I've vnc-java running on an Ubuntu box, with the IP address 192.168.1.68, using port 5800 (because port 5900 is being used for normal VNC).
If I connect to 192.168.1.68:5800 using another computer on the network, I can use VNC fine.
Using www.whatismyip.com, I find out what my IP address from the outside world is, and if I go directly to that, I get to access my modem/router. If I try to navigate to that IP address, with ':5800' on the end, I get a "This web page is not available." error.
I have port forwarding set up in the router as follows:
Application Name External Packet Internal Host IP Address Protocol Port IP Address Port VNC ALL TCP/UDP 5800 192.168.1.68 5800
What else do I need to do to get this to work?