One document matched: draft-rfced-exp-beals-00.txt

INTERNET DRAFT          EXPIRES MAY 1998        INTERNET DRAFT


Network Working Group                                        A. S. Beals
Internet Draft                                             Cisco Systems
                                                         4 November 1997


                The TPING option for the Telnet protocol
                     <draft-rfced-exp-beals-00.txt>

Status of This Memo

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Distribution of this document is unlimited.


Overview and Rational

When using the telnet protocol to talk to a remote device, as one would
with RFC 2217, it would be useful to be able to determine 
if the remote server is active or not.  In contrast with 
the ''Are You There'' sub-option, the return message is not mixed 
into the data stream presented to the user or client program, it is
simply passed between the telnet client/server pair.



1. Command names and codes


TPING.................45



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Internet Draft            Telnet TPING Option            4 November 1997


  As a convenience, standard TELNET text and codes for commands used in
  this document are reproduced here (excerpted from [1]):

   All TELNET commands consist of at least a two byte sequence:  the
   "Interpret as Command" (IAC) escape character followed by the code
   for the command.  The commands dealing with option negotiation are
   three byte sequences, the third byte being the code for the option
   referenced. ... [O]nly the IAC need be doubled to be sent as data,
   and the other 255 codes may be passed transparently.  The
   following are [some of] the defined TELNET commands.  Note that
   these codes and code sequences have the indicated meaning only
   when immediately preceded by an IAC.

         NAME          CODE  MEANING

         WILL          251   Indicates the desire to begin
                             performing, or confirmation that
                             you are now performing, the
                             indicated option.

         WON'T         252   Indicates the refusal to perform,
                             or continue performing, the
                             indicated option.

         DO            253   Indicates the request that the
                             other party perform, or
                             confirmation that you are expecting
                             the other party to perform, the
                             indicated option.

         DON'T         254   Indicates the demand that the other
                             party stop performing, or
                             confirmation that you are no longer
                             expecting the other party to
                             perform, the indicated option.

         IAC          255    Data Byte 255.

2.   Command Meanings

   A very simple meta-syntax is used, where most tokens represent
   previously defined items (such as IAC); angle-brackets ("<>") are
   used for items to be further defined; curly-braces ("{}") are used
   around optional items; ellipses represent repeated sequences of
   items; and quotes are used for literal strings.

   IAC DO TPING
    The sender REQUESTS the remote server to respond with a



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Internet Draft            Telnet TPING Option            4 November 1997


    WILL TPING.


   IAC WILL TPING
    Sent in response to a DO TPING packet.  If unsolicited,
    it should be ignored.

   IAC WON'T TPING
    No meaning.  Should be ignored by the recipient.

   IAC DON'T TPING
    No meaning.  Should be ignored by the recipient.

Discussion

   This option is most useful in the case where telnet is a hidden intermediary
   service.  The user only knows that he is using a remote resource that appears
   to be local and does not want to know about the infrastructure imbetween.  The
   telnet ping option allows the hidden client/server pair ascertain if its
   peer is active.

References

   [1] Postel, J. and J. Reynolds, "Telnet Protocol
   Specification", STD 8, RFC 854, ISI, May 1983.


Author's Address

   Andrew S. Beals
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134-1706

   Phone: (408) 526-8838

   EMail: asb@cisco.com



   INTERNET DRAFT                  EXPIRES MAY 1998        INTERNET DRAFT