[EIGRP] Configuring Route Summarization

In this lab, we will see how to configure EIGRP route summarization.

Here’s the topology we will use:

EIGRP Route Summarization Topology

Here’s the RIPv2 configuration before summarization:

For R1:

R1(config)#router eigrp 100
R1(config-router)#no auto-summary 
R1(config-router)#network 192.168.1.1 0.0.0.0
R1(config-router)#network 172.16.0.1 0.0.0.0 
R1(config-router)#network 172.16.1.1 0.0.0.0

For R2:

R2(config-if)#router eigrp 100
R2(config-router)#no auto-summary 
R2(config-router)#network 192.168.1.2 0.0.0.

The routing table of router R2 will look like this:

R2#show ip route eigrp 
     172.16.0.0/24 is subnetted, 2 subnets
D       172.16.0.0 [90/156160] via 192.168.1.1, 00:00:26, FastEthernet0/0
D       172.16.1.0 [90/156160] via 192.168.1.1, 00:00:26, FastEthernet0/0

Above you see both networks. Now let’s create a summary:

172.16.0.0 = 172.16.00000000.0/24
172.16.1.0 = 172.16.00000001.0/24
             --------------------
           = 172.16.0.0/23

The /23 is the more specific because it only covers 172.16.0.0/24 and 172.16.1.0/24

R1(config)#interface fastEthernet 0/0
R1(config-if)#ip summary-address eigrp 100 172.16.0.0 255.255.254.0
*Mar  1 00:04:44.787: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 192.168.1.2 (FastEthernet0/0) is down: summary configured
R1(config-if)#
*Mar  1 00:04:44.791: destroy peer: 192.168.1.2
*Mar  1 00:04:47.031: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 192.168.1.2 (FastEthernet0/0) is up: new adjacency

As you can see, the neighborship between the two routers goes down/up, because a new summary was configured.

This is what it looks like on router R2:

R2#show ip route eigrp 
     172.16.0.0/23 is subnetted, 1 subnets
D       172.16.0.0 [90/156160] via 192.168.1.1, 00:00:39, FastEthernet0/0

I hope this been informative for you, enjoy !

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