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:

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: