VPN suddenly stopped working

2 weeks ago we had a working VPN. Now it is impossible to connect.

Set up:

Demon UK ADSL, fixed IP business service.
Belkin Router
Windows 2003 server (up to date)
WinXP SP1 and SP2 clients

Bear in mind this set up was functioning perfectly for over 8 months
(the server was NT4 SBS for another 4 months that but with the rest
the same).

Symptoms:

A. Each client gets error 721 when connecting, which we understand is
a lack of GRE, protocol 47, communication.

B. We can connect internally (ie. local LAN PC connects to W2003
server as a VPN client).

C. If we plug a PC into the ADSL router directly, we can VPN into
that.

D. Cannot VPN into any other Windows XP PC on the network.

E. Did packet trace using ethereal. This showed that it certainly was
the GRE traffic that was being blocked. The negotiation stopped
immediately a GRE packet would be required.

Solutions attempted:

1. Called Demon, they claim not to be blocking anything, which would
seem to be true from C.

2. Reset Belkin router to factory and entered all settings again (from
printouts or config that had been working for 8 months). No
difference.

3. Changed router hardware. No difference. Changed it back again.

4. Rolled back a Sept 15th patch to W2003 (the jpeg vuln), no
difference.

5. Various changes in Routing and Remote Access, nothing that we had
any confidence would work, and nothing did.

Posting basically in desperation. Can't think of anything else to try
at the moment. The symptoms would seem to point to the router, but
maybe something on the server (which is our DNS and domain server) is
stopping this working. Since the router worked for so long, and has
been reset and exchanged, I am at a loss.

ANY help or advice greatly appreciated!

Dominic Fitzpatrick

I would focus on the router.

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"Fidtz" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
>2 weeks ago we had a working VPN. Now it is impossible to connect.
>
> Set up:
>
> Demon UK ADSL, fixed IP business service.
> Belkin Router
> Windows 2003 server (up to date)
> WinXP SP1 and SP2 clients
>
> Bear in mind this set up was functioning perfectly for over 8 months
> (the server was NT4 SBS for another 4 months that but with the rest
> the same).
>
> Symptoms:
>
> A. Each client gets error 721 when connecting, which we understand is
> a lack of GRE, protocol 47, communication.
>
> B. We can connect internally (ie. local LAN PC connects to W2003
> server as a VPN client).
>
> C. If we plug a PC into the ADSL router directly, we can VPN into
> that.
>
> D. Cannot VPN into any other Windows XP PC on the network.
>
> E. Did packet trace using ethereal. This showed that it certainly was
> the GRE traffic that was being blocked. The negotiation stopped
> immediately a GRE packet would be required.
>
> Solutions attempted:
>
> 1. Called Demon, they claim not to be blocking anything, which would
> seem to be true from C.
>
> 2. Reset Belkin router to factory and entered all settings again (from
> printouts or config that had been working for 8 months). No
> difference.
>
> 3. Changed router hardware. No difference. Changed it back again.
>
> 4. Rolled back a Sept 15th patch to W2003 (the jpeg vuln), no
> difference.
>
> 5. Various changes in Routing and Remote Access, nothing that we had
> any confidence would work, and nothing did.
>
> Posting basically in desperation. Can't think of anything else to try
> at the moment. The symptoms would seem to point to the router, but
> maybe something on the server (which is our DNS and domain server) is
> stopping this working. Since the router worked for so long, and has
> been reset and exchanged, I am at a loss.
>
> ANY help or advice greatly appreciated!
>
> Dominic Fitzpatrick