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. Hello Rene,

    I have a question regarding ip summary-address command in above lesson.
    By applying ip aummary-address command in fastethrnet 2/0 interface,
    how come heart router know about the summary address.
    As my understanding ip summary address is per interface basis.
    I should apply ip summary-address in fastethernet 1/0 interface.
    Would you correct me and help me to understand better.

    Thanks.

  2. Hi Toral,

    I just changed the picture because the interface number didn’t match. You configure a summary outbound on an interface facing towards your EIGRP neighbor.

    Rene

  3. Simple but effective workout to understand EIGRP summerizing

  4. thanks for the nice lesson, keep up the good work

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