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Windows XP notebook suddenly stops accepting GRE packets

sjors1309
sjors1309 asked
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Last Modified: 2012-05-11
Hi All,

My windows XP SP3 notebook (Dell precision) cannot connect to any network through a VPN. I've been using this computer to connect to clients' VPN's for years. A few days ago, I suspect a security update, it stopped connecting. The window stating that the accountname/password are verified on the remote network appears and remains until error 721 is reported.

Just this one laptop computer has this. My other systems can connect to the VPN server from behind the same firewall.

I setup a test:
- VPN server and my laptop computer in a LAN (no firewalls installed on server or notebook)
- Wireshark running at both ends
When starting the PPTP protocol I see a successfull TCP traffic setup (port 1723). After GRE parameters are established both server and client send LCP Configuration Request packets (encapsulated in GRE). Packets from the client are seen by the server, but packets that the server sends aren't seen at the client. They simply don't appear in wireshark.

I've scanned my system for infections. Nothing came up.

Any ideas?

Thanks in avance.

Regards
Sjors
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Rob KnightConsultant
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Commented:
Hi,

Are you using the inbuilt or 3rd party VPN client?

Cisco VPN clients have been seen to cause issues which necessatred removal, registry cleaning anf re-installation.

Regards,


Rob.

Author

Commented:
Hi Rob,

I'm using the inbuild VPN client.

I also have the Cisco VPN client installed. That client (not using PPTP but IPSec over UDP) is working fine. I can connect to remote networks from my machine with the Cisco client.
Consultant
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Commented:
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Author

Commented:
That's it!

I would have never guessed!

This configuration has been working for years. Using the XP Client for VPN access through PPTP and the Cisco client to connect to other neworks that have Cisco PIX/ASA fw's installed.

Do you have a logical explanation for this sudden change in behaviour?
Rob KnightConsultant
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Commented:
Hi,

I don't have an explanation, just am aware of the issue.

Regards,


RobMobility.

Author

Commented:
Thanks
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