RFC 1571 (rfc1571) - Page 1 of 4

Telnet Environment Option Interoperability Issues

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Network Working Group                                          D. Borman
Request for Comments: 1571                           Cray Research, Inc.
Updates: 1408                                               January 1994
Category: Informational


           Telnet Environment Option Interoperability Issues

Status of this Memo

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

1.  Overview

   RFC 1408 [1], the specification for the Telnet Environment Option,
   specifies definitions for VAR and VALUE that are reversed from the
   BSD implementation of the Telnet Environment option.  Since the BSD
   implementation was the reference implementation that the RFC was
   supposed to document, and is the base for many existing
   implementations, there exists an interoperability problem between
   implementations with conflicting definitions for VAR and VALUE.

   This document describes a method for allowing implementors to ensure
   that their implementation of the Environment option will be
   interoperable with as many other implementations as possible, by
   providing a set of heuristics that can be used to help identify which
   definitions for VAR and VALUE are being used by the other side of the
   connection.

2.  Client Telnet: Parsing a SEND

   The SEND suboption should only contain VAR and USERVAR commands.  It
   should never contain a VALUE.  If while parsing a SEND suboption, a
   VALUE is encountered, the client should assume that the server has
   reversed values for VAR and VALUE, and from that point on the client
   should reverse those values, both in parsing the rest of the SEND
   suboption, and when generating an IS or INFO suboption.  If both
   VALUE and VAR commands are encountered, the SEND command is not well
   formed, and it is implementation dependent as to what will happen.

   If there are not VAR or VALUE commands in the SEND suboption, then
   the client cannot know what values the server is expecting for VAR
   and VALUE.  In this case, it should just assume that the server has
   the correct definitions, and use the correct values for VAR and
   VALUE.




Telnet Working Group
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