Here's a very good document on EIGRP to OSPF by Michael Gibbs,CCIE#7417 of Riverstone Networks.
'EIGRP to OSPF Migration Strategies'
Hope this helps -
Thanks for the article. I have a question though. Where would you recommend creating Area 0? I have three sites. HQ has 4 routers (2 at the edge and 2 in the core). The other two remote sites have one WAN router each.
First I would like to know if you can tell us, the reasons why you want to migrate from EIGRP to OSPF. DO you have any vendor equipment other than Cisco ?
If all your Routers (not other equipment) are going to be Cisco, there is no gain that you achieve by migrating to OSPF.
Regarding your question, Your network is really small and would not matter, if you put all of them in a single area.
For this small of a network, I would make the entire network area 0. Of course, I wouldn't migrate a network from EIGRP to OSPF, unless I had a very specific reason to do so, and clearly defined goals for doing it. :-)
There is no "best" routing protocol, regardless of what you may hear different people say. It's all a matter of your network design, and what you are trying to do.
I heard some comment from other network engineer that eigrp doesn't scale well and I wonder what's the limit (like how big is too big)?
We're using eigrp as our internal routing protocol, and we have less than 20 routers involved, in this case, I don't think we need to switch the protocol to ospf, at least I haven't encountered any problem with eigrp at this point. Do you have any suggestion?
I wouldn't switch, unless I had some specific capability or reason to.... EIGRP not scaling? I don't know... I know of several EIGRP networks over 2000 routers, which seems pretty big to me.... :-) I know that with EIGRP, if you summarize right, and bound your queries right, there's really no limit in terms of routers.