go to /router in your browser (just type /router in your address bar) to access your router internally. Go to firewall settings, and forward whatever port your server is running on TO the same port number. In essence, you're forwarding the outside port with the inside port so that they connect to each other. After that, if you have another modem through your ISP, you have to know its IP (google multiple router scanner and download/run it and it will tell you the ip of the second router) and put that ip into your address bar like you did /router, and DISABLE DMZ. it will have an option somewhere in there depending on your router brand. that should allow all users inside or outside of your LAN to connect to it successfully. Make sure also you have enough memory and internet bandwidth to allow it.