We have a Cisco 2801 router, Serial interface is connected to T1 passing voice and data between the branch office and the main office and works fine. Interface f0 is connected to the internal network of the branch office, we would like to connect interface f1 to a wireless bridge that connects to the main office. We would like to have the wireless bridge to be the main route the main office and the T1 to be the backup route in case there was a failure on the wireless. how to configure the 2801 (version 12.3) to allow redundancy and eliminate the loops.
a further refinement to what Jon has suggested in order to improve convergence
you can track the reachability of the wireless lan IP next hop.
Hope to help
The simplest solution is to use 2 default-routes
ip route 0.0.0.0 0.0.0.0
ip route 0.0.0.0 0.0.0.0 200
Note the 200 at the end of the second default-route. This makes the route a floating static. If the next-hop via the wireless becomes unreachable then the next-hop via the T1 will be used. If the wireless comes back up then it will revert to the wireless next-hop.