VPN not verifying user/password from one location

Hi,

We've successfully been using a RAS running on Win2K Server to allow certain
users to connect remotely to our domain using a VPN connection.

Some of these users connect from our Head Office, and again this has been
working fine for the last 12 months.

On Friday, I visited HO and was using my laptop (WinXP Pro) on their
network. When I tried to connect to our network from HO using the VPN
connection, it would get as far as "Verifying username and password", but
would hang and after about a minute, would time out, stating that the remote
server did not respond.

This was then the case for anyone at HO trying to connect to our VPN.

Over the weekend, I tested my VPN connection at another location, using my
laptop, and it worked fine.

This morning, we tested it again and I was astonished to find the firewall
on my laptop alert me to an incoming connection from the HO IP address,
using IP protocol 47 (GRE).

Our router is set to forward VPN traffic to our RAS server. This is the
only forwarding employed by the router, so this suggests that the HO users
are hitting the RAS and somehow either being redirected, or requesting, to
authenticate(?) with my laptop.

Here is what we've tried:
- flushing the remote PCs DNS cache and checking HO's DNS server for any
relevant entries (none found)
- taking my laptop off the network (problem persists)
- changing the IP address of my laptop (the GRE requests still find my laptop)
- checking if HO are running a WINS server (not sure if this has any
relevance - either way, they aren't running WINS server)

Looking in the system event viewer on my laptop I noticed lots of error
events, ID: 4321, source: NetBT, description:

The name "<our domain name> :1d" could not be registered on the
Interface with IP address 10.0.0.244. The machine with the IP address
10.0.0.103 did not allow the name to be claimed by this machine.

.....where .244 is my laptop IP and .103 is the RAS/AD machine. I then
noticed my subnet mask was wrong: 255.0.0.0. Changing this to 255.255.255.0
stopped the errors occurring. 255.0.0.0 was the subnet mask my laptop had
when I first connected to the HO network (before changing to DHCP as their
subnet was different), and no errors occurred at this point.

Everything seems to suggest that my laptop has somehow "registered"
something on their network which is causing their VPN connections to us to
request something from my laptop.

Connections from other locations connect to our network fine, as do outgoing
connections from HO to other networks than ours.

Any ideas how I can sort this problem out?

(Sorry for the loooong post but I figured it's best to provide as much info
as possible.)

Cheers,
Simon Liddle

After much fiddling about in settings and checking/rechecking everything, I
finally sorted the problem by removing RAS and reinstalling it!

Cheers,
Simon Liddle

Thank you for the update.

Bob Lin, MS-MVP, MCSE & CNE
Networking, Internet, Routing, VPN Troubleshooting on http://www.ChicagoTech.net
How to Setup Windows, Network, VPN & Remote Access on http://www.HowToNetworking.com
"Simon Liddle" <(E-Mail Removed)> wrote in message news:(E-Mail Removed)...
After much fiddling about in settings and checking/rechecking everything, I
finally sorted the problem by removing RAS and reinstalling it!

Cheers,
Simon Liddle