The Free On-line Dictionary of Computing (30 December 2018):

assigned numbers

    The RFC STD 2 documenting the currently
   assigned values from several series of numbers used in network
   protocol implementations.  This RFC is updated periodically
   and, in any case, current information can be obtained from the
   Internet Assigned Numbers Authority (IANA).  If you are
   developing a protocol or application that will require the use
   of a link, socket, port, protocol, etc., you should
   contact the IANA to receive a number assignment.

   (1996-08-19)