I'm stumped on this one. I'm running Ubuntu on one computer and windows XP on another computer. I have a Linksys WRT54GS and both computers are plugged into the wired LAN ports. I have a wireless broadband service which is interfacing to the WAN port of the router.

Everything was working fine, then all of a sudden, I could no longer get an IP from my router on my linux box. Mind you that my windows xp box keeps getting an IP and accessing the net fine. I tried all of the software/kernel experiments I could think of and find on the web to no avail. And here is a list of the hardware experiments I did:

1. Used the same ethernet cable that was successfully servicing my XP box. FAIL. This should absolve the ethernet cable between my linux box and the LAN port on the router assuming a single point of failure.
2. I removed the WAN connection from my router and plugged it directly into my linux box and I got an IP! So this means that the network card, driver, and such are fine.
3. When I reconnected my linux box back to the router, I actually saw a DHCPNAK from the messages in dhclient. This is because the lease obtained from the WAN connection was asking for the same IP again and the router denied it. So this seems to indicate that there is indeed a connection being made, at least temporarily between my linux box and the router. When I removed the old lease, the router reverted back to simply ignoring my box.

Now I don't have any MAC filtering active which would exclude this box. So I am completely stumped. Any help would be greatly appreciated.

Carl...

So, DHCP on Linux seems to be working, since it can ask for an IP when it's connected directly to your broadband interface (ie without router).

However, DHCP no longer works when the router is in place.

The cable Linux - router isn't the problem as your test shows.

Have you checked your router's config?

Also try hooking your Linux box to the router port of the XP box. Shouldn't make a difference, though.

Thanks Timmeke, I think I already tried your last experiment when I took the cat5 cable out of my xp box and plugged it into the linux box. I know that that cable and the LAN port on the router were good since it was servicing the xp box. Tonight I'm going to try to reboot everything (router & dish) to see if anything helps. Also, I'm going to try to upgrade the firmware on the router. Both long shots though. I'll post my resuts, but any more ideas would be greatly appreciated. Thanks again.

I was just thinking:

It works when your Linux box is directly connected and it doesn't when the router is in place.
Is there anything different -configuration wise- on your Linux box in both cases?

And then, it hit me:
How can your box be asking for an IP of a WIRELESS interface, whereas it is now connected via a WIRE to your router? Both network interfaces, wlan0 and eth0 (probably) should have different IPs. And if they don't, please make sure that only one of the 2 interfaces is up at any time. Otherwise, you can get into trouble.

So, "ifdown" wlan0 when eth0 is up and vice-versa...

I'm sorry to have been vague in my original posting. What I meant to convey was that the two computers, the xp box and the linux box, both have WIRED network interfaces into the linksys WIRED ports. The linksys router has 4 wired connections plus a wireless interface.

However, I do have good news. For reasons I can't explain, the combination of upgrading the firmware and resetting the router to its factory defaults has solved my problems. The linux box can now grab an IP fine. Unfortunately, I performed both of these acts in series and I'm not sure if just one of these actions would have solved my problem alone.

Thanks again so much for your time and help on this matter.

You're very welcome. I'm just glad you managed to resolve the issue.