TCP Wrappers

TCP Wrappers is a program designed by Wietse Venema at Eindhoven University in the Netherlands. It does whitelisting and blacklisting of peers that connect to TCP sockets. It is easy to set up with the inetd superserver.

It has been expanded into a general use library as well. This allows for daemons not typically run via inetd (such as Apache and OpenSSH) to use it, and provides more centralized access control.