8.7.1 Overview

Route summarization is a method of representing routing information from one or more source routes by generating routing information that is shorter than the network masks that include information about the corresponding paths. If the information for multiple routes is condensed into one set of routing information containing the information for the multiple routes, and then that summarized information is reported to (for example) neighboring routers, the number of items of routing information on the network is reduced. For example, the switch can generate the summarized route 172.16.0.0/16 having learned routing information for addresses 172.16.178.0/24 and 172.16.179.0/24.

You must explicitly enable route summarization by executing the ip summary-address configuration command. You can assign a distance to a summarized route. If you do not specify a distance, the default of 130 is used. The switch cannot generate a summarized route without first learning the routing information that serves as its source.