Dunno if this is a networking no-brainer but here goes... had the issue where my friend could join but I(host) could not. I used the localhost solution a while ago which worked. However this will not work for two machines connecting to a server running on the same network. My girlfriend, my friend, and I wanted to join our server but my girlfriends machine would not connect since her and I were on the same network. We could not run LAN because my friend is in another state.
The solution was to connect to the host machines local IP address instead of the server address. Open up terminal on the host machine and run "ipconfig /all" and use the local IPv4 address there. All machines on the same network as the host machine will have to connect with this address. Even the host machine itself. Anyone outside of the network will have to use the actual IP.
