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Network Working Group J. Postel Request for Comments: 866 ISI

                                                              May 1983

                            Active Users

This RFC specifies a standard for the ARPA Internet community. Hosts on the ARPA Internet that choose to implement an Active Users Protocol are expected to adopt and implement this standard.

A useful debugging and measurement tool is an active users service. An active users service simply sends a list of the currently active users on the host without regard to the input.

An active user is one logged in, such as listed in SYSTAT or WHO.

TCP Based Active Users Service

 One active users service is defined as a connection based application
 on TCP.  A server listens for TCP connections on TCP port 11.  Once a
 connection is established a list of the currently active users is
 sent out the connection (and any data received is thrown away).  The
 service closes the connection after sending the list.

UDP Based Active Users Service

 Another active users service service is defined as a datagram based
 application on UDP.  A server listens for UDP datagrams on UDP port
 11.  When a datagram is received, an answering datagram is sent
 containing a list of the currently active users (the data in the
 received datagram is ignored).

 If the list does not fit in one datagram then send a sequence of
 datagrams but don't break the information for a user (a line) across
 a datagram.  The user side should wait for a timeout for all
 datagrams to arrive.  Note that they are not necessarily in order.

User List Syntax

 There is no specific syntax for the user list.  It is recommended
 that it be limited to the ASCII printing characters, space, carriage
 return, and line feed.  Each user should be listed on a separate
 line.

Postel [Page 1]