summary-address (IS-IS)




summary-address address mask { level-1| level-1-2| level-2}


no summary-address address mask { level-1| level-1-2| level-2}

Syntax Description:


Summary address designated for a range of addresses.


IP subnet mask used for the summary route.


Only routes redistributed into Level 1 are summarized with the configured address and mask value.


Summary routes are applied when redistributing routes into Level 1 and Level 2 IS-IS, and when Level 2 IS-IS advertises Level 1 routes as reachable in its area.


Routes learned by Level 1 routing are summarized into the Level 2 backbone with the configured address and mask value. Redistributed routes into Level 2 IS-IS will be summarized also.


Command Description:

Multiple groups of addresses can be summarized for a given level. Routes learned from other routing protocols can also be summarized. The metric used to advertise the summary is the smallest metric of all the more specific routes. This command helps reduce the size of the routing table.

This command also reduces the size of the link-state packets (LSPs) and thus the link-state database (LSDB). It also helps stability because a summary advertisement is depending on many more specific routes. A single route flap does not cause the summary advertisement to flap in most cases.

The drawback of summary addresses is that other routes might have less information to calculate the most optimal routing table for all individual destinations.


The following example redistributes Routing Information Protocol (RIP) routes into IS-IS. In a RIP network, there are IP routes for 10.1.1, 10.1.2, 10.1.3, 10.1.4, and so on. This example advertises only into the IS-IS Level 1 link-state PDU.

Router(config)# router isis

Router(config-router)# net01.0000.0000.0001.00

Router(config-router)# redistribute rip level-1 metric40

Router(config-router)# summary-address10.1.0.0 level-1



Related commands:



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