Cisco Systems 78-11741-02 manual Configuring Summary Aggregate Addresses, IPC-263

Configuring EIGRP

EIGRP Configuration Task List

Command	Purpose
Router(config-router)# no auto-summary	Disables automatic summarization.

Route summarization works in conjunction with the ip summary-address eigrp interface configuration command, in which additional summarization can be performed. If automatic summarization is in effect, there usually is no need to configure network level summaries using the ip summary-address eigrp command.

Configuring Summary Aggregate Addresses

You can configure a summary aggregate address for a specified interface. If any more specific routes are in the routing table, EIGRP will advertise the summary address out the interface with a metric equal to the minimum of all more specific routes.

To configure a summary aggregate address, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)#ip summary-address eigrp	Configures a summary aggregate address.
autonomous-system-number ip-address mask

See the “Route Summarization Example” at the end of this chapter for an example of summarizing aggregate addresses.

Configuring Floating Summary Routes

You can also 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 following scenarios illustrates the behavior of this enhancement.

Figure 46 shows a network with three routers, Router-A, Router-B, and Router-C. Router-A learns a default route from elsewhere in the network and then advertises this route to Router-B. Router-B is configured so that only a default summary route is advertised to Router-C. The default summary route is applied to interface 0/1 on Router-B with the following configuration:

Router(config)# interface Serial 0/1

Router(config-if)#ip summary-address eigrp 100 0.0.0.0 0.0.0.0

Cisco IOS IP Configuration Guide

IPC-263