Making your Left 4 Dead 2 server private is a great way to keep out uninvited players and ensure only trusted friends or community members can join. The simplest method is to restrict access to a specific Steam Group.
You can easily limit access to members of a Steam Group by editing your server’s configuration file.
Log in to the ChipHead Control Panel.

Stop your server.

Go to the Files tab & navigate to: “server.cfg”

Find or add the following line:
sv_steamgroup <YourGroupID>Replace <YourGroupID> with the numerical ID of your Steam Group.
Below that, set the following line:
sv_steamgroup_exclusive 1This makes the server accessible only to members of the specified group.
Click “Save Content”.

Start your server.
