Priority based routing

[CanEHdian]

I've got 2 available links between my two corporate office locations. How can I configure my core cat-4510 at one end to point (static) to link #1 as the primary route to reach the other network and to link #2 as a backup in case the first one dies?

Thanks..

[Richard Burts]

Al

The normal answer for how to configure one link as primary and the other link as backup is to use floating static routes. You define the static route for the primary as a normal static route and you configure the floating static route with a higher administrative distance. For example:

ip route 0.0.0.0 0.0.0.0 ser0/0

ip route 0.0.0.0 0.0.0.0 ser 0/1 250

You will then have one entry in the routing table using the primary interface and if it fails then the other route gets installed in the routing table.

The potential issue with this approach is whether the primary route gets withdrawn if you lose connectivity over the primary link. With traditional point to point connections it usually works but with most LAN connections it has problems because you may lose connectivity to the other end but the interface stays up and the primary route stays in the routing table. Cisco has introduced a feature that deals with this. It may be available depending on the version and feature set that you are running. The feature is static routes with object tracking.

HTH

Rick

[CanEHdian]

Thanks Rick, good info... especially the object tracking feature.

That is the issue, my core points to a 1721 router which is the first hop towards the p2point T1 link between our offices. If the T1 link dies, the router's ethernet interface is still up, so the 'first hop' for the route entry is still up, hence no failover... or am I missing something?

[Richard Burts]

Al

I think you are facing the classic problem of trying to do floating static routes (primary and backup) where the routes point at LAN interfaces where you may lose end to end connectivity but the interface is still up up. The new feature I mentioned is what Cisco has introduced to address this situation. This URL:

http://www.cisco.com/en/US/products/sw/iosswrel/ps5413/products_feature_guide09186a00801d862d.html

should give you enough information on it to get you started with it. I believe that it will provide a solution for your situation.

HTH

Rick