TELNET KERMIT OPTION
RFC 2840

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Network Working Group                                          J. Altman
Request for Comments: 2840                                    F. da Cruz
Category: Informational                              Columbia University
                                                                May 2000

                          TELNET KERMIT OPTION

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119.

ABSTRACT

   This document describes an extension to the Telnet protocol to allow
   the negotiation, coordination, and use of the Kermit file transfer
   and management protocol over an existing Telnet protocol connection.

CONTENTS

   1. MOTIVATION . . . . . . . . . . . . . . . . . . . . . . . .  2
   2. DEFINITIONS. . . . . . . . . . . . . . . . . . . . . . . .  2
   3. COMMANDS AND CODES . . . . . . . . . . . . . . . . . . . .  3
   4. COMMAND MEANINGS . . . . . . . . . . . . . . . . . . . . .  3
   5. KERMIT PROTOCOL IMPLICATIONS . . . . . . . . . . . . . . .  5
   6. EXAMPLES . . . . . . . . . . . . . . . . . . . . . . . . .  6
   6.1. EXAMPLE 1. . . . . . . . . . . . . . . . . . . . . . . .  6
   6.2. EXAMPLE 2. . . . . . . . . . . . . . . . . . . . . . . .  7
   6.3. EXAMPLE 3. . . . . . . . . . . . . . . . . . . . . . . .  8
   6.4. EXAMPLE 4. . . . . . . . . . . . . . . . . . . . . . . .  9
   6.5. EXAMPLE 5. . . . . . . . . . . . . . . . . . . . . . . . 10
   7. SECURITY CONSIDERATIONS. . . . . . . . . . . . . . . . . . 11
   8. REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . 11
   9. AUTHORS' ADDRESSES . . . . . . . . . . . . . . . . . . . . 11
   10. FULL COPYRIGHT STATEMENT. . . . . . . . . . . . . . . . . 12

Altman & da Cruz             Informational                      [Page 1]
RFC 2840                  TELNET KERMIT OPTION                  May 2000

1. MOTIVATION

   The Kermit protocol [KER] performs error-corrected file transfer and
   management over many types of connections, including terminal
   connections, among diverse hardware and software platforms.  It is
   supported by a large number of Telnet clients and is also widely
   available on the Internet hosts to which Telnet connections are made.

   Traditionally, the Kermit protocol connection is started manually by
   a user, or perhaps by an automated script.  It is the user's
   responsibility to start the Kermit server on one end of the
   connection and the Kermit client on the other, or to start a Kermit
   "send" operation on one end and a Kermit "receive" on the other.

   This procedure grew out of necessity on ordinary direct-dial
   connections, and serves its purpose within the limitations of that
   context.  But it introduces timing and dexterity problems, and lacks
   an effective way for each Kermit program to determine the "mode" of
   the other, or even its very presence, and therefore to know with
   certainty which operations and procedures are legal on the connection
   at any given time.

   When Kermit services are offered on the Internet, however, a strong
   coupling can be established between the two end applications by
   having the Telnet protocol [TEL] serve as a supervisor for Kermit
   sessions, ensuring that a valid and known relationship is always
   obtained.  Kermit sessions are, in effect, embedded within Telnet
   sessions, with Telnet providing the mechanism for starting and
   stopping them and defining which end is the Kermit client and which
   is the Kermit server, possibly changing the relationship in response
   to user actions.

2. DEFINITIONS

   Kermit server
      A software program that is ready to accept and act upon commands
      in the form of well-defined Kermit packets [KER].

   Kermit client
      A software program that receives requests through its user
      interface from a human agent (or a script or other source) and
      translates them to command packets, which it sends to a Kermit
      server, thus initiating a Kermit protocol transaction such as the
      transfer of one or more files.

Altman & da Cruz             Informational                      [Page 2]
RFC 2840                  TELNET KERMIT OPTION                  May 2000

   Availability of Kermit server
      For the purposes of this document, a Kermit server is said to be
      available if, through the negotiations described herein, its
      Telnet partner knows that it is a Kermit server.

3. COMMANDS AND CODES

   Support for a Kermit server is negotiated separately in each
   direction, allowing Kermit service to be embedded in the Telnet
   client, the Telnet server, or in both.  The proposed Telnet