You can use a floating summary route when configuring the ip summary-address eigrp command. This enhancement was introduced in Cisco IOS Release 12.2. The
floating summary route is created by applying a default route and
administrative distance at the interface level.
The default summary route is applied to interface with the following configuration:
Router(config)# interface Router(config-if)# ip summary-address eigrp 10 0.0.0.0 0.0.0.0
The configuration of the default summary route on
Router-1 sends a 0.0.0.0/0 summary route to Router-2 and blocks all
other routes, including the all route, from being advertised to
Router-2. However, this also generates a local discard route on
Router-1, a route for 0.0.0.0/0 to the null 0 interface with an
administrative distance of 5. When this route is created, it overrides
the EIGRP learned default route. Router-1 will no longer be able to
reach destinations that it would normally reach through the 0.0.0.0.0/0
route.
This problem is resolved by applying a floating summary route to the
interface on Router-1 that connects to Router-2. The floating summary
route is applied by applying an administrative distance to the default
summary route on the interface of Router-1 with the following statement:
Router(config-if)# ip summary-address eigrp 10 0.0.0.0 0.0.0.0 250
The administrative distance of 250, applied in the
above statement, is now assigned to the discard route generated on
Router-1. The 0.0.0.0/0 is learned through EIGRP and
installed in the local routing table. Routing to Router-2 is restored.
The summary address is not advertised to the peer if the administrative distance is configured as 255
http://www.cisco.com/en/US/docs/ios/12_2/ip/configuration/guide/1cfeigrp.htmlhttp://www.cisco.com/en/US/docs/ios-xml/ios/iproute_eigrp/command/ire-i1.html
http://www.cisco.com/en/US/docs/ios-xml/ios/iproute_eigrp/configuration/xe-3s/asr1000/ire-cfg-eigrp.html#GUID-6A20D55E-4611-4FC7-9CF4-EC7ACA5DF440
