The Harmful Consequences of the Robustness Principle
draft-iab-protocol-maintenance-00

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Last updated 2018-08-04 (latest revision 2018-05-03)
Replaces draft-thomson-postel-was-wrong
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Network Working Group                                         M. Thomson
Internet-Draft                                                   Mozilla
Intended status: Informational                              May 03, 2018
Expires: November 4, 2018

          The Harmful Consequences of the Robustness Principle
                   draft-iab-protocol-maintenance-00

Abstract

   Jon Postel's famous statement of "Be liberal in what you accept, and
   conservative in what you send" is a principle that has long guided
   the design and implementation of Internet protocols.  The posture
   this statement advocates promotes interoperability, but can produce
   negative effects in the protocol ecosystem in the long term.  Those
   effects can be avoided by maintaining protocols.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on November 4, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Fallibility of Specifications . . . . . . . . . . . . . . . .   3
   3.  Protocol Decay  . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Ecosystem Effects . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Active Protocol Maintenance . . . . . . . . . . . . . . . . .   5
   6.  The Role of Feedback  . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Error Handling  . . . . . . . . . . . . . . . . . . . . .   7
     6.2.  Feedback from Implementations . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  Informative References  . . . . . . . . . . . . . . . . . . .   8
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Of the great many contributions Jon Postel made to the Internet, his
   remarkable technical achievements are often shadowed by his
   contribution of a design and implementation philosophy known as the
   robustness principle:

      Be strict when sending and tolerant when receiving.
      Implementations must follow specifications precisely when sending
      to the network, and tolerate faulty input from the network.  When
      in doubt, discard faulty input silently, without returning an
      error message unless this is required by the specification.

   This being the version of the text that appears in IAB RFC 1958
   [PRINCIPLES].

   Postel's robustness principle has been hugely influential in shaping
   the Internet and the systems that use Internet protocols.  Many
   consider the application of the robustness principle to be
   instrumental in the success of the Internet as well as the design of
   interoperable protocols in general.

   Over time, considerable experience has been accumulated with
   protocols that were designed by the application of Postel's maxim.
   That experience shows that there are negative long-term consequences
   to interoperability if an implementation applies Postel's advice.

   This document shows that flaw in Postel's logic originates from the
   presumption of immutability of protocol specifications.  Thus rather

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   than apply the robustness principle, this document recommends
   continuing maintenance for protocols beyond their initial design and
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