CCIE Routing and Switching v4.0 Quick Reference

Abstract

Summarization is the process in which the administrator collapses many routes with a long mask to form another route with a shorter mask. Route summarization reduces the sizeof routing tables and makes the routing function more efficient. Route summarization also helps to make networks more stable by reducing the number of updates sent when subnets change state. Route summarization makes classless interdomain routing (CIDR) possible. Variable-length subnet masking (VLSM) promotes the use of route summarization. Some dynamic routing protocols engage in route summarization automatically for changes in a major classful network, whereas others do not. For any routing protocol within the scope of the CCIE written exam, an administrator can disable any automatic summarization that might occur and configure manual summarization.