Solved: OSPF Multiarea question

telecodi · ‎05-30-2007

Hi, this is Dani from Barcelona

I have a question for you about multiarea deployments. In my lab (see attached file), I have 2 routers in the Datacenter (area0 ) and one remote site (area 1). The preferred path to the remote site is obviously the point-to-point link; that's why I forced the OSPF cost to 10. The backup tunnel has an OSPF cost of 150.

If it were a single area everything would work fine but in a multiarea environment, the DATACENTER-2 routing table shows the path to REMOTESITE via the backup Tunnel, eventthough its cost is greater the the path learned through ethernet via DATACENTER-1. It happens because for DATACENTER-2, the route to Remotesite is considered as an INTRA-area route whereas the route via DATACENTER-1 is an INTER-area route. OSPF will install always the INTRA-area route before the INTER-area routes, is that correct? If so, how can I fix it?

The area 0 is much bigger than shown in the picture.

Thanks everybody

Dani

sundar.palaniappan · ‎05-30-2007

Dani,

Your understanding is correct. OSPF would always choose intra-area route over inter-area route though the cost may be higher via the intra-area route.

One way to address this problem is you can set the admin distance to a higher value, any value more than 110, on DATACENTER-2 router for the routes learned from that remote site. This would force all the traffic to go over the DATACENTER-1 router while retaining the redundancy in case of an outage.

HTH

Sundar

View solution in original post

sundar.palaniappan · ‎05-30-2007

Dani,

Your understanding is correct. OSPF would always choose intra-area route over inter-area route though the cost may be higher via the intra-area route.

One way to address this problem is you can set the admin distance to a higher value, any value more than 110, on DATACENTER-2 router for the routes learned from that remote site. This would force all the traffic to go over the DATACENTER-1 router while retaining the redundancy in case of an outage.

HTH

Sundar

telecodi · ‎05-30-2007

Hi Sundar

thank you very much for your answer. I will follow your suggest !!

Dani