Looking for a script to ban all Ips that are not in my server.

Hello guys,
Just searched the forum for any kind of script regarding iptables bad scripts to ban all ips that are not in my peer list.
Does that even exist? I want to do that because i share with people and after sometime they remove me but unfortunately still connected at my line so i want to ban them all, too many. Hope that could lower cpu usage too.

Any help is appreciated.

peace

ppv