Right, I dug out the manual and tried to remember what it is.
To get to a command line on it, make sure Telnet is enabled (through the web interface). Then click start>run and type in telnet 192.168.1.1 or whatever the router's IP is. Login.
Press 24, enter for the system maintenence menu and then 8, enter for the command interpreter. Just type in "ip nat loopback on" and hit enter, nat loopback is now on. Test it out by opening the web server's WAN address from a LAN client.
Problem is, that's not all of it

When I did it, I thought wow that wasn't so bad. However, just doing that, nat loopback is no longer enabled the next time the router restarts since it isn't actually stored in the config anywhere, and that's the tricky bit. To add nat loopback to the config you have to edit the file autoexec.net, and add ip nat loopback on the last line (well any line will do but meh). The big diificulty with this is that the text editor, like I said, was not very intuitive.
The command to edit autoexec.net is "sys edit autoexec.net". However it's so long since I did so I just can't remember how to use the editor so you'll have to work it out for yourself. To quote something I found on Google while searching as a memory aid:
had a few typing problems ("pilot error") while editing autoexec.net, so I started over by reloading the firmware. I highly recommend using the serial port connection between the PC and router when doing firmware upgrades. The only issue with the serial connection is strange cursor behavior on menu 24.10 (but this menu works fine using the Telnet interface).
That's pretty much the same as what happened to me, though I didn't realise immediately that I could upload a new firmware via the serial port. But I don't really see any point in me explaining how to do this, since I can't remember anyway you may as well just look at the manual:
ftp://ftp.zyxel.dk/P650_series/document/P650_series_v3-40_UsersGuide.pdf
That's the one for my 652H because I know for fact that it tells you how to restore the firmware. It should be the same procedure for yours. Don't forget that you of course need a firmware to upload to it, so it might be worth downloading one before editing autoexec.net just in case it does go wrong
And, I think, that's just about it. Finally, have you considered remapping the WebGUI's port to 8080? Then you could run your web service thing on port 80, saving having to specify 8080 every time, unless that's what you want...
HTH, null
