AT 2500TX / DHCP problems

Hello.

I'm using an Allied Telesyn 2500TX network card in my desktop computer,
which is a dual-boot Windows 2000 / Slackware Linux 10.1.
The card works fine if I give it a static IP. I can see eth0 up and
running, and I've transfered several files from my laptop to my desktop
successfully.

But I've been trying to use the card with a Motorola SBV5120 cable modem
with DHCP and it fails. On Windows, it just gets a bogus IP address
but no gateway and no DNS server, and on Linux, running "/sbin/dhcpcd -d
-t 10" results in a timeout but no IP address (says it can't contact a
DHCP server). Increasing the timeout didn't work, either.

I should mention that this all works just fine with my laptop's 3com
card - on both Slackware Linux 10.1 and Windows 2000 - so the problem is
not with the modem or the network settings. Also, I've tried to force
the network card to 100/full-duplex, 100/half-duplex, 10/full-duplex,
10/half-duplex on Windows and try to redo the DHCP connect sequence, but
to no avail.

I've tried to debug the problem but all I got was that an IP has been
obtained (on Windows, the garbage IP), or that attempting to contact a
DHCP server timed out (on Slackware).

Ideas on how to either debug the problem further, or better yet solve it
alltogether, are greatly appreciated.

Thanks.

Funny update. I managed to fool the DHCP server into thinking that the
NIC on the desktop is actually the NIC from my laptop (changed the LAA
manually to be the MAC address of the NIC from the laptop), and it worked.

Unfortunately I still can't make it on Linux. Neither the -I parameter
to dhcpcd, nor the send dhcp-client-identifier <mac_address>; for
dhclient work. Oh well.

Again, any ideas appreciated. Why would a DHCP server not work for a MAC
address but work for another? This is an ISP we're talking about, they
shouldn't be making assumptions about the clients' MAC addresses.
Perhaps they're just incompetent.

Nevermind, apparently I was the incompetent one :-). Looks like this
monolgue-like thread's conclusion is that cable modem "marry" the 1st
MAC address they see, and need to be reset in non-trivial ways before
accepting a new MAC address.

The best solution is to just fool the modem into thinking all the
computers have the same MAC address. The solution to do this in Linux is
to do an "ifconfig eth0 hw ether <mac_address>" before running dhclient
or dhcpcd.

I found some more interesting information on the matter at

http://www.duxcw.com/faq/ics/cablemac.htm

and

http://homepage.ntlworld.com/robin.d...tips/swap.html .

Hope it helps some other poor confused soul.