Configuring OSPF

This module describes how to configure Open Shortest Path First (OSPF). OSPF is an Interior Gateway

Protocol (IGP) developed by the OSPF working group of the Internet Engineering Task Force (IETF). OSPF

was designed expressly for IP networks and it supports IP subnetting and tagging of externally derived routing

information. OSPF also allows packet authentication and uses IP multicast when sending and receiving packets.

Cisco supports RFC 1253, OSPF Version 2 Management Information Base, August 1991. The OSPF MIB

defines an IP routing protocol that provides management information related to OSPF and is supported by

Cisco routers.

For protocol-independent features that work with OSPF, see the "Configuring IP Routing Protocol-Independent

Features" module.

• Finding Feature Information, on page 1

• Information About OSPF, on page 1

• How to Configure OSPF, on page 9

• Configuration Examples for OSPF, on page 32

• Additional References for OSPF Not-So-Stubby Areas (NSSA), on page 50

• Feature Information for Configuring OSPF, on page 51

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and

feature information, see Bug Search Tool and the release notes for your platform and software release. To

find information about the features documented in this module, and to see a list of the releases in which each

feature is supported, see the feature information table.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support.

To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Information About OSPF

Cisco OSPF Implementation

The Cisco implementation conforms to the OSPF Version 2 specifications detailed in the Internet RFC 2328.

The following list outlines key features supported in the Cisco OSPF implementation:

Configuring OSPF

• Stub areas—The definition of stub areas is supported.

• Route redistribution—Routes learned via any IP routing protocol can be redistributed into any other IP

routing protocol. At the intradomain level, OSPF can import routes learned via Interior Gateway Routing

Protocol (IGRP), Routing Information Protocol (RIP), and Intermediate System-to-Intermediate System

(IS-IS). OSPF routes can also be exported into IGRP, RIP, and IS-IS. At the interdomain level, OSPF

can import routes learned via Exterior Gateway Protocol (EGP) and Border Gateway Protocol (BGP).

OSPF routes can be exported into EGP and BGP.

• Authentication—Plain text and message-digest algorithm 5 (MD5) authentication among neighboring

routers within an area is supported.

• Routing interface parameters—Configurable parameters supported include interface output cost,

retransmission interval, interface transmit delay, router priority, router “dead” and hello intervals, and

authentication key.

• Virtual links—Virtual links are supported.

• Not-so-stubby area (NSSA)—RFC 3101, which replaces and is backward compatible with RFC 1587.

• OSPF over demand circuit—RFC 1793.

Router Coordination for OSPF

OSPF typically requires coordination among many internal routers: Area Border Routers (ABRs), which are

routers connected to multiple areas, and Autonomous System Boundary Routers (ASBRs). At a minimum,

OSPF-based routers or access servers can be configured with all default parameter values, no authentication,

and interfaces assigned to areas. If you intend to customize your environment, you must ensure coordinated

configurations of all routers.

Route Distribution for OSPF

You can specify route redistribution; see the task “Redistribute Routing Information” in the Network Protocols

Configuration Guide, Part 1, for information on how to configure route redistribution.

The Cisco OSPF implementation allows you to alter certain interface-specific OSPF parameters, as needed.

You are not required to alter any of these parameters, but some interface parameters must be consistent across

all routers in an attached network. Those parameters are controlled by the ip ospf hello-interval, ip ospf

dead-interval, and ip ospf authentication-key interface configuration commands. Therefore, if you do

configure any of these parameters, ensure that the configurations for all routers on your network have compatible

values.

By default, OSPF classifies different media into the following three types of networks:

• Broadcast networks (Ethernet, Token Ring, and FDDI)

• Nonbroadcast multiaccess (NBMA) networks (Switched Multimegabit Data Service [SMDS], Frame

Relay, and X.25)

• Point-to-point networks (High-Level Data Link Control [HDLC] and PPP)

You can configure your network as either a broadcast or an NBMA network.

Configuring OSPF

Router Coordination for OSPF

X.25 and Frame Relay provide an optional broadcast capability that can be configured in the map to allow

OSPF to run as a broadcast network. See the x25 map and frame-relay map command pages in the Cisco

IOS Wide-Area Networking Command Reference publication for more detail.

OSPF Network Type

You have the choice of configuring your OSPF network type as either broadcast or NBMA, regardless of the

default media type. Using this feature, you can configure broadcast networks as NBMA networks when, for

example, you have routers in your network that do not support multicast addressing. You also can configure

NBMA networks (such as X.25, Frame Relay, and SMDS) as broadcast networks. This feature saves you

from needing to configure neighbors, as described in the “Configuring OSPF for Nonbroadcast

Networks”section later in this module.

Configuring NBMA networks as either broadcast or nonbroadcast assumes that there are virtual circuits (VCs)

from every router to every router, that is, a fully meshed network. This is not true in some cases, for example,

because of cost constraints or when you have only a partially meshed network. In these cases, you can configure

the OSPF network type as a point-to-multipoint network. Routing between two routers that are not directly

connected will go through the router that has VCs to both routers. Note that you need not configure neighbors

when using this feature.

An OSPF point-to-multipoint interface is defined as a numbered point-to-point interface having one or more

neighbors. It creates multiple host routes. An OSPF point-to-multipoint network has the following benefits

compared to NBMA and point-to-point networks:

• Point-to-multipoint is easier to configure because it requires no configuration of neighbor commands, it

consumes only one IP subnet, and it requires no designated router election.

• It costs less because it does not require a fully meshed topology.

• It is more reliable because it maintains connectivity in the event of VC failure.

On point-to-multipoint broadcast networks, there is no need to specify neighbors. However, you can specify

neighbors with the neighbor router configuration command, in which case you should specify a cost to that

neighbor.

Before the point-to-multipoint keyword was added to the ip ospf network interface configuration command,

some OSPF point-to-multipoint protocol traffic was treated as multicast traffic. Therefore, the neighbor router

configuration command was not needed for point-to-multipoint interfaces because multicast took care of the

traffic. Hello, update, and acknowledgment messages were sent using multicast. In particular, multicast hello

messages discovered all neighbors dynamically.

On any point-to-multipoint interface (broadcast or not), the Cisco IOS software assumed that the cost to each

neighbor was equal. The cost was configured with the ip ospf cost interface configuration command. In reality,

the bandwidth to each neighbor is different, so the cost should differ. With this feature, you can configure a

separate cost to each neighbor. This feature applies to point-to-multipoint interfaces only.

Because many routers might be attached to an OSPF network, a designated router is selected for the network.

Special configuration parameters are needed in the designated router selection if broadcast capability is not

configured.

These parameters need only be configured in those devices that are themselves eligible to become the designated

router or backup designated router (in other words, routers with a nonzero router priority value).

You can specify the following neighbor parameters, as required:

• Priority for a neighboring router

Configuring OSPF

OSPF Network Type

• Nonbroadcast poll interval

On point-to-multipoint, nonbroadcast networks, use the neighbor router configuration command to identify

neighbors. Assigning a cost to a neighbor is optional.

Prior to Cisco IOS Release 12.0, some customers were using point-to-multipoint on nonbroadcast media (such

as classic IP over ATM), so their routers could not dynamically discover their neighbors. This feature allows

the neighbor router configuration command to be used on point-to-multipoint interfaces.

Area Parameters

Use OSPF Not-So-Stubby Areas (NSSA) feature to simplify administration if you are an Internet service

provider (ISP) or a network administrator that must connect a central site that is using OSPF to a remote site

that is using a different routing protocol.

Prior to NSSA, the connection between the corporate site border router and the remote router could not be

run as an OSPF stub area because routes for the remote site could not be redistributed into the stub area, and

two routing protocols needed to be maintained. A simple protocol such as RIP was usually run and handled

the redistribution. With NSSA, you can extend OSPF to cover the remote connection by defining the area

between the corporate router and the remote router as an NSSA.

As with OSPF stub areas, NSSA areas cannot be injected with distributed routes via Type 5 LSAs. Route

redistribution into an NSSA area is possible only with a special type of LSA that is known as Type 7 that can

exist only in an NSSA area. An NSSA ASBR generates the Type 7 LSA so that the routes can be redistributed,

and an NSSA ABR translates the Type 7 LSA into a Type 5 LSA, which can be flooded throughout the whole

OSPF routing domain. Summarization and filtering are supported during the translation.

RFC 3101 allows you to configure an NSSA ABR router as a forced NSSA LSA translator. This means that

the NSSA ABR router will unconditionally assume the role of LSA translator, preempting the default behavior,

which would only include it among the candidates to be elected as translator.

Even a forced translator might not translate all LSAs; translation depends on the contents of each LSA.

Note

The figure below shows a network diagram in which OSPF Area 1 is defined as the stub area. The Enhanced

Interior Gateway Routing Protocol (EIGRP) routes cannot be propagated into the OSPF domain because

routing redistribution is not allowed in the stub area. However, once OSPF Area 1 is defined as an NSSA, an

NSSA ASBR can inject the EIGRP routes into the OSPF NSSA by creating Type 7 LSAs.

Configuring OSPF

Area Parameters

Figure 1: OSPF NSSA

The redistributed routes from the RIP router will not be allowed into OSPF Area 1 because NSSA is an

extension to the stub area. The stub area characteristics will still exist, including the exclusion of Type 5 LSAs.

Route summarization is the consolidation of advertised addresses. This feature causes a single summary route

to be advertised to other areas by an ABR. In OSPF, an ABR will advertise networks in one area into another

area. If the network numbers in an area are assigned in a way such that they are contiguous, you can configure

the ABR to advertise a summary route that covers all the individual networks within the area that fall into the

specified range.

When routes from other protocols are redistributed into OSPF (as described in the module "Configuring IP

Routing Protocol-Independent Features"), each route is advertised individually in an external LSA. However,

you can configure the Cisco IOS software to advertise a single route for all the redistributed routes that are

covered by a specified network address and mask. Doing so helps decrease the size of the OSPF link-state

database.

In OSPF, all areas must be connected to a backbone area. If there is a break in backbone continuity, or the

backbone is purposefully partitioned, you can establish a virtual link. The two endpoints of a virtual link are

ABRs. The virtual link must be configured in both routers. The configuration information in each router

consists of the other virtual endpoint (the other ABR) and the nonbackbone area that the two routers have in

common (called the transit area). Note that virtual links cannot be configured through stub areas.

You can force an ASBR to generate a default route into an OSPF routing domain. Whenever you specifically

configure redistribution of routes into an OSPF routing domain, the router automatically becomes an ASBR.

However, an ASBR does not, by default, generate a defaultroute into the OSPF routing domain.

You can configure OSPF to look up Domain Naming System (DNS) names for use in all OSPF show EXEC

command displays. You can use this feature to more easily identify a router, because the router is displayed

by name rather than by its router ID or neighbor ID.

OSPF uses the largest IP address configured on the interfaces as its router ID. If the interface associated with

this IP address is ever brought down, or if the address is removed, the OSPF process must recalculate a new

router ID and resend all its routing information out its interfaces.

Configuring OSPF

Area Parameters

If a loopback interface is configured with an IP address, the Cisco IOS software will use this IP address as its

router ID, even if other interfaces have larger IP addresses. Because loopback interfaces never go down,

greater stability in the routing table is achieved.

OSPF automatically prefers a loopback interface over any other kind, and it chooses the highest IP address

among all loopback interfaces. If no loopback interfaces are present, the highest IP address in the router is

chosen. You cannot tell OSPF to use any particular interface.

In Cisco IOS Release 10.3 and later releases, by default OSPF calculates the OSPF metric for an interface

according to the bandwidth of the interface. For example, a 64-kbps link gets a metric of 1562, and a T1 link

gets a metric of 64.

The OSPF metric is calculated as the ref-bw value divided by the bandwidth value, with the ref-bw value

equal to 108 by default, and the bandwidth value determined by the bandwidth interface configuration command.

The calculation gives FDDI a metric of 1. If you have multiple links with high bandwidth, you might want

to specify a larger number to differentiate the cost on those links.

An administrative distance is a rating of the trustworthiness of a routing information source, such as an

individual router or a group of routers. Numerically, an administrative distance is an integer from 0 to 255.

In general, the higher the value, the lower the trust rating. An administrative distance of 255 means the routing

information source cannot be trusted at all and should be ignored.

OSPF uses three different administrative distances: intra-area, interarea, and external. Routes within an area

are intra-area; routes to another area are interarea; and routes from another routing domain learned via

redistribution are external. The default distance for each type of route is 110.

Because simplex interfaces between two devices on an Ethernet represent only one network segment, for

OSPF you must configure the sending interface to be a passive interface. This configuration prevents OSPF

from sending hello packets for the sending interface. Both devices are able to see each other via the hello

packet generated for the receiving interface.

You can configure the delay time between when OSPF receives a topology change and when it starts a shortest

path first (SPF) calculation. You can also configure the hold time between two consecutive SPF calculations.

The OSPF on-demand circuit is an enhancement to the OSPF protocol that allows efficient operation over

on-demand circuits such as ISDN, X.25 switched virtual circuits (SVCs), and dialup lines. This feature supports

RFC 1793, Extending OSPF to Support Demand Circuits.

Prior to this feature, OSPF periodic hello and LSA updates would be exchanged between routers that connected

the on-demand link, even when no changes occurred in the hello or LSA information.

With this feature, periodic hellos are suppressed and the periodic refreshes of LSAs are not flooded over the

demand circuit. These packets bring up the link only when they are exchanged for the first time, or when a

change occurs in the information they contain. This operation allows the underlying data link layer to be

closed when the network topology is stable.

This feature is useful when you want to connect telecommuters or branch offices to an OSPF backbone at a

central site. In this case, OSPF for on-demand circuits allows the benefits of OSPF over the entire domain,

without excess connection costs. Periodic refreshes of hello updates, LSA updates, and other protocol overhead

are prevented from enabling the on-demand circuit when there is no "real" data to send.

Overhead protocols such as hellos and LSAs are transferred over the on-demand circuit only upon initial setup

and when they reflect a change in the topology. This means that critical changes to the topology that require

new SPF calculations are sent in order to maintain network topology integrity. Periodic refreshes that do not

include changes, however, are not sent across the link.

The OSPF LSA group pacing feature allows the router to group OSPF LSAs and pace the refreshing,

checksumming, and aging functions. The group pacing results in more efficient use of the router.

Configuring OSPF

Area Parameters

The router groups OSPF LSAs and paces the refreshing, checksumming, and aging functions so that sudden

increases in CPU usage and network resources are avoided. This feature is most beneficial to large OSPF

networks.

OSPF LSA group pacing is enabled by default. For typical customers, the default group pacing interval for

refreshing, checksumming, and aging is appropriate and you need not configure this feature.

Original LSA Behavior

Each OSPF LSA has an age, which indicates whether the LSA is still valid. Once the LSA reaches the maximum

age (1 hour), it is discarded. During the aging process, the originating router sends a refresh packet every 30

minutes to refresh the LSA. Refresh packets are sent to keep the LSA from expiring, whether there has been

a change in the network topology or not. Checksumming is performed on all LSAs every 10 minutes. The

router keeps track of LSAs that it generates and LSAs that it receives from other routers. The router refreshes

LSAs that it generated; it ages the LSAs that it received from other routers.

Prior to the LSA group pacing feature, the Cisco software would perform refreshing on a single timer and

checksumming and aging on another timer. In the case of refreshing, for example, the software would scan

the whole database every 30 minutes, refreshing every LSA that the router generated, no matter how old it

was. The figure below illustrates all the LSAs being refreshed at once. This process wasted CPU resources

because only a small portion of the database needed to be refreshed. A large OSPF database (several thousand

LSAs) could have thousands of LSAs with different ages. Refreshing on a single timer resulted in the age of

all LSAs becoming synchronized, which resulted in much CPU processing at once. Furthermore, a large

number of LSAs could cause a sudden increase of network traffic, consuming a large amount of network

resources in a short time.

Figure 2: OSPF LSAs on a Single Timer Without Group Pacing

LSA Group Pacing with Multiple Timers

Configuring each LSA to have its own timer avoids excessive CPU processing and sudden network-traffic

increase. To again use the example of refreshing, each LSA gets refreshed when it is 30 minutes old,

independent of other LSAs. So the CPU is used only when necessary. However, LSAs being refreshed at

frequent, random intervals would require many packets for the few refreshed LSAs that the router must send,

which would be inefficient use of bandwidth.

Therefore, the router delays the LSA refresh function for an interval of time instead of performing it when

the individual timers are reached. The accumulated LSAs constitute a group, which is then refreshed and sent

out in one packet or more. Thus, the refresh packets are paced, as are the checksumming and aging. The pacing

interval is configurable; it defaults to 4 minutes, which is randomized to further avoid synchronization.

The figure below illustrates the case of refresh packets. The first timeline illustrates individual LSA timers;

the second timeline illustrates individual LSA timers with group pacing.

Configuring OSPF

Original LSA Behavior

Figure 3: OSPF LSAs on Individual Timers with Group Pacing

The group pacing interval is inversely proportional to the number of LSAs that the router is refreshing,

checksumming, and aging. For example, if you have approximately 10,000 LSAs, decreasing the pacing

interval would benefit you. If you have a very small database (40 to 100 LSAs), increasing the pacing interval

to 10 to 20 minutes might benefit you slightly.

The default value of pacing between LSA groups is 240 seconds (4 minutes). The range is from 10 seconds

to 1800 seconds (30 minutes).

By default, OSPF floods new LSAs over all interfaces in the same area, except the interface on which the

LSA arrives. Some redundancy is desirable, because it ensures robust flooding. However, too much redundancy

can waste bandwidth and might destabilize the network due to excessive link and CPU usage in certain

topologies. An example would be a fully meshed topology.

You can block OSPF flooding of LSAs in two ways, depending on the type of networks:

• On broadcast, nonbroadcast, and point-to-point networks, you can block flooding over specified OSPF

interfaces.

• On point-to-multipoint networks, you can block flooding to a specified neighbor.

The growth of the Internet has increased the importance of scalability in IGPs such as OSPF. By design, OSPF

requires LSAs to be refreshed as they expire after 3600 seconds. Some implementations have tried to improve

the flooding by reducing the frequency to refresh from 30 minutes to about 50 minutes. This solution reduces

the amount of refresh traffic but requires at least one refresh before the LSA expires. The OSPF flooding

reduction solution works by reducing unnecessary refreshing and flooding of already known and unchanged

information. To achieve this reduction, the LSAs are now flooded with the higher bit set. The LSAs are now

set as “do not age.”

Cisco routers do not support LSA Type 6 Multicast OSPF (MOSPF), and they generate syslog messages if

they receive such packets. If the router is receiving many MOSPF packets, you might want to configure the

router to ignore the packets and thus prevent a large number of syslog messages.

The former OSPF implementation for sending update packets needed to be more efficient. Some update

packets were getting lost in cases where the link was slow, a neighbor could not receive the updates quickly

enough, or the router was out of buffer space. For example, packets might be dropped if either of the following

topologies existed:

Configuring OSPF

LSA Group Pacing with Multiple Timers

• A fast router was connected to a slower router over a point-to-point link.

• During flooding, several neighbors sent updates to a single router at the same time.

OSPF update packets are now automatically paced so they are not sent less than 33 milliseconds apart. Pacing

is also added between resends to increase efficiency and minimize lost retransmissions. Also, you can display

the LSAs waiting to be sent out an interface. The benefit of pacing is that OSPF update and retransmission

packets are sent more efficiently. There are no configuration tasks for this feature; it occurs automatically.

You can display specific statistics such as the contents of IP routing tables, caches, and databases. Information

provided can be used to determine resource utilization and solve network problems. You can also display

information about node reachability and discover the routing path that your device packets are taking through

the network.

How to Configure OSPF

To configure OSPF, perform the tasks described in the following sections. The tasks in the “Enabling OSPF”

section are required; the tasks in the remaining sections are optional, but might be required for your application.

For information about the maximum number of interfaces, see the “Restrictions for OSPF” section.

Enabling OSPF

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. network ip-address wildcard-mask area area-id

5. end

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

• Enter your password if prompted.

Device> enable

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Enables OSPF routing and enters router configuration mode.

router ospf process-id

Example:

Step 3

Device(config)# router ospf 109

Configuring OSPF

How to Configure OSPF

PurposeCommand or Action

Defines an interface on which OSPF runs and defines the

area ID for that interface.

network ip-address wildcard-mask area area-id

Example:

Step 4

Device(config-router)# network 192.168.129.16

0.0.0.3 area 20

Exits router configuration mode and returns to privileged

EXEC mode.

end

Example:

Step 5

Device(config-router)# end

Configuring OSPF Interface Parameters

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. ip ospf cost cost

5. ip ospf retransmit-interval seconds

6. ip ospf transmit-delay seconds

7. ip ospf priority number-value

8. ip ospf hello-interval seconds

9. ip ospf dead-interval seconds

10. ip ospf authentication-key key

11. ip ospf message-digest-key key-id md5 key

12. ip ospf authentication [message-digest | null]

13. end

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

• Enter your password if prompted.

Device> enable

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Configures an interface type and enters interface

configuration mode.

interface type number

Example:

Step 3

Configuring OSPF

Configuring OSPF Interface Parameters

PurposeCommand or Action

Device(config)# interface Gigabitethernet 0/0

Explicitly specifies the cost of sending a packet on an

OSPF interface.

ip ospf cost cost

Example:

Step 4

Device(config-if)# ip ospf cost 65

Specifies the number of seconds between link-state

advertisement (LSA) retransmissions for adjacencies

belonging to an OSPF interface.

ip ospf retransmit-interval seconds

Example:

Device(config-if)# ip ospf retransmit-interval 1

Step 5

Sets the estimated number of seconds required to send a

link-state update packet on an OSPF interface.

ip ospf transmit-delay seconds

Example:

Step 6

Device(config-if)# ip ospf transmit-delay

Sets priority to help determine the OSPF designated router

for a network.

ip ospf priority number-value

Example:

Step 7

Device(config-if)# ip ospf priority 1

Specifies the length of time between the hello packets that

the Cisco IOS software sends on an OSPF interface.

ip ospf hello-interval seconds

Example:

Step 8

Device(config-if)# ip ospf hello-interval 1

Sets the number of seconds that a device must wait before

it declares a neighbor OSPF router down because it has

not received a hello packet.

ip ospf dead-interval seconds

Example:

Device(config-if)# ip ospf dead-interval 1

Step 9

Assigns a password to be used by neighboring OSPF

routers on a network segment that is using the OSPF simple

password authentication.

ip ospf authentication-key key

Example:

Device(config-if)# ip ospf authentication-key 1

Step 10

Enables OSPF MD5 authentication. The values for the

key-id and key arguments must match values specified for

other neighbors on a network segment.

ip ospf message-digest-key key-id md5 key

Example:

Device(config-if)# ip ospf message-digest-key 1

md5 23456789

Step 11

Specifies the authentication type for an interface.ip ospf authentication [message-digest | null]

Example:

Step 12

Configuring OSPF

Configuring OSPF Interface Parameters

PurposeCommand or Action

Device(config-if)# ip ospf authentication

message-digest

Exits interface configuration mode and returns to privileged

EXEC mode.

end

Example:

Step 13

Device(config-if)# end

Configuring OSPF over Different Physical Networks

Configuring OSPF for Point-to-Multipoint Broadcast Networks

SUMMARY STEPS

1. configure terminal

2. interface type number

3. ip ospf network point-to-multipoint

4. exit

5. router ospf process-id

6. neighbor ip-address [cost number]

DETAILED STEPS

PurposeCommand or Action

Enters global configuration mode.configure terminal

Example:

Step 1

Device# configure terminal

Specifies an interface type and number, and enters interface

configuration mode.

interface type number

Example:

Step 2

Device(config)# interface gigabitethernet 0/0/0

Configures an interface as point-to-multipoint for broadcast

media.

ip ospf network point-to-multipoint

Example:

Step 3

Device#(config-if) ip ospf network

point-to-multipoint

Enters global configuration mode.exit

Example:

Step 4

Device#(config-if) exit

Configuring OSPF

Configuring OSPF over Different Physical Networks

PurposeCommand or Action

Configures an OSPF routing process and enters router

configuration mode.

router ospf process-id

Example:

Step 5

Device#(config) router ospf 109

Specifies a neighbor and assigns a cost to the neighbor.

neighbor ip-address [cost number]

Step 6

Example:

Repeat this step for each neighbor if you want

to specify a cost. Otherwise, neighbors will

assume the cost of the interface, based on the ip

ospf cost interface configuration command.

Note

Device#(config-router) neighbor 192.168.3.4 cost

180

Configuring OSPF for Nonbroadcast Networks

SUMMARY STEPS

1. configure terminal

2. interface type number

3. ip ospf network point-to-multipoint non-broadcast

4. exit

5. router ospf process-id

6. neighbor ip-address [cost number]

DETAILED STEPS

PurposeCommand or Action

Enters global configuration mode.configure terminal

Example:

Step 1

Device# configure terminal

Specifies an interface type and number, and enters interface

configuration mode.

interface type number

Example:

Step 2

Device(config)# interface gigabitethernet 0/0/0

Configures an interface as point-to-multipoint for

nonbroadcast media.

ip ospf network point-to-multipoint non-broadcast

Example:

Step 3

Device#(config-if) ip ospf network

point-to-multipoint non-broadcast

Enters global configuration mode.exit

Example:

Step 4

Device#(config-if) exit

Configuring OSPF

Configuring OSPF for Nonbroadcast Networks

PurposeCommand or Action

Configures an OSPF routing process and enters router

configuration mode.

router ospf process-id

Example:

Step 5

Device#(config) router ospf 109

Specifies a neighbor and assigns a cost to the neighbor.

neighbor ip-address [cost number]

Step 6

Example:

Repeat this step for each neighbor if you want

to specify a cost. Otherwise, neighbors will

assume the cost of the interface, based on the ip

ospf cost interface configuration command.

Note

Device#(config-router) neighbor 192.168.3.4 cost

180

Configuring OSPF Area Parameters

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. area area-id authentication

5. area area-id stub [no summary]

6. area area-id default-cost cost

7. end

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

• Enter your password if prompted.

Device> enable

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Enables OSPF routing and enters router configuration mode.

router ospf process-id

Example:

Step 3

Device(config)# router ospf 10

Enables authentication for an OSPF area.

area area-id authentication

Example:

Step 4

Configuring OSPF

Configuring OSPF Area Parameters

PurposeCommand or Action

Device(config-router)# area 10.0.0.0 authentication

Defines an area to be a stub area.

area area-id stub [no summary]

Example:

Step 5

Device(config-router)# area 10.0.0.0 stub

no-summary

Specifies a cost for the default summary route that is sent

into a stub area or not-so-stubby area (NSSA)

area area-id default-cost cost

Example:

Step 6

Device(config-router)# area 10.0.0.0 default-cost

Exits router configuration mode and returns to privileged

EXEC mode.

end

Example:

Step 7

Device(config-router)# end

Configuring OSPFv2 NSSA

Configuring an OSPFv2 NSSA Area and Its Parameters

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. redistribute protocol [process-id] {level-1 | level-1-2 | level-2} [autonomous-system-number] [metric

{metric-value | transparent}] [metric-type type-value] [match {internal | external 1 | external 2}]

[tag tag-value] [route-map map-tag] [subnets] [nssa-only]

5. network ip-address wildcard-mask area area-id

6. area area-id nssa [no-redistribution] [default-information-originate [metric] [metric-type]]

[no-summary] [nssa-only]

7. summary-address prefix mask [not-advertise] [tag tag] [nssa-only]

8. end

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

• Enter your password if prompted.

Device> enable

Configuring OSPF

Configuring OSPFv2 NSSA

PurposeCommand or Action

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Enables OSPF routing and enters router configuration mode.

router ospf process-id

Step 3

Example:

• The process-id argument identifies the OSPF process.

The range is from 1 to 65535.

Device(config)# router ospf 10

Redistributes routes from one routing domain to another

routing domain.

redistribute protocol [process-id] {level-1 | level-1-2 |

level-2} [autonomous-system-number] [metric

Step 4

{metric-value | transparent}] [metric-type type-value]

• In the example, Routing Information Protocol (RIP)

subnets are redistributed into the OSPF domain.

[match {internal | external 1 | external 2}] [tag tag-value]

[route-map map-tag] [subnets] [nssa-only]

Example:

Device(config-router)# redistribute rip subnets

Defines the interfaces on which OSPF runs and the area ID

for those interfaces.

network ip-address wildcard-mask area area-id

Example:

Step 5

Device(config-router)# network 192.168.129.11

0.0.0.255 area 1

Configures a Not-So-Stubby Area (NSSA) area.

area area-id nssa [no-redistribution]

[default-information-originate [metric] [metric-type]]

[no-summary] [nssa-only]

Step 6

Example:

Device(config-router)# area 1 nssa

Controls the route summarization and filtering during the

translation and limits the summary to NSSA areas.

summary-address prefix mask [not-advertise] [tag tag]

[nssa-only]

Example:

Step 7

Device(config-router)# summary-address 10.1.0.0

255.255.0.0 not-advertise

Exits router configuration mode and returns to privileged

EXEC mode.

end

Example:

Step 8

Device(config-router)# end

Configuring OSPF

Configuring an OSPFv2 NSSA Area and Its Parameters

Configuring an NSSA ABR as a Forced NSSA LSA Translator

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. area area-id nssa translate type7 always

5. area area-id nssa translate type7 suppress-fa

6. end

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

• Enter your password if prompted.

Device> enable

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Enables OSPF routing and enters router configuration mode.

router ospf process-id

Step 3

Example:

• The process-id argument identifies the OSPF process.

The range is from 1 to 65535.

Device(config)# router ospf 1

Configures a Not-So-Stubby Area Area Border Router

(NSSA ABR) device as a forced NSSA Link State

Advertisement (LSA) translator.

area area-id nssa translate type7 always

Example:

Device(config-router)# area 10 nssa translate type7

always

Step 4

You can use the always keyword in the area

nssa translate command to configure an NSSA

ABR device as a forced NSSA LSA translator.

This command can be used if RFC 3101 is

disabled and RFC 1587 is used.

Note

Allows ABR to suppress the forwarding address in

translated Type-5 LSA.

area area-id nssa translate type7 suppress-fa

Example:

Step 5

Device(config-router)# area 10 nssa translate type7

suppress-fa

Exits router configuration mode and returns to privileged

EXEC mode.

end

Example:

Step 6

Configuring OSPF

Configuring an NSSA ABR as a Forced NSSA LSA Translator

PurposeCommand or Action

Device(config-router)# end

Disabling RFC 3101 Compatibility and Enabling RFC 1587 Compatibility

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. compatible rfc1587

5. end

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

• Enter your password if prompted.

Device> enable

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Enables OSPF routing and enters router configuration mode.

router ospf process-id

Step 3

Example:

• The process-id argument identifies the OSPF process.

Device(config)# router ospf 1

• Use router ospf process-id command to enable

OSPFv2 routing.

Enables the device to be RFC 1587 compliant.compatible rfc1587

Example:

Step 4

Device(config-router)# compatible rfc1587

Exits router configuration mode and returns to privileged

EXEC mode.

end

Example:

Step 5

Device(config-router)# end

Configuring OSPF

Disabling RFC 3101 Compatibility and Enabling RFC 1587 Compatibility

Configuring OSPF NSSA Parameters

Prerequisites

Evaluate the following considerations before you implement this feature:

• You can set a Type 7 default route that can be used to reach external destinations. When configured, the

device generates a Type 7 default into the Not-So-Stubby Area (NSSA or the NSSA Area Border Router

(ABR).

• Every device within the same area must agree that the area is NSSA; otherwise, the devices cannot

communicate.

Configuring Route Summarization Between OSPF Areas

Configuring Route Summarization When Redistributing Routes into OSPF

SUMMARY STEPS

1. summary-address {ip-address mask | prefix mask} [not-advertise][tag tag [nssa-only]

DETAILED STEPS

PurposeCommand or Action

Specifies an address and mask that covers redistributed

routes, so that only one summary route is advertised.

summary-address {ip-address mask | prefix mask}

[not-advertise][tag tag [nssa-only]

Example:

Step 1

• You can use the optional not-advertise keyword to

filter out a set of routes.

Device#(config-router) summary-address 10.1.0.0

255.255.0.0

Establishing Virtual Links

SUMMARY STEPS

1. area area-id virtual-link router-id [authentication [message-digest | null]] [hello-interval seconds]

[retransmit-interval seconds] [transmit-delay seconds] [dead-interval seconds] [authentication-key

key | message-digest-key key-id md5 key]

DETAILED STEPS

PurposeCommand or Action

Establishes a virtual link.

area area-id virtual-link router-id [authentication

[message-digest | null]] [hello-interval seconds]

Step 1

[retransmit-interval seconds] [transmit-delay seconds]

[dead-interval seconds] [authentication-key key |

message-digest-key key-id md5 key]

Configuring OSPF

Configuring OSPF NSSA Parameters

PurposeCommand or Action

Example:

Device(config-router-af)# area 1 virtual-link

10.1.1.1 router1

Generating a Default Route

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. default-information originate [always] [metric metric-value] [metric-type type-value] [route-map

map-name]

5. end

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

• Enter your password if prompted.

Device> enable

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Enables OSPF routing and enters router configuration mode.

router ospf process-id

Example:

Step 3

Device(config)# router ospf 109

Forces the ASBR to generate a default route into the OSPF

routing domain.

default-information originate [always] [metric

metric-value] [metric-type type-value] [route-map

map-name]

Step 4

The always keyword includes the following

exception when a route map is used. When a

route map is used, the origination of the default

route by OSPF is not bound to the existence of

a default route in the routing table.

Note

Example:

Device(config-router)# default-information

originate always

Exits router configuration mode and returns to privileged

EXEC mode.

end

Example:

Step 5

Device(config-router)# end

Configuring OSPF

Generating a Default Route

Configuring Lookup of DNS Names

SUMMARY STEPS

1. enable

2. configure terminal

3. ip ospf name-lookup

4. end

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

• Enter your password if prompted.

Device> enable

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Enables OSPF routing and enters router configuration mode.ip ospf name-lookup

Example:

Step 3

Device# ip ospf name-lookup

Exits global configuration mode and returns to privileged

EXEC mode.

end

Example:

Step 4

Device(config)# end

Forcing the Router ID Choice with a Loopback Interface

SUMMARY STEPS

1. configure terminal

2. interface type number

3. ip address ip-address mask

DETAILED STEPS

PurposeCommand or Action

Enters global configuration mode.configure terminal

Example:

Step 1

Configuring OSPF

Configuring Lookup of DNS Names

PurposeCommand or Action

Device# configure terminal

Creates a loopback interface and enters interface

configuration mode.

interface type number

Example:

Step 2

Device(config)# interface loopback 0

Assigns an IP address to this interface.

ip address ip-address mask

Example:

Step 3

Device#(config-if) ip address 192.108.1.27

255.255.255.0

Controlling Default Metrics

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. auto-cost reference-bandwidth ref-bw

5. end

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

• Enter your password if prompted.

Device> enable

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Enables OSPF routing and enters router configuration mode.

router ospf process-id

Example:

Step 3

Device# router ospf 109

Differentiates high -bandwidth links.

auto-cost reference-bandwidth ref-bw

Example:

Step 4

Configuring OSPF

Controlling Default Metrics

PurposeCommand or Action

Device(config-router)# auto-cost

reference-bandwidth 101

Exits router configuration mode and returns to privileged

EXEC mode.

end

Example:

Step 5

Device(config-router)# end

Changing the OSPF Administrative Distances

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. distance ospf {intra-area | inter-area | external} dist

5. end

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

• Enter your password if prompted.

Device> enable

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Enables OSPF routing and enters router configuration mode.

router ospf process-id

Example:

Step 3

Device(config)# router ospf 109

Changes the OSPF distance values.

distance ospf {intra-area | inter-area | external} dist

Example:

Step 4

Device(config-router)# distance ospf external 200

Exits router configuration mode and returns to privileged

EXEC mode.

end

Example:

Step 5

Configuring OSPF

Changing the OSPF Administrative Distances

PurposeCommand or Action

Device(config-router)# end

Configuring OSPF on Simplex Ethernet Interfaces

PurposeCommand

Suppresses the sending of hello packets through the

specified interface.

passive-interface interface-type

interface-number

Configuring Route Calculation Timers

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. timers throttle spf spf-start spf-hold spf-max-wait

5. end

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

• Enter your password if prompted.

Device> enable

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Enables OSPF routing and enters router configuration mode.

router ospf process-id

Example:

Step 3

Device(config)# router ospf 109

Configures route calculation timers.

timers throttle spf spf-start spf-hold spf-max-wait

Example:

Step 4

Device(config-router)# timers throttle spf 5 1000

9000

Configuring OSPF

Configuring OSPF on Simplex Ethernet Interfaces

PurposeCommand or Action

Exits router configuration mode and returns to privileged

EXEC mode.

end

Example:

Step 5

Device(config-router)# end

Configuring OSPF over On-Demand Circuits

SUMMARY STEPS

1. router ospf process-id

2. interface type number

3. ip ospf demand-circuit

DETAILED STEPS

PurposeCommand or Action

Enables OSPF operation.

router ospf process-id

Step 1

Enters interface configuration mode.

interface type number

Step 2

Configures OSPF over an on-demand circuit.ip ospf demand-circuit

Step 3

What to do next

You can prevent an interface from accepting demand-circuit requests from other routers to by specifying the

ignore keyword in the ip ospf demand-circuit command.

Note

Prerequisites

Evaluate the following considerations before implementing the On-Demand Circuits feature:

• Because LSAs that include topology changes are flooded over an on-demand circuit, we recommend

that you put demand circuits within OSPF stub areas or within NSSAs to isolate the demand circuits

from as many topology changes as possible.

• Every router within a stub area or NSSA must have this feature loaded in order to take advantage of the

on-demand circuit functionality. If this feature is deployed within a regular area, all other regular areas

must also support this feature before the demand circuit functionality can take effect because Type 5

external LSAs are flooded throughout all areas.

• Hub-and-spoke network topologies that have a point-to-multipoint (P2MP) OSPF interface type on a

hub might not revert to nondemand circuit mode when needed. You must simultaneously reconfigure

OSPF on all interfaces on the P2MP segment when reverting them from demand circuit mode to

nondemand circuit mode.

Configuring OSPF

Configuring OSPF over On-Demand Circuits

• Do not implement this feature on a broadcast-based network topology because the overhead protocols

(such as hello and LSA packets) cannot be successfully suppressed, which means the link will remain

up.

• Configuring the router for an OSPF on-demand circuit with an asynchronous interface is not a supported

configuration. The supported configuration is to use dialer interfaces on both ends of the circuit. For

more information, refer to Why OSPF Demand Circuit Keeps Bringing Up the Link .

Logging Neighbors Going Up or Down

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. log-adjacency-changes [detail]

5. end

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

• Enter your password if prompted.

Device> enable

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Enables OSPF routing and enters router configuration mode.

router ospf process-id

Example:

Step 3

Device(config)# router ospf 109

Changes the group pacing of LSAs.log-adjacency-changes [detail]

Example:

Step 4

Configure the log-adjacency-changes command

if you want to know about OSPF neighbors going

up or down without turning on the debug ip ospf

adjacency EXEC command because the

log-adjacency-changes command provides a

higher-level view of the peer relationship with

less output. Configure the

log-adjacency-changes detail command if you

want to see messages for each state change.

Note

Device(config-router)# log-adjacency-changes detail

Configuring OSPF

Logging Neighbors Going Up or Down

PurposeCommand or Action

Exits router configuration mode and returns to privileged

EXEC mode.

end

Example:

Step 5

Device(config-router)# end

Changing the LSA Group Pacing Interval

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. timers pacing lsa-group seconds

5. end

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

• Enter your password if prompted.

Device> enable

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Enables OSPF routing and enters router configuration mode.

router ospf process-id

Example:

Step 3

Device(config)# router ospf 109

Changes the group pacing of LSAs.

timers pacing lsa-group seconds

Example:

Step 4

Device(config-router)# timers pacing lsa-group 60

Exits router configuration mode and returns to privileged

EXEC mode.

end

Example:

Step 5

Device(config-router)# end

Configuring OSPF

Changing the LSA Group Pacing Interval

Blocking OSPF LSA Flooding

PurposeCommand

Blocks the flooding of OSPF LSA packets to the interface.

ip ospf database-filter all out

On point-to-multipoint networks, to block flooding of OSPF LSAs, use the following command in router

configuration mode:

PurposeCommand

Blocks the flooding of OSPF LSA packets to the

specified neighbor.

neighbor ip-address database-filter

all out

Reducing LSA Flooding

PurposeCommand

Suppresses the unnecessary flooding of LSAs in stable topologies.

ip ospf flood-reduction

Ignoring MOSPF LSA Packets

PurposeCommand

Prevents the router from generating syslog messages when it receives MOSPF LSA

packets.

ignore lsa mospf

Monitoring and Maintaining OSPF

PurposeCommand

Displays general information about

OSPF routing processes.

show ip ospf [process-id]

Displays the internal OSPF routing

table entries to the ABR and ASBR.

show ip ospf border-routers

Configuring OSPF

Blocking OSPF LSA Flooding

PurposeCommand

Displays lists of information related

to the OSPF database.

Configuring OSPF

Monitoring and Maintaining OSPF

PurposeCommand

show ip ospf [process-id

[area-id]] database

show ip ospf [process-id

[area-id]] database [database-summary]

show ip ospf [process-id

[area-id]] database [router] [self-originate]

show ip ospf [process-id

[area-id]] database [router] [adv-router [ip-address]]

show ip ospf [process-id

[area-id]] database [router] [link-state-id]

show ip ospf [process-id

[area-id]] database [network] [link-state-id]

show ip ospf [process-id

[area-id]] database [summary] [link-state-id]

show ip ospf [process-id

[area-id]] database [asbr-summary] [link-state-id]

show ip ospf [process-id

[Router# area-id]] database [external] [link-state-id]

show ip ospf [process-id

[area-id]] database [nssa-external] [link-state-id]

show ip ospf [process-id

[area-id]] database [opaque-link] [link-state-id]

Configuring OSPF

Monitoring and Maintaining OSPF

PurposeCommand

show ip ospf [process-id

[area-id]] database [opaque-area] [link-state-id]

show ip ospf [process-id

[area-id]] database [opaque-as] [link-state-id]

Displays a list of LSAs waiting to be

flooded over an interface (to observe

OSPF packet pacing).

show ip ospf flood-list interface type

Displays OSPF-related interface

information.

show ip ospf interface [type number]

Displays OSPF neighbor information

on a per-interface basis.

show ip ospf neighbor [interface-name] [neighbor-id]

detail

Displays a list of all LSAs requested

by a router.

show ip ospf request-list [neighbor] [interface]

[interface-neighbor]

Displays a list of all LSAs waiting to

be re-sent.

show ip ospf retransmission-list [neighbor]

[interface] [interface-neighbor]

Displays a list of all summary address

redistribution information configured

under an OSPF process.

show ip ospf [process-id] summary-address

Displays OSPF-related virtual links

information.

show ip ospf virtual-links

To restart an OSPF process, use the following command in EXEC mode:

PurposeCommand

Clears redistribution based on the OSPF routing

process ID. If the pid option is not specified, all OSPF

processes are cleared.

clear ip ospf [pid] {process |

redistribution | counters [neighbor

[ neighbor - interface]

[neighbor-id]]}

Displaying OSPF Update Packet Pacing

SUMMARY STEPS

1. show ip ospf flood-list interface-type interface-number

Configuring OSPF

Displaying OSPF Update Packet Pacing

DETAILED STEPS

PurposeCommand or Action

Displays a list of OSPF LSAs waiting to be flooded over

an interface.

show ip ospf flood-list interface-type interface-number

Example:

Step 1

Device> show ip ospf flood-list ethernet 1

Restrictions for OSPF

On systems with a large number of interfaces, it may be possible to configure OSPF such that the number of

links advertised in the router LSA causes the link-state update packet to exceed the size of a “huge” Cisco

buffer. To resolve this problem, reduce the number of OSPF links or increase the huge buffer size by entering

the buffers huge size size command.

A link-state update packet containing a router LSA typically has a fixed overhead of 196 bytes, and an

additional 12 bytes are required for each link description. With a huge buffer size of 18024 bytes, there can

be a maximum of 1485 link descriptions.

Because the maximum size of an IP packet is 65,535 bytes, there is still an upper bound on the number of

links possible on a router.

Configuration Examples for OSPF

Example: OSPF Point-to-Multipoint

In the figure below, Router 1 uses data-link connection identifier (DLCI) 201 to communicate with Router 2,

DLCI 202 to communicate with Router 4, and DLCI 203 to communicate with Router 3. Router 2 uses DLCI

101 to communicate with Router 1 and DLCI 102 to communicate with Router 3. Router 3 communicates

with Router 2 (DLCI 401) and Router 1 (DLCI 402). Router 4 communicates with Router 1 (DLCI 301).

Configuration examples follow the figure.

Figure 4: OSPF Point-to-Multipoint Example

Router 1 Configuration

hostname Router 1

Configuring OSPF

Restrictions for OSPF

interface serial 1

ip address 10.0.0.2 255.0.0.0

ip ospf network point-to-multipoint

encapsulation frame-relay

frame-relay map ip 10.0.0.1 201 broadcast

frame-relay map ip 10.0.0.3 202 broadcast

frame-relay map ip 10.0.0.4 203 broadcast

router ospf 1

network 10.0.0.0 0.0.0.255 area 0

Router 2 Configuration

hostname Router 2

interface serial 0

ip address 10.0.0.1 255.0.0.0

ip ospf network point-to-multipoint

encapsulation frame-relay

frame-relay map ip 10.0.0.2 101 broadcast

frame-relay map ip 10.0.0.4 102 broadcast

router ospf 1

network 10.0.0.0 0.0.0.255 area 0

Router 3 Configuration

hostname Router 3

interface serial 3

ip address 10.0.0.4 255.0.0.0

ip ospf network point-to-multipoint

encapsulation frame-relay

clock rate 1000000

frame-relay map ip 10.0.0.1 401 broadcast

frame-relay map ip 10.0.0.2 402 broadcast

router ospf 1

network 10.0.0.0 0.0.0.255 area 0

Router 4 Configuration

hostname Router 4

interface serial 2

ip address 10.0.0.3 255.0.0.0

ip ospf network point-to-multipoint

encapsulation frame-relay

clock rate 2000000

frame-relay map ip 10.0.0.2 301 broadcast

router ospf 1

network 10.0.0.0 0.0.0.255 area 0

Example: OSPF Point-to-Multipoint with Broadcast

The following example illustrates a point-to-multipoint network with broadcast:

Configuring OSPF

Example: OSPF Point-to-Multipoint with Broadcast

interface Serial0

ip address 10.0.1.1 255.255.255.0

encapsulation frame-relay

ip ospf cost 100

ip ospf network point-to-multipoint

frame-relay map ip 10.0.1.3 202 broadcast

frame-relay map ip 10.0.1.4 203 broadcast

frame-relay map ip 10.0.1.5 204 broadcast

frame-relay local-dlci 200

router ospf 1

network 10.0.1.0 0.0.0.255 area 0

neighbor 10.0.1.5 cost 5

neighbor 10.0.1.4 cost 10

The following example shows the configuration of the neighbor at 10.0.1.3:

interface serial 0

ip address 10.0.1.3 255.255.255.0

ip ospf network point-to-multipoint

encapsulation frame-relay

frame-relay local-dlci 301

frame-relay map ip 10.0.1.1 300 broadcast

no shutdown

router ospf 1

network 10.0.1.0 0.0.0.255 area 0

The output shown for neighbors in the first configuration is as follows:

Device# show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

172.16.1.1 1 FULL/ - 00:01:50 10.0.1.5 Serial0

172.16.1.4 1 FULL/ - 00:01:47 10.0.1.4 Serial0

172.16.1.8 1 FULL/ - 00:01:45 10.0.1.3 Serial0

The route information in the first configuration is as follows:

Device# show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default

U - per-user static route, o - ODR

Gateway of last resort is not set

C 1.0.0.0/8 is directly connected, Loopback0

10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks

O 10.0.1.3/32 [110/100] via 10.0.1.3, 00:39:08, Serial0

C 10.0.1.0/24 is directly connected, Serial0

O 10.0.1.5/32 [110/5] via 10.0.1.5, 00:39:08, Serial0

O 10.0.1.4/32 [110/10] via 10.0.1.4, 00:39:08, Serial0

Example: OSPF Point-to-Multipoint with Nonbroadcast

The following example illustrates a point-to-multipoint network with nonbroadcast:

interface Serial0

ip address 10.0.1.1 255.255.255.0

Configuring OSPF

Example: OSPF Point-to-Multipoint with Nonbroadcast

ip ospf network point-to-multipoint non-broadcast

encapsulation frame-relay

no keepalive

frame-relay local-dlci 200

frame-relay map ip 10.0.1.3 202

frame-relay map ip 10.0.1.4 203

frame-relay map ip 10.0.1.5 204

no shutdown

router ospf 1

network 10.0.1.0 0.0.0.255 area 0

neighbor 10.0.1.3 cost 5

neighbor 10.0.1.4 cost 10

neighbor 10.0.1.5 cost 15

The following example is the configuration for the router on the other side:

interface Serial9/2

ip address 10.0.1.3 255.255.255.0

encapsulation frame-relay

ip ospf network point-to-multipoint non-broadcast

no ip mroute-cache

no keepalive

no fair-queue

frame-relay local-dlci 301

frame-relay map ip 10.0.1.1 300

no shutdown

router ospf 1

network 10.0.1.0 0.0.0.255 area 0

The output shown for neighbors in the first configuration is as follows:

Device# show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

172.16.1.1 1 FULL/ - 00:01:52 10.0.1.5 Serial0

172.16.1.4 1 FULL/ - 00:01:52 10.0.1.4 Serial0

172.16.1.8 1 FULL/ - 00:01:52 10.0.1.3 Serial0

Example: Variable-Length Subnet Masks

OSPF, static routes, and IS-IS support variable-length subnet masks (VLSMs). With VLSMs, you can use

different masks for the same network number on different interfaces, which allows you to conserve IP addresses

and more efficiently use available address space.

In the following example, a 30-bit subnet mask is used, leaving two bits of address space reserved for serial-line

host addresses. There is sufficient host address space for two host endpoints on a point-to-point serial link.

interface ethernet 0

ip address 172.16.10.1 255.255.255.0

! 8 bits of host address space reserved for ethernets

interface serial 0

ip address 172.16.20.1 255.255.255.252

! 2 bits of address space reserved for serial lines

! Router is configured for OSPF and assigned AS 107

router ospf 107

! Specifies network directly connected to the router

network 172.16.0.0 0.0.255.255 area 0.0.0.0

Configuring OSPF

Example: Variable-Length Subnet Masks

Example: Configuring OSPF NSSA

In the following example, an Open Shortest Path First (OSPF) stub network is configured to include OSPF

Area 0 and OSPF Area 1, using five devices. Device 3 is configured as the NSSA Autonomous System Border

Router (ASBR). Device 2 configured to be the NSSA Area Border Router (ABR). OSPF Area 1 is defined

as a Not-So-Stubby Area (NSSA).

Device 1

hostname Device1

interface Loopback1

ip address 10.1.0.1 255.255.255.255

interface Ethernet0/0

ip address 192.168.0.1 255.255.255.0

ip ospf 1 area 0

no cdp enable

interface Serial10/0

description Device2 interface s11/0

ip address 192.168.10.1 255.255.255.0

ip ospf 1 area 1

serial restart-delay 0

no cdp enable

router ospf 1

area 1 nssa

end

Device 2

hostname Device2

interface Loopback1

ip address 10.1.0.2 255.255.255.255

interface Serial10/0

description Device1 interface s11/0

no ip address

shutdown

serial restart-delay 0

no cdp enable

interface Serial11/0

description Device1 interface s10/0

ip address 192.168.10.2 255.255.255.0

ip ospf 1 area 1

serial restart-delay 0

no cdp enable

interface Serial14/0

description Device3 interface s13/0

ip address 192.168.14.2 255.255.255.0

ip ospf 1 area 1

serial restart-delay 0

no cdp enable

Configuring OSPF

Example: Configuring OSPF NSSA

router ospf 1

area 1 nssa

end

Device 3

hostname Device3

interface Loopback1

ip address 10.1.0.3 255.255.255.255

interface Ethernet3/0

ip address 192.168.3.3 255.255.255.0

no cdp enable

interface Serial13/0

description Device2 interface s14/0

ip address 192.168.14.3 255.255.255.0

ip ospf 1 area 1

serial restart-delay 0

no cdp enable

router ospf 1

log-adjacency-changes

area 1 nssa

redistribute rip subnets

router rip

version 2

redistribute ospf 1 metric 15

network 192.168.3.0

end

Device 4

hostname Device4

interface Loopback1

ip address 10.1.0.4 255.255.255.255

interface Ethernet3/0

ip address 192.168.3.4 255.255.255.0

no cdp enable

interface Ethernet4/1

ip address 192.168.41.4 255.255.255.0

router rip

version 2

network 192.168.3.0

network 192.168.41.0

end

Device 5

hostname Device5

interface Loopback1

Configuring OSPF

Example: Configuring OSPF NSSA

ip address 10.1.0.5 255.255.255.255

interface Ethernet0/0

ip address 192.168.0.10 255.255.255.0

ip ospf 1 area 0

no cdp enable

interface Ethernet1/1

ip address 192.168.11.10 255.255.255.0

ip ospf 1 area 0

router ospf 1

end

Example: OSPF NSSA Area with RFC 3101 Disabled and RFC 1587 Active

In the following example, the output for the show ip ospf and show ip ospf database nssa commands shows

an Open Shortest Path First Not-So-Stubby Area (OSPF NSSA) area where RFC 3101 is disabled, RFC 1587

is active, and an NSSA Area Border Router (ABR) device is configured as a forced NSSA LSA translator. If

RFC 3101 is disabled, the forced NSSA LSA translator remains inactive.

Device# show ip ospf

Routing Process "ospf 1" with ID 10.0.2.1

Start time: 00:00:25.512, Time elapsed: 00:01:02.200

Supports only single TOS(TOS0) routes

Supports opaque LSA

Supports Link-local Signaling (LLS)

Supports area transit capability

Supports NSSA (compatible with RFC 1587)

Event-log enabled, Maximum number of events: 1000, Mode: cyclic

Router is not originating router-LSAs with maximum metric

Initial SPF schedule delay 5000 msecs

Minimum hold time between two consecutive SPFs 10000 msecs

Maximum wait time between two consecutive SPFs 10000 msecs

Incremental-SPF disabled

Minimum LSA interval 5 secs

Minimum LSA arrival 1000 msecs

LSA group pacing timer 240 secs

Interface flood pacing timer 33 msecs

Retransmission pacing timer 66 msecs

Number of external LSA 0. Checksum Sum 0x000000

Number of opaque AS LSA 0. Checksum Sum 0x000000

Number of DCbitless external and opaque AS LSA 0

Number of DoNotAge external and opaque AS LSA 0

Number of areas in this router is 1. 0 normal 0 stub 1 nssa

Number of areas transit capable is 0

External flood list length 0

IETF NSF helper support enabled

Cisco NSF helper support enabled

Reference bandwidth unit is 100 mbps

Area 1

Number of interfaces in this area is 1

It is a NSSA area

Configured to translate Type-7 LSAs, inactive (RFC3101 support

disabled)

Area has no authentication

SPF algorithm last executed 00:00:07.160 ago

SPF algorithm executed 3 times

Area ranges are

Configuring OSPF

Example: OSPF NSSA Area with RFC 3101 Disabled and RFC 1587 Active

Number of LSA 3. Checksum Sum 0x0245F0

Number of opaque link LSA 0. Checksum Sum 0x000000

Number of DCbitless LSA 0

Number of indication LSA 0

Number of DoNotAge LSA 0

Flood list length 0

The table below describes the show ip ospf display fields and their descriptions.

Table 1: show ip ospf Field Descriptions

DescriptionField

Specifies that RFC 1587 is active or that the OSPF NSSA area

is RFC 1587 compatible.

Supports NSSA (compatible with RFC

1587)

Specifies that OSPF NSSA area has an ABR device configured

to act as a forced translator of Type 7 LSAs. However, it is

inactive because RFC 3101 is disabled

Configured to translate Type-7 LSAs,

inactive (RFC3101 support disabled)

Device2# show ip ospf database nssa

Router Link States (Area 1)

LS age: 28

Options: (No TOS-capability, DC)

LS Type: Router Links

Link State ID: 10.0.2.1

Advertising Router: 10.0.2.1

LS Seq Number: 80000004

Checksum: 0x5CA2

Length: 36

Area Border Router

AS Boundary Router

Unconditional NSSA translator

Number of Links: 1

Link connected to: a Stub Network

(Link ID) Network/subnet number: 192.0.2.5

(Link Data) Network Mask: 255.255.255.0

Number of MTID metrics: 0

TOS 0 Metrics: 10

The table below describes the show ip ospf database nssa display fields and their descriptions.

Table 2: show ip ospf database nssa Field Descriptions

DescriptionField

Specifies that NSSA ASBR device is a forced NSSA LSA translatorUnconditional NSSA translator

Example: OSPF Routing and Route Redistribution

OSPF typically requires coordination among many internal routers, ABRs, and ASBRs. At a minimum,

OSPF-based routers can be configured with all default parameter values, with no authentication, and with

interfaces assigned to areas.

Three types of examples follow:

• The first is a simple configuration illustrating basic OSPF commands.

Configuring OSPF

Example: OSPF Routing and Route Redistribution

• The second example illustrates a configuration for an internal router, ABR, and ASBRs within a single,

arbitrarily assigned, OSPF autonomous system.

• The third example illustrates a more complex configuration and the application of various tools available

for controlling OSPF-based routing environments.

Example: Basic OSPF Configuration

The following example illustrates a simple OSPF configuration that enables OSPF routing process 9000,

attaches Ethernet interface 0 to area 0.0.0.0, and redistributes RIP into OSPF and OSPF into RIP:

interface ethernet 0

ip address 10.93.1.1 255.255.255.0

ip ospf cost 1

interface ethernet 1

ip address 10.94.1.1 255.255.255.0

router ospf 9000

network 10.93.0.0 0.0.255.255 area 0.0.0.0

redistribute rip metric 1 subnets

router rip

network 10.94.0.0

redistribute ospf 9000

default-metric 1

Example: Basic OSPF Configuration for Internal Router ABR and ASBRs

The following example illustrates the assignment of four area IDs to four IP address ranges. In the example,

OSPF routing process 109 is initialized, and four OSPF areas are defined: 10.9.50.0, 2, 3, and 0. Areas

10.9.50.0, 2, and 3 mask specific address ranges, and area 0 enables OSPF for all other networks.

router ospf 109

network 192.168.10.0 0.0.0.255 area 10.9.50.0

network 192.168.20.0 0.0.255.255 area 2

network 192.168.30.0 0.0.0.255 area 3

network 192.168.40.0 255.255.255.255 area 0

! Interface Ethernet0 is in area 10.9.50.0:

interface ethernet 0

ip address 192.168.10.5 255.255.255.0

! Interface Ethernet1 is in area 2:

interface ethernet 1

ip address 192.168.20.5 255.255.255.0

! Interface Ethernet2 is in area 2:

interface ethernet 2

ip address 192.168.20.7 255.255.255.0

! Interface Ethernet3 is in area 3:

interface ethernet 3

ip address 192.169.30.5 255.255.255.0

! Interface Ethernet4 is in area 0:

interface ethernet 4

ip address 192.168.40.1 255.255.255.0

Configuring OSPF

Example: Basic OSPF Configuration

! Interface Ethernet5 is in area 0:

interface ethernet 5

ip address 192.168.40.12 255.255.0.0

Each network area router configuration command is evaluated sequentially, so the order of these commands

in the configuration is important. The Cisco software sequentially evaluates the address/wildcard-mask pair

for each interface. See the network area command page in the Cisco IOS IP Routing: OSPF Command

Reference for more information.

Consider the first network area command. Area ID 10.9.50.0 is configured for the interface on which subnet

192.168.10.0 is located. Assume that a match is determined for Ethernet interface 0. Ethernet interface 0 is

attached to area 10.9.50.0 only.

The second network area command is evaluated next. For area 2, the same process is then applied to all

interfaces (except Ethernet interface 0). Assume that a match is determined for Ethernet interface 1. OSPF is

then enabled for that interface, and Ethernet interface 1 is attached to area 2.

This process of attaching interfaces to OSPF areas continues for all network area commands. Note that the

last network area command in this example is a special case. With this command, all available interfaces

(not explicitly attached to another area) are attached to area 0.

Example: Complex Internal Router with ABR and ASBR

The following example outlines a configuration for several routers within a single OSPF autonomous system.

The figure below provides a general network map that illustrates this sample configuration.

Configuring OSPF

Example: Complex Internal Router with ABR and ASBR

Figure 5: Sample OSPF Autonomous System Network Map

In this configuration, five routers are configured with OSPF:

• Router A and Router B are both internal routers within area 1.

• Router C is an OSPF ABR. Note that for Router C, Area 1 is assigned to E3 and area 0 is assigned to

S0.

• Router D is an internal router in area 0 (backbone area). In this case, both network router configuration

commands specify the same area (area 0, or the backbone area).

• Router E is an OSPF ASBR. Note that BGP routes are redistributed into OSPF and that these routes are

advertised by OSPF.

You do not need to include definitions of all areas in an OSPF autonomous system in the configuration of all

routers in the autonomous system. Only the directly connected areas must be defined. In the example that

follows, routes in area 0 are learned by the routers in area 1 (Router A and Router B) when the ABR (Router

C) injects summary LSAs into area 1.

Note

Configuring OSPF

Example: Complex Internal Router with ABR and ASBR

The OSPF domain in BGP autonomous system 109 is connected to the outside world via the BGP link to the

external peer at IP address 10.0.0.6. Sample configurations follow.

Following is the sample configuration for the general network map shown in the figure above.

Router A Configuration—Internal Router

interface ethernet 1

ip address 192.168.1.1 255.255.255.0

router ospf 1

network 192.168.0.0 0.0.255.255 area 1

Router B Configuration—Internal Router

interface ethernet 2

ip address 192.168.1.2 255.255.255.0

router ospf 202

network 192.168.0.0 0.0.255.255 area 1

Router C Configuration—ABR

interface ethernet 3

ip address 192.168.1.3 255.255.255.0

interface serial 0

ip address 192.168.2.3 255.255.255.0

router ospf 999

network 192.168.1.0 0.0.0.255 area 1

network 192.168.2.0 0.0.0.255 area 0

Router D Configuration—Internal Router

interface ethernet 4

ip address 10.0.0.4 255.0.0.0

interface serial 1

ip address 192.168.2.4 255.255.255.0

router ospf 50

network 192.168.2.0 0.0.0.255 area 0

network 10.0.0.0 0.255.255.255 area 0

Router E Configuration—ASBR

interface ethernet 5

ip address 10.0.0.5 255.0.0.0

interface serial 2

ip address 172.16.1.5 255.255.255.0

router ospf 65001

network 10.0.0.0 0.255.255.255 area 0

redistribute bgp 109 metric 1 metric-type 1

router bgp 109

network 192.168.0.0

network 10.0.0.0

neighbor 172.16.1.6 remote-as 110

Configuring OSPF

Example: Complex Internal Router with ABR and ASBR

Example: Complex OSPF Configuration for ABR

The following sample configuration accomplishes several tasks in setting up an ABR. These tasks can be split

into two general categories:

• Basic OSPF configuration

• Route redistribution

The specific tasks outlined in this configuration are detailed briefly in the following descriptions. The figure

below illustrates the network address ranges and area assignments for the interfaces.

Figure 6: Interface and Area Specifications for OSPF Sample Configuration

The basic configuration tasks in this example are as follows:

• Configure address ranges for Ethernet interface 0 through Ethernet interface 3.

• Enable OSPF on each interface.

• Set up an OSPF authentication password for each area and network.

• Assign link-state metrics and other OSPF interface configuration options.

• Create a stub area with area ID 36.0.0.0. (Note that the authentication and stub options of the area

router configuration command are specified with separate area command entries, but can be merged into

a single area command.)

• Specify the backbone area (area 0).

Configuration tasks associated with redistribution are as follows:

• Redistribute IGRP and RIP into OSPF with various options set (including including metric-type, metric,

tag, and subnet).

• Redistribute IGRP and OSPF into RIP.

The following is a sample OSPF configuration:

interface ethernet 0

Configuring OSPF

Example: Complex OSPF Configuration for ABR

ip address 192.0.2.201 255.255.255.0

ip ospf authentication-key abcdefgh

ip ospf cost 10

interface ethernet 1

ip address 172.19.251.202 255.255.255.0

ip ospf authentication-key ijklmnop

ip ospf cost 20

ip ospf retransmit-interval 10

ip ospf transmit-delay 2

ip ospf priority 4

interface ethernet 2

ip address 172.19.254.2 255.255.255.0

ip ospf authentication-key abcdefgh

ip ospf cost 10

interface ethernet 3

ip address 10.56.0.0 255.255.0.0

ip ospf authentication-key ijklmnop

ip ospf cost 20

ip ospf dead-interval 80

In the following configuration, OSPF is on network 172.16.0.0:

router ospf 201

network 10.10.0.0 0.255.255.255 area 10.10.0.0

network 192.42.110.0 0.0.0.255 area 192.42.110.0

network 172.16.0.0 0.0.255.255 area 0

area 0 authentication

area 10.10.0.0 stub

area 10.10.0.0 authentication

area 10.10.0.0 default-cost 20

area 192.42.110.0 authentication

area 10.10.0.0 range 10.10.0.0 255.0.0.0

area 192.42.110.0 range 192.42.110.0 255.255.255.0

area 0 range 172.16.251.0 255.255.255.0

area 0 range 172.16.254.0 255.255.255.0

redistribute igrp 200 metric-type 2 metric 1 tag 200 subnets

redistribute rip metric-type 2 metric 1 tag 200

In the following configuration, IGRP autonomous system 200 is on 192.0.2.1:

router igrp 200

network 172.31.0.0

! RIP for 192.168.110

router rip

network 192.168.110.0

redistribute igrp 200 metric 1

redistribute ospf 201 metric 1

Examples: Route Map

The examples in this section illustrate the use of redistribution, with and without route maps. Examples from

the IP and Connectionless Network Service (CLNS) routing protocols are given.

The following example redistributes all OSPF routes into IGRP:

Configuring OSPF

Examples: Route Map

router igrp 109

redistribute ospf 110

The following example redistributes RIP routes with a hop count equal to 1 into OSPF. These routes will be

redistributed into OSPF as external LSAs with a metric of 5, a metric type of Type 1, and a tag equal to 1.

router ospf 109

redistribute rip route-map rip-to-ospf

route-map rip-to-ospf permit

match metric 1

set metric 5

set metric-type type1

set tag 1

The following example redistributes OSPF learned routes with tag 7 as a RIP metric of 15:

router rip

redistribute ospf 109 route-map 5

route-map 5 permit

match tag 7

set metric 15

The following example redistributes OSPF intra-area and interarea routes with next-hop routers on serial

interface 0 into BGP with an INTER_AS metric of 5:

router bgp 109

redistribute ospf 109 route-map 10

route-map 10 permit

match route-type internal

match interface serial 0

set metric 5

The following example redistributes two types of routes into the integrated IS-IS routing table (supporting

both IP and CLNS). The first type is OSPF external IP routes with tag 5; these routes are inserted into Level

2 IS-IS link state packets (LSPs) with a metric of 5. The second type is ISO-IGRP derived CLNS prefix routes

that match CLNS access list 2000; these routes will be redistributed into IS-IS as Level 2 LSPs with a metric

of 30.

router isis

redistribute ospf 109 route-map 2

redistribute iso-igrp nsfnet route-map 3

route-map 2 permit

match route-type external

match tag 5

set metric 5

set level level-2

route-map 3 permit

match address 2000

set metric 30

With the following configuration, OSPF external routes with tags 1, 2, 3, and 5 are redistributed into RIP with

metrics of 1, 1, 5, and 5, respectively. The OSPF routes with a tag of 4 are not redistributed.

router rip

Configuring OSPF

Examples: Route Map

redistribute ospf 109 route-map 1

route-map 1 permit

match tag 1 2

set metric 1

route-map 1 permit

match tag 3

set metric 5

route-map 1 deny

match tag 4

route map 1 permit

match tag 5

set metric 5

In the following configuration, a RIP-learned route for network 192.168.0.0 and an ISO-IGRP-learned route

with prefix 49.0001.0002 are redistributed into an IS-IS Level 2 LSP with a metric of 5:

router isis

redistribute rip route-map 1

redistribute iso-igrp remote route-map 1

route-map 1 permit

match ip address 1

match clns address 2

set metric 5

set level level-2

access-list 1 permit 192.168.0.0 0.0.255.255

clns filter-set 2 permit 49.0001.0002...

The following configuration example illustrates how a route map is referenced by the default-information

router configuration command. This type of reference is called conditional default origination. OSPF will

originate the default route (network 0.0.0.0) with a Type 2 metric of 5 if 172.16.0.0 is in the routing table.

Only routes external to the OSPF process can be used for tracking, such as non-OSPF routes or OSPF routes

from a separate OSPF process.

Note

route-map ospf-default permit

match ip address 1

set metric 5

set metric-type type-2

access-list 1 permit 172.16.0.0 0.0.255.255

router ospf 109

default-information originate route-map ospf-default

Example: Changing the OSPF Administrative Distances

The following configuration changes the external distance to 200, making it less trustworthy. The figure below

illustrates the example.

Configuring OSPF

Example: Changing the OSPF Administrative Distances

Figure 7: OSPF Administrative Distance

Router A Configuration

router ospf 1

redistribute ospf 2 subnet

distance ospf external 200

router ospf 2

redistribute ospf 1 subnet

distance ospf external 200

Router B Configuration

router ospf 1

redistribute ospf 2 subnet

distance ospf external 200

router ospf 2

redistribute ospf 1 subnet

distance ospf external 200

Example: OSPF over On-Demand Routing

The following configuration allows OSPF over an on-demand circuit, as shown in the figure below. Note that

the on-demand circuit is defined on one side only (BRI 0 on Router A); it is not required to be configured on

both sides.

Configuring OSPF

Example: OSPF over On-Demand Routing

Figure 8: OSPF over On-Demand Circuit

Router A Configuration

username RouterB password 7 060C1A2F47

isdn switch-type basic-5ess

ip routing

interface TokenRing0

ip address 192.168.50.5 255.255.255.0

no shutdown

interface BRI0

no cdp enable

description connected PBX 1485

ip address 192.168.45.30 255.255.255.0

encapsulation ppp

ip ospf demand-circuit

dialer map ip 192.0.2.6 name RouterB broadcast 61484

dialer-group 1

ppp authentication chap

no shutdown

router ospf 100

network 192.168.45.0 0.0.0.255 area 0

network 192.168.45.50 0.0.0.255 area 0

dialer-list 1 protocol ip permit

Router B Configuration

username RouterA password 7 04511E0804

isdn switch-type basic-5ess

ip routing

interface Ethernet0

ip address 192.168.50.16 255.255.255.0

no shutdown

interface BRI0

no cdp enable

description connected PBX 1484

ip address 192.168.45.17 255.255.255.0

encapsulation ppp

dialer map ip 192.168.45.19 name RouterA broadcast 61485

dialer-group 1

ppp authentication chap

no shutdown

router ospf 100

network 192.168.45.0 0.0.0.255 area 0

network 192.168.45.50 0.0.0.255 area 0

dialer-list 1 protocol ip permit

Configuring OSPF

Example: OSPF over On-Demand Routing

Example: LSA Group Pacing

The following example changes the OSPF pacing between LSA groups to 60 seconds:

router ospf

timers pacing lsa-group 60

Example: Blocking OSPF LSA Flooding

The following example prevents flooding of OSPF LSAs to broadcast, nonbroadcast, or point-to-point networks

reachable through Ethernet interface 0:

interface ethernet 0

ip ospf database-filter all out

The following example prevents flooding of OSPF LSAs to point-to-multipoint networks to the neighbor at

IP address 10.10.10.45:

router ospf 109

neighbor 10.10.10.45 database-filter all out

Example: Ignoring MOSPF LSA Packets

The following example configures the router to suppress the sending of syslog messages when it receives

MOSPF packets:

router ospf 109

ignore lsa mospf

Additional References for OSPF Not-So-Stubby Areas (NSSA)