In my EIGRP Route Advertising post I said “in order for two routers to exchange EIGRP routes, they must both be part of the same subnet and have a network command specifying that particular subnet, or, at the very least, their specific IP address on that subnet”. In that entry I then went on to use the routers’ specific IP addresses. In this entry, I’m going to explain how you can specify a larger subnet in order to reduce the number of network commands you must apply.
To do this, I’ll use the following topology:
We’ll configure the R2 and R3 in the same way as we did previous, by specifying the exact addresses of the interfaces we want to advertise.
R2(config-router)#do sh run | begin router eigrp router eigrp 10 network 10.34.19.1 0.0.0.0 network 192.168.20.2 0.0.0.0 no auto-summary
R3(config-router)#do sh run | begin router eigrp router eigrp 10 network 10.34.19.2 0.0.0.0 network 192.168.10.2 0.0.0.0 no auto-summary
Note: Please see my no auto-summary post for more information on what this command does.
In regards to the above two configurations, we have used one “network” command per interface, however, with R1, as its two interfaces have the same two octets, you can use one “network” command that covers both interfaces. Here’s how:
R1(config-router)#do sh run | begin router eigrp router eigrp 10 network 192.168.0.0 0.0.255.255 no auto-summary
Doing this has the exact same affect as using two separate network commands, as you can see by R1’s neighbor table:
R1(config-router)#do sh ip ei ne IP-EIGRP neighbors for process 10 H Address Interface Hold Uptime SRTT RTO Q Seq (sec) (ms) Cnt Num 1 192.168.10.2 Fa0/0 11 00:12:26 169 1014 0 13 0 192.168.20.2 Fa0/1 11 00:17:14 1311 5000 0 8
Please note though that it is best practice to be as specific as possible when dealing with things like route advertisements. Using a blanket “network” statement like the one used in this example is not always a good idea, especially when dealing with large, complex networks.
As always, if you have any questions or have a topic that you would like me to discuss, please feel free to post a comment at the bottom of this blog entry, e-mail at firstname.lastname@example.org, or drop me a message on Reddit (OzNetNerd).
Note: The opinions expressed in this blog are my own and not those of my employer.