2nd route:

You can use a floating static route:

ip route 0.0.0.0 0.0.0.0 [IP of OTHER end of PTP] 250

The floating static ONLY works if the actual interface goes down, it does not account for upstream failures.

If you want to account for upstream failures, you can use an IP SLA and use a tracked object. You can set the IP SLA to ping an IP on the internet, if the IP is unreachable, remove that route and use the other one.

Example:

ip sla 190

icmp-echo 4.2.2.2 source-interface [DSL interface]

frequency 30 {pings every 30 seconds}

ip sla schedule 190 life forever start-time now

track 190 ip sla 190 reachability

ip route 0.0.0.0 0.0.0.0 [DSL IP] track 190

ip route 0.0.0.0 0.0.0.0 [IP of OTHER end of PTP] 250

The example creates an SLA that pings 4.2.2.2 every 30 seconds from the DSL internface. You then create a tracking object to keep track of the state of the SLA and link it to the static route. If the tracked object is in the "DOWN" state, the route that's linked to the tracked object is removed from the routing table and the floating static is put in.

Once the IP is reachable again, the route would go back to the DSL connection automatically. You still need the floating static route as well.

Other routes:

just use static routes. If for example the servers on the other side of the PTP are on the 10.1.1.x/24 network:

ip route 10.1.1.x 255.255.255.0 [IP of OTHER end of PTP]