map returns true.
Note
Step 5
default-metric cost
Step 6
copy running-config startup-config
If you redistribute static routes, Cisco NX-OS
also redistributes the default static route.
This command ignores match statements in
the route map.
Sets the cost metric for the redistributed routes. This
does not apply to directly connected routes. Use a
Example:
route map to set the default metric for directly
switch(config-router)# default-metric 25
connected routes.
(Optional) Saves this configuration change.
Example:
switch(config-router)# copy
running-config startup-config
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Configuring Advanced OSPFv2
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This example shows how to redistribute the Border Gateway Protocol (BGP) into OSPF:
switch# configure terminal
switch(config)# router ospf 201
switch(config-router)# redistribute bgp route-map FilterExternalBGP
switch(config-router)# copy running-config startup-config
Limiting the Number of Redistributed Routes
Route redistribution can add many routes to the OSPFv2 route table. You can configure a maximum limit
to the number of routes accepted from external protocols. OSPFv2 provides the following options to
configure redistributed route limits:
•
Fixed limit—Log a message when OSPFv2 reaches the maximum the configured maximum.
OSPFv2 does not accept any more redistributed routes. You can optionally configure a threshold
percentage of the maximum where OSPFv2 will log a warning when that threshold is passed.
•
Warning only—Log a warning only when OSPFv2 reaches the maximum. OSPFv2 continues to
accept redistributed routes.
•
Widthdraw—Start the timeout period when OSPFv2 reaches the maximum. After the timeout
period, OSPFv2 requests all redistributed routes if the current number of redistributed routes is less
than the maximum limit. If the current number of redistributed routes is at the maximum limit,
OSPFv2 withdraws all redistributed routes. You must clear this condition before OSPFv2 accepts
more redistributed routes.
You can optionally configure the timeout period.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the “Enabling the OSPFv2 Feature” section on
page 3-13).
SUMMARY STEPS
1.
configure terminal
2.
router ospf instance-tag
3.
redistribute {bgp id | direct| eigrp id | ospf id | rip id | static} route-map map-name
4.
redistribute maximum-prefix max [threshold] [warning-only | withdraw [num-retries timeout]]
5.
(Optional) show running-config ospf
6.
(Optional) copy running-config startup-config
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Configuring Advanced OSPFv2
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router ospf instance-tag
Example:
switch(config)# router ospf 201
switch(config-router)#
Step 3
redistribute {bgp id | direct | eigrp id
| ospf id | rip id | static} route-map
map-name
Creates a new OSPFv2 instance with the configured
instance tag.
Redistributes the selected protocol into OSPF through
the configured route map.
Example:
switch(config-router)# redistribute bgp
route-map FilterExternalBGP
Step 4
redistribute maximum-prefix max
[threshold] [warning-only | withdraw
[num-retries timeout]]
Example:
switch(config-router)# redistribute
maximum-prefix 1000 75 warning-only
Step 5
show running-config ospf
Specifies a maximum number of prefixes that OSPFv2
will distribute. The range is from 0 to 65536.
Optionally specifies the following:
•
threshold—Percent of maximum prefixes that will
trigger a warning message.
•
warning-only—Logs an warning message when
the maximum number of prefixes is exceeded.
•
withdraw—Withdraws all redistributed routes.
Optionally tries to retrieve the redistributed
routes. The num-retries range is from 1 to 12. The
timeout is 60 to 600 seconds. The default is 300
seconds. Use clear ip ospf redistribution if all
routes are withdrawn.
(Optional) Displays the OSPFv2 configuration.
Example:
switch(config-router)# show
running-config ospf
Step 6
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router)# copy
running-config startup-config
This example shows how to limit the number of redistributed routes into OSPF:
switch# configure terminal
switch(config)# router ospf 201
switch(config-router)# redistribute bgp route-map FilterExternalBGP
switch(config-router)# redistribute maximum-prefix 1000 75
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Configuring Advanced OSPFv2
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Configuring Route Summarization
You can configure route summarization for inter-area routes by configuring an address range that is
summarized. You can also configure route summarization for external, redistributed routes by
configuring a summary address for those routes on an ASBR. See the “Route Summarization” section
on page 3-10.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the “Enabling the OSPFv2 Feature” section on
page 3-13).
SUMMARY STEPS
1.
configure terminal
2.
router ospf instance-tag
3.
area area-id range ip-prefix/length [no-advertise]
4.
summary-address ip-prefix/length [no-advertise | tag tag-id]
5.
(Optional) show ip ospf summary-address
6.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router ospf instance-tag
Example:
switch(config)# router ospf 201
switch(config-router)#
Step 3
area area-id range ip-prefix/length
[no-advertise]
Example:
switch(config-router)# area 0.0.0.10
range 10.3.0.0/16
Step 4
summary-address ip-prefix/length
[no-advertise | tag tag]
Example:
switch(config-router)# summary-address
10.5.0.0/16 tag 2
Creates a new OSPFv2 instance with the configured
instance tag.
Creates a summary address on an ABR for a range of
addresses and optionally does note advertise this
summary address in a Network Summary (type 3)
LSA.
Creates a summary address on an ASBR for a range of
addresses and optionally assigns a tag for this
summary address that can be used for redistribution
with route maps.
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Step 5
Command
Purpose
show ip ospf summary-address
(Optional) Displays information about OSPF summary
addresses.
Example:
switch(config-router)# show ip ospf
summary-address
Step 6
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router)# copy
running-config startup-config
This example shows how to create summary addresses between areas on an ABR:
switch# configure terminal
switch(config)# router ospf 201
switch(config-router)# area 0.0.0.10 range 10.3.0.0/16
switch(config-router)# copy running-config startup-config
This example shows how to create summary addresses on an ASBR;
switch# configure terminal
switch(config)# router ospf 201
switch(config-router)# summary-address 10.5.0.0/16
switch(config-router)# copy running-config startup-config
Configuring Stub Route Advertisements
Use Stub Route Advertisements when you want to limit the OSPFv2 traffic through this router for a short
time. See the “OSPFv2 Stub Router Advertisements” section on page 3-11.
Stub route advertisements can be configured with the following optional parameters:
•
On startup—Sends stub route advertisements for the specified announce time.
•
Wait for BGP—Sends stub router advertisements until BGP converges.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the “Enabling the OSPFv2 Feature” section on
page 3-13).
SUMMARY STEPS
Note
1.
configure terminal
2.
router ospf instance-tag
3.
max-metric router-lsa [on-startup [announce-time] [wait-for bgp tag]]
4.
(Optional) copy running-config startup-config
You should not save the running configuration of a router when it is configured for a graceful shutdown
because the router will continue to advertise a maximum metric after it is reloaded.
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Configuring OSPFv2
Configuring Advanced OSPFv2
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router ospf instance-tag
Example:
switch(config)# router ospf 201
switch(config-router)#
Creates a new OSPFv2 instance with the configured
instance tag.
Step 3
max-metric router-lsa [on-startup
[announce-time] [wait-for bgp tag]]
Example:
switch(config-router)# max-metric
router-lsa
Configures OSPFv2 stub route advertisements.
Step 4
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router)# copy
running-config startup-config
This example shows how to enable the Stub Router Advertisements feature on startup for the default 600
seconds:
switch# configure terminal
switch(config)# router ospf 201
switch(config-router)# max-metric router-lsa on-startup
switch(config-router)# copy running-config startup-config
Modifying the Default Timers
OSPFv2 includes a number of timers that control the behavior of protocol messages and shortest path
first (SPF) calculations. OSPFv2 includes the following optional timer parameters:
•
LSA arrival time—Sets the minimum interval allowed between LSAs arriving from a neighbor.
LSAs that arrive faster than this time are dropped.
•
Pacing LSAs—Set the interval at which LSAs are collected into a group and refreshed,
checksummed, or aged. This timer controls how frequently LSA updates occur and optimizes how
many are sent in an LSA update message (see the “Flooding and LSA Group Pacing” section on
page 3-6).
•
Throttle LSAs—Set rate limits for generating LSAs. This timer controls how frequently an LSA is
generated if no topology change occurs.
•
Throttle SPF calculation—Controls how frequently the SPF calculation is run.
At the interface level, you can also control the following timers:
•
Retransmit interval—Sets the estimated time between successive LSAs.
•
Transmit delay—Sets the estimated time to transmit an LSA to a neighbor.
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Configuring Advanced OSPFv2
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See the “Configuring Networks in OSPFv2” section on page 3-16 for information about the hello
interval and dead timer.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the “Enabling the OSPFv2 Feature” section on
page 3-13).
SUMMARY STEPS
1.
configure terminal
2.
router ospf instance-tag
3.
timers lsa-arrival msec
4.
timers lsa-group-pacing seconds
5.
timers throttle lsa start-time hold-interval max-time
6.
timers throttle spf delay-time hold-time
7.
interface type slot/port
8.
no switchport
9.
ip ospf hello-interval seconds
10. ip ospf dead-interval seconds
11. ip ospf retransmit-interval seconds
12. ip ospf transmit-delay seconds
13. (Optional) show ip ospf
14. (Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router ospf instance-tag
Example:
switch(config)# router ospf 201
switch(config-router)#
Step 3
timers lsa-arrival msec
Example:
switch(config-router)# timers
lsa-arrival 2000
Creates a new OSPFv2 instance with the configured
instance tag.
Sets the LSA arrival time in milliseconds. The range is
from 10 to 600000. The default is 1000 milliseconds.
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Configuring Advanced OSPFv2
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Step 4
Command
Purpose
timers lsa-group-pacing seconds
Sets the interval in seconds for grouping LSAs. The
range is from 1 to 1800. The default is 240 seconds.
Example:
switch(config-router)# timers
lsa-group-pacing 1800
Step 5
timers throttle lsa start-time
hold-interval max-time
Sets the rate limit in milliseconds for generating LSAs
with the following timers:
Example:
switch(config-router)# timers throttle
lsa 3000 6000 6000
start-time—The range is from 50 to 5000 milliseconds.
The default value is 50 milliseconds.
hold-interval—The range is from 50 to 30,000
milliseconds. The default value is 5000 milliseconds.
max-time—The range is from 50 to 30,000
milliseconds. The default value is 5000 milliseconds.
Step 6
Step 7
Example:
switch(config-router)# timers throttle
spf 3000 2000 4000
Sets the SPF best path schedule initial delay time and
the minimum hold time in seconds between SPF best
path calculations. The range is from 1 to 600000. The
default is no delay time and 5000 millisecond hold
time.
interface type slot/port
Enters interface configuration mode.
timers throttle spf delay-time hold-time
max-wait
Example:
switch(config)# interface ethernet 1/2
switch(config-if)#
Step 8
no switchport
Configures the interface as a Layer 3 routed interface.
Example:
switch(config-if)# no switchport
Step 9
ip ospf hello-interval seconds
Example:
switch(config-if)# ip ospf
retransmit-interval 30
Step 10
ip ospf dead-interval seconds
Example:
switch(config-if)# ip ospf dead-interval
30
Step 11
ip ospf retransmit-interval seconds
Example:
switch(config-if)# ip ospf
retransmit-interval 30
Step 12
ip ospf transmit-delay seconds
Example:
switch(config-if)# ip ospf
transmit-delay 450
switch(config-if)#
Sets the hello interval this interface. The range is from
1 to 65535. The default is 10.
Sets the dead interval for this interface. The range is
from 1 to 65535.
Sets the estimated time in seconds between LSAs
transmitted from this interface. The range is from 1 to
65535. The default is 5.
Sets the estimated time in seconds to transmit an LSA
to a neighbor. The range is from 1 to 450. The default
is 1.
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Step 13
Command
Purpose
show ip ospf
(Optional) Displays information about OSPF.
Example:
switch(config-if)# show ip ospf
Step 14
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-if)# copy running-config
startup-config
This example shows how to control LSA flooding with the lsa-group-pacing option:
switch# configure terminal
switch(config)# router ospf 201
switch(config-router)# timers lsa-group-pacing 300
switch(config-router)# copy running-config startup-config
Restarting an OSPFv2 Instance
You can restart an OSPv2 instance. This clears all neighbors for the instance.
To restart an OSPFv2 instance and remove all associated neighbors, use the following command:
Command
Purpose
restart ospf instance-tag
Restarts the OSPFv2 instance and removes all
neighbors.
Example:
switch(config)# restart ospf 201
Configuring OSPFv2 with Virtualization
You can create multiple VRFs and use the same or multiple OSPFv2 instances in each VRF. You assign
an OSPFv2 interface to a VRF.
Note
Configure all other parameters for an interface after you configure the VRF for an interface. Configuring
a VRF for an interface deletes all the configuration for that interface.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the “Enabling the OSPFv2 Feature” section on
page 3-13).
SUMMARY STEPS
1.
configure terminal
2.
vrf context vrf_name
3.
router ospf instance-tag
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4.
vrf vrf-name
5.
maximum-paths paths
6.
interface interface-type slot/port
7.
no switchport
8.
vrf member vrf-name
9.
ip-address ip-prefix/length
10. ip router ospf instance-tag area area-id
11. (Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
vrf context vrf-name
Example:
switch(config)# vrf context
RemoteOfficeVRF
switch(config-vrf)#
Step 3
router ospf instance-tag
Example:
switch(config-vrf)# router ospf 201
switch(config-router)#
Step 4
vrf vrf-name
Creates a new VRF and enters VRF configuration
mode.
Creates a new OSPFv2 instance with the configured
instance tag.
Enters VRF configuration mode.
Example:
switch(config-router)# vrf
RemoteOfficeVRF
switch(config-router-vrf)#
Step 5
maximum-paths paths
Example:
switch(config-router-vrf)# maximum-paths
4
Step 6
interface interface-type slot/port
(Optional) Configures the maximum number of equal
OSPFv2 paths to a destination in the route table for this
VRF. Used for load balancing.
Enters interface configuration mode.
Example:
switch(config-router-vrf)# interface
ethernet 1/2
switch(config-if)#
Step 7
no switchport
Configures the interface as a Layer 3 routed interface.
Example:
switch(config-if)# no switchport
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Step 8
Command
Purpose
vrf member vrf-name
Adds this interface to a VRF.
Example:
switch(config-if)# vrf member
RemoteOfficeVRF
Step 9
Configures an IP address for this interface. You must
do this step after you assign this interface to a VRF.
ip address ip-prefix/length
Example:
switch(config-if)# ip address
192.0.2.1/16
Step 10
ip router ospf instance-tag area area-id
Example:
switch(config-if)# ip router ospf 201
area 0
Step 11
Assigns this interface to the OSPFv2 instance and area
configured.
(Optional) Saves this configuration change.
copy running-config startup-config
Example:
switch(config)# copy running-config
startup-config
This example shows how to create a VRF and add an interface to the VRF:
switch# configure terminal
switch(config)# vrf context NewVRF
switch(config)# router ospf 201
switch(config)# interface ethernet 1/2
switch(config-if)# no switchport
switch(config-if)# vrf member NewVRF
switch(config-if)# ip address 192.0.2.1/16
switch(config-if)# ip router ospf 201 area 0
switch(config)# copy running-config startup-config
Verifying the OSPFv2 Configuration
To display the OSPFv2 configuration information, perform one of the following tasks:
Command
Purpose
show ip ospf
Displays the OSPFv2 configuration.
show ip ospf border-routers [vrf
{vrf-name | all | default | management}]
Displays the OSPFv2 border router configuration.
show ip ospf database [vrf {vrf-name | all Displays the OSPFv2 link-state database summary.
| default | management}]
show ip ospf interface number [vrf
{vrf-name | all | default | management}]
Displays the OSPFv2 interface configuration.
show ip ospf lsa-content-changed-list
interface-type number
Displays the OSPFv2 LSAs that have changed.
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Command
Purpose
show ip ospf neighbors [neighbor-id]
[detail] [interface-type number] [vrf
{vrf-name | all | default | management}]
[summary]
Displays the list of OSPFv2 neighbors.
show ip ospf request-list neighbor-id
[interface-type number]
Displays the list of OSPFv2 link-state requests.
show ip ospf retransmission-list
neighbor-id [interface-type number]
Displays the list of OSPFv2 link-state retransmissions.
show ip ospf route [ospf-route]
Displays the internal OSPFv2 routes.
[summary] [vrf {vrf-name | all | default |
management}]
show ip ospf summary-address [vrf
{vrf-name | all | default | management}]
Displays information about the OSPFv2 summary
addresses.
show ip ospf virtual-links [brief] [vrf
{vrf-name | all | default | management}]
Displays information about OSPFv2 virtual links.
show ip ospf vrf {vrf-name | all | default | Displays information about VRF-based OSPFv2
management}
configuration.
show running-configuration ospf
Displays the current running OSPFv2 configuration.
Displaying OSPFv2 Statistics
To display OSPFv2 statistics, use the following commands:
Command
Purpose
show ip ospf policy statistics area area-id
filter-list {in | out} [vrf {vrf-name | all |
default | management}]
Displays the OSPFv2 route policy statistics for an area.
show ip ospf policy statistics redistribute Displays the OSPFv2 route policy statistics.
{bgp id| direct | eigrp id | ospf id | rip id |
static} vrf {vrf-name | all | default |
management}]
show ip ospf statistics [vrf {vrf-name | all Displays the OSPFv2 event counters.
| default | management}]
show ip ospf traffic [interface-type
number] [vrf {vrf-name | all | default |
management}]
Displays the OSPFv2 packet counters.
Configuration Examples for OSPFv2
This example shows how to configure OSPFv2:
feature ospf
router ospf 201
router-id 290.0.2.1
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Additional References
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
interface ethernet 1/2
no switchport
ip router ospf 201 area 0.0.0.10
ip ospf authentication
ip ospf authentication-key 0 mypass
Additional References
For additional information related to implementing OSPF, see the following sections:
•
Related Documents, page 3-43
•
MIBs, page 3-43
Related Documents
Related Topic
Document Title
OSPFv2 CLI commands
Cisco Nexus 3000 Series Command Reference,
Route maps
Chapter 13, “Configuring Route Policy Manager”
MIBs
MIBs
MIBs Link
•
OSPF-MIB
To locate and download MIBs, go to the following URL:
•
OSPF-TRAP-MIB
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
Feature History for OSPFv2
Table 3-3 lists the release history for this feature.
Table 3-3
Feature History for IOSPFv2
Feature Name
Releases
Feature Information
OSPFv2
5.0(3)U1(1)
This feature was introduced.
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CH A P T E R
4
Configuring EIGRP
This chapter describes how to configure the Enhanced Interior Gateway Routing Protocol (EIGRP) on
the Cisco NX-OS switch.
This chapter includes the following sections:
•
Information About EIGRP, page 4-1
•
Licensing Requirements for EIGRP, page 4-7
•
Prerequisites for EIGRP, page 4-7
•
Guidelines and Limitations, page 4-7
•
Default Settings, page 4-8
•
Configuring Basic EIGRP, page 4-9
•
Configuring Advanced EIGRP, page 4-13
•
Configuring Virtualization for EIGRP, page 4-25
•
Verifying the EIGRP Configuration, page 4-27
•
Displaying EIGRP Statistics, page 4-27
•
Configuration Examples for EIGRP, page 4-28
•
Related Topics, page 4-28
•
Additional References, page 4-28
•
Feature History for EIGRP, page 4-29
Information About EIGRP
EIGRP combines the benefits of distance vector protocols with the features of link-state protocols.
EIGRP sends out periodic Hello messages for neighbor discovery. Once EIGRP learns a new neighbor,
it sends a one-time update of all the local EIGRP routes and route metrics. The receiving EIGRP router
calculates the route distance based on the received metrics and the locally assigned cost of the link to
that neighbor. After this initial full route table update, EIGRP sends incremental updates to only those
neighbors affected by the route change. This process speeds convergence and minimizes the bandwidth
used by EIGRP.
This section includes the following topics:
•
EIGRP Components, page 4-2
•
EIGRP Route Updates, page 4-3
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Information About EIGRP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
•
Advanced EIGRP, page 4-4
EIGRP Components
EIGRP has the following basic components:
•
Reliable Transport Protocol, page 4-2
•
Neighbor Discovery and Recovery, page 4-2
•
Diffusing Update Algorithm, page 4-3
Reliable Transport Protocol
The Reliable Transport Protocol guarantees ordered delivery of EIGRP packets to all neighbors. (See
the “Neighbor Discovery and Recovery” section on page 4-2.) The Reliable Transport Protocol supports
an intermixed transmission of multicast and unicast packets. The reliable transport can send multicast
packets quickly when unacknowledged packets are pending. This provision helps to ensure that the
convergence time remains low for various speed links. See the “Configuring Advanced EIGRP” section
on page 4-13 for details about modifying the default timers that control the multicast and unicast packet
transmissions.
The Reliable Transport Protocol includes the following message types:
•
Hello—Used for neighbor discovery and recovery. By default, EIGRP sends a periodic multicast
Hello message on the local network at the configured hello interval. By default, the hello interval is
5 seconds.
•
Acknowledgement—Verify reliable reception of Updates, Queries, and Replies.
•
Updates—Send to affected neighbors when routing information changes. Updates include the route
destination, address mask, and route metrics such as delay and bandwidth. The update information
is stored in the EIGRP topology table.
•
Queries and Replies—Sent as necessary as part of the Diffusing Update Algorithm used by EIGRP.
Neighbor Discovery and Recovery
EIGRP uses the Hello messages from the Reliable Transport Protocol to discover neighboring EIGRP
routers on directly attached networks. EIGRP adds neighbors to the neighbor table. The information in
the neighbor table includes the neighbor address, the interface it was learned on, and the hold time, which
indicates how long EIGRP should wait before declaring a neighbor unreachable. By default, the hold
time is three times the hello interval or 15 seconds.
EIGRP sends a series of Update messages to new neighbors to share the local EIGRP routing
information. This route information is stored in the EIGRP topology table. After this initial transmission
of the full EIGRP route information, EIGRP sends Update messages only when a routing change occurs.
These Update messages contain only the new or changed information and are sent only to the neighbors
affected by the change. See the “EIGRP Route Updates” section on page 4-3.
EIGRP also uses the Hello messages as a keepalive to its neighbors. As long as Hello messages are
received, Cisco NX-OS can determine that a neighbor is alive and functioning.
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Diffusing Update Algorithm
The Diffusing Update Algorithm (DUAL) calculates the routing information based on the destination
networks in the topology table. The topology table includes the following information:
•
IPv4 address/mask—The network address and network mask for this destination.
•
Successors—The IP address and local interface connection for all feasible successors or neighbors
that advertise a shorter distance to the destination than the current feasible distance.
•
Feasibility distance (FD)—The lowest calculated distance to the destination. The feasibility
distance is the sum of the advertised distance from a neighbor plus the cost of the link to that
neighbor.
DUAL uses the distance metric to select efficient, loop-free paths. DUAL selects routes to insert into
the unicast Routing Information Base (RIB) based on feasible successors. When a topology change
occurs, DUAL looks for feasible successors in the topology table. If there are feasible successors, DUAL
selects the feasible successor with the lowest feasible distance and inserts that into the unicast RIB,
avoiding unnecessary recomputation.
When there are no feasible successors but there are neighbors advertising the destination, DUAL
transitions from the passive state to the active state and triggers a recomputation to determine a new
successor or next-hop router to the destination. The amount of time required to recompute the route
affects the convergence time. EIGRP sends Query messages to all neighbors, searching for feasible
successors. Neighbors that have a feasible successor send a Reply message with that information.
Neighbors that do not have feasible successors trigger a DUAL recomputation.
EIGRP Route Updates
When a topology change occurs, EIGRP sends an Update message with only the changed routing
information to affected neighbors. This Update message includes the distance information to the new or
updated network destination.
The distance information in EIGRP is represented as a composite of available route metrics, including
bandwidth, delay, load utilization, and link reliability. Each metric has an associated weight that
determines if the metric is included in the distance calculation. You can configure these metric weights.
You can fine-tune link characteristics to achieve optimal paths, but we recommend that you use the
default settings for most configurable metrics.
This section includes the following topics:
•
Internal Route Metrics, page 4-3
•
External Route Metrics, page 4-4
•
EIGRP and the Unicast RIB, page 4-4
Internal Route Metrics
Internal routes are routes that occur between neighbors within the same EIGRP autonomous system.
These routes have the following metrics:
•
Next hop—The IP address of the next-hop router.
•
Delay—The sum of the delays configured on the interfaces that make up the route to the destination
network. Configured in tens of microseconds.
•
Bandwidth—The calculation from the lowest configured bandwidth on an interface that is part of
the route to the destination.
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Information About EIGRP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
We recommend that you use the default bandwidth value. This bandwidth parameter is also used
by EIGRP.
Note
•
MTU—The smallest maximum transmission unit value along the route to the destination.
•
Hop count—The number of hops or routers that the route passes through to the destination. This
metric is not directly used in the DUAL computation.
•
Reliability—An indication of the reliability of the links to the destination.
•
Load—An indication of how much traffic is on the links to the destination.
By default, EIGRP uses the bandwidth and delay metrics to calculate the distance to the destination. You
can modify the metric weights to include the other metrics in the calculation.
External Route Metrics
External routes are routes that occur between neighbors in different EIGRP autonomous systems. These
routes have the following metrics:
•
Next hop—The IP address of the next-hop router.
•
Router ID—The router ID of the router that redistributed this route into EIGRP.
•
AS Number—The autonomous system number of the destination.
•
Protocol ID—A code that represents the routing protocol that learned the destination route.
•
Tag—An arbitrary tag that can be used for route maps.
•
Metric—The route metric for this route from the external routing protocol.
EIGRP and the Unicast RIB
EIGRP adds all learned routes to the EIGRP topology table and the unicast RIB. When a topology
change occurs, EIGRP uses these routes to search for a feasible successor. EIGRP also listens for
notifications from the unicast RIB for changes in any routes redistributed to EIGRP from another routing
protocol.
Advanced EIGRP
You can use the advanced features of EIGRP to optimize your EIGRP configuration.
This section includes the following topics:
•
Address Families, page 4-5
•
Authentication, page 4-5
•
Stub Routers, page 4-5
•
Route Summarization, page 4-6
•
Route Redistribution, page 4-6
•
Load Balancing, page 4-6
•
Split Horizon, page 4-6
•
Virtualization Support, page 4-7
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Information About EIGRP
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Address Families
EIGRP supports the IPv4 address family.
Address family configuration mode includes the following EIGRP features:
•
Authentication
•
AS number
•
Default route
•
Metrics
•
Distance
•
Graceful restart
•
Logging
•
Load balancing
•
Redistribution
•
Router ID
•
Stub router
•
Timers
You cannot configure the same feature in more than one configuration mode. For example, if you
configure the default metric in router configuration mode, you cannot configure the default metric in
address family mode.
Authentication
You can configure authentication on EIGRP messages to prevent unauthorized or invalid routing updates
in your network. EIGRP authentication supports MD5 authentication digest.
You can configure the EIGRP authentication per virtual routing and forwarding (VRF) instance or
interface using key-chain management for the authentication keys. Key-chain management allows you
to control changes to the authentication keys used by MD5 authentication digest. See the Cisco Nexus
7000 Series NX-OS Security Configuration Guide, Release 5.x, for more details about creating
key-chains.
For MD5 authentication, you configure a password that is shared at the local router and all remote
EIGRP neighbors. When an EIGRP message is created, Cisco NX-OS creates an MD5 one-way message
digest based on the message itself and the encrypted password and sends this digest along with the
EIGRP message. The receiving EIGRP neighbor validates the digest using the same encrypted password.
If the message has not changed, the calculation is identical and the EIGRP message is considered valid.
MD5 authentication also includes a sequence number with each EIGRP message that is used to ensure
that no message is replayed in the network.
Stub Routers
You can use the EIGRP stub routing feature to improve network stability, reduce resource usage, and
simplify stub router configuration. Stub routers connect to the EIGRP network through a remote router.
See the “Stub Routing” section on page 1-7.
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Information About EIGRP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
When using EIGRP stub routing, you need to configure the distribution and remote routers to use EIGRP
and configure only the remote router as a stub. EIGRP stub routing does not automatically enable
summarization on the distribution router. In most cases, you need to configure summarization on the
distribution routers.
Without EIGRP stub routing, even after the routes that are sent from the distribution router to the remote
router have been filtered or summarized, a problem might occur. For example, if a route is lost
somewhere in the corporate network, EIGRP could send a query to the distribution router. The
distribution router could then send a query to the remote router even if routes are summarized. If a
problem communicating over the WAN link between the distribution router and the remote router occurs,
EIGRP could get stuck in active condition and cause instability elsewhere in the network. EIGRP stub
routing allows you to prevent queries to the remote router.
Route Summarization
You can configure a summary aggregate address for a specified interface. Route summarization
simplifies route tables by replacing a number of more-specific addresses with an address that represents
all the specific addresses. For example, you can replace 10.1.1.0/24, 10.1.2.0/24, and 10.1.3.0/24 with
one summary address, 10.1.0.0/16.
If more specific routes are in the routing table, EIGRP advertises the summary address from the interface
with a metric equal to the minimum metric of the more specific routes.
Note
EIGRP does not support automatic route summarization.
Route Redistribution
You can use EIGRP to redistribute direct routes, static routes, routes learned by other EIGRP
autonomous systems, or routes from other protocols. You configure route map with the redistribution to
control which routes are passed into EIGRP. A route map allows you to filter routes based on attributes
such as the destination, origination protocol, route type, route tag, and so on. See Chapter 13,
“Configuring Route Policy Manager.”
You also configure the default metric that is used for all imported routes into EIGRP.
Load Balancing
You can use load balancing to allow a router to distribute traffic over all the router network ports that are
the same distance from the destination address. Load balancing increases the utilization of network
segments which increases effective network bandwidth.
Cisco NX-OS supports the Equal Cost Multiple Paths (ECMP) feature with up to 16 equal-cost paths in
the EIGRP route table and the unicast RIB. You can configure EIGRP to load balance traffic across some
or all of those paths.
Note
EIGRP in Cisco NX-OS does not support unequal cost load balancing.
Split Horizon
You can use split horizon to ensure that EIGRP never advertises a route out of the interface where it was
learned.
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Split horizon is a method that controls the sending of EIGRP update and query packets. When you enable
split horizon on an interface, Cisco NX-OS does not send update and query packets for destinations that
were learned from this interface. Controlling update and query packets in this manner reduces the
possibility of routing loops.
Split horizon with poison reverse configures EIGRP to advertise a learned route as unreachable back
through that the interface that EIGRP learned the route from.
EIGRP uses split horizon or split horizon with poison reverse in the following scenarios:
•
Exchanging topology tables for the first time between two routers in startup mode.
•
Advertising a topology table change.
•
Sending a query message.
By default, the split horizon feature is enabled on all interfaces.
Virtualization Support
Cisco NX-OS supports multiple instances of the EIGRP protocol that runs on the same system. EIGRP
supports Virtual Routing and Forwarding instances (VRFs). By default, Cisco NX-OS places you in the
default VRF unless you specifically configure another VRF. See Chapter 11, “Configuring Layer 3
Virtualization.”
By default, every instance uses the same system router ID. You can optionally configure a unique router
ID for each instance.
Licensing Requirements for EIGRP
The following table shows the licensing requirements for this feature:
Product
License Requirement
Cisco NX-OS
Full EIGRP requires a Enterprise Services license, however EIGRP stub requires a LAN Base Services
license. For a complete explanation of the Cisco NX-OS licensing scheme and how to obtain and apply
licenses, see the Cisco NX-OS Licensing Guide.
Prerequisites for EIGRP
EIGRP has the following prerequisites:
•
You must enable the EIGRP feature (see the “Enabling the EIGRP Feature” section on page 4-9).
Guidelines and Limitations
EIGRP has the following configuration guidelines and limitations:
•
A metric configuration (either through the default-metric configuration option or through a route
map) is required for redistribution from any other protocol, connected routes, or static routes (see
Chapter 13, “Configuring Route Policy Manager”).
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Default Settings
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Note
•
For graceful restart, an NSF-aware router must be up and completely converged with the network
before it can assist an NSF-capable router in a graceful restart operation.
•
For graceful restart, neighboring switches participating in the graceful restart must be NSF-aware
or NSF-capable.
•
Cisco NX-OS EIGRP is compatible with EIGRP in the Cisco IOS software.
•
Do not change the metric weights without a good reason. If you change the metric weights, you must
apply the change to all EIGRP routers in the same autonomous system.
•
Consider using stubs for larger networks.
•
Avoid redistribution between different EIGRP autonomous systems because the EIGRP vector
metric will not be preserved.
•
The no ip next-hop-self command does not guarantee reachability of the next hop.
•
The ip passive-interface eigrp command suppresses neighbors from forming.
•
Cisco NX-OS does not support IGRP or connecting IGRP and EIGRP clouds.
•
Autosummarization is not enabled by default.
•
Cisco NX-OS supports only IP.
If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature
might differ from the Cisco IOS commands that you would use.
Default Settings
Table 4-1 lists the default settings for EIGRP parameters.
Table 4-1
Default EIGRP Parameters
Parameters
Administrative distance
Bandwidth percent
Default metric for redistributed routes
Default
•
Internal routes—90
•
External routes—170
50 percent
•
bandwidth—100000 Kb/s
•
delay—100 (10 microsecond units)
•
reliability—255
•
loading—1
•
MTU—1500
EIGRP feature
Disabled
Hello interval
5 seconds
Hold time
15 seconds
Equal-cost paths
8
Metric weights
10100
Next-hop address advertised
IP address of local interface
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Table 4-1
Default EIGRP Parameters (continued)
Parameters
Default
NSF convergence time
120
NSF route-hold time
240
NSF signal time
20
Redistribution
Disabled
Split horizon
Enabled
Configuring Basic EIGRP
This section includes the following topics:
•
Enabling the EIGRP Feature, page 4-9
•
Creating an EIGRP Instance, page 4-10
•
Restarting an EIGRP Instance, page 4-12
•
Shutting Down an EIGRP Instance, page 4-13
•
Shutting Down EIGRP on an Interface, page 4-13
Enabling the EIGRP Feature
You must enable the EIGRP feature before you can configure EIGRP.
SUMMARY STEPS
1.
configure terminal
2.
feature eigrp
3.
(Optional) show feature
4.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
Enables the EIGRP feature.
feature eigrp
Example:
switch(config)# feature eigrp
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Step 3
Command
Purpose
show feature
(Optional) Displays information about enabled
features.
Example:
switch(config)# show feature
Step 4
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
Use the no feature eigrp command to disable the EIGRP feature and remove all associated
configuration.
Command
Purpose
no feature eigrp
Disables the EIGRP feature and removes all
associated configuration.
Example:
switch(config)# no feature eigrp
Creating an EIGRP Instance
You can create an EIGRP instance and associate an interface with that instance. You assign a unique
autonomous system number for this EIGRP process (see the “Autonomous Systems” section on
page 1-5). Routes are not advertised or accepted from other autonomous systems unless you enable route
redistribution.
BEFORE YOU BEGIN
Ensure that you have enabled the EIGRP feature (see the “Enabling the EIGRP Feature” section on
page 4-9).
EIGRP must be able to obtain a router ID (for example, a configured loopback address) or you must
configure the router ID option.
If you configure an instance tag that does not qualify as an AS number, you must configure the AS
number explicitly or this EIGRP instance will remain in the shutdown state.
SUMMARY STEPS
1.
configure terminal
2.
router eigrp instance-tag
3.
(Optional) autonomous-system as-number
4.
(Optional) log-adjacency-changes
5.
(Optional) log-neighbor-warnings [seconds]
6.
interface interface-type slot/port
7.
no switchport
8.
ip router eigrp instance-tag
9.
show ip eigrp interfaces
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10. (Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router eigrp instance-tag
Example:
switch(config)# router eigrp Test1
switch(config-router)#
Creates a new EIGRP process with the configured
instance tag. The instance tag can be any
case-sensitive, alphanumeric string up to 20
characters.
If you configure an instance-tag that does not qualify
as an AS number, you must use the
autonomous-system command to configure the AS
number explicitly or this EIGRP instance will remain
in the shutdown state.
Step 3
autonomous-system as-number
Example:
switch(config-router)# autonomous-system
33
Step 4
log-adjacency-changes
Example:
switch(config-router)#
log-adjacency-changes
Step 5
log-neighbor-warnings [seconds]
Example:
switch(config-router)#
log-neighbor-warnings
Step 6
interface interface-type slot/port
Example:
switch(config-router)# interface
ethernet 1/2
switch(config-if)#
Step 7
(Optional) Configures a unique AS number for this
EIGRP instance. The range is from 1 to 65535.
(Optional). Generates a system message whenever an
adjacency changes state. This command is enabled by
default.
(Optional) Generates a system message whenever a
neighbor warning occurs. You can configure the time
between warning messages, from 1 to 65535, in
seconds. The default is 10 seconds. This command is
enabled by default.
Enters interface configuration mode. Use ? to
determine the slot and port ranges.
Configures the interface as a Layer 3 routed interface.
no switchport
Example:
switch(config-if)# no switchport
Step 8
Associates this interface with the configured EIGRP
process. The instance tag can be any case-sensitive,
Example:
alphanumeric string up to 20 characters.
switch(config-if)# ip router eigrp Test1
ip router eigrp instance-tag
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Step 9
Command
Purpose
show ip eigrp interfaces
Displays information about EIGRP interfaces.
Example:
switch(config-if)# show ip eigrp
interfaces
Step 10
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
Use the no router eigrp command to remove the EIGRP process and the associated configuration.
Command
Purpose
no router eigrp instance-tag
Deletes the EIGRP process and all associated
configuration.
Example:
switch(config)# no router eigrp Test1
Note
You should also remove any EIGRP commands configured in interface mode if you remove the EIGRP
process.
This example shows how to create an EIGRP process and configure an interface for EIGRP:
switch# configure terminal
switch(config)# router eigrp Test1
switch(config)# interface ethernet 1/2
switch(config-if)# no switchport
switch(config-if)# ip router eigrp Test1
switch(config-if)# no shutdown
switch(config-if)# copy running-config startup-config
For more information about other EIGRP parameters, see the “Configuring Advanced EIGRP” section
on page 4-13.
Restarting an EIGRP Instance
You can restart an EIGRP instance. This clears all neighbors for the instance.
To restart an EIGRP instance and remove all associated neighbors, use the following commands:
Command
Purpose
flush-routes
(Optional) Flushes all EIGRP routes in the unicast
RIB when this EIGRP instance restarts.
Example:
switch(config)# flush-routes
restart eigrp instance-tag
Example:
switch(config)# restart eigrp Test1
Restarts the EIGRP instance and removes all
neighbors. The instance tag can be any
case-sensitive, alphanumeric string up to 20
characters.
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Shutting Down an EIGRP Instance
You can gracefully shut down an EIGRP instance. This action moves all routes and adjacencies but
preserves the EIGRP configuration.
To disable an EIGRP instance, use the following command in router configuration mode:
Command
Purpose
switch(config-router)# shutdown
Disables this instance of EIGRP. The EIGRP router
configuration remains.
Example:
switch(config-router)# shutdown
Configuring a Passive Interface for EIGRP
You can configure a passive interface for EIGRP. A passive interface does not participate in EIGRP
adjacency but the network address for the interface remains in the EIGRP topology table.
To configure a passive interface for EIGRP, use the following command in interface configuration mode:
Command
Purpose
ip passive-interface eigrp instance-tag
Suppresses EIGRP hellos, which prevents neighbors
from forming and sending routing updates on an
EIGRP interface. The instance tag can be any
case-sensitive, alphanumeric string up to 20
characters.
Shutting Down EIGRP on an Interface
You can gracefully shut down EIGRP on an interface. This action removes all adjacencies and stops
EIGRP traffic on this interface but preserves the EIGRP configuration.
To disable EIGRP on an interface, use the following command in interface configuration mode:
Command
Purpose
switch(config-if)# ip eigrp instance-tag
shutdown
Disables EIGRP on this interface. The EIGRP
interface configuration remains. The instance tag can
be any case-sensitive, alphanumeric string up to 20
characters.
Example:
switch(config-router)# ip eigrp Test1
shutdown
Configuring Advanced EIGRP
This section includes the following topics:
•
Configuring Authentication in EIGRP, page 4-14
•
Configuring EIGRP Stub Routing, page 4-16
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•
Configuring a Summary Address for EIGRP, page 4-17
•
Redistributing Routes into EIGRP, page 4-17
•
Limiting the Number of Redistributed Routes, page 4-19
•
Configuring Load Balancing in EIGRP, page 4-21
•
Adjusting the Interval Between Hello Packets and the Hold Time, page 4-22
•
Disabling Split Horizon, page 4-23
•
Tuning EIGRP, page 4-23
Configuring Authentication in EIGRP
You can configure authentication between neighbors for EIGRP. See the “Authentication” section on
page 4-5.
You can configure EIGRP authentication for the EIGRP process or for individual interfaces. Interface
EIGRP authentication configuration overrides the EIGRP process-level authentication configuration.
BEFORE YOU BEGIN
Ensure that you have enabled the EIGRP feature (see the “Enabling the EIGRP Feature” section on
page 4-9).
Ensure that all neighbors for an EIGRP process share the same authentication configuration, including
the shared authentication key.
Create the key-chain for this authentication configuration. See the Cisco Nexus 7000 Series NX-OS
Security Configuration Guide, Release 5.x.
SUMMARY STEPS
1.
configure terminal
2.
router eigrp instance-tag
3.
address-family ipv4 unicast
4.
authentication key-chain key-chain
5.
authentication mode md5
6.
interface interface-type slot/port
7.
no switchport
8.
ip router eigrp instance-tag
9.
ip authentication key-chain eigrp instance-tag key-chain
10. ip authentication mode eigrp instance-tag md5
11. (Optional) copy running-config startup-config
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DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router eigrp instance-tag
Example:
switch(config)# router eigrp Test1
switch(config-router)#
Creates a new EIGRP process with the configured
instance tag. The instance tag can be any
case-sensitive, alphanumeric string up to 20
characters.
If you configure an instance-tag that does not qualify
as an AS number, you must use the
autonomous-system command to configure the AS
number explicitly or this EIGRP instance will remain
in the shutdown state.
Step 3
address-family ipv4 unicast
Example:
switch(config-router)# address-family
ipv4 unicast
switch(config-router-af)#
Step 4
authentication key-chain key-chain
Example:
switch(config-router-af)# authentication
key-chain routeKeys
Step 5
authentication mode md5
Example:
switch(config-router-af)# authentication
mode md5
Step 6
interface interface-type slot/port
Example:
switch(config-router-af) interface
ethernet 1/2
switch(config-if)#
Step 7
Enters the address-family configuration mode. This
command is optional for IPv4.
Associates a key chain with this EIGRP process for
this VRF. The key chain can be any case-sensitive,
alphanumeric string up to 20 characters.
Configures MD5 message digest authentication mode
for this VRF.
Enters interface configuration mode. Use ? to find the
supported interfaces.
Configures the interface as a Layer 3 routed interface.
no switchport
Example:
switch(config-if)# no switchport
Step 8
ip router eigrp instance-tag
Step 9
ip authentication key-chain eigrp
instance-tag key-chain
Associates this interface with the configured EIGRP
process. The instance tag can be any case-sensitive,
Example:
alphanumeric string up to 20 characters.
switch(config-if)# ip router eigrp Test1
Example:
switch(config-if)# ip authentication
key-chain eigrp Test1 routeKeys
Associates a key chain with this EIGRP process for
this interface. This configuration overrides the
authentication configuration set in the router VRF
mode.
The instance tag can be any case-sensitive,
alphanumeric string up to 20 characters.
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Step 10
Command
Purpose
ip authentication mode eigrp
instance-tag md5
Configures the MD5 message digest authentication
mode for this interface. This configuration overrides
the authentication configuration set in the router VRF
mode.
Example:
switch(config-if)# ip authentication
mode eigrp Test1 md5
Step 11
copy running-config startup-config
The instance tag can be any case-sensitive,
alphanumeric string up to 20 characters.
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
This example shows how to configure MD5 message digest authentication for EIGRP over Ethernet
interface 1/2:
switch# configure terminal
switch(config)# router eigrp Test1
switch(config-router)# exit
switch(config)# interface ethernet 1/2
switch(config-if)# no switchport
switch(config-if)# ip router eigrp Test1
switch(config-if)# ip authentication key-chain eigrp Test1 routeKeys
switch(config-if)# ip authentication mode eigrp Test1 md5
switch(config-if)# copy running-config startup-config
Configuring EIGRP Stub Routing
To configure a router for EIGRP stub routing, use the following command in address-family
configuration mode:
Command
Purpose
switch(config-router-af)# stub [direct |
receive-only | redistributed [direct]
leak-map map-name]
Configures a remote router as an EIGRP stub router.
The map name can be any case-sensitive,
alphanumeric string up to 20 characters.
Example:
switch(config-router-af)# eigrp stub
redistributed
This example shows how to configure a stub router to advertise directly connected and redistributed
routes:
switch# configure terminal
switch(config)# router eigrp Test1
switch(config-router)# address-family ipv4 unicast
switch(config-router-af)# stub direct redistributed
switch(config-router-af)# copy running-config startup-config
Use the show ip eigrp neighbor detail command to verify that a router has been configured as a stub
router. The last line of the output shows the stub status of the remote or spoke router. This example shows
the output from the show ip eigrp neighbor detail command:
Router# show ip eigrp neighbor detail
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IP-EIGRP neighbors for process 201
H
Address
Interface
0
Hold Uptime
SRTT
(sec)
(ms)
10.1.1.2
Se3/1
11 00:00:59
1
Version 12.1/1.2, Retrans: 2, Retries: 0
Stub Peer Advertising ( CONNECTED SUMMARY ) Routes
RTO
Q Seq Type
Cnt Num
4500 0 7
Configuring a Summary Address for EIGRP
You can configure a summary aggregate address for a specified interface. If any more specific routes are
in the routing table, EIGRP will advertise the summary address out the interface with a metric equal to
the minimum of all more specific routes. See the “Route Summarization” section on page 4-6.
To configure a summary aggregate address, use the following command in interface configuration mode:
Command
Purpose
switch(config-if)# ip summary-address
eigrp instance-tag ip-prefix/length
[distance | leak-map map-name]
Configures a summary aggregate address as either
an IP address and network mask, or an IP
prefix/length. The instance tag and map name can
be any case-sensitive, alphanumeric string up to 20
characters.
Example:
switch(config-if)# ip summary-address
eigrp Test1 192.0.2.0/8
You can optionally configure the administrative
distance for this aggregate address. The default
administrative distance is 5 for aggregate
addresses.
This example causes EIGRP to summarize network 192.0.2.0 out Ethernet 1/2 only:
switch(config)# interface ethernet 1/2
switch(config-if)# no switchport
switch(config-if)# ip summary-address eigrp Test1 192.0.2.0 255.255.255.0
Redistributing Routes into EIGRP
You can redistribute routes in EIGRP from other routing protocols.
BEFORE YOU BEGIN
Ensure that you have enabled the EIGRP feature (see the “Enabling the EIGRP Feature” section on
page 4-9).
You must configure the metric (either through the default-metric configuration option or through a route
map) for routes redistributed from any other protocol.
You must create a route map to control the types of routes that are redistributed into EIGRP. See
Chapter 13, “Configuring Route Policy Manager.”
SUMMARY STEPS
1.
configure terminal
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2.
router eigrp instance-tag
3.
address-family ipv4 unicast
4.
redistribute {bgp as | {eigrp | ospf | ospfv3 | rip} instance-tag | direct | static} route-map name
5.
default-metric bandwidth delay reliability loading mtu
6.
show ip eigrp route-map statistics redistribute
7.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router eigrp instance-tag
Example:
switch(config)# router eigrp Test1
switch(config-router)#
Creates a new EIGRP process with the
configured instance tag. The instance tag can
be any case-sensitive, alphanumeric string up
to 20 characters.
If you configure an instance-tag that does not
qualify as an AS number, you must use the
autonomous-system command to configure
the AS number explicitly or this EIGRP
instance will remain in the shutdown state.
Step 3
address-family ipv4 unicast
Example:
switch(config-router)# address-family ipv4
unicast
switch(config-router-af)#
Step 4
redistribute {bgp as| {eigrp | ospf | ospfv3 |
rip} instance-tag | direct | static} route-map
name
Example:
switch(config-router-af)# redistribute bgp 100
route-map BGPFilter
Step 5
default-metric bandwidth delay reliability
loading mtu
Example:
switch(config-router-af)# default-metric
500000 30 200 1 1500
Enters the address-family configuration mode.
This command is optional for IPv4.
Injects routes from one routing domain into
EIGRP. The instance tag and map name can be
any case-sensitive, alphanumeric string up to
20 characters.
Sets the metrics assigned to routes learned
through route redistribution. The default
values are as follows:
•
bandwidth—100000 Kb/s
•
delay—100 (10 microsecond units)
•
reliability—255
•
loading—1
•
MTU—1492
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Configuring EIGRP
Configuring Advanced EIGRP
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Step 6
Command
Purpose
show ip eigrp route-map statistics
redistribute
Displays information about EIGRP route map
statistics.
Example:
switch(config-router-af)# show ip eigrp
route-map statistics redistribute bgp
Step 7
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
This example shows how to redistribute BGP into EIGRP for IPv4:
switch# configure terminal
switch(config)# router eigrp Test1
switch(config-router)# redistribute bgp 100 route-map BGPFilter
switch(config-router)# default-metric 500000 30 200 1 1500
switch(config-router)# copy running-config startup-config
Limiting the Number of Redistributed Routes
Route redistribution can add many routes to the EIGRP route table. You can configure a maximum limit
to the number of routes accepted from external protocols. EIGRP provides the following options to
configure redistributed route limits:
•
Fixed limit—Logs a message when EIGRP reaches the configured maximum. EIGRP does not
accept any more redistributed routes. You can optionally configure a threshold percentage of the
maximum where EIGRP will log a warning when that threshold is passed.
•
Warning only—Logs a warning only when EIGRP reaches the maximum. EIGRP continues to
accept redistributed routes.
•
Withdraw—Start the timeout period when EIGRP reaches the maximum. After the timeout period,
EIGRP requests all redistributed routes if the current number of redistributed routes is less than the
maximum limit. If the current number of redistributed routes is at the maximum limit, EIGRP
withdraws all redistributed routes. You must clear this condition before EIGRP accepts more
redistributed routes.
You can optionally configure the timeout period.
BEFORE YOU BEGIN
Ensure that you have enabled the EIGRP feature (see the “Enabling the EIGRP Feature” section on
page 4-9).
SUMMARY STEPS
1.
configure terminal
2.
router eigrp instance-tag
3.
redistribute {bgp id | direct | eigrp id | ospf id | rip id | static} route-map map-name
4.
redistribute maximum-prefix max [threshold] [warning-only | withdraw [num-retries timeout]]
5.
(Optional) show running-config eigrp
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Configuring EIGRP
Configuring Advanced EIGRP
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6.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router eigrp instance-tag
Example:
switch(config)# router eigrp Test1
switch(config-router)#
Step 3
redistribute {bgp id | direct | eigrp id
| ospf id | rip id | static} route-map
map-name
Creates a new EIGRP instance with the configured
instance tag.
Redistributes the selected protocol into EIGRP
through the configured route map.
Example:
switch(config-router)# redistribute bgp
route-map FilterExternalBGP
Step 4
redistribute maximum-prefix max
[threshold] [warning-only | withdraw
[num-retries timeout]]
Example:
switch(config-router)# redistribute
maximum-prefix 1000 75 warning-only
Step 5
show running-config eigrp
Specifies a maximum number of prefixes that EIGRP
will distribute. The range is from 0 to 65536.
Optionally specifies the following:
•
threshold—Percent of maximum prefixes that will
trigger a warning message.
•
warning-only—Logs an warning message when
the maximum number of prefixes is exceeded.
•
withdraw—Withdraws all redistributed routes.
Optionally tries to retrieve the redistributed
routes. The num-retries range is from 1 to 12. The
timeout is from 60 to 600 seconds. The default is
300 seconds. Use clear ip eigrp redistribution if
all routes are withdrawn.
(Optional) Displays the EIGRP configuration.
Example:
switch(config-router)# show
running-config eigrp
Step 6
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router)# copy
running-config startup-config
This example shows how to limit the number of redistributed routes into EIGRP:
switch# configure terminal
switch(config)# router eigrp Test1
switch(config-router)# redistribute bgp route-map FilterExternalBGP
switch(config-router)# redistribute maximum-prefix 1000 75
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Configuring EIGRP
Configuring Advanced EIGRP
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Configuring Load Balancing in EIGRP
You can configure load balancing in EIGRP. You can configure the number of Equal Cost Multiple Path
(ECMP) routes using the maximum paths option. See the “Configuring Load Balancing in EIGRP”
section on page 4-21.
BEFORE YOU BEGIN
Ensure that you have enabled the EIGRP feature (see the “Enabling the EIGRP Feature” section on
page 4-9).
SUMMARY STEPS
1.
configure terminal
2.
router eigrp instance-tag
3.
address-family ipv4 unicast
4.
maximum-paths num-paths
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router eigrp instance-tag
Example:
switch(config)# router eigrp Test1
switch(config-router)#
Creates a new EIGRP process with the
configured instance tag. The instance tag can
be any case-sensitive, alphanumeric string up
to 20 characters.
If you configure an instance-tag that does not
qualify as an AS number, you must use the
autonomous-system command to configure
the AS number explicitly or this EIGRP
instance will remain in the shutdown state.
Step 3
address-family ipv4 unicast
Example:
switch(config-router)# address-family ipv4
unicast
switch(config-router-af)#
Enters the address-family configuration mode.
This command is optional for IPv4.
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Configuring Advanced EIGRP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Step 4
Step 5
Command
Purpose
maximum-paths num-paths
Example:
switch(config-router-af)# maximum-paths 5
Sets the number of equal cost paths that
EIGRP will accept in the route table. The
range is from 1 to 16. The default is 8.
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router-af)# copy running-config
startup-config
This example shows how to configure equal cost load balancing for EIGRP over IPv4 with a maximum
of six equal cost paths:
switch# configure terminal
switch(config)# router eigrp Test1
switch(config-router)# maximum-paths 6
switch(config-router)# copy running-config startup-config
Adjusting the Interval Between Hello Packets and the Hold Time
You can adjust the interval between Hello messages and the hold time.
By default, Hello messages are sent every 5 seconds. The hold time is advertised in Hello messages and
indicates to neighbors the length of time that they should consider the sender valid. The default hold time
is three times the hello interval, or 15 seconds.
To change the interval between hello packets, use the following command in interface configuration
mode:
Command
Purpose
switch(config-if)# ip hello-interval
eigrp instance-tag seconds
Configures the hello interval for an EIGRP routing
process. The instance tag can be any case-sensitive,
alphanumeric string up to 20 characters. The range is
from 1 to 65535 seconds. The default is 5.
Example:
switch(config-if)# ip hello-interval
eigrp Test1 30
On very congested and large networks, the default hold time might not be sufficient time for all routers
to receive hello packets from their neighbors. In this case, you might want to increase the hold time.
To change the hold time, use the following command in interface configuration mode:
Command
Purpose
switch(config-if)# ip hold-time eigrp
instance-tag seconds
Configures the hold time for an EIGRP routing process.
The instance tag can be any case-sensitive,
alphanumeric string up to 20 characters. The range is
from 1 to 65535.
Example:
switch(config-if)# ip hold-time eigrp
Test1 30
Use the show ip eigrp interface detail command to verify timer configuration.
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Configuring EIGRP
Configuring Advanced EIGRP
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Disabling Split Horizon
You can use split horizon to block route information from being advertised by a router out of any
interface from which that information originated. Split horizon usually optimizes communications
among multiple routing switches, particularly when links are broken.
By default, split horizon is enabled on all interfaces.
To disable split horizon, use the following command in interface configuration mode:
Command
Purpose
switch(config-if)# no ip split-horizon eigrp
instance-tag
Disables split horizon.
Example:
switch(config-if)# no ip split-horizon eigrp
Test1
Tuning EIGRP
You can configure optional parameters to tune EIGRP for your network.
You can configure the following optional parameters in address-family configuration mode:
Command
Purpose
default-information originate [always |
route-map map-name]
Originates or accepts the default route with prefix
0.0.0.0/0. When a route-map is supplied, the
default route is originated only when the route map
yields a true condition. The map name can be any
case-sensitive, alphanumeric string up to 20
characters.
Example:
switch(config-router-af)#
default-information originate always
distance internal external
Example:
switch(config-router-af)# distance 25 100
metric maximum-hops hop-count
Example:
switch(config-router-af)# metric
maximum-hops 70
Configures the administrative distance for this
EIGRP process. The range is from 1 to 255. The
internal value sets the distance for routes learned
from within the same autonomous system (the
default value is 90). The external value sets the
distance for routes learned from an external
autonomous system (the default value is 170).
Sets maximum allowed hops for an advertised
route. Routes over this maximum are advertised as
unreachable. The range is from 1 to 255. The
default is 100.
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Configuring Advanced EIGRP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Command
Purpose
metric weights tos k1 k2 k3 k4 k5
Adjusts the EIGRP metric or K value. EIGRP uses
the following formula to determine the total metric
to the network:
Example:
switch(config-router-af)# metric weights 0
1 3 2 1 0
metric = [k1*bandwidth + (k2*bandwidth)/(256 –
load) + k3*delay] * [k5/(reliability + k4)]
Default values and ranges are as follows:
timers active-time {time-limit | disabled}
Example:
switch(config-router-af)# timers
active-time 200.
•
TOS—0. The range is from 0 to 8.
•
k1—1. The range is from 0 to 255.
•
k2—0. The range is from 0 to 255.
•
k3—1. The range is from 0 to 255.
•
k4—0. The range is from 0 to 255.
•
k5—0. The range is from 0 to 255.
Sets the time the router waits in minutes (after
sending a query) before declaring the route to be
stuck in the active (SIA) state. The range is from 1
to 65535. The default is 3.
You can configure the following optional parameters in interface configuration mode:
Command
Purpose
ip bandwidth eigrp instance-tag bandwidth
Configures the bandwidth metric for EIGRP on an
interface. The instance tag can be any
case-sensitive, alphanumeric string up to 20
characters. The bandwidth range is from 1 to
2,560,000,000 Kb/s.
Example:
switch(config-if)# ip bandwidth eigrp
Test1 30000
ip bandwidth-percent eigrp instance-tag
percent
Example:
switch(config-if)# ip bandwidth-percent
eigrp Test1 30
no ip delay eigrp instance-tag delay
Example:
switch(config-if)# ip delay eigrp Test1
100
ip distribute-list eigrp instance-tag
{prefix-list name| route-map name} {in |
out}
Example:
switch(config-if)# ip distribute-list
eigrp Test1 route-map EigrpTest in
Configures the percentage of bandwidth that
EIGRP might use on an interface. The instance tag
can be any case-sensitive, alphanumeric string up
to 20 characters.
The percent range is from 0 to 100. The default is
50.
Configures the delay metric for EIGRP on an
interface. The instance tag can be any
case-sensitive, alphanumeric string up to 20
characters. The delay range is from 1 to 16777215
(in tens of microseconds).
Configures the route filtering policy for EIGRP on
this interface. The instance tag, prefix list name,
and route map name can be any case-sensitive,
alphanumeric string up to 20 characters.
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Configuring EIGRP
Configuring Virtualization for EIGRP
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Command
Purpose
no ip next-hop-self eigrp instance-tag
Configures EIGRP to use the received next-hop
address rather than the address for this interface.
The default is to use the IP address of this interface
for the next-hop address. The instance tag can be
any case-sensitive, alphanumeric string up to 20
characters.
Example:
switch(config-if)# ip next-hop-self eigrp
Test1
ip offset-list eigrp instance-tag
{prefix-list name| route-map name} {in |
out} offset
Example:
switch(config-if)# ip offfset-list eigrp
Test1 prefix-list EigrpList in
ip passive-interface eigrp instance-tag
Example:
switch(config-if)# ip passive-interface
eigrp Test1
Adds an offset to incoming and outgoing metrics to
routes learned by EIGRP. The instance tag, prefix
list name, and route map name can be any
case-sensitive, alphanumeric string up to 20
characters.
Suppresses EIGRP hellos, which prevents
neighbors from forming and sending routing
updates on an EIGRP interface. The instance tag
can be any case-sensitive, alphanumeric string up
to 20 characters.
Configuring Virtualization for EIGRP
You can create multiple VRFs and use the same or multiple EIGRP processes in each VRF. You assign
an interface to a VRF.
Note
Configure all other parameters for an interface after you configure the VRF for an interface. Configuring
a VRF for an interface deletes all other configuration for that interface.
BEFORE YOU BEGIN
Ensure that you have enabled the EIGRP feature (see the “Enabling the EIGRP Feature” section on
page 4-9).
Create the VRFs.
SUMMARY STEPS
1.
configure terminal
2.
vrf context vrf-name
3.
router eigrp instance-tag
4.
interface ethernet slot/port
5.
no switchport
6.
vrf member vrf-name
7.
ip router eigrp instance-tag
8.
(Optional) copy running-config startup-config
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Configuring Virtualization for EIGRP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
vrf context vrf-name
Example:
switch(config)# vrf context
RemoteOfficeVRF
switch(config-vrf)#
Step 3
router eigrp instance-tag
Example:
switch(config)# router eigrp Test1
switch(config-router)#
Creates a new VRF and enters VRF configuration
mode. The VRN name can be any case-sensitive,
alphanumeric string up to 20 characters.
Creates a new EIGRP process with the configured
instance tag. The instance tag can be any
case-sensitive, alphanumeric string up to 20
characters.
If you configure an instance-tag that does not qualify
as an AS number, you must use the
autonomous-system command to configure the AS
number explicitly or this EIGRP instance will remain
in the shutdown state.
Step 4
interface ethernet slot/port
Example:
switch(config)# interface ethernet 1/2
switch(config-if)#
Step 5
no switchport
Enters interface configuration mode. Use ? to find the
slot and port ranges.
Configures the interface as a Layer 3 routed interface.
Example:
switch(config-if)# no switchport
Step 6
vrf member vrf-name
Example:
switch(config-if)# vrf member
RemoteOfficeVRF
Step 7
ip router eigrp instance-tag
Step 8
copy running-config startup-config
Adds this interface to a VRF. The VRF name can be
any case-sensitive, alphanumeric string up to 20
characters.
Adds this interface to the EIGRP process. The instance
tag can be any case-sensitive, alphanumeric string up
Example:
to 20 characters.
switch(config-if)# ip router eigrp Test1
(Optional) Saves this configuration change.
Example:
switch(config-if)# copy running-config
startup-config
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Configuring EIGRP
Verifying the EIGRP Configuration
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
This example shows how to create a VRF and add an interface to the VRF:
switch# configure terminal
switch(config)# vrf context NewVRF
switch(config-vrf)# router eigrp Test1
switch(config-router)# interface ethernet 1/2
switch(config-if)# no switchport
switch(config-if)# ip router eigrp Test1
switch(config-if)# vrf member NewVRF
switch(config-if)# copy running-config startup-config
Verifying the EIGRP Configuration
To display the EIGRP configuration information, perform one of the following tasks:
Command
Purpose
show ip eigrp [instance-tag]
Displays a summary of the configured EIGRP processes.
show ip eigrp [instance-tag] interfaces
[type number] [brief] [detail]
Displays information about all configured EIGRP
interfaces.
show ip eigrp instance-tag neighbors [type Displays information about all the EIGRP neighbors. Use
number]
this command to verify the EIGRP neighbor
configuration.
show ip eigrp [instance-tag] route
[ip-prefix/length] [active] [all-links]
[detail-links] [pending] [summary]
[zero-successors] [vrf vrf-name]
Displays information about all the EIGRP routes.
show ip eigrp [instance-tag] topology
[ip-prefix/length] [active] [all-links]
[detail-links] [pending] [summary]
[zero-successors] [vrf vrf-name]
Displays information about the EIGRP topology table.
show running-configuration eigrp
Displays the current running EIGRP configuration.
Displaying EIGRP Statistics
To display EIGRP statistics, use the following commands:
Command
Purpose
show ip eigrp [instance-tag] accounting
[vrf vrf-name]
Displays accounting statistics for EIGRP.
show ip eigrp [instance-tag] route-map
statistics redistribute
Displays redistribution statistics for EIGRP.
show ip eigrp [instance-tag] traffic [vrf
vrf-name]
Displays traffic statistics for EIGRP.
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Configuration Examples for EIGRP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Configuration Examples for EIGRP
This example shows how to configure EIGRP:
feature eigrp
interface ethernet 1/2
no switchport
ip address 192.0.2.55/24
ip router eigrp Test1
no shutdown
router eigrp Test1
router-id 192.0.2.1
Related Topics
See Chapter 13, “Configuring Route Policy Manager” for more information on route maps.
Additional References
For additional information related to implementing EIGRP, see the following sections:
•
Related Documents, page 4-29
•
MIBs, page 4-29
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Configuring EIGRP
Feature History for EIGRP
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Related Documents
Related Topic
Document Title
EIGRP CLI commands
Cisco Nexus 3000 Series Command Reference,
http://www.cisco.com/warp/public/103/1.html
Introduction to EIGRP Tech Note
http://www.cisco.com/en/US/tech/tk365/technologies
_q_and_a_item09186a008012dac4.shtml
EIGRP Frequently Asked Questions
MIBs
MIBs
MIBs Link
CISCO-EIGRP-MIB
To locate and download MIBs, go to the following URL:
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
Feature History for EIGRP
Table 4-2 lists the release history for this feature.
Table 4-2
Feature History for EIGRP
Feature Name
Releases
Feature Information
EIGRP
5.0(3)U1(1)
This feature was introduced.
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Feature History for EIGRP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
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CH A P T E R
5
Configuring Basic BGP
This chapter describes how to configure Border Gateway Protocol (BGP) on a Cisco NX-OS switch.
This chapter includes the following sections:
•
Information About Basic BGP, page 5-1
•
Licensing Requirements for Basic BGP, page 5-7
•
Prerequisites for BGP, page 5-7
•
Guidelines and Limitations for BGP, page 5-8
•
CLI Configuration Modes, page 5-8
•
Default Settings, page 5-10
•
Configuring Basic BGP, page 5-10
•
Verifying the Basic BGP Configuration, page 5-21
•
Displaying BGP Statistics, page 5-23
•
Configuration Examples for Basic BGP, page 5-23
•
Related Topics, page 5-23
•
Where to Go Next, page 5-23
•
Additional References, page 5-23
•
Feature History for BGP, page 5-24
Information About Basic BGP
Cisco NX-OS supports BGP version 4, which includes multiprotocol extensions that allow BGP to carry
routing information for IP multicast routes and multiple Layer 3 protocol address families. BGP uses
TCP as a reliable transport protocol to create TCP sessions with other BGP-enabled switches.
BGP uses a path-vector routing algorithm to exchange routing information between BGP-enabled
networking switches or BGP speakers. Based on this information, each BGP speaker determines a path
to reach a particular destination while detecting and avoiding paths with routing loops. The routing
information includes the actual route prefix for a destination, the path of autonomous systems to the
destination, and additional path attributes.
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Information About Basic BGP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
BGP selects a single path, by default, as the best path to a destination host or network. Each path carries
well-known mandatory, well-known discretionary, and optional transitive attributes that are used in BGP
best-path analysis. You can influence BGP path selection by altering some of these attributes by
configuring BGP policies. See the “Route Policies and Resetting BGP Sessions” section on page 6-3 for
more information.
BGP also supports load balancing or equal-cost multipath (ECMP). See the “Load Sharing and
Multipath” section on page 6-6 for more information.
This section includes the following topics:
•
BGP Autonomous Systems, page 5-2
•
Administrative Distance, page 5-2
•
BGP Peers, page 5-3
•
BGP Router Identifier, page 5-4
•
BGP Path Selection, page 5-4
•
BGP and the Unicast RIB, page 5-7
•
BGP Virtualization, page 5-7
BGP Autonomous Systems
An autonomous system (AS) is a network controlled by a single administration entity. An autonomous
system forms a routing domain with one or more interior gateway protocols (IGPs) and a consistent set
of routing policies. BGP supports 16-bit and 32-bit autonomous system numbers. For more information,
see the “Autonomous Systems” section on page 1-5.
Separate BGP autonomous systems dynamically exchange routing information through external BGP
(eBGP) peering sessions. BGP speakers within the same autonomous system can exchange routing
information through internal BGP (iBGP) peering sessions.
4-Byte AS Number Support
BGP supports 2-byte or 4-byte AS numbers. Cisco NX-OS displays 4-byte AS numbers in plain-text
notation (that is, as 32-bit integers). You can configure 4-byte AS numbers as either plain-text notation
(for example, 1 to 4294967295), or AS.dot notation (for example, 1.0). For more information, see the
“Autonomous Systems” section on page 1-5.
Administrative Distance
An administrative distance is a rating of the trustworthiness of a routing information source. By default,
BGP uses the administrative distances shown in Table 5-1.
Table 5-1
BGP Default Administrative Distances
Distance
Default Value
Function
External
20
Applied to routes learned from eBGP.
Internal
200
Applied to routes learned from iBGP.
Local
200
Applied to routes originated by the router.
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Note
The administrative distance does not influence the BGP path selection algorithm, but it does influence
whether BGP-learned routes are installed in the IP routing table.
For more information, see the “Administrative Distance” section on page 1-7.
BGP Peers
A BGP speaker does not discover another BGP speaker automatically. You must configure the
relationships between BGP speakers. A BGP peer is a BGP speaker that has an active TCP connection
to another BGP speaker.
BGP Sessions
BGP uses TCP port 179 to create a TCP session with a peer. When a TCP connection is established
between peers, each BGP peer initially exchanges all of its routes—the complete BGP routing
table—with the other peer. After this initial exchange, the BGP peers send only incremental updates
when a topology change occurs in the network or when a routing policy change occurs. In the periods of
inactivity between these updates, peers exchange special messages called keepalives. The hold time is
the maximum time limit that can elapse between receiving consecutive BGP update or keepalive
messages.
Cisco NX-OS supports the following peer configuration options:
•
Individual IPv4 or IPv4 address—BGP establishes a session with the BGP speaker that matches the
remote address and AS number.
•
IPv4 prefix peers for a single AS number—BGP establishes sessions with BGP speakers that match
the prefix and the AS number.
•
Dynamic AS number prefix peers—BGP establishes sessions with BGP speakers that match the
prefix and an AS number from a list of configured AS numbers.
Dynamic AS Numbers for Prefix Peers
Cisco NX-OS accepts a range or list of AS numbers to establish BGP sessions. For example, if you
configure BGP to use IPv4 prefix 192.0.2.0/8 and AS numbers 33, 66, and 99, BGP establishes a session
with 192.0.2.1 with AS number 66 but rejects a session from 192.0.2.2 with AS number 50.)
Cisco NX-OS does not associate prefix peers with dynamic AS numbers as either interior BGP (iBGP)
or external BGP (eBGP) sessions until after the session is established. See Chapter 6, “Configuring
Advanced BGP,” for more information on iBGP and eBGP.
Note
The dynamic AS number prefix peer configuration overrides the individual AS number configuration
that is inherited from a BGP template. See Chapter 6, “Configuring Advanced BGP,” for more
information on templates.
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BGP Router Identifier
To establish BGP sessions between peers, BGP must have a router ID, which is sent to BGP peers in the
OPEN message when a BGP session is established. The BGP router ID is a 32-bit value that is often
represented by an IPv4 address. You can configure the router ID. By default, Cisco NX-OS sets the
router ID to the IPv4 address of a loopback interface on the router. If no loopback interface is configured
on the router, then the software chooses the highest IPv4 address configured to a physical interface on
the router to represent the BGP router ID. The BGP router ID must be unique to the BGP peers in a
network.
If BGP does not have a router ID, it cannot establish any peering sessions with BGP peers.
BGP Path Selection
Although BGP might receive advertisements for the same route from multiple sources, BGP selects only
one path as the best path. BGP puts the selected path in the IP routing table and propagates the path to
its peers.
The best-path algorithm runs each time that a path is added or withdrawn for a given network. The
best-path algorithm also runs if you change the BGP configuration. BGP selects the best path from the
set of valid paths available for a given network.
Cisco NX-OS implements the BGP best-path algorithm in the following steps:
Step 1
Compares two paths to determine which is better (see the “Step 1—Comparing Pairs of Paths” section
on page 5-5).
Step 2
Iterates over all paths and determines in which order to compare the paths to select the overall best path
(see the “Step 2—Determining the Order of Comparisons” section on page 5-6).
Step 3
Determines whether the old and new best paths differ enough so that the new best path should be used
(see the “Step 3—Determining the Best-Path Change Suppression” section on page 5-6).
Note
The order of comparison determined in Part 2 is important. Consider the case where you have three
paths, A, B, and C. When Cisco NX-OS compares A and B, it chooses A. When Cisco NX-OS compares
B and C, it chooses B. But when Cisco NX-OS compares A and C, it might not choose A because some
BGP metrics apply only among paths from the same neighboring autonomous system and not among all
paths.
The path selection uses the BGP AS-path attribute. The AS-path attribute includes the list of autonomous
system numbers (AS numbers) traversed in the advertised path. If you subdivide your BGP autonomous
system into a collection or confederation of autonomous systems, the AS path contains confederation
segments that list these locally defined autonomous systems.
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Step 1—Comparing Pairs of Paths
This first step in the BGP best-path algorithm compares two paths to determine which path is better. The
following sequence describes the basic steps that Cisco NX-OS uses to compare two paths to determine
the better path:
1.
Cisco NX-OS chooses a valid path for comparison. (For example, a path that has an unreachable
next hop is not valid.)
2.
Cisco NX-OS chooses the path with the highest weight.
3.
Cisco NX-OS chooses the path with the highest local preference.
4.
If one of the paths is locally originated, Cisco NX-OS chooses that path.
5.
Cisco NX-OS chooses the path with the shorter AS path.
Note
When calculating the length of the AS path, Cisco NX-OS ignores confederation segments, and
counts AS sets as 1. See the “AS Confederations” section on page 6-4 for more information.
6.
Cisco NX-OS chooses the path with the lower origin. Interior Gateway Protocol (IGP) is considered
lower than EGP.
7.
Cisco NX-OS chooses the path with the lower multi- exit discriminator (MED).
You can configure a number of options that affect whether or not this step is performed. In general,
Cisco NX-OS compares the MED of both paths if the paths were received from peers in the same
autonomous system; otherwise, Cisco NX-OS skips the MED comparison.
You can configure Cisco NX-OS to always perform the best-path algorithm MED comparison,
regardless of the peer autonomous system in the paths. See the “Tuning the Best-Path Algorithm”
section on page 6-9 for more information. Otherwise, Cisco NX-OS will perform a MED
comparison that depends on the AS-path attributes of the two paths being compared:
a. If a path has no AS path or the AS path starts with an AS_SET, then the path is internal, and
Cisco NX-OS compares the MED to other internal paths.
b. If the AS path starts with an AS_SEQUENCE, then the peer autonomous system is the first AS
number in the sequence, and Cisco NX-OS compares the MED to other paths that have the same
peer autonomous system.
c. If the AS path contains only confederation segments or starts with confederation segments
followed by an AS_SET, the path is internal and Cisco NX-OS compares the MED to other
internal paths.
d. If the AS path starts with confederation segments followed by an AS_SEQUENCE, then the
peer autonomous system is the first AS number in the AS_SEQUENCE, and Cisco NX-OS
compares the MED to other paths that have the same peer autonomous system.
Note
If Cisco NX-OS receives no MED attribute with the path, then Cisco NX-OS considers the
MED to be 0 unless you configure the best-path algorithm to set a missing MED to the
highest possible value. See the “Tuning the Best-Path Algorithm” section on page 6-9 for
more information.
e. If the nondeterministic MED comparison feature is enabled, the best path algorithm uses the
Cisco IOS style of MED comparison. See the “Tuning the Best-Path Algorithm” section on
page 6-9 for more information.
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8.
If one path is from an internal peer and the other path is from an external peer, then Cisco NX-OS
chooses the path from the external peer.
9.
If the paths have different IGP metrics to their next-hop addresses, then Cisco NX-OS chooses the
path with the lower IGP metric.
10. Cisco NX-OS uses the path that was selected by the best-path algorithm the last time that it was run.
If all path parameters in Step 1 through Step 9 are the same, then you can configure the best-path
algorithm to compare the router IDs. See the “Tuning the Best-Path Algorithm” section on page 6-9 for
more information. If the path includes an originator attribute, then Cisco NX-OS uses that attribute as
the router ID to compare to; otherwise, Cisco NX-OS uses the router ID of the peer that sent the path. If
the paths have different router IDs, Cisco NX-OS chooses the path with the lower router ID.
Note
When using the attribute originator as the router ID, it is possible that two paths have the same
router ID. It is also possible to have two BGP sessions with the same peer router, and therefore
you can receive two paths with the same router ID.
11. Cisco NX-OS selects the path with the shorter cluster length. If a path was not received with a cluster
list attribute, the cluster length is 0.
12. Cisco NX-OS chooses the path received from the peer with the lower IP address. Locally generated
paths (for example, redistributed paths) have a peer IP address of 0.
Note
Paths that are equal after step 9 can be used for multipath if you configure multipath. See the “Load
Sharing and Multipath” section on page 6-6 for more information.
Step 2—Determining the Order of Comparisons
The second step of the BGP best-path algorithm implementation is to determine the order in which Cisco
NX-OS compares the paths:
1.
Cisco NX-OS partitions the paths into groups. Within each group Cisco NX-OS compares the MED
among all paths. Cisco NX-OS uses the same rules as in the “Step 1—Comparing Pairs of Paths”
section on page 5-5 to determine whether MED can be compared between any two paths. Typically,
this comparison results in one group being chosen for each neighbor autonomous system. If you
configure the bgp bestpath med always command, then Cisco NX-OS chooses just one group that
contains all the paths.
2.
Cisco NX-OS determines the best path in each group by iterating through all paths in the group and
keeping track of the best one so far. Cisco NX-OS compares each path with the temporary best path
found so far and if the new path is better, it becomes the new temporary best path and Cisco NX-OS
compares it with the next path in the group.
3.
Cisco NX-OS forms a set of paths that contain the best path selected from each group in Step 2.
Cisco NX-OS selects the overall best path from this set of paths by going through them as in Step 2.
Step 3—Determining the Best-Path Change Suppression
The next part of the implementation is to determine whether Cisco NX-OS will use the new best path or
suppress the new best path. The router can continue to use the existing best path if the new one is
identical to the old path (if the router ID is the same). Cisco NX-OS continues to use the existing best
path to avoid route changes in the network.
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You can turn off the suppression feature by configuring the best-path algorithm to compare the router
IDs. See the “Tuning the Best-Path Algorithm” section on page 6-9 for more information. If you
configure this feature, the new best path is always preferred to the existing one.
You cannot suppress the best-path change if any of the following conditions occur:
•
The existing best path is no longer valid.
•
Either the existing or new best paths were received from internal (or confederation) peers or were
locally generated (for example, by redistribution).
•
The paths were received from the same peer (the paths have the same router ID).
•
The paths have different weights, local preferences, origins, or IGP metrics to their next-hop
addresses.
•
The paths have different MEDs.
BGP and the Unicast RIB
BGP communicates with the unicast routing information base (unicast RIB) to store IPv4 routes in the
unicast routing table. After selecting the best path, if BGP determines that the best path change needs to
be reflected in the routing table, it sends a route update to the unicast RIB.
BGP receives route notifications regarding changes to its routes in the unicast RIB. It also receives route
notifications about other protocol routes to support redistribution.
BGP also receives notifications from the unicast RIB regarding next-hop changes. BGP uses these
notifications to keep track of the reachability and IGP metric to the next-hop addresses.
Whenever the next-hop reachability or IGP metrics in the unicast RIB change, BGP triggers a best-path
recalculation for affected routes.
BGP Virtualization
BGP supports Virtual Routing and Forwarding instances (VRFs). By default, Cisco NX-OS places you
in the default VRF unless you specifically configure another VRF. For more information, see
Chapter 11, “Configuring Layer 3 Virtualization.”
Licensing Requirements for Basic BGP
The following table shows the licensing requirements for this feature:
Product
License Requirement
Cisco NX-OS
BGP requires a LAN Enterprise Services license. For a complete explanation of the Cisco NX-OS licensing
scheme and how to obtain and apply licenses, see the Cisco NX-OS Licensing Guide.
Note
Make sure the LAN Base Services license is installed on the switch to enable Layer 3 interfaces.
Prerequisites for BGP
BGP has the following prerequisites:
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•
You must enable the BGP feature (see the “Enabling the BGP Feature” section on page 5-11).
•
You should have a valid router ID configured on the system.
•
You must have an AS number, either assigned by a Regional Internet Registry (RIR) or locally
administered.
•
You must configure at least one IGP that is capable of recursive next-hop resolution.
•
You must configure an address family under a neighbor for the BGP session establishment.
Guidelines and Limitations for BGP
BGP has the following configuration guidelines and limitations:
•
The dynamic AS number prefix peer configuration the overrides individual AS number
configuration inherited from a BGP template.
•
If you configure a dynamic AS number for prefix peers in an AS confederation, BGP establishes
sessions with only the AS numbers in the local confederation.
•
BGP sessions created through a dynamic AS number prefix peer ignore any configured eBGP
multihop time-to-live (TTL) value or a disabled check for directly connected peers.
•
You must configure a router ID for BGP to avoid automatic router ID changes and session flaps.
•
You must use the maximum-prefix configuration option per peer to restrict the number of routes
received and system resources used.
•
You must configure the update-source to establish a session with BGP/eBGP multihop sessions.
•
You must specify a BGP policy if you configure redistribution.
•
You must define the BGP router ID within a VRF.
•
If you decrease the keepalive and hold timer values, you might experience BGP session flaps.
•
If you configure VRFs, enter the desired VRF (see Chapter 11, “Configuring Layer 3
Virtualization”).
CLI Configuration Modes
The following sections describe how to enter each of the CLI configuration modes for BGP. From a
mode, you can enter the ? command to display the commands available in that mode.
This section includes the following topics:
•
Global Configuration Mode, page 5-9
•
Address Family Configuration Mode, page 5-9
•
Neighbor Configuration Mode, page 5-9
•
Neighbor Address Family Configuration Mode, page 5-10
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Global Configuration Mode
Use global configuration mode to create a BGP process and configure advanced features such as AS
confederation and route dampening. For more information, see Chapter 6, “Configuring Advanced
BGP.”
This example shows how to enter router configuration mode:
switch# configuration
switch(config)# router bgp 64496
switch(config-router)#
BGP supports Virtual Routing and Forwarding (VRF). You can configure BGP within the appropriate
VRF if you are using VRFs in your network. See the “Configuring Virtualization” section on page 6-37
for more information.
This example shows how to enter VRF configuration mode:
switch(config)# router bgp 64497
switch(config-router)# vrf vrf_A
switch(config-router-vrf)#
Address Family Configuration Mode
You can optionally configure the address families that BGP supports. Use the address-family command
in router configuration mode to configure features for an address family. Use the address-family
command in neighbor configuration mode to configure the specific address family for the neighbor.
You must configure the address families if you are using route redistribution, address aggregation, load
balancing, and other advanced features.
This example shows how to enter address family configuration mode from the router configuration
mode:
switch(config)# router bgp 64496
switch(config-router)# address-family ipv4 unicast
switch(config-router-af)#
This example shows how to enter VRF address family configuration mode if you are using VRFs:
switch(config)# router bgp 64497
switch(config-router)# vrf vrf_A
switch(config-router-vrf)# address-family ipv4 unicast
switch(config-router-vrf-af)#
Neighbor Configuration Mode
Cisco NX-OS provides the neighbor configuration mode to configure BGP peers. You can use neighbor
configuration mode to configure all parameters for a peer.
This example shows how to enter neighbor configuration mode:
switch(config)# router bgp 64496
switch(config-router)# neighbor 192.0.2.1
switch(config-router-neighbor)#
This example shows how to enter VRF neighbor configuration mode:
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Default Settings
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switch(config)# router bgp 64497
switch(config-router)# vrf vrf_A
switch(config-router-vrf)# neighbor 192.0.2.1
switch(config-router-vrf-neighbor)#
Neighbor Address Family Configuration Mode
An address family configuration submode inside the neighbor configuration submode is available for
entering address family-specific neighbor configuration and enabling the address family for the
neighbor. Use this mode for advanced features such as limiting the number of prefixes allowed for this
neighbor and removing private AS numbers for eBGP.
This example shows how to enter neighbor address family configuration mode:
switch(config)# router bgp 64496
switch(config-router# neighbor 192.0.2.1
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor-af)#
This example shows how to enter VRF neighbor address family configuration mode:
switch(config)# router bgp 64497
switch(config-router)# vrf vrf_A
switch(config-router-vrf)# neighbor 209.165.201.1
switch(config-router-vrf-neighbor)# address-family ipv4 unicast
switch(config-router-vrf-neighbor-af)#
Default Settings
Table 5-2 lists the default settings for BGP parameters.
Table 5-2
Default BGP Parameters
Parameters
Default
BGP feature
Disabled
keep alive interval
60 seconds
hold timer
180 seconds
Configuring Basic BGP
To configure a basic BGP, you need to enable BGP and configure a BGP peer. Configuring a basic BGP
network consists of a few required tasks and many optional tasks. You must configure a BGP routing
process and BGP peers.
This section includes the following topics:
•
Enabling the BGP Feature, page 5-11
•
Creating a BGP Instance, page 5-12
•
Restarting a BGP Instance, page 5-13
•
Shutting Down BGP, page 5-14
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Note
•
Configuring BGP Peers, page 5-14
•
Configuring Dynamic AS Numbers for Prefix Peers, page 5-16
•
Clearing BGP Information, page 5-18
If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature
might differ from the Cisco IOS commands that you would use.
Enabling the BGP Feature
You must enable the BGP feature before you can configure BGP.
SUMMARY STEPS
1.
configure terminal
2.
feature bgp
3.
(Optional) show feature
4.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
Enables the BGP feature.
feature bgp
Example:
switch(config)# feature bgp
Step 3
(Optional) Displays enabled and disabled features.
show feature
Example:
switch(config)# show feature
Step 4
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
Use the no feature bgp command to disable the BGP feature and remove all associated configuration.
Command
Purpose
no feature bgp
Disables the BGP feature and removes all
associated configuration.
Example:
switch(config)# no feature bgp
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Creating a BGP Instance
You can create a BGP instance and assign a router ID to the BGP instance. See the “BGP Router
Identifier” section on page 5-4. Cisco NX-OS supports 2-byte or 4-byte autonomous system (AS)
numbers in plain-text notation or as.dot notation. See the “4-Byte AS Number Support” section on
page 5-2 for more information.
BEFORE YOU BEGIN
Ensure that you have enabled the BGP feature (see the “Enabling the BGP Feature” section on
page 5-11).
BGP must be able to obtain a router ID (for example, a configured loopback address).
SUMMARY STEPS
1.
configure terminal
2.
router bgp autonomous-system-number
3.
(Optional) router-id ip-address
4.
(Optional) address-family ipv4 {unicast | multicast}
5.
(Optional) network ip-prefix [route-map map-name]
6.
(Optional) show bgp all
7.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router bgp autonomous-system-number
Example:
switch(config)# router bgp 64496
switch(config-router)#
Step 3
router-id ip-address
Example:
switch(config-router)# router-id
192.0.2.255
Step 4
address-family ipv4{unicast | multicast}
Example:
switch(config-router)# address-family
ipv4 unicast
switch(config-router-af)#
Enables BGP and assigns the AS number to the local
BGP speaker. The AS number can be a 16-bit integer
or a 32-bit integer in the form of a higher 16-bit
decimal number and a lower 16-bit decimal number in
xx.xx format.
(Optional) Configures the BGP router ID. This IP
address identifies this BGP speaker. This command
triggers an automatic notification and session reset for
the BGP neighbor sessions.
(Optional) Enters global address family configuration
mode for the IPv4 address family. This command
triggers an automatic notification and session reset for
all BGP neighbors.
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Step 5
Command
Purpose
network ip-prefix [route-map map-name]
(Optional) Specifies a network as local to this
autonomous system and adds it to the BGP routing
table.
Example:
switch(config-router-af)# network
192.0.2.0
Step 6
show bgp all
Example:
switch(config-router-af)# show bgp all
Step 7
copy running-config startup-config
For exterior protocols, the network command controls
which networks are advertised. Interior protocols use
the network command to determine where to send
updates.
(Optional) Displays information about all BGP address
families.
(Optional) Saves this configuration change.
Example:
switch(config-router-af)# copy
running-config startup-config
Use the no router bgp command to remove the BGP process and the associated configuration.
Command
Purpose
no router bgp autonomous-system-number
Deletes the BGP process and the associated
configuration.
Example:
switch(config)# no router bgp 201
This example shows how to enable BGP with the IPv4 unicast address family and manually add one
network to advertise:
switch# configure terminal
switch(config)# router bgp 64496
switch(config-router)# address-family ipv4 unicast
switch(config-router-af)# network 192.0.2.0
switch(config-router-af)# copy running-config startup-config
Restarting a BGP Instance
You can restart a BGP instance and clear all peer sessions for the instance.
To restart a BGP instance and remove all associated peers, use the following command:
Command
Purpose
restart bgp instance-tag
Restarts the BGP instance and resets or
reestablishes all peering sessions.
Example:
switch(config)# restart bgp 201
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Configuring Basic BGP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Shutting Down BGP
You can shut down the BGP protocol and gracefully disable BGP and retain the configuration.
To shut down BGP, use the following command in router configuration mode:
Command
Purpose
shutdown
Gracefully shuts down BGP.
Example:
switch(config-router)# shutdown
Configuring BGP Peers
You can configure a BGP peer within a BGP process. Each BGP peer has an associated keepalive timer
and hold timers. You can set these timers either globally or for each BGP peer. A peer configuration
overrides a global configuration.
Note
You must configure the address family under neighbor configuration mode for each peer.
BEFORE YOU BEGIN
Ensure that you have enabled the BGP feature (see the “Enabling the BGP Feature” section on
page 5-11).
SUMMARY STEPS
1.
configure terminal
2.
router bgp autonomous-system-number
3.
neighbor ip-address remote-as as-number
4.
(Optional) description text
5.
(Optional) timers keepalive-time hold-time
6.
(Optional) shutdown
7.
address-family ipv4 {unicast | multicast}
8.
(Optional) show bgp ipv4 {unicast | multicast} neighbors
9.
(Optional) copy running-config startup-config
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DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router bgp autonomous-system-number
Example:
switch(config)# router bgp 64496
switch(config-router)#
Step 3
neighbor ip-address remote-as as-number
Example:
switch(config-router)# neighbor
209.165.201.1 remote-as 64497
switch(config-router-neighbor)#
Step 4
description text
Example:
switch(config-router-neighbor)#
description Peer Router B
switch(config-router-neighbor)#
Step 5
timers keepalive-time hold-time
Example:
switch(config-router-neighbor)# timers
30 90
Step 6
shutdown
Step 7
address-family ipv4 {unicast |
multicast}
Enables BGP and assigns the AS number to the local
BGP speaker. The AS number can be a 16-bit integer
or a 32-bit integer in the form of a higher 16-bit
decimal number and a lower 16-bit decimal number in
xx.xx format.
Configures the IPv4 address and AS number for a
remote BGP peer. The ip-address format is x.x.x.x.
(Optional) Adds a description for the neighbor. The
description is an alphanumeric string up to 80
characters.
(Optional) Adds the keepalive and hold time BGP
timer values for the neighbor. The range is from 0 to
3600 seconds. The default is 60 seconds for the
keepalive time and 180 seconds for the hold time.
(Optional) Administratively shuts down this BGP
neighbor. This command triggers an automatic
Example:
notification and session reset for the BGP neighbor
switch(config-router-neighbor)# shutdown
sessions.
Enters neighbor address family configuration mode for
the unicast IPv4 address family.
Example:
switch(config-router-neighbor)#
address-family ipv4 unicast
switch(config-router-neighbor-af)#
Step 8
show bgp ipv4 {unicast | multicast}
neighbors
(Optional) Displays information about BGP peers.
Example:
switch(config-router-neighbor-af)# show
bgp ipv4 unicast neighbors
Step 9
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router-neighbor-af) copy
running-config startup-config
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This example shows how to configure a BGP peer:
switch# configure terminal
switch(config)# router bgp 64496
switch(config-router)# neighbor 192.0.2.1 remote-as 64497
switch(config-router-neighbor)# description Peer Router B
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor-af)# copy running-config startup-config
Configuring Dynamic AS Numbers for Prefix Peers
You can configure multiple BGP peers within a BGP process. You can limit BGP session establishment
to a single AS number or multiple AS numbers in a route map.
BGP sessions configured through dynamic AS numbers for prefix peers ignore the ebgp-multihop
command and the disable-connected-check command.
You can change the list of AS numbers in the route map, but you must use the no neighbor command to
change the route-map name. Changes to the AS numbers in the configured route map affect only new
sessions.
BEFORE YOU BEGIN
Ensure that you have enabled the BGP feature (see the “Enabling the BGP Feature” section on
page 5-11).
SUMMARY STEPS
1.
configure terminal
2.
router bgp autonomous-system-number
3.
neighbor prefix remote-as route-map map-name
4.
(Optional) show bgp ipv4 {unicast | multicast} neighbors
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router bgp autonomous-system-number
Example:
switch(config)# router bgp 64496
switch(config-router)#
Enables BGP and assigns the AS number to the local
BGP speaker. The AS number can be a 16-bit integer
or a 32-bit integer in the form of a higher 16-bit
decimal number and a lower 16-bit decimal number in
xx.xx format.
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Step 3
Command
Purpose
neighbor prefix remote-as route-map
map-name
Configures the IPv 4 prefix and a route map for the list
of accepted AS numbers for the remote BGP peers.
The prefix format for IPv4 is x.x.x.x/length. The length
range is from 1 to 32.
Example:
switch(config-router)# neighbor
192.0.2.0/8 remote-as routemap BGPPeers
switch(config-router-neighbor)#
Step 4
show bgp ipv4 {unicast | multicast}
neighbors
The map-name can be any case-sensitive,
alphanumerics string up to 63 characters.
(Optional) Displays information about BGP peers.
Example:
switch(config-router-neighbor-af)# show
bgp ipv4 unicast neighbors
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router-neighbor-af) copy
running-config startup-config
This example shows how to configure dynamic AS numbers for a prefix peer:
switch# configure terminal
switch(config)# route-map BGPPeers
switch(config-route-map)# match as-number 64496, 64501-64510
switch(config-route-map)# match as-number as-path-list List1, List2
switch(config-route-map)# exit
switch(config)# router bgp 64496
switch(config-router)# neighbor 192.0.2.0/8 remote-as route-map BGPPeers
switch(config-router-neighbor)# description Peer Router B
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor-af)# copy running-config startup-config
See Chapter 13, “Configuring Route Policy Manager” for information on route maps.
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Clearing BGP Information
To clear BGP information, use the following commands:
Command
Purpose
clear bgp all {neighbor | * | as-number |
peer-template name | prefix} [vrf vrf-name]
Clears one or more neighbors from all address
families. * clears all neighbors in all address
families. The arguments are as follows:
•
neighbor—IPv4 address of a neighbor.
•
as-number— Autonomous system number.
The AS number can be a 16-bit integer or a
32-bit integer in the form of higher 16-bit
decimal number and a lower 16-bit decimal
number in xx.xx format.
•
name—Peer template name. The name can be
any case-sensitive, alphanumeric string up to
64 characters.
•
prefix—IPv4 prefix. All neighbors within that
prefix are cleared.
•
vrf-name—VRF name. All neighbors in that
VRF are cleared. The name can be any
case-sensitive, alphanumeric string up to 64
characters.
clear bgp all dampening [vrf vrf-name]
Clears route flap dampening networks in all
address families. The vrf-name can be any
case-sensitive, alphanumeric string up to 64
characters.
clear bgp all flap-statistics [vrf vrf-name]
Clears route flap statistics in all address families.
The vrf-name can be any case-sensitive,
alphanumeric string up to 64 characters.
clear bgp ip {unicast | multicast} dampening
[vrf vrf-name]
Clears route flap dampening networks in the
selected address family. The vrf-name can be any
case-sensitive, alphanumeric string up to 64
characters.
clear bgp ip {unicast | multicast} flap-statistics Clears route flap statistics in the selected address
[vrf vrf-name]
family. The vrf-name can be any case-sensitive,
alphanumeric string up to 64 characters.
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Command
Purpose
clear bgp ip {unicast | multicast} {neighbor | * Clears one or more neighbors from the selected
| as-number | peer-template name | prefix} [vrf address family. * clears all neighbors in the
vrf-name]
address family. The arguments are as follows:
•
neighbor—IPv4 address of a neighbor.
•
as-number— Autonomous system number.
The AS number can be a 16-bit integer or a
32-bit integer in the form of higher 16-bit
decimal number and a lower 16-bit decimal
number in xx.xx format.
•
name—Peer template name. The name can be
any case-sensitive, alphanumeric string up to
64 characters.
•
prefix—IPv4 prefix. All neighbors within that
prefix are cleared.
•
vrf-name—VRF name. All neighbors in that
VRF are cleared. The name can be any
case-sensitive, alphanumeric string up to 64
characters.
clear ip bgp {ip {unicast | multicast}}
Clears one or more neighbors. * clears all
{neighbor | * | as-number | peer-template name | neighbors in the address family. The arguments
prefix} [vrf vrf-name]
are as follows:
•
neighbor—IPv4 address of a neighbor.
•
as-number— Autonomous system number.
The AS number can be a 16-bit integer or a
32-bit integer in the form of higher 16-bit
decimal number and a lower 16-bit decimal
number in xx.xx format.
•
name—Peer template name. The name can be
any case-sensitive, alphanumeric string up to
64 characters.
•
prefix—IPv4 prefix. All neighbors within that
prefix are cleared.
•
vrf-name—VRF name. All neighbors in that
VRF are cleared. The name can be any
case-sensitive, alphanumeric string up to 64
characters.
clear ip bgp dampening [ip-neighbor | ip-prefix] Clears route flap dampening in one or more
[vrf vrf-name]
networks. The arguments are as follows:
•
ip-neighbor—IPv4 address of a neighbor.
•
ip-prefix—IPv4. All neighbors within that
prefix are cleared.
•
vrf-name—VRF name. All neighbors in that
VRF are cleared. The name can be any
case-sensitive, alphanumeric string up to 64
characters.
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Command
Purpose
clear ip bgp flap-statistics [ip-neighbor |
ip-prefix] [vrf vrf-name]
Clears route flap statistics in one or more
networks. The arguments are as follows:
•
ip-neighbor—IPv4 address of a neighbor.
•
ip-prefix—IPv4. All neighbors within that
prefix are cleared.
•
vrf-name—VRF name. All neighbors in that
VRF are cleared. The name can be any
case-sensitive, alphanumeric string up to 64
characters.
clear ip mbgp {ip {unicast | multicast}}
Clears one or more neighbors. * clears all
{neighbor | * | as-number | peer-template name | neighbors in the address family. The arguments
prefix} [vrf vrf-name]
are as follows:
•
neighbor—IPv4 address of a neighbor.
•
as-number— Autonomous system number.
The AS number can be a 16-bit integer or a
32-bit integer in the form of higher 16-bit
decimal number and a lower 16-bit decimal
number in xx.xx format.
•
name—Peer template name. The name can be
any case-sensitive, alphanumeric string up to
64 characters.
•
prefix—IPv4 prefix. All neighbors within that
prefix are cleared.
•
vrf-name—VRF name. All neighbors in that
VRF are cleared. The name can be any
case-sensitive, alphanumeric string up to 64
characters.
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Command
Purpose
clear ip mbgp dampening [ip-neighbor |
ip-prefix] [vrf vrf-name]
Clears route flap dampening in one or more
networks. The arguments are as follows:
clear ip mbgp flap-statistics [ip-neighbor |
ip-prefix] [vrf vrf-name]
•
ip-neighbor—IPv4 address of a neighbor.
•
ip-prefix—IPv4. All neighbors within that
prefix are cleared.
•
vrf-name—VRF name. All neighbors in that
VRF are cleared. The name can be any
case-sensitive, alphanumeric string up to 64
characters.
Clears route flap statistics one or more networks.
The arguments are as follows:
•
ip-neighbor—IPv4 address of a neighbor.
•
ip-prefix—IPv4. All neighbors within that
prefix are cleared.
•
vrf-name—VRF name. All neighbors in that
VRF are cleared. The name can be any
case-sensitive, alphanumeric string up to 64
characters.
Verifying the Basic BGP Configuration
To display the BGP configuration information, perform the following tasks:
Command
Purpose
show bgp all [summary] [vrf vrf-name]
Displays the BGP information for all address
families.
show bgp convergence [vrf vrf-name]
Displays the BGP information for all address
families.
show bgp ip {unicast | multicast} [ip-address]
community {regexp expression | [community]
[no-advertise] [no-export]
[no-export-subconfed]} [vrf vrf-name]
Displays the BGP routes that match a BGP
community.
show bgp [vrf vrf-name] ip {unicast | multicast} Displays the BGP routes that match a BGP
[ip-address] community-list list-name [vrf
community list.
vrf-name]
show bgp ip {unicast | multicast} [ip-address]
extcommunity {regexp expression | generic
[non-transitive | transitive] aa4:nn
[exact-match]} [vrf vrf-name]
Displays the BGP routes that match a BGP
extended community.
show bgp ip {unicast | multicast} [ip-address] Displays the BGP routes that match a BGP
extcommunity-list list-name [exact-match] [vrf extended community list.
vrf-name]
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Command
Purpose
show bgp ip {unicast | multicast} [ip-address]
{dampening dampened-paths [regexp
expression]} [vrf vrf-name]
Displays the information for BGP route
dampening. Use the clear bgp dampening
command to clear the route flap dampening
information.
show bgp ip {unicast | multicast} [ip-address] Displays the BGP route history paths.
history-paths [regexp expression] [vrf vrf-name]
show bgp ip {unicast | multicast} [ip-address]
filter-list list-name [vrf vrf-name]
Displays the information for the BGP filter list.
show bgp ip {unicast | multicast} [ip-address]
neighbors [ip-address] [vrf vrf-name]
Displays the information for BGP peers. Use the
clear bgp neighbors command to clear these
neighbors.
show bgp ip {unicast | multicast} [ip-address]
{nexthop | nexthop-database} [vrf vrf-name]
Displays the information for the BGP route next
hop.
show bgp paths
Displays the BGP path information.
show bgp ip {unicast | multicast} [ip-address]
policy name [vrf vrf-name]
Displays the BGP policy information. Use the
clear bgp policy command to clear the policy
information.
show bgp ip {unicast | multicast} [ip-address]
prefix-list list-name [vrf vrf-name]
Displays the BGP routes that match the prefix list.
show bgp ip {unicast | multicast} [ip-address]
received-paths [vrf vrf-name]
Displays the BGP paths stored for soft
reconfiguration.
show bgp ip {unicast | multicast} [ip-address]
regexp expression [vrf vrf-name]
Displays the BGP routes that match the AS_path
regular expression.
show bgp ip {unicast | multicast} [ip-address]
route-map map-name [vrf vrf-name]
Displays the BGP routes that match the route
map.
show bgp peer-policy name [vrf vrf-name]
Displays the information about BGP peer
policies.
show bgp peer-session name [vrf vrf-name]
Displays the information about BGP peer
sessions.
show bgp peer-template name [vrf vrf-name]
Displays the information about BGP peer
templates. Use the clear bgp peer-template
command to clear all neighbors in a peer template.
show bgp process
Displays the BGP process information.
show ip bgp options
Displays the BGP status and configuration
information. This command has multiple options.
See the Cisco Nexus 3000 Series Command
Reference,, for more information.
show ip mbgp options
Displays the BGP status and configuration
information. This command has multiple options.
See the Cisco Nexus 3000 Series Command
Reference,, for more information.
show running-configuration bgp
Displays the current running BGP configuration.
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Displaying BGP Statistics
To display BGP statistics, use the following commands:
Command
Purpose
show bgp ip {unicast | multicast}
[ip-address] flap-statistics [vrf vrf-name]
Displays the BGP route flap statistics. Use the clear bgp
flap-statistics command to clear these statistics.
show bgp sessions [vrf vrf-name]
Displays the BGP sessions for all peers. Use the clear
bgp sessions command to clear these statistics.
show bgp sessions [vrf vrf-name]
Displays the BGP sessions for all peers. Use the clear
bgp sessions command to clear these statistics.
show bgp statistics
Displays the BGP statistics.
Configuration Examples for Basic BGP
This example shows a basic BGP configuration:
feature bgp
router bgp 64496
neighbor 2001:ODB8:0:1::55 remote-as 64496
address-family ipv4 unicast
next-hop-self
Related Topics
The following topics relate to BGP:
•
Chapter 13, “Configuring Route Policy Manager.”
Where to Go Next
See Chapter 6, “Configuring Advanced BGP” for details on the following features:
•
Peer templates
•
Route redistribution
•
Route maps
Additional References
For additional information related to implementing BGP, see the following sections:
•
Related Documents, page 5-24
•
MIBs, page 5-24
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Feature History for BGP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Related Documents
Related Topic
Document Title
BGP CLI commands
Cisco Nexus 3000 Series Command Reference,
MIBs
MIBs
MIBs Link
BGP4-MIB
To locate and download MIBs, go to the following URL:
CISCO-BGP4-MIB
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
Feature History for BGP
Table 5-3 lists the release history for this feature.
Table 5-3
Feature History for BGP
Feature Name
Releases
Feature Information
BGP
5.0(3)U1(1)
This feature was introduced.
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CH A P T E R
6
Configuring Advanced BGP
This chapter describes how to configure advanced features of the Border Gateway Protocol (BGP) on the
Cisco NX-OS switch.
This chapter includes the following sections:
•
Information About Advanced BGP, page 6-1
•
Licensing Requirements for Advanced BGP, page 6-9
•
Prerequisites for BGP, page 6-10
•
Guidelines and Limitations for BGP, page 6-10
•
Default Settings, page 6-10
•
Configuring Advanced BGP, page 6-11
•
Verifying the Advanced BGP Configuration, page 6-39
•
Displaying BGP Statistics, page 6-40
•
Related Topics, page 6-40
•
Additional References, page 6-41
•
Feature History for BGP, page 6-41
Information About Advanced BGP
BGP is an interdomain routing protocol that provides loop-free routing between organizations or
autonomous systems. Cisco NX-OS supports BGP version 4. BGP version 4 includes multiprotocol
extensions that allow BGP to carry routing information for IP multicast routes and multiple Layer 3
protocol address families. BGP uses TCP as a reliable transport protocol to create TCP sessions with
other BGP-enabled switches called BGP peers. When connecting to an external organization, the router
creates external BGP (eBGP) peering sessions. BGP peers within the same organization exchange
routing information through internal BGP (iBGP) peering sessions.
This section includes the following topics:
•
Peer Templates, page 6-2
•
Authentication, page 6-2
•
Route Policies and Resetting BGP Sessions, page 6-3
•
eBGP, page 6-3
•
iBGP, page 6-3
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Information About Advanced BGP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
•
Capabilities Negotiation, page 6-5
•
Route Dampening, page 6-6
•
Load Sharing and Multipath, page 6-6
•
Route Aggregation, page 6-7
•
BGP Conditional Advertisement, page 6-7
•
BGP Next-Hop Address Tracking, page 6-7
•
Route Redistribution, page 6-8
•
BFD, page 6-8
•
Tuning BGP, page 6-8
•
Multiprotocol BGP, page 6-9
•
Virtualization Support, page 6-9
Peer Templates
BGP peer templates allow you to create blocks of common configuration that you can reuse across
similar BGP peers. Each block allows you to define a set of attributes that a peer then inherits. You can
choose to override some of the inherited attributes as well, making it a very flexible scheme for
simplifying the repetitive nature of BGP configurations.
Cisco NX-OS implements three types of peer templates:
•
The peer-session template defines BGP peer session attributes, such as the transport details, remote
autonomous system number of the peer, and session timers. A peer-session template can also inherit
attributes from another peer-session template (with locally defined attributes that override the
attributes from an inherited peer-session).
•
A peer-policy template defines the address-family dependent policy aspects for a peer including the
inbound and outbound policy, filter-lists, and prefix-lists. A peer-policy template can inherit from a
set of peer-policy templates. Cisco NX-OS evaluates these peer-policy templates in the order
specified by the preference value in the inherit configuration. The lowest number is preferred over
higher numbers.
•
The peer template can inherit the peer-session and peer-policy templates to allow for simplified peer
definitions. It is not mandatory to use a peer template but it can simplify the BGP configuration by
providing reusable blocks of configuration.
Authentication
You can configure authentication for a BGP neighbor session. This authentication method adds an MD5
authentication digest to each TCP segment sent to the neighbor to protect BGP against unauthorized
messages and TCP security attacks.
Note
The MD5 password must be identical between BGP peers.
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Configuring Advanced BGP
Information About Advanced BGP
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Route Policies and Resetting BGP Sessions
You can associate a route policy to a BGP peer. Route policies use route maps to control or modify the
routes that BGP recognizes. You can configure a route policy for inbound or outbound route updates.
The route policies can match on different criteria, such as a prefix or AS_path attribute, and selectively
accept or deny the routes. Route policies can also modify the path attributes.
When you change a route policy applied to a BGP peer, you must reset the BGP sessions for that peer.
Cisco NX-OS supports the following three mechanisms to reset BGP peering sessions:
Note
•
Hard reset—A hard reset tears down the specified peering sessions, including the TCP connection,
and deletes routes coming from the specified peer. This option interrupts packet flow through the
BGP network. Hard reset is disabled by default.
•
Soft reconfiguration inbound—A soft reconfiguration inbound triggers routing updates for the
specified peer without resetting the session. You can use this option if you change an inbound route
policy. Soft reconfiguration inbound saves a copy of all routes received from the peer before
processing the routes through the inbound route policy. If you change the inbound route policy,
Cisco NX-OS passes these stored routes through the modified inbound route policy to update the
route table without tearing down existing peering sessions. Soft reconfiguration inbound can use
significant memory resources to store the unfiltered BGP routes. Soft reconfiguration inbound is
disabled by default.
•
Route Refresh—A route refresh updates the inbound routing tables dynamically by sending route
refresh requests to supporting peers when you change an inbound route policy. The remote BGP peer
responds with a new copy of its routes that the local BGP speaker processes with the modified route
policy. Cisco NX-OS automatically sends an outbound route refresh of prefixes to the peer.
•
BGP peers advertise the route refresh capability as part of the BGP capability negotiation when
establishing the BGP peer session. Route refresh is the preferred option and enabled by default.
BGP also uses route maps for route redistribution, route aggregation, route dampening, and other
features. See Chapter 13, “Configuring Route Policy Manager,” for more information on route maps.
eBGP
External BGP (eBGP) allows you to connect BGP peers from different autonomous systems to exchange
routing updates. Connecting to external networks enables traffic from your network to be forwarded to
other networks and across the Internet.
You should use loopback interfaces for establishing eBGP peering sessions because loopback interfaces
are less susceptible to interface flapping. An interface flap occurs when the interface is administratively
brought up or down because of a failure or maintenance issue. See the “Configuring eBGP” section on
page 6-22 for information on multihop, fast external failovers, and limiting the size of the AS-path
attribute.
iBGP
Internal BGP (iBGP) allows you to connect BGP peers within the same autonomous system. You can use
iBGP for multihomed BGP networks (networks that have more than one connection to the same external
autonomous system).
Figure 6-1 shows an iBGP network within a larger BGP network.
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Figure 6-1
iBGP Network
AS10
Z
A
C
eBGP
iBGP
iBGP
iBGP
iBGP
B
iBGP
185055
AS20
D
iBGP networks are fully meshed. Each iBGP peer has a direct connection to all other iBGP peers to
prevent network loops.
Note
You should configure a separate interior gateway protocol in the iBGP network.
This section includes the following topics:
•
AS Confederations, page 6-4
•
Route Reflector, page 6-5
AS Confederations
A fully meshed iBGP network becomes complex as the number of iBGP peers grows. You can reduce
the iBGP mesh by dividing the autonomous system into multiple subautonomous systems and grouping
them into a single confederation. A confederation is a group of iBGP peers that use the same autonomous
system number to communicate to external networks. Each subautonomous system is fully meshed
within itself and has a few connections to other subautonomous systems in the same confederation.
Figure 6-2 shows the BGP network from Figure 6-1, split into two subautonomous systems and one
confederation.
Figure 6-2
AS Confederation
AS10
Z
AS1 A
eBGP
AS2 C
Confederation
peers
iBGP
iBGP
B
D
185056
AS20
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In this example, AS10 is split into two subautonomous systems, AS1 and AS2. Each subautonomous
system is fully meshed, but there is only one link between the subautonomous systems. By using AS
confederations, you can reduce the number of links compared to the fully meshed autonomous system
in Figure 6-1.
Route Reflector
You can alternately reduce the iBGP mesh by using a route reflector configuration. route reflectors pass
learned routes to neighbors so that all iBGP peers do not need to be fully meshed.
Figure 6-1 shows a simple iBGP configuration with four meshed iBGP speakers (router A, B, C, and D).
Without route reflectors, when router A receives a route from an external neighbor, it advertises the route
to all three iBGP neighbors.
When you configure an iBGP peer to be a route reflector, it becomes responsible for passing iBGP
learned routes to a set of iBGP neighbors.
In Figure 6-3, router B is the route reflector. When the route reflector receives routes advertised from
router A, it advertises (reflects) the routes to routers C and D. Router A no longer has to advertise to both
routers C and D.
Figure 6-3
Route Reflector
AS20
AS10
Z
A
C
eBGP
B
D
185057
iBGP
iBGP
The route reflector and its client peers form a cluster. You do not have to configure all iBGP peers to act
as client peers of the route reflector. You must configure any nonclient peer as fully meshed to guarantee
that complete BGP updates reach all peers.
Capabilities Negotiation
A BGP speaker can learn about BGP extensions supported by a peer by using the capabilities negotiation
feature. Capabilities negotiation allows BGP to use only the set of features supported by both BGP peers
on a link.
If a BGP peer does not support capabilities negotiation, Cisco NX-OS will attempt a new session to the
peer without capabilities negotiation if you have configured the address family as IPv4.
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Route Dampening
Route dampening is a BGP feature that minimizes the propagation of flapping routes across an
internetwork. A route flaps when it alternates between the available and unavailable states in rapid
succession.
For example, consider a network with three BGP autonomous systems: AS1, AS2, and AS3. Suppose
that a route in AS1 flaps (it becomes unavailable). Without route dampening, AS1 sends a withdraw
message to AS2. AS2 propagates the withdrawal message to AS3. When the flapping route reappears,
AS1 sends an advertisement message to AS2, which sends the advertisement to AS3. If the route
repeatedly becomes unavailable, and then available, AS1 sends many withdrawal and advertisement
messages that propagate through the other autonomous systems.
Route dampening can minimize flapping. Suppose that the route flaps. AS2 (in which route dampening
is enabled) assigns the route a penalty of 1000. AS2 continues to advertise the status of the route to
neighbors. Each time that the route flaps, AS2 adds to the penalty value. When the route flaps so often
that the penalty exceeds a configurable suppression limit, AS2 stops advertising the route, regardless of
how many times that it flaps. The route is now dampened.
The penalty placed on the route decays until the reuse limit is reached. At that time, AS2 advertises the
route again. When the reuse limit is at 50 percent, AS2 removes the dampening information for the route.
Note
The router does not apply a penalty to a resetting BGP peer when route dampening is enabled, even
though the peer reset withdraws the route.
Load Sharing and Multipath
BGP can install multiple equal-cost eBGP or iBGP paths into the routing table to reach the same
destination prefix. Traffic to the destination prefix is then shared across all the installed paths.
The BGP best-path algorithm considers the paths as equal-cost paths if the following attributes are
identical:
•
Weight
•
Local preference
•
AS_path
•
Origin code
•
Multi-exit discriminator (MED)
•
IGP cost to the BGP next hop
BGP selects only one of these multiple paths as the best path and advertises the path to the BGP peers.
Note
Paths received from different AS confederations are considered as equal-cost paths if the external
AS_path values and the other attributes are identical.
Note
When you configure a route reflector for iBGP multipath, and the route reflector advertises the selected
best path to its peers, the next hop for the path is not modified.
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Route Aggregation
You can configure aggregate addresses. Route aggregation simplifies route tables by replacing a number
of more specific addresses with an address that represents all the specific addresses. For example, you
can replace these three more specific addresses, 10.1.1.0/24, 10.1.2.0/24, and 10.1.3.0/24 with one
aggregate address, 10.1.0.0/16.
Aggregate prefixes are present in the BGP route table so that fewer routs are advertised.
Note
Cisco NX-OS does not support automatic route aggregation.
Route aggregation can lead to forwarding loops. To avoid this problem, when BGP generates an
advertisement for an aggregate address, it automatically installs a summary discard route for that
aggregate address in the local routing table. BGP sets the administrative distance of the summary discard
to 220 and sets the route type to discard. BGP does not use discard routes for next-hop resolution.
BGP Conditional Advertisement
BGP conditional advertisement allows you to configure BGP to advertise or withdraw a route based on
whether or not a prefix exists in the BGP table. This feature is useful, for example, in multihomed
networks, in which you want BGP to advertise some prefixes to one of the providers only if information
from the other provider is not present.
Consider an example network with three BGP autonomous systems: AS1, AS2, and AS3, where AS1 and
AS3 connect to the Internet and to AS2. Without conditional advertisement, AS2 propagates all routes
to both AS1 and AS3. With conditional advertisement, you can configure AS2 to advertise certain routes
to AS3 only if routes from AS1 do not exist (if for example, the link to AS1 fails).
BGP conditional advertisement adds an exist or not-exist test to each route that matches the configured
route map. See the “Configuring BGP Conditional Advertisement” section on page 6-29 for more
information.
BGP Next-Hop Address Tracking
BGP monitors the next-hop address of installed routes to verify next-hop reachability and to select,
install, and validate the BGP best path. BGP next-hop address tracking speeds up this next-hop
reachability test by triggering the verification process when routes change in the RIB that may affect
BGP next-hop reachability.
BGP receives notifications from the RIB when next-hop information changes (event-driven
notifications). BGP is notified when any of the following events occurs:
•
Next hop becomes unreachable.
•
Next hop becomes reachable.
•
Fully recursed IGP metric to the next hop changes.
•
First hop IP address or first hop interface changes.
•
Next hop becomes connected.
•
Next hop becomes unconnected.
•
Next hop becomes a local address.
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•
Note
Next hop becomes a nonlocal address.
Reachability and recursed metric events trigger a best-path recalculation.
Event notifications from the RIB are classified as critical and noncritical. Notifications for critical and
noncritical events are sent in separate batches. However, a noncritical event is sent with the critical
events if the noncritical event is pending and there is a request to read the critical events.
•
Critical events are related to the reachability (reachable and unreachable), connectivity (connected
and unconnected), and locality (local and nonlocal) of the next hops. Notifications for these events
are not delayed.
•
Noncritical events include only the IGP metric changes.
See the “Configuring BGP Next-Hop Address Tracking” section on page 6-21 for more information.
Route Redistribution
You can configure BGP to redistribute static routes or routes from other protocols. You configure a route
policy with the redistribution to control which routes are passed into BGP. A route policy allows you to
filter routes based on attributes such as the destination, origination protocol, route type, route tag, and
so on. See Chapter 13, “Configuring Route Policy Manager,” for more information.
BFD
This feature supports bidirectional forwarding detection (BFD). BFD is a detection protocol designed to
provide fast forwarding-path failure detection times. BFD provides subsecond failure detection between
two adjacent devices and can be less CPU-intensive than protocol hello messages because some of the
BFD load can be distributed onto the data plane on supported modules.
BFD for BGP is supported on eBGP single-hop peers and iBGP single-hop peers. For iBGP single-hop
peers using BFD, you must configure the update-source option in neighbor configuration mode. BFD is
not supported on other iBGP peers or for multihop eBGP peers.
BFD is supported for the following types of interfaces:
•
L3 physical and subinterface
•
L3 port-channel and subinterface
•
SVI
BFD for BGP does not support authentication or per-link BFD sessions on a port-channel.
See Chapter 7, “Configuring Bidirectional Forwarding Detection for BGP” for more information.
Tuning BGP
You can modify the default behavior of BGP through BGP timers and by adjusting the best-path
algorithm.
This section includes the following topics:
•
BGP Timers, page 6-9
•
Tuning the Best-Path Algorithm, page 6-9
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BGP Timers
BGP uses different types of timers for neighbor session and global protocol events. Each established
session has a minimum of two timers for sending periodic keepalive messages and for timing out
sessions when peer keepalives do not arrive within the expected time. In addition, there are other timers
for handling specific features. Typically, you configure these timers in seconds. The timers include a
random adjustment so that the same timers on different BGP peers trigger at different times.
Tuning the Best-Path Algorithm
You can modify the default behavior of the best-path algorithm through optional configuration
parameters, including changing how the algorithm handles the MED attribute and the router ID.
Multiprotocol BGP
BGP on Cisco NX-OS supports multiple address families. Multiprotocol BGP (MP-BGP) carries
different sets of routes depending on the address family. For example, BGP can carry one set of routes
for IPv4 unicast routing, and one set of routes for IPv4 multicast routing. You can use MP-BGP for
reverse-path forwarding (RPF) checks in IP multicast networks.
Note
Because Multicast BGP does not propagate multicast state information, you need a multicast protocol,
such as Protocol Independent Multicast (PIM).
Use the router address-family and neighbor address-family configuration modes to support
multiprotocol BGP configurations. MP-BGP maintains separate RIBs for each configured address
family, such as a unicast RIB and a multicast RIB for BGP.
A multiprotocol BGP network is backward compatible but BGP peers that do not support multiprotocol
extensions cannot forward routing information, such as address family identifier information, that the
multiprotocol extensions carry.
Virtualization Support
Cisco NX-OS supports multiple instances of BGP that run on the same system. BGP supports Virtual
Routing and Forwarding instances (VRFs).
By default, Cisco NX-OS places you in the default VRF unless you specifically configure another VRF.
See Chapter 11, “Configuring Layer 3 Virtualization.”
Licensing Requirements for Advanced BGP
The following table shows the licensing requirements for this feature:
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Product
License Requirement
Cisco NX-OS
BGP requires an LAN Enterprise Services license. For a complete explanation of the Cisco NX-OS licensing
scheme and how to obtain and apply licenses, see the Cisco NX-OS Licensing Guide.
Make sure the LAN Base Services license is installed on the switch to enable Layer 3 interfaces.
Note
Prerequisites for BGP
BGP has the following prerequisites:
•
You must enable the BGP feature (see the “Enabling the BGP Feature” section on page 5-11).
•
You should have a valid router ID configured on the system.
•
You must have an AS number, either assigned by a Regional Internet Registry (RIR) or locally
administered.
•
You must have reachability (such as an interior gateway protocol (IGP), a static route, or a direct
connection) to the peer that you are trying to make a neighbor relationship with.
•
You must explicitly configure an address family under a neighbor for the BGP session
establishment.
Guidelines and Limitations for BGP
BGP has the following configuration guidelines and limitations:
•
The dynamic AS number prefix peer configuration overrides the individual AS number
configuration inherited from a BGP template.
•
If you configure a dynamic AS number for prefix peers in an AS confederation, BGP establishes
sessions with only the AS numbers in the local confederation.
•
BGP sessions created through a dynamic AS number prefix peer ignore any configured eBGP
multihop time-to-live (TTL) value or a disabled check for directly connected peers.
•
Configure a router ID for BGP to avoid automatic router ID changes and session flaps.
•
Use the maximum-prefix configuration option per peer to restrict the number of routes received and
system resources used.
•
Configure the update-source to establish a session with eBGP multihop sessions.
•
Specify a BGP route map if you configure redistribution.
•
Configure the BGP router ID within a VRF.
•
If you decrease the keepalive and hold timer values, the network might experience session flaps.
Default Settings
Table 6-1 lists the default settings for BGP parameters.
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Table 6-1
Default BGP Parameters
Parameters
Default
BGP feature
disabled
keep alive interval
60 seconds
hold timer
180 seconds
Configuring Advanced BGP
This section describes how to configure advanced BGP and includes the following topics:
Note
•
Configuring BGP Session Templates, page 6-12
•
Configuring BGP Peer-Policy Templates, page 6-14
•
Configuring BGP Peer Templates, page 6-16
•
Configuring Prefix Peering, page 6-19
•
Configuring BGP Authentication, page 6-20
•
Resetting a BGP Session, page 6-20
•
Modifying the Next-Hop Address, page 6-21
•
Configuring BGP Next-Hop Address Tracking, page 6-21
•
Configuring Next-Hop Filtering, page 6-22
•
Disabling Capabilities Negotiation, page 6-22
•
Configuring eBGP, page 6-22
•
Configuring AS Confederations, page 6-25
•
Configuring Route Reflector, page 6-25
•
Configuring Route Dampening, page 6-27
•
Configuring Load Sharing and ECMP, page 6-28
•
Configuring Maximum Prefixes, page 6-28
•
Configuring Dynamic Capability, page 6-28
•
Configuring Aggregate Addresses, page 6-29
•
Configuring BGP Conditional Advertisement, page 6-29
•
Configuring Route Redistribution, page 6-31
•
Configuring Multiprotocol BGP, page 6-33
•
Tuning BGP, page 6-34
•
Configuring Virtualization, page 6-37
If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature
might differ from the Cisco IOS commands that you would use.
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Configuring BGP Session Templates
You can use BGP session templates to simplify BGP configuration for multiple BGP peers with similar
configuration needs. BGP templates allow you to reuse common configuration blocks. You configure
BGP templates first, and then apply these templates to BGP peers.
With BGP session templates, you can configure session attributes such as inheritance, passwords, timers,
and security.
A peer-session template can inherit from one other peer-session template. You can configure the second
template to inherit from a third template. The first template also inherits this third template. This indirect
inheritance can continue for up to seven peer-session templates.
Any attributes configured for the neighbor take priority over any attributes inherited by that neighbor
from a BGP template.
BEFORE YOU BEGIN
Ensure that you have enabled the BGP feature (see the “Enabling the BGP Feature” section on
page 5-11).
Note
When editing a template, you can use the no form of a command at either the peer or template level to
explicitly override a setting in a template. You must use the default form of the command to reset that
attribute to the default state.
SUMMARY STEPS
1.
configure terminal
2.
router bgp autonomous-system-number
3.
template peer-session template-name
4.
password number password
5.
timers keepalive hold
6.
exit
7.
neighbor ip-address remote-as as-number
8.
inherit peer-session template-name
9.
(Optional) description text
10. (Optional) show bgp peer-session template-name
11. (Optional) copy running-config startup-config
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DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router bgp autonomous-system-number
Example:
switch(config)# router bgp 65536
switch(config-router)#
Step 3
template peer-session template-name
Enables BGP and assigns the autonomous system
number to the local BGP speaker.
Enters peer-session template configuration mode.
Example:
switch(config-router)# template
peer-session BaseSession
switch(config-router-stmp)#
Step 4
password number password
Example:
switch(config-router-stmp)# password 0
test
Step 5
timers keepalive hold
Example:
switch(config-router-stmp)# timers 30 90
Step 6
(Optional) Adds the clear text password test to the
neighbor. The password is stored and displayed in type
3 encrypted form (3DES).
(Optional) Adds the BGP keepalive and holdtimer
values to the peer-session template.
The default keepalive interval is 60. The default hold
time is 180.
Exits peer-session template configuration mode.
exit
Example:
switch(config-router-stmp)# exit
switch(config-router)#
Step 7
neighbor ip-address remote-as as-number
Example:
switch(config-router)# neighbor
192.168.1.2 remote-as 65536
switch(config-router-neighbor)#
Step 8
inherit peer-session template-name
Places the router in the neighbor configuration mode
for BGP routing and configures the neighbor IP
address.
Applies a peer-session template to the peer.
Example:
switch(config-router-neighbor)# inherit
peer-session BaseSession
switch(config-router-neighbor)
Step 9
(Optional) Adds a description for the neighbor.
description text
Example:
switch(config-router-neighbor)#
description Peer Router A
switch(config-router-neighbor)
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Step 10
Command
Purpose
show bgp peer-session template-name
(Optional) Displays the peer-policy template.
Example:
switch(config-router-neighbor)# show bgp
peer-session BaseSession
Step 11
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router-neighbor)# copy
running-config startup-config
Use the show bgp neighbor command to see the template applied. See the Cisco Nexus 3000 Series
Command Reference,, for details on all commands available in the template.
This example shows how to configure a BGP peer-session template and apply it to a BGP peer:
switch# configure terminal
switch(config)# router bgp 65536
switch(config-router)# template peer-session BaseSession
switch(config-router-stmp)# timers 30 90
switch(config-router-stmp)# exit
switch(config-router)# neighbor 192.168.1.2 remote-as 65536
switch(config-router-neighbor)# inherit peer-session BaseSession
switch(config-router-neighbor)# description Peer Router A
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor)# copy running-config startup-config
Configuring BGP Peer-Policy Templates
You can configure a peer-policy template to define attributes for a particular address family. You assign
a preference to each peer-policy template and these templates are inherited in the order specified, for up
to five peer-policy templates in a neighbor address family.
Cisco NX-OS evaluates multiple peer policies for an address family using the preference value. The
lowest preference value is evaluated first. Any attributes configured for the neighbor take priority over
any attributes inherited by that neighbor from a BGP template.
Peer-policy templates can configure address family-specific attributes such as AS-path filter lists, prefix
lists, route reflection, and soft reconfiguration.
BEFORE YOU BEGIN
Ensure that you have enabled the BGP feature (see the “Enabling the BGP Feature” section on
page 5-11).
Note
When editing a template, you can use the no form of a command at either the peer or template level to
explicitly override a setting in a template. You must use the default form of the command to reset that
attribute to the default state.
SUMMARY STEPS
1.
configure terminal
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2.
router bgp autonomous-system-number
3.
template peer-policy template-name
4.
advertise-active-only
5.
maximum-prefix number
6.
exit
7.
neighbor ip-address remote-as as-number
8.
address-family ipv4 {multicast | unicast}
9.
inherit peer-policy template-name preference
10. (Optional) show bgp peer-policy template-name
11. (Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router bgp autonomous-system-number
Example:
switch(config)# router bgp 65536
switch(config-router)#
Step 3
template peer-policy template-name
Enables BGP and assigns the autonomous system
number to the local BGP speaker.
Creates a peer-policy template.
Example:
switch(config-router)# template
peer-policy BasePolicy
switch(config-router-ptmp)#
Step 4
advertise-active-only
(Optional) Advertises only active routes to the peer.
Example:
switch(config-router-ptmp)#
advertise-active-only
Step 5
maximum-prefix number
Example:
switch(config-router-ptmp)#
maximum-prefix 20
Step 6
(Optional) Sets the maximum number of prefixes
allowed from this peer.
Exits peer-policy template configuration mode.
exit
Example:
switch(config-router-ptmp)# exit
switch(config-router)#
Step 7
neighbor ip-address remote-as as-number
Example:
switch(config-router)# neighbor
192.168.1.2 remote-as 65536
switch(config-router-neighbor)#
Places the router in neighbor configuration mode for
BGP routing and configures the neighbor IP address.
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Step 8
Command
Purpose
address-family ipv4 {multicast |
unicast}
Enters global address family configuration mode for
the IPv4 address family.
Example:
switch(config-router-neighbor)#
address-family ipv4 unicast
switch(config-router-neighbor-af)#
Step 9
inherit peer-policy template-name
preference
Example:
switch(config-router-neighbor-af)#
inherit peer-policy BasePolicy 1
Step 10
show bgp peer-policy template-name
Applies a peer-policy template to the peer address
family configuration and assigns the preference value
for this peer policy.
(Optional) Displays the peer-policy template.
Example:
switch(config-router-neighbor-af)# show
bgp peer-policy BasePolicy
Step 11
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router-neighbor-af)# copy
running-config startup-config
Use the show bgp neighbor command to see the template applied. See the Cisco Nexus 3000 Series
Command Reference,, for details on all commands available in the template.
This example shows how to configure a BGP peer-session template and apply it to a BGP peer:
This example shows how to configure a BGP peer-policy template and apply it to a BGP peer:
switch# configure terminal
switch(config)# router bgp 65536
switch(config-router)# template peer-session BasePolicy
switch(config-router-ptmp)# maximum-prefix 20
switch(config-router-ptmp)# exit
switch(config-router)# neighbor 192.168.1.1 remote-as 65536
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor-af)# inherit peer-policy BasePolicy
switch(config-router-neighbor-af)# copy running-config startup-config
Configuring BGP Peer Templates
You can configure BGP peer templates to combine session and policy attributes in one reusable
configuration block. Peer templates can also inherit peer-session or peer-policy templates. Any attributes
configured for the neighbor take priority over any attributes inherited by that neighbor from a BGP
template. You configure only one peer template for a neighbor, but that peer template can inherit
peer-session and peer-policy templates.
Peer templates support session and address family attributes, such as eBGP multihop time-to-live,
maximum prefix, next-hop self, and timers.
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BEFORE YOU BEGIN
Ensure that you have enabled the BGP feature (see the “Enabling the BGP Feature” section on
page 5-11).
Note
When editing a template, you can use the no form of a command at either the peer or template level to
explicitly override a setting in a template. You must use the default form of the command to reset that
attribute to the default state.
SUMMARY STEPS
1.
configure terminal
2.
router bgp autonomous-system-number
3.
template peer template-name
4.
(Optional) inherit peer-session template-name
5.
(Optional) address-family ipv4 {multicast | unicast}
6.
(Optional) inherit peer template-name
7.
exit
8.
(Optional) timers keepalive hold
9.
exit
10. neighbor ip-address
11. inherit peer template-name
12. (Optional) timers keepalive hold
13. (Optional) show bgp peer-template template-name
14. (Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router bgp autonomous-system-number
Example:
switch(config)# router bgp 65536
Step 3
template peer template-name
Enters BGP mode and assigns the autonomous system
number to the local BGP speaker.
Enters peer template configuration mode.
Example:
switch(config-router)# template peer
BasePeer
switch(config-router-neighbor)#
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Step 4
Command
Purpose
inherit peer-session template-name
(Optional) Inherits a peer-session template in the peer
template.
Example:
switch(config-router-neighbor)# inherit
peer-session BaseSession
Step 5
address-family ipv4{multicast | unicast}
Example:
switch(config-router-neighbor)#
address-family ipv4 unicast
switch(config-router-neighbor-af)#
Step 6
inherit peer template-name
Example:
switch(config-router-neighbor-af)#
inherit peer BasePolicy
Step 7
exit
Example:
switch(config-router-neighbor-af)# exit
switch(config-router-neighbor)#
Step 8
Step 9
(Optional) Configures the global address family
configuration mode for the IPv4 address family.
(Optional) Applies a peer template to the neighbor
address family configuration.
Exits BGP neighbor address family configuration
mode.
timers keepalive hold
(Optional) Adds the BGP timer values to the peer.
Example:
switch(config-router-neighbor)# timers
45 100
These values override the timer values in the
peer-session template, BaseSession.
exit
Exits BGP peer template configuration mode.
Example:
switch(config-router-neighbor)# exit
switch(config-router)#
Step 10
neighbor ip-address remote-as as-number
Example:
switch(config-router)# neighbor
192.168.1.2 remote-as 65536
switch(config-router-neighbor)#
Step 11
inherit peer template-name
Places the router in neighbor configuration mode for
BGP routing and configures the neighbor IP address.
Inherits the peer template.
Example:
switch(config-router-neighbor)# inherit
peer BasePeer
Step 12
Step 13
timers keepalive hold
(Optional) Adds the BGP timer values to this neighbor.
Example:
switch(config-router-neighbor)# timers
60 120
These values override the timer values in the peer
template and the peer-session template.
show bgp peer-template template-name
(Optional) Displays the peer template.
Example:
switch(config-router-neighbor-af)# show
bgp peer-template BasePeer
Step 14
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router-neighbor-af)# copy
running-config startup-config
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Use the show bgp neighbor command to see the template applied. See the Cisco Nexus 3000 Series
Command Reference,, for details on all commands available in the template.
This example shows how to configure a BGP peer template and apply it to a BGP peer:
switch# configure terminal
switch(config)# router bgp 65536
switch(config-router)# template peer BasePeer
switch(config-router-neighbor)# inherit peer-session BaseSession
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor-af)# inherit peer-policy BasePolicy 1
switch(config-router-neighbor-af)# exit
switch(config-router-neighbor)# exit
switch(config-router)# neighbor 192.168.1.2 remote-as 65536
switch(config-router-neighbor)# inherit peer BasePeer
switch(config-router-neighbor)# copy running-config startup-config
Configuring Prefix Peering
BGP supports the definition of a set of peers using a prefix for both IPv4. This feature allows you to not
have to add each neighbor to the configuration.
When defining a prefix peering, you must specify the remote AS number with the prefix. BGP accepts
any peer that connects from that prefix and autonomous system if the prefix peering does not exceed the
configured maximum peers allowed.
When a BGP peer that is part of a prefix peering disconnects, Cisco NX-OS holds its peer structures for
a defined prefix peer timeout value. An established peer can reset and reconnect without danger of being
blocked because other peers have consumed all slots for that prefix peering.
To configure the BGP prefix peering timeout value, use the following command in router configuration
mode:
Command
Purpose
timers prefix-peer-timeout value
Configures the timeout value for prefix peering.
The range is from 0 to 1200 seconds. The default
value is 30.
Example:
switch(config-router-neighbor)# timers
prefix-peer-timeout 120
To configure the maximum number of peers, use the following command in neighbor configuration
mode:
Command
Purpose
maximum-peers value
Configures the maximum number of peers for this
prefix peering. The range is from 1 to 1000.
Example:
switch(config-router-neighbor)#
maximum-peers 120
This example shows how to configure a prefix peering that accepts up to 10 peers:
switch(config)# router bgp 65536
switch(config-router)# timers prefix-peer-timeout 120
switch(config-router)# neighbor 10.100.200.0/24 remote-as 65536
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switch(config-router-neighbor)# maximum-peers 10
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor-af)#
Use the show ip bgp neighbor command to show the details of the configuration for that prefix peering
with a list of the currently accepted instances and the counts of active, maximum concurrent, and total
accepted peers.
Configuring BGP Authentication
You can configure BGP to authenticate route updates from peers using MD5 digests.
To configure BGP to use MD5 authentication, use the following command in neighbor configuration
mode:
Command
Purpose
password [0 | 3 | 7] string
Configures an MD5 password for BGP neighbor
sessions.
Example:
switch(config-router-neighbor)# password
BGPpassword
Resetting a BGP Session
If you modify a route policy for BGP, you must reset the associated BGP peer sessions. If the BGP peers
do not support route refresh, you can configure a soft reconfiguration for inbound policy changes. Cisco
NX-OS automatically attempts a soft reset for the session.
To configure soft reconfiguration inbound, use the following command in neighbor address-family
configuration mode:
Command
Purpose
soft-reconfiguration inbound
Enables soft reconfiguration to store the inbound
BGP route updates. This command triggers an
automatic soft clear or refresh of BGP neighbor
sessions.
Example:
switch(config-router-neighbor-af)#
soft-reconfiguration inbound
To reset a BGP neighbor session, use the following command in any mode:
Command
Purpose
clear bgp ip {unicast | multicast}
ip-address soft {in | out}
Resets the BGP session without tearing down the
TCP session.
Example:
switch# clear bgp ip unicast 192.0.2.1
soft in
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Modifying the Next-Hop Address
You can modify the next-hop address used in a route advertisement in the following ways:
•
Disable the next-hop calculation and use the local BGP speaker address as the next-hop address.
•
Set the next-hop address as a third-party address. Use this feature in situations where the original
next-hop address is on the same subnet as the peer that the route is being sent to. Using this feature
saves an extra hop during forwarding.
To modify the next-hop address, use the following parameters in commands address-family
configuration mode:
Command
Purpose
next-hop-self
Uses the local BGP speaker address as the next-hop
address in route updates. This command triggers an
automatic soft clear or refresh of BGP neighbor
sessions.
Example:
switch(config-router-neighbor-af)#
next-hop-self
next-hop-third-party
Example:
switch(config-router-neighbor-af)#
next-hop-third-party
Sets the next-hop address as a third-party address.
Use this command for single-hop EBGP peers that
do not have next-hop-self configured.
Configuring BGP Next-Hop Address Tracking
BGP next-hop address tracking is enabled by default and cannot be disabled.
You can modify the delay interval between RIB checks to increase the performance of BGP next-hop
tracking. You can configure the critical timer for routes that affect BGP next-hop reachability, and you
can configure the noncritical timer for all other routes in the BGP table.
To modify the BGP next-hop address tracking, use the following commands address-family
configuration mode:
Command
Purpose
nexthop trigger-delay {critical |
non-critical} milliseconds
Specifies the next-hop address tracking delay timer
for critical next-hop reachability routes and for
noncritical routes. The range is from 1 to
4294967295 milliseconds. The critical timer
default is 3000. The noncritical timer default is
10000.
Example:
switch(config-router-af)# nexthop
trigger-delay critical 5000
nexthop route-map name
Example:
switch(config-router-af)# nexthop
route-map nextHopLimits
Specifies a route map to match the BGP next-hop
addresses to. The name can be any case-sensitive,
alphanumeric string up to 63 characters.
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Configuring Next-Hop Filtering
BGP next-hop filtering allows you to specify that when a next-hop address is checked with the RIB, the
underlying route for that next-hop address is passed through the route map. If the route map rejects the
route, the next-hop address is treated as unreachable.
BGP marks all next hops that are rejected by the route policy as invalid and does not calculate the best
path for the routes that use the invalid next-hop address.
To configure BGP next-hop filtering, use the following command in address-family configuration mode:
Command
Purpose
nexthop route-map name
Specifies a route map to match the BGP next-hop
route to. The name can be any case-sensitive,
alphanumeric string up to 63 characters.
Example:
switch(config-router-af)# nexthop
route-map nextHopLimits
Disabling Capabilities Negotiation
You can disable capabilities negotiations to interoperate with older BGP peers that do not support
capabilities negotiation.
To disable capabilities negotiation, use the following command in neighbor configuration mode:
Command
Purpose
dont-capability-negotiate
Disables capabilities negotiation. You must
manually reset the BGP sessions after configuring
this command.
Example:
switch(config-router-neighbor)#
dont-capability-negotiate
Configuring eBGP
This section includes the following topics:
•
Disabling eBGP Single-Hop Checking, page 6-22
•
Configuring eBGP Multihop, page 6-23
•
Disabling a Fast External Failover, page 6-23
•
Limiting the AS-path Attribute, page 6-24
•
Configuring Local AS Support, page 6-24
Disabling eBGP Single-Hop Checking
You can configure eBGP to disable checking whether a single-hop eBGP peer is directly connected to
the local router. Use this option for configuring a single-hop loopback eBGP session between directly
connected switches.
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To disable checking whether or not a single-hop eBGP peer is directly connected, use the following
command in neighbor configuration mode:
Command
Purpose
disable-connected-check
Disables checking whether or not a single-hop
eBGP peer is directly connected. You must
manually reset the BGP sessions after using this
command.
Example:
switch(config-router-neighbor)#
disable-connected-check
Configuring eBGP Multihop
You can configure the eBGP time-to-live (TTL) value to support eBGP multihop. In some situations, an
eBGP peer is not directly connected to another eBGP peer and requires multiple hops to reach the remote
eBGP peer. You can configure the eBGP TTL value for a neighbor session to allow these multihop
sessions.
To configure eBGP multihop, use the following command in neighbor configuration mode:
Command
Purpose
ebgp-multihop ttl-value
Configures the eBGP TTL value for eBGP
multihop. The range is from 2 to 255. You must
manually reset the BGP sessions after using this
command.
Example:
switch(config-router-neighbor)#
ebgp-multihop 5
Disabling a Fast External Failover
Typically, when a BGP router loses connectivity to a directly connected eBGP peer, BGP triggers a fast
external failover by resetting the eBGP session to the peer. You can disable this fast external failover to
limit the instability caused by link flaps.
To disable fast external failover, use the following command in router configuration mode:
Command
Purpose
no fast-external-failover
Disables a fast external failover for eBGP peers.
This command is enabled by default.
Example:
switch(config-router)# no
fast-external-failover
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Limiting the AS-path Attribute
You can configure eBGP to discard routes that have a high number of AS numbers in the AS-path
attribute.
To discard routes that have a high number of AS numbers in the AS-path attribute, use the following
command in router configuration mode:
Command
Purpose
maxas-limit number
Discards eBGP routes that have a number of
AS-path segments that exceed the specified limit.
The range is from 1 to 2000.
Example:
switch(config-router)# maxas-limit 50
Configuring Local AS Support
The local AS feature allows a router to appear to be a member of a second autonomous system (AS), in
addition to its real AS. Local AS allows two ISPs to merge without modifying peering arrangements.
Routers in the merged ISP become members of the new autonomous system but continue to use their old
AS numbers for their customers.
Local AScan only be used for true eBGP peers. You cannot use this feature for two peers that are
members of different confederation sub-autonomous systems.
To configure eBGP local AS support, use the following command in neighbor configuration mode:
Command
Purpose
local-as number [no-prepend [replace-as
[dual-as]]]
Configures eBGP to prepend the local AS number
to the AS_PATH attribute.
Example:
switch(config-router-neighbor)# local-as
1.1
The local-as number can be a 16-bit integer or a
32-bit integer in the form of a higher 16-bit decimal
number and a lower 16-bit decimal number in xx.xx
format.
The no-prepend keyword ensures that the local-as
number is not prepended to any downstream BGP
neighbors except for the partner who is peering
with the local-as number.
The replace-as keyword ensures that only the
local-as number of the peering session is
prepended to the AS_PATH attribute. The
autonomous-system number from the local BGP
routing process is not prepended.
The dual-as keyword configures the eBGP
neighbor to establish a peering session using the
real autonomous-system number (from the local
BGP routing process) or by using the
autonomous-system number configured as the
Local AS).
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Configuring AS Confederations
To configure an AS confederation, you must specify a confederation identifier. To the outside world, the
group of autonomous systems within the AS confederation look like a single autonomous system with
the confederation identifier as the autonomous system number.
To configure a BGP confederation identifier, use the following command in router configuration mode:
Command
Purpose
confederation identifier as-number
Configures a confederation identifier for an AS
confederation. This command triggers an
automatic notification and session reset for the
BGP neighbor sessions.
Example:
switch(config-router)# confederation
identifier 4000
To configure the autonomous systems that belong to the AS confederation, use the following command
in router configuration mode:
Command
Purpose
bgp confederation peers as-number
[as-number2...]
Specifies a list of autonomous systems that belong
to the confederation. This command triggers an
automatic notification and session reset for the
BGP neighbor sessions.
Example:
switch(config-router)# bgp confederation
peers 5 33 44
Configuring Route Reflector
You can configure iBGP peers as route reflector clients to the local BGP speaker, which acts as the route
reflector. Together, a route reflector and its clients form a cluster. A cluster of clients usually has a single
route reflector. In such instances, the cluster is identified by the router ID of the route reflector. To
increase redundancy and avoid a single point of failure in the network, you can configure a cluster with
more than one route reflector. You must configure all route reflectors in the cluster with the same 4-byte
cluster ID so that a route reflector can recognize updates from route reflectors in the same cluster.
BEFORE YOU BEGIN
Ensure that you have enabled the BGP feature (see the “Enabling the BGP Feature” section on
page 5-11).
SUMMARY STEPS
1.
configure terminal
2.
router bgp as-number
3.
cluster-id cluster-id
4.
address-family ipv4 {unicast | multicast}
5.
(Optional) client-to-client reflection
6.
exit
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7.
neighbor ip-address remote-as as-number
8.
address-family ipv4 {unicast | multicast}
9.
route-reflector-client
10. show bgp ip {unicast | multicast} neighbors
11. (Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router bgp as-number
Example:
switch(config)# router bgp 65536
switch(config-router)#
Step 3
cluster-id cluster-id
Example:
switch(config-router)# cluster-id
192.0.2.1
Step 4
address-family ipv4 {unicast |
multicast}
Enters BGP mode and assigns the autonomous system
number to the local BGP speaker.
Configures the local router as one of the route reflectors
that serve the cluster. You specify a cluster ID to identify
the cluster. This command triggers an automatic soft
clear or refresh of BGP neighbor sessions.
Enters router address family configuration mode for the
specified address family.
Example:
switch(config-router)# address-family
ipv4 unicast
switch(config-router-af)#
Step 5
Step 6
Example:
switch(config-router-af)#
client-to-client reflection
(Optional) Configures client-to-client route reflection.
This feature is enabled by default. This command triggers
an automatic soft clear or refresh of BGP neighbor
sessions.
exit
Exits router address configuration mode.
client-to-client reflection
Example:
switch(config-router-neighbor)# exit
switch(config-router)#
Step 7
neighbor ip-address remote-as
as-number
Configures the IP address and AS number for a remote
BGP peer.
Example:
switch(config-router)# neighbor
192.0.2.10 remote-as 65536
switch(config-router-neighbor)#
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Step 8
Command or Action
Purpose
address-family ipv4 {unicast |
multicast}
Enters neighbor address family configuration mode for
the unicast IPv4 address family.
Example:
switch(config-router-neighbor)#
address-family ipv4 unicast
switch(config-router-neighbor-af)#
Step 9
route-reflector-client
Example:
switch(config-router-neighbor-af)#
route-reflector-client
Step 10
show bgp ip {unicast | multicast}
neighbors
Configures the switch as a BGP route reflector and
configures the neighbor as its client. This command
triggers an automatic notification and session reset for
the BGP neighbor sessions.
(Optional) Displays the BGP peers.
Example:
switch(config-router-neighbor-af)#
show bgp ip unicast neighbors
Step 11
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router-neighbor-af)#
copy running-config startup-config
This example shows how to configure the router as a route reflector and add one neighbor as a client:
switch(config)# router bgp 65536
switch(config-router)# neighbor 192.0.2.10 remote-as 65536
switch(config-router-neighbor)# address-family ip unicast
switch(config-router-neighbor-af)# route-reflector-client
switch(config-router-neighbor-af)# copy running-config startup-config
Configuring Route Dampening
You can configure route dampening to minimize route flaps propagating through your iBGP network.
To configure route dampening, use the following command in address-family or VRF address family
configuration mode:
Command
Purpose
dampening [{half-life reuse-limit
suppress-limit max-suppress-time |
route-map map-name}]
Disables capabilities negotiation. The parameter
values are as follows:
Example:
switch(config-router-af)# dampening
route-map bgpDamp
•
half-life—The range is from 1 to 45.
•
reuse-limit—The range is from 1 to 20000.
•
suppress-limit—The range is from 1 to 20000.
•
max-suppress-time—The range is from 1 to
255.
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Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Configuring Load Sharing and ECMP
You can configure the maximum number of paths that BGP adds to the route table for equal-cost
multipath load balancing.
To configure the maximum number of paths, use the following command in router address-family
configuration mode:
Command
Purpose
maximum-paths [ibgp] maxpaths
Configures the maximum number of equal-cost
paths for load sharing. The range is from 1 to 16.
The default is 1.
Example:
switch(config-router-af)# maximum-paths 12
Configuring Maximum Prefixes
You can configure the maximum number of prefixes that BGP can receive from a BGP peer. If the
number of prefixes exceeds this value, you can optionally configure BGP to generate a warning message
or tear down the BGP session to the peer.
To configure the maximum allowed prefixes for a BGP peer, use the following command in neighbor
address-family configuration mode:
Command
Purpose
maximum-prefix maximum [threshold]
[restart time | warming-only]
Configures the maximum number of prefixes from
a peer. The parameter ranges are as follows:
Example:
switch(config-router-neighbor-af)#
maximum-prefix 12
•
maximum—The range is from 1 to 300000.
•
Threshold—The range is from 1 to 100
percent. The default is 75 percent.
•
time—The range is from 1 to 65535 minutes.
This command triggers an automatic notification
and session reset for the BGP neighbor sessions if
the prefix limit is exceeded.
Configuring Dynamic Capability
You can configure dynamic capability for a BGP peer.
To configure dynamic capability, use the following command in neighbor configuration mode:
Command
Purpose
dynamic-capability
Enables dynamic capability. This command
triggers an automatic notification and session reset
for the BGP neighbor sessions.
Example:
switch(config-router-neighbor)#
dynamic-capability
This command is disabled by default.
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Configuring Aggregate Addresses
You can configure aggregate address entries in the BGP route table.
To configure an aggregate address, use the following command in router address-family configuration
mode:
Command
Purpose
aggregate-address ip-prefix/length
[as-set] [summary-only] [advertise-map
map-name] [attribute-map map-name]
[suppress-map map-name]
Creates an aggregate address. The path advertised
for this route is an autonomous system set that
consists of all elements contained in all paths that
are being summarized:
Example:
switch(config-router-af)#
aggregate-address 192.0.2.0/8 as-set
•
The as-set keyword generates autonomous
system set path information and community
information from contributing paths.
•
The summary-only keyword filters all more
specific routes from updates.
•
The advertise-map keyword and argument
specify the route map used to select attribute
information from selected routes.
•
The attribute-map keyword and argument
specify the route map used to select attribute
information from the aggregate.
•
The suppress-map keyword and argument
conditionally filters more specific routes.
Configuring BGP Conditional Advertisement
You can configure BGP conditional advertisement to limit the routes that BGP propagates. You define
the following two route maps:
•
Advertise map—Specifies the conditions that the route must match before BGP considers the
conditional advertisement. This route map can contain any appropriate match statements.
•
Exist map or nonexist map—Defines the prefix that must exist in the BGP table before BGP
propagates a route that matches the advertise map. The nonexist map defines the prefix that must not
exist in the BGP table before BGP propagates a route that matches the advertise map. BGP processes
only the permit statements in the prefix list match statements in these route maps.
If the route does not pass the condition, BGP withdraws the route if it exists in the BGP table.
BEFORE YOU BEGIN
Ensure that you have enabled the BGP feature (see the “Enabling the BGP Feature” section on
page 5-11).
SUMMARY STEPS
1.
configure terminal
2.
router bgp as-number
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3.
neighbor ipaddress remote-as as-number
4.
address-family ipv4 {unicast | multicast}
5.
advertise-map adv-map {exist-map exist-rmap | non-exist-map nonexist-rmap}
6.
(Optional) show ip bgp neighbor
7.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router bgp as-number
Example:
switch(config)# router bgp 65536
switch(config-router)#
Step 3
neighbor ip-address remote-as as-number
Example:
switch(config-router)# neighbor
192.168.1.2 remote-as 65537
switch(config-router-neighbor)#
Step 4
address-family ipv4 {unicast |
multicast}
Enters BGP mode and assigns the autonomous system
number to the local BGP speaker.
Places the router in neighbor configuration mode for
BGP routing and configures the neighbor IP address.
Enters address family configuration mode.
Example:
switch(config-router-neighbor)#
address-family ipv4 multicast
switch(config-router-neighbor-af)#
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Step 5
Command
Purpose
advertise-map adv-map {exist-map
exist-rmap | non-exist-map
nonexist-rmap}
Configures BGP to conditionally advertise routes
based on the two configured route maps:
•
adv-map—Specifies a route map with match
statements that the route must pass before BGP
passes the route to the next route map. The
adv-map is a case-sensitive, alphanumeric string
up to 63 characters.
•
exist-rmap—Specifies a route map with match
statements for a prefix list. A prefix in the BGP
table must match a prefix in the prefix list before
BGP will advertise the route. The exist-rmap is a
case-sensitive, alphanumeric string up to 63
characters.
•
nonexist-rmap—Specifies a route map with match
statements for a prefix list. A prefix in the BGP
table must not match a prefix in the prefix list
before BGP will advertise the route. The
nonexist-rmap is a case-sensitive, alphanumeric
string up to 63 characters.
Example:
switch(config-router-neighbor-af)#
advertise-map advertise exist-map exist
Step 6
show ip bgp neighbor
Example:
switch(config-router-neighbor-af)# show
ip bgp neighbor
Step 7
copy running-config startup-config
(Optional) Displays information about BGP and the
configured conditional advertisement route maps.
(Optional) Saves this configuration change.
Example:
switch(config-router-neighbor-af)# copy
running-config startup-config
This example shows how to configure BGP conditional advertisement:
switch# configure terminal
switch(config)# router bgp 65536
switch(config-router)# neighbor 192.0.2.2 remote-as 65537
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor-af)# advertise-map advertise exist-map exist
switch(config-router-neighbor-af)# exit
switch(config-router-neighbor)# exit
switch(config-router)# exit
switch(config)# route-map advertise
switch(config-route-map)# match as-path pathList
switch(config-route-map)# exit
switch(config)# route-map exit
switch(config-route-map)# match ip address prefix-list plist
switch(config-route-map)# exit
switch(config)# ip prefix-list plist permit 209.165.201.0/27
Configuring Route Redistribution
You can configure BGP to accept routing information from another routing protocol and redistribute that
information through the BGP network. Optionally, you can assign a default route for redistributed routes.
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BEFORE YOU BEGIN
Ensure that you have enabled the BGP feature (see the “Enabling the BGP Feature” section on
page 5-11).
SUMMARY STEPS
1.
configure terminal
2.
router bgp as-number
3.
address-family ipv4 {unicast | multicast}
4.
redistribute {direct | {eigrp | ospf | ospfv3 | rip} instance-tag | static} route-map map-name
5.
(Optional) default-metric value
6.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router bgp as-number
Example:
switch(config)# router bgp 65536
switch(config-router)#
Step 3
address-family ipv4 {unicast |
multicast}
Enters BGP mode and assigns the autonomous system
number to the local BGP speaker.
Enters address family configuration mode.
Example:
switch(config-router)# address-family
ipv4 unicast
switch(config-router-af)#
Step 4
redistribute {direct | {eigrp | ospf |
ospfv3 | rip} instance-tag | static}
route-map map-name
Redistributes routes from other protocols into BGP.
See the “Configuring Route Maps” section on
page 13-12 for more information about route maps.
Example:
switch(config-router-af)# redistribute
eigrp 201 route-map Eigrpmap
Step 5
default-metric value
(Optional) Generates a default route into BGP.
Example:
switch(config-router-af)# default-metric
33
Step 6
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router-af)# copy
running-config startup-config
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This example shows how to redistribute EIGRP into BGP:
switch# configure terminal
switch(config)# router bgp 65536
switch(config-router)# address-family ipv4 unicast
switch(config-router-af)# redistribute eigrp 201 route-map Eigrpmap
switch(config-router-af)# copy running-config startup-config
Configuring Multiprotocol BGP
You can configure MP-BGP to support multiple address families, including IPv4 unicast and multicast
routes.
BEFORE YOU BEGIN
Ensure that you have enabled the BGP feature (see the “Enabling the BGP Feature” section on
page 5-11).
SUMMARY STEPS
1.
configure terminal
2.
router bgp as-number
3.
neighbor ip-address remote-as as-number
4.
address-family ipv4 {unicast | multicast}
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router bgp as-number
Example:
switch(config)# router bgp 65536
switch(config-router)#
Step 3
neighbor ip-address remote-as as-number
Example:
switch(config-router)# neighbor
192.168.1.2 remote-as 65537
switch(config-router-neighbor)#
Enters BGP mode and assigns the autonomous system
number to the local BGP speaker.
Places the router in neighbor configuration mode for
BGP routing and configures the neighbor IP address.
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Step 4
Command
Purpose
address-family ipv4 {unicast |
multicast}
Enters address family configuration mode.
Example:
switch(config-router-neighbor)#
address-family ipv4 multicast
switch(config-router-neighbor-af)#
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router-neighbor-af)# copy
running-config startup-config
This example shows how to enable advertising and receiving IPv4 routes for multicast RPF for a
neighbor:
switch# configure terminal
switch(config)# interface ethernet 2/1
switch(config-if)# ipv4 address 2001:0DB8::1
switch(config-if)# router bgp 65536
switch(config-router)# neighbor 192.168.1.2 remote-as 35537
switch(config-router-neighbor)# address-family ipv4 multicast
switch(config-router-neighbor-af)# exit
switch(config-router-neighbor)# address-family ipv4 multicast
switch(config-router-neighbor-af)# copy running-config startup-config
Tuning BGP
You can tune BGP characteristics through a series of optional parameters.
To tune BGB, use the following ofptional commands in router configuration mode:
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Command
Purpose
bestpath [always-compare-med |
compare-routerid | med {missing-as-worst |
non-deterministic}| as-path
multipath-relax]
Modifies the best-path algorithm. The optional
parameters are as follows:
Example:
switch(config-router)# bestpath
always-compare-med
switch(config-router)# bestpath as-path
multipath-relax
enforce-first-as
Example:
switch(config-router)# enforce-first-as
log-neighbor-changes
Example:
switch(config-router)#
log-neighbor-changes
router-id id
Example:
switch(config-router)# router-id
209.165.20.1
timers [bestpath-delay delay | bgp
keepalive holdtime | prefix-peer-timeout
timeout]
•
always-compare-med—Compares MED on
paths from different autonomous systems.
•
compare-routerid—Compares the router IDs
for identical eBGP paths.
•
med missing-as-worst—Treats a missing
MED as the highest MED.
•
med non-deterministic—Does not always
pick the best MED path from among the paths
from the same autonomous system.
•
as-path multipath-relax—Beginning with
Cisco NX-OS Release 5.0(3)U1(2), allows the
switch to treat paths received from different
AS’s for multipath, if their AS-path lengths are
the same and other multipath conditions are
met.
Enforces the neighbor autonomous system to be the
first AS number listed in the AS_path attribute for
eBGP.
Generates a system message when a neighbor
changes state.
Manually configures the router ID for this BGP
speaker.
Sets the BGP timer values. The optional parameters
are as follows:
•
delay—Initial best-path timeout value after a
restart. The range is from 0 to 3600 seconds.
The default value is 300.
•
keepalive—BGP session keepalive time. The
range is from 0 to 3600 seconds. The default
value is 60.
•
holdtime—BGP session hold time.The range is
from 0 to 3600 seconds. The default value is
180.
•
timeout—Prefix peer timeout value. The range
is from 0 to 1200 seconds. The default value is
30.
Example:
switch(config-router)# timers bgp 90 270
You must manually reset the BGP sessions after
configuring this command.
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To tune BGP, use the following optional command in router address-family configuration mode:
Command
Purpose
distance ebgp-distance ibgp distance
local-distance
Sets the administrative distance for BGP. The range
is from 1 to 255. The defaults are as follows:
Example:
switch(config-router-af)# distance 20 100
200
•
eBGP distance—20.
•
iBGP distance—200.
•
local distance—220. Local-distance is the
administrative distance used for aggregate
discard routes when they are installed in the
RIB.
To tune BGP, use the following optional commands in neighbor configuration mode:
Command
Purpose
description string
Sets a descriptive string for this BGP peer. The
string can be up to 80 alphanumeric characters.
Example:
switch(config-router-neighbor)#
description main site
low-memory exempt
Example:
switch(config-router-neighbor)# low-memory
exempt
transport connection-mode passive
Example:
switch(config-router-neighbor)# transport
connection-mode passive
remove-private-as
Example:
switch(config-router-neighbor)#
remove-private-as
update-source interface-type number
Example:
switch(config-router-neighbor)#
update-source ethernet 2/1
Exempts this BGP neighbor from a possible
shutdown due to a low memory condition.
Allows a passive connection setup only. This BGP
speaker does not initiate a TCP connection to a
BGP peer. You must manually reset the BGP
sessions after configuring this command.
Removes private AS numbers from outbound route
updates to an eBGP peer. This command triggers an
automatic soft clear or refresh of BGP neighbor
sessions.
Configures the BGP speaker to use the source IP
address of the configured interface for BGP
sessions to the peer. This command triggers an
automatic notification and session reset for the
BGP neighbor sessions.
To tune BGP, use the following optional commands in neighbor address-family configuration mode:
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Command
Purpose
suppress-inactive
Advertises the best (active) routes only to the BGP
peer. This command triggers an automatic soft
clear or refresh of BGP neighbor sessions.
Example:
switch(config-router-neighbor-af)#
suppress-inactive
default-originate [route-map map-name]
Generates a default route to the BGP peer.
Example:
switch(config-router-neighbor-af)#
default-originate
filter-list list-name {in | out}
Example:
switch(config-router-neighbor-af)#
filter-list BGPFilter in
prefix-list list-name {in | out}
Example:
switch(config-router-neighbor-af)#
prefix-list PrefixFilter in
send-community
Example:
switch(config-router-neighbor-af)#
send-community
send-extcommunity
Example:
switch(config-router-neighbor-af)#
send-extcommunity
Applies an AS_path filter list to this BGP peer for
inbound or outbound route updates. This command
triggers an automatic soft clear or refresh of BGP
neighbor sessions.
Applies a prefix list to this BGP peer for inbound
or outbound route updates. This command triggers
an automatic soft clear or refresh of BGP neighbor
sessions.
Sends the community attribute to this BGP peer.
This command triggers an automatic soft clear or
refresh of BGP neighbor sessions.
Sends the extended community attribute to this
BGP peer. This command triggers an automatic soft
clear or refresh of BGP neighbor sessions.
Configuring Virtualization
You can create multiple VRFs and use the same BGP process in each VRF.
BEFORE YOU BEGIN
Ensure that you have enabled the BGP feature (see the “Enabling the BGP Feature” section on
page 5-11).
SUMMARY STEPS
1.
configure terminal
2.
vrf context vrf-name
3.
exit
4.
router bgp as-number
5.
vrf vrf-name
6.
neighbor ip-address remote-as as-number
7.
bestpath as-path multipath-relax
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8.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
vrf context vrf-name
Example:
switch(config)# vrf context
RemoteOfficeVRF
switch(config-vrf)#
Step 3
exit
Creates a new VRF and enters VRF configuration
mode.
Exits VRF configuration mode.
Example:
switch(config-vrf)# exit
switch(config)#
Step 4
router bgp as-number
Example:
switch(config)# router bgp 65536
switch(config-router)#
Step 5
vrf vrf-name
Example:
switch(config-router)# vrf
RemoteOfficeVRF
switch(config-router-vrf)#
Step 6
neighbor ip-address remote-as as-number
Example:
switch(config-router-vrf)# neighbor
209.165.201.1 remote-as 65536
switch(config-router--vrf-neighbor)#
Step 7
bestpath as-path multipath-relax
Example:
switch(config-router-vrf)# bestpath
as-path multipath-relax
Step 8
copy running-config startup-config
Creates a new BGP process with the configured
autonomous system number.
Enters the router VRF configuration mode and
associates this BGP instance with a VRF.
Configures the IP address and AS number for a remote
BGP peer.
(Optional) Beginning with Cisco NX-OS
Release 5.0(3)U1(2), allows the switch to treat paths
received from different AS’s for multipath, if their
AS-path lengths are the same and other multipath
conditions are met.
(Optional) Saves this configuration change.
Example:
switch(config-router-vrf-neighbor)# copy
running-config startup-config
This example shows how to create a VRF and configure the router ID in the VRF:
switch# configure terminal
switch(config)# vrf context NewVRF
switch(config-vrf)# exit
switch(config)# router bgp 65536
switch(config-router)# vrf NewVRF
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S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
switch(config-router-vrf)# neighbor 209.165.201.1 remote-as 65536
switch(config-router-vrf-neighbor)# copy running-config startup-config
Verifying the Advanced BGP Configuration
To display the BGP configuration information, perform one of the following tasks:
Command
Purpose
show bgp all [summary] [vrf vrf-name]
Displays the BGP information for all address
families.
show bgp convergence [vrf vrf-name]
Displays the BGP information for all address
families.
show bgp ip {unicast | multicast} [ip-address]
community {regexp expression | [community]
[no-advertise] [no-export]
[no-export-subconfed]} [vrf vrf-name]
Displays the BGP routes that match a BGP
community.
show bgp [vrf vrf-name] ip {unicast | multicast} Displays the BGP routes that match a BGP
[ip-address] community-list list-name [vrf
community list.
vrf-name]
show bgp ip {unicast | multicast} [ip-address]
extcommunity {regexp expression | generic
[non-transitive | transitive] aa4:nn
[exact-match]} [vrf vrf-name]
Displays the BGP routes that match a BGP
extended community.
show bgp ip {unicast | multicast} [ip-address] Displays the BGP routes that match a BGP
extcommunity-list list-name [exact-match] [vrf extended community list.
vrf-name]
show bgp ip {unicast | multicast} [ip-address]
{dampening dampened-paths [regexp
expression]} [vrf vrf-name]
Displays the information for BGP route
dampening. Use the clear bgp dampening
command to clear the route flap dampening
information.
show bgp ip {unicast | multicast} [ip-address] Displays the BGP route history paths.
history-paths [regexp expression] [vrf vrf-name]
show bgp ip {unicast | multicast} [ip-address]
filter-list list-name [vrf vrf-name]
Displays the information for the BGP filter list.
show bgp ip {unicast | multicast} [ip-address]
neighbors [ip-address] [vrf vrf-name]
Displays the information for BGP peers. Use the
clear bgp neighbors command to clear these
neighbors.
show bgp ip {unicast | multicast} [ip-address]
{nexthop | nexthop-database} [vrf vrf-name]
Displays the information for the BGP route next
hop.
show bgp paths
Displays the BGP path information.
show bgp ip {unicast | multicast} [ip-address]
policy name [vrf vrf-name]
Displays the BGP policy information. Use the
clear bgp policy command to clear the policy
information.
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Displaying BGP Statistics
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Command
Purpose
show bgp ip {unicast | multicast} [ip-address]
prefix-list list-name [vrf vrf-name]
Displays the BGP routes that match the prefix list.
show bgp ip {unicast | multicast} [ip-address]
received-paths [vrf vrf-name]
Displays the BGP paths stored for soft
reconfiguration.
show bgp ip {unicast | multicast} [ip-address]
regexp expression [vrf vrf-name]
Displays the BGP routes that match the AS_path
regular expression.
show bgp ip {unicast | multicast} [ip-address]
route-map map-name [vrf vrf-name]
Displays the BGP routes that match the route
map.
show bgp peer-policy name [vrf vrf-name]
Displays the information about BGP peer
policies.
show bgp peer-session name [vrf vrf-name]
Displays the information about BGP peer
sessions.
show bgp peer-template name [vrf vrf-name]
Displays the information about BGP peer
templates. Use the clear bgp peer-template
command to clear all neighbors in a peer template.
show bgp process
Displays the BGP process information.
show ip bgp options
Displays the BGP status and configuration
information. This command has multiple options.
See the Cisco Nexus 3000 Series Command
Reference,, for more information.
show ip mbgp options
Displays the BGP status and configuration
information. This command has multiple options.
See the Cisco Nexus 3000 Series Command
Reference,, for more information.
show running-configuration bgp
Displays the current running BGP configuration.
Displaying BGP Statistics
To display BGP statistics, use the following commands:
Command
Purpose
show bgp ip {unicast | multicast}
[ip-address] flap-statistics [vrf vrf-name]
Displays the BGP route flap statistics. Use the clear bgp
flap-statistics command to clear these statistics.
show bgp sessions [vrf vrf-name]
Displays the BGP sessions for all peers. Use the clear
bgp sessions command to clear these statistics.
show bgp sessions [vrf vrf-name]
Displays the BGP sessions for all peers. Use the clear
bgp sessions command to clear these statistics.
show bgp statistics
Displays the BGP statistics.
Related Topics
The following topics can give more information on BGP:
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Additional References
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
•
Chapter 6, “Configuring Advanced BGP”
•
Chapter 13, “Configuring Route Policy Manager”
Additional References
For additional information related to implementing BGP, see the following sections:
•
Related Documents, page 6-41
•
MIBs, page 6-41
Related Documents
Related Topic
Document Title
BGP CLI commands
Cisco Nexus 3000 Series Command Reference,
MIBs
MIBs
MIBs Link
BGP4-MIB
To locate and download MIBs, go to the following URL:
CISCO-BGP4-MIB
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
Feature History for BGP
Table 6-2 lists the release history for this feature.
Table 6-2
Feature History for BGP
Feature Name
Releases
Feature Information
BGP
5.0(3)U1(1)
This feature was introduced.
BFD
5.0(3)U2(2)
Added support for BFD. See Chapter 7, “Configuring
Bidirectional Forwarding Detection for BGP” for more
information.
BGP
5.0(3)U2(2a)
Added support for Local AS. See the “Configuring Local
AS Support” section on page 6-24 for more information.
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Feature History for BGP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
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CH A P T E R
7
Configuring Bidirectional Forwarding Detection
for BGP
This chapter describes how to configure Bidirectional Forwarding Detection (BFD) for BGP.
This chapter includes the following sections:
•
Information About BFD, page 7-1
•
Licensing Requirements for BFD, page 7-3
•
Prerequisites for BFD, page 7-3
•
Guidelines and Limitations, page 7-3
•
Default Settings, page 7-4
•
Configuring BFD, page 7-5
•
Verifying the BFD Configuration, page 7-14
•
Monitoring BFD, page 7-14
•
Feature History for BFD, page 7-15
Information About BFD
BFD is a detection protocol designed to provide fast forwarding-path failure detection times for media
types, encapsulations, topologies, and routing protocols. You can use BFD to detect forwarding path
failures at a uniform rate, rather than the variable rates for different protocol hello mechanisms. BFD
makes network profiling and planning easier and reconvergence time consistent and predictable.
BFD provides subsecond failure detection between two adjacent devices.
This section includes the following topics:
•
Asynchronous Mode, page 7-2
•
BFD Detection of Failures, page 7-2
•
BFD Echo Function, page 7-2
•
Security, page 7-3
•
Virtualization Support, page 7-3
•
Virtualization Support, page 7-3
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Information About BFD
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Asynchronous Mode
Cisco NX-OS supports the BFD asynchronous mode, which sends BFD control packets between two
adjacent devices to activate and maintain BFD neighbor sessions between the devices. You configure
BFD on both devices (or BFD neighbors). Once BFD has been enabled on the appropriate protocols,
Cisco NX-OS creates a BFD session, negotiates BFD session parameters, and begins to send BFD
control packets to each BFD neighbor at the negotiated interval. The BFD session parameters include
the following:
•
Desired minimum transmit interval—The interval at which this device wants to send BFD hello
messages.
•
Required minimum receive interval—The minimum interval at which this device can accept BFD
hello messages from another BFD device.
•
Detect multiplier—The number of missing BFD hello messages from another BFD device before
this local device detects a fault in the forwarding path.
BFD Detection of Failures
Once a BFD session has been established and timer negotiations are complete, BFD neighbors send BFD
control packets that act in the same manner as an IGP hello protocol to detect liveliness, except at a more
accelerated rate. BFD detects a failure, but the protocol must take action to bypass a failed peer.
BFD sends a failure detection notice to the BFD-enabled protocols when it detects a failure in the
forwarding path. The local device can then initiate the protocol recalculation process and reduce the
overall network convergence time.
When a failure occurs in the network:
Note
1.
The BFD neighbor session with the BFD neighbor router is torn down.
2.
BFD notifies the local BFD process that the BFD neighbor is no longer reachable.
3.
The local BFD process tears down the BFD neighbor relationship.
4.
If an alternative path is available, the routers immediately start converging on it.
The BFD failure detection occurs in less than a second.
BFD Echo Function
The BFD echo function sends echo packets from the forwarding engine to the remote BFD neighbor. The
BFD neighbor forwards the echo packet back along the same path in order to perform detection; the BFD
neighbor does not participate in the actual forwarding of the echo packets. The echo function and the
forwarding engine are responsible for the detection process. BFD can use the slow timer to slow down
the asycnhronous session when the echo function is enabled and reduce the number of BFD control
packets that are sent between two BFD neighbors. Also, the forwarding engine tests the forwarding path
on the remote (neighbor) system without involving the remote system, so there is less interpacket delay
variability and faster failure detection times.
The echo function is without asymmetry when both BFD neighbors are running echo function.
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Licensing Requirements for BFD
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Security
Cisco NX-OS uses the packet Time to Live (TTL) value to verify that the BFD packets came from an
adjacent BFD peer. For all asynchronous and echo request packets, the BFD neighbor sets the TTL value
to 255 and the local BFD process verifies the TTL value as 255 before processing the incoming packet.
For the echo response packet, BFD sets the TTL value to 254.
Virtualization Support
BFD supports virtual routing and forwarding instances (VRFs). VRFs exist within virtual device
contexts (VDCs). By default, Cisco NX-OS places you in the default VDC and default VRF unless you
specifically configure another VDC and VRF.
Licensing Requirements for BFD
The following table shows the licensing requirements for this feature:
Product
License Requirement
Cisco NX-OS
BFD requires no license. Any feature not included in a license package is bundled with the Cisco NX-OS
system images and is provided at no extra charge to you. For a complete explanation of the Cisco NX-OS
licensing scheme, see the Cisco NX-OS Licensing Guide.
Prerequisites for BFD
BFD has the following prerequisites:
•
You must enable the BFD feature (see the “Enabling the BFD Feature” section on page 7-6).
•
For any client protocols that you want to enable BFD on, you enable BFD in that client protocol.
See the “Configuring BFD on BGP” section on page 7-13.
•
Disable Internet Control Message Protocol (ICMP) redirect messages on a BFD-enabled interfaces.
•
See other detailed prerequisites that are listed with the configuration tasks.
Guidelines and Limitations
BFD has the following configuration guidelines and limitations:
•
BFD supports BFD version 1.
•
BFD supports IPv4.
•
BFD supports single-hop BFD.
•
BFD for BGP supports single-hop eBGP peers and single-hop iBGP peers with update-source.
•
BFD supports the following Layer 3 interfaces—physical interfaces, port channels, subinterfaces,
and VLAN interfaces (SVI).
•
BFD for BGP does not support authentication for BFD or per-link BFD sessions on a port channel.
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Default Settings
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
•
BFD depends on a Layer 3 adjacency information to discover topology changes, including Layer 2
topology changes. A BFD session on a VLAN interface (SVI) may not be up after the convergence
of the Layer 2 topology if there is no Layer 3 adjacency information available.
•
Port channel configuration limitations:
– For Layer 3 port channels used by BFD, you must enable LACP on the port channel.
– For Layer 2 port channels used by SVI sessions, you must enable LACP on the port channel.
•
SVI limitations:
– An ASIC reset will cause traffic disruption for other ports. This event could possibly cause SVI
sessions on other ports to flap. Some triggers for an ASIC reset are port moves between VDCs
or reloading a VDC. In these cases, BFD is not supported over the SVI interface.
– When you change the topology (for example, add or delete a link into a VLAN, delete a member
from a Layer 2 port channel, and so on), the SVI session could be affected. It may go down first
and then come up after the topology discovery is finished.
If you do not want the SVI sessions to flap and you need to change the topology, you can disable
the BFD feature before making the changes and reenable BFD after the changes have been made.
You can also configure the BFD timer to be a large value (for example, 5 seconds), and change
it back to a fast timer after the above events complete.
Tip
•
Cisco NX-OS does not distribute the BFD operation to compatible modules to offload the CPU for
BFD packet processing.
•
BFD does not support stateless restarts and in-service software upgrades (ISSUs).
•
If you want to enable BFD for a peer reachable through a port channel, you must configure LACP
on the port channel.
•
BFD echo mode and Unicast Reverse Path Forwarding (URPF) are mutually exclusive and cannot
both be enabled on a BFD interface. If you want to configure an interface for BFD, you must disable
either BFD echo mode or URPF.
Default Settings
Table 7-1 lists the default settings for BFD parameters.
Table 7-1
Default BFD Parameters
Parameters
Default
BFD feature
Disabled
Required minimum receive interval
250 milliseconds
Desired minimum transmit interval
250 milliseconds
Detect multiplier
3
Echo function
Enabled
Mode
Asynchronous
Port channel
Logical mode (one session per source-destination
pair address).
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Table 7-1
Default BFD Parameters (continued)
Parameters
Default
Slow timer
2000 milliseconds
Subinterface optimization
Disabled
Configuring BFD
This section includes the following topics:
•
Configuration Hierarchy, page 7-5
•
Task Flow for Configuring BFD, page 7-5
•
Enabling the BFD Feature, page 7-6
•
Configuring Global BFD Parameters, page 7-6
•
Configuring BFD on an Interface, page 7-8
•
Configuring BFD on a Port Channel, page 7-9
•
Configuring BFD Echo Function, page 7-10
•
Optimizing BFD on Subinterfaces, page 7-11
•
Configuring BFD on BGP, page 7-13
Configuration Hierarchy
You can configure BFD at the global level, VRF level, at the interface or port channel level, or at the
subinterface level (for physical interfaces and port channels). The VRF configuration overrides global
configuration. The interface or port channel configuration overrides VRF or global configuration. On
supported interfaces, the subinterface-level configuration overrides the interface or port channel
configuration unless subinterface optimization is enabled. See the “Optimizing BFD on Subinterfaces”
section on page 7-11 for more information.
For physical ports that are members of a port channel, the member port inherits the master port channel
BFD configuration. The member port subinterfaces can override the master port channel BFD
configuration, unless subinterface optimization is enabled.
Task Flow for Configuring BFD
Follow these steps to configure BFD:
Step 1
Enabling the BFD Feature.
Step 2
Configuring Global BFD Parameters or Configuring BFD on an Interface.
Step 3
Configuring BFD on BGP.
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Configuring BFD
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Enabling the BFD Feature
You must enable the BFD feature before you can configure BFD on an interface and protocol within a
device (VDC).
BEFORE YOU BEGIN
Ensure that you are in the correct VDC (or use the switchto vdc command).
SUMMARY STEPS
1.
configure terminal
2.
feature bfd
3.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
Enables the BFD feature.
feature bfd
Example:
switch(config)# feature bfd
Step 3
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
Use the no feature bfd command to disable the BFD feature and remove all associated configuration.
Command
Purpose
no feature bfd
Disables the BFD feature and removes all
associated configuration.
Example:
switch(config)# no
bfd
Configuring Global BFD Parameters
You can configure the BFD session parameters for all BFD sessions on the device. The BFD session
parameters are negotiated between the BFD peers in a three-way handshake.
See the “Configuring BFD on an Interface” section on page 7-8 to override these global session
parameters on an interface.
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Configuring BFD
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
BEFORE YOU BEGIN
Ensure that you are in the correct VDC (or use the switchto vdc command).
Enable the BFD feature. See the “Enabling the BFD Feature” section on page 7-6.
SUMMARY STEPS
1.
configure terminal
2.
bfd interval mintx min_rx msec multiplier value
3.
bfd slow-timer [interval]
4.
(Optional) show running-config bfd
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
bfd interval mintx min_rx msec
multiplier value
Example:
switch(config)# bfd interval 250 min_rx
250 multiplier 3
Configures the BFD session parameters for all BFD
sessions on the device. You can override these values
by configuring the BFD session parameters on an
interface. The mintx and msec range is from 250 to 999
milliseconds and the default is 250. The multiplier
range is from 3to 50. The multiplier default is 3.
To return to the default settings, use the no bfd
interval command.
Step 3
bfd slow-timer [interval]
Example:
switch(config)# bfd slow-timer 2000.
Configures the slow timer. This value determines how
fast BFD starts up a new session and is used to slow
down the asynchrounous sessions when the BFD echo
function is enabled. The range is from 1000 to 30000
milliseconds. The default is 2000.
To return to the default settings, use the no bfd
command.
slow-timer
Step 4
show running-config bfd
(Optional) Displays the BFD running configuration.
Example:
switch(config)# show running-config bfd
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
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Configuring BFD
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Configuring BFD on an Interface
You can configure the BFD session parameters for all BFD sessions on an interface. The BFD session
parameters are negotiated between the BFD peers in a three-way handshake.
This configuration overrides the global session parameters for the configured interface.
BEFORE YOU BEGIN
Ensure that you are in the correct VDC (or use the switchto vdc command).
Enable the BFD feature. See the “Enabling the BFD Feature” section on page 7-6.
SUMMARY STEPS
1.
configure terminal
2.
interface int-if
3.
bfd interval mintx min_rx msec multiplier value
4.
(Optional) show running-config bfd
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface int-if
Example:
switch(config)# interface ethernet 2/1
switch(config-if)#
Step 3
bfd interval mintx min_rx msec
multiplier value
Example:
switch(config-if)# bfd interval 250
min_rx 250 multiplier 3
Enters interface configuration mode. Use the ?
keyword to display the supported interfaces.
Configures the BFD session parameters for all BFD
sessions on the interface. This overrides the global
BFD session parameters. The mintx and msec range is
from 250 to 999 milliseconds and the default is 250.
The multiplier range is from 3 to 50. The multiplier
default is 3.
To return to the default settings, use the no bfd
interval command.
Step 4
show running-config bfd
(Optional) Displays the BFD running configuration.
Example:
switch(config-if)# show running-config
bfd
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-if)# copy running-config
startup-config
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Configuring BFD
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Configuring BFD on a Port Channel
You can configure the BFD session parameters for all BFD sessions on a port channel. For example, if
the BFD session for one link on a port channel is up, BFD informs client protocols, such as BGP, that
the port channel is up. The BFD session parameters are negotiated between the BFD peers in a three-way
handshake.
This configuration overrides the global session parameters for the configured port channel. The member
ports of the port channel inherit the port channel BFD session parameters, unless you configure
subinterface-level BFD parameters on a member port. In that case, the member port subinterface uses
the subinterface BFD configuration if subinterface optimization is not enabled. See the “Optimizing
BFD on Subinterfaces” section on page 7-11 for more information.
BEFORE YOU BEGIN
Ensure that you are in the correct VDC (or use the switchto vdc command).
Ensure that you enable LACP on the port channel before you enable BFD.
Enable the BFD feature. See the “Enabling the BFD Feature” section on page 7-6.
SUMMARY STEPS
1.
configure terminal
2.
interface port-channel number
3.
(Optional) bfd interval mintx min_rx msec multiplier value
4.
(Optional) show running-config bfd
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface port-channel number
Example:
switch(config)# interface port-channel 2
switch(config-if)#
Step 3
bfd interval mintx min_rx msec
multiplier value
Example:
switch(config-if)# bfd interval 250
min_rx 250 multiplier 3
Enters port channel configuration mode. Use the ?
keyword to display the supported number range.
(Optional) Configures the BFD session parameters for
all BFD sessions on the port channel. This overrides
the global BFD session parameters. The mintx and
msec range is from 250 to 999 milliseconds and the
default is 250. The multiplier range is from 3 to 50.
The multiplier default is 3.
To return to the default settings, use the no bfd
command.
interval
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Configuring BFD
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Step 4
Command
Purpose
show running-config bfd
(Optional) Displays the BFD running configuration.
Example:
switch(config-if)# show running-config
bfd
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-if)# copy running-config
startup-config
Configuring BFD Echo Function
You can configure the BFD echo function on one or both ends of a BFD-monitored link. The echo
function slows down the required minimum receive interval, based on the configured slow timer. The
RequiredMinEchoRx BFD session parameter is set to zero if the echo function is disabled. The slow
timer becomes the required minimum receive interval if the echo function is enabled.
BEFORE YOU BEGIN
Ensure that you are in the correct VDC (or use the switchto vdc command).
Enable the BFD feature. See the “Enabling the BFD Feature” section on page 7-6.
Configure the BFD session parameters. See the “Configuring Global BFD Parameters” section on
page 7-6 or the “Configuring BFD on an Interface” section on page 7-8.
Ensure that Internet Control Message Protocol (ICMP) redirect messages are disabled on BFD-enabled
interfaces. Use the no ip redirects command on the interface.
SUMMARY STEPS
1.
configure terminal
2.
bfd slow-timer echo-interval
3.
interface int-if
4.
bfd echo
5.
(Optional) show running-config bfd
6.
(Optional) copy running-config startup-config
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Configuring BFD
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
bfd slow-timer echo-interval
Example:
switch(config)# bfd slow-timer 2000
Configures the slow timer used in the echo function.
This value determines how fast BFD starts up a new
session and is used to slow down the asynchrounous
sessions when the BFD echo function is enabled. This
value overwrites the required minimum receive
interval when the echo function is enabled. The range
is from 1000 to 30000 milliseconds. The default is
2000.
To return to the default settings, use the no bfd
command.
slow-timer
Step 3
interface int-if
Example:
switch(config)# interface ethernet 2/1
switch(config-if)#
Step 4
Step 5
Enters interface configuration mode. Use the ?
keyword to display the supported interfaces.
bfd echo
Enables the echo function. The default is enabled.
Example:
switch(config-if)# bfd echo
To disable the echo function, use the no bfd echo
command.
show running-config bfd
(Optional) Displays the BFD running configuration.
Example:
switch(config-if)# show running-config
bfd
Step 6
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-if)# copy running-config
startup-config
Optimizing BFD on Subinterfaces
You can optimize BFD on subinterfaces. BFD creates sessions for all configured subinterfaces. BFD sets
the subinterface with the lowest configured VLAN ID as the master subinterface and that subinterface
uses the BFD session parameters of the parent interface. The remaining subinterfaces use the slow timer.
If the optimized subinterface session detects an error, BFD marks all subinterfaces on that physical
interface as down.
BEFORE YOU BEGIN
Ensure that you are in the correct VDC (or use the switchto vdc command).
Enable the BFD feature. See the “Enabling the BFD Feature” section on page 7-6.
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Configuring BFD
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Configure the BFD session parameters. See the “Configuring Global BFD Parameters” section on
page 7-6 or the “Configuring BFD on an Interface” section on page 7-8.
Ensure that these subinterfaces connect to another Cisco NX-OS device. This feature is supported on
Cisco NX-OS only.
SUMMARY STEPS
1.
configure terminal
2.
interface int-if
3.
bfd optimize subinterface
4.
(Optional) show running-config bfd
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface int-if
Example:
switch(config)# interface ethernet 2/1
switch(config-if)#
Step 3
bfd optimize subinterface
Example:
switch(config-if)# bfd optimize
subinterface
Step 4
show running-config bfd
Enters interface configuration mode. Use the ?
keyword to display the supported interfaces.
Optimizes subinterfaces on a BFD-enabled interface.
The default is disabled.
To disable optimized subinterfaces, use the no bfd
optimize subinterfaces command.
(Optional) Displays the BFD running configuration.
Example:
switch(config-if)# show running-config
bfd
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-if)# copy running-config
startup-config
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Configuring BFD
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Configuring BFD on BGP
You can configure BFD for the Border Gateway Protocol (BGP).
BEFORE YOU BEGIN
Ensure that you are in the correct VDC (or use the switchto vdc command).
Enable the BFD feature. See the “Enabling the BFD Feature” section on page 7-6.
Configure the BFD session parameters. See the “Configuring Global BFD Parameters” section on
page 7-6 or the “Configuring BFD on an Interface” section on page 7-8.
Enable the BGP feature. See the Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide,
Release 5.x, for more information.
SUMMARY STEPS
1.
configure terminal
2.
router bgp as-number
3.
neighbor {ip-address | ipv6-address} remote-as as-number
4.
bfd
5.
(Optional) show running-config bgp
6.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router bgp as-number
Example:
switch(config)# router bgp 64496
switch(config-router)#
Step 3
neighbor {ip-address | ipv6-address}
remote-as as-number
Example:
switch(config-router)# neighbor
209.165.201.1 remote-as 64497
switch(config-router-neighbor)#
Step 4
Enables BGP and assigns the AS number to the local
BGP speaker. The AS number can be a 16-bit integer
or a 32-bit integer in the form of a higher 16-bit
decimal number and a lower 16-bit decimal number in
xx.xx format.
Configures the IPv4 or IPv6 address and AS number
for a remote BGP peer. The ip-address format is
x.x.x.x. The ipv6-address format is A:B::C:D.
Enables BFD for this BGP peer.
bfd
Example:
switch(config-router-neighbor)# bfd
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Verifying the BFD Configuration
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Step 5
Command
Purpose
show running-config bgp
(Optional) Displays the BGP running configuration.
Example:
switch(config-router-neighbor)# show
running-config bgp
Step 6
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router-neighbor)# copy
running-config startup-config
Verifying the BFD Configuration
To display BFD configuration information, perform one of the following tasks:
Command
Purpose
show running-config bfd
Displays the running BFD configuration.
show startup-config bfd
Displays the BFD configuration that will be
applied on the next system startup.
For detailed information about the fields in the output from these commands, see the Cisco Nexus 7000
Series NX-OS Interfaces Command Reference, Release 5.x.
Monitoring BFD
Use the following commands to display BFD:
Command
Purpose
show bfd neighbors [application name]
[details]
Displays information about BFD for a supported
application, such as BGP.
show bfd neighbors [interface int-if] [details]
Displays information about BGP sessions on an
interface.
show bfd neighbors [dest-ip ip-address] [src-ip Displays information about the specified BGP
ip-address][details]
session on an interface.
show bfd neighbors [vrf vrf-name] [details]
Displays information about BFD for a VRF.
For detailed information about the fields in the output from these commands, see the Cisco Nexus 3000
Series Command Reference,.
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Feature History for BFD
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Feature History for BFD
Table 7-2 lists the release history for this feature.
Table 7-2
Feature History for BGP
Feature Name
Releases
Feature Information
BFD for BGP
5.0(3)U2(2)
Added support for BFD for BGP. See Chapter 7,
“Configuring Bidirectional Forwarding Detection for BGP”
for more information.
BFD for BGP
5.0(3)U2(2a)
Added guidelines and limitations for LACP configuration,
and for BFD echo and URFP. See the “Guidelines and
Limitations” section on page 7-3 for more information.
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Feature History for BFD
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
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CH A P T E R
8
Configuring ECMP for Host Routes
This chapter describes how to configure the equal-cost multipathing (ECMP) protocol for host routes on
the Cisco NX-OS switch.
This chapter includes the following sections:
•
Information About ECMP for Host Routes, page 8-1
•
Licensing Requirements for ECMP for Host Routes, page 8-1
•
Prerequisites for ECMP for Host Routes, page 8-2
•
Default Settings, page 8-2
•
Configuring ECMP for Host Routes, page 8-2
•
Verifying the ECMP for Host Routes Configuration, page 8-4
•
Configuration Examples for ECMP for Host Routes, page 8-4
•
Additional References, page 8-4
•
Feature History for ECMP for Host Routes, page 8-5
Information About ECMP for Host Routes
When you enable ECMP support for host routes, all unicast host routes are programmed into the
longest-prefix match algorithm (LPM) table. ECMP for host routes is provided in the switch hardware.
You configure this feature in the CLI using the hardware profile unicast enable-host-ecmp command.
Note
Host entries are stored in the LPM routing table instead of the host table when ECMP is configured for
IPv4 (/32) routes and IPv6 (/128) routes.
Licensing Requirements for ECMP for Host Routes
The following table shows the licensing requirements for this feature:
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Prerequisites for ECMP for Host Routes
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Product
License Requirement
Cisco NX-OS
ECMP for host routes requires no license. Any feature not included in a license package is bundled with the
Cisco NX-OS system images and is provided at no extra charge to you. For a complete explanation of the
Cisco NX-OS licensing scheme, see the Cisco NX-OS Licensing Guide.
Prerequisites for ECMP for Host Routes
ECMP for host routes has the following prerequisites:
•
Before you use this command, we recommend that you disable Unicast Reverse Path Forwarding
(URPF) globally on the switch using the system urpf disable command, and then save the
configuration and reload the switch. Disabling URPF globally extends the LPM table size.
Default Settings
ECMP for host routes is disabled by default.
Configuring ECMP for Host Routes
This section includes the following topics:
•
Enabling the EMCP for Host Routes Feature, page 8-2
Enabling the EMCP for Host Routes Feature
You can enable the ECMP for host routes feature.
SUMMARY STEPS
1.
configure terminal
2.
(Optional) system urpf disable
3.
hardware profile unicast enable-host-ecmp
4.
copy running-config startup-config
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Configuring ECMP for Host Routes
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
system urpf disable
(Optional) Disables URPT globally on the switch.
Example:
switch(config)# system urpf disable
Step 3
hardware profile unicast
enable-host-ecmp
Enables ECMP for host routes globally on the switch.
Example:
switch(config)# hardware profile unicast
enable-host-ecmp
Step 4
copy running-config startup-config
Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
Disabling the EMCP for Host Routes Feature
You can disable the ECMP for host routes feature.
SUMMARY STEPS
1.
configure terminal
2.
no hardware profile unicast enable-host-ecmp
3.
copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
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Verifying the ECMP for Host Routes Configuration
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Step 2
Command
Purpose
no hardware profile unicast
enable-host-ecmp
Disables ECMP for host routes globally on the switch
and removes all associated configuration.
Example:
switch(config)# no hardware profile
unicast enable-host-ecmp
Step 3
copy running-config startup-config
Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
Verifying the ECMP for Host Routes Configuration
To display the ECMP for host routes configuration information, perform one of the following tasks:
Command
Purpose
show hardware profile status
Displays the unicast and multicast routing entries in
hardware tables.
show running-config
Displays the running system configuration.
Configuration Examples for ECMP for Host Routes
This example shows how to disable URPF and configure ECMP for host routes:
switch# configure terminal
switch(config)# system urpf disable
switch(config)# hardware profile unicast enable-host-ecmp
switch(config)# copy running-config startup-config
This example show how to disable ECMP for host routes:
switch# configure terminal
switch(config)# no hardware profile unicast enable-host-ecmp
switch(config)# copy running-config startup-config
Additional References
For additional information related to implementing ECMP for host routes, see the following sections:
•
Related Documents, page 8-5
•
Feature History for ECMP for Host Routes, page 8-5
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Additional References
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Related Documents
Related Topic
Document Title
ECMP for host routes CLI commands
Cisco Nexus 3000 Series Command Reference,
Feature History for ECMP for Host Routes
Table 8-1 lists the release history for this feature.
Table 8-1
Feature History for ECMP for Host Routes
Feature Name
Releases
Feature Information
ECMP for Host Routes
5.0(3)U1(2)
This feature was introduced.
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Additional References
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
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CH A P T E R
9
Configuring RIP
This chapter describes how to configure the Routing Information Protocol (RIP).
This chapter includes the following sections:
•
Information About RIP, page 9-1
•
Licensing Requirements for RIP, page 9-4
•
Prerequisites for RIP, page 9-4
•
Guidelines and Limitations, page 9-4
•
Default Settings, page 9-4
•
Configuring RIP, page 9-5
•
Verifying the RIP Configuration, page 9-17
•
Displaying RIP Statistics, page 9-17
•
Configuration Examples for RIP, page 9-18
•
Related Topics, page 9-18
•
Additional References, page 9-18
•
Feature History for RIP, page 9-19
Information About RIP
This section includes the following topics:
•
RIP Overview, page 9-2
•
RIPv2 Authentication, page 9-2
•
Split Horizon, page 9-2
•
Route Filtering, page 9-3
•
Route Summarization, page 9-3
•
Route Redistribution, page 9-3
•
Load Balancing, page 9-3
•
Virtualization Support, page 9-4
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Information About RIP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
RIP Overview
RIP uses User Datagram Protocol (UDP) data packets to exchange routing information in small
internetworks. RIPv2 supports IPv4. RIPv2 uses an optional authentication feature supported by the
RIPv2 protocol (see the “RIPv2 Authentication” section on page 9-2).
RIP uses the following two message types:
•
Request—Sent to the multicast address 224.0.0.9 to request route updates from other RIP-enabled
routers.
•
Response—Sent every 30 seconds by default (see the “Verifying the RIP Configuration” section on
page 9-17). The router also sends response messages after it receives a Request message. The
response message contains the entire RIP route table. RIP sends multiple response packets for a
request if the RIP routing table cannot fit in one response packet.
RIP uses a hop count for the routing metric. The hop count is the number of routers that a packet can
traverse before reaching its destination. A directly connected network has a metric of 1; an unreachable
network has a metric of 16. This small range of metrics makes RIP an unsuitable routing protocol for
large networks.
RIPv2 Authentication
You can configure authentication on RIP messages to prevent unauthorized or invalid routing updates in
your network. Cisco NX-OS supports a simple password or an MD5 authentication digest.
You can configure the RIP authentication per interface by using key-chain management for the
authentication keys. Key-chain management allows you to control changes to the authentication keys
used by an MD5 authentication digest or simple text password authentication. See the Cisco Nexus 7000
Series NX-OS Security Configuration Guide, Release 5.x for more details about creating key-chains.
To use an MD5 authentication digest, you configure a password that is shared at the local router and all
remote RIP neighbors. Cisco NX-OS creates an MD5 one-way message digest based on the message
itself and the encrypted password and sends this digest with the RIP message (Request or Response).
The receiving RIP neighbor validates the digest by using the same encrypted password. If the message
has not changed, the calculation is identical and the RIP message is considered valid.
An MD5 authentication digest also includes a sequence number with each RIP message to ensure that
no message is replayed in the network.
Split Horizon
You can use split horizon to ensure that RIP never advertises a route out of the interface where it was
learned.
Split horizon is a method that controls the sending of RIP update and query packets. When you enable
split horizon on an interface, Cisco NX-OS does not send update packets for destinations that were
learned from this interface. Controlling update packets in this manner reduces the possibility of routing
loops.
You can use split horizon with poison revers to configure an interface to advertise routes learned by RIP
as unreachable over the interface that learned the routes. Figure 9-1 shows a sample RIP network with
split horizon with poison reverse enabled.
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Information About RIP
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Figure 9-1
RIP with Split Horizon Poison Reverse
route x
route x
route x
185058
route x unreachable
route x unreachable
Router A
Router B
Router C
Router C learns about route X and advertises that route to router B. Router B in turn advertises route X
to router A, but sends a route X unreachable update back to router C.
By default, split horizon is enabled on all interfaces.
Route Filtering
You can configure a route policy on a RIP-enabled interface to filter the RIP updates. Cisco NX-OS
updates the route table with only those routes that the route policy allows.
Route Summarization
You can configure multiple summary aggregate addresses for a specified interface. Route summarization
simplifies route tables by replacing a number of more-specific addresses with an address that represents
all the specific addresses. For example, you can replace 10.1.1.0/24, 10.1.2.0/24, and 10.1.3.0/24 with
one summary address, 10.1.0.0/16.
If more specific routes are in the routing table, RIP advertises the summary address from the interface
with a metric equal to the maximum metric of the more specific routes.
Note
Cisco NX-OS does not support automatic route summarization.
Route Redistribution
You can use RIP to redistribute static routes or routes from other protocols. You configure redistribution
use a route policy to control which routes are passed into RIP. A route policy allows you to filter routes
based on attributes such as the destination, origination protocol, route type, route tag, and so on. For
more information, see Chapter 13, “Configuring Route Policy Manager.”
Whenever you redistribute routes into a RIP routing domain, Cisco NX-OS does not, by default,
redistribute the default route into the RIP routing domain. You can generate a default route into RIP,
which can be controlled by a route policy.
You also configure the default metric that is used for all imported routes into RIP.
Load Balancing
You can use load balancing to allow a router to distribute traffic over all the router network ports that are
the same distance from the destination address. Load balancing increases the utilization of network
segments and increases effective network bandwidth.
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Licensing Requirements for RIP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Cisco NX-OS supports the Equal Cost Multiple Paths (ECMP) feature with up to 16 equal-cost paths in
the RIP route table and the unicast RIB. You can configure RIP to load balance traffic across some or all
of those paths.
Virtualization Support
Cisco NX-OS supports multiple instances of the RIP protocol that runs on the same system. RIP supports
Virtual Routing and Forwarding instances (VRFs).
By default, Cisco NX-OS places you in the default VRF unless you specifically configure another VRF.
See Chapter 11, “Configuring Layer 3 Virtualization.”
Licensing Requirements for RIP
The following table shows the licensing requirements for this feature:
Product
License Requirement
Cisco NX-OS
RIP requires no license. Any feature not included in a license package is bundled with the Cisco NX-OS
system images and is provided at no extra charge to you. For a complete explanation of the Cisco NX-OS
licensing scheme, see the Cisco NX-OS Licensing Guide.
Make sure the LAN Base Services license is installed on the switch to enable Layer 3 interfaces.
Note
Prerequisites for RIP
RIP has the following prerequisites:
•
You must enable the RIP feature (see the “Enabling the RIP Feature” section on page 9-5).
Guidelines and Limitations
RIP has the following configuration guidelines and limitations:
•
Cisco NX-OS does not support RIPv1. If Cisco NX-OS receives a RIPv1 packet, it logs a message
and drops the packet.
•
Cisco NX-OS does not establish adjacencies with RIPv1 routers.
Default Settings
Table 9-1 lists the default settings for RIP parameters.
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S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Table 9-1
Default RIP Parameters
Parameters
Default
Maximum paths for load balancing
16
RIP feature
Disabled
Split horizon
Enabled
Configuring RIP
This section includes the following topics:
Note
•
Enabling the RIP Feature, page 9-5
•
Creating a RIP Instance, page 9-6
•
Configuring RIP on an Interface, page 9-8
•
Configuring a Passive Interface, page 9-11
•
Configuring Route Summarization, page 9-11
•
Configuring Route Summarization, page 9-11
•
Configuring Route Redistribution, page 9-12
•
Configuring Virtualization, page 9-13
•
Tuning RIP, page 9-16
If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature
might differ from the Cisco IOS commands that you would use.
Enabling the RIP Feature
You must enable the RIP feature before you can configure RIP.
SUMMARY STEPS
1.
configure terminal
2.
feature rip
3.
(Optional) show feature
4.
(Optional) copy running-config startup-config
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Configuring RIP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
feature rip
Enables the RIP feature.
Example:
switch(config)# feature rip
Step 3
show feature
(Optional) Displays enabled and disabled features.
Example:
switch(config)# show feature
Step 4
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
Use the no feature rip command to disable the RIP feature and remove all associated configuration.
Command
Purpose
no feature rip
Disables the RIP feature and removes all associated
configuration.
Example:
switch(config)# no feature rip
Creating a RIP Instance
You can create a RIP instance and configure the address family for that instance.
BEFORE YOU BEGIN
Ensure that you have enabled the RIP feature (see the “Enabling the RIP Feature” section on page 9-5).
SUMMARY STEPS
1.
configure terminal
2.
router rip instance-tag
3.
address-family ipv4 unicast
4.
(Optional) show ip rip [instance instance-tag] [vrf vrf-name]
5.
(Optional) copy running-config startup-config
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Configuring RIP
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router rip instance-tag
Example:
switch(config)# router RIP Enterprise
switch(config-router)#
Creates a new RIP instance with the configured
instance-tag.
Step 3
address-family ipv4 unicast
Example:
switch(config-router)# address-family
ipv4 unicast
switch(config-router-af)#
Configures the address family for this RIP instance and
enters address-family configuration mode.
Step 4
show ip rip [instance instance-tag] [vrf
vrf-name]
(Optional) Displays a summary of RIP information for
all RIP instances.
Example:
switch(config-router-af)# show ip rip
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router-af)# copy
running-config startup-config
Use the no router rip command to remove the RIP instance and the associated configuration.
Command
Purpose
no router rip instance-tag
Deletes the RIP instance and all associated
configuration.
Example:
switch(config)# no router rip Enterprise
Note
You must also remove any RIP commands configured in interface mode.
You can configure the following optional parameters for RIP in address-family configuration mode:
Command
Purpose
distance value
Sets the administrative distance for RIP. The range
is from 1 to 255. The default is 120. See the
“Administrative Distance” section on page 1-7.
Example:
switch(config-router-af)# distance 30
maximum-paths number
Example:
switch(config-router-af)# maximum-paths 6
Configures the maximum number of equal-cost
paths that RIP maintains in the route table. The
range is from 1 to 16. The default is 16.
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Configuring RIP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
This example shows how to create a RIP instance for IPv4 and set the number of equal-cost paths for
load balancing:
switch# configure terminal
switch(config)# router rip Enterprise
switch(config-router)# address-family ipv4 unicast
switch(config-router-af)# max-paths 10
switch(config-router-af)# copy running-config startup-config
Restarting a RIP Instance
You can restart a RIP instance. This clears all neighbors for the instance.
To restart an RIP instance and remove all associated neighbors, use the following command:
Command
Purpose
restart rip instance-tag
Restarts the RIP instance and removes all
neighbors.
Example:
switch(config)# restart rip Enterprise
Configuring RIP on an Interface
You can add an interface to a RIP instance.
BEFORE YOU BEGIN
Ensure that you have enabled the RIP feature (see the “Enabling the RIP Feature” section on page 9-5).
SUMMARY STEPS
1.
configure terminal
2.
interface interface-type slot/port
3.
no switchport
4.
ip rip instance-tag
5.
(Optional) show ip rip [instance instance-tag] interface [interface-type slot/port] [vrf vrf-name]
[detail]
6.
(Optional) copy running-config startup-config
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Configuring RIP
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface interface-type slot/port
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 1/2
switch(config-if)#
Step 3
Configures the interface as a Layer 3 routed interface.
no switchport
Example:
switch(config-if)# no switchport
Step 4
ip router rip instance-tag
Associates this interface with a RIP instance.
Example:
switch(config-if)# ip router rip
Enterprise
Step 5
show ip rip [instance instance-tag]
interface [interface-type slot/port]
[vrf vrf-name] [detail]
(Optional) Displays RIP information for an interface.
Example:
switch(config-if)# show ip rip
Enterprise tethernet 1/2
Step 6
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-if)# copy running-config
startup-config
This example shows how to add the Ethernet 1/2 interface to a RIP instance:
switch# configure terminal
switch(config)# interface ethernet 1/2
switch(config-if)# no switchport
switch(config-if)# ip router rip Enterprise
switch(config)# copy running-config startup-config
Configuring RIP Authentication
You can configure authentication for RIP packets on an interface.
BEFORE YOU BEGIN
Ensure that you have enabled the RIP feature (see the “Enabling the RIP Feature” section on page 9-5).
Configure a key chain if necessary before enabling authentication. See the Cisco Nexus 7000 Series
NX-OS Security Configuration Guide, Release 5.x for details on implementing key chains.
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Configuring RIP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
SUMMARY STEPS
1.
configure terminal
2.
interface interface-type slot/port
3.
no switchport
4.
ip rip authentication mode{text | md5}
5.
ip rip authentication key-chain key
6.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface interface-type slot/port
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 1/2
switch(config-if)#
Step 3
no switchport
Configures the interface as a Layer 3 routed interface.
Example:
switch(config-if)# no switchport
Step 4
ip rip authentication mode {text | md5}
Example:
switch(config-if)# ip rip authentication
mode md5
Step 5
ip rip authentication key-chain key
Example:
switch(config-if)# ip rip authentication
keychain RIPKey
Step 6
copy running-config startup-config
Sets the authentication type for RIP on this interface as
cleartext or MD5 authentication digest.
Configures the authentication key used for RIP on this
interface.
(Optional) Saves this configuration change.
Example:
switch(config-if)# copy running-config
startup-config
This example shows how to create a key chain and configure MD5 authentication on a RIP interface:
switch# configure terminal
switch(config)# key chain RIPKey
switch(config)# key-string myrip
switch(config)# accept-lifetime 00:00:00 Jan 01 2000 infinite
switch(config)# send-lifetime 00:00:00 Jan 01 2000 infinite
switch(config)# interface ethernet 1/2
switch(config-if)# no switchport
switch(config-if)# ip rip authentication mode md5
switch(config-if)# ip rip authentication keychain RIPKey
switch(config-if)# copy running-config startup-config
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Configuring RIP
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Configuring a Passive Interface
You can configure a RIP interface to receive routes but not send route updates by setting the interface to
passive mode.
To configure a RIP interface in passive mode, use the following command in interface configuration
mode:
Command
Purpose
ip rip passive-interface
Sets the interface into passive mode.
Example:
switch(config-if)# ip rip
passive-interface
Configuring Split Horizon with Poison Reverse
You can configure an interface to advertise routes learned by RIP as unreachable over the interface that
learned the routes by enabling poison reverse.
To configure split horizon with poison reverse on an interface, use the following command in interface
configuration mode:
Command
Purpose
ip rip poison-reverse
Enables split horizon with poison reverse. Split
horizon with poison reverse is disabled by default.
Example:
switch(config-if)# ip rip poison-reverse
Configuring Route Summarization
You can create aggregate addresses that are represented in the routing table by a summary address. Cisco
NX-OS advertises the summary address metric that is the smallest metric of all the more-specific routes.
To configure a summary address on an interface, use the following command in interface configuration
mode:
Command
Purpose
ip rip summary-address ip-prefix/mask-len
Configures a summary address for RIP for IPv4
addresses.
Example:
switch(config-if)# ip router rip
summary-address 192.0.2.0/24
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Configuring RIP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Configuring Route Redistribution
You can configure RIP to accept routing information from another routing protocol and redistribute that
information through the RIP network. Redistributed routes can optionally be assigned a default route.
BEFORE YOU BEGIN
Ensure that you have enabled the RIP feature (see the “Enabling the RIP Feature” section on page 9-5).
Configure a route map before configuring redistribution. See the“Configuring Route Maps” section on
page 13-12 for details on configuring route maps.
SUMMARY STEPS
1.
configure terminal
2.
router rip instance-tag
3.
address-family ipv4 unicast
4.
redistribute {bgp as | direct | eigrp | ospf | ospfv3 | rip} instance-tag | static} route-map
map-name
5.
(Optional) default-information originate [always] [route-map map-name]
6.
(Optional) default-metric value
7.
(Optional) show ip rip route [{ip-prefix [longer-prefixes | shorter-prefixes]] [vrf vrf-name]
[summary]
8.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router rip instance-tag
Example:
switch(config)# router rip Enterprise
switch(config-router)#
Step 3
address-family ipv4 unicast
Creates a new RIP instance with the configured
instance-tag.
Enters address family configuration mode.
Example:
switch(config-router)# address-family
ipv4 unicast
switch(config-router-af)#
Step 4
redistribute {bgp as | direct |{eigrp |
ospf | ospfv3 | rip} instance-tag |
static} route-map map-name
Redistributes routes from other protocols into RIP. See
the “Configuring Route Maps” section on page 13-12
for more information about route maps.
Example:
switch(config-router-af)# redistribute
eigrp 201 route-map RIPmap
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Step 5
Command
Purpose
default-information originate [always]
[route-map map-name]
(Optional) Generates a default route into RIP,
optionally controlled by a route map.
Example:
switch(config-router-af)#
default-information originate always
Step 6
default-metric value
Example:
switch(config-router-af)# default-metric
10
Step 7
show ip rip route [ip-prefix
[longer-prefixes | shorter-prefixes]
[vrf vrf-name] [summary]
(Optional) Sets the default metric for all redistributed
routes. The range is from 1 to 15. The default is 1.
(Optional) Shows the routes in RIP.
Example:
switch(config-router-af)# show ip rip
route
Step 8
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router-af)# copy
running-config startup-config
This example shows how to redistribute EIGRP into RIP:
switch# configure terminal
switch(config)# router rip Enterprise
switch(config-router)# address-family ipv4 unicast
switch(config-router-af)# redistribute eigrp 201 route-map RIPmap
switch(config-router-af)# copy running-config startup-config
Configuring Virtualization
You can create multiple VRFs and use the same or multiple RIP instances in each VRF. You assign a RIP
interface to a VRF.
Note
Configure all other parameters for an interface after you configure the VRF for an interface. Configuring
a VRF for an interface deletes all the configuration for that interface.
BEFORE YOU BEGIN
Ensure that you have enabled the RIP feature (see the “Enabling the RIP Feature” section on page 9-5).
SUMMARY STEPS
1.
configure terminal
2.
vrf vrf-name
3.
exit
4.
router rip instance-tag
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Configuring RIP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
5.
vrf context vrf_name
6.
(Optional) address-family ipv4 unicast
7.
(Optional) redistribute {bgp as | direct | {eigrp | ospf | ospfv3 | rip} instance-tag | static}
route-map map-name
8.
interface ethernet slot/port
9.
no switchport
10. vrf member vrf-name
11. ip-address ip-prefix/length
12. ip router rip instance-tag
13. (Optional) show ip rip [instance instance-tag] interface [interface-type slot/port] [vrf vrf-name]
14. (Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
vrf vrf-name
Creates a new VRF.
Example:
switch(config)# vrf RemoteOfficeVRF
switch(config-vrf)#
Step 3
exit
Exits VRF configuration mode.
Example:
switch(config-vrf)# exit
switch(config)#
Step 4
router rip instance-tag
Example:
switch(config)# router rip Enterprise
switch(config-router)#
Step 5
vrf context vrf-name
Example:
switch(config)# vrf context
RemoteOfficeVRF
switch(config-vrf)#
Step 6
address-family ipv4 unicast
Example:
switch(config-router-vrf)#
address-family ipv4 unicast
switch(config-router-vrf-af)#
Creates a new RIP instance with the configured
instance tag.
Creates a new VRF and enters VRF configuration
mode.
(Optional) Configures the VRF address family for this
RIP instance.
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Configuring RIP
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Step 7
Command
Purpose
redistribute {bgp as | direct | {eigrp |
ospf | ospfv3 | rip} instance-tag |
static} route-map map-name
(Optional) Redistributes routes from other protocols
into RIP. See the “Configuring Route Maps” section
on page 13-12 for more information about route maps.
Example:
switch(config-router-vrf-af)#
redistribute eigrp 201 route-map RIPmap
Step 8
interface ethernet slot/port
Enters interface configuration mode.
Example:
switch(config-router-vrf-af)# interface
ethernet 1/2
switch(config-if)#
Step 9
Configures the interface as a Layer 3 routed interface.
no switchport
Example:
switch(config-if)# no switchport
Step 10
vrf member vrf-name
Adds this interface to a VRF.
Example:
switch(config-if)# vrf member
RemoteOfficeVRF
Step 11
ip address ip-prefix/length
Example:
switch(config-if)# ip address
192.0.2.1/16
Step 12
ip router rip instance-tag
Configures an IP address for this interface. You must
do this step after you assign this interface to a VRF.
Associates this interface with a RIP instance.
Example:
switch(config-if)# ip router rip
Enterprise
Step 13
show ip rip [instance instance-tag]
interface [interface-type slot/port]
[vrf vrf-name]
(Optional) Displays RIP information for an interface.
in a VRF.
Example:
switch(config-if)# show ip rip
Enterprise ethernet 1/2
Step 14
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-if)# copy running-config
startup-config
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Configuring RIP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
This example shows how to create a VRF and add an interface to the VRF:
switch# configure terminal
switch(config)# vrf context RemoteOfficeVRF
switch(config-vrf)# exit
switch(config)# router rip Enterprise
switch(config-router)# vrf RemoteOfficeVRF
switch(config-router-vrf)# address-family ipv4 unicast
switch(config-router-vrf-af)# redistribute eigrp 201 route-map RIPmap
switch(config-router-vrf-af)# interface ethernet 1/2
switch(config-if)# no switchport
switch(config-if)# vrf member RemoteOfficeVRF
switch(config-if)# ip address 192.0.2.1/16
switch(config-if)# ip router rip Enterprise
switch(config-if)# copy running-config startup-config
Tuning RIP
You can tune RIP to match your network requirements. RIP uses several timers that determine the
frequency of routing updates, the length of time before a route becomes invalid, and other parameters.
You can adjust these timers to tune routing protocol performance to better suit your internetwork needs.
Note
You must configure the same values for the RIP timers on all RIP-enabled routers in your network.
You can use the following optional commands in address-family configuration mode to tune RIP:
Command
Purpose
timers basic update timeout holddown
garbage-collection
Example:
switch(config-router-af)# timers basic 40
120 120 100
Sets the RIP timers in seconds. The parameters are
as follows:
•
update—The range is from 5 to any positive
integer. The default is 30.
•
timeout—The time that Cisco NX-OS waits
before declaring a route as invalid. If Cisco
NX-OS does not receive route update
information for this route before the timeout
interval ends, Cisco NX-OS declares the route
as invalid. The range is from 1 to any positive
integer. The default is 180.
•
holddown—The time during which Cisco
NX-OS ignores better route information for an
invalid route. The range is from 0 to any
positive integer. The default is 180.
•
garbage-collection—The time from when
Cisco NX-OS marks a route as invalid until
Cisco NX-OS removes the route from the
routing table. The range is from 1 to any
positive integer. The default is 120.
You can use the following optional commands in interface configuration mode to tune RIP:
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Verifying the RIP Configuration
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Command
Purpose
ip rip metric-offset value
Adds a value to the metric for every router received
on this interface. The range is from 1 to 15. The
default is 1.
Example:
switch(config-if)# ip rip metric-offset 10
ip rip route-filter {prefix-list list-name
| route-map map-name| [in | out]
Specifies a route map to filter incoming or outgoing
RIP updates.
Example:
switch(config-if)# ip rip route-filter
route-map InputMap in
Verifying the RIP Configuration
To display the RIP configuration information, perform one of the following tasks:
Command
Purpose
show ip rip instance [instance-tag] [vrf
vrf-name]
Displays the status for an instance of RIP.
show ip rip [instance instance-tag] interface
slot/port detail [vrf vrf-name]
Displays the RIP status for an interface.
show ip rip [instance instance-tag] neighbor
[interface-type number] [vrf vrf-name]
Displays the RIP neighbor table.
show ip} rip [instance instance-tag] route
[ip-prefix/lengh [longer-prefixes |
shorter--prefixes]] [summary] [vrf vrf-name]
Displays the RIP route table.
show running-configuration rip
Displays the current running RIP configuration.
Displaying RIP Statistics
To display the RIP statistics, use the following commands:
Command
Purpose
show ip rip [instance instance-tag] policy Displays the RIP policy status.
statistics redistribute {bgp as | direct |
{eigrp | ospf | ospfv3 | rip} instance-tag |
static} [vrf vrf-name]
show ip rip [instance instance-tag]
statistics interface-type number] [vrf
vrf-name]
Displays the RIP statistics.
Use the clear ip rip policy command to clear policy statistics.
Use the clear ip rip statistics command to clear RIP statistics.
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Configuration Examples for RIP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Configuration Examples for RIP
This example creates the Enterprise RIP instance in a VRF and adds Ethernet interface 1/2 to this RIP
instance. The example also configures authentication for Ethernet interface 1/2 and redistributes EIGRP
into this RIP domain.
vrf context NewVRF
!
feature rip
router rip Enterprise
vrf NewVRF
address-family ip unicast
redistribute eigrp 201 route-map RIPmap
max-paths 10
!
interface ethernet 1/2
no switchport
vrf NewVRF
ip address 192.0.2.1/16
ip router rip Enterprise
ip rip authentication mode md5
ip rip authentication keychain RIPKey
Related Topics
See Chapter 13, “Configuring Route Policy Manager” for more information on route maps.
Additional References
For additional information related to implementing RIP, see the following sections:
•
Related Documents, page 9-19
•
Standards, page 9-19
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Feature History for RIP
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Related Documents
Related Topic
Document Title
RIP CLI commands
Cisco Nexus 3000 Series Command Reference,
Standards
Standards
Title
No new or modified standards are supported by this
—
feature, and support for existing standards has not been
modified by this feature.
Feature History for RIP
Table 9-2 lists the release history for this feature.
Table 9-2
Feature History for RIP
Feature Name
Releases
Feature Information
RIP
5.0(3)U1(1)
This feature was introduced.
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CH A P T E R
10
Configuring Static Routing
This chapter describes how to configure static routing on the switch.
This chapter includes the following sections:
•
Information About Static Routing, page 10-1
•
Licensing Requirements for Static Routing, page 10-3
•
Prerequisites for Static Routing, page 10-3
•
Guidelines and Limitations, page 10-3
•
Default Settings, page 10-3
•
Configuring Static Routing, page 10-4
•
Verifying the Static Routing Configuration, page 10-6
•
Configuration Examples for Static Routing, page 10-6
•
Additional References, page 10-6
•
Feature History for Static Routing, page 10-7
Information About Static Routing
Routers forward packets using either route information from route table entries that you manually
configure or the route information that is calculated using dynamic routing algorithms.
Static routes, which define explicit paths between two routers, cannot be automatically updated; you
must manually reconfigure static routes when network changes occur. Static routes use less bandwidth
than dynamic routes. No CPU cycles are used to calculate and analyze routing updates.
You can supplement dynamic routes with static routes where appropriate. You can redistribute static
routes into dynamic routing algorithms but you cannot redistribute routing information calculated by
dynamic routing algorithms into the static routing table.
You should use static routes in environments where network traffic is predictable and where the network
design is simple. You should not use static routes in large, constantly changing networks because static
routes cannot react to network changes. Most networks use dynamic routes to communicate between
routers but may have one or two static routes configured for special cases. Static routes are also useful
for specifying a gateway of last resort (a default router to which all unroutable packets are sent).
This section includes the following topics:
•
Administrative Distance, page 10-2
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Information About Static Routing
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
•
Directly Connected Static Routes, page 10-2
•
Fully Specified Static Routes, page 10-2
•
Floating Static Routes, page 10-2
•
Remote Next Hops for Static Routes, page 10-3
•
Virtualization Support, page 10-3
Administrative Distance
An administrative distance is the metric used by routers to choose the best path when there are two or
more routes to the same destination from two different routing protocols. An administrative distance
guides the selection of one routing protocol (or static route) over another, when more than one protocol
adds the same route to the unicast routing table. Each routing protocol is prioritized in order of most to
least reliable using an administrative distance value.
Static routes have a default administrative distance of 1. A router prefers a static route to a dynamic route
because the router considers a route with a low number to be the shortest. If you want a dynamic route
to override a static route, you can specify an administrative distance for the static route. For example, if
you have two dynamic routes with an administrative distance of 120, you would specify an
administrative distance that is greater than 120 for the static route if you want the dynamic route to
override the static route.
Directly Connected Static Routes
You need to specify only the output interface (the interface on which all packets are sent to the
destination network) in a directly connected static route. The router assumes the destination is directly
attached to the output interface and the packet destination is used as the next hop address. The next-hop
can be an interface, only for point-to-point interfaces. For broadcast interfaces, the next-hop must be an
IPv4 address.
Fully Specified Static Routes
You must specify either the output interface (the interface on which all packets are sent to the destination
network) or the next hop address in a fully specified static route. You can use a fully specified static route
when the output interface is a multi-access interface and you need to identify the next-hop address. The
next-hop address must be directly attached to the specified output interface.
Floating Static Routes
A floating static route is a static route that the router uses to back up a dynamic route. You must configure
a floating static route with a higher administrative distance than the dynamic route that it backs up. In
this instance, the router prefers a dynamic route to a floating static route. You can use a floating static
route as a replacement if the dynamic route is lost.
Note
By default, a router prefers a static route to a dynamic route because a static route has a smaller
administrative distance than a dynamic route.
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Licensing Requirements for Static Routing
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Remote Next Hops for Static Routes
You can specify the next-hop address of a neighboring router which is not directly connected to the
router for static routes with remote (non-directly attached) next-hops. If a static route has remote
next-hops during data-forwarding, the next-hops are recursively used in the unicast routing table to
identify the corresponding directly attached next-hop(s) that have reachability to the remote next-hops
Virtualization Support
Static routes support Virtual Routing and Forwarding instances (VRFs). By default, Cisco NX-OS places
you in the default VRF unless you specifically configure another VRF. For more information, see
Chapter 11, “Configuring Layer 3 Virtualization.”
Licensing Requirements for Static Routing
The following table shows the licensing requirements for this feature:
Product
License Requirement
Cisco NX-OS
Static routing requires no license. Any feature not included in a license package is bundled with the Cisco
NX-OS system images and is provided at no extra charge to you. For a complete explanation of the Cisco
NX-OS licensing scheme, see the Cisco NX-OS Licensing Guide.
Make sure the LAN Base Services license is installed on the switch to enable Layer 3 interfaces.
Note
Prerequisites for Static Routing
Static routing has the following prerequisites:
•
If the next-hop address for a static route is unreachable, the static route will not be added to the
unicast routing table.
Guidelines and Limitations
Static routing has the following configuration guidelines and limitations:
•
You can specify an interface as the next-hop address for a static route only for point-to-point
interfaces such as GRE tunnels.
Default Settings
Table 10-1 lists the default settings for static routing parameters.
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Configuring Static Routing
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Table 10-1
Default Static Routing Parameters
Parameters
Default
administrative distance
1
RIP feature
disabled
Configuring Static Routing
This section includes the following topics:
Note
•
Configuring a Static Route, page 10-4
•
Configuring Virtualization, page 10-5
If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature
might differ from the Cisco IOS commands that you would use.
Configuring a Static Route
You can configure a static route on the router.
SUMMARY STEPS
1.
configure terminal
2.
ip route {ip-prefix | ip-addr ip-mask} {[next-hop | nh-prefix] | [interface next-hop | nh-prefix]} [tag
tag-value [pref]]
3.
(Optional) show ip static-route
4.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
ip route {ip-prefix | ip-addr ip-mask}
{[next-hop | nh-prefix] | [interface
next-hop | nh-prefix]} [tag tag-value
[pref]
Configures a static route and the interface for this
static route. You can optionally configure the next-hop
address. The preference value sets the administrative
distance. The range is from 1 to 255. The default is 1.
Example:
switch(config)# ip route 192.0.2.0/8
ethernet 1/2 192.0.2.4
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Configuring Static Routing
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Step 3
Command
Purpose
show ip static-route
(Optional) Displays information about static routes.
Example:
switch(config)# show ip static-route
Step 4
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
This example shows how to configure a static route:
switch# configure terminal
switch(config)# ip route 192.0.2.0/8 192.0.2.10
switch(config)# copy running-config startup-config
Use the no ip static-route command to remove the static route.
Configuring Virtualization
You can configure a static route in a VRF.
SUMMARY STEPS
1.
configure terminal
2.
vrf context vrf-name
3.
ip route {ip-prefix | ip-addr ip-mask} {next-hop | nh-prefix | interface} [tag tag-value [pref]
4.
(Optional) show ip static-route vrf vrf-name
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
vrf context vrf-name
Creates a VRF and enters VRF configuration mode.
Example:
switch(config)# vrf context StaticVrf
Step 3
ip route {ip-prefix | ip-addr ip-mask}
{next-hop | nh-prefix | interface} [tag
tag-value [pref]
Example:
switch(config-vrf)# ip route 192.0.2.0/8
ethernet 1/2
Configures a static route and the interface for this
static route. You can optionally configure the next-hop
address. The preference value sets the administrative
distance. The range is from 1 to 255. The default is 1.
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Verifying the Static Routing Configuration
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Step 4
Command
Purpose
show ip static-route vrf vrf-name
(Optional) Displays information on static routes.
Example:
switch(config-vrf)# show ip static-route
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-vrf)# copy running-config
startup-config
This example shows how to configure a static route:
switch# configure terminal
switch(config)# vrf context StaticVrf
switch(config-vrf)# ip route 192.0.2.0/8 192.0.2.10
switch(config-vrf)# copy running-config startup-config
Verifying the Static Routing Configuration
To display the static routing configuration information, perform one of the following tasks:
Command
Purpose
show ip static-route
Displays the configured static routes.
Configuration Examples for Static Routing
This example shows how to configure static routing:
configure terminal
ip route 192.0.2.0/8 192.0.2.10
copy running-config startup-config
Additional References
For additional information related to implementing static routing, see the following sections:
•
Related Documents, page 10-7
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Feature History for Static Routing
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Related Documents
Related Topic
Document Title
Static Routing CLI
Cisco Nexus 3000 Series Command Reference,
Feature History for Static Routing
Table 10-2 lists the release history for this feature.
Table 10-2
Feature History for Static Routing
Feature Name
Releases
Feature Information
Static Routing
5.0(3)U1(1)
This feature was introduced.
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CH A P T E R
11
Configuring Layer 3 Virtualization
This chapter describes how to configure Layer 3 virtualization.
This chapter includes the following sections:
•
Layer 3 Virtualization, page 11-1
•
Licensing Requirements for VRFs, page 11-5
•
Prerequisites for VRF, page 10-6
•
Guidelines and Limitations, page 11-5
•
Default Settings, page 11-6
•
Configuring VRFs, page 11-6
•
Verifying the VRF Configuration, page 11-13
•
Configuration Examples for VRF, page 11-13
•
Related Topics, page 11-14
•
Additional References, page 11-14
•
Feature History for VRF, page 11-14
Layer 3 Virtualization
This section includes the following topics:
•
Overview of Layer 3 Virtualization, page 11-1
•
VRF and Routing, page 11-2
•
VRF-Aware Services, page 11-3
Overview of Layer 3 Virtualization
Cisco NX-OS supports virtual routing and forwarding instances (VRFs). Each VRF contains a separate
address space with unicast and multicast route tables for IPv4 and makes routing decisions independent of
any other VRF.
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Layer 3 Virtualization
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Each router has a default VRF and a management VRF. All Layer 3 interfaces and routing protocols exist
in the default VRF until you assign them to another VRF. The mgmt0 interface exists in the management
VRF.With the VRF-lite feature, the switch supports multiple VRFs in customer edge (CE) switches.
VRF-lite allows a service provider to support two or more Virtual Private Networks (VPNs) with
overlapping IP addresses using one interface.
Note
The switch does not use Multiprotocol Label Switching (MPLS) to support VPNs.
VRF and Routing
All unicast and multicast routing protocols support VRFs. When you configure a routing protocol in a
VRF, you set routing parameters for the VRF that are independent of routing parameters in another VRF
for the same routing protocol instance.
You can assign interfaces and route protocols to a VRF to create virtual Layer 3 networks. An interface
exists in only one VRF. Figure 11-1 shows one physical network split into two virtual networks with two
VRFs. Routers Z, A, and B exist in VRF Red and form one address domain. These routers share route
updates that do not include router C because router C is configured in a different VRF.
Figure 11-1
VRFs in a Network
Router B
Router Z
Ethernet 1/1
VRF Red
Ethernet 2/1
VRF Red
Ethernet 2/2
VRF Blue
Router C
186416
Router A
By default, Cisco NX-OS uses the VRF of the incoming interface to select which routing table to use for
a route lookup. You can configure a route policy to modify this behavior and set the VRF that Cisco
NX-OS uses for incoming packets.
Cisco NX-OS prevents route leakage(import or export) between VRFs.
VRF-Lite
VRF-lite is a feature that enables a service provider to support two or more VPNs, where IP addresses
can be overlapped among the VPNs. VRF-lite uses input interfaces to distinguish routes for different
VPNs and forms virtual packet-forwarding tables by associating one or more Layer 3 interfaces with
each VRF. Interfaces in a VRF can be either physical, such as Ethernet ports, or logical, such as VLAN
SVIs, but a Layer 3 interface cannot belong to more than one VRF at any time.
Note
Multiprotocol Label Switching (MPLS) and MPLS control plane are not supported in the VRF-lite
implementation.
Note
VRF-lite interfaces must be Layer 3 interfaces.
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Layer 3 Virtualization
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VRF-Aware Services
A fundamental feature of the Cisco NX-OS architecture is that every IP-based feature is VRF aware.
The following VRF-aware services can select a particular VRF to reach a remote server or to filter
information based on the selected VRF:
•
AAA—See the Cisco Nexus 7000 Series NX-OS Security Configuration Guide, Release 5.x, for more
information.
•
Call Home—See the Cisco Nexus 7000 Series NX-OS System Management Configuration Guide,
Release 5.x, for more information.
•
HSRP—See Chapter 14, “Configuring HSRP” for more information.
•
HTTP—See the Cisco Nexus 7000 Series NX-OS Fundamentals Configuration Guide, Release 5.x,
for more information.
•
Licensing—See theCisco NX-OS Licensing Guide for more information.
•
NTP—See the Cisco Nexus 7000 Series NX-OS System Management Configuration Guide, Release
5.x, for more information.
•
RADIUS—See the Cisco Nexus 7000 Series NX-OS Security Configuration Guide, Release 5.x, for
more information.
•
Ping and Traceroute —See the Cisco Nexus 7000 Series NX-OS Fundamentals Configuration Guide,
Release 5.x, for more information.
•
SSH—See the Cisco Nexus 7000 Series NX-OS Fundamentals Configuration Guide, Release 5.x, for
more information.
•
SNMP—See the Cisco Nexus 7000 Series NX-OS System Management Configuration Guide,
Release 5.x, for more information.
•
Syslog—See the Cisco Nexus 7000 Series NX-OS System Management Configuration Guide,
Release 5.x, for more information.
•
TACACS+—See the Cisco Nexus 7000 Series NX-OS Security Configuration Guide, Release 5.x, for
more information.
•
TFTP—See the Cisco Nexus 7000 Series NX-OS Fundamentals Configuration Guide, Release 5.x,
for more information.
•
VRRP—See Chapter 15, “Configuring VRRP” for more information.
See the appropriate configuration guide for each service for more information on configuring VRF
support in that service.
This section contains the following topics:
•
Reachability, page 11-3
•
Filtering, page 11-4
•
Combining Reachability and Filtering, page 11-4
Reachability
Reachability indicates which VRF contains the routing information necessary to get to the server
providing the service. For example, you can configure an SNMP server that is reachable on the
management VRF. When you configure that server address on the router, you also configure which VRF
that Cisco NX-OS must use to reach the server.
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Layer 3 Virtualization
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Figure 11-2 shows an SNMP server that is reachable over the management VRF. You configure router A
to use the management VRF for SNMP server host 192.0.2.1.
Figure 11-2
Service VRF Reachability
SNMP Server
192.0.2.1
Router A
mgmt0
186417
VRF management
Filtering
Filtering allows you to limit the type of information that goes to a VRF-aware service based on the VRF.
For example, you can configure a syslog server to support a particular VRF. Figure 11-3 shows two
syslog servers with each server supporting one VRF. syslog server A is configured in VRF Red, so Cisco
NX-OS sends only system messages generated in VRF Red to syslog server A.
Figure 11-3
Service VRF Filtering
Syslog Server A
Ethernet 2/1
VRF Red
Router A
VRF Blue
Syslog Server B
186418
Ethernet 2/2
Combining Reachability and Filtering
You can combine reachability and filtering for VRF-aware services. You configure the VRF that Cisco
NX-OS uses to connect to that service as well as the VRF that the service supports. If you configure a
service in the default VRF, you can optionally configure the service to support all VRFs.
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Licensing Requirements for VRFs
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Figure 11-4 shows an SNMP server that is reachable on the management VRF. You can configure the
SNMP server to support only the SNMP notifications from VRF Red, for example.
Figure 11-4
Service VRF Reachability Filtering
Router B
Router A
mgmt0
VRF management
Ethernet 2/1
VRF Red
Ethernet 2/2
VRF Blue
Router C
186419
SNMP Server
192.0.2.1
Licensing Requirements for VRFs
The following table shows the licensing requirements for this feature:
Product
License Requirement
Cisco NX-OS
The default inband and outband management VRFs require no license. Any feature not included in a license
package is bundled with the Cisco NX-OS system images and is provided at no extra charge to you. For a
complete explanation of the Cisco NX-OS licensing scheme, see the Cisco NX-OS Licensing Guide.
Cisco NX-OS
VRF-lite requires an Enterprise services license. For a complete explanation of the Cisco NX-OS licensing
scheme, see the Cisco NX-OS Licensing Guide.
Guidelines and Limitations
VRFs have the following configuration guidelines and limitations:
•
When you make an interface a member of an existing VRF, Cisco NX-OS removes all Layer 3
configuration. You should configure all Layer 3 parameters after adding an interface to a VRF.
•
You should add the mgmt0 interface to the management VRF and configure the mgmt0 IP address
and other parameters after you add it to the management VRF.
•
If you configure an interface for a VRF before the VRF exists, the interface is operationally down
until you create the VRF.
•
Cisco NX-OS creates the default and management VRFs by default. You should make the mgmt0
interface a member of the management VRF.
•
The write erase boot command does not remove the management VRF configuration. You must use
the write erase command and then the write erase boot command.
VRF-lite has the following guidelines and limitations:
•
A switch with VRF-lite has a separate IP routing table for each VRF, which is separate from the
global routing table.
•
Because VRF-lite uses different VRF tables, the same IP addresses can be reused. Overlapped IP
addresses are allowed in different VPNs.
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Default Settings
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
•
VRF-lite does not support all MPLS-VRF functionality; it does not support label exchange, LDP
adjacency, or labeled packets.
•
Multiple virtual Layer 3 interfaces can be connected to a VRF-lite switch.
•
The switch supports configuring a VRF by using physical ports, VLAN SVIs, or a combination of
both. The SVIs can be connected through an access port or a trunk port.
•
The Layer 3 TCAM resource is shared between all VRFs. To ensure that any one VRF has sufficient
CAM space, use the maximum routes command.
•
The total number of routes supported by all the VRF's is limited by the size of the TCAM.
•
VRF-lite supports BGP, RIP, and static routing.
•
VRF-lite does not support EIGRP.
•
VRF-lite does not affect the packet switching rate.
•
Multicast cannot be configured on the same Layer 3 interface at the same time.
•
VRF-lite is supported only on an IPv4 network.
Default Settings
Table 11-1 lists the default settings for VRF parameters.
Table 11-1
Default VRF Parameters
Parameters
Default
Configured VRFs
default, management
routing context
default VRF
Configuring VRFs
This section contains the following topics:
Note
•
Creating a VRF, page 11-6
•
Assigning VRF Membership to an Interface, page 11-8
•
Configuring VRF Parameters for a Routing Protocol, page 11-9
•
Configuring a VRF-Aware Service, page 11-11
•
Setting the VRF Scope, page 11-12
If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature
might differ from the Cisco IOS commands that you would use.
Creating a VRF
You can create a VRF in a switch.
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Configuring VRFs
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
SUMMARY STEPS
1.
configure terminal
2.
vrf context name
3.
ip route {ip-prefix | ip-addr ip-mask} {[next-hop | nh-prefix] | [interface next-hop | nh-prefix]} [tag
tag-value [pref]
4.
(Optional) show vrf [vrf-name]
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
vrf context name
Example:
switch(config)# vrf definition
Enterprise
switch(config-vrf)#
Step 3
ip route {ip-prefix | ip-addr ip-mask}
{[next-hop | nh-prefix] | [interface
next-hop | nh-prefix]} [tag tag-value
[pref]
Creates a new VRF and enters VRF configuration
mode. The name can be any case-sensitive,
alphanumeric string up to 32 characters.
Configures a static route and the interface for this
static route. You can optionally configure the next-hop
address. The preference value sets the administrative
distance. The range is from 1 to 255. The default is 1.
Example:
switch(config-vrf)# ip route 192.0.2.0/8
ethernet 1/2 192.0.2.4
Step 4
show vrf [vrf-name]
(Optional) Displays VRF information.
Example:
switch(config-vrf)# show vrf Enterprise
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
Use the no vrf context command to delete the VRF and the associated configuration:
Command
Purpose
no vrf context name
Deletes the VRF and all associated configuration.
Example:
switch(config)# no vrf context Enterprise
Any commands available in global configuration mode are also available in VRF configuration mode.
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Configuring VRFs
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
This example shows how to create a VRF and add a static route to the VRF:
switch# configure terminal
switch(config)# vrf context Enterprise
switch(config-vrf)# ip route 192.0.2.0/8 ethernet 1/2
switch(config-vrf)# exit
switch(config)# copy running-config startup-config
Assigning VRF Membership to an Interface
You can make an interface a member of a VRF.
BEFORE YOU BEGIN
Assign the IP address for an interface after you have configured the interface for a VRF.
SUMMARY STEPS
1.
configure terminal
2.
interface interface-type slot/port
3.
vrf member vrf-name
4.
ip-address ip-prefix/length
5.
(Optional) show vrf vrf-name interface interface-type number
6.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface interface-type slot/port
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 1/2
switch(config-if)#
Step 3
vrf member vrf-name
Adds this interface to a VRF.
Example:
switch(config-if)# vrf member
RemoteOfficeVRF
Step 4
ip address ip-prefix/length
Example:
switch(config-if)# ip address
192.0.2.1/16
Configures an IP address for this interface. You must
do this step after you assign this interface to a VRF.
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Configuring VRFs
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Step 5
Command
Purpose
show vrf vrf-name interface
interface-type number
(Optional) Displays VRF information.
Example:
switch(config-vrf)# show vrf Enterprise
interface ethernet 1/2
Step 6
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
This example shows how to add an interface to the VRF:
switch# configure terminal
switch(config)# interface ethernet 1/2
switch(config-if)# vrf member RemoteOfficeVRF
switch(config-if)# ip address 192.0.2.1/16
switch(config-if)# copy running-config startup-config
Configuring VRF Parameters for a Routing Protocol
You can associate a routing protocol with one or more VRFs. See the appropriate chapter for information
on how to configure VRFs for the routing protocol. This section uses OSPFv2 as an example protocol
for the detailed configuration steps.
SUMMARY STEPS
1.
configure terminal
2.
router ospf instance-tag
3.
vrf vrf-name
4.
(Optional) maximum-paths paths
5.
interface interface-type slot/port
6.
vrf member vrf-name
7.
ip address ip-prefix/length
8.
ip router ospf instance-tag area area-id
9.
(Optional) copy running-config startup-config
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Configuring VRFs
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
router ospf instance-tag
Example:
switch(config-vrf)# router ospf 201
switch(config-router)#
Step 3
vrf vrf-name
Creates a new OSPFv2 instance with the configured
instance tag.
Enters VRF configuration mode.
Example:
switch(config-router)# vrf
RemoteOfficeVRF
switch(config-router-vrf)#
Step 4
maximum-paths paths
Example:
switch(config-router-vrf)# maximum-paths
4
Step 5
interface interface-type slot/port
(Optional) Configures the maximum number of equal
OSPFv2 paths to a destination in the route table for this
VRF. Used for load balancing.
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 1/2
switch(config-if)#
Step 6
vrf member vrf-name
Adds this interface to a VRF.
Example:
switch(config-if)# vrf member
RemoteOfficeVRF
Step 7
ip address ip-prefix/length
Example:
switch(config-if)# ip address
192.0.2.1/16
Step 8
ip router ospf instance-tag area area-id
Example:
switch(config-if)# ip router ospf 201
area 0
Step 9
copy running-config startup-config
Configures an IP address for this interface. You must
do this step after you assign this interface to a VRF.
Assigns this interface to the OSPFv2 instance and area
configured.
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
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Configuring VRFs
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
This example shows how to create a VRF and add an interface to the VRF:
switch# configure terminal
switch(config)# vrf context RemoteOfficeVRF
switch(config-vrf)# exit
switch(config)# router ospf 201
switch(config-router)# vrf RemoteOfficeVRF
switch(config-router-vrf)# maximum-paths 4
switch(config-router-vrf)# interface ethernet 1/2
switch(config-if)# vrf member RemoteOfficeVRF
switch(config-if)# ip address 192.0.2.1/16
switch(config-if)# ip router ospf 201 area 0
switch(config-if)# exit
switch(config)# copy running-config startup-config
Configuring a VRF-Aware Service
You can configure a VRF-aware service for reachability and filtering. See the “VRF-Aware Services”
section on page 11-3 for links to the appropriate chapter or configuration guide for information on how
to configure the service for VRFs. This section uses SNMP and IP domain lists as example services for
the detailed configuration steps.
SUMMARY STEPS
1.
configure terminal
2.
snmp-server host ip-address [filter_vrf vrf-name] [use-vrf vrf-name]
3.
vrf context [vrf-name]
4.
ip domain-list domain-name [all-vrfs][use-vrf vrf-name]
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
snmp-server host ip-address [filter-vrf
vrf-name] [use-vrf vrf-name]
Example:
switch(config)# snmp-server host
192.0.2.1 use-vrf Red
switch(config-vrf)#
Step 3
vrf context vrf-name
Configures a global SNMP server and configures the
VRF that Cisco NX-OS uses to reach the service Use
the filter-vrf keyword to filter information from the
selected VRF to this server.
Creates a new VRF.
Example:
switch(config)# vrf context Blue
switch(config-vrf)#
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Step 4
Command
Purpose
ip domain-list domain-name
[all-vrfs][use-vrf vrf-name]
Configures the domain list in the VRF and optionally
configures the VRF that Cisco NX-OS uses to reach
the domain name listed.
Example:
switch(config-vrf)# ip domain-list List
all-vrfs use-vrf Blue
switch(config-vrf)#
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
This example shows how to send SNMP information for all VRFs to SNMP host 192.0.2.1, reachable on
VRF Red:
switch# configure terminal
switch(config)# snmp-server host 192.0.2.1 for-all-vrfs use-vrf Red
switch(config)# copy running-config startup-config
This example shows how to Filter SNMP information for VRF Blue to SNMP host 192.0.2.12, reachable
on VRF Red:
switch# configure terminal
switch(config)# vrf definition Blue
switch(config-vrf)# snmp-server host 192.0.2.12 use-vrf Red
switch(config)# copy running-config startup-config
Setting the VRF Scope
You can set the VRF scope for all EXEC commands (for example, show commands). This automatically
restricts the scope of the output of EXEC commands to the configured VRF. You can override this scope
by using the VRF keywords available for some EXEC commands.
To set the VRF scope, use the following command in EXEC mode:
Command
Purpose
routing-context vrf vrf-name
Sets the routing context for all EXEC commands.
Default routing context is the default VRF.
Example:
switch# routing-context vrf red
switch%red#
To return to the default VRF scope, use the following command in EXEC mode:
Command
Purpose
routing-context vrf default
Sets the default routing context.
Example:
switch%red# routing-context vrf default
switch#
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Verifying the VRF Configuration
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Verifying the VRF Configuration
To display the VRF configuration information, perform one of the following tasks:
Command
Purpose
show vrf [vrf-name]
Displays the information for all or one VRF.
show vrf [vrf-name] detail
Displays detailed information for all or one VRF.
show vrf [vrf-name] [interface interface-type
slot/port]
Displays the VRF status for an interface.
Configuration Examples for VRF
This example shows how to configure VRF Red, add an SNMP server to that VRF, and add an instance
of OSPF to VRF Red:
configure terminal
vrf context Red
snmp-server host 192.0.2.12 use-vrf Red
router ospf 201
interface ethernet 1/2
vrf member Red
ip address 192.0.2.1/16
ip router ospf 201 area 0
This example shows how to configure VRF Red and Blue, add an instance of OSPF to each VRF, and
create an SNMP context for each OSPF instance in each VRF.:
configure terminal
!Create the VRFs
vrf context Red
vrf context Blue
!Create the OSPF instances and associate them with each VRF
feature ospf
router ospf Lab
vrf Red
router ospf Production
vrf Blue
!Configure one interface to use ospf Lab on VRF Red
interface ethernet 1/2
vrf member Red
ip address 192.0.2.1/16
ip router ospf Lab area 0
no shutdown
!Configure another interface to use ospf Production on VRF Blue
interface ethernet 10/2
vrf member Blue
ip address 192.0.2.1/16
ip router ospf Production area 0
no shutdown
!configure the SNMP server
snmp-server user admin network-admin auth md5 nbv-12345
snmp-server community public ro
!Create the SNMP contexts for each VRF
snmp-server context lab instance Lab vrf Red
snmp-server context production instance Production vrf Blue
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Related Topics
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Use the SNMP context lab to access the OSPF-MIB values for the OSPF instance Lab in VRF Red in
this example.
Related Topics
The following topics can give more information on VRFs:
•
Cisco Nexus 7000 Series NX-OS Fundamentals Configuration Guide, Release 5.x
•
Cisco Nexus 7000 Series NX-OS System Management Configuration Guide, Release 5.x
Additional References
For additional information related to implementing virtualization, see the following sections:
•
Related Documents, page 11-14
•
Standards, page 11-14
Related Documents
Related Topic
Document Title
VRF CLI
Cisco Nexus 3000 Series Command Reference,
Standards
Standards
Title
—
No new or modified standards are supported by this
feature, and support for existing standards has not been
modified by this feature.
Feature History for VRF
Table 11-2 lists the release history for this feature.
Table 11-2
Feature History for VRF
Feature Name
Releases
Feature Information
VRF
5.0(3)U1(1)
This feature was introduced.
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CH A P T E R
12
Managing the Unicast RIB and FIB
This chapter describes how to manage routes in the unicast Routing Information Base (RIB) and the
Forwarding Information Base (FIB) on the Cisco NX-OS switch.
This chapter includes the following sections:
•
Information About the Unicast RIB and FIB, page 12-1
•
Licensing Requirements for the Unicast RIB and FIB, page 12-3
•
Managing the Unicast RIB and FIB, page 12-3
•
Verifying the Unicast RIB and FIB Configuration, page 12-10
•
Additional References, page 12-10
•
Feature History for Unicast RIB and FIB, page 12-10
Information About the Unicast RIB and FIB
The unicast RIB (IPv4 RIB) and FIB are part of the Cisco NX-OS forwarding architecture, as shown in
Figure 12-1.
Figure 12-1
Cisco NX-OS Forwarding Architecture
EIGRP
Switch components
BGP
OSPF
URIB
ARP
Adjacency Manager (AM)
Unicast Forwarding Information Base (UFIB)
239086
Unicast FIB Distribution Module (uFDM)
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Information About the Unicast RIB and FIB
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
The unicast RIB maintains the routing table with directly connected routes, static routes, and routes
learned from dynamic unicast routing protocols. The unicast RIB also collects adjacency information
from sources such as the Address Resolution Protocol (ARP). The unicast RIB determines the best next
hop for a given route and populates the unicast forwarding information base (FIBs) by using the services
of the unicast FIB distribution module (FDM).
Each dynamic routing protocol must update the unicast RIB for any route that has timed out. The unicast
RIB then deletes that route and recalculates the best next hop for that route (if an alternate path is
available).
This section includes the following topics:
•
Layer 3 Consistency Checker, page 12-2
•
FIB Tables, page 12-2
•
Virtualization Support, page 12-2
Layer 3 Consistency Checker
In rare instances, an inconsistency can occur between the unicast RIB and the FIB on each module. Cisco
NX-OS supports the Layer 3 consistency checker. This feature detects inconsistencies between the
unicast IPv4 RIB and the FIB on each interface module. Inconsistencies include the following:
•
Missing prefix
•
Extra prefix
•
Wrong next-hop address
•
Incorrect Layer 2 rewrite string in the ARP or neighbor discovery (ND) cache
The Layer 3 consistency checker compares the FIB entries to the latest adjacency information from the
Adjacency Manager (AM) and logs any inconsistencies. The consistency checker then compares the
unicast RIB prefixes to the module FIB and logs any inconsistencies. See the “Triggering the Layer 3
Consistency Checker” section on page 12-7.
You can then manually clear any inconsistencies. See the “Clearing Forwarding Information in the FIB”
section on page 12-8.
FIB Tables
The hardware provides two tables, a TCAM table and a Hash table. The TCAM table is shared between
the longest prefix match (LPM) route and the /32 unicast route. The Hash table is shared between the /32
unicast entries and the multicast entries. Each table has approximately 8000 routes.
Virtualization Support
The Unicast RIB and FIB support Virtual Routing and Forwarding instances (VRFs). By default, Cisco
NX-OS places you in the default VRF unless you specifically configure another VRF. For more
information, see Chapter 11, “Configuring Layer 3 Virtualization.”
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Licensing Requirements for the Unicast RIB and FIB
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Licensing Requirements for the Unicast RIB and FIB
The following table shows the licensing requirements for this feature:
Product
License Requirement
Cisco NX-OS
The unicast RIB and FIB require no license. Any feature not included in a license package is bundled with
the Cisco NX-OS system images and is provided at no extra charge to you. For a complete explanation of
the Cisco NX-OS licensing scheme, see the Cisco NX-OS Licensing Guide.
Managing the Unicast RIB and FIB
This section includes the following topics:
Note
•
Displaying Module FIB Information, page 12-3
•
Configuring Load Sharing in the Unicast FIB, page 12-4
•
Configuring Per-Packet Load Sharing, page 12-5
•
Displaying Routing and Adjacency Information, page 12-6
•
Triggering the Layer 3 Consistency Checker, page 12-7
•
Clearing Forwarding Information in the FIB, page 12-8
•
Estimating Memory Requirements for Routes, page 12-9
•
Clearing Routes in the Unicast RIB, page 12-9
If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature
might differ from the Cisco IOS commands that you would use.
Displaying Module FIB Information
You can display the FIB information on a switch.
DETAILED STEPS
To display the FIB information on a switch, use the following commands in any mode:
Command
Purpose
show ip fib adjacency
Displays the adjacency information for IPv4.
Example:
switch# show ip fib adjacency
show forwarding ipv4 adjacency
Displays the adjacency information for IPv4.
Example:
switch# show forwarding ipv4
adjacency
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Managing the Unicast RIB and FIB
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Command
Purpose
show ip fib interfaces
Displays the FIB interface information for IPv4.
Example:
switch# show ip fib interfaces
show ip fib route
Displays the route table for IPv4.
Example:
switch# show ip fib route
show forwarding ipv4 route
Displays the route table for IPv4.
Example:
switch# show forwarding ipv4 route
This example shows the FIB contents on a switch:
switch# show ip fib route
IPv4 routes for table default/base
------------------+------------------+--------------------Prefix
| Next-hop
| Interface
------------------+------------------+--------------------0.0.0.0/32
Drop
Null0
255.255.255.255/32 Receive
sup-eth1
Configuring Load Sharing in the Unicast FIB
Dynamic routing protocols, such as Open Shortest Path First (OSPF), support load balancing with
equal-cost multipath (ECMP). The routing protocol determines its best routes based on the metrics
configured for the protocol and installs up to the protocol-configured maximum paths in the unicast RIB.
The unicast RIB compares the administrative distances of all routing protocol paths in the RIB and
selects a best path set from all of the path sets installed by the routing protocols. The unicast RIB installs
this best path set into the FIB for use by the forwarding plane.
The forwarding plane uses a load-sharing algorithm to select one of the installed paths in the FIB to use
for a given data packet.
You can globally configure the following load-sharing settings:
Note
•
load-share mode—Selects the best path based on the destination address and port or the source and
the destination address and port.
•
Universal ID—Sets the random seed for the hash algorithm. You do not need to configure the
Universal ID. Cisco NX-OS chooses the Universal ID if you do not configure it.
Load sharing uses the same path for all packets in a given flow. A flow is defined by the load-sharing
method that you configure. For example, if you configure source-destination load sharing, then all
packets with the same source IP address and destination IP address pair follow the same path.
To configure the unicast FIB load-sharing algorithm, use the following command in global configuration
mode:
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S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Command
Purpose
ip load-sharing address {destination
port destination | source-destination
[port source-destination]}
[universal-id seed]
Configures the unicast FIB load-sharing algorithm for
data traffic. The universal-id range is from 1 to
4294967295.
Example:
switch(config)# ip load-sharing
address source-destination
To display the unicast FIB load-sharing algorithm, use the following command in any mode:
Command
Purpose
show ip load-sharing
Displays the unicast FIB load-sharing algorithm for data
traffic.
Example:
switch(config)# show ip load-sharing
To display the route that the unicast RIB and FIB use for a particular source address and destination
address, use the following command in any mode:
Command
Purpose
show routing hash source-addr
dest-addr [source-port dest-port]
[vrf vrf-name]
Displays the route that the unicast RIB FIB use for a
source and destination address pair. The source address
and destination address format is x.x.x.x. The source port
and destination port range is from 1 to 65535. The VRF
name can be any case-sensitive, alphanumeric string up to
64 characters.
Example:
switch# show routing hash 192.0.2.1
10.0.0.1
This example shows the route selected for a source/destination pair:
switch# show routing hash 10.0.0.5 30.0.0.2
Load-share parameters used for software forwarding:
load-share mode: address source-destination port source-destination
Universal-id seed: 0xe05e2e85
Hash for VRF "default"
Hashing to path *20.0.0.2 (hash: 0x0e), for route:
Configuring Per-Packet Load Sharing
You can use per-packet load sharing to evenly distribute data traffic in an IP network over multiple
equal-cost connections. Per-packet load sharing allows the router to send successive data packets over
paths on a packet-by-packet basis rather than on a per-flow basis.
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Note
Using per-packet load sharing can result in out-of-order packets. Packets for a given pair of
source-destination hosts might take different paths and arrive at the destination out of order. Make sure
you understand the implications of out-of-order packets to your network and applications. Per-packet
load sharing is not appropriate for all networks. Per-flow load sharing ensures packets always arrive in
the order that they were sent.
Per-packet load sharing uses the round-robin method to determine which path each packet takes to the
destination. With per-packet load sharing enabled on interfaces, the router sends one packet for
destination1 over the first path, the second packet for (the same) destination1 over the second path, and
so on. Per-packet load sharing ensures balancing over multiple links.
Use per-packet load sharing to ensure that a path for a single source-destination pair does not get
overloaded. If most of the traffic passing through parallel links is for a single pair, per-destination load
sharing will overload a single link while other links will have very little traffic. Enabling per-packet load
sharing allows you to use alternate paths to the same busy destination.
Note
Per-packet load sharing on an interface overrides the global load-sharing configuration.
You configure per-packet load sharing on the input interface. This configuration determines the output
interface that Cisco NX-OS chooses for the packet.
For example, if you have ECMP paths on two output interfaces, Cisco NX-OS uses the following
load-sharing methods for input packets on Ethernet 1/1:
•
Per-packet load sharing if you configure per-packet load sharing on Ethernet 1/1.
•
Per-flow load sharing.
The configuration for the other interfaces have no effect on the load-sharing method used for Ethernet
1/1 in this example.
To configure per-packet load sharing, use the following command in interface configuration mode:
Command
Purpose
ip load-sharing per-packet
Configures per-packet load sharing on an interface.
Example:
switch(config-if)# ip load-sharing
per-packet
Displaying Routing and Adjacency Information
You can display the routing and adjacency information.
To display the routing and adjacency information, use the following commands in any mode:
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S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Command
Purpose
show ip route [route-type | interface
int-type number | next-hop]
Displays the unicast route table. The route-type argument
can be a single route prefix, direct, static, or a dynamic
route protocol. Use the ? command to see the supported
interfaces.
Example:
switch# show ip route
show ip adjacency [prefix |
interface-type number [summary]|
non-best] [detail] [vrf vrf-id]
Displays the adjacency table. The argument ranges are as
follows:
Example:
switch# show ip adjacency
show ip routing [route-type |
interface int-type number | next-hop
| recursive-next-hop | summary |
updated {since | until} time]
•
prefix—Any IPv4 prefix address.
•
interface-type number—Use the ? command to see
the supported interfaces.
•
vrf-id—Any case-sensitive, alphanumeric string up
to 32 characters.
Displays the unicast route table. The route-type argument
can be a single route prefix, direct, static, or a dynamic
route protocol. Use the ? command to see the supported
interfaces.
Example:
switch# show routing summary
This example displays the unicast route table:
switch# show ip route
IP Route Table for VRF "default"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
192.168.0.2/24, ubest/mbest: 1/0, attached
*via 192.168.0.32, Eth1/5, [0/0], 22:34:09, direct
192.168.0.32/32, ubest/mbest: 1/0, attached
*via 192.168.0.32, Eth1/5, [0/0], 22:34:09, local
This example shows the adjacency information:
switch# show ip adjacency
IP Adjacency Table for VRF default
Total number of entries: 2
Address
Age
MAC Address
10.1.1.1
02:20:54 00e0.b06a.71eb
10.1.1.253
00:06:27 0014.5e0b.81d1
Pref Source
50
arp
50
arp
Interface
mgmt0
mgmt0
Best
Yes
Yes
Triggering the Layer 3 Consistency Checker
You can manually trigger the Layer 3 consistency checker.
To manually trigger the Layer 3 consistency checker, use the following commands in global
configuration mode:
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Command
Purpose
test [ipv4] [unicast] forwarding
inconsistency [vrf vrf-name] [module
{slot| all}]
Starts a Layer 3 consistency check. The vrf-name can be
any case-sensitive, alphanumeric string up to 32
characters. The slot range is from 1 to 10.
Example:
switch(config)# test forwarding
inconsistency
To stop the Layer 3 consistency checker, use the following commands in global configuration mode:
Command
Purpose
test forwarding [ipv4] [unicast]
inconsistency [vrf vrf-name] [module
{slot| all}] stop
Stops a Layer 3 consistency check. The vrf-name can be
any case-sensitive, alphanumeric string up to 64
characters. The slot range is from 1 to 10.
Example:
switch(config)# test forwarding
inconsistency stop
To display the Layer 3 inconsistencies, use the following commands in any mode:
Command
Purpose
show forwarding [ipv4] inconsistency
[vrf vrf-name] [module {slot| all}]
Displays the results of a Layer 3 consistency check. The
vrf-name can be any case-sensitive, alphanumeric string
up to 32 characters. The slot range is from 1 to 10.
Example:
switch(config)# show forwarding
inconsistency
Clearing Forwarding Information in the FIB
You can clear one or more entries in the FIB. Clearing a FIB entry does not affect the unicast RIB.
Caution
The clear forwarding command disrupts forwarding on the switch.
To clear an entry in the FIB, including a Layer 3 inconsistency, use the following command in any mode:
Command
Purpose
clear forwarding {ipv4} route {* |
prefix} [vrf vrf-name] [module {slot|
all}]
Clears one or more entries from the FIB. The route
options are as follows:
Example:
switch(config)# clear forwarding ipv4
route *
•
*—All routes.
•
prefix—Any IP prefix.
The vrf-name can be any case-sensitive, alphanumeric
string up to 32 characters. The slot range is from 1 to 10.
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Managing the Unicast RIB and FIB
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Estimating Memory Requirements for Routes
You can estimate the memory that a number of routes and next-hop addresses will use.
To estimate the memory requirements for routes, use the following command in any mode:
Command
Purpose
show routing memory estimate routes
num-routes next-hops num-nexthops
Displays the memory requirements for routs. The
num-routes range is from 1000 to 1000000. The
num-nexthops range is from 1 to 16.
Example:
switch# show routing memory estimate
routes 1000 next-hops 1
Clearing Routes in the Unicast RIB
You can clear one or more routes from the unicast RIB.
Caution
The * keyword is severely disruptive to routing.
To clear one or more entries in the unicast RIB, use the following commands in any mode:
Command
Purpose
clear ip route {* | {route |
prefix/length}[next-hop interface]}
[vrf vrf-name]
Clears one or more routes from both the unicast RIB and
all the module FIBs. The route options are as follows:
Example:
switch(config)# clear ip route
10.2.2.2
•
*—All routes.
•
route—An individual IP route.
•
prefix/length—Any IP prefix.
•
next-hop—The next-hop address
•
interface—The interface to reach the next-hop
address.
The vrf-name can be any case-sensitive, alphanumeric
string up to 32 characters.
clear routing [multicast | unicast]
[ip | ipv4] {* | {route |
prefix/length}[next-hop interface]}
[vrf vrf-name]
Example:
switch(config)# clear routing ip
10.2.2.2
Clears one or more routes from the unicast RIB. The
route options are as follows:
•
*—All routes.
•
route—An individual IP route.
•
prefix/length—Any IP prefix.
•
next-hop—The next-hop address
•
interface—The interface to reach the next-hop
address.
The vrf-name can be any case-sensitive, alphanumeric
string up to 32 characters.
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Verifying the Unicast RIB and FIB Configuration
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Verifying the Unicast RIB and FIB Configuration
To display the unicast RIB and FIB configuration information, perform one of the following tasks:
Command
Purpose
show forwarding adjacency
Displays the adjacency table on a module.
show forwarding distribution {clients |
fib-state}
Displays the FIB distribution information.
show forwarding interfaces module slot
Displays the FIB information for a module.
show forwarding ipv4 route
Displays routes in the FIB.
show hardware forwarding
dynamic-allocation status
Displays information about the TCAM allocation.
show ip adjacency
Displays the adjacency table.
show ip route
Displays IPv4 routes from the unicast RIB.
show routing
Displays routes from the unicast RIB.
Additional References
For additional information related to managing unicast RIB and FIB, see the following sections:
•
Related Documents, page 12-10
•
Feature History for Unicast RIB and FIB, page 12-10
Related Documents
Related Topic
Document Title
Unicast RIB and FIB CLI commands
Cisco Nexus 3000 Series Command Reference,
Feature History for Unicast RIB and FIB
Table 12-1 lists the release history for this feature.
Table 12-1
Feature History for Unicast RIB and FIB
Feature Name
Releases
Feature Information
Unicast RIB and FIB
5.0(3)U1(1)
This feature was introduced.
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CH A P T E R
13
Configuring Route Policy Manager
This chapter describes how to configure the Route Policy Manager on the Cisco NX-OS switch.
This chapter includes the following sections:
•
Information About Route Policy Manager, page 13-1
•
Licensing Requirements for Route Policy Manager, page 13-5
•
Guidelines and Limitations, page 13-5
•
Default Settings, page 13-5
•
Configuring Route Policy Manager, page 13-6
•
Verifying the Route Policy Manager Configuration, page 13-17
•
Configuration Examples for Route Policy Manager, page 13-17
•
Related Topics, page 13-18
•
Additional References, page 13-18
•
Feature History for Route Policy Manager, page 13-18
Information About Route Policy Manager
Route Policy Manager supports route maps and IP prefix lists. These features are used for route
redistribution. A prefix list contains one or more IPv4 network prefixes and the associated prefix length
values. You can use a prefix list by itself in features such as Border Gateway Protocol (BGP) templates,
route filtering, or redistribution of routes that are exchanged between routing domains.
Route maps can apply to both routes and IP packets. Route filtering and redistribution pass a route
through a route map.
This section includes the following topics:
•
Prefix Lists, page 13-2
•
Route Maps, page 13-2
•
Route Redistribution and Route Maps, page 13-5
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Prefix Lists
You can use prefix lists to permit or deny an address or range of addresses. Filtering by a prefix list
involves matching the prefixes of routes or packets with the prefixes listed in the prefix list. An implicit
deny is assumed if a given prefix does not match any entries in a prefix list.
You can configure multiple entries in a prefix list and permit or deny the prefixes that match the entry.
Each entry has an associated sequence number that you can configure. If you do not configure a sequence
number, Cisco NX-OS assigns a sequence number automatically. Cisco NX-OS evaluates prefix lists
starting with the lowest sequence number. Cisco NX-OS processes the first successful match for a given
prefix. Once a match occurs, Cisco NX-OS processes the permit or deny statement and does not evaluate
the rest of the prefix list.
Note
An empty prefix list permits all routes.
MAC Lists
You can use MAC lists to permit or deny MAC address or range of addresses. A MAC list consists of a
list of MAC addresses and optional MAC masks. A MAC mask is a wild-card mask that is logically
AND-ed with the MAC address when the rout map matches on the MAC list entry. Filtering by a MAC
list involves matching the MAC address of packets with the MAC addresses listed in the MAC list. An
implicit deny is assumed if a given MAC address does not match any entries in a MAC list.
You can configure multiple entries in a MAC list and permit or deny the MAC addresses that match the
entry. Each entry has an associated sequence number that you can configure. If you do not configure a
sequence number, Cisco NX-OS assigns a sequence number automatically. Cisco NX-OS evaluates
MAC lists starting with the lowest sequence number. Cisco NX-OS processes the first successful match
for a given MAC address. Once a match occurs, Cisco NX-OS processes the permit or deny statement
and does not evaluate the rest of the MAC list.
Route Maps
You can use route maps for route redistribution. Route map entries consist of a list of match and set
criteria. The match criteria specify match conditions for incoming routes or packets, and the set criteria
specify the action taken if the match criteria are met.
You can configure multiple entries in the same route map. These entries contain the same route map
name and are differentiated by a sequence number.
You create a route map with one or more route map entries arranged by the sequence number under a
unique route map name. The route map entry has the following parameters:
•
Sequence number
•
Permission—permit or deny
•
Match criteria
•
Set changes
By default, a route map processes routes or IP packets in a linear fashion, that is, starting from the lowest
sequence number. You can configure the route map to process in a different order using the continue
statement, which allows you to determine which route map entry to process next.
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Match Criteria
You can use a variety of criteria to match a route or IP packet in a route map. Some criteria, such as BGP
community lists, are applicable only to a specific routing protocol, while other criteria, such as the IP
source or the destination address, can be used for any route or IP packet.
When Cisco NX-OS processes a route or packet through a route map, it compares the route or packet to
each of the match statements configured. If the route or packet matches the configured criteria, Cisco
NX-OS processes it based on the permit or deny configuration for that match entry in the route map and
any set criteria configured.
The match categories and parameters are as follows:
•
BGP parameters—Match based on AS numbers, AS-path, community attributes, or extended
community attributes.
•
Prefix lists—Match based on an address or range of addresses.
•
Multicast parameters—Match based on rendezvous point, groups, or sources.
•
Other parameters—Match based on IP next-hop address or packet length.
Set Changes
Once a route or packet matches an entry in a route map, the route or packet can be changed based on one
or more configured set statements.
The set changes are as follows:
•
BGP parameters—Change the AS-path, tag, community, extended community, dampening, local
preference, origin, or weight attributes.
•
Metrics—Change the route-metric, the route-tag, or the route-type.
•
Other parameters—Change the forwarding address or the IP next-hop address.
Access Lists
IP access lists can match the packet to a number of IP packet fields such as the following:
•
Source or destination IPv4 address
•
Protocol
•
Precedence
•
ToS
See the Cisco Nexus 7000 Series NX-OS Security Configuration Guide, Release 5.x, for more
information on ACLs.
AS Numbers for BGP
You can configure a list of AS numbers to match against BGP peers. If a BGP peer matches an AS
number in the list and matches the other BGP peer configuration, BGP creates a session. If the BGP peer
does not match an AS number in the list, BGP ignores the peer. You can configure the AS numbers as a
list, a range of AS numbers, or you can use an AS-path list to compare the AS numbers against a regular
expression.
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AS-path Lists for BGP
You can configure an AS-path list to filter inbound or outbound BGP route updates. If the route update
contains an AS-path attribute that matches an entry in the AS-path list, the router processes the route
based on the permit or deny condition configured. You can configure AS-path lists within a route map.
You can configure multiple AS-path entries in an AS-path list by using the same AS-path list name. The
router processes the first entry that matches.
Community Lists for BGP
You can filter BGP route updates based on the BGP community attribute by using community lists in a
route map. You can match the community attribute based on a community list, and you can set the
community attribute using a route map.
A community list contains one or more community attributes. If you configure more than one community
attribute in the same community list entry, then the BGP route must match all community attributes listed
to be considered a match.
You can also configure multiple community attributes as individual entries in the community list by
using the same community list name. In this case, the router processes the first community attribute that
matches the BGP route, using the permit or deny configuration for that entry.
You can configure community attributes in the community list in one of the following formats:
•
A named community attribute, such as internet or no-export.
•
In aa:nn format, where the first two bytes represent the two-byte AS number and the last two bytes
represent a user-defined network number.
•
A regular expression.
See the Cisco Nexus 3000 Series Command Reference,, for more information on regular expressions.
Extended Community Lists for BGP
Extended community lists support 4-byte AS numbers. You can configure community attributes in the
extended community list in one of the following formats:
•
In aa4:nn format, where the first four bytes represent the four-byte AS number and the last two bytes
represent a a user-defined network number.
•
A regular expression.
See the Cisco Nexus 3000 Series Command Reference,, for more information on regular expressions.
Cisco NX-OS supports generic specific extended community lists, which provide similar functionality
to regular community lists for four-byte AS numbers. You can configure generic specific extended
community lists with the following properties:
•
Transitive—BGP propagates the community attributes across autonomous systems.
•
Nontransitive—BGP removes community attributes before propagating the route to another
autonomous system.
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Route Redistribution and Route Maps
You can use route maps to control the redistribution of routes between routing domains. Route maps
match on the attributes of the routes to redistribute only those routes that pass the match criteria. The
route map can also modify the route attributes during this redistribution using the set changes.
The router matches redistributed routes against each route map entry. If there are multiple match
statements, the route must pass all of the match criteria. If a route passes the match criteria defined in a
route map entry, the actions defined in the entry are executed. If the route does not match the criteria,
the router compares the route against subsequent route map entries. Route processing continues until a
match is made or the route is processed by all entries in the route map with no match. If the router
processes the route against all entries in a route map with no match, the router accepts the route (inbound
route maps) or forwards the route (outbound route maps).
Licensing Requirements for Route Policy Manager
The following table shows the licensing requirements for this feature:
Product
License Requirement
Cisco NX-OS
Route Policy Manager requires no license. Any feature not included in a license package is bundled with
the Cisco NX-OS system images and is provided at no extra charge to you. For a complete explanation of
the Cisco NX-OS licensing scheme, see the Cisco NX-OS Licensing Guide.
Guidelines and Limitations
Route Policy Manager has the following configuration guidelines and limitations:
•
An empty route map denies all the routes.
•
An empty prefix list permits all the routes.
•
Without any match statement in a route-map entry, the permission (permit or deny) of the route-map
entry decides the result for all the routes or packets.
•
If referred policies (for example, prefix lists) within a match statement of a route-map entry return
either a no-match or a deny-match, Cisco NX-OS fails the match statement and processes the next
route-map entry.
•
When you change a route map, Cisco NX-OS hold all the changes until you exit from the route- map
configuration submode. Cisco NX-OS then sends all the changes to the protocol clients to take
effect.
•
Because you can use a route map before you define it, verify that all your route maps exist when you
finish a configuration change.
•
You can view the route-map usage for redistribution and filtering. Each individual routing protocol
provides a way to display these statistics.
Default Settings
Table 13-1 lists the default settings for Route Policy Manager.
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Table 13-1
Default Route Policy Manager Parameters
Parameters
Default
Route Policy Manager
Enabled
Configuring Route Policy Manager
Route Policy Manager configuration includes the following topics:
Note
•
Configuring IP Prefix Lists, page 13-6
•
Configuring MAC Lists, page 13-7
•
Configuring AS-path Lists, page 13-8
•
Configuring Community Lists, page 13-9
•
Configuring Extended Community Lists, page 13-11
•
Configuring Route Maps, page 13-12
If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature
might differ from the Cisco IOS commands that you would use.
Configuring IP Prefix Lists
IP prefix lists match the IP packet or route against a list of prefixes and prefix lengths. You can create
an IP prefix list for IPv4.
You can configure the prefix list entry to match the prefix length exactly, or to match any prefix with a
length that matches the configured range of prefix lengths.
Use the ge and lt keywords to create a range of possible prefix lengths. The incoming packet or route
matches the prefix list if the prefix matches and if the prefix length is greater than or equal to the ge
keyword value (if configured) and less than or equal to the lt keyword value (if configured).
SUMMARY STEPS
1.
configure terminal
2.
(Optional) ip prefix-list name description string
3.
ip prefix-list name [seq number] [{permit | deny} prefix {[eq prefix-length] | [ge prefix-length] [le
prefix-length]}]
4.
(Optional) show ip prefix-list name
5.
(Optional) copy running-config startup-config
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DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
ip prefix-list name description string
Example:
switch(config)# ip prefix-list
AllowPrefix description allows
engineering server
Step 3
ip prefix-list name [seq number]
[{permit | deny} prefix {[eq
prefix-length] | [ge prefix-length] [le
prefix-length]}]
Example:
switch(config)# ip prefix-list
AllowPrefix seq 10 permit 192.0.2.0 eq
24
Step 4
show ip prefix-list name
(Optional) Adds an information string about the prefix
list.
Creates an IPv4 prefix list or adds a prefix to an
existing prefix list. The prefix length is matched as
follows:
•
eq—Matches the exact prefix length.
•
ge—Matches a prefix length that is equal to or
greater than the configured prefix length.
•
le—Matches a prefix length that is equal to or less
than the configured prefix length.
(Optional) Displays information about prefix lists.
Example:
switch(config)# show ip prefix-list
AllowPrefix
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch# copy running-config
startup-config
This example shows how to create an IPv4 prefix list with two entries and apply the prefix list to a BGP
neighbor:
switch# configure terminal
switch(config)# ip prefix-list allowprefix seq 10 permit 192.0.2.0/24 eq 24
switch(config)# ip prefix-list allowprefix seq 20 permit 209.165.201.0/27 eq 27
switch(config)# router bgp 65536:20
switch(config-router)# neighbor 192.0.2.1/16 remote-as 65535:20
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor-af)# prefix-list allowprefix in
Configuring MAC Lists
You can configure a MAC list to permit or deny a range of MAC addresses.
SUMMARY STEPS
1.
configure terminal
2.
mac-list name [seq number] {permit | deny} mac-address [mac-mask]
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3.
(Optional) show mac-list name
4.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
Step 3
Example:
switch(config)# mac-list AllowMac seq 1
permit 0022.5579.a4c1 ffff.ffff.0000
Creates a MAC list or adds a MAC address to an
existing MAC list. The seq range is from 1 to
4294967294. The mac-mask specifies the portion of
the MAC address to match against and is in MAC
address format.
show mac-list name
(Optional) Displays information about MAC lists.
mac-list name [seq number] {permit |
deny} mac-address {mac-mask]
Example:
switch(config)# show mac-list AllowMac
Step 4
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch# copy running-config
startup-config
Configuring AS-path Lists
You can specify an AS-path list filter on both inbound and outbound BGP routes. Each filter is an access
list based on regular expressions. If the regular expression matches the representation of the AS-path
attribute of the route as an ASCII string, then the permit or deny condition applies.
SUMMARY STEPS
1.
configure terminal
2.
ip as-path access-list name {deny | permit} expression
3.
(Optional) show ip as-path list name
4.
(Optional) copy running-config startup-config
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DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
ip as-path access-list name {deny |
permit} expression
Creates a BGP AS-path list using a regular expression.
Example:
switch(config)# ip as-path access-list
Allow40 permit 40
Step 3
show ip as-path-access-list name
Example:
switch(config)# show ip
as-path-access-list Allow40
Step 4
copy running-config startup-config
(Optional) Displays information about as-path access
lists.
(Optional) Saves this configuration change.
Example:
switch# copy running-config
startup-config
This example shows how to create an AS-path list with two entries and apply the AS path list to a BGP
neighbor:
switch# configure terminal
switch(config)# ip as-path access-list AllowAS permit 64510
switch(config)# ip as-path access-list AllowAS permit 64496
switch(config)# copy running-config startup-config
switch(config)# router bgp 65536:20
switch(config-router)# neighbor 192.0.2.1/16 remote-as 65535:20
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor-af)# filter-list AllowAS in
Configuring Community Lists
You can use community lists to filter BGP routes based on the community attribute. The community
number consists of a 4-byte value in the aa:nn format. The first two bytes represent the autonomous
system number, and the last two bytes represent a user-defined network number.
When you configure multiple values in the same community list statement, all community values must
match to satisfy the community list filter. When you configure multiple values in separate community
list statements, the first list that matches a condition is processed.
Use community lists in a match statement to filter BGP routes based on the community attribute.
SUMMARY STEPS
1.
configure terminal
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2.
ip community-list standard list-name {deny | permit} [community-list ] [internet] [local-AS]
[no-advertise] [no-export]
or
ip community-list expanded list-name {deny | permit} expression
3.
(Optional) show ip community-list name
4.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
ip community-list standard list-name
{deny | permit} [community-list]
[internet] [local-AS] [no-advertise]
[no-export]
Creates a standard BGP community list. The list-name
can be any case-sensitive, alphanumeric string up to 63
characters. The community-list can be one or more
communities in the aa:nn format.
Example:
switch(config)# ip community-list
standard BGPCommunity permit
no-advertise 65536:20
ip community-list expanded list-name
{deny | permit} expression
Creates an expanded BGP community list using a
regular expression.
Example:
switch(config)# ip community-list
expanded BGPComplex deny
50000:[0-9][0-9]_
Step 3
show ip community-list name
Example:
switch(config)# show ip community-list
BGPCommunity
Step 4
copy running-config startup-config
(Optional) Displays information about community
lists.
(Optional) Saves this configuration change.
Example:
switch# copy running-config
startup-config
This example shows how to create a community list with two entries:
switch# configure terminal
switch(config)# ip community-list standard BGPCommunity permit no-advertise 65536:20
switch(config)# ip community-list standard BGPCommunity permit local-AS no-export
switch(config)# copy running-config startup-config
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Configuring Extended Community Lists
You can use extended community lists to filter BGP routes based on the community attribute. The
community number consists of a 6-byte value in the aa4:nn format. The first four bytes represent the
autonomous system number, and the last two bytes represent a user-defined network number.
When you configure multiple values in the same extended community list statement, all extended
community values must match to satisfy the extended community list filter. When you configure multiple
values in separate extended community list statements, the first list that matches a condition is processed.
Use extended community lists in a match statement to filter BGP routes based on the extended
community attribute.
SUMMARY STEPS
1.
configure terminal
2.
ip extcommunity-list standard list-name {deny | permit} 4bytegeneric {transitive |
non-transitive} aa4:nn
or
ip extcommunit-list expanded list-name {deny | permit} expression
3.
(Optional) show ip extcommunity-list name
4.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
ip extcommunity-list standard list-name
{deny | permit} 4bytegeneric {transitive
| nontransitive} community1
[community2...]
Creates a standard BGP extended community list. The
community can be one or more extended communities
in the aa4:nn format.
Example:
switch(config)# ip extcommunity-list
standard BGPExtCommunity permit
4bytegeneric transitive 65536:20
ip extcommunity-list expanded list-name
{deny | permit} expression
Creates an expanded BGP extended community list
using a regular expression.
Example:
switch(config)# ip extcommunity-list
expanded BGPExtComplex deny
1.5:[0-9][0-9]_
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Step 3
Command
Purpose
show ip community-list name
(Optional) Displays information about extended
community lists.
Example:
switch(config)# show ip community-list
BGPCommunity
Step 4
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch# copy running-config
startup-config
This example shows how to create a generic specific extended community list:
switch# configure terminal
switch(config)# ip extcommunity-list standard test1 permit 4bytegeneric transitive
65536:40 65536:60
switch(config)# copy running-config startup-config
Configuring Route Maps
You can use route maps for route redistribution or route filtering. Route maps can contain multiple match
criteria and multiple set criteria.
Configuring a route map for BGP triggers an automatic soft clear or refresh of BGP neighbor sessions.
SUMMARY STEPS
1.
configure terminal
2.
route-map map-name [permit | deny] [seq]
3.
(Optional) continue seq
4.
(Optional) exit
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
route-map map-name [permit | deny] [seq]
Example:
switch(config)# route-map Testmap permit
10
switch(config-route-map)#
Step 3
continue seq
Example:
switch(config-route-map)# continue 10
Creates a route map or enters route-map configuration
mode for an existing route map. Use seq to order the
entries in a route map.
(Optional) Determines what sequence statement to
process next in the route map. Used only for filtering
and redistribution.
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Step 4
Command
Purpose
exit
(Optional) Exits route-map configuration mode.
Example:
switch(config-route-map)# exit
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config
startup-config
You can configure the following optional match parameters for route maps in route-map configuration
mode:
Note
The default-information originate command ignores match statements in the optional route
map.
Command
Purpose
match as-path name [name...]
Matches against one or more AS-path lists. Create
the AS-path list with the ip as-path access-list
command.
Example:
switch(config-route-map)# match as-path
Allow40
match as-number {number [,number...] |
as-path-list name [name...]}
Example:
switch(config-route-map)# match as-number
33,50-60
match community name
[name...][exact-match]
Example:
switch(config-route-map)# match community
BGPCommunity
match extcommunity name
[name...][exact-match]
Example:
switch(config-route-map)# match
extcommunity BGPextCommunity
match interface interface-type number
[interface-type number...]
Example:
switch(config-route-map)# match interface
e 1/2
match ip address prefix-list name
[name...]
Matches against one or more AS numbers or
AS-path lists. Create the AS-path list with the ip
as-path access-list command. The number range is
from 1 to 65535. The AS-path list name can be any
case-sensitive, alphanumeric string up to 63
characters.
Matches against one or more community lists.
Create the community list with the ip
community-list command.
Matches against one or more extended community
lists. Create the community list with the ip
extcommunity-list command.
Matches any routes that have their next hop out one
of the configured interfaces. Use ? to find a list of
supported interface types.
Matches against one or more IPv4 prefix lists. Use
the ip prefix-list command to create the prefix list.
Example:
switch(config-route-map)# match ip address
prefix-list AllowPrefix
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Command
Purpose
match ip multicast [source ipsource]
[[group ipgroup] [rp iprp]]
Matches an IPv4 multicast packet based on the
multicast source, group, or rendezvous point.
Example:
switch(config-route-map)# match ip
multicast rp 192.0.2.1
match ip next-hop prefix-list name
[name...]
Example:
switch(config-route-map)# match ip
next-hop prefix-list AllowPrefix
match ip route-source prefix-list name
[name...]
Example:
switch(config-route-map)# match ip
route-source prefix-list AllowPrefix
match mac-list name [name...]
Example:
switch(config-route-map)# match mac-list
AllowMAC
match metric value [+- deviation.]
[value..]
Example:
switch(config-route-map)# match mac-list
AllowMAC
match route-type route-type
Example:
switch(config-route-map)# match route-type
level 1 level 2
match tag tagid [tagid...]
Example:
switch(config-route-map)# match tag 2
match vlan vlan-id [vlan-range]
Matches the IPv4 next-hop address of a route to one
or more IP prefix lists. Use the ip prefix-list
command to create the prefix list.
Matches the IPv4 route source address of a route to
one or more IP prefix lists. Use the ip prefix-list
command to create the prefix list.
Matches against one or more MAC lists. Use the
mac-list command to create the MAC list.
Matches the route metric against one or more
metric values or value ranges. Use +- deviation
argument to set a metric range. The route map
matches any route metric that falls the range:
value - deviation to value + deviation.
Matches against a type of route. The route-type can
be one or more of the following:
•
external
•
internal
•
level-1
•
level-2
•
local
•
nssa-external
•
type-1
•
type-2
Matches a route against one or more tags for
filtering or redistribution.
Matches against a VLAN.
Example:
switch(config-route-map)# match vlan 3,
5-10
You can configure the following optional set parameters for route maps in route-map configuration
mode:
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Command
Purpose
set as-path {tag | prepend {last-as number
| as-1 [as-2...]}}
Modifies an AS-path attribute for a BGP route. You
can prepend the configured number of last AS
numbers or a string of particular AS-path values
(as-1 as-2...as-n).
Example:
switch(config-route-map)# set as-path
prepend 10 100 110
set comm-list name delete
Example:
switch(config-route-map)# set comm-list
BGPCommunity delete
set community {none | additive | local-AS
| no-advertise | no-export | community-1
[community-2...]}
Removes communities from the community
attribute of an inbound or outbound BGP route
update. Use the ip community-list command to
create the community list.
Sets the community attribute for a BGP route
update.
Note
When you use both the set community and
set comm-list delete commands in the
same sequence of a route map attribute, the
deletion operation is performed before the
set operation.
Note
Use the send-community command in
BGP neighbor address family configuration
mode to propagate BGP community
attributes to BGP peers.
Example:
switch(config-route-map)# set community
local-AS
set dampening halflife reuse suppress
duration
Example:
switch(config-route-map)# set dampening 30
1500 10000 120
set extcomm-list name delete
Example:
switch(config-route-map)# set extcomm-list
BGPextCommunity delete
Sets the following BGP route dampening
parameters:
•
halflife—The range is from 1 to 45 minutes.
The default is 15.
•
reuse—The range is from is 1 to 20000
seconds. The default is 750.
•
suppress—The range is from is 1 to 20000. The
default is 2000.
•
duration—The range is from is 1 to 255
minutes. The default is 60.
Removes communities from the extended
community attribute of an inbound or outbound
BGP route update. Use the ip extcommunity-list
command to create the extended community list.
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Command
Purpose
set extcommunity generic {transitive |
nontransitive} {none | additive]
community-1 [community-2...]}
Sets the extended community attribute for a BGP
route update.
Note
When you use both the set extcommunity
and set extcomm-list delete commands in
the same sequence of a route map attribute,
the deletion operation is performed before
the set operation.
Note
Use the send-community command in
BGP neighbor address family configuration
mode to propagate BGP extended
community attributes to BGP peers.
Example:
switch(config-route-map)# set extcommunity
generic transitive 1.0:30
set forwarding-address
Sets the forwarding address for OSPF.
Example:
switch(config-route-map)# set
forwarding-address
set level {backbone | level-1 | level-1-2
| level-2}
Example:
switch(config-route-map)# set level
backbone
set local-preference value
Example:
switch(config-route-map)# set
local-preference 4000
set metric [+ | -]bandwidth-metric
Example:
switch(config-route-map)# set metric +100
set metric bandwidth [delay reliability
load mtu]
Sets what area to import routes to for IS-IS. The
options for IS-IS are level-1, level-1-2, or level-2.
The default is level-1.
Sets the BGP local preference value. The range is
from 0 to 4294967295.
Adds or subtracts from the existing metric value.
The metric is in Kb/s. The range is from 0 to
4294967295.
Sets the route metric values.
Metrics are as follows:
Example:
switch(config-route-map)# set metric 33 44
100 200 1500
•
metric0—Bandwidth in Kb/s. The range is
from 0 to 4294967295.
•
metric1—Delay in 10-microsecond units.
•
metric2—Reliability. The range is from 0 to
255 (100 percent reliable).
•
metric3—Loading. The range is from 1 to 200
(100 percent loaded).
•
metric4—MTU of the path. The range is from
1 to 4294967295.
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Command
Purpose
set metric-type {external | internal |
type-1 | type-2}
Sets the metric type for the destination routing
protocol. The options are as follows:
Example:
switch(config-route-map)# set metric-type
internal
external—IS-IS external metric
internal— IGP metric as the MED for BGP
type-1—OSPF external type 1 metric
type-2—OSPF external type 2 metric
set origin {egp as-number | igp |
incomplete}
Sets the BGP origin attribute. The EGP as-number
range is from 0 to 65535.
Example:
switch(config-route-map)# set origin
incomplete
set tag name
Example:
switch(config-route-map)# set tag 33
set weight count
Example:
switch(config-route-map)# set weight 33
Sets the tag value for the destination routing
protocol. The name parameter is an unsigned
integer.
Sets the weight for the BGP route. The range is
from 0 to 65535.
The set metric-type internal command affects an outgoing policy and an eBGP neighbor only. If you
configure both the metric and metric-type internal commands in the same BGP peer outgoing policy,
then Cisco NX-OS ignores the metric-type internal command.
Verifying the Route Policy Manager Configuration
To display the route policy manager configuration information, perform one of the following tasks:
Command
Purpose
show ip community-list [name]
Displays information about a community list.
show ip extcommunity-list [name]
Displays information about an extended
community list.
show [ip] prefix-list [name]
Displays information about an IPv4 prefix list.
show route-map [name]
Displays information about a route map.
Configuration Examples for Route Policy Manager
This example shows how to use an address family to configure BGP so that any unicast and multicast
routes from neighbor 209.0.2.1 are accepted if they match access list 1:
router bgp 64496
address-family ipv4 unicast
network 192.0.2.0/24
network 209.165.201.0/27 route-map filterBGP
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Related Topics
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
route-map filterBGP
match ip next-hop prefix-list AllowPrefix
ip prefix-list AllowPrefix 10 permit 192.0.2.0 eq 24
ip prefix-list AllowPrefix 20 permit 209.165.201.0 eq 27
Related Topics
The following topics can give more information on Route Policy Manager:
•
Chapter 5, “Configuring Basic BGP”
Additional References
For additional information related to implementing IP, see the following sections:
•
Related Documents, page 13-18
•
Standards, page 13-18
Related Documents
Related Topic
Document Title
Route Policy Manager CLI commands
Cisco Nexus 3000 Series Command Reference,
Standards
Standards
Title
No new or modified standards are supported by this
—
feature, and support for existing standards has not been
modified by this feature.
Feature History for Route Policy Manager
Table 13-2 lists the release history for this feature.
Table 13-2
Feature History for BGP
Feature Name
Releases
Feature Information
Route Policy Manager
5.0(3)U1(1)
This feature was introduced.
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PA R T
3
First-Hop Redundancy Protocols
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
CH A P T E R
14
Configuring HSRP
This chapter describes how to configure the Hot Standby Router Protocol (HSRP) on the Cisco NX-OS
switch.
This chapter includes the following sections:
•
Information About HSRP, page 14-1
•
Licensing Requirements for HSRP, page 14-6
•
Prerequisites for HSRP, page 14-6
•
Guidelines and Limitations, page 14-6
•
Default Settings, page 14-6
•
Configuring HSRP, page 14-7
•
Verifying the HSRP Configuration, page 14-16
•
Configuration Examples for HSRP, page 14-16
•
Additional References, page 14-16
•
Feature History for HSRP, page 14-17
Information About HSRP
HSRP is a first-hop redundancy protocol (FHRP) that allows a transparent failover of the first-hop IP
router. HSRP provides first-hop routing redundancy for IP hosts on Ethernet networks configured with
a default router IP address. You use HSRP in a group of routers for selecting an active router and a
standby router. In a group of routers, the active router is the router that routes packets; the standby router
is the router that takes over when the active router fails or when preset conditions are met.
Many host implementations do not support any dynamic router discovery mechanisms but can be
configured with a default router. Running a dynamic router discovery mechanism on every host is not
feasible for a number of reasons, including administrative overhead, processing overhead, and security
issues. HSRP provides failover services to these hosts.
This section includes the following topics:
•
HSRP Overview, page 14-2
•
HSRP for IPv4, page 14-3
•
HSRP Versions, page 14-4
•
HSRP Authentication, page 14-4
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Information About HSRP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
•
HSRP Messages, page 14-4
•
HSRP Load Sharing, page 14-4
•
Object Tracking and HSRP, page 14-5
•
Virtualization Support, page 14-5
HSRP Overview
When you use HSRP, you configure the HSRP virtual IP address as the host’s default router (instead of
the IP address of the actual router). The virtual IP address is an IPv4 address that is shared among a group
of routers that run HSRP.
When you configure HSRP on a network segment, you provide a virtual MAC address and a virtual IP
address for the HSRP group. You configure the same virtual address on each HSRP-enabled interface in
the group. You also configure a unique IP address and MAC address on each interface that acts as the
real address. HSRP selects one of these interfaces to be the active router. The active router receives and
routes packets destined for the virtual MAC address of the group.
HSRP detects when the designated active router fails. At that point, a selected standby router assumes
control of the virtual MAC and IP addresses of the HSRP group. HSRP also selects a new standby router
at that time.
HSRP uses a priority mechanism to determine which HSRP-configured interface becomes the default
active router. To configure an interface as the active router, you assign it with a priority that is higher
than the priority of all the other HSRP-configured interfaces in the group. The default priority is 100, so
if you configure just one interface with a higher priority, that interface becomes the default active router.
Interfaces that run HSRP send and receive multicast User Datagram Protocol (UDP)-based hello
messages to detect a failure and to designate active and standby routers. When the active router fails to
send a hello message within a configurable period of time, the standby router with the highest priority
becomes the active router. The transition of packet forwarding functions between the active and standby
router is completely transparent to all hosts on the network.
You can configure multiple HSRP groups on an interface.
Figure 14-1 shows a network configured for HSRP. By sharing a virtual MAC address and a virtual IP
address, two or more interfaces can act as a single virtual router.
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Information About HSRP
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Figure 14-1
HSRP Topology With Two Enabled Routers
Internet or
ISP backbone
Active
router
192.0.2.1
Virtual
router
192.0.2.2
Standby
router
192.0.2.3
Host A
Host B
Host C
Host D
185061
LAN
The virtual router does not physically exist but represents the common default router for interfaces that
are configured to provide backup to each other. You do not need to configure the hosts on the LAN with
the IP address of the active router. Instead, you configure them with the IP address (virtual IP address)
of the virtual router as their default router. If the active router fails to send a hello message within the
configurable period of time, the standby router takes over, responds to the virtual addresses, and becomes
the active router, assuming the active router duties. From the host perspective, the virtual router remains
the same.
Note
Packets received on a routed port destined for the HSRP virtual IP address will terminate on the local
router, regardless of whether that router is the active HSRP router or the standby HSRP router. This
includes ping and Telnet traffic. Packets received on a Layer 2 (VLAN) interface destined for the HSRP
virtual IP address will terminate on the active router.
HSRP for IPv4
HSRP routers communicate with each other by exchanging HSRP hello packets. These packets are sent
to the destination IP multicast address 224.0.0.2 (reserved multicast address used to communicate to all
routers) on UDP port 1985. The active router sources hello packets from its configured IP address and
the HSRP virtual MAC address while the standby router sources hellos from its configured IP address
and the interface MAC address, which may or may not be the burned-in address (BIA). The BIA is the
last six bytes of the MAC address that is assigned by the manufacturer of the network interface card
(NIC).
Because hosts are configured with their default router as the HSRP virtual IP address, hosts must
communicate with the MAC address associated with the HSRP virtual IP address. This MAC address is
a virtual MAC address, 0000.0C07.ACxy, where xy is the HSRP group number in hexadecimal based on
the respective interface. For example, HSRP group 1 uses the HSRP virtual MAC address of
0000.0C07.AC01. Hosts on the adjoining LAN segment use the normal Address Resolution Protocol
(ARP) process to resolve the associated MAC addresses.
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Information About HSRP
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HSRP version 2 uses the new IP multicast address 224.0.0.102 to send hello packets instead of the
multicast address of 224.0.0.2, which is used by version 1. HSRP version 2 permits an expanded group
number range of 0 to 4095 and uses a new MAC address range of 0000.0C9F.F000 to 0000.0C9F.FFFF.
HSRP Versions
Cisco NX-OS supports HSRP version 1 by default. You can configure an interface to use HSRP version
2.
HSRP version 2 has the following enhancements to HSRP version 1:
•
Expands the group number range. HSRP version 1 supports group numbers from 0 to 255. HSRP
version 2 supports group numbers from 0 to 4095.
•
For IPv4, uses the IPv4 multicast address 224.0.0.102 to send hello packets instead of the multicast
address of 224.0.0.2, which is used by HSRP version 1.
•
Uses the MAC address range from 0000.0C9F.F000 to 0000.0C9F.FFFF for IPv4. HSRP version 1
uses the MAC address range 0000.0C07.AC00 to 0000.0C07.ACFF.
•
Adds support for MD5 authentication.
When you change the HSRP version, Cisco NX-OS reinitializes the group because it now has a new
virtual MAC address.
HSRP version 2 has a different packet format than HSRP version 1. The packet format uses a
type-length-value (TLV) format. HSRP version 2 packets received by an HSRP version 1 router are
ignored.
HSRP Authentication
HSRP message digest 5 (MD5) algorithm authentication protects against HSRP-spoofing software and
uses the industry-standard MD5 algorithm for improved reliability and security. HSRP includes the IPv4
address in the authentication TLVs.
HSRP Messages
Routers that are configured with HSRP exchange the following three types of multicast messages:
•
Hello—The hello message conveys the HSRP priority and state information of the router to other
HSRP routers.
•
Coup—When a standby router wants to assume the function of the active router, it sends a coup
message.
•
Resign—A router that is the active router sends this message when it is about to shut down or when
a router that has a higher priority sends a hello or coup message.
HSRP Load Sharing
HSRP allows you to configure multiple groups on an interface. You can configure two overlapping IPv4
HSRP groups to load share traffic from the connected hosts while providing the default router
redundancy expected from HSRP. Figure 14-2 shows an example of a load-sharing HSRP IPv4
configuration.
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Information About HSRP
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Figure 14-2
HSRP Load Sharing
User Group A
Default Gateway = 192.0.2.1
Active
Router A
Standby
Standby
Router B
Active
User Group B
Default Gateway = 192.0.2.2
Group B = 192.0.2.2
185059
Group A = 192.0.2.1
Figure 14-2 shows two routers A and B and two HSRP groups. Router A is the active router for group
A but is the standby router for group B. Similarly, router B is the active router for group B and the
standby router for group A. If both routers remain active, HSRP load balances the traffic from the hosts
across both routers. If either router fails, the remaining router continues to process traffic for both hosts.
Object Tracking and HSRP
You can use object tracking to modify the priority of an HSRP interface based on the operational state
of another interface. Object tracking allows you to route to a standby router if the interface to the main
network fails.
Two objects that you can track are the line protocol state of an interface or the reachability of an IP route.
If the specified object goes down, Cisco NX-OS reduces the HSRP priority by the configured amount.
For more information, see the “Configuring HSRP Object Tracking” section on page 14-12.
Virtualization Support
HSRP supports Virtual Routing and Forwarding instances (VRFs). By default, Cisco NX-OS places you
in the default VRF unless you specifically configure another VRF.
If you change the VRF membership of an interface, Cisco NX-OS removes all Layer 3 configuration,
including HSRP.
For more information, see Chapter 11, “Configuring Layer 3 Virtualization.”
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Licensing Requirements for HSRP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Licensing Requirements for HSRP
The following table shows the licensing requirements for this feature:
Product
License Requirement
Cisco NX-OS
HSRP requires no license. Any feature not included in a license package is bundled with the Cisco NX-OS
system images and is provided at no extra charge to you. For a complete explanation of the Cisco NX-OS
licensing scheme, see the Cisco NX-OS Licensing Guide.
Make sure the LAN Base Services license is installed on the switch to enable Layer 3 interfaces.
Note
Prerequisites for HSRP
HSRP has the following prerequisites:
•
You must enable the HSRP feature in a switch before you can configure and enable any HSRP
groups.
Guidelines and Limitations
HSRP has the following configuration guidelines and limitations:
•
The minimum hello timer value is 250 milliseconds.
•
The minimum hold timer value is 750 milliseconds.
•
You must configure an IP address for the interface that you configure HSRP on and enable that
interface before HSRP becomes active.
•
For IPv4, the virtual IP address must be in the same subnet as the interface IP address.
•
We recommend that you do not configure more than one first-hop redundancy protocol on the same
interface.
•
HSRP version 2 does not interoperate with HSRP version 1. An interface cannot operate both
version 1 and version 2 because both versions are mutually exclusive. However, the different
versions can be run on different physical interfaces of the same router.
•
You cannot change from version 2 to version 1 if you have configured groups above the group
number range allowed for version 1 (0 to 255).
•
Cisco NX-OS removes all Layer 3 configuration on an interface when you change the interface VRF
membership, port channel membership, or when you change the port mode to Layer 2.
Default Settings
Table 14-1 lists the default settings for HSRP parameters.
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Table 14-1
Default HSRP Parameters
Parameters
Default
HSRP
Disabled
Authentication
Enabled as text for version 1, with cisco as the
password
HSRP version
Version 1
Preemption
disabled
Priority
100
virtual MAC address
Derived from HSRP group number
Configuring HSRP
This section includes the following topics:
Note
•
Enabling the HSRP Feature, page 14-7
•
Configuring the HSRP Version, page 14-8
•
Configuring an HSRP Group for IPv4, page 14-8
•
Configuring the HSRP Virtual MAC Address, page 14-10
•
Authenticating HSRP, page 14-10
•
Configuring HSRP Object Tracking, page 14-12
•
Configuring the HSRP Priority, page 14-14
•
Customizing HSRP, page 14-14
If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature
might differ from the Cisco IOS commands that you would use.
Enabling the HSRP Feature
You must globally enable the HSRP feature before you can configure and enable any HSRP groups.
DETAILED STEPS
To enable the HSRP feature, use the following command in global configuration mode:
Command
Purpose
feature hsrp
Enables HSRP.
Example:
switch(config)# feature hsrp
To disable the HSRP feature and remove all associated configuration, use the following command in
global configuration mode:
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Command
Purpose
no feature hsrp
Disables HSRP.
Example:
switch(config)# no feature hsrp
Configuring the HSRP Version
You can configure the HSRP version. If you change the version for existing groups, Cisco NX-OS
reinitializes HSRP for those groups because the virtual MAC address changes. The HSRP version
applies to all groups on the interface.
To configure the HSRP version, use the following command in interface configuration mode:
Command
Purpose
hsrp version {1 | 2}
Configures the HSRP version. Version 1 is the
default.
Example:
switch(config-if)# hsrp version 2
Configuring an HSRP Group for IPv4
You can configure an HSRP group on an IPv4 interface and configure the virtual IP address and virtual
MAC address for the HSRP group.
BEFORE YOU BEGIN
Ensure that you have enabled the HSRP feature (see the “Enabling the HSRP Feature” section on
page 14-7).
Cisco NX-OS enables an HSRP group once you configure the virtual IP address on any member interface
in the group. You should configure HSRP attributes such as authentication, timers, and priority before
you enable the HSRP group.
SUMMARY STEPS
1.
configure terminal
2.
interface type number
3.
no switchport
4.
ip ip-address/length
5.
hsrp group-number [ipv4]
6.
ip [ip-address [secondary]]
7.
exit
8.
no shutdown
9.
(Optional) show hsrp [group group-number] [ipv4]
10. (Optional) copy running-config startup-config
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DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface type number
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 1/2
switch(config-if)#
Step 3
Configures the interface as a Layer 3 routed interface.
no switchport
Example:
switch(config-if)# no switchport
Step 4
ip ip-address/length
Configures the IPv4 address of the interface.
Example:
switch(config-if)# ip 192.0.2.2/8
Step 5
hsrp group-number [ipv4]
Example:
switch(config-if)# hsrp 2
switch(config-if-hsrp)#
Step 6
Step 7
Creates an HSRP group and enters hsrp configuration
mode. The range for HSRP version 1 is from 0 to 255.
The range is for HSRP version 2 is from 0 to 4095. The
default value is 0.
Example:
switch(config-if-hsrp)# ip 192.0.2.1
Configures the virtual IP address for the HSRP group
and enables the group. This address should be in the
same subnet as the IPv4 address of the interface.
exit
Exits HSRP configuration mode.
ip [ip-address [secondary]]
Example:
switch(config-if-hsrp)# exit
Step 8
Enables the interface.
no shutdown
Example:
switch(config-if)# no shutdown
Step 9
show hsrp [group group-number] [ipv4]
(Optional) Displays HSRP information.
Example:
switch(config-if)# show hsrp group 2
Step 10
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-if)# copy running-config
startup-config
Note
You should use the no shutdown command to enable the interface after you finish the configuration.
This example shows how to configure an HSRP group on Ethernet 1/2:
switch# configure terminal
switch(config)# interface ethernet 1/2
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switch(config-if)# no switchport
switch(config-if)# ip 192.0.2.2/8
switch(config-if)# hsrp 2
switch(config-if-hsrp)# ip 192.0.2.1
switch(config-if-hsrp)# exit
switch(config-if)# no shutdown
switch(config-if)# copy running-config startup-config
Configuring the HSRP Virtual MAC Address
You can override the default virtual MAC address that HSRP derives from the configured group number.
To manually configure the virtual MAC address for an HSRP group, use the following command in hsrp
configuration mode:
Command
Purpose
mac-address string
Configures the virtual MAC address for an HSRP
group. The string uses the standard MAC address
format (xxxx.xxxx.xxxx).
Example:
switch(config-if-hsrp)# mac-address
5000.1000.1060
To configure HSRP to use the burned-in MAC address of the interface for the virtual MAC address, use
the following command in interface configuration mode:
Command
Purpose
hsrp use-bia [scope interface]
Configures HSRP to use the burned-in MAC
address of the interface for the HSRP virtual MAC
address. You can optionally configure HSRP to use
the burned-in MAC address for all groups on this
interface by using the scope interface keywords.
Example:
switch(config-if)# hsrp use-bia
Authenticating HSRP
You can configure HSRP to authenticate the protocol using cleartext or MD5 digest authentication. MD5
authentication uses a key chain (see the Cisco Nexus 7000 Series NX-OS Security Configuration Guide,
Release 5.x).
BEFORE YOU BEGIN
Ensure that you have enabled the HSRP feature (see the “Enabling the HSRP Feature” section on
page 14-7).
You must configure the same authentication and keys on all members of the HSRP group.
Ensure that you have created the key chain if you are using MD5 authentication.
SUMMARY STEPS
1.
configure terminal
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2.
interface interface-type slot/port
3.
no switchport
4.
hsrp group-number [ipv4]
5.
authentication text string
or
authentication md5 {key-chain key-chain | key-string {0 | 7} text [timeout seconds]}
6.
(Optional) show hsrp [group group-number]
7.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface interface-type slot/port
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 1/2
switch(config-if)#
Step 3
Configures the interface as a Layer 3 routed interface.
no switchport
Example:
switch(config-if)# no switchport
Step 4
hsrp group-number [ipv4]
Example:
switch(config-if)# hsrp 2
switch(config-if-hsrp)#
Step 5
authentication text string
Example:
switch(config-if-hsrp)# authentication
text mypassword
authentication md5 {key-chain key-chain
| key-string {0 | 7} text [timeout
seconds]}
Example:
switch(config-if-hsrp)# authentication
md5 key-chain hsrp-keys
Step 6
show hsrp [group group-number]
Creates an HSRP group and enters HSRP
configuration mode.
Configures cleartext authentication for HSRP on this
interface.
Configures MD5 authentication for HSRP on this
interface. You can use a key chain or key string. If you
use a key string, you can optionally set the timeout for
when HSRP will only accept a new key. The range is
from 0 to 32767 seconds.
(Optional) Displays HSRP information.
Example:
switch(config-if-hsrp)# show hsrp group
2
Step 7
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-if-hsrp)# copy
running-config startup-config
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This example shows how to configure MD5 authentication for HSRP on Ethernet 1/2 after creating the
key chain:
switch# configure terminal
switch(config)# key chain hsrp-keys
switch(config-keychain)# key 0
switch(config-keychain-key)# key-string 7 zqdest
switch(config-keychain-key) accept-lifetime 00:00:00 Jun 01 2008 23:59:59 Sep 12 2008
switch(config-keychain-key) send-lifetime 00:00:00 Jun 01 2008 23:59:59 Aug 12 2008
switch(config-keychain-key) key 1
switch(config-keychain-key) key-string 7 uaeqdyito
switch(config-keychain-key) accept-lifetime 00:00:00 Aug 12 2008 23:59:59 Dec 12 2008
switch(config-keychain-key) send-lifetime 00:00:00 Sep 12 2008 23:59:59 Nov 12 2008
switch(config-keychain-key)# interface ethernet 1/2
switch(config-if)# no switchport
switch(config-if)# hsrp 2
switch(config-if-hsrp)# authenticate md5 key-chain hsrp-keys
switch(config-if-hsrp)# copy running-config startup-config
Configuring HSRP Object Tracking
You can configure an HSRP group to adjust its priority based on the availability of other interfaces or
routes. The priority of a switch can change dynamically if it has been configured for object tracking and
the object that is being tracked goes down. The tracking process periodically polls the tracked objects
and notes any value change. The value change triggers HSRP to recalculate the priority. The HSRP
interface with the higher priority becomes the active router if you configure the HSRP interface for
preemption.
HSRP supports tracked objects and track lists. See Chapter 16, “Configuring Object Tracking” for more
information on track lists.
BEFORE YOU BEGIN
Ensure that you have enabled the HSRP feature (see the “Enabling the HSRP Feature” section on
page 14-7).
SUMMARY STEPS
1.
configure terminal
2.
track object-id interface interface-type number {ip routing | line-protocol}
or
track object-id ip route ip-prefix/length reachability
3.
interface interface-type slot/port
4.
no switchport
5.
hsrp group-number [ipv4]
6.
priority [value]
7.
track object-number [decrement value]
8.
preempt [delay minimum seconds] [reload seconds] [sync seconds]
9.
(Optional) show hsrp interface interface-type number
10. (Optional) copy running-config startup-config
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DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
track object-id interface
interface-type number {ip routing |
line-protocol}
Example:
switch(config)# track 1 interface
ethernet 2/2 line-protocol
switch(config-track#
track object-id ip route
ip-prefix/length reachability
Configures the interface that this HSRP interface tracks.
Changes in the state of the interface affect the priority of
this HSRP interface as follows:
•
You configure the interface and corresponding object
number that you use with the track command in hsrp
configuration mode.
•
The line-protocol keyword tracks whether the interface
is up. The ip keyword also checks that IP routing is
enabled on the interface and an IP address is
configured.
Creates a tracked object for a route and enters tracking
configuration mode. The object-id range is from 1 to 500.
Example:
switch(config)# track 2 ip route
192.0.2.0/8 reachability
switch(config-track#
Step 3
interface interface-type slot/port
Enters interface configuration mode.
Example:
switch(config)# interface ethernet
1/2
switch(config-if)#
Step 4
Configures the interface as a Layer 3 routed interface.
no switchport
Example:
switch(config-if)# no switchport
Step 5
hsrp group-number [ipv4]
Creates an HSRP group and enters hsrp configuration mode.
Example:
switch(config-if)# hsrp 2
switch(config-if-hsrp)#
Step 6
priority [value]
Example:
switch(config-if-hsrp)# priority 254
Step 7
Sets the priority level used to select the active router in an
HSRP group. The range is from 0 to 255. The default is 100.
track object-number [decrement
value]
Specifies an object to be tracked that affects the weighting
of an HSRP interface.
Example:
switch(config-if-hsrp)# track 1
decrement 20
The value argument specifies a reduction in the priority of
an HSRP interface when a tracked object fails. The range is
from 1 to 255. The default is 10.
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Step 8
Command
Purpose
preempt [delay [minimum seconds]
[reload seconds] [sync seconds]]
Configures the router to take over as the active router for an
HSRP group if it has a higher priority than the current active
router. This command is disabled by default. The range is
from 0 to 3600 seconds.
Example:
switch(config-if-hsrp)# preempt
delay minimum 60
Step 9
show hsrp interface interface-type
number
(Optional) Displays HSRP information for an interface.
Example:
switch(config-if-hsrp)# show hsrp
interface ethernet 1/2
Step 10
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-if-hsrp)# copy
running-config startup-config
This example shows how to configure HSRP object tracking on Ethernet 1/2:
switch# configure terminal
switch(config)# track 1 interface ethernet 2/2 line-protocol
switch(config)# interface ethernet 1/2
switch(config-if)# no switchport
switch(config-if)# hsrp 2
switch(config-if-hsrp)# track 1 decrement 20
switch(config-if-hsrp)# copy running-config startup-config
Configuring the HSRP Priority
You can configure the HSRP priority on an interface. HSRP uses the priority to determine which HSRP
group member acts as the active router.
To configure the HSRP priority, use the following command in interface configuration mode:
Command
Purpose
priority level [forwarding-threshold lower
lower-value upper upper-value]
Sets the priority level used to select the active
router in an HSRP group. The level range is from
0 to 255. The default is 100.
Example:
switch(config-if-hsrp)# priority 60
forwarding-threshold lower 40 upper 50
Customizing HSRP
You can optionally customize the behavior of HSRP. Be aware that as soon as you enable an HSRP group
by configuring a virtual IP address, that group is now operational. If you first enable an HSRP group
before customizing HSRP, the router could take control over the group and become the active router
before you finish customizing the feature. If you plan to customize HSRP, you should do so before you
enable the HSRP group.
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Configuring HSRP
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To customize HSRP, use the following commands in hsrp configuration mode:
Command
Purpose
name string
Specifies the IP redundancy name for an HSRP group.
The string is from 1 to 255 characters. The default string
has the following format:
Example:
switch(config-if-hsrp)# name HSRP-1
hsrp-<interface-short-name>-<group-id>. For example,
hsrp-Eth2/1-1.
preempt [delay [minimum seconds]
[reload seconds] [sync seconds]]
Example:
switch(config-if-hsrp)# preempt delay
minimum 60
timers [msec] hellotime [msec]
holdtime
Example:
switch(config-if-hsrp)# timers 5 18
Configures the router to take over as an active router for
an HSRP group if it has a higher priority than the current
active router. This command is disabled by default. The
range is from 0 to 3600 seconds.
Configures the hello and hold time for this HSRP member
as follows:
•
hellotime—The interval between successive hello
packets sent. The range is from 1 to 254 seconds.
•
holdtime—The interval before the information in the
hello packet is considered invalid. The range is from
3 to 255.
The optional msec keyword specifies that the argument is
expressed in milliseconds, instead of the default seconds.
The timer ranges for milliseconds are as follows:
•
hellotime—The interval between successive hello
packets sent. The range is from 255 to 999
milliseconds.
•
holdtime—The interval before the information in the
hello packet is considered invalid. The range is from
750 to 3000 milliseconds.
To customize HSRP, use the following commands in interface configuration mode:
Command or Action
Purpose
hsrp delay minimum seconds
Specifies the minimum amount of time that HSRP waits
after a group is enabled before participating in the group.
The range is from 0 to 10000 seconds. The default is 0.
Example:
switch(config-if)# hsrp delay minimum
30
hsrp delay reload seconds
Example:
switch(config-if)# hsrp delay reload
30
Specifies the minimum amount of time that HSRP waits
after reload before participating in the group. The range
is from 0 to 10000 seconds. The default is 0.
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Verifying the HSRP Configuration
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Verifying the HSRP Configuration
To display the HSRP configuration information, perform one of the following tasks:
Command
Purpose
show hsrp [group group-number]
Displays the HSRP status for all groups or one
group.
show hsrp delay [interface interface-type
slot/port]
Displays the HSRP delay value for all interfaces
or one interface.
show hsrp [interface interface-type slot/port]
Displays the HSRP status for an interface.
show hsrp [group group-number] [interface
interface-type slot/port] [active] [all] [init]
[learn] [listen] [speak] [standby]
Displays the HSRP status for a group or interface
for virtual forwarders in the active, init, learn,
listen, or standby state. Use the all keyword to see
all states, including disabled.
show hsrp [group group-number] [interface
interface-type slot/port] active] [all] [init]
[learn] [listen] [speak] [standby] brief
Displays a brief summary of the HSRP status for
a group or interface for virtual forwarders in the
active, init, learn, listen, or standby state. Use the
all keyword to see all states, including disabled.
Configuration Examples for HSRP
This example shows how to enable HSRP on an interface with MD5 authentication and interface
tracking:
key chain hsrp-keys
key 0
key-string 7 zqdest
accept-lifetime 00:00:00 Jun 01 2008 23:59:59 Sep 12 2008
send-lifetime 00:00:00 Jun 01 2008 23:59:59 Aug 12 2008
key 1
key-string 7 uaeqdyito
accept-lifetime 00:00:00 Aug 12 2008 23:59:59 Dec 12 2008
send-lifetime 00:00:00 Sep 12 2008 23:59:59 Nov 12 2008
feature hsrp
track 2 interface ethernet 2/2 ip
interface ethernet 1/2
no switchport
ip address 192.0.2.2/8
hsrp 1
authenticate md5 key-chain hsrp-keys
priority 90
track 2 decrement 20
ip-address 192.0.2.10
no shutdown
Additional References
For additional information related to implementing HSRP, see the following sections:
•
Related Documents, page 14-17
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Feature History for HSRP
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•
MIBs, page 14-17
Related Documents
Related Topic
Document Title
Configuring the Virtual Router Redundancy protocol
Chapter 15, “Configuring VRRP”
HSRP CLI commands
Cisco Nexus 3000 Series Command Reference,
MIBs
MIBs
MIBs Link
CISCO-HSRP-MIB
To locate and download MIBs, go to the following URL:
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
Feature History for HSRP
Table 14-2 lists the release history for this feature.
Table 14-2
Feature History for HSRP
Feature Name
Releases
Feature Information
HSRP
5.0(3)U1(1)
This feature was introduced.
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Feature History for HSRP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
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CH A P T E R
15
Configuring VRRP
This chapter describes how to configure the Virtual Router Redundancy Protocol (VRRP) on a switch
This chapter includes the following sections:
•
Information About VRRP, page 15-1
•
Licensing Requirements for VRRP, page 15-6
•
Guidelines and Limitations, page 15-6
•
Default Settings, page 15-6
•
Configuring VRRP, page 15-7
•
Verifying the VRRP Configuration, page 15-17
•
Displaying VRRP Statistics, page 15-17
•
Configuration Examples for VRRP, page 15-18
•
Additional References, page 15-19
•
Feature History for VRRP, page 15-19
Information About VRRP
VRRP allows for transparent failover at the first-hop IP router, by configuring a group of routers to share
a virtual IP address. VRRP selects a master router in that group to handle all packets for the virtual IP
address. The remaining routers are in standby and take over in the event that the master router fails.
This section includes the following topics:
•
VRRP Operation, page 15-2
•
VRRP Benefits, page 15-3
•
Multiple VRRP Groups, page 15-3
•
VRRP Router Priority and Preemption, page 15-4
•
VRRP Advertisements, page 15-5
•
VRRP Authentication, page 15-5
•
VRRP Tracking, page 15-5
•
Virtualization Support, page 15-5
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Information About VRRP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
VRRP Operation
A LAN client can determine which router should be the first hop to a particular remote destination by
using a dynamic process or static configuration. Examples of dynamic router discovery are as follows:
•
Proxy ARP—The client uses Address Resolution Protocol (ARP) to get the destination it wants to
reach, and a router will respond to the ARP request with its own MAC address.
•
Routing protocol—The client listens to dynamic routing protocol updates (for example, from
Routing Information Protocol [RIP]) and forms its own routing table.
•
ICMP Router Discovery Protocol (IRDP) client—The client runs an Internet Control Message
Protocol (ICMP) router discovery client.
The disadvantage to dynamic discovery protocols is that they incur some configuration and processing
overhead on the LAN client. Also, in the event of a router failure, the process of switching to another
router can be slow.
An alternative to dynamic discovery protocols is to statically configure a default router on the client.
Although, this approach simplifies client configuration and processing, it creates a single point of
failure. If the default gateway fails, the LAN client is limited to communicating only on the local IP
network segment and is cut off from the rest of the network.
VRRP can solve the static configuration problem by enabling a group of routers (a VRRP group) to share
a single virtual IP address. You can then configure the LAN clients with the virtual IP address as their
default gateway.
Figure 15-1 shows a basic VLAN topology. In this example, Routers A, B, and C form a VRRP group.
The IP address of the group is the same address that was configured for the Ethernet interface of Router
A (10.0.0.1).
Basic VRRP Topology
Router A
Virtual router
master
10.0.0.1
Client 1
Router B
Virtual router
backup
10.0.0.2
Client 2
Router C
Virtual router
backup
Virtual
router group
IP address = 10.0.0.1
10.0.0.3
Client 3
56623
Figure 15-1
Because the virtual IP address uses the IP address of the physical Ethernet interface of Router A, Router
A is the master (also known as the IP address owner). As the master, Router A owns the virtual IP address
of the VRRP group r and forwards packets sent to this IP address. Clients 1 through 3 are configured
with the default gateway IP address of 10.0.0.1.
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Routers B and C function as backups. If the master fails, the backup router with the highest priority
becomes the master and takes over the virtual IP address to provide uninterrupted service for the LAN
hosts. When router A recovers, it becomes the r master again. For more information, see the “VRRP
Router Priority and Preemption” section.
Note
Packets received on a routed port destined for the VRRP virtual IP address will terminate on the local
router, regardless of whether that router is the master VRRP router or a backup VRRP router. This
includes ping and telnet traffic. Packets received on a Layer 2 (VLAN) interface destined for the VRRP
virtual IP address will terminate on the master router.
VRRP Benefits
The benefits of VRRP are as follows:
•
Redundancy–Enables you to configure multiple routers as the default gateway router, which reduces
the possibility of a single point of failure in a network.
•
Load Sharing–Allows traffic to and from LAN clients to be shared by multiple routers. The traffic
load is shared more equitably among available routers.
•
Multiple VRRP groups–Supports up to 255 VRRP groups on a router physical interface if the
platform supports multiple MAC addresses. Multiple VRRP groups enable you to implement
redundancy and load sharing in your LAN topology.
•
Multiple IP Addresses–Allows you to manage multiple IP addresses, including secondary IP
addresses. If you have multiple subnets configured on an Ethernet interface, you can configure
VRRP on each subnet.
•
Preemption–Enables you to preempt a backup router that has taken over for a failing master with a
higher priority backup router that has become available.
•
Advertisement Protocol–Uses a dedicated Internet Assigned Numbers Authority (IANA) standard
multicast address (224.0.0.18) for VRRP advertisements. This addressing scheme minimizes the
number of routers that must service the multicasts and allows test equipment to accurately identify
VRRP packets on a segment. IANA has assigned the IP protocol number 112 to VRRP.
•
VRRP Tracking–Ensures that the best VRRP router is the master for the group by altering VRRP
priorities based on interface states.
Multiple VRRP Groups
You can configure up to 255 VRRP groups on a physical interface. The actual number of VRRP groups
that a router interface can support depends on the following factors:
•
Router processing capability
•
Router memory capability
In a topology where multiple VRRP groups are configured on a router interface, the interface can act as
a master for one VRRP group and as a backup for one or more other VRRP groups.
Figure 15-2 shows a LAN topology in which VRRP is configured so that Routers A and B share the
traffic to and from clients 1 through 4. Routers A and B act as backups to each other if either router fails.
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Information About VRRP
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Figure 15-2
Load Sharing and Redundancy VRRP Topology
Router A
Master for virtual router 1
Backup for virtual router 2
10.0.0.2
129284
10.0.0.1
Router B
Backup for virtual router 1
Master for virtual router 2
Client 1
Default gateway =
10.0.0.1
Client 2
Default gateway =
10.0.0.1
Client 3
Default gateway =
10.0.0.2
Client 4
Default gateway =
10.0.0.2
In this topology contains two virtual IP addresses for two VRRP groups that overlap. For VRRP group
1, Router A is the owner of IP address 10.0.0.1 and is the master. Router B is the backup to router A.
Clients 1 and 2 are configured with the default gateway IP address of 10.0.0.1.
For VRRP group 2, Router B is the owner of IP address 10.0.0.2 and is the master. Router A is the backup
to router B. Clients 3 and 4 are configured with the default gateway IP address of 10.0.0.2.
VRRP Router Priority and Preemption
An important aspect of the VRRP redundancy scheme is the VRRP router priority because the priority
determines the role that each VRRP router plays and what happens if the master router fails.
If a VRRP router owns the virtual IP address and the IP address of the physical interface, this router
functions as the master. The priority of the master is 255.
Priority also determines if a VRRP router functions as a backup router and the order of ascendancy to
becoming a master if the master fails.
For example, if router A, the master in a LAN topology, fails, VRRP must determine if backups B or C
should take over. If you configure router B with priority 101 and router C with the default priority of
100, VRRP selects router B to become the master because it has the higher priority. If you configure
routers B and C with the default priority of 100, VRRP selects the backup with the higher IP address to
become the master.
VRRP uses preemption to determine what happens after a VRRP backup router becomes the master.
With preemption enabled by default, VRRP will switch to a backup if that backup comes online with a
priority higher than the new master. For example, if Router A is the master and fails, VRRP selects
Router B (next in order of priority). If Router C comes online with a higher priority than Router B, VRRP
selects Router C as the new master, even though Router B has not failed.
If you disable preemption, VRRP will only switch if the original master recovers or the new master fails.
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Information About VRRP
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
VRRP Advertisements
The VRRP master sends VRRP advertisements to other VRRP routers in the same group. The
advertisements communicate the priority and state of the master. Cisco NX-OS encapsulates the VRRP
advertisements in IP packets and sends them to the IP multicast address assigned to the VRRP group.
Cisco NX-OS sends the advertisements once every second by default, but you can configure a different
advertisement interval.
VRRP Authentication
VRRP supports the following authentication mechanisms:
•
No authentication
•
Plain text authentication
VRRP rejects packets in any of the following cases:
•
The authentication schemes differ on the router and in the incoming packet.
•
Text authentication strings differ on the router and in the incoming packet.
VRRP Tracking
VRRP supports the following two options for tracking:
•
Native interface tracking— Tracks the state of an interface and use that state to determine the
priority of the VRRP router in a VRRP group. The tracked state is down if the interface is down or
if the interface does not have a primary IP address.
•
Object tracking—Tracks the state of a configured object and use that state to determine the priority
of the VRRP router in a VRRP group. See Chapter 16, “Configuring Object Tracking” for more
information on object tracking.
If the tracked state (interface or object) goes down, VRRP updates the priority based on what you
configure the new priority to be for the tracked state. When the tracked state comes up, VRRP restores
the original priority for the virtual router group.
For example, you may want to lower the priority of a VRRP group member if its uplink to the network
goes down so another group member can take over as master for the VRRP group. See the “Configuring
VRRP Interface State Tracking” section on page 15-15 for more information.
Note
VRRP does not support Layer 2 interface tracking.
Virtualization Support
VRRP supports Virtual Routing and Forwarding instances (VRFs). By default, Cisco NX-OS places you
in the default VRF unless you specifically configure another VRF.
If you change the VRF membership of an interface, Cisco NX-OS removes all Layer 3 configuration,
including VRRP.
For more information, see Chapter 11, “Configuring Layer 3 Virtualization.”
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Licensing Requirements for VRRP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Licensing Requirements for VRRP
The following table shows the licensing requirements for this feature:
Product
License Requirement
Cisco NX-OS
VRRP requires no license. Any feature not included in a license package is bundled with the Cisco NX-OS
system images and is provided at no extra charge to you. For a complete explanation of the Cisco NX-OS
licensing scheme, see the Cisco NX-OS Licensing Guide.
Make sure the LAN Base Services license is installed on the switch to enable Layer 3 interfaces.
Note
Guidelines and Limitations
VRRP has the following configuration guidelines and limitations:
•
You cannot configure VRRP on the management interface.
•
When VRRP is enabled, you should replicate the VRRP configuration across switches in your
network.
•
We recommend that you do not configure more than one first-hop redundancy protocol on the same
interface.
•
You must configure an IP address for the interface that you configure VRRP on and enable that
interface before VRRP becomes active.
•
Cisco NX-OS removes all Layer 3 configuration on an interface when you change the interface VRF
membership, port channel membership, or when you change the port mode to Layer 2.
•
When you configure VRRP to track a Layer 2 interface, you must shut down the Layer 2 interface
and reenable the interface to update the VRRP priority to reflect the state of the Layer 2 interface.
Default Settings
Table 15-1 lists the default settings for VRRP parameters.
Table 15-1
Default VRRP Parameters
Parameters
Default
advertisement interval
1 seconds
authentication
no authentication
preemption
enabled
priority
100
VRRP feature
disabled
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Configuring VRRP
This section includes the following topics:
Note
•
Enabling the VRRP Feature, page 15-7
•
Configuring VRRP Groups, page 15-8
•
Configuring VRRP Priority, page 15-9
•
Configuring VRRP Authentication, page 15-11
•
Configuring Time Intervals for Advertisement Packets, page 15-12
•
Disabling Preemption, page 15-14
•
Configuring VRRP Interface State Tracking, page 15-15
If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature
might differ from the Cisco IOS commands that you would use.
Enabling the VRRP Feature
You must globally enable the VRRP feature before you can configure and enable any VRRP groups.
To enable the VRRP feature, use the following command in global configuration mode:
Command
Purpose
feature vrrp
Enables VRRP.
Example:
switch(config)# feature vrrp
To disable the VRRP feature and remove all associated configuration, use the following command in
global configuration mode:
Command
Purpose
no feature vrrp
Disables the VRRP feature.
Example:
switch(config)# no feature vrrp
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Configuring VRRP Groups
You can create a VRRP group, assign the virtual IP address, and enable the group.
You can configure one virtual IPv4 address for a VRRP group. By default, the master VRRP router drops
the packets addressed directly to the virtual IP address because the VRRP master is only intended as a
next-hop router to forward packets. Some applications require that Cisco NX-OS accept packets
addressed to the virtual router IP. Use the secondary option to the virtual IP address to accept these
packets when the local router is the VRRP master.
Once you have configured the VRRP group, you must explicitly enable the group before it becomes
active.
BEFORE YOU BEGIN
Ensure that you configure an IP address on the interface (see the “Configuring IPv4 Addressing” section
on page 2-7.
SUMMARY STEPS
1.
configure terminal
2.
interface interface-type slot/port
3.
no switchport
4.
vrrp number
5.
address ip-address [secondary]
6.
no shutdown
7.
(Optional) show vrrp
8.
(Optional) copy running-config startup-config
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DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface interface-type slot/port
Enters interface configuration mode.
Example:
switch(config)#
switch(config-if)# interface ethernet 2/1
Step 3
no switchport
Example:
switch(config-if)# no switchport
Step 4
vrrp number
Example:
switch(config-if)# vrrp 250
switch(config-if-vrrp)#
Step 5
address ip-address [secondary]
Example:
switch(config-if-vrrp)# address 192.0.2.8
Configures the interface as a Layer 3
routed interface.
Creates a virtual router group. The range
is from 1 to 255.
Configures the virtual IPv4 address for
the specified VRRP group. This address
should be in the same subnet as the IPv4
address of the interface.
Use the secondary option only if
applications require that VRRP routers
accept the packets sent to the virtual
router’s IP address and deliver to
applications.
Step 6
no shutdown
Example:
switch(config-if-vrrp)# no shutdown
switch(config-if-vrrp)#
Step 7
Enables the VRRP group. Disabled by
default.
(Optional) Displays VRRP information.
show vrrp
Example:
switch(config-if-vrrp)# show vrrp
Step 8
copy running-config startup-config
Example:
switch(config-if-vrrp)# copy running-config
startup-config
(Optional) Saves this configuration
change.
Configuring VRRP Priority
The valid priority range for a virtual router is from 1 to 254 (1 is the lowest priority and 254 is the
highest). The default priority value for backups is 100. For switches whose interface IP address is the
same as the primary virtual IP address (the master), the default value is 255.
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BEFORE YOU BEGIN
Ensure that you have enabled the VRRP feature (see the “Configuring VRRP” section on page 15-7).
Ensure that you have configured an IP address on the interface (see the “Configuring IPv4 Addressing”
section on page 2-7.
SUMMARY STEPS
1.
configure terminal
2.
interface interface-type slot/port
3.
no switchport
4.
vrrp number
5.
shutdown
6.
priority level [forwarding-threshold lower lower-value upper upper-value]
7.
no shutdown
8.
(Optional) show vrrp
9.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface interface-type slot/port
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 2/1
switch(config-if)#
Step 3
no switchport
Example:
switch(config-if)# no switchport
Step 4
vrrp number
Configures the interface as a Layer 3 routed
interface.
Creates a virtual router group.
Example:
switch(config-if)# vrrp 250
switch(config-if-vrrp)#
Step 5
shutdown
Disables the VRRP group. Disabled by default.
Example:
switch(config-if-vrrp)# shutdown
switch(config-if-vrrp)#
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Step 6
Step 7
Command
Purpose
priority level [forwarding-threshold lower
lower-value upper upper-value]
Example:
switch(config-if-vrrp)# priority 60
forwarding-threshold lower 40 upper 50
Sets the priority level used to select the active
router in an VRRP group. The level range is
from 1 to 254. The default is 100 for backups
and 255 for a master that has an interface IP
address equal to the virtual IP address.
no shutdown
Enables the VRRP group. Disabled by default.
Example:
switch(config-if-vrrp)# no shutdown
switch(config-if-vrrp)#
Step 8
show vrrp
Example:
switch(config-if-vrrp)# show vrrp
Step 9
copy running-config startup-config
(Optional) Displays a summary of VRRP
information.
(Optional) Saves this configuration change.
Example:
switch(config-if-vrrp)# copy running-config
startup-config
Configuring VRRP Authentication
You can configure simple text authentication for a VRRP group.
BEFORE YOU BEGIN
Ensure that the authentication configuration is identical for all VRRP switches in the network.
Ensure that you have enabled the VRRP feature (see the “Configuring VRRP” section on page 15-7).
Ensure that you have configured an IP address on the interface (see the “Configuring IPv4 Addressing”
section on page 2-7.
SUMMARY STEPS
1.
configure terminal
2.
interface interface-type slot/port
3.
no switchport
4.
vrrp number
5.
shutdown
6.
authentication text password
7.
no shutdown
8.
(Optional) show vrrp
9.
(Optional) copy running-config startup-config
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DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface interface-type slot/port
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 2/1
switch(config-if)#
Step 3
no switchport
Example:
switch(config-if)# no switchport
Step 4
vrrp number
Configures the interface as a Layer 3 routed
interface.
Creates a virtual router group.
Example:
switch(config-if)# vrrp 250
switch(config-if-vrrp)#
Step 5
shutdown
Disables the VRRP group. Disabled by default.
Example:
switch(config-if-vrrp)# shutdown
switch(config-if-vrrp)#
Step 6
authentication text password
Example:
switch(config-if-vrrp)# authentication md5
prd555oln47espn0 spi 0x0
Step 7
no shutdown
Assigns the simple text authentication option and
specifies the keyname password. The keyname
range is from 1 to 255 characters. We recommend
that you use at least 16 characters. The text
password is up to eight alphanumeric characters.
Enables the VRRP group. Disabled by default.
Example:
switch(config-if-vrrp)# no shutdown
switch(config-if-vrrp)#
Step 8
show vrrp
Example:
switch(config-if-vrrp)# show vrrp
Step 9
copy running-config startup-config
(Optional) Displays a summary of VRRP
information.
(Optional) Saves this configuration change.
Example:
switch(config-if-vrrp)# copy
running-config startup-config
Configuring Time Intervals for Advertisement Packets
You can configure the time intervals for advertisement packets.
BEFORE YOU BEGIN
Ensure that you have enabled the VRRP feature (see the “Configuring VRRP” section on page 15-7).
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Ensure that you have configured an IP address on the interface (see the “Configuring IPv4 Addressing”
section on page 2-7.
SUMMARY STEPS
1.
configure terminal
2.
interface interface-type slot/port
3.
no switchport
4.
vrrp number
5.
shutdown
6.
advertisement-interval seconds
7.
no shutdown
8.
(Optional) show vrrp
9.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface interface-type slot/port
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 2/1
switch(config-if)#
Step 3
no switchport
Example:
switch(config-if)# no switchport
Step 4
Configures the interface as a Layer 3
routed interface.
Creates a virtual router group.
vrrp number
Example:
switch(config-if)# vrrp 250
switch(config-if-vrrp)#
Step 5
shutdown
Example:
switch(config-if-vrrp)# shutdown
switch(config-if-vrrp)#
Step 6
advertisement-interval seconds
Example:
switch(config-if-vrrp)# advertisement-interval 15
Disables the VRRP group. Disabled by
default.
Sets the interval time in seconds between
sending advertisement frames. The range
is from 1 to 254. The default is 1 second.
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Step 7
Command
Purpose
no shutdown
Enables the VRRP group. Disabled by
default.
Example:
switch(config-if-vrrp)# no shutdown
switch(config-if-vrrp)#
Step 8
show vrrp
Example:
switch(config-if-vrrp)# show vrrp
Step 9
copy running-config startup-config
Example:
switch(config-if-vrrp)# copy running-config
startup-config
(Optional) Displays a summary of VRRP
information.
(Optional) Saves this configuration
change.
Disabling Preemption
You can disable preemption for a VRRP group member. If you disable preemption, a higher-priority back
up router will not take over for a lower-priority master router. Preemption is enabled by default.
BEFORE YOU BEGIN
Ensure that you have enabled the VRRP feature (see the “Configuring VRRP” section on page 15-7).
Ensure that you have configured an IP address on the interface (see the “Configuring IPv4 Addressing”
section on page 2-7.
SUMMARY STEPS
1.
configure terminal
2.
interface interface-type slot/port
3.
no switchport
4.
vrrp number
5.
shutdown
6.
no preempt
7.
no shutdown
8.
(Optional) show vrrp
9.
(Optional) copy running-config startup-config
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Configuring VRRP
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface interface-type slot/port
Enters interface configuration mode.
Example:
switch(config)# interface ethernet
2/1
switch(config-if)#
Step 3
Configures the interface as a Layer 3 routed interface.
no switchport
Example:
switch(config-if)# no switchport
Step 4
Creates a virtual router group.
vrrp number
Example:
switch(config-if)# vrrp 250
switch(config-if-vrrp)#
Step 5
Enables the VRRP group. Disabled by default.
no shutdown
Example:
switch(config-if-vrrp)# no
shutdown
Step 6
no preempt
Example:
switch(config-if-vrrp)# no preempt
Step 7
Disables the preempt option and allows the master to remain
when a higher-priority backup appears.
Enables the VRRP group. Disabled by default.
no shutdown
Example:
switch(config-if-vrrp)# no
shutdown
Step 8
(Optional) Displays a summary of VRRP information.
show vrrp
Example:
switch(config-if-vrrp)# show vrrp
Step 9
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-if-vrrp)# copy
running-config startup-config
Configuring VRRP Interface State Tracking
Interface state tracking changes the priority of the virtual router based on the state of another interface
in the switch. When the tracked interface goes down or the IP address is removed, Cisco NX-OS assigns
the tracking priority value to the virtual router. When the tracked interface comes up and an IP address
is configured on this interface, Cisco NX-OS restores the configured priority to the virtual router (see
the“Configuring VRRP Priority” section on page 15-9).
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Configuring VRRP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Note
For interface state tracking to function, you must enable preemption on the interface.
Note
VRRP does not support Layer 2 interface tracking.
BEFORE YOU BEGIN
Ensure that you have enabled the VRRP feature (see the “Configuring VRRP” section on page 15-7).
Ensure that you have configured an IP address on the interface (see the “Configuring IPv4 Addressing”
section on page 2-7.
Ensure that you have enabled the virtual router (see the “Configuring VRRP Groups” section on
page 15-8).
SUMMARY STEPS
1.
configure terminal
2.
interface interface-type slot/port
3.
no switchport
4.
vrrp number
5.
shutdown
6.
track interface type number priority value
7.
no shutdown
8.
(Optional) show vrrp
9.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
interface interface-type slot/port
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 2/1
switch(config-if)#
Step 3
no switchport
Configures the interface as a Layer 3 routed interface.
Example:
switch(config-if)# no switchport
Step 4
vrrp number
Creates a virtual router group.
Example:
switch(config-if)# vrrp 250
switch(config-if-vrrp)#
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Step 5
Command
Purpose
shutdown
Disables the VRRP group. Disabled by default.
Example:
switch(config-if-vrrp)# shutdown
switch(config-if-vrrp)#
Step 6
track interface type number priority
value
Enables interface priority tracking for a VRRP group.
The priority range is from 1 to 254.
Example:
switch(config-if-vrrp)# track interface
ethernet 2/10 priority 254
Step 7
Enables the VRRP group. Disabled by default.
no shutdown
Example:
switch(config-if-vrrp)# no shutdown
switch(config-if-vrrp)#
Step 8
(Optional) Displays a summary of VRRP information.
show vrrp
Example:
switch(config-if-vrrp)# show vrrp
Step 9
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-if-vrrp)# copy
running-config startup-config
Verifying the VRRP Configuration
To display the VRRP configuration information, perform one of the following tasks:
Command
Purpose
show vrrp
Displays the VRRP status for all groups.
show vrrp vr group-number
Displays the VRRP status for a VRRP group.
show vrrp vr number interface interface-type
port configuration
Displays the virtual router configuration for an
interface.
show vrrp vr number interface interface-type
port status
Displays the virtual router status for an interface.
Displaying VRRP Statistics
To display VRRP statistics, use the following commands:
Command
Purpose
show vrrp vr number interface interface-type
port statistics
Displays the virtual router information.
show vrrp statistics
Displays the VRRP statistics.
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Configuration Examples for VRRP
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Use the clear vrrp vr command to clear the IPv4 VRRP statistics for a specified interface.
Configuration Examples for VRRP
In this example, Router A and Router B each belong to three VRRP groups. In the configuration, each
group has the following properties:
•
Group 1:
– Virtual IP address is 10.1.0.10.
– Router A will become the master for this group with priority 120.
– Advertising interval is 3 seconds.
– Preemption is enabled.
•
Group 5:
– Router B will become the master for this group with priority 200.
– Advertising interval is 30 seconds.
– Preemption is enabled.
•
Group 100:
– Router A will become the master for this group first because it has a higher IP address
(10.1.0.2).
– Advertising interval is the default 1 second.
– Preemption is disabled.
Router A
interface ethernet 1/0
no switchport
ip address 10.1.0.2/16
no shutdown
vrrp 1
priority 120
authentication text cisco
advertisement-interval 3
address 10.1.0.10
no shutdown
vrrp 5
priority 100
advertisement-interval 30
address 10.1.0.50
no shutdown
vrrp 100
no preempt
address 10.1.0.100
no shutdown
Router B
interface ethernet 1/0
no switchport
ip address 10.2.0.1/2
no shutdown
vrrp 1
priority 100
authentication text cisco
advertisement-interval 3
address 10.2.0.10
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Additional References
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
no shutdown
vrrp 5
priority 200
advertisement-interval 30
address 10.2.0.50
no shutdown
vrrp 100
no preempt
address 10.2.0.100
no shutdown
Additional References
For additional information related to implementing VRRP, see the following sections:
•
Related Documents, page 15-19
Related Documents
Related Topic
Document Title
Configuring the hot standby routing protocol
Chapter 14, “Configuring HSRP”
VRRP CLI commands
Cisco Nexus 3000 Series Command Reference,
Feature History for VRRP
Table 15-2 lists the release history for this feature.
Table 15-2
Feature History for VRRP
Feature Name
Releases
Feature Information
VRRP
5.0(3)U1(1)
This feature was introduced.
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CH A P T E R
16
Configuring Object Tracking
This chapter describes how to configure object tracking on Cisco NX-OS switches.
This chapter includes the following sections:
•
Information About Object Tracking, page 16-1
•
Licensing Requirements for Object Tracking, page 16-3
•
Guidelines and Limitations, page 16-3
•
Default Settings, page 16-3
•
Configuring Object Tracking, page 16-3
•
Verifying the Object Tracking Configuration, page 16-13
•
Configuration Examples for Object Tracking, page 16-13
•
Related Topics, page 16-13
•
Additional References, page 16-13
•
Feature History for Object Tracking, page 16-14
Information About Object Tracking
Object tracking allows you to track specific objects on the switch, such as the interface line protocol
state, IP routing, and route reachability, and to take action when the tracked object’s state changes. This
feature allows you to increase the availability of the network and shorten recovery time if an object state
goes down.
This section includes the following topics:
•
Object Tracking Overview, page 16-1
•
Object Track List, page 16-2
•
Virtualization Support, page 16-2
Object Tracking Overview
The object tracking feature allows you to create a tracked object that multiple clients can use to modify
the client behavior when a tracked object changes. Several clients register their interest with the tracking
process, track the same object, and take different actions when the object state changes.
Clients include the following features:
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Information About Object Tracking
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
•
Hot Standby Redundancy Protocol (HSRP)
•
Virtual Router Redundancy Protocol (VRRP)
The object tracking monitors the status of the tracked objects and communicates any changes made to
interested clients. Each tracked object is identified by a unique number that clients can use to configure
the action to take when a tracked object changes state.
Cisco NX-OS tracks the following object types:
•
Interface line protocol state—Tracks whether the line protocol state is up or down.
•
Interface IP routing state—Tracks whether the interface has an IPv4 address and if IPv4 routing is
enabled and active.
•
IP route reachability—Tracks whether an Ipv4 route exists and is reachable from the local switch.
For example, you can configure HSRP to track the line protocol of the interface that connects one of the
redundant routers to the rest of the network. If that link protocol goes down, you can modify the priority
of the affected HSRP router.
Object Track List
An object track list allows you to track the combined states of multiple objects. Object track lists support
the following capabilities:
•
Boolean "and" function—Each object defined within the track list t must be in an up state so that
the track list object can become up.
•
Boolean "or" function—At least one object defined within the track list must be in an up state so
that the tracked object can become up.
•
Threshold percentage—The percentage of up objects in the tracked list must be greater than the
configured up threshold for the tracked list to be in the up state. If the percentage of down objects
in the tracked list is above the configured track list down threshold, the tracked list is marked as
down.
•
Threshold weight—Assign a weight value to each object in the tracked list, and a weight threshold
for the track list. If the combined weights of all up objects exceeds the track list weight up threshold,
the track list is in an up state. If the combined weights of all the down objects exceeds the track list
weight down threshold, the track list is in the down state.
See the “Configuring an Object Track List with a Boolean Expression” section on page 16-6 for more
information on track lists.
Virtualization Support
Object tracking supports Virtual Routing and Forwarding (VRF) instances. By default, Cisco NX-OS
places you in the default VRF unless you specifically configure another VRF. By default, Cisco NX-OS
tracks the route reachability state of objects in the default VRF. If you want to track objects in another
VRF, you must configure the object to be a member of that VRF (see the “Configuring Object Tracking
for a Nondefault VRF” section on page 16-12).
For more information, see Chapter 11, “Configuring Layer 3 Virtualization.”
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Licensing Requirements for Object Tracking
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Licensing Requirements for Object Tracking
The following table shows the licensing requirements for this feature:
Product
License Requirement
Cisco NX-OS
Object tracking requires no license. Any feature not included in a license package is bundled with the Cisco
NX-OS system images and is provided at no extra charge to you. For a complete explanation of the Cisco
NX-OS licensing scheme, see the Cisco NX-OS Licensing Guide.
Guidelines and Limitations
Object tracking has the following configuration guidelines and limitations:
•
Supports up to 500 tracked objects.
•
Supports Ethernet, subinterfaces, tunnels, port channels, loopback interfaces, and VLAN interfaces.
•
Supports one tracked object per HSRP group.
Default Settings
Table 16-1 lists the default settings for object tracking parameters.
Table 16-1
Default Object Tracking Parameters
Parameters
Default
Tracked Object VRF
Member of default VRF
Configuring Object Tracking
This section includes the following topics:
Note
•
Configuring Object Tracking for an Interface, page 16-4
•
Configuring Object Tracking for Route Reachability, page 16-5
•
Configuring an Object Track List with a Boolean Expression, page 16-6
•
Configuring an Object Track List with a Percentage Threshold, page 16-7
•
Configuring an Object Track List with a Weight Threshold, page 16-8
•
Configuring an Object Tracking Delay, page 16-10
•
Configuring Object Tracking for a Nondefault VRF, page 16-12
If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature
might differ from the Cisco IOS commands that you would use.
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Configuring Object Tracking
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Configuring Object Tracking for an Interface
You can configure Cisco NX-OS to track the line protocol or IPv4 routing state of an interface.
SUMMARY STEPS
1.
configure terminal
2.
track object-id interface interface-type number {ip routing | line-protocol}
3.
(Optional) show track [object-id]
4.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
track object-id interface interface-type
number {ip routing | line-protocol}
Example:
switch(config)# track 1 interface
ethernet 1/2 line-protocol
switch(config-track#
Step 3
show track [object-id]
Creates a tracked object for an interface and enters
tracking configuration mode. The object-id range is
from 1 to 500.
(Optional) Displays object tracking information.
Example:
switch(config-track)# show track 1
Step 4
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-track)# copy
running-config startup-config
This example shows how to configure object tracking for the line protocol state on Ethernet 1/2:
switch# configure terminal
switch(config)# track 1 interface ethernet 1/2 line-protocol
switch(config-track)# copy running-config startup-config
This example shows how to configure object tracking for the IPv4 routing state on Ethernet 1/2:
switch# configure terminal
switch(config)# track 2 interface ethernet 1/2 ip routing
switch(config-track)# copy running-config startup-config
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Configuring Object Tracking
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Configuring Object Tracking for Route Reachability
You can configure Cisco NX-OS to track the existence and reachability of an IP route.
SUMMARY STEPS
1.
configure terminal
2.
track object-id ip route prefix/length reachability
3.
(Optional) show track [object-id]
4.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
track object-id ip route prefix/length
reachability
Example:
switch(config)# track 2 ip route
192.0.2.0/8 reachability
switch(config-track)#
Step 3
show track [object-id]
Creates a tracked object for a route and enters tracking
configuration mode. The object-id range is from 1 to
500. The prefix format for IP is A.B.C.D/length, where
the length range is from 1 to 32.
(Optional) Displays object tracking information.
Example:
switch(config-track)# show track 1
Step 4
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-track)# copy
running-config startup-config
This example shows how to configure object tracking for an IPv4 route in the default VRF.
switch# configure terminal
switch(config)# track 4 ip route 192.0.2.0/8 reachability
switch(config-track)# copy running-config startup-config
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Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Configuring an Object Track List with a Boolean Expression
You can configure an object track list that contains multiple tracked objects. A tracked list contains one
or more objects. The Boolean expression enables two types of calculation by using either "and" or "or"
operators. For example, when tracking two interfaces using the "and" operator, up means that both
interfaces are up, and down means that either interface is down.
SUMMARY STEPS
1.
configure terminal
2.
track track-number list boolean {and | or}
3.
object object-number [not]
4.
(Optional) show track
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
Configures a tracked list object and enters tracking
configuration mode. Specifies that the state of the
tracked list is based on a Boolean calculation. The
Example:
switch(config)# track 1 list boolean and keywords are as follows:
switch(config-track#
• and—Specifies that the list is up if all objects are
up, or down if one or more objects are down. For
example when tracking two interfaces, up means
that both interfaces are up, and down means that
either interface is down.
track track-number list boolean {and |
or}
•
or—Specifies that the list is up if at least one
object is up. For example, when tracking two
interfaces, up means that either interface is up, and
down means that both interfaces are down.
The track-number range is from 1 to 500.
Step 3
object object-id [not]
Example:
switch(config-track)# object 10
Adds a tracked object to the track list. The object-id
range is from 1 to 500. The not keyword optionally
negates the tracked object state.
Note
The example means that when object 10 is up,
the tracked list detects object 10 as down.
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Step 4
Command
Purpose
show track
(Optional) Displays object tracking information.
Example:
switch(config-track)# show track
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-track)# copy
running-config startup-config
This example shows how to configure a track list with multiple objects as a Boolean “and”:
switch# configure terminal
switch(config)# track 1 list boolean and
switch(config-track)# object 10
switch(config-track)# object 20 not
Configuring an Object Track List with a Percentage Threshold
You can configure an object track list that contains a percentage threshold. A tracked list contains one
or more objects. The percentage of up objects must exceed the configured track list up percent threshold
before the track list is in an up state. For example, if the tracked list has three objects, and you configure
an up threshold of 60 percent, two of the objects must be in the up state (66 percent of all objects) for
the track list to be in the up state.
SUMMARY STEPS
1.
configure terminal
2.
track track-number list threshold percentage
3.
threshold percentage up up-value down down-value
4.
object object-number
5.
(Optional) show track
6.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
track track-number list threshold
percentage
Example:
switch(config)# track 1 list threshold
percentage
switch(config-track#
Configures a tracked list object and enters tracking
configuration mode. Specifies that the state of the
tracked list is based on a configured threshold percent.
The track-number range is from 1 to 500.
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Step 3
Command
Purpose
threshold percentage up up-value down
down-value
Configures the threshold percent for the tracked list.
The range from 0 to 100 percent.
Example:
switch(config-track)# threshold
percentage up 70 down 30
Step 4
object object-id
Example:
switch(config-track)# object 10
Step 5
show track
Adds a tracked object to the track list. The object-id
range is from 1 to 500.
(Optional) Displays object tracking information.
Example:
switch(config-track)# show track
Step 6
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-track)# copy
running-config startup-config
This example shows how to configure a track list with an up threshold of 70 percent and a down threshold
of 30 percent:
switch# configure terminal
switch(config)# track 1 list threshold percentage
switch(config-track)# threshold percentage up 70 down 30
switch(config-track)# object 10
switch(config-track)# object 20
switch(config-track)# object 30
Configuring an Object Track List with a Weight Threshold
You can configure an object track list that contains a weight threshold. A tracked list contains one or
more objects. The combined weight of up objects must exceed the configured track list up weight
threshold before the track list is in an up state. For example, if the tracked list has three objects with the
default weight of 10 each, and you configure an up threshold of 15, two of the objects must be in the up
state (combined weight of 20) for the track list to be in the up state.
SUMMARY STEPS
1.
configure terminal
2.
track track-number list threshold weight
3.
threshold weight up up-value down down-value
4.
object object-number weight value
5.
(Optional) show track
6.
(Optional) copy running-config startup-config
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Configuring Object Tracking
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DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
track track-number list threshold weight
Example:
switch(config)# track 1 list threshold
weight
switch(config-track#
Step 3
threshold weight up up-value down
down-value
Configures a tracked list object and enters tracking
configuration mode. Specifies that the state of the
tracked list is based on a configured threshold weight.
The track-number range is from 1 to 500.
Configures the threshold weight for the tracked list.
The range from 1 to 255.
Example:
switch(config-track)# threshold weight
up 30 down 10
Step 4
object object-id weight value
Example:
switch(config-track)# object 10 weight
15
Step 5
Adds a tracked object to the track list. The object-id
range is from 1 to 500. The value range is from 1 to
255. The default weight value is 10.
(Optional) Displays object tracking information.
show track
Example:
switch(config-track)# show track
Step 6
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-track)# copy
running-config startup-config
This example shows how to configure a track list with an up weight threshold of 30 and a down threshold
of 10:
switch# configure terminal
switch(config)# track 1 list threshold
switch(config-track)# threshold weight
switch(config-track)# object 10 weight
switch(config-track)# object 20 weight
switch(config-track)# object 30
weight
up 30 down 10
15
15
In this example, the track list is up if object 10 and object 20 are up, and the track list goes to the down
state if all three objects are down.
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Configuring Object Tracking
Configuring Object Tracking
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Configuring an Object Tracking Delay
You can configure a delay for a tracked object or an object track list that delays when the object or list
triggers a stage change. The tracked object or track list starts the delay timer when a state change occurs
but does not recognize a state change until the delay timer expires. At that point, Cisco NX-OS checks
the object state again and records a state change only if the object or list currently has a changed state.
Object tracking ignores any intermediate state changes before the delay timer expires.
For example, for an interface line-protocol tracked object that is in the up state with a 20 second down
delay, the delay timer starts when the line protocol goes down. The object is not in the down state unless
the line protocol is down 20 seconds later.
You can configure independent up delay and down delay for a tracked object or track list. When you
delete the delay, object tracking deletes both the up and down delay.
You can change the delay at any point. If the object or list is already counting down the delay timer from
a triggered event, the new delay is computed as the following:
•
If the new configuration value is less than the old configuration value, the timer starts with the new
value.
•
If the new configuration value is more than the old configuration value, the timer is calculated as the
new configuration value minus the current timer countdown minus the old configuration value.
1.
configure terminal
2.
track object-id {parameters}
3.
track track-number list {parameters}
4.
delay {up up-time [down down-time] | down down-time [up up-time]}
5.
(Optional) show track
6.
(Optional) copy running-config startup-config
SUMMARY STEPS
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
track object-id {parameters}
Example:
switch(config)# track 2 ip route
192.0.2.0/8 reachability
switch(config-track)#
Step 3
track track-number list {parameters}
Example:
switch(config)# track 1 list threshold
weight
switch(config-track#
Creates a tracked object for a route and enters tracking
configuration mode. The object-id range is from 1 to
500. The prefix format for IP is A.B.C.D/length, where
the length range is from 1 to 32.
Configures a tracked list object and enters tracking
configuration mode. Specifies that the state of the
tracked list is based on a configured threshold weight.
The track-number range is from 1 to 500.
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Configuring Object Tracking
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Step 4
Command
Purpose
delay {up up-time [down down-time] |
down down-time [up up-time]}
Configures the object delay timers. The range is from
0 to 180 seconds.
Example:
switch(config-track)# delay up 20 down
30
Step 5
(Optional) Displays object tracking information.
show track
Example:
switch(config-track)# show track 3
Step 6
(Optional) Saves this configuration change.
copy running-config startup-config
Example:
switch(config-track)# copy
running-config startup-config
This example shows how to configure object tracking for a route and use delay timers:
switch# configure terminal
switch(config)# track 2 ip route 209.165.201.0/8 reachability
switch(config-track)# delay up 20 down 30
switch(config-track)# copy running-config startup-config
This example shows how to configure a track list with an up weight threshold of 30 and a down threshold
of 10 with delay timers:
switch# configure terminal
switch(config)# track 1 list threshold
switch(config-track)# threshold weight
switch(config-track)# object 10 weight
switch(config-track)# object 20 weight
switch(config-track)# object 30
switch(config-track)# delay up 20 down
weight
up 30 down 10
15
15
30
This example shows the delay timer in the show track command output before and after an interface is
shut down:
switch(config-track)# show track
Track 1
Interface loopback1 Line Protocol
Line Protocol is UP
1 changes, last change 00:00:13
Delay down 10 secs
switch(config-track)# interface loopback 1
switch(config-if)# shutdown
switch(config-if)# show track
Track 1
Interface loopback1 Line Protocol
Line Protocol is delayed DOWN (8 secs remaining)<------- delay timer counting down
1 changes, last change 00:00:22
Delay down 10 secs
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Configuring Object Tracking
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Configuring Object Tracking for a Nondefault VRF
You can configure Cisco NX-OS to track an object in a specific VRF.
SUMMARY STEPS
1.
configure terminal
2.
track object-id ip route prefix/length reachability
3.
vrf member vrf-name
4.
(Optional) show track [object-id]
5.
(Optional) copy running-config startup-config
DETAILED STEPS
Step 1
Command
Purpose
configure terminal
Enters configuration mode.
Example:
switch# configure terminal
switch(config)#
Step 2
track object-id ip route prefix/length
reachability
Example:
switch(config)# track 2 ip route
192.0.2.0/8 reachability
switch(config-track)#
Step 3
vrf member vrf-name
Example:
switch(config-track)# vrf member Red
Step 4
show track [object-id]
Creates a tracked object for a route and enters tracking
configuration mode. The object-id range is from 1 to
500. The prefix format for IP is A.B.C.D/length, where
the length range is from 1 to 32.
Configures the VRF to use for tracking the configured
object.
(Optional) Displays object tracking information.
Example:
switch(config-track)# show track 3
Step 5
copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-track)# copy
running-config startup-config
This example shows how to configure object tracking for a route and use VRF Red to look up
reachability information for this object:
switch# configure terminal
switch(config)# track 2 ip route 209.165.201.0/8 reachability
switch(config-track)# vrf member Red
switch(config-track)# copy running-config startup-config
This example shows how to modify tracked object 2 to use VRF Blue instead of VRF RED to look up
reachability information for this object:
switch# configure terminal
switch(config)# track 2
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Configuring Object Tracking
Verifying the Object Tracking Configuration
S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
switch(config-track)# vrf member Blue
switch(config-track)# copy running-config startup-config
Verifying the Object Tracking Configuration
To display the object tracking configuration information, perform one of the following tasks:
Command
Purpose
show track [object-id] [brief]
Displays the object tracking information for one
or more objects.
show track [object-id] interface [brief]
Displays the interface-based object tracking
information.
show track [object-id] ip route [brief]
Displays the IPv4 route-based object tracking
information.
Configuration Examples for Object Tracking
This example shows how to configure object tracking for route reachability and use VRF Red to look up
reachability information for this route:
switch# configure terminal
switch(config)# track 2 ip route 209.165.201.0/8 reachability
switch(config-track)# vrf member Red
switch(config-track)# copy running-config startup-config
Related Topics
See the following topics for information related to object tracking:
•
Chapter 11, “Configuring Layer 3 Virtualization”
•
Chapter 14, “Configuring HSRP”
Additional References
For additional information related to implementing object tracking, see the following sections:
•
Related Documents, page 16-14
•
Standards, page 16-14
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Feature History for Object Tracking
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Related Documents
Related Topic
Document Title
Object Tracking CLI commands
Cisco Nexus 3000 Series Command Reference,
Standards
Standards
Title
No new or modified standards are supported by this
—
feature, and support for existing standards has not been
modified by this feature.
Feature History for Object Tracking
Table 16-2 lists the release history for this feature.
Table 16-2
Feature History for Object Tracking
Feature Name
Releases
Feature Information
Object tracking
5.0(3)U1(1)
This feature was introduced.
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A P P E N D I X
A
IETF RFCs
This appendix lists the IETF RFCs supported in Cisco NX-OS Release 5.0(3)U1(1) and
NX-OS Release 5.0(3)U1(2).
BGP RFCs
RFCs
Title
RFC 1997
BGP Communities Attribute
RFC 2385
Protection of BGP Sessions via the TCP MD5 Signature Option
RFC 2439
BGP Route Flap Damping
RFC 2519
A Framework for Inter-Domain Route Aggregation
RFC 2858
Multiprotocol Extensions for BGP-4
RFC 3065
Autonomous System Confederations for BGP
RFC 3392
Capabilities Advertisement with BGP-4
RFC 4271
A Border Gateway Protocol 4 (BGP-4)
RFC 4273
Definitions of Managed Objects for BGP-4
RFC 4456
BGP Route Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)
RFC 4486
Subcodes for BGP Cease Notification Message
RFC 4893
BGP Support for Four-octet AS Number Space
RFC 5004
Avoid BGP Best Path Transitions from One External to Another
draft-ietf-idr-bgp4-mib-15.txt
BGP4-MIB
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Appendix A
IETF RFCs
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
First-Hop Redundancy Protocols RFCs
RFCs
Title
RFC 2281
Hot Standby Redundancy Protocol
RFC 3768
Virtual Router Redundancy Protocol
IP Services RFCs
RFCs
Title
RFC 786
UDP
RFC 791
IP
RFC 792
ICMP
RFC 793
TCP
RFC 826
ARP
RFC 1027
Proxy ARP
RFC 1591
DNS Client
RFC 1812
IPv4 routers
OSPF RFCs
RFCs
Title
RFC 2328
OSPF Version 2
RFC 3101
The OSPF Not-So-Stubby Area (NSSA) Option
RFC 2370
The OSPF Opaque LSA Option
RFC 3137
OSPF Stub Router Advertisement
RIP RFCs
RFCs
Title
RFC 2453
RIP Version 2
RFC 2082
RIP-2 MD5 Authentication
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GLOSSARY
A
ABR
See area border router.
address family
A specific type of network addressing supported by a routing protocol. Examples include IPv4 unicast
and IPv4 multicast.
adjacency
Two OSPF routers that have compatible configurations and have synchronized their link-state
databases.
administrative
distance
A rating of the trustworthiness of a routing information source. In general, the higher the value, the
lower the trust rating.
area
A logical division of routers and links within an OSPF domain that creates separate subdomains. LSA
flooding is contained within an area.
area border router
A router that connects one OSPF area to another OSPF area.
ARP
Address resolution protocol. ARP discovers the MAC address for a known IPv4 address.
AS
See autonomous system.
ASBR
See autonomous system border router.
attributes
Properties of a route that are sent in BGP UPDATE messages. These attributes include the path to the
advertised destination as well as configurable options that modify the best path selection process.
autonomous
system
A network controlled by a single technical administration entity.
autonomous
system border
router
A router that connect a an OSPF autonomous system to an external autonomous system.
AVF
Active virtual forwarder. A gateway within a GLBP group elected to forward traffic for a specified
virtual MAC address.
AVG
Active virtual gateway. One virtual gateway within a GLBP group is elected as the active virtual
gateway and is responsible for the operation of the protocol.
v
B
backup designated
router
See BDR.
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Glossary
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
bandwidth
The available traffic capacity of a link.
BDR
Backup designated router. An elected router in a multi-access OSPF network that acts as the backup if
the designated router fails. All neighbors form adjacencies with the backup designated router (BDR)
as well as the designated router.
BGP
Border Gateway Protocol. BGP is an interdomain or exterior gateway protocol.
BGP peer
A remote BGP speaker that is an established neighbor of the local BGP speaker.
BGP speaker
BGP-enabled router.
C
communication cost Measure of the operating cost to route over a link.
converged
The point at which all routers in a network have identical routing information.
convergence
See converged.
D
dead interval
The time within which an OSPF router must receive a Hello packet from an OSPF neighbor. The dead
interval is usually a multiple of the hello interval. If no Hello packet is received, the neighbor adjacency
is removed.
default gateway
A router to which all unroutable packets are sent. Also called the router of last resort.
delay
The length of time required to move a packet from the source to the destination through the
internetwork.
designated router
See DR.
DHCP
Dynamic Host Control Protocol.
Diffusing Update
Algorithm
See DUAL.
distance vector
Defines routes by distance (for example, the number of hops to the destination) and direction (for
example, the next-hop router) and then broadcasts to the directly connected neighbor routers.
DNS client
Domain Name System client. Communicates with DNS server to translate a host name to an IP address.
DR
Designated router. An elected router in a multi-access OSPF network that sends LSAs on behalf of all
its adjacent neighbors. All neighbors establish adjacency with only the designated router and the
backup designated router.
DUAL
Diffusing Update Algorithm. EIGRP algorithm used to select optimal routes to a destination.
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S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
E
eBGP
External Border Gateway Protocol (BGP). Operates between external systems.
EIGRP
Enhanced Interior Gateway Protocol. A Cisco routing protocol that uses the Diffusing Update
Algorithm to provide fast convergence and minimized bandwidth utilization.
F
feasible distance
The lowest calculated distance to a network destination in EIGRP. The feasibility distance is the sum
of the advertised distance from a neighbor plus the cost of the link to that neighbor.
feasible successor
Neighbors in EIGRP that advertise a shorter distance to the destination than the current feasibility
distance.
FIB
Fowarding Information Base. The forwarding table on each module that is used to make the Layer 3
forwarding decisions per packet.
G
gateway
A switch or router that forwards Layer 3 traffic from a LAN to the rest of the network.
h
H
hello interval
The configurable time between each Hello packet sent by an OSPF or EIGRP router.
hello packet
A special message used by OSPF or IS-IS to discover neighbors. Also acts as a keep alive messages
between established neighbors.
hold time
In BGP - Maximum time limit allowed in BGP between UPDATE or KEEPALIVE messages. If this
time is exceeded, the TCP connection between the BGP peers is closed.
In EIGRP, the maximum time allowed between EIGRP Hello messages. If this time is exceeded, the
neighbor is declared unreachable.
hop count
The number of routers that can be traversed in a route. Used by RIP.
I
iBGP
Internal Border Gateway Protocol (BGP). Operates within an autonomous system.
ICMP
IETF RFCs
Internet Engineering Task Force Request for Comments.
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Glossary
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
IGP
Interior gateway protocol. Used between routers within the same autonomous system.
instance
An independent, configurable entity, typically a protocol.
IP tunnels
Internet Protocol version 4.
IPv4
K
A special message sent between routing peers to verify and maintain communications between the pair.
keepalive
L
link cost
An arbitrary number configured on an OSPF interface which is in shortest path first calculations.
link-state
Shares information about a link, link cost to neighboring routers.
link-state
advertisement
See LSA.
LSA
Link-state advertisement. An OSPF message to share information on the operational state of a link, link
cost, and other OSPF neighbor information.
link-state database
OSPF database of all LSAs received. OSPF uses this database to calculate the best path to each
destination in the network.
link-state refresh
The time that OSPF floods the network with LSAs to ensure all OSPF routers have the same
information.
load
The degree to which a network resource, such as a router, is busy.
load balancing
The distribution of network traffic across multiple paths to a given destination.
M
message digest
A one-way hash applied to a message using a shared password and appended to the message to
authenticate the message and ensure the message has not been altered in transit.
metric
A standard of measurement, such as the path bandwidth, that is used by routing algorithms to determine
the optimal path to a destination.
MD5 authentication A cryptographic construction that is calculated based on an authentication key and the original message
digest
and sent along with the message to the destination. Allows the destination to determine the authenticity
of the sender and guarantees that the message has not been tampered with during transmission.
MTU
Maximum transmission unit. The largest packet size that a network link will transmit without
fragmentation.
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N
network layer
reachability
information
BGP network layer reachability information (NRLI). Contains the a list of network IP addresses and
network masks for networks that are reachable from the advertising BGP peer.
next hop
The next router that a packet is sent to on its way to the destination address.
NSSA
Not-So-Stubby-Area. Limits AS external LSAs in an OSPF area.
O
OSPF
Open Shortest Path First. An IETF link-state protocol. OSPFv2 supports IPv4.
P
path length
Sum of all link costs or the hop count that a packet experiences when routed from the source to the
destination.
R
redistribution
One routing protocol accepts route information from another routing protocol and advertises it in the
local autonomous system.
Reliable Transport
Protocol
Responsible for guaranteed, ordered delivery of EIGRP packets to all neighbors.
reliability
The dependability (usually described in terms of the bit-error rate) of each network link.
RIB
Routing Information Base. Maintains the routing table with directly connected routes, static routes, and
routes learned from dynamic unicast routing protocols.
routing information See RIB.
base
route map
A construct used to map a route or packet based on match criteria and optionally alter the route or
packet based on set criteria. Used in route redistribution.
route
summarization
A process that replaces a series of related, specific routes in a route table with a more generic route.
router ID
A unique identifier used by routing protocols. If not manually configured, the routing protocol selects
the highest IP address configured on the system.
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Glossary
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
S
SPF algorithm
Shortest Path First algorithm. Dijkstra’s algorithm used by OSPF to determine the shortest route
through a network to a particular destination.
split horizon
Routes learned from an interface are not advertised back along the interface they were learned on,
preventing the router from seeing its own route updates.
split horizon with
poison reverse
Routes learned from an interface are set as unreachable and advertised back along the interface they
were learned on, preventing the router from seeing its own route updates.
static route
A manually configured route.
stub area
An OSPF area that does not allow AS External (type 5) LSAs.
stub router
A router that has no direct connection to the main network and which routes to that network using a
known remote router.
SVI
Switched Virtual Interface.
U
UFIB
Unicast IPv4 forwarding information base.
URIB
Unicast IPv4 routing information base. The unicast routing table that gathers information from all
routing protocols and updates the forwarding information base for each module.
V
virtualization
A method of making a physical entity act as multiple, independent logical entities.
VRF
Virtual Routing and Forwarding. A method used to create separate, independent Layer 3 entities within
a system.
VRRP
Virtual Router Redundancy Protocol.
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INDEX
description
A
ABR
3-4
B
address formats
IPv4
2-2
bandwidth
address resolution protocol. See ARP
BDR
administrative distance
BFD
description
1-7
static routing
1-4
3-3
BGP
10-2
6-8
configuring for BGP
ARP
7-13
configuring on an interface
caching
2-3
2-12
configuring Local Proxy ARP
configuring Proxy ARP
2-2
2-5
Local Proxy ARP
2-5
process (figure)
2-3
2-5
Reverse ARP
description
echo function
2-9
AS. See autonomous system
3-5
7-6
7-3
7-14
optimizing subinterfaces
session parameters
verifying
2-4
7-6
7-2
enable the feature
monitoring
7-11
7-2
7-14
virtualization support
BGP
7-6
7-1 to 7-3
disable the feature
licensing
gratuitous ARP
Proxy ARP
2-11
2-10
configuring static ARP entries
description
7-8, 7-9
configuring session parameters
configuring gratuitous ARP
ASBR
1-5
7-3
5-7
administrative distances (table)
AS confederations
BFD
6-8
configuring
6-25
clearing neighbors
description
6-4
conditional advertisement
AS numbers
5-2
5-18
6-7
conditional advertisement example
4-byte support.
ranges (table)
1-5
1-5
AS-path lists
configuration modes
6-31
5-8
configuring conditional advertisement
configuring dynamic capability
6-28
configuring
13-8
configuring maximum prefixes
6-28
description
13-4
configuring prefix peering
autonomous system
6-29
6-19
configuring route dampening
6-27
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Index
Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
default settings
description
5-10, 6-10
BGP community lists
5-1 to 5-7, 6-1 to 6-9
configuring
13-9, 13-11
description
13-4
disable the feature
5-11
displaying statistics
eBGP
description
6-3
enable the feature
5-23
feature history (table)
5-24, 13-18
generic specific extended community lists
guidelines
limitations
5-7, 6-9
deleting
5-13
restarting
5-13
BGP peers
6-35
modifying next-hop address
6-21
6-9
next-hop address tracking
path selection
router ID
6-7
5-14, 5-16
description
5-3
6-2
6-7
BGP route dampening
5-4
6-6
BGP route redistribution
5-1
6-34
5-7
verifying configuration
virtualization support
5-21, 6-39
5-7, 6-9
BGP aggregate addresses
configuring
configuring
description
5-7, 6-10
unicast RIB
authentication (note)
BGP route aggregation
5-4
prerequisites
6-6
BGP multipath. See BGP loadsharing
4-29, 5-24
MP-BGP
6-28
BGP loadsharing
description
5-8, 6-10
modifying AS-paths
tuning
5-12
configuring
6-3
speakers
13-4
creating
BGP load balancing
5-8, 6-10
licensing requirements
MIBs
13-4
BGP instance
5-11
example configuration
iBGP
BGP extended community lists
5-23, 6-40
6-29
BGP AS-path lists
configuring
6-31
description
6-8
BGP sessions
reset options
resetting
6-3
6-20
route policies
6-3
BGP templates
configuring
13-8
configuring peer-policy templates
description
13-4
configuring peer templates
BGP authentication
6-20
description
description
6-2
peer-policy templates
BGP autonomous systems
description
5-2
BGP capabilities negotiation
description
disabling
6-16
configuring session templates
configuring
6-12
6-2
peer-session templates
peer template
6-14
6-2
6-2
6-2
Border Gateway Protocol. See BGP
6-5
6-22
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S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
C
communication cost
1-4
community lists
disabling fast external failover
6-23
disabling single-hop checking
6-22
limiting the AS-path attribute
6-24
eBGP AS confederations. See AS confederations
configuring
13-9, 13-11
ECMP. See equal cost multipath
description
13-4
ECMP for host routes
comparing
default settings
link-state and distance vector routing algorithms
1-9
8-2
example configuration
8-4
feature history (table)
information about
D
default gateway
description
HSRP
14-6
IP
creating an instance
default settings
Route Policy Manager
static routing
delay
configuring stub routing
16-3
description
10-3
displaying statistics
DUAL algorithm
distribution
ECMP
9-3
4-13
4-10
4-27
4-6
4-9
example configuration
E
configuring
configuring AS confederations
configuring multihop
description
4-4
feature history (table)
4-29
hold time
6-22
6-3
6-23
6-25
4-28
external route metrics
guidelines
eBGP
4-23
4-3
enabling the feature
3-3
4-16
4-1 to ??
disabling the feature
1-9
4-17
4-12
disabling split horizon
15-6
distance vector routing algorithms
DR
4-21
4-8
disabling an instance
11-6
1-4
RIP
4-22
4-10
deleting an instance
13-5
4-17
4-14
configuring route redistribution
9-4
VRRP
4-5
configuring load balancing
3-12
VRF
8-4
configuring hello interval
object tracking
RIP
verifying configuration
configuring authentication
8-2
2-7
OSPF
8-1
configuring a summary address
ECMP for host routes
4-8
licensing requirements
authentication
5-10, 6-10
EIGRP
8-1
EIGRP
1-8
default settings
BGP
8-5
4-7
4-2
internal route metrics
licensing requirements
limitations
4-3
4-7
4-7
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Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
limit redistributed routes
load balancing
prerequisites
4-2
4-7
restarting an instance
4-6
route summarization
glean throttling
4-6
enabling
4-3
split horizon
4-13
2-14
maximum number
4-6
timeout
4-5
4-4
verifying configuration
virtualization support
2-15
2-16
configuring
2-12
description
2-5
4-27
4-7
H
eigrp
passive interface
equal cost multipath
4-13
Hot Standby Router Protocol. See HSRP
1-6
HSRP
extended community lists
description
addressing
13-4
external BGP. See eBGP
14-3
configuring a group
14-8
configuring priority
14-14
customizing
14-14
default settings
F
description
FIB
clearing routes
description
12-8
1-11, 12-1
displaying
licensing requirements
12-3
12-10
disabling the feature
14-7
enabling the feature
14-7
guidelines
12-2
1-11
licensing requirements
Fibre Channel interfaces
default settings
14-4
14-6
standby router
forwarding
14-2
verifying configuration
adjacency manager
architecture
1-11
1-10, 12-1
14-6
14-4
prerequisites
7-4
14-17
14-6
load sharing
messages
14-16
14-6
limitations
virtualization support
VRFs
14-2 to 14-5
feature history (table)
12-10
verifying
14-6
example configuration
12-3
feature history (table)
FIB
2-17
gratuitous ARP
4-23
unicast RIB
2-5
generating a syslog
shutting down on an interface
tuning
G
4-12
route redistribution
route updates
1-11
forwarding information base. See FIB
4-6
neighbor discovery
stub routers
unicast forwarding distribution module
4-19
virtualization support
14-16
14-5
HSRP authentication
1-11
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S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
configuring
14-10
limitations
description
14-4
prerequisites
HSRP object tracking
2-6
2-6
secondary addresses (note)
configuring
14-12
subnet masks
description
14-5
verifying configuration
HSRP versions
2-1
virtualization support
configuring
14-8
description
14-4
14-10
description
14-2
Layer 3 consistency checker
triggering
I
12-2
12-7
licensing requirements
iBGP
BGP
configuring route reflector
6-9
EIGRP
6-3
FIB
ICMP
HSRP
IP
2-6
with local proxy ARP (note)
12-3
14-6
2-6
OSPF
RIP
8-1
interfaces
3-11
9-4
static routing
7-4
internal BGP. See iBGP
uRIB
12-3
Internet Control Message Protocol. See ICMP
VRF
11-5
IP
VRRP
3-1
2-1 to 2-6, ?? to 12-2
feature history (table)
2-9
1-9
1-4
load balancing
1-6
Local Proxy ARP
2-7
example configuration
load
2-7
configuring secondary addresses
guidelines
15-6
link-state routing algorithms
configuring addresses
default settings
13-5
10-3
link-state advertisements
2-2
ARP. See ARP
description
16-3
Route Policy Manager
default settings
addresses
8-1
4-7
object tracking
2-6
information about
ECMP for host routes
5-7
ECMP for host routes
6-25
iBGP route reflector. See route reflector
description
2-6
L
description
description
2-18
IPv4. See IP
HSRP virtual MAC address
configuring
2-2
2-18
configuring
2-11
description
2-5
2-19
2-6
ICMP. See ICMP
licensing requirements
2-6
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Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
track list
M
16-2
verifying configuration
MAC lists
16-13
virtualization support
description
13-2
Open Shortest Path First. See OSPF
management interfaces
default settings
OSPF
7-4
adjacency
mgmt0 interfaces
3-1, 3-3
area border router
default settings
7-4
areas
MIBs
4-29, 5-24
OSPF
authentication
3-43, 14-17
MP-BGP
3-4
3-1, 3-4
AS border router
BGP
16-2
3-5
3-7
backup designated router
6-9
configuring area authentication
configuring
6-33
configuring authentication
see MP-BGP
configuring ECMP
N
3-18
new and changed features (table)
3-16
3-23
configuring load balancing
ii-xix
3-16
configuring MD5 authentication
1-2
configuring networks
3-9
configuring NSSA
3-26
3-20
3-18
configuring filter lists
configuring
3-25
configuring authentication on an interface
configuring DR priority
NSSA
3-19
configuring a totally stubby area
Multiprotocol BGP
next hop
3-3
3-20
3-16
3-26
configuring on an interface
3-16
configuring optional parameters on an interface
O
configuring redistribution
configuring a delay
configuring a track list with percentage
configuring for a nonDefault VRF
configuring for route reachability
configuring on an interface
default settings
feature history (table)
guidelines
limitations
16-13
16-14
16-3
configuring the hello interval
configuring virtual links
creating an instance
16-3
3-35
3-18
3-28
3-14
3-2
3-12
delete an instance
description
3-20
3-24
configuring stub route advertisements
3-15
3-1 to ??
designated router
16-3
licensing requirements
16-5
configuring stub areas
default settings
16-1
example configuration
16-4
16-12
16-7, 16-8
16-6
dead interval
16-3
3-34
configuring simple password authentication
16-10
configuring a track list with boolean expression
description
3-30
configuring route summarization
object tracking
3-18
disable the feature
displaying statistics
3-3
3-14
3-42
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S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
enable the feature
virtual link (figure)
3-13
example configuration
feature history (table)
guidelines
3-42
P
3-2
hello packet
3-2
path length
licensing requirements
limitations
link cost
3-11
3-6
3-7
LSA pacing
LSAs
3-6
description
13-2
configuring
2-10
description
2-5
3-5 to 3-7
R
3-6
3-43, 14-17
redistiribution
modifying default timers
multiple instances
neighbors
3-36
3-11
description
redistribution
3-2
BGP
not-so-stubby area
NSSA
13-6
3-6
LSA types (table)
MIBs
configuring
Proxy ARP
3-1
LSA flooding
1-4
prefix lists
3-12
link-state database
LSA
OSPFv2. See OSPF
3-43
3-12
hello interval
3-10
3-9
1-6
1-5
6-8
configuring for OSPF
3-9
configuring in BGP
3-30
6-31
opaque LSAs
3-7
configuring in RIP
prerequisites
3-12
configuring on EIGRP
redistributed routes
3-32
restarting an instance
EIGRP
3-39
3-10
with route maps
reliability
3-10
stub area
3-18
3-11
3-8
3-9
unicast RIB
limitations
2-4
2-4
1-11, 12-2
see uRIB
3-7
virtualization support
virtual link
2-4
description
3-11
verifying configuration
13-5
RIB
stub router advertisements
description
3-32
1-4
description
RFC
stub area (figure)
4-19
Reverse ARP
shutting down an instance
SPF optimization
4-6
maximum limit for OSPF
route summarization
description
4-17
maximum limit for EIGRP
route redistribution
description
9-12
RIP
3-41
3-11
clearing statistics
9-17
configuring a passive interface
9-11
3-9
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Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
configuring on an interface
default settings
description
configuring match parameters
9-8
configuring set parameters
9-4
description
9-2
disable the feature
displaying statistics
9-17
match criteria
13-3
enabling the feature
9-5
redistribution
13-5
example configuration
feature history (table)
guidelines
delay
load
9-4
route filtering
1-4
reliability
9-16
verifying configuration
1-4
1-4
path length
9-3
virtualization support
1-4
communication cost
9-4
9-4
prerequisites
13-3
bandwidth
9-4
limitations
13-17
route metric
9-19
licensing requirements
tuning
set changes
9-18
1-4
1-4
Route Policy Manager
9-17
default settings
9-4
RIP authentication
13-5
example configuration
configuring
9-9
guidelines
description
9-2
licensing requirements
RIP instance
9-6
deleting
9-7
13-5
description
13-1 to ??
verifying configuration
9-7
RIP load balancing
configuring
6-25
configuring
9-7
description
6-5
description
9-3
router ID
description
RIP route distribution
configuring
9-12
3-34
configuring on EIGRP
configuring
9-11
EIGRP
description
9-3
RIP
RIP split horizon
4-17
4-6
9-3
route table
configuring with poison reverse
9-2
9-11
description
1-2
routing algorithms
distance vector
route maps
configuring
12-9
route summarization
RIP route summarization
description
1-5
routes, estimating memory requirements
9-3
RIP route redistribution
configuring
13-17
route reflector
9-8
description
13-5
route policy manager
optional parameters
restarting
13-17
13-5
limitations
creating
13-14
13-2
example configuration
9-6
13-13
13-12
link-state
1-9
1-9
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S e n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
Routing Information Protocol. See RIP
U
routing metrics
description
uRIB
1-2
clearing routes
routing protocols
administrative distance
description
1-7
12-9
12-1
comparing link-state algorithms to distance vector
algorithms 1-9
displaying
displaying (example)
12-7
convergence. convergence
feature history (table)
12-10
description
1-1 to 1-8
distance vector
link-state
next hop
1-6
12-6
Layer 3 consistency checker
1-9
licensing requirements
1-9
verifying
1-2
1-5, 1-6
virtualization
1-10
12-3
12-10
virtualization support
redistribution
12-2
12-2
V
virtualization
S
description
static routes
Virtual Router Redundancy Protocol. See VRRP
description
1-8
VRF
virtualization support
with ARP
10-3
2-3
static routing
configuring
default settings
11-9
limitations
10-7
1-7
11-13
11-5
licensing requirements
10-6
11-5
11-5
setting the routing context
setting the scope
10-3
11-12
11-12
verifying configuration
11-13
vrf
10-3
stub routing
11-6
11-7
guidelines
10-3
verifying configuration
11-6
example configuration
10-3
licensing requirements
prerequisites
configuring routing parameters
deleting
10-5
10-1
feature history (table)
limitations
11-8
default settings
10-3
example configuration
guidelines
10-2
10-4
configuring with VRFs
description
assigning an interface to a VRF
creating
administrative distance
description
1-10
feature history (table)
10-6
11-14
VRF-aware services
configuring
11-11
description
11-3
VRF filtering
description
11-4
example configuration
11-12
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Se n d d o c u m e n t c o m m e n t s t o n ex u s 3 k - d o c f e e d b a ck @ c i s c o . c o m .
VRF-Lite
description
11-2
guidelines
11-5
limitations
11-5
VRF reachability
description
11-3
example configuration
11-12
VRRP
benefits
15-3
configuring time intervals for advertisement
packets 15-12
default settings
description
15-6
15-1 to 15-5
disabling the feature
15-7
displaying statistics
15-17
enabling the feature
15-7
example configuration
feature history (table)
guidelines
15-19
15-6
licensing requirements
limitations
15-18
15-6
15-6
verifying configuration
virtualization support
15-17
15-5
VRRP advertisements
description
15-5
VRRP authentication
configuring
15-11
description
15-5
VRRP groups
configuring
15-8
description
15-3
VRRP priority
configuring
15-9
description
15-4
disabling preemption
preemption
15-14
15-4
VRRP tracking
configuring
15-15
description
15-5
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