I hate to be the fifty millionth person to ask for help about this, but I've searched around a bit and honestly can't find a fix. When I try to host a server, other people can't join, nor can I join using my public IP, private IP obviously works like a charm but that's no help. http://imgur.com/a/fHZhK As you can see, the port is open and the server does receive a request, however when you try to connect to it from the game, nothing shows up and you get that error. I would try it with Join Game, but obviously that won't work for myself when I'm testing it and my friend doesn't own the game on steam I've tried hosting servers and it appears to be something similar, the ports are open and are listening, but people can't join. Things used to work out great until my router/modem gave in and I had to reset it to factory settings, since then it hasn't been working as before [Solved] Turns out I should have just bothered my friend more often. You can't connect to your public IP if you're on the same IP, so all the testing and fixes I tried were for naught.