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EIGRP Routing Design Question

johndennison
Level 1
Level 1

hello all.

i inherited a large frame-relay hub and spoke network with multiple hubs and using only static routing. there are about 10 hubs, and each remote router is connected to one of these hubs, plus a backup hub (the same for every router). we would like to implement a dynamic routing protocol, and i have experience with OSPF and EIGRP. we've decided on EIGRP, but here's the issue and hence my question: the WAN addresses *within* each hub are unique, but there is overlap from one hub to another. for instance, 10.1.1.1 is a WAN interface on Hub1, Hub2, Hub3, etc. Is this a problem for EIGRP? We don't really care about learning the WAN routes, just the loopbacks on the remote routers and some static routes, both of which *are* unique, unlike the WAN addresses.

i hope i made this clear. i understand the IP overlap is not ideal, but getting those changed is an even bigger project than implementing a routing protocol, so if i can avoid it, i will. i believe EIGRP should work, but i know

OSPF won't, because it won't be able to build an accurate picture of the network with all that overlap.

thanks for your time!

7 Replies 7

lamav
Level 8
Level 8

" for instance, 10.1.1.1 is a WAN interface on Hub1, Hub2, Hub3"

Huh? You lost me...can you elaborate further on that?

From my experience, the most efficient way to implement eigrp on a frame relay hub and spoke environment is to create point-to-point subinterfaces on the hub and spoke, with /30 subnets on the WAN links.

HTH

Victor

sorry, yes, that is what we have done. the problem is that 10.1.1.0/30 is used for a WAN subinterface on Hub1, Hub2, and Hub3, etc.

Im still not understanding it.

Are you saying you have duplicate addresses on your network?? How can you assign the same subnet to 3 different serial interfaces on 3 different routers?

What am I missing?

yes, we have duplicate addresses.

Hello John,

OSPF is out of discussion.

EIGRP can support this but:

be aware that EIGRP external routes have a field that contain the EIGRP router-id.

So you need to verify that the overlapping ip address is not chosen by any router as eigrp router-id.

sh ip eigrp topology should report the router-id.

in case you can force the EIGRP router-id with eigrp router-id command

see

http://www.cisco.com/en/US/docs/ios/12_2/iproute/command/reference/1rfeigrp.html#wp1031884

Readdressing can be performed on a link by link basis provided that you access the remote router from the backup hub (that I hope it is fine) make your changes on the primary link and verify connectivity.

I would think of readdressing you can do it gradually over time.

Hope to help

Giuseppe

Alrighty then....

Giuseppe is right, of course. You need to re-address your network. Honestly, I have never seen such a cockamamie set up. Why on earth would anyone deliberately assign duplicate IP addresses on their network? What could that possibly buy them?

Giuseppe, you've confirmed my thoughts, thank you.

FYI, we would configure the loopback on each router to be the EIGRP router-id.

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