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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

2 comments

  1. Actually I was trying to create a new post but I did not figure out how yet
    I am at my final stages of the CCIE LAB preperation for the R&S track and wanted to share my knowledge with the others.

    As you know the LAB is all about time time time and accuracy, so it is good to have a straegy and a methodological approach for each pert in the lab.

    Below is my RIP strategy that I develooped over the long time labbing:

    Opening Move:
    ————-
    conf t
    router rip
    ver 2
    no auto
    pass def

    do sh ip int br
    network
    no pass

    !Broadcast v2 update:
    ———————
    (config-if)#ip rip v2-broadcast

    !Unicast updates:
    —————–
    1- send unicast updates
    (config-router)#neighbor A.B.C.D “Neighbor address”
    2- stop broadcast/multicast updates
    passiv

    Differet subnets:
    —————–
    (config-router)#NO validate-update-source

    !check split horizon

    Show commds:
    ————
    Sh ip protocols
    Routing Information Sources:
    Gateway Distance Last Update

    Killing the Route:
    ——————
    1- Distribute list
    2- offset list (poison the metric)
    3- admin distance (poison the distance)

  2. Thanks Aly for sharing the knowledge, keep up the good work

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