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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

Lottor [Page 1]  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.

Lottor [Page 2]