Summarizing Routes

You can summarize routes redistributed into IS-IS or within IS-IS by creating aggregate addresses for the routes. Use the summary-address command for IP routes and the summary-prefix command for IPv6 routes.

Optionally, you can set a route tag for an IS-IS aggregate (summary) address by including the tag keyword and a numeric tag value in the command.

summary-address

• See summary-address

summary-prefix

• Use to create aggregate addresses of routes that are redistributed from other protocols in the routing table or distributed between level 1 and level 2 by a summary address. This process is called route summarization.
• A single summary address includes groups of addresses for a given level.
• Use the summary-address command for IP routes. Use the summary-prefix command for IPv6 routes.
• The metric value is used when the router advertises the summary address. When the metric value is not used, the value of the lowest cost route (the default) is used.
• This command reduces the size of the neighbor’s routing table and improves stability because a summary advertisement depends on many more specific routes.
• A disadvantage of summary addresses is that other routes might have less information to calculate the optimal routing table for all individual destinations.
• Use the optional tag keyword to specify a tag value for an IS-IS summary address. The tag value must be a number in the range 1–4294967295.
• Example 1—For IP routes

  host1(config-router)#summary-address 10.2.0.82 255.255.0.0 level-1-2 tag 34

• Example 2—For IPv6 routes

  host1(config-router-af)#summary-prefix 2001:2000::0/8 level-1 metric 10 tag 100

• Use the no version to restore the default, the value of the lowest-cost route.
• See summary-prefix

Copyright © 2008, Juniper Networks, Inc. All rights reserved. Trademark Notice.