I'm trying to establish a VPN tunnel from my laptop over GPRS to my office LAN. VPN works fine from broadband or dialup, but GPRS fails.
Client is Windows XP, Server is pptpd/pppd on a Snapgear appliance, mobile provider is O2 Germany. It seems the GPRS connection works via NAT and that this may be the cause of the problem. The log shows "LCP: timeout sending Config-Requests" which might also indicate that my side couldn't answer because of NAT.
Is there anything I can do about that concerning the server configuration? I do have good knowledge about Linux and partly about networking but exactly none about pptpd/pppd, I just use the web interface provided by the router. I can edit configuration files (pptpd.conf and options.pptp as I understand) directly if necessary.
Other possible causes might be MTU or the GPRS gateway not allowing highly encrypted authentication. I tried everything down to even no authentication, nothing worked over GPRS. MTU seems to be at normal 1500. So, I think both are not relevant here.