RFC1078

Network Working Group M. Lottor Request For Comments: 1078 SRI-NIC

                                                          November 1988

                TCP Port Service Multiplexer (TCPMUX)

Status of this Memo

  This RFC proposes an Internet standard which can be used by future
  TCP services instead of using 'well-known ports'.  Distribution of
  this memo is unlimited.

Overview

  Ports are used in the TCP 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.  The
  contact port is sometimes called the "well-known port".  Standard TCP
  services are assigned unique well-known port numbers in the range of
  0-255.  These ports are of limited number and are typically only
  assigned to official Internet protocols.

  This RFC defines a protocol to contact multiple services on a single
  well-known TCP port using a service name instead of a well-known
  number.  In addition, private protocols can make use of the service
  without needing an official TCP port assignment.

The Protocol

  A TCP client connects to a foreign host on TCP port 1.  It sends the
  service name followed by a carriage-return line-feed <CRLF>.  The
  service name is never case sensitive.  The server replies with a
  single character indicating positive ("+") or negative ("-")
  acknowledgment, immediately followed by an optional message of
  explanation, terminated with a <CRLF>.  If the reply was positive,
  the selected protocol begins; otherwise the connection is closed.

Service Names

  The name "HELP" is reserved.  If received, the server will output a
  multi-line message and then close the connection.  The reply to the
  name "HELP" must be a list of the service names of the supported
  services, one name per line.

  The names listed in the "Protocol and Service Names" section of the
  current edition of "Assigned Numbers" (RFC-1010 at this time) are
  reserved to have exactly the definitions specified there.  Services

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RFC 1078 TCPMUX November 1988

  with distinct assigned ports must be available on those ports and may
  optionally be available via this port service multiplexer on port 1.

  Private protocols should use a service name that has a high chance of
  being unique.  A good practice is to prefix the protocol name with
  the name of your organization.

  Multiple versions of a protocol can suffix the service name with a
  protocol version number.

Implementation Notes

  A negative reply will typically be returned by the port-multiplexing
  process when it can't find the requested service.  A positive reply
  will typically be returned by the process invoked by the port
  multiplexer for the requested service.

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