IP Routing Configuration Guide, Cisco IOS XE 17.15.x (Catalyst 9500 Switches) - Configuring OSPF Limit on Number of Redistributed Routes [Support] (2024)

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.

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.

IP Routing Configuration Guide, Cisco IOS XE 17.15.x (Catalyst 9500 Switches) - Configuring OSPF Limit on Number of Redistributed Routes [Support] (1)

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

Step1

enable

Example:

Device> enable

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

Step2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step3

router ospf process-id

Example:

Device(config)# router ospf 1

Configures an OSPF routing process.

Step4

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.

Step5

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.

Step6

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

Step1

enable

Example:

Device> enable

Enables privileged EXEC mode.

Enter your password, if prompted.

Step2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step3

router ospfv3 process-id

Example:

Device(config)# router ospfv3 1

Configures an OSPFv3 routing process.

Step4

address-family ipv6 [unicast]

Example:

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

Enters IPv6 address family configuration mode.

Step5

Example:

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

Redistributes routes from one routing domain into another routing domain.

Step6

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.

Step7

exit-address-family

Example:

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

Exits IPv6 address family configuration mode.

Step8

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
Step1	enable Example: `Device> enable`	Enables privileged EXEC mode. Enter your password, if prompted.
Step2	configure terminal Example: `Device# configure terminal`	Enters global configuration mode.
Step3	router ospf `process-id` Example: `Device(config)# router ospf 1`	Configures an OSPF routing process.
Step4	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.
Step5	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
Step6	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
Step1	enable Example: `Device> enable`	Enables privileged EXEC mode. Enter your password, if prompted.
Step2	configure terminal Example: `Device# configure terminal`	Enters global configuration mode.
Step3	router ospfv3 `process-id` Example: `Device(config)# router ospfv3 1`	Configures an OSPFv3 routing process.
Step4	address-family ipv6 [unicast] Example: `Device(config-router)# address-family ipv6 unicast`	Enters IPv6 address family configuration mode.
Step5	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.
Step6	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
Step7	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> enableDevice# configure terminalDevice(config)# router ospf 1Device(config-router-af)# redistribute static subnetsDevice(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> enableDevice# configure terminalDevice(config)# router ospfv3 1Device(config-router)# address-family ipv6Device(config-router-af)# redistribute static subnetsDevice(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> enableDevice# configure terminal Device(config)# router ospf 11Device(config-router-af)# redistribute eigrp 10 subnetsDevice(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> enableDevice# configure terminal Device(config)# router ospfv3 11Device(config-router)# address-family ipv6Device(config-router-af)# redistribute eigrp 10 subnetsDevice(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	Support for this feature was introduced on the C9500X-28C8D model of the Cisco Catalyst 9500 Series Switches.
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 http://www.cisco.com/go/cfn.

IP Routing Configuration Guide, Cisco IOS XE 17.15.x (Catalyst 9500 Switches) - Configuring OSPF Limit on Number of Redistributed Routes [Support] (2024)

Restrictions for OSPF Limit on Number of Redistributed Routes

Prerequisites for OSPF Limit on Number of Redistributed Routes

Information About OSPF Limit on Number of Redistributed Routes

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

Limiting the Number of OSPF Redistributed Routes

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Limiting the Number of OSPFv3 Redistributed Routes

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

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

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Configuration Examples for OSPF Limit on Number of Redistributed Routes

Example: OSPF Limit on Number of Redistributed Routes

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

Feature History for OSPF Limit on Number of Redistributed Routes

References