My aim is to have a backup line so that when one line goes down the traffic should go through other leased line.
Ip route 0.0.0.0 0.0.0.0 serial 0 Ip route 0.0.0.0 0.0.0.0 serial 1
This will load balance the traffic between the two lines. If you don't want load balancing, and want second line purely as backup, then your configuration would look like –
Ip route 0.0.0.0 0.0.0.0 serial0 Ip route 0.0.0.0 0.0.0.0 serial1 150
The 150 command in the second route here tells the router that the administrative distance for the second route is 150 (for normal static route it is 1). So the second route has a less preference than the first route, and should only be used when the first route fails.
This was first published in April 2004