Hey Alucard, mine's a Dl-704 so the menu's likely almost the same. I think this will work.
Firstly, on your web, browser, type in the address
http://192.168.0.1/ (or click this link). You are now at you're router's built-in menu. The default password is "admin" if that doesn't work, I reccommend restarting your router by holding the reset button in while powering it up to revert back to the factory settings. At the bottom of the screen (once logged on) click the "advanced" link then the "Special AP" link. Under "trigger" and "incoming ports", type in the port number and check the "enable" box. Remember to save your settings. Tell me if this works, or if the menus are different....