"This article describes how to use TCP wrappers to tighten the
security of the machine's services."
"They work by checking the hostname of who is trying to get in
and compare it to preconfigured access files using the tcpd daemon.
Only services activated by inetd can use TCP wrappers. This article
does not address installing them, as all Linux distributions I am
aware of install these by default. If you need to download and
install them, they are available at ftp.cert.org."