Hi,
I suppose you're natting traffic so first you must do this for NAT:
1) create 2 route-maps
route-map SERIAL
match ip add 1
match interface serialx/x
route-map DSL
match ip address 1
match interface dialerx
2) create the ACL 1
access-list 1 permit x.x.x.x y.y.y.y where x.x.x.x is the subnet you want to be natted and y.y.y.y is wildcard mask
3) create 2 dynamic nat entries
ip nat inside source route-map SERIAL interface serialx/x overload
ip nat inside source route-map DSL interface dialerx overload
Now for failover you must use reliable static default route with ip sla:
1) create the ip sla action
ip sla 1
icmp-echo x.x.x.x.x where x.x.x.x is the next-hop on serial link
timeout xxx how many time without a response so ip sla fails and tracked object is down
frequency xxx how often you send the ping
exit
ip sla schedule 1 start-time now life forever start the ip sla action
2) create the tracking object:
track 1 rtr 1 reachability
3) create 2 default routes, the backup one has an AD higher than primary and you gonna track the primary
I suppose primary is Serial:
ip route 0.0.0.0 0.0.0.0 serialx/x track 1
ip route 0.0.0.0 0.0.0.0 dialer x 100
Regards.
Alain.
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