Friday, January 25, 2008

Failed connecting to VPN using a cellular modem

I bought a cellular data package of few gigs and tried to connect to the internet (using my cellular phone as modem, connecting it to my laptop with bluetooth). Everything was working except VPNs. Any VPN I tried connecting to hanged during the authentication (e.g. "Authenticating username and password").

This is a symptom that the network does work correctly with GRE protocol (which is not UDP/TCP). Usually I would look for a firewall or port forwarding issue, but since I got the same result with my 2 VPNs (which worked just fine with my ADSL connection) - I decide to call my cellular operator.

The answer was very simple, and I don't understand why I didn't find it on the web.

1. Open the "Network Connection" you defined for the connection, and find the name of the modem you're using for the connection (since I was using bluetooth the modem name was a generic one).
2. Open "Control Panel" -> "Phone and Modem options".
3. Select the "Modems" tab and open the modem properties.
3. In the advanced tab put the following string: