I need some advise on the following design.
I am designing a campus network using routed access with OSPF. I will have 3 tiers - core, distribution and access. I am looking to configure the core/distribution links in OSPF area 0 and then the distribution/access links in a non-backbone area such as 1. I will then be able to filter/summarize etc as the ABR boundary.
I only have 2 links from my core to distribution layer and I'm planning to terminate them on separate distribution switches (dist1 and dist2), see attached diagram.
The links facing the DC will be in area0 and the links facing the access will be area1 but what area should the distribution to distribution link be in? I understand that if it is in the non-backbone area1 then I will loose the ability to use the link to the second core as intra area routes will be preferred by dist1. Are there any other considerations here? Should I connect two links between the the 4500s and configure 1 link in area 0 and 1 link in area1?
I would add a link between Dist1 to Core2 and Dist2 to Core1 if possible. This will improve convergence as you would have triangles instead of square topology. You would then have equal cost routes towards the access switches so if a link fails then there is already a route in the RIB/FIB.
Regarding which area to put the Dist to Dist link in it would depend on if you expect most traffic to arrive towards area 0 or toward other areas. By the look of your design it seems you will be using mostly the backbone to transport traffic and put hosts/servers etc in their own areas?
Another option is to have dual adjacencies between the Dists. One in area 0 and one in area 1. Then you would have optimal forwarding even if a link fails.