6.7 Summarizing  EIGRP Routes for IP
6.7.2 Manual summarization example
Enhanced IGRP does not summarize received routes. If a network was not summarized at the major network boundary, for example, routers A and B of the main figure, then all of the subnet routes will be carried into the routing table of router C and other routers in the rest of the world. To keep that route advertisement small, manual summarization forces a summary route out to the rest of the world.
Lab Activity
  In this lab, you will learn how to reduce the number of routes in the EIGRP routing table through interface summarization..