ntl cable DSL and default route

[ifconf]

I have several home users that have ADSL connections. Most of them are on BT lines and using SB107 routers. I configure these with the following route statement to connect to the internet;
ip route 0.0.0.0 0.0.0.0 D0
This works perfectly well as expected.
However, some of my remote users have Cable modems with NTL and on these I use the SB101 plugged into the NTL provided modem. In these cases the above route statement has no effect, pinging an internet IP address will either fail or produce !.!.! if I'm lucky. The only way to get it to work is to find the ntl gateway and ammend the route statement to read;
ip route 0.0.0.0 0.0.0.0 xxx.xxx.xxx.xxx (whatever the local gateway is.) Which is a bit of a pain. Any one have any ideas?

 

[directlyconnected]

The only thing I can figure is PPPoA (cable) versus PPPoE (DSL). If it's PPPoE, the dialer interface can use an ip address supplied by the isp RADIUS server (interface D0, ip address negotiate). If it is PPPoA, I am not sure how the dialer interface interacts with the isp---the default route points to the dialer interface, which does all the PPPoE negotiations. Don't know about PPPoA.