CISCO IOS in a Nutshell

Name

summary-address — router, OSPF, IS-IS, BGP

Synopsis

BGP:

summary-address address 
               subnet-mask
no summary-address address 
               subnet-mask

OSPF:

summary-address address 
               subnet-mask [not-advertise] [tag tag-value]
no summary-address address 
               subnet-mask

IS-IS:

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

Configures

Route summarization

Default

Disabled

Description

This command allows you to create a single route that covers a set of smaller routes, thus reducing the number of routes in the routing table. Use the no form of the command to return to the default, where the router does not summarize routes.

address

The destination address for the summarized route.

subnet-mask

A subnet mask that indicates which addresses should be included in the summarized route.

level-1, level-2, level-1-2

IS-IS only. The router summarizes only routes that are being redistributed into the given level.

not-advertise

Optional. OSPF only. Routes are not advertised when translating a type 7 link state announcement from OSPF.

tag tag-value

Optional. OSPF only. Used as a match value for route maps.

Example

Assume that we know routes for 10.10.1.0, 10.10.2.0, 10.10.3.0, and so on. Instead of advertising separate routes, we can summarize by combining these routes into a single route for 10.10.0.0:

summary-address 10.10.0.0 255.255.0.0