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 172.16.0.0R2(config)#router eigrp 1
R2(config-router)#no auto-summary
R2(config-router)#network 192.168.12.0Just 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, FastEthernet0/0Two entries as expected. Now let’s create that summary:
R1(config)#interface fastEthernet 2/0
R1(config-if)#ip summary-address eigrp 1 172.16.0.0 255.255.254.0Use the ip summary-address eigrp command to specify the summary. Now the routing table will look like this:
Amit,
... Continue reading in our forumOnly on the router where the summarization is configured does the Query process stop–not on the router that originates the Query. So for example, if you have three routers A, B, and C with a topology of A—B---C. B has created a summary, say 10.10.0.0/16. Suppose Router A has a route 10.10.10.0/24 that goes active. Router A will still send the Query message to B, but B will see that 10.10.10.0/24 is contained within its own configured summary of 10.10.0.0/16. This will cause Router B to stop propagation of the Query to router C. Additionally, Router
We have these two networks:
The most optimal summary rounte for 172.16.0.0/24 and 172.16.1.0/24 is 172.16.0.0/23.
In binary, these two look like this:
* 10101100 00010000 00000000 00000000
* 10101100 00010000 00000001 00000000
Above you can see that the first 23 bits are the same, that’s why we use the /23 summary.
Rene
Sorry, I have solved it.
Yes, thank you very much!
Thanks Lazaros,
Now it is clear for me very nice explanation.