User blog comment:H3rosnvrfall/Trouble Port Forwarding/@comment-4089433-20110622213724/@comment-4087340-20110622214838

Be sure you are forwarding it to the IP address assigned to the computer you are hosting on. There should be a list of clients in your router's options somewhere or you can use the CMD and ipconfig command to find it. It will be something along the lines of "192.168.1.XX" with the XX being the number assigned to your computer. Also, make sure to have the "Enabled" checkbox checked after you forward port 7777. If this doesn't solve your problem try enabling DMZ (its in the same section as the port forwarding options in your router). Also make sure to either allow Terraria.exe and TerrariaServer.exe through Windows Firewall or disable Windows Firewall altogether.