iptables newbie.

[ken at flyingtoasters.net]

Hi, all.  To date, I'd implemented security at home by simply having only
services I needed running.  However, I've gotten to the point where I'd
like my Linux box to be running stuff like NFS, and I do -NOT- want NFS
showing up on the 'net.  I've RTFM'd some, and toyed around some, but am
clearly missing the magical iptables incantation.  What I'd like is pretty
darn easy, methinks, and I just haven't stumbled upon the right
permutation yet.

I've got a couple of NICs, both physical and virtual.  Basically, I'd like
to restrict eth0 (my cable modem) to only allow 80, 25, and 22 in-bound,
and everything else (lo, eth1, ppp0), I'd like wide open.  Any
suggestions/pointers as to how to do that?  Should NAT (which I have
implemented) cause me any grief?

Thanks,

-Ken