Something strange happened to network setup on XP Pro machine

Hello

I observe a rather strange loss of network functionality on my XP Pro machine.
Maybe someone can help me to figure out what happened.

I have the following setup: two XP Pro machines (desktop and laptop) are
connected by wires to a Linksys WRT54GS router at 192.168.1.1, which is in turn
connected to a RCA/Thomson cable modem for Internet access. The desktop is
configured with static IP (192.168.1.2 and 192.168.1.1 is specified as its
default gateway), while the laptop obtains its address dynamically from the
router (normally it gets 192.168.1.4). Everything was working perfectly for
several years.

Last night something happened. In the morning I discovered that neither machine
can access Internet, even though the modem's and router's lights seem to
indicate that everything is fine. I rebooted all devices, which restored the
Internet access for the laptop, but the desktop still refused to go online. The
interesting part here is that the desktop can perfectly fine ping the laptop and
access the laptop's shares, it has no problems accessing the internal setup
pages of the router (192.168.1.1), it can also access the internal status pages
of the cable modem (192.168.100.1) without any problems, but it cannot resolve
URLs and it cannot ping/go to external IP addresses, even if they are specified
explicitly.

To figure out what's happening, I decided to try connecting the machines to the
modem directly (eliminate the router). Not surprisingly, there was no problem
with the laptop. In order to connect the desktop I had to set its TCP/IP to
automatic confuguration. I connected the machine directly to the modem and
rebooted everything. The desktop got stuck in "Acquiring network address" mode
forever. 'ipconfig' would report '0.0.0.0' and there was no Internet or LAN
access, of course.

I connected everything back the way it was before (connected both machines to
the router), still keeping the desktop in automatic TCP/IP config mode. After
booting up the desktop, once again got stuck with "Acquiring network address"
indefinitely. (Yes, the router's DHCP has enough dynamic IP adresses available).

I reconfigured the desktop back to the static 192.168.1.2, rebooted it and
everything went back to the way it was this morning. The desktop had no problem
accessing LAN, including the internals of the router and the modem, but no WAN
access. The laptop had stable WAN access.

As an additional experiment, I pulled out of the closet my previous router -
Linksys BEFSR41 - and repeated all these steps with this router as well. I got
exactly the same results. The desktop can't obtain a dynamic IP, can't access
Internet, but works fine with LAN addresses when configured statically.

To take things even further, I disabled the desktop's integrated NIC and
inserted a "standalone" PCI NIC. Makes no difference. The problem apparently in
with the software config, not the hardware.

I tried switching cables, connectors, routers, everything. The problem seems to
be with the TCP/IP setup of the desktop machine. I tried resetting winsock and
TCP/IP settings using 'netch' - no effect at all.

I also noticed, that when I access the modems internal page (192.168.100.1) from
the statically configured desktop, I can see it reflected in router's log under
desktop's IP (192.168.1.2). Any attempts of WAN access from the desktop leave
absolutely no trace in router's log. It looks like the desktop is not even
trying to consider the router for Internet access.

Can anybody please suggest something? What could be the reason for this behavior?

Thank you,
Andrey
.

Relevant Pages

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    (microsoft.public.windowsxp.network_web)
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