Adding OSPF Clouds to an EIGRP WAN

[bohdel]

I have an EIGRP network with about 100 or so sites that all run within the same EIGRP AS. About a year ago we were purchased by another company that is comprised of many smaller network clouds, that use differnt routing protocols (both RIP, and OSPF as well as EIGRP with a different AS #). One by one we have been connecting these clouds to our WAN. We typically do this with one or even two links in which redistributing OSPF into EIGRP or static routing with costing works fine. More recently, the networks are becoming more meshed, and I'm trying to decide the best way to connect. For example, we have 3 links to one OSPF cloud. All 3 links are in seperate locations. This would bring 3 peering points into one network, and I'm not sure the best way to do this. Recommendations ? We are trying to standardize the routing protocols, but until then, I have to try to get as much dynamic routing in place as possible. Thanks !

[Gilles Dufour]

I'm not sure to see what you're looking for. Your question is too large to get an answer.

The best would be to do a complete redesign of all these networks and migrate them to OSPF (or any other protocol you will chose - but only one).

As you said, this is not your problem right now.

Regarding your 3 links, do you want to put them in ospf and do the redistribution in Eigrp at the peering site ?

Do you want to do the redistribution at the central site ?

Is there any connection between the 3 sites ?

When you start redistribution, if you have multiple point of redistribution, you need to be carefull to avoid loop.

This can be done by using TAG. I believe there are some examples on www.cisco.com/tac

If there is a specific thing you need hel with, please try to focus on it and give us more detail.

Thanks,

Gilles.

[bohdel]

What I am trying to find out is the best way to integrate an OSPF network into an EIGRP network, when there are links to the OSPF cloud in 3 places. So I have a 100 node EIGRP network. Three of it's nodes are the locations, let's say NY, SF, and Chicago. These same 3 locations will also now connect to an OSPF cloud that has say 40 nodes. What's the best way to do this without causing loops? Redistribute in only one place (ie NY for example), or put both OSPF and EIGRP on the router at each location and don't redistribute any routes, etc. Does that make more sense ?

[doug.lockwood]

There are several ways to prevent routing loops with mutual redistribution.

EIGRP sets external routes to a higher Administrative distance (170) than EIGRP routes. OSPF does not do this by default, but it is possible to configure.

By setting the administrative distance of external OSPF routes to 170 on your OSPF routers, Both EIGRP and OSPF will ignore routes that might otherwise cause loops.

Other options are to tag incoming routes, then filter out tagged routes when redistributing. Also, Since you know which routes are redistributed, block those routes from re-entering the Routing Domain.

In the long run, its safer and less complex to run a single routing protocol.

If you are looking for a good re-distribution text, Routing TCP/IP by Jeff Doyle is a great reference.

Regards;

Doug