“How to join friend’s game?” is probably the most asked question on the Killing Floor forums.
This is because virtually every time you try Steam’s “Join Game” menu item you will get “Server not responding”. I’m not sure WHY this happens, but here is how to get around it.
If your friend is playing on a dedicated server, all you need to do is click the “View Game Info” menu item on your Friends List and copy the IP for the server. Then, in the Killing Floor game, click Multiplayer->Internet Games tab->Right click on background->Open IP then paste the IP address your friend is on. Your friend’s game should now load for you.
If your friend is playing on a listen server (i.e. he is hosting the current game on his own computer) then it is more complicated. First, he has to go the killing floor folder then system folder and open KillingFloor.ini. Change [UPNP] Enabled to false and ServerBehindNAT set it to True. If he has a firewall he has to use port forwarding.
The following is a list of ports used by Killing Floor. Make sure they are open in the router/firewall. (You will need these to host a listen server)
7707 UDP/IP (Game Port)
7708 UDP/IP (Query Port)
7717 UDP/IP (GameSpy Query Port)
28852 TCP/IP and UDP (Allows your Server to Connect to the Master Server Browser)
8075 TCP/IP (Port set via ListenPort that your WebAdmin will run on)
20560 UDP/IP (Steam Port)
Additionally, if you have used Killing Floor SDK or have it installed, it creates a file that will block multiplayer server access. Simply delete the file “steamappid.txt” commonly located in C:\Program Files\Steam\steamapps\common\KillingFloor\System\steamappid.txt
The above should fix most issues with hosting a listen server. If not, it is likely something specific to your computer/router/connection.