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