EIGRP: Route Summarization

The EIGRP route summarization is done exactly the same like RIP summarization, which makes sense because both protocols have the Distance Vector nature. It can also be done on ANY of the routers within the same EIGRP process, unlike the Link State protocols. It's done on the Interface using the command:

R2(config-if)#ip summary-address eigrp 100 3.0.0.0 255.0.0.0

And dont be afraid when you see the following message:
*Apr 27 12:53:32.203: %DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 10.1.12.1 (Serial1/0) is resync: summary configured

The interface towards Null0 Interface is created automatically. So dont worry, because EIGRP adds this ""discard route" for Loop Avoidance.

Check if "it worked":

R2#show ip route | i summ
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
D        3.0.0.0/8 is a summary, 00:02:52, Null0


EIGRP Leak Maps

If you wish to have greater granular control the solution presented since 12.3(13) is - the LEAK MAP

If the Leak Map is configured, and:
- It references a non-existing Route Map - The summary route is advertised, more specific routes are suppressed
- If the Route Map however exists, and references a non-existing ACCESS LIST - both the summary route and the more specific routes are advertised
- If the Access List also exists - it lets us define the routes that will be advertised IN ADDITION to the Summarized Route!

To configure the Leak Map just attach a route-map to the "eigrp summary" command:

R2(config-if)#ip summary-address eigrp 100 2.2.4.0 255.255.252.0 leak-map ROUTE_MAP


EIGRP Default Gateway

The command we all know from OSPF and BGP "default-information originate [always]" will not work in EIGRP. Instead we need to:
 Option 1: Configure the static route and redistribute it into the EIGRP
 Option 2: Summarize the routes into a Default Route using the previously described summarization method (leak map is added if we wish to inject another routes besides the default route)

 R2(config-if)#ip summary-address eigrp 100 0.0.0.0 0.0.0.0 [leak-map ROUTE_MAP]