Configuring OSPF Limit on Number of Redistributed Routes

Restrictions for OSPF Limit on Number of Redistributed Routes

OSPFv3 Limit on Number of Redistributed Routes is supported only for the IPv6 address family.

Prerequisites for OSPF Limit on Number of Redistributed Routes

You must have Open Shortest Path First (OSPF) configured in your network either along with another protocol, or another OSPF process for redistribution.

Information About OSPF Limit on Number of Redistributed Routes

OSPF supports a user-defined maximum number of prefixes (routes) that can be redistributed into OSPF from other protocols or other OSPF processes. Such a limit helps prevent the device from being flooded by too many redistributed routes.

For example, if a large number of IP routes are sent into OSPF for a network that allows redistribution of Border Gateway Protocol (BGP) into OSPF, the network can get severely flooded. Limiting the number of redistributed routes prevents this potential problem.

From Cisco IOS XE Dublin 17.11.1, the command redistribute maximum-prefix maximum[threshold] is enabled with the default number of routes set at 10240 routes. The default number of routes is to protect the OSPF processes from being flooded with routes. You can still configure the number of routes using the redistribute maximum-prefix command.

The OSPF Limit on Number of Redistributed Routes feature is applicable to OSPF, OSPFv2 and OSPFv3.

How to Configure an OSPF Limit on the Number of Redistributed Routes

The following sections provide information on configuring an OSPF limit on the number of redistributed routes.


Note

The following procedures are mutually exclusive, that is, you can either limit the number of redistributed routes, or request a warning about the number of routes redistributed into OSPF.

Limiting the Number of OSPF Redistributed Routes

This task describes how to limit the number of OSPF redistributed routes. If the number of redistributed routes reaches the maximum value configured, no more routes are redistributed.

Procedure

  Command or Action Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode. Enter your password, if prompted.

Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

router ospf process-id

Example:

Device(config)# router ospf 1

Configures an OSPF routing process.

Step 4

redistribute protocol [process-id] [as-number] [include-connected {level-1 | level-1-2 | level-2} [metric metric-value ] [metric-type type-value] [nssa-only] [tag tag-value] [route-map map-tag]

Example:

Device(config-router-af)# redistribute eigrp 10

Redistributes routes from one routing domain into another routing domain.

Step 5

redistribute maximum-prefix maximum [threshold]

Example:

Device(config-router-af)# redistribute maximum-prefix 100 80

Sets a maximum number of IP prefixes that are allowed to be redistributed into OSPF.

  • The default value for the maximum argument is set at 10240 routes.

  • The threshold value defaults to 75 percent.

Note

 

If the warning-only keyword is configured in this command, no limit is enforced; a warning message is logged.

Step 6

end

Example:

Device(config-router)# end

Exits router configuration mode.

Limiting the Number of OSPFv3 Redistributed Routes

This task describes how to limit the number of OSPFv3 redistributed routes. If the number of redistributed routes reaches the maximum value configured, no more routes are redistributed.

Procedure

  Command or Action Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

Enter your password, if prompted.

Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

router ospfv3 process-id

Example:

Device(config)# router ospfv3 1

Configures an OSPFv3 routing process.

Step 4

address-family ipv6 [unicast]

Example:

Device(config-router)# address-family ipv6 unicast

Enters IPv6 address family configuration mode.

Step 5

redistribute protocol [process-id] [as-number] [include-connected {level-1 | level-1-2 | level-2} [metric metric-value ] [metric-type type-value] [nssa-only] [tag tag-value] [route-map map-tag]

Example:

Device(config-router-af)# redistribute eigrp 10

Redistributes routes from one routing domain into another routing domain.

Step 6

redistribute maximum-prefix maximum [threshold]

Example:

Device(config-router-af)# redistribute maximum-prefix 100 80

Sets a maximum number of IPv6 prefixes that are allowed to be redistributed into OSPFv3.

  • The default value for the maximum argument is set at 10240 routes.

  • The threshold value defaults to 75 percent.

Note

 

If the warning-only keyword is configured in this command, no limit is enforced; a warning message is logged.

Step 7

exit-address-family

Example:

Device(config-router-af)# exit-address-family

Exits IPv6 address family configuration mode.

Step 8

end

Example:

Device(config-router)# end

Exits router configuration mode.

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

To request a warning message when the number of routes redistributed into OSPF exceeds the configuration limit, perform this procedure:

Procedure

  Command or Action Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode. Enter your password, if prompted.

Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

router ospf process-id

Example:

Device(config)# router ospf 1

Configures an OSPF routing process.

Step 4

redistribute protocol [process-id] [as-number] [include-connected {level-1 | level-1-2 | level-2} [metric metric-value ] [metric-type type-value] [nssa-only] [tag tag-value] [route-map map-tag]

Example:

Device(config-router-af)# redistribute eigrp 10

Redistributes routes from one routing domain into another routing domain.

Step 5

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

Example:

Device(config-router-af)# redistribute maximum-prefix 1000 80 warning-only

Causes a warning message to be logged when the maximum number of IP prefixes have been redistributed to OSPFv3.

  • Because the warning-only keyword is included, no limit is imposed on the number of redistributed prefixes into OSPF.

  • The threshold value defaults to 75 percent.

  • This example causes two warnings: one at 80 percent of 1000 (800 routes redistributed) and another at 1000 routes redistributed

Step 6

end

Example:

Device(config-router)# end

Exits router configuration mode.

Requesting a Warning Message About the Number of Routes Redistributed into OSPFv3

To request a warning message when the number of routes redistributed into OSPFv3 exceeds the configuration limit, perform this procedure:

Procedure

  Command or Action Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

Enter your password, if prompted.

Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

router ospfv3 process-id

Example:

Device(config)# router ospfv3 1

Configures an OSPFv3 routing process.

Step 4

address-family ipv6 [unicast]

Example:

Device(config-router)# address-family ipv6 unicast

Enters IPv6 address family configuration mode.

Step 5

redistribute protocol [process-id] [as-number] [include-connected {level-1 | level-1-2 | level-2} [metric metric-value ] [metric-type type-value] [nssa-only] [tag tag-value] [route-map map-tag]

Example:

Device(config-router-af)# redistribute eigrp 10

Redistributes routes from one routing domain into another routing domain.

Step 6

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

Example:

Device(config-router-af)# redistribute maximum-prefix 1000 80 warning-only

Causes a warning message to be logged when the maximum number of IP prefixes have been redistributed to OSPFv3.

  • Because the warning-only keyword is included, no limit is imposed on the number of redistributed prefixes into OSPFv3.

  • The threshold value defaults to 75 percent.

  • This example causes two warnings: one at 80 percent of 1000 (800 routes redistributed) and another at 1000 routes redistributed

Step 7

end

Example:

Device(config-router)# end

Exits router configuration mode.

Configuration Examples for OSPF Limit on Number of Redistributed Routes

The following sections provide configuration examples for OSPF Limit on Number of Redistributed Routes.

Example: OSPF Limit on Number of Redistributed Routes

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


Device> enable
Device# configure terminal
Device(config)# router ospf 1
Device(config-router-af)# redistribute static subnets
Device(config-router-af)# redistribute maximum-prefix 1200 80

This example shows how to set a maximum of 1200 prefixes that can be redistributed into the OSPFv3 process 1.

Device> enable
Device# configure terminal
Device(config)# router ospfv3 1
Device(config-router)# address-family ipv6
Device(config-router-af)# redistribute static subnets
Device(config-router-af)# redistribute maximum-prefix 1200 80

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

This example shows how to enable two warning messages to be logged, the first if the number of prefixes that are 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. 


Device> enable
Device# configure terminal 
Device(config)# router ospf 11
Device(config-router-af)# redistribute eigrp 10 subnets
Device(config-router-af)# redistribute maximum-prefix 600 85 warning-only

This example shows how to enable two warnings to be logged for an OSSPv3 process.


Device> enable
Device# configure terminal 
Device(config)# router ospfv3 11
Device(config-router)# address-family ipv6
Device(config-router-af)# redistribute eigrp 10 subnets
Device(config-router-af)# redistribute maximum-prefix 600 85 warning-only

Feature History for OSPF Limit on Number of Redistributed Routes

This table provides release and related information for the features explained in this module.

These features are available in all the releases subsequent to the one they were introduced in, unless noted otherwise.

Release

Feature

Feature Information

Cisco IOS XE Gibraltar 16.11.1

OSPF Limit on Number of Redistributed Routes

OSPF supports a user-defined maximum number of prefixes (routes) that can be redistributed into OSPFv3 from other protocols or other OSPFv3 processes.

Cisco IOS XE Cupertino 17.7.1

OSPF Limit on Number of Redistributed Routes

This feature was implemented on the Cisco Catalyst 9600 Series Supervisor 2 Module (C9600X-SUP-2).
Cisco IOS XE Dublin 17.11.1

Default Value for Number of Redistributed Routes

Sets a default value of 10240 routes for the redistribute maximum-prefix command. The default is to protect the device from being flooded with routes.

Use the Cisco Feature Navigator to find information about platform and software image support. To access Cisco Feature Navigator, go to https://cfnng.cisco.com/.