[This page is outdated. See this post for information ]
Click on the screen shots to enlarge them
Let us say you want to forward incoming VNC connections to a computer on your LAN. VNC uses the TCP port 5900. You can easily achieve that by creating a firewall rule that will forward the incoming traffic to the local computer.
In the GUI, go to “Advanced Settings”, “Lan Servers” and click “New Entry”.
We now need to define the port that will be forwarded under “Public start port” and “Public end port”. For VNC, the port should be defined as “TCP” and address should be 5900. The local IP address refers to the computer you want to reach.
Click Apply and return to the main “Lan servers” screen. Click Apply again and you are set. From now on, all incoming connections on port 5900 will be redirected to your internal computer.