Two nics; only one works at a time

[Kent West <westk@acu.edu>]

I've got a freshly installed Debian Stable box with two NICs, a 3c509 
and a 3c509c. In /etc/network/interfaces, I have them defined thusly:

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp

auto eth1
iface eth1 dhcp

When I (re)start networking, ifconfig shows both cards to be configured 
with all the proper numbers, but networking out is "iffy" (I haven't 
been able to pin down a pattern), and I can ping from a different subnet 
the eth1 card but never the eth0 card.

If I comment out one of the cards (it doesn't matter which one) in 
"interfaces" and restart networking, I can then ping from the different 
subnet the card not commented out. In other words, both cards work, but 
only one at a time.

I've also tried static IP addresses with essentially the same results.

I've booted off a Knoppix 3.3 CD, and both cards worked as expected, and 
I was able to ping both cards from a different subnet.

I actually wiped the drive and did a clean install of Stable, only to 
find the same results afterward. I also upgraded from the 2.2 kernel to 
2.4.18-1-686; it made no difference.

I've been googling all day trying to find an answer, and haven't hit the 
right answer yet. If this isn't solved by tomorrow, the decision makers 
are going to go with Redhat (because we're in a time crunch). Does 
anyone have any insight as to what I need to do to get both NICs working 
properly?

Thanks!

--
Kent