[ih] History of the TCP/UDP port space

[Bob Braden]

Barbara Denny asked me "when the port number space was divided into 3
groups (well-known ports, registered ports and dynamic ports)."  I
thought the following reply might be of more general historical
interest.

Bob Braden

__________________________________________________________________

Barbara,

I just spent 2 minutes in the RFC search engine, and here is what
I learned.

Before March 1990 (I traced it as far back as RFC 760 in Jan 1981),
the port space was divided into well-known ports and dynamic ports,
where the WK ports occupied the lowest 255 values and the rest was
dynamic.

Around 1984, BSD UNIX became a factor in the Internet, and BSD reserved
some ports in the range 256-1024 for their specific use.  These were
not-quite-so-well-known ports, in effect.  For some years, the
Internetters tried to ignore this intrusion on the prerogatives of the
protocol jocks by the OS jocks.  But in March 1990, Jon Postel conceded
to the reality of BSD importance by including "Unix Ports" in Assigned
Numbers (RFC 1060), with the comment:

   "By convention, ports in the range 256 to 1024 are used for "Unix
   Standard" services.  Listed here are some of the normal uses of these
   port numbers."

Jon resolved this untidiness in July 1992 in RFC 1340.  This Assigned
Numbers RFC expanded the well-known port space to 0-1023 and defined
the rest (1024-65535) as "Registered".  Registered Ports had the comment:

   "The Registered Ports are not controlled by the IANA and on most systems
   can be used by ordinary user processes or programs executed by ordinary
   users.

   Ports are used in the TCP [45,106] to name the ends of logical
   connections which carry long term conversations.  For the purpose of
   providing services to unknown callers, a service contact port is
   defined.  This list specifies the port used by the server process as its
   contact port.  While the IANA can not control uses of these ports it
   does register or list uses of these ports as a convienence to the
   community.

   The Registered Ports are in the range 1024-65535."

The Unix ports were then listed in the Registered Ports space.

Hope this helps,

Bob