Don't forget Linux and the various BSD stuff. Quite a few people
run modems with these as terminal servers. Certainly this
would be trivial in Linux, from experience.
It would probably be advisable to be able to disable this on a per
i/f basis as there are a few people who intentionally have locally
assymetric routing (pile of Maxen with 2 routers for redundancy
and load-sharing for instance) but could still work
with spoofed source IP address filtering on the modem
ends.
Alex Bligh
Xara Networks