reserving a tcp port

[Mark Nagel]

Suppose one has a program that always needs to use a specific tcp port
number (like telnet, ftp, etc.).  Is there some central authority that
doles out new port numbers so that one might feel secure in thinking
that no one else will use that number or should one just force connections
to that port to identify themselves with a magic number?

Mark D. Nagel
  UC Irvine - Dept of Info and Comp Sci | The probability of someone
  nagel at ics.uci.edu             (ARPA)  | watching you is proportional to
  {sdcsvax|ucbvax}!ucivax!nagel (UUCP)  | the stupidity of your action.