Windows XP notebook suddenly stops accepting GRE packets
Posted on 2011-04-27
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.
Thanks in avance.