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| 5.5 |  | Configuring EIGRP |
| 5.5.5 |  | Summarizing EIGRP Routes: Interface Summarization |

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:

> R

outer(config-if)#ip summary-address eigrp autonomous-system-number ip-address mask administrative-distance

EIGRP summary routes have an administrative distance of 5 by default. Optionally, they can be configured for a value between 1 and 255.

In the figure, RTC can be configured using the following commands shown:

> RTC(config)#router eigrp 2446
> RTC(config-router)#no auto-summary
> RTC(config-router)#exit
> RTC(config)#interface serial0/0
> RTC(config-if)#ip summary-address eigrp 2446 2.1.0.0 255.255.0.0

Therefore, RTC will add a route to its table, as follows:

> 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. That is because this route is used for advertisement purposes and does not represent a path that RTC can take to reach that network. On RTC, this route has an administrative distance of 5.

In the figure, RTD is oblivious to the summarization but accepts the route. It assigns the route the administrative distance of a "normal" EIGRP route, which is 90, by default. In the configuration for RTC, automatic summarization is turned off, with

no auto-summary command. Otherwise RTD would receive two routes, the manual summary address of 2.1.0.0/16 and the automatic, classfull address of 2.0.0.0/8.

In most cases, when using manual summarization, the

no auto-summary command should be configured.

| Lab Activity e-Lab Activity: Summarizing EIGRP Routes for IP This lab is to use manual route summarization for EIGRP.