Controller, and "OTHER" to specify any other operating system not
      yet registered with the NIC.










RFC 931                                                     January 1985
Authentication Server


   ERROR

      For some reason the owner of  could not be determined,
      <additional-info> tells why.  The following are suggested values
      of <additional-info> and their meanings.

      INVALID-PORT

         Either the local or foreign port was improperly specified.

      NO-USER

         The connection specified by the port pair is not currently in
         use.

      UNKNOWN-ERROR

         Can't determine connection owner; reason unknown.  Other values
         may be specified as necessary.

CAVEATS

   Unfortunately, the trustworthiness of the various host systems that
   might implement an authentication server will vary quite a bit.  It
   is up to the various applications that will use the server to
   determine the amount of trust they will place in the returned
   information.  It may be appropriate in some cases restrict the use of
   the server to within a locally controlled subnet.

APPLICATIONS

   1) Automatic user authentication for FTP

      A user-FTP may send a USER command with no argument to the
      server-FTP to request automatic authentication.  The server-FTP
      will reply with a 230 (user logged in) if it can use the
      authentication.  It will reply with a 530 (not logged in) if it
      cannot authenticate the user.  It will reply with a 500 or 501
      (syntax or parameter problem) if it does not implement automatic
      authentication.  Please note that no change is needed to currently
      implemented servers to handle the request for authentication; they
      will reject it normally as a parameter problem.  This is a
      suggested implementation for experimental use only.

   2) Verification for privileged network operations.  For example,
   having the server start or stop special purpose servers.






RFC 931                                                     January 1985
Authentication Server


   3) Elimination of "double login" for TAC and other TELNET users.

      This will be implemented as a TELNET option.

FORMAL SYNTAX

        ::=   

      ::= <integer-number> "," <integer-number>

          ::=   

     ::= <error-reply> | 

   <error-reply> ::=  ":" ERROR ":" 

     ::=  ":" USERID ":"  ":" 

     ::= INVALID-PORT | NO-USER | UNKNOWN-ERROR

          ::= TAC | OTHER | MULTICS | UNIX ...etc.
                     (See "Assigned Numbers")

   Notes on Syntax:

      1)  White space (blanks and tab characters) between tokens is not
      important and may be ignored.