RFC 1571 (rfc1571) - Page 1 of 4
Telnet Environment Option Interoperability Issues
Alternative Format: Original Text Document
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