Using a Windows 7 host and a PPTP connection I've been unable to get the VPN working with a VM running a RedHat Linux derivative. Sharing the host's PPTP connection with VirtualBox's host-only network seems to break any connection to the host and the VPN.
Trying to connect to the VPN from within the VM appears to work with VirtualBox's bridged adapter, but after establishing the connection resources inside the VPN are still inaccessible. The "netstat -rn" table lists the VPN as the first destination which is what I'd expect. Yet "tracepath" commands all appear to be using localhost, the non-VPN connection, or get no reply.
netstat -rn Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface 10.x.y.z 0.0.0.0 255.255.255.255 UH 0 0 0 ppp0 207.x.y.z 192.168.x.1 255.255.255.255 UGH 0 0 0 eth0 192.168.x.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth0 0.0.0.0 192.168.x.1 0.0.0.0 UG 0 0 0 eth0
Using Windows' network bridging from it's PPTP adapter appears to be out of the question. The host consistently works with the VPN. I've also tried disabling the guest VM's firewall entirely.
EDIT: Included routes.