I've run into a bit of a puzzle and haven't had much luck finding a solution. Right now I am (sadly) connected to the net via Verizon 3G. They filter all incoming traffic so it is impossible for me to open ports to accept connections.
I currently have a Linux virtual machine at linode.com, and the thought crossed my mind to install pptpd and attempt to do some iptables port forwarding. I have pptpd installed and my home machine connects happily. That said, here's some general info:
Server (Debian) WAN IP: x.x.x.x on eth0 - pptpd IP: y.y.y.1 on ppp0 - Client VPN IP: y.y.y.100
To verify I wasn't going insane, I attempted some connections from the server to the open ports on the client, and the client does accept the connections via the VPN IP.
What I want to accomplish is this:
Internet -> WAN IP:Port -> Forward to Client VPN IP:Port
So for instance, if I had port 6000 open on my client, a person could telnet in to x.x.x.x:6000, and the server would catch that and forward it to 192.168.3.100:6000.
I have tried at least 20 different Googled up iptables configs and none have worked yet. Does anyone have any ideas, or perhaps even a totally different approach I might not be aware of? The goal here is to listen through a horribly firewalled connection, preferably both TCP and UDP traffic.