OSPF in a hub & spoke topology with two hubs 1

[dozier]

Hello.

I am trying to setup OSPF on a frame-relay network. I have a 3745 in my primary site to which all of the remote routers (spokes) have 56k PVCs built to. Then there is my secondary site with another 3745 to which the same remote routers have 56k PVCs built to. There is a point-to-point T3 connecting the two 3745's, and those interfaces are in Area 0. All of the WAN links from the remotes to both hubs are in Area 3. The primary 3745 has a default OSPF cost of 5, while the secondary has a default OSPF cost of 10, thereby making the primary PVCs the preferred. My problem is this:

I shutdown the subinterface on the secondary 3745 for one of the remotes (R1). The routes installed on the secondary 3745 for reaching networks attached to R1 now point to another remote router (R2) instead of across Area 0 (the T3 to the primary 3745). I assume that this happens because intra-area routes are preferred above inter-area ones despite bandwidth costs?

If I need to post some configs I will.

Thanks.

 

[KiscoKid]

You're absolutely right in your hypothesis that intra-area routes are always preferred over inter-area.

In the past Cisco advised to create 2 ospf processes as this negated this ospf path preference algorithm, i.e. the router used AD's and metrics instead.. which is probably what you want it to do.

However, I understand you may be able to disable rfc1583 compatibility in the ospf process. This actually modifies the path preference used by OSPF. I *believe* (I say believe because I've never had reason to configure this), this will mean intra and inter area routes are treated equally, i.e. the router will use metrics as the tie-breaker regardless if it's an O or O IA route.

HTH

 

[dozier]

KiscoKid, thank you for directly addressing the validity of my hypothesis and then offering solutions. I will look into both of those possibilities. Thanks.