Does anyone know of a Linux script or other mechanism to allow a PPP
dialup connection act as a backup for an ADSL connection? Hopefully
something that would autodial if the "main" connection failed, would
hangup after some idle time, and only dial out again when the main
connection was not working. This is for a Linux router machine.

This *must* have been answered before, but I did not find it. Please
excuse me if this has been answered too many times already.