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