I have set up a PPTP VPN on Ubuntu 12.04, and it seems to be working. I am able to connect to it from a remote device, and once connected, I can see the VPN Server, SSH into it, and so on, all without any problem. So clearly it is working.
However, I cannot access any other devices on the same network. I have set up IP forwarding by uncommenting the line net.ipv4.ip_forwarding=1 and restarting syctl. I thought that I had opened the firewall to allow it, but something is not working, and the only device I can access on the remote network is the VPN server itself. I actually have another VPN Server on a different network set up similarly, except it is working, so clearly something is different.