ip route 0.0.0.0 0.0.0.0 Serial0/0/0 -> this router will remain in routing table, until the serial interface goes down.
Typically, your serial port is connected to a Telco device (CSU/DSU). This means that if there is a network failure (behind the telco device), your serial port will still be up/up, even if there is no connectivity.
You may use an IP SLA to track the reachability of a remote IP, and add the track to the route command.
Regarding the DSL link, ATM is just the lower layer, you shouldn't configure L3 there. You need to add a dialer interface over it, and use the dialer in the NAT/route commands.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...