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Summarizing Routes
summary-address
summary-prefix
Avoiding Transient Black Holes
Copyright © 2010, Juniper Networks, Inc.
Use the no version to restore the default value, level-1-2.
See is-type
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.
See summary-address
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
When you start or reload a transit router that is running both IS-IS and BGP, the router is
temporarily unavailable to the routing domain. Other routers in that routing domain must
select alternative paths to destinations that used the transit router. When the transit
Chapter 6: Configuring IS-IS
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