Killing Floor - Ports

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)

Since the game is running with the Steam backend, if you are running more than 1 server per IP, you will need to make sure that you have some additional ports open beyond the default KF ports. If you change the default Game Port from 7707, this change will be reflected in the Master Server Port (28852) and the Steam Port (20560) as well.

(Thank you for the above information Yoshiro)

IN PRACTICE

Locate your KillingFloor.ini file in the 'system' folder. If you don't have one then simply copy and paste the default.ini file and rename the copy to KillingFloor.ini

I made a second server by changing the [url] Port from 7707 to 7710 in the KillingFloor.ini file in the system folder and of course opening the port in my router. This is a +3 increase that also reflects in my Master Server Port (28852 > 28855) and the Steam Port (20560 > 20563) openings. These 2 ports only need to be opened in the router and do not require file edits.

I also changed my [UWeb.WebServer] ListenPort for WebAdmin (8075 > 8078) by the same increment to maintain the same values. This also needs to be edited in the KillingFloor.ini file as well as opened in the router. All these changes will ensure there are no port conflicts for the 2 game servers.

Some server hosts have reported a crash when attempting to launch a second server but were able to run their server successfully after changing the [IpDrv.UdpGamespyQuery] OldQueryPortNumber= to the same increase they used for other ports on their second server.

This crash will only occur if you are copying files for your second server from your existing server that has already launched. If you copy the files from the original server then you'll also need to edit the [IpDrv.UdpGamespyQuery] OldQueryPortNumber from 7717 by the same increment, in my case 7720.

If your second server is a totally clean install then this entry will not have been added to your KillingFloor.ini and will be applied by the same increment automatically once you launch the server.