How-to:Configure RIP route summarization

In the following example I am going to show you how to configure route summarization under RIP using two methods.

Our topology is shown below:

R1 routing table before implementing summarization:

R1(config-router)#do sh ip route rip
2.0.0.0/32 is subnetted, 4 subnets
R       2.2.2.2 [120/1] via 172.16.123.2, 00:00:02, Serial1/0
R       2.2.2.3 [120/1] via 172.16.123.2, 00:00:02, Serial1/0
R       2.2.2.1 [120/1] via 172.16.123.2, 00:00:02, Serial1/0
R       2.2.2.4 [120/1] via 172.16.123.2, 00:00:02, Serial1/0

Task: Summarize Lo0,Lo1 and Lo2 interfaces of R2 when sent to R1 using two methods.

Method1: IP summary-address command

This command is applied under the interface you want to generate the summary from. Only one summary command can be applied to each interface. Only the summary route is advertised and all routes that match the summary route will no be advertised.

R2(config-if)#int s1/0
R2(config-if)#ip summary-address rip 2.2.2.0 255.255.255.252

!--R1 routing table after summarization: Only summary and 2.2.2.4 loopback

R1(config-router)#do sh ip route rip
     2.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
R       2.2.2.0/30 [120/1] via 172.16.123.2, 00:00:04, Serial1/0
R       2.2.2.4/32 [120/1] via 172.16.123.2, 00:00:04, Serial1/0

Method2: Auto-summarization

Auto summarization can be used also, but the main difference is that auto-summary affects the whole router with all advertised networks and interfaces for this specific routing protocol. As shown in the output below all networks belonging to the main classful network 2.0.0.0 were summarized.

!-- Enable auto summarization on R2
router rip
auto-summary

!-- R1 table:All networks belonging to the classful boundary are summarized

R1(config-router)#do sh ip rout rip
     1.0.0.0/8 is variably subnetted, 5 subnets, 2 masks
R       1.0.0.0/8 [120/2] via 172.16.123.2, 00:00:11, Serial1/0
R    2.0.0.0/8 [120/1] via 172.16.123.2, 00:00:11, Serial1/0