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prefix-export-limit (Protocols IS-IS)


Hierarchy Level


Configure a limit to the number of prefixes exported into IS-IS.

By default, there is no limit to the number of prefixes that can be exported into IS-IS. To configure a limit to the number of prefixes that can be exported into IS-IS, include the prefix-export-limit statement. The prefix-export-limit statement protects the rest of the network from a malicious policy by applying a threshold filter for exported routes.

The number of prefixes depends on the size of your network. Good design advice is to set it to double the total number of IS-IS Level 1 and Level 2 routing devices in your network.

If the number of prefixes exported into IS-IS exceeds the configured limit, the overload bit is set and the overload state is reached. When other routers detect that this bit is set, they do not use this routing device for transit traffic, but they do use it for packets destined to the overloaded routing device’s directly connected networks and IP prefixes. The overload state can be cleared by using the clear isis overload command.

The show isis overview command displays the prefix export limit when it is configured.

You can prevent IS-IS from enterning the overload state even after the prefixes reach the configured limit, by using the no-overload-on-prefix-export-limit command.


number—Prefix limit.

  • Range: 0 through 4,294,967,295 (232 – 1)

  • Default: None

Required Privilege Level

routing—To view this statement in the configuration.

routing-control—To add this statement to the configuration.

Release Information

Statement introduced before Junos OS Release 7.4.