RFC 1143 (rfc1143) - Page 1 of 10

The Q Method of Implementing TELNET Option Negotiation

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Network Working Group                                       D. Bernstein
Request for Comments: 1143                                           NYU
                                                           February 1990


         The Q Method of Implementing TELNET Option Negotiation


Status of This Memo

   This is RFC discusses an implementation approach to option
   negotiation in the Telnet protocol (RFC 854).  It does not propose
   any changes to the TELNET protocol.  Rather, it discusses the
   implementation of the protocol of one feature, only.  This is not a
   protocol specification.  This is an experimental method of
   implementing a protocol.  This memo is not a recommendation of the
   Telnet Working Group of the Internet Engineering Task Force (IETF).
   This RFC is Copyright 1990, Daniel J. Bernstein.  However,
   distribution of this memo in original form is unlimited.

1. Introduction

   This RFC amplifies, supplements, and extends the RFC 854 [7] option
   negotiation rules and guidelines, which are insufficient to prevent
   all option negotiation loops.  This RFC also presents an example of
   correct implementation.

   DISCUSSION:

   The two items in this RFC of the most interest to implementors are
   1. the examples of option negotiation loops given below; and 2. the
   example of a TELNET state machine preventing loops.

      1. Implementors of TELNET should read the examples of option
         negotiation loops and beware that preventing such loops is a
         nontrivial task.

      2. Section 7 of this RFC shows by example a working method
         of avoiding loops.  It prescribes the state information that
         you must keep about each side of each option; it shows what
         to do in each state when you receive WILL/WONT/DO/DONT from
         the network, and when the user or process requests that an
         option be enabled or disabled.  An implementor who uses the
         procedures given in that example need not worry about
         compliance with this RFC or with a large chunk of RFC 854.

   In short, all implementors should be familiar with TELNET loops, and
   some implementors may wish to use the pre-written example here in



Bernstein
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