Gateway doesn't work.

[Sam Neth <sam neth com>]

I'm rather new to Linux, and while I've done a lot of work on Unix boxes
(mostly Solaris), I've never had to get my hands this dirty.  I've got a
Linux box set up (4.0) on a small network that also hosts a few Windows
machines.  I have a cable modem for access to the outside world.  

My machines can see each other (so the network works), and the Windows
machines can get out to the Internet (so the cable modem works), but the
Linux machine can't get out.  It first became clear I had a problem when
I tried to telnet in from one of the Windows machines.  It takes a long
time to respond.  I suspect it was flailing on a reverse DNS lookup.  As
it happens, no traffic in or out of the Linux box is getting through my
cable modem.

This seems like a simple problem, but I've been searching the lists for
any help and haven't found any.  Everyone seems to be using PPP.  I can
provide any config file information required to diagnose the problem-
I'm not really sure what's relevant.