igrp / eigrp coexistance

[KTD1]

Hi all - I have a pretty basic WAN - 7 sites\T1's & igrp for routing. I have purchased a new 2821 to replace an aging 2503 and found that the IOS that came with does not support igrp, but it does support eigrp - the version is: C2800NM-IPBASE-M), Version 12.3(8)T8

If I config a the same router group for eigrp and connect, will it propagate routes with igrp peers?

Many kind regards.

Dave

[Tony.henry]

Dave,

If you put this router in place running only EIGRP your other IGRP routers won't talk to it.

If you however put this router in place, running EIGRP, and the routers that it connects get configured to run EIGRP on the same AS as IGRP.

eg

router igrp 10

network X.X.X.X

Router EIGRP 10

network the serial interface subnet

You'll find that redistribution happens automatically. Sort of the same effect. Wouldn't something I'd be looking to do in the middle of the production day. but it would let people know you exist if you did it ;) not in a good way obviously.

Tony Henry

Tony

[Richard Burts]

Tony is giving good advice and is correct that a router running IGRP on a connection will not exchange routing information with another router running EIGRP on that connection. And the best way to integrate the new router into the network is to have the new router run EIGRP on its interface(s) and to have any router connected to the new router to run EIGRP on the interface connecting to the new router and to run IGRP with the same AS on all the other interfaces.

I will point out that the redistributed routes in IGRP will function right along with the native routes and can not be distinguished. But in EIGRP the redistributed routes learned from IGRP will be advertised as external routes with Administrative Distance of 170 rather than as internal routes with Administrative Distance of 90. Depending on the topology this might not make a difference but there are circumstances where it might.

HTH

Rick