Software Reference, OSPF

1
OSPF
August 2000
Software Reference
OSPF
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OSPF
Software Reference
Table of Contents
Table of Contents
OSPF
A
REFERENCE
5
1
Open Shortest Path First (OSPF)
6
1.1
Setup Tool Menus
6
1.1.1
OSPF
6
1.1.2
Static Settings
7
1.1.3
Interfaces
8
1.1.4
Areas
13
1.1.5
Monitoring and Debugging
14
1.2
Overview of the OSPF Protocol
18
1.2.1
Shortest Path Routing
19
1.2.2
OSPF Routers and Link State Advertisement
21
1.2.3
OSPF Virtual Links
22
1.2.4
Router Types
22
1.2.5
Link State Advertisement Types
23
1.2.6
Router Identification
25
1.2.7
Initialization
25
1.2.8
Neighbor Identification
26
1.2.9
Designated / Backup Designated Router Election
26
1.2.10
Building up the LSD and the SPT
27
1.2.11
Authentication
28
1.2.12
OSPF over Demand Circuits
28
1.3
Example OSPF Installation
29
1.3.1
Configuration Overview
31
1.3.2
Configuration Steps for BRICK-XL2
32
1.3.3
Configuration Steps for BRICK-XM
34
Software Reference
OSPF
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Table of Contents
4
1.3.4
Configuration Steps for BRICK-XS
36
1.3.5
Configuring OSPF Virtual Links
38
1.4
Controlling Link State Database Overflow
38
1.5
Enabling Demand Circuit Support
40
1.6
Import / Export of Routing Information
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OSPF
Software Reference
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Software Reference
REFERENCE
OSPF
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Open Shortest Path First (OSPF)
1
Open Shortest Path First (OSPF)
In this chapter we will describe the Setup Tool menus and settings you will see
while using Setup Tool to configure the Open Shortest Path First (OSPF) protocol on your router.
After that, we have included an overview of the OSPF protocol as well as an
example OSPF installation using different BinTec routers.
1.1
Setup Tool Menus
After entering setup from the shell prompt, Setup Tool’s Main Menu is displayed as below. Depending on your hardware setup and software configuration your router’s menu may differ slightly.
OSPF
BinTec router Setup Tool
BinTec Communications AG
MyRouter
Licences
System
Slot1:
Slot2:
CM-BNC/TP, Ethernet
CM-2XBRI, ISDN S0, Unit 0
CM-2XBRI, ISDN S0, Unit 1
Slot3:
CM-1BRI, ISDN S0
WAN Partner
IP
IPX
PPP
X.25
VPN
Configuration Management
Monitoring and Debugging
Exit
Press <Ctrl-n>, <Ctrl-p> to scroll through menu items, <Return> to
enter
1.1.1
OSPF
The starting point for all OSPF settings:
➤ Go to IP ➧ OSPF.
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Setup Tool Menus
OSPF on the router can be configured from Setup Tool using the three menus
available here:
BinTec router Setup Tool
[IP] [OSPF]: OSPF Configuration
BinTec Communications AG
MyRouter
Static Settings
Interfaces
Areas
Exit
Press <Ctrl-n>, <Ctrl-p> to scroll through menu items, <Return> to
enter
Field
Meaning
Static Settings
Contains global OSPF parameters. This is
where OSPF is enabled on the router.
Interfaces
Lists all OSPF capable router interfaces and is
used for configuring interface-specific settings.
Areas
Lists all known OSPF areas and is used for
adding/configuring area-specific settings.
Table A-1: OSPF CONFIGURATION
1.1.2
Static Settings
To obtain the global settings for the OSPF protocol:
➤ Go to STATIC SETTINGS.
Software Reference
OSPF
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Open Shortest Path First (OSPF)
BinTec router Setup Tool
[IP][OSPF][STATIC]: OSPF Static Settings
BinTec Communications AG
MyRouter
OSPF
Generate Default Route for the AS
disabled
no
SAVE
CANCEL
Use <Space> to select
Field
Meaning
OSPF
Is used to enable or disable OSPF. A valid
license is also required before OSPF can be
used on the router.
Generate Default Route
for the AS
When set to yes the router advertises a default
route over all active OSPF interfaces (see the
Admin Status field in the IP ➧ OSPF ➧
INTERFACES menu).
Table A-2: OSPF STATIC SETTINGS
Special consideration should be given to deciding which router is to provide a
default route. This router should have the appropriate routes so that it can
properly handle traffic for the AS.
1.1.3
Interfaces
To obtain a list of the router interfaces OSPF can be configured for:
➤ Go to INTERFACES.
By default, all IP compatible interfaces (present at the time OSPF was enabled)
are added to this list and are placed in the passive state.
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Setup Tool Menus
To configure an interface:
➤ Scroll to the appropriate entry and press Enter.
The fields shown in the resulting EDIT menu shown below can be configured separately for each interface.
Interface Configuration via Setup Tool
BinTec router Setup Tool
BinTec Communications AG
[IP][OSPF][INTERFACE][EDIT]: Configure Interface en1
MyRouter
Admin Status
Area ID
passive (propagate routes)
0.0.0.0
Metric Determination
Metric (direct routes)
auto (ifSpeed)
10
Authentication Type
Authentication Key
none
Export indirect static routes
no
SAVE
CANCEL
Use <Space> to select
Once an interface is placed in the active state (and saved to memory), OSPF
connections may be established over the interface resulting in appropriate
costs for dial-up interfaces.
For dialup interfaces the Base Metric Value changes dynamically as ISDN
channels are added/removed while the link is up. For leased line interfaces the
base metric is equivalent to the result of the same function less 20 (i.e., 1542
for one leased B-Channel, 781 for two B-channels).
Software Reference
OSPF
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Open Shortest Path First (OSPF)
Field
Meaning
Admin Status
The status of an OSPF interface defines
whether routes and/or OSPF protocol packets
are propagated over the interface.
If OSPF has not been enabled yet, only the
Admin Status field is displayed (in which case
changes are irrelevant).
OSPF routers propagate a Router Link (RL),
one per Area, which identifies the router’s interfaces in that Area. Both active and passive interfaces are identified in the RL. Status may be active, passive, or off with the following results:
■ Active: OSPF is running over this interface
■ Passive: OSPF is not running over this interface
OSPF protocol packets are neither sent nor
received over the interface, however this interface may be included in other Router
Links.
■ Off: OSPF is not running over this interface
this interface is not included in Router
Links.
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OSPF
Area ID
Identifies the Area this interface is assigned to.
Metric Determination
Determines how the metric for this interface is
calculated. This is the cost of the link that is
propagated via link state advertisements see
table A-4, page 12.
Software Reference
A
Setup Tool Menus
Field
Meaning
Metric
Identifies the base metric value, or cost of this
interface. For auto determination values (see
table A-4, page 12) the actual metric used is
adjusted starting a base metric value which is a
simple function of the bandwidth of the physical
medium (except leased line interfaces) use the
function
1000, 000, 000
Base Metric Value = ------------------------------------------------bandwidth in bps
This results in 10 for ethernet, 6 for token ring,
and 1562 for dialup ISDN interfaces (1 B-Channel).
For fixed determination values (see previous
field) the base metric value can be configured
here.
Authentication Type
The type of authentication to use when sending
(or verifying incoming) OSPF packets via this
OSPF interface. This determines how the key
in the Authentication Key field is used.
By default this is set to none. With simple, Key
is transmitted as a text string in each packet.
With md5, Key is used to create (verify) an
encrypted digest which is sent with each
packet.
Authentication Key
Software Reference
A text string to use in connection with the
Authentication Type set above.
OSPF
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Open Shortest Path First (OSPF)
Field
Meaning
Import indirect static
routes
If set to no (default) only direct routes for this
interface are propagated over active OSPF
interfaces (see the Admin Status field). When
set to yes, indirect static routes are also propagated over active interfaces and are contained
in external advertisements.
Table A-3: CONFIGURE INTERFACE EN1
Although practical for sites using WAN interfaces without transfer networks,
caution should be given to avoiding routing loops when importing indirect static
routes.
Determination
Meaning
auto
The metric = the value of the base metric which
is based on the bandwidth (ifSpeed) of the
interface.
fixed
The metric defined (configurable) in the following field is always used (no adjustment).
auto + adjust
When the dial-up interface is in the up state, the
metric = <base metric value> – 10.
Otherwise
metric = <base metric value>.
(Only valid for Dial-up
interfaces)
fixed + adjust
When the dial-up interface is in the up state the
metric = <base metric value> – 10.
Otherwise
metric = <base metric value>.
Table A-4: Metric Determination
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Setup Tool Menus
1.1.4
Areas
To obtain a list of the OSPF Areas known to the router:
➤ Go to AREAS.
Before a router interface can be assigned to an Area, the Area ID must first
be added here.
The exception is the backbone area which is automatically generated at boot
time if no other area is configured and which all interface assignments default
to if not explicitly assigned.
➤ To edit area-specific settings select the Area ID and press Enter.
BinTec router Setup Tool
[IP][OSPF][AREA][ADD]: Area Configuration
BinTec Communications AG
MyRouter
Area ID
0.0.0.0
Import external routes
no
Area Ranges>
SAVE
CANCEL
Enter IP address (a.b.c.d or resolvable hostname)
Field
Meaning
Area ID
Identifies the OSPF Area this entry corresponds to. The backbone area is 0.0.0.0.
Import external routes
Specifies whether external routes should be
imported for this area. When set to no, this
Area is defined as an OSPF Stub Area.
Area Ranges
This submenu specifies IP Address ranges for
route condensation among areas.
Table A-5: AREA CONFIGURATION
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Open Shortest Path First (OSPF)
1.1.5
Monitoring and Debugging
This menu consists of several submenus which allow you to monitor the router’s
operational status (and debug problems) in different ways:
➤ Go to MONITORING AND DEBUGGING.
BinTec router Setup Tool
[MONITOR]: Monitoring and Debugging
BinTec Communications AG
MyRouter
ISDN Monitor
X.25 Monitor
Interfaces
Messages
TCP/IP
OSPF
EXIT
Field
Meaning
ISDN Monitor
lets you track incoming and outgoing ISDN
calls
X.25 Monitor
lets you track incoming and outgoing X.25 calls
Interfaces
lets you monitor traffic by interface
Messages
displays system messages generated by the
router´s system logging and accounting mechanisms.
TCP/IP
menu lets you monitor IP traffic by protocol
OSPF
menu lets you monitor OSPF related information
Table A-6: MONITORING AND DEBUGGING
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Setup Tool Menus
➤ Go to OSPF.
The OSPF monitor is divided horizontally in three sections and displays information relating to OSPF Interfaces, Neighbors, and Areas.
BinTec router Setup Tool
[MONITOR][OSPF]: OSPF Monitor
BinTec Communications AG
MyRouter
Interface
en1
brickxs
DR
192.168.30.1
0.0.0.0
BDR
Admin Status
192.168.30.0 active
0.0.0.0
active
State
BDR
PTP
Neighbor
Router ID
Interface
Retx Queue
State
192.168.30.1
12.0.0.2
10.0.1.1
11.0.0.2
en1
brickxs
0
0
full
full
Area
0.0.0.0
0.0.0.0
11.0.0.0
11.0.0.0
EXIT
Type
Link State ID
Summary Net 10.0.0.0
Network Link 192.168.30.1
Router Link 11.0.0.2
Summary Net 0.0.0.0
Router ID
Sequence
10.0.1.1
0x800000003
10.0.1.1
0x800000001
11.0.0.2
0x800000009
192.168.40.3 0x800000001
Age
1641=
361 I
1
I
2
V
Press <Ctrl-n>, <Ctrl-p> to scroll
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Interfaces Section
The Interfaces section lists all enabled OSPF interfaces (interfaces that have
NOT been turned “off” in the IP ➧ OSPF ➧ INTERFACES menu)
Field
Meaning
Interface
The router interface the entry corresponds to.
Designed Router (DR)
The Designated Router’s IP address on this
interface (a DR is not shown for Point-To-Point
interfaces).
Backup Designed
Router (BDR)
The Backup Designated Router’s IP address
on this interface (a BDR is not shown for PointTo-Point interface).
Admin Status
Only active and passive interfaces are shown
here (see the IP ➧ OSPF ➧ INTERFACES
menu in "Interface Configuration via Setup
Tool", page 9).
State
The OSPF status (ospfIfState) of the interface
shown here may be
■ down: OSPF is not running on this interface.
■ wait: The initial phase of OSPF where DR
and BDR are determined.
■ PTP: The interface is a Point-To-Point interface. No DR or BDR is shown.
■ DR: The router is the Designated Router for
this interface.
■ BDR: The router is the Backup Designated
Router for this interface.
■ DRouter: Another router is the DR/BDR for
this interface.
Table A-7: OSPF MONITOR
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Setup Tool Menus
Neighbor Section
The Neighbor section lists the OSPF neighbor routers that have been identified
via the HELLO protocol.
Field
Meaning
Neighbor
The neighbor router’s address on this interface.
Router ID
The neighbor router’s system wide Router ID.
Interface
The router interface this router was identified
over.
Retx Queue
The size of the retransmission queue for this
neighbor. This is the number of advertisements
that need to be sent to (and acknowledged
from) this neighbor.
State
The state of OSPF with this neighbor router may
be
■ init: The initial phase. A HELLO packet was
received from this neighbor.
■ twoWay: Bidirectional communication with
the neighbor. Transmitted HELLO packets
have been accepted by the neighbor router
(parameters are correct).
■ EXstart: The exchange of Database Description Packets between the router and
neighbor has begun.
■ exchange: Actively exchanging Database
Description Packets with the neighbor router.
■ loading: The router and the neighbor router
are now exchanging Link State Advertisements.
■ full: The router and neighbor routers’ Link
State Database are now synchronized.
Table A-8: NEIGHBOR SECTION
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LSDB Section
The Link State Database section lists the headers for all Link State Advertisements (LSA).
Field
Meaning
Area
The Area database to which this LSA belongs
Type
The type of LSA. Five types of LSAs exist:
Router Link, Network Link, Summary Link,
Summary ASBR, and AS External
Link State ID
The LSA’s Link State ID. The Link State ID’s
meaning depends on the Type of advertisement
Router ID
Identifies the router that generated this LSA
Sequence
This advertisement’s sequence number.
Sequence numbers allow routers to determine
if their database is current or if needs to request
an update.
Age
The age (in seconds) of this LSA
Table A-9: LSDB SECTION
1.2
Overview of the OSPF Protocol
OSPF (Open Shortest Path First), is an interior routing protocol that is often
used by larger network installations as an alternative to RIP (Routing Information Protocol). It was originally designed to address some of the limitations of
RIP (when used in larger networks). Here are some of the problems (with RIP)
that OSPF addresses:
■ Faster Network Convergence
Changes in routing information are propagated immediately when changes
occur and not periodically as with RIP.
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Overview of the OSPF Protocol
■ Reduced Network Load
After a brief initialization phase, routing information does not need to be refreshed as in RIP where the entire routing table is broadcast every 30 seconds.
■ Routing Authentication
Routers advertising OSPF routes can be authenticated.
■ Routing Traffic Control
OSPF areas can be closed to limit the amount of traffic resulting from routing advertisements.
■ Link-Costs
When calculating a route’s cost OSPF can account for the different transport mediums such as LAN or WAN links.
■ No hop-count limitations
In RIP, routes spanning more than 15 hops are unreachable.
Although the OSPF protocol is more complex than RIP the basic concept
is the same; the best interface must be calculated for forwarding packets to
a particular station.
1.2.1
Shortest Path Routing
With RIP, routes are measured and selected according to the number of hops
it takes for a packet to reach its destination. In the diagram below, each node
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represents an IP router. According to RIP, the best route for a packet travelling
from A to C will always be ABC.
B
C
6
2
2
1
E
A
3
1
3
G
4
F
D
2
4
3
H
Figure A-1: Shortest Path Routing
In OSPF each link has a cost associated with it (typically some fixed number
divided by the bandwidth of the link). Routes are calculated and selected according to the least cost of the overall path a packet will travel. Thus in shortestpath routing the best path is also the fastest path (theoretically), regardless of
the number of stations a packet travels through.
Assuming the relative costs of the links in the diagram above (shown in blue),
according to OSPF the best route for a packet travelling from A to C is ABEFC
(cost = 6). This route requires 4 hops as opposed to the 2 hop route (ABC) selected.
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Overview of the OSPF Protocol
1.2.2
OSPF Routers and Link State Advertisement
OSPF is based on a concept of Areas. An Autonomous System (AS) consists
of one or more Areas defined by network management. An Area may contain
one or more IP networks.
If an AS does contain more than one area, one must be designated as the backbone, area: 0.0.0.0. All Area Border Routers (see section A, chapter 1.2.4,
page 22) in an AS must have a physical connection to the backbone.
Autonomous System 1000
Area 1
ABR
IR
backbone
0.0.0.0
ASBR
Area 2
ASBR
Area 1
Autonomous System 2000
Figure A-2: OSPF Routers and Link State Advertisement
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Any of the routers shown above could additionally be the Designated Router or
Backup Designated Router for its respective network.
1.2.3
OSPF Virtual Links
Note that in OSPF the backbone, Area 0.0.0.0, is the center for all areas in the
Autonomous System. However, sometimes it is not possible to physically connect all areas to the backbone. By configuring a “Virtual Link” between two area
border routers a remote area can still be assigned to the backbone.
As shown in the diagram below, a virtual link is established between two Area
Border Routers that share a common area; called the “transit area”. Both routers must be physically connected to the backbone.
Area 0.0.0.0
(virtual area)
Virtual Link
Brick-B
10.0.1.2
Brick-A
10.0.1.1
Area 10.0.0.0
(transit area)
Area 0.0.0.0
(backbone)
Figure A-3: OSPF Virtual Links
1.2.4
Router Types
The location of a router’s interface with respect to an area determines the type
of router it is and the types of Link State Advertisements it exchanges with other
routers in that area.
■ Internal Routers (IR)
A router whose interfaces are within the same area. All Internal Routers
compute the shortest path tree to all destinations within its area.
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Overview of the OSPF Protocol
■ Area Border Router (ABR)
A router with interfaces in different areas but within the same autonomous
system. Topological information is gathered (and stored) for each attached
area allowing the ABR to compute the shortest path tree for each area separately.
■ Autonomous System Border Router (ASBR)
A router that acts as a gateway between OSPF and external routes (i.e.,
routes provided by other routing protocols, static indirect routes, etc.).
These routers propagate routes to external networks.
■ Designated Router (DR)
On broadcast networks (token ring and ethernet) where more than two routers are present only the DR needs to synchronize its link state database
with other routers.
■ Backup Designated Router (BDR)
A backup router assumes the responsibilities performed by the DR if that
system goes down.
1.2.5
Link State Advertisement Types
OSPF routers exchange routing information via Link State Advertisements
(LSAs) that contain information about the networks that can be reached over
the router’s interfaces.
Link State Advertisements are broken down into five different types shown in
the table below. The example network shown on the previous page is redisplayed below and shows where the different types of LSAs would be found in
an OSPF network.
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Open Shortest Path First (OSPF)
LSA Type
Purpose
Router Links
Generated by: All OSPF Routers.
Purpose: Contains information regarding the
state of a router’s interfaces within a particular
area. Router Links are only flooded within a single area.
Network Links
Generated by: The Designated Router (or
Backup Designated Router).
Purpose: Identifies all OSPF routers present on
the network segment and their state. These
links are only flooded within a single area.
Summary Links
Generated by: Area Border Routers.
Purpose: Identifies the presence of networks
within an AS but outside the (local) area. Provides Inter-Area routes allowing routers to learn
of networks in other Areas but within the AS.
ASBR Summary Links
Generated by: An Area Border Router.
Purpose: A special type of summary link that
provides routes to Autonomous System Border
Routers allowing other routers in the AS to find
their way out of the system.
External Links
Generated by: An Autonomous System
Border Router.
Purpose: Contains information about other
Autonomous Systems and allows routers to
learn about routes to networks there. External
links are flooded into all areas except stub
areas.
Table A-10: Link State Advertisement Types
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Overview of the OSPF Protocol
Autonomous System 1000
ABR
Router Links
Network Links
Area 1
Router
Links
Summary Links
IR
Network
Links
ASBR
External
Links
Area 2
Router Links
Network Links
ASBR
Area 1
Autonomous System 2000
Figure A-4: Different LSA Types in OSPF Network
1.2.6
Router Identification
All OSPF routers in an Autonomous System must have a unique Router ID that
identifies the router with respect to the AS. Generally an OSPF router’s Router
ID is taken to be the highest IP address for its first LAN interface.
1.2.7
Initialization
OSPF networks are said to be much “quieter” in comparison to RIP based networks. This is because in OSPF once the initialization phase is complete routing
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Open Shortest Path First (OSPF)
information is only exchanged when link state changes occur. This is much different than with RIP where every 30 seconds a router’s complete routing table
is broadcast and verified over the network.
The initialization phase of OSPF is completed once the Link State Database for
the area has stabilized and generally occurs once:
■ The OSPF Neighbors have been identified.
■ The Designated and Backup Designated Routers have been established.
1.2.8
Neighbor Identification
When first coming into service an OSPF router attempts to identify its neighbor
OSPF routers using the HELLO protocol. Two routers are neighbors if they:
■ Share a common network.
■ Are using the same Area Number for that segment.
■ Are using the same Authentication for the segment.
■ Are using the same parameters (HELLO interval, etc.).
Neighbor routers then decide whether to synchronize their Link State Database
(LSDB) with one another. All routers on the segment synchronize their LSDBs
with the Designated Router (DR) and the Backup Designated Router (BDR).
1.2.9
Designated / Backup Designated Router Election
When Neighbor routers are identified (via the HELLO protocol) the DR and BDR
are also identified. This is sometimes called DR and BDR election and is
achieved via IP multicast packets which a router broadcasts via each network
segment. For each segment the router with the highest OSPF priority generally
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Overview of the OSPF Protocol
becomes the DR. In case of a tie, the router with the higher Router ID becomes
the DR.
Net 10.1.1.0
RTR-A
ID=10.1.1.1
Net 10.1.2.0
RTR-C
ID=10.1.2.1
P=1
P=1
RTR-B
ID=10.1.1.2
P=2
P=1
P=2 Net 10.1.3.0
P=0
Figure A-5: Designated/Backup Designated Router Election
The DR and BDRs for the three networks shown above would be elected as follows:
Network
DR
BDR
10.1.1.0
RTR-B
RTR-A
10.1.2.0
RTR-A
RTR-C
10.1.3.0
RTR-C
RTR-B
1.2.10
Link State Database
(LSD)
Building up the LSD and the SPT
Link State Advertisements contain information about a router´s interfaces (i.e.,
link’s IP address, mask, network type, networks reachable over the link, etc.).
All routers within an area receive all link state information for all routers in the
area. Once synchronized each router has an identical image of the link state database that describes the topological structure of the area.
Shortest Path Tree
(SPT)
Software Reference
This database allows each router to separately calculate a shortest path tree
(SPT), using itself as the root, to any destination in the area. The SPT is used
to determine the best interface to route a packet. As in RIP the lowest cost route
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is used however the cost to a destination is calculated differently. In OSPF the
cost (or metric) of a link is a function of the bandwidth provided by the link. The
higher the bandwidth, the lower the cost.
1.2.11
Authentication
OSPF allows packets containing OSPF routing information to be individually
authenticated. Two authentication methods are available which must be configured separately for each network segment.
■ Simple (password) authentication
A simple text string is sent with each packet. This method is less secure
since packet contents can be “sniffed” off the wire using a link analyzer.
■ MD5 (cryptographic) authentication
When MD5 (Message Digest) is used, each packet is appended with a 16
byte encrypted digest. The digest is a function of an authentication key and
the contents of the packet. This method is more secure since the key is not
sent with the packet.
With MD5 authentication, only the digest is encrypted and not the actual contents of the OSPF packet.
1.2.12
OSPF over Demand Circuits
Although OSPF generates less network traffic than RIP, the occasional exchange of routing information (HELLO packets, Link State Database updates or
changes, etc.) can lead to increased costs for dial-up interfaces.
To help minimize these costs, OSPF on the BinTec router has been implemented to include special extensions for Demand Circuits as defined in RFC 1793,
OSPF over Demand Circuits. These extensions allow for efficient use of dial-up
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Example OSPF Installation
interfaces with OSPF and avoiding excessive ISDN costs. In particular, this
means:
■ The exchange of HELLO packets between neighbors is suppressed once
the BinTec router has synchronized its LSDB with that neighbor (a dial-up
connection is initially opened to synchronize the database.)
Link State advertisements are only flooded to neighbor routers when an actual
change needs to be propagated.
Each LSA is marked with a special DoNotAge flag (identifiable by the DC-bit of
the LSA or OSPF packet)
If a router without RFC 1793 support is removed from the domain in which this
feature has been used it is recommended that all OSPF routers be briefly
deactivated and re-activated to ensure that all LSAs generated by the removed
router are actually flushed.
1.3
Example OSPF Installation
A typical network installation showing how OSPF could be put to use is shown
in the diagram below. Highlights for this setup are shown below. Following the
diagram is a Configuration Overview and following that a detailed listing of the
configuration steps is provided for each router.
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Figure A-6: OSPF Installation
Area 11.0.0.0
(Stub Area)
ISDN
BRICK-XS
11.0.0.0
255.255.255.0 en1
10.0.1.0
255.255.255.0
10.0.2.0
255.255.255.0
Def. Route
for AS
.1
192.168.30.0
255.255.255.128
Area 10.0.0.0
Def. Route
for Area
12.0.0.0
BRICK-XL2
.1
.1
en1
en2
.1
en1
en3
en2
.1
BRICK-XM
192.168.40.0
255.255.255.128
Area 0.0.0.0
(backbone)
Open Shortest Path First (OSPF)
OSPF
Autonomous System 3000
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Example OSPF Installation
Area 11.0.0.0 (stub area)
■ Since the remote LAN in Area 11.0.0.0 is linked to the backbone via an
ISDN dialup link this area is configured as a stub area. This means that external routing information advertisements will not flow into this area. The
default route for this area is provided by the router BRICK-XL2.
■ Because OSPF on the BinTec router includes support for Demand Circuits
(RFC 1793) the dialup link is only opened when changes in routing information must be propagated.
Area 0.0.0.0 (backbone)
Area 0.0.0.0 is the backbone of the Autonomous System. The router at BRICKXL2 will provide the default route for the entire AS and a default route for Area
11.0.0.0.
Area 10.0.0.0
Area 10.0.0.0 is connected to the backbone via the border router BRICK-XM.
Since this is the only link between networks in this area and any external networks (such as the Internet) BRICK-XM will provide Summary Links to routers
in other areas. This means that routing information about networks in Area
10.0.0.0 will be combined (or aggregated) into a single advertisement. This
lessens the amount of traffic on the backbone and keeps the size of the link
state database for area 0.0.0.0 small.
1.3.1
Configuration Overview
Prerequisite for all BinTec routers:
■ A valid OSPF license must be installed. This can be added to the
biboAdmLicenseTable or from Setup Tool’s LICENCES menu.
■ OSPF must be enabled by setting ospfAdminStat to enabled, or from Setup Tool’s IP ➧ OSPF ➧ STATIC SETTINGS menu.
BRICK-XL2 Overview
➤ Create the dial-up partner interface to BRICK-XS.
➤ Have BRICK-XL2 advertise the default route for the AS.
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➤ Create the Area entry for Area 11.0.0.0.
➤ Assign the new dialup partner interface to Area 11.0.0.0 and set the interface to active.
BRICK-XM Overview
➤ Create the Area entry for Area 10.0.0.0.
➤ Assign ethernet interfaces en1 and en2 to Area 10.0.0.0 and set both interfaces to active.
➤ Verify ethernet interface en3 is assigned to Area 11.0.0.0 and set the interface to active.
➤ Create the OSPF aggregate for the LANs attached to en1 and en2 to reduce the routing traffic sent over en3.
BRICK-XS Overview
➤ Create the dial-up partner interface to BRICK-XL2.
➤ Create the Area entry for Area 11.0.0.0.
➤ Assign the ethernet interface (en1) to Area 11.0.0.0 and set the interface to
active.
➤ Assign the new dial-up interface to Area 0.0.0.0 and set the interface to
active.
1.3.2
Configuration Steps for BRICK-XL2
➤ Enable OSPF and create the partner interface to BRICK-XS. Note that our
example uses a transfer network (network 12.0.0.0).
➤ Since BRICK-XL2 should advertise the default route for the AS go to IP ➧
OSPF ➧ STATIC SETTINGS and set the Generate Default Route for the
AS field to yes.
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Example OSPF Installation
BinTec router Setup Tool
[IP][OSPF][STATIC]: OSPF Static Settings
BinTec Communications AG
MyRouter
OSPF
Generate Default Route for the AS
SAVE
enabled
yes
CANCEL
Enter IP address (a.b.c.d or resolvable hostname)
➤ In the IP ➧ OSPF ➧ AREAS menu create an entry for Area 11.0.0.0. Define this area as a Stub Area and have BRICK-XL2 generate the default
route for this area.
BinTec routerSetup Tool
[IP][OSPF][AREA][ADD]: Area Configuration
BinTec Communications AG
MyRouter
Area ID
11.0.0.0
Import external routes
Import summary routes
Create area default route (only ABR)
no
no
yes
Area Ranges>
SAVE
CANCEL
Enter IP address (a.b.c.d or resolvable hostname)
➤ In the IP ➧ OSPF ➧ INTERFACES menu locate the dialup interface entry
created before and press Enter to edit the settings.
➤ Set the Admin Status to active and assign it to Area 11.0.0.0 (or the area
created before) and select SAVE.
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Open Shortest Path First (OSPF)
BinTec router Setup Tool
BinTec Communications AG
[IP][OSPF][INTERFACE]: Configure Interface BRICK
MyRouter
Admin Status
Area ID
active (propagate routes + run OSPF)
11.0.0.0
Metric Determination
Metric (direct routes)
auto (ifSpeed)
1562
Authentication Type
Authentication Key
none
Import indirect static routes
no
SAVE
CANCEL
Use (Space) to select
By default, dial-up interfaces are set to passive in the Admin Status field.
➤ In IP ➧ OSPF ➧ INTERFACES menu verify the ethernet interfaces en1
and en2 are assigned to the backbone, (Area 0.0.0.0 which is the default
area).
➤ Set the Admin Status to active and assign it to Area 11.0.0.0 (or the value
from the step before) and select SAVE.
1.3.3
Configuration Steps for BRICK-XM
➤ Enable OSPF in IP ➧ OSPF ➧ STATIC SETTINGS.
➤ Then create an area entry for Area 10.0.0.0 in the IP ➧ OSPF ➧ AREAS
menu.
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Example OSPF Installation
BinTec router Setup Tool
[IP][OSPF][AREA][ADD]: Area Configuration
Area ID
Import external routes
BinTec Communications AG
MyRouter
10.0.0.0
yes
Area Ranges>
SAVE
CANCEL
Enter IP address (a.b.c.d or resolvable hostname)
➤ In the IP ➧ OSPF ➧ INTERFACES menu assign ethernet interfaces en1
and en2 to Area 10.0.0.0 (or the value from the previous step) and set the
Admin Status for each interface to active.
BinTec router Setup Tool
[IP][OSPF][AREA][ADD]: Area Configuration
BinTec Communications AG
MyRouter
Admin Status
Area ID
active (propagate routes + run OSPF)
10.0.0.0
Metric Determination
Metric (direct routes)
auto (ifSpeed)
10
Authentication Type
Authentication Key
none
Import indirect routes
no
SAVE
CANCEL
Use (Space) to select
➤ Ethernet interface en3 should already be assigned to the backbone, Area
0.0.0.0 which is the default.
➤ In the IP ➧ OSPF ➧ INTERFACES menu verify this setting and change the
Admin Status to active.
➤ Return to the IP ➧ OSPF ➧ AREAS menu and scroll to the Area ID entry for the backbone and press Enter.
➤ Move to the AREA RANGES submenu to add an OSPF aggregate for the
LANs attached to en1 and en2. The Address and Mask entries shown below will match any routes with a destinations starting with 10, or 10.*.*.*.
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BinTec router Setup Tool
BinTec Communications AG
[IP][OSPF][AREA][RANGE][ADD]: Configure Address range for AreaMyRouter
Address
Mask
10.0.0.0
255.0.0.0
Advertise Matching
yes
SAVE
CANCEL
Enter IP address (a.b.c.d or resolvable hostname)
This entry means that BRICK-XM will consolidate multiple routes (routes for
destinations in Area 10.0.0.0) into a single link state advertisement.
This will effectively reduce the amount of traffic sent over the backbone as
will help keep the size of the link state database and routing tables for routers in other areas to a minimum.
1.3.4
Configuration Steps for BRICK-XS
➤ Enable OSPF and create the dial-up partner interface to BRICK-XL2. In our
example a transfer network (12.0.0.0) is used.
➤ In the IP ➧ OSPF ➧ AREAS menu create Area 11.0.0.0. and define it as
a Stub Area.
BinTec router Setup Tool
[IP][OSPF][AREA][ADD]: Area Configuration
BinTec Communications AG
MyRouter
Area ID
11.0.0.0
Import external routes
Import summary routes
Create area default route (only ABR)
no
no
no
Area Ranges>
SAVE
CANCEL
Enter IP address (a.b.c.d or resolvable hostname)
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Example OSPF Installation
➤ In the IP
➧ OSPF ➧ INTERFACES menu assign the ethernet interface
(en1) to Area 11.0.0.0 and make sure the Admin Status is set to active.
BinTec router Setup Tool
BinTec Communications AG
[IP][OSPF][INTERFACES] Configure Interface en1
MyRouter
Admin Status
Area ID
active (propagate routes + run OSPF)
11.0.0.0
Metric Determination
Metric (direct routes)
auto (ifSpeed)
10
Authentication Type
Authentication Key
none
Import indirect routes
no
SAVE
CANCEL
Use (Space) to select
➤ In IP ➧ OSPF ➧ INTERFACES menu locate the dialup interface (created
in step 1) and assign the interface to Area 11.0.0.0 (or the value used in the
step before).
➤ Set the Admin Status for the dialup interface to active and select SAVE.
BinTec router Setup Tool
BinTec Communications AG
[IP][OSPF][INTERFACES] Configure Interface dialup
MyRouter
Admin Status
Area ID
active (propagate routes + run OSPF)
11.0.0.0
Metric Determination
Metric (direct routes)
auto(ifSpeed)
1562
Authentication Type
Authentication Key
none
SAVE
CANCEL
Use (Space) to select
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1.3.5
Configuring OSPF Virtual Links
A virtual interface must be defined on each of the ABRs by creating an entry in
the ospfVirtIfTable. This is done by setting the ospfVirtIfNeighbor and
ospfVirtIfAreaID objects.
■ ospfVirtIfNeighbor should be set to the Router ID of the Area Border Router at the other end of the virtual link.
■ ospfVirtIfAreaID should be set to the Area ID of the transit area.
The virtual link in the diagram here would be configured on BRICK-A as follows:
BRICK-A:system> ospfVirtIfTable
inx
AreaID(rw*)
Retrasitinterval(rw)
State(ro)
Status(-rw)
Neighbor(rw*)
TransitDelay(rw)
Hellointerval(rw) RtrDeadInterval(rw)
Events(ro)
AuthKey(rw)
AuthType(rw)
BRICK-A:ospdVirtIfTable> AreaID=10.0.0.0 Neighbor=10.0.1.2
This creates a new OSPF virtual interface (on BRICK-A) that links two parts of
the backbone via the transit area 10.0.0.0. The respective interface would be
created
on
BRICK-B
using
almost
the
same
command
(ospfVirtIfAreaID=10.0.0.0 ospfVirtIfNeighbor=10.0.1.1).
Remember that the area being used as the transit area must already be
defined in the ospfAreaTable.
1.4
Controlling Link State Database Overflow
Sites with large (or complicated) network installations that are running OSPF
may notice the Link State Database (LSDB) becoming large. Most often this is
the case where external routes are being imported as external advertisements.
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Controlling Link State Database Overflow
One way to minimize the size of the LSDB (on the BinTec router) is to use the
ospfExtLsdbLimit variable. This object defines the maximum number of external LSAs to store in the database (the local copy).
Once the limit is reached the BinTec router goes into Overflow State. In Overflow State two things happen:
■ The BinTec router begins to flush all external advertisements generated locally.
■ The BinTec router ignores all new external advertisements.
The maximum size of the LSDB must be the same for all OSPF routers in the
domain for this feature to perform efficiently.
By default the BinTec router remains in overflow state but can optionally be configured to leave overflow state (and continue to process new external LSAs) automatically after a time period. The ospfExtOverflowInterval variable defines
the number of seconds to wait before leaving overflow state automatically. The
default is 0 seconds (i.e., stay in overflow state). After waiting
ospfExtOverflowInterval seconds the number of external LSAs in the LSDB is
compared to the ospfExtLsdbLimit. If there is room in the database for new
LSAs, the BinTec router leaves overflow state; otherwise another time interval
is waited.
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The diagram shown below attempts to illustrate the behavior of database overflow control using the ospfExtLsdbLimit and ospfExtOverflowInterval variables.
ospfExtLsdbLimit=100
ospfExtOverflowInterval=30
LSDB Size
(100)
(80)
time
n
n+Interval
flushing...
accepting
ignoring
External LSAs
Figure A-7: Database Overflow Control
1.5
Enabling Demand Circuit Support
Demand Circuit support for dial-up partner interfaces is enabled by default
when an existing interface is enabled for OSPF (AdminStatus is set to active).
Support can be manually controlled by setting the interface’s IfDemand object
(ospfIfTable) to true or false. When set to false, the state of this interface is always up.
Setting this variable to true for one side of the connection is sufficient (that is,
as long as OSPF has been enabled on both sides, i.e., ipExtIfOspf=active) if
both sides support RFC 1793.
Until a neighbor router has been identified HELLO packets are periodically
transmitted (default, ospfIfPollInterval = 120 seconds) over the interface. This
results in the link being opened. Once the LSDB has been synchronized, the
HELLO protocol is then suppressed.
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Import / Export of Routing Information
1.6
Import / Export of Routing Information
When different routing protocols are used within the same domain it is sometimes useful to be able to exchange (import or export) routing information between these protocols.
Using the ipImportTable routing information generated by one protocol
(ipImportSrcProto) can be imported or exported to another protocol
(ipImportDstProto).
Currently the following SrcProto ↔DstProto combinations are possible:
ipIipImportDstProtorotoportDstP
rip
ipImportSrcProto
ospf
✓(1)
default route
(see table 2-11)
direct
✓(2)
static
(see table 2-11)
rip
ospf
✓(3)
(see table 2-11)
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For further control, the fields of the ipImportTable allow how (and what) routing
information is imported.
Variable
Meaning
ipImportSrcProto (1)
default_route ipImportDstProto=ospf
This entry forces an external Link State Advertisement to be generated that defines a default
route for the Autonomous System.
ipImportSrcProto (2)
static ipImportDstProto=ospf
With this entry statically configured indirect
routes will be propagated via OSPF as external
LSAs.
ipImportSrcProto (3)
ospf ipImportDstProto=rip
With this entry, all routes learned via OSPF are
imported to RIP. If an OSPF route changes, the
import to RIP will trigger an immediate broadcast of the entire routing table.
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ipImportMetric1
The metric in the context of the destination protocol the imported routes should get. If set to -1
these routes get a protocol-specific default metric.
ipImportType
This object might define protocol specific properties of the imported routes in the context of
the destination protocol.
ipImportAddr
Specifies (together with ipImportMask) the
range of IP addresses for which the table entry
should be valid. The entry is valid if the destination IP address of the route lies in the range
specified by both objects. If both objects are set
to 0.0.0.0, the table entry will be valid for destination.
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Import / Export of Routing Information
Variable
Meaning
ipImportMask
Together with ipImportAddr specifies the
range of IP addresses for which the table entry
should be valid. For example, if Addr=X.X.0.0
and Mask=255.255.0.0 then addresses X.X.0.0
through X.X.255.255 are valid.
ipImportEffect
Defines the effect of this entry. If set to import
importation from SrcProto to DstProto takes
place. If set to doNotImport importation is prevented.
ipImportIfIndex
Specifies the interface index of the interface for
which the entry should be valid. If set to 0 the
entry is valid for all interfaces.
Table A-11: ipImportTable
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