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Event ID 20209 - A connection between the VPN server and the VPN client has been established, but the VPN connection cannot be completed.

 VPN Error 721, 800 or 806

Symptom: When try to establish a VPN, the VPN client may receive error 721, 800 or 806. The RRAS Event Viewer may have Event ID 20209 - A connection between the VPN server and the VPN client has been established, but the VPN connection cannot be completed. The most common cause for this is that a firewall or router between the VPN server and the VPN client is
not configured to allow Generic Routing Encapsulation (GRE) packets  (protocol 47). Verify that the firewalls and routers between your VPN server and the Internet allow GRE packets. Make sure the firewalls and routers on the user's network are also configured to allow GRE packets. If the problem
persists, have the user contact the Internet service provider (ISP) to determine whether the ISP might be blocking GRE packets.

Cases and Solutions

Case 1: The client can establish the VPN if he removed the router and connect to the Server directly.

Solution: Upgrade the router firmware.

Case 2: The client can’t establish the VPN using wireless. However, if he try to use wired, he can make the VPN connection.

Case 3: The client can VPN to his office from all places except home. At home, he has satellite service.

Possible cause: Many wireless/mobile carriers block that sort of data unless you pay them extra or order a static IP.

Case 4: The VPN on Windows 2003 server worked for one year. It stops to work after installed SP1. If removing the SP1, the VPN works fine.

Possible solution: Troubleshooting Windows 2003 SP1 issues

Case 5: The user can establish the VPN from the desktop at home but not from the laptop.

Troubleshooting: He loaded Microsoft OneCare software that blocks the GRE. Reconfigured the OneCare settings fixes the problem.

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