NIC problem

["Glenn Evanish" <glenn@example.com>]

I've got a box that I'm trying to set up as a ADSL firewall and router, so
of course I need two net cards in it.  The net cards seem to set up just
fine and look good in ifconfig - IP, netmask, and broadcast - and they
answer pings from the console.  However, if I ping another box or my router,
the network is unreachable.  It's extremely frustrating.

I don't know what to do next.  The cards are just fine in other boxes, but
when they go into that box, they're "looking at themselves" only.  I've had
this happen in other situations, too, including on this one I'm typing on
now.

What would make a card that appears fine in ifconfig not be able to ping
another box or answer a ping from another (local) box?  How to troubleshoot?

TIA,

Glenn