(I have been using this for years.)
This is an RPC portmapper that prevents theft of NIS (YP), NFS,
and other sensitive information via the portmapper. As an option,
the program supports access control in the style of the TCP Wrappers
(log_tcp) package.
Daemons that offer RPC services tell the portmapper on what port
they listen. And clients asks the portmapper what port the daemon
is using. RPC network port numbers may change each time the system
is booted.
This is Wietse Venema's fourth replacement portmapper. It is
derived from source code in the RPCSRC 4.0 and the TIRPC source
distributions.