EIGRP auto-summary

本文出自Simmy的个人blog：西米在线  http://simmyonline.com/archives/540.html

 

EIGRP automatically summarizes routes at the classful boundary, the boundary where the
network address ends as defined by class-based addressing. In most cases, auto
summarization is a good thing, keeping the routing tables as compact as possible
In the presence of discontiguous subnetworks, automatic summarization must be disabled

for routing to work properly. To turn off auto-summarization, use the following
command:
Router(config-router)#no auto-summary

EIGRP also enables manual configuration of a prefix to use as a summary address.
Manual summary routes are configured on a per-interface basis. The interface that will
propagate the route summary must first be selected and then defined with the ip
summary-address eigrp command, which has the following syntax:
Router(config-if)#ip summary-address eigrp autonomous-system-number ip-address
mask administrative-distance
D 2.1.0.0/16 is a summary, 00:00:22, Null0
Notice that the summary route is sourced from Null0, and not an actual interface.