How to configure EIGRP Summarization

In this lesson we’ll take a look at EIGRP summarization. The cool thing about EIGRP and summarization is that it’s easy to do and can be done on the interface-level. Here’s the topology that we’ll use:

eigrp summarization lab topology

Let’s create a basic EIGRP configuration:

R1(config)#router eigrp 1
R1(config-router)#no auto-summary 
R1(config-router)#network 192.168.12.0
R1(config-router)#network 172.16.0.0
R2(config)#router eigrp 1
R2(config-router)#no auto-summary 
R2(config-router)#network 192.168.12.0

Just a basic EIGRP configuration. This is what the routing table of R2 looks like:

R2#show ip route eigrp 
     172.16.0.0/24 is subnetted, 2 subnets
D       172.16.0.0 [90/30720] via 192.168.12.1, 00:02:28, FastEthernet0/0
D       172.16.1.0 [90/30720] via 192.168.12.1, 00:02:28, FastEthernet0/0

Two entries as expected. Now let’s create that summary:

R1(config)#interface fastEthernet 2/0
R1(config-if)#ip summary-address eigrp 1 172.16.0.0 255.255.254.0

Use the ip summary-address eigrp command to specify the summary. Now the routing table will look like this:

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Forum Replies

  1. Amit,
    Only on the router where the summarization is configured does the Query process stop–not on the router that originates the Query. So for example, if you have three routers A, B, and C with a topology of A—B---C. B has created a summary, say 10.10.0.0/16. Suppose Router A has a route 10.10.10.0/24 that goes active. Router A will still send the Query message to B, but B will see that 10.10.10.0/24 is contained within its own configured summary of 10.10.0.0/16. This will cause Router B to stop propagation of the Query to router C. Additionally, Router

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  2. Yes, thank you very much!

  3. Thanks Lazaros,
    Now it is clear for me very nice explanation.

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