iproute_ospf

OSPF Limit on Number of Redistributed Routes

Last Updated: February 26, 2010

Open Shortest Path First (OSPF) supports a user-defined maximum number of prefixes (routes) that are allowed to be redistributed into OSPF from other protocols or other OSPF processes. Such a limit could help prevent the router from being flooded by too many redistributed routes.

Finding Feature Information

For the latest feature information and caveats, see 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 for OSPF Limit on Number of Redistributed Routes" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

•Prerequisites for OSPF Limit on Number of Redistributed Routes

•Information About OSPF Limit on Number of Redistributed Routes

•How to Limit the Number of OSPF Redistributed Routes or Receive a Warning About the Number of OSPF Redistributed Routes

•Configuration Examples for OSPF Limit on Number of Redistributed Routes

•Additional References

•Feature Information for OSPF Limit on Number of Redistributed Routes

Prerequisites for OSPF Limit on Number of Redistributed Routes

It is presumed that you have OSPF configured in your network, along with another protocol or another OSPF process you are redistributing.

Information About OSPF Limit on Number of Redistributed Routes

If someone mistakenly injects a large number of IP routes into OSPF, perhaps by redistributing Border Gateway Protocol (BGP) into OSPF, the network can be severely flooded. Limiting the number of redistributed routes prevents this potential problem.

How to Limit the Number of OSPF Redistributed Routes or Receive a Warning About the Number of OSPF Redistributed Routes

This section contains the following procedures, which are mutually exclusive. That is, you cannot both limit redistributed prefixes and also choose to be warned.

•Limiting the Number of Redistributed Routes

•Requesting a Warning About the Number of Routes Redistributed into OSPF

Limiting the Number of Redistributed Routes

Note You cannot both limit redistributed prefixes and also choose to be warned.

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. redistribute protocol [process-id | as-number] [metric metric-value] [metric-type type-value] [match {internal | external 1 | external 2}] [tag tag-value] [route-map map-tag] [subnets]

5. redistribute maximum-prefix maximum [threshold]

6. end

7. show ip ospf [process-id]

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	router ospf process-id Example: Router(config)# router ospf 1	Configures an OSPF routing process.
Step 4	redistribute protocol [process-id | as-number] [metric metric-value] [metric-type type-value] [match {internal | external 1 | external 2}] [tag tag-value] [route-map map-tag] [subnets] Example: Router(config-router)# redistribute eigrp 10	Redistributes routes from one routing domain into another routing domain.
Step 5	redistribute maximum-prefix maximum [threshold] Example: Router(config-router)# redistribute maximum-prefix 100 80	Sets a maximum number of IP prefixes that are allowed to be redistributed into OSPF. •There is no default value for the maximum argument. •The threshold value defaults to 75 percent. Note If the warning-only keyword had been configured in this command, no limit would be enforced; a warning message is simply logged.
Step 6	end Example: Router(config-router)# end	Exits router configuration mode.
Step 7	show ip ospf [process-id] Example: Router# show ip ospf 1	(Optional) Displays general information about OSPF routing processes. •If a redistribution limit was configured, the output will include the maximum limit of redistributed prefixes and the threshold for warning messages.

Requesting a Warning About the Number of Routes Redistributed into OSPF

Note You cannot both limit redistributed prefixes and also choose to be warned.

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. redistribute protocol [process-id | as-number] [metric metric-value] [metric-type type-value] [match {internal | external 1 | external 2}] [tag tag-value] [route-map map-tag] [subnets]

5. redistribute maximum-prefix maximum [threshold] warning-only

6. end

DETAILED STEPS

Configuration Examples for OSPF Limit on Number of Redistributed Routes

This section contains the following examples:

•Example: OSPF Limit the Number of Redistributed Routes

•Example: Requesting a Warning About the Number of Redistributed Routes

Example: OSPF Limit the Number of Redistributed Routes

This example sets a maximum of 1200 prefixes that can be redistributed into OSPF process 1. Prior to reaching the limit, when the number of prefixes redistributed reaches 80 percent of 1200 (960 prefixes), a warning message is logged. Another warning is logged when the limit is reached and no more routes are redistributed.

router ospf 1 
 router-id 10.0.0.1 
 domain-id 5.6.7.8 
 log-adjacency-changes 
 timers lsa-interval 2 
 network 10.0.0.1 0.0.0.0 area 0 
 network 10.1.5.1 0.0.0.0 area 0 
 network 10.2.2.1 0.0.0.0 area 0 
 redistribute static subnets

 redistribute maximum-prefix 1200 80

Example: Requesting a Warning About the Number of Redistributed Routes

This example allows two warning messages to be logged, the first if the number of prefixes redistributed reaches 85 percent of 600 (510 prefixes), and the second if the number of redistributed routes reaches 600. However, the number of redistributed routes is not limited.

router ospf 1

 network 10.0.0.0 0.0.0.255 area 0 
 redistribute eigrp 10 subnets

 redistribute maximum-prefix 600 85 warning-only

Additional References

The following sections provide references related to the OSPF Limit on Number of Redistributed Routes feature.

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for OSPF Limit on Number of Redistributed Routes

Table 1 lists the release history for this feature.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 1 lists only the Cisco IOS XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.

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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

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