Got server set up and running, friend can't connect. The server is on the DMZ, so ports are open. The server also has no firewall running. Windows firewall is disabled. sv_region is 255, sv_allow_lobby_connect_only is 0, sv_lan is 0, sv_steamgroup_exclusive is 0... but he gets the server not responding error. I am able to get in just fine though. Wat do?
I tried an old school trick from the Quake days: adding -ip xxx.xxx.xxx.xxx (replace x with my IP) and it didn't work. Tried specifically configuring port 27015 for the server, even though it's already on the DMZ, still doesn't work. I also noticed that the option to invite to game option has disappeared from the list in the drop-down menu next to someone's name in the chat (although I can still invite people using the invite players button at the bottom, but it just gives a server not responding error on the other end).
I run a Quake server (original Quake 1) server, and people can connect to it all day.