I have my raspberry pi set up as a PPTP vpn server for home. The right settings are enabled on my Virgin Media Superhub 2. I have set up a user as needed in CHAP secrets. I have entered the info in to my Android Smartphone and I get 'Server Hung up'. I then tethered another computer to my phone and it also refused to connect. Can my Superhub 2 do what I want it to do (I think GRE packets are the issue)?
Virgin's forums are as useless as ever. 'Oh Sorry, we don't know'
PPTP uses port 1723. Make sure this is allowed out of your firewall to start off with.
Have a check here if you need any more info. Introduction to VPN - PPTP - Point to Point Transfer Protocol
Yeah, I have forwarded port 1723 and have turned the SuperDud's firewall off as it was causing issues previously
Le edit: Here is the tutorial I used