Allowing access through your firewall
By default, the CLC Server listens for TCP-connections on port 7777. Information on changing the port is provided in Changing the listening port.
If you are running a firewall on your server system you will have to allow incoming TCP-connections on this port before clients can contact the CLC Server. Consult the documentation of your firewall for information on how to do this.
Besides the public port described above the CLC Server also uses an internal port on 7776. There is no need to allow incoming connections from client machines to this port.