Long-term Viability of Protocol Extension Mechanisms
draft-thomson-use-it-or-lose-it-04

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Network Working Group                                         M. Thomson
Internet-Draft                                                   Mozilla
Intended status: Informational                             July 08, 2019
Expires: January 9, 2020

          Long-term Viability of Protocol Extension Mechanisms
                   draft-thomson-use-it-or-lose-it-04

Abstract

   The ability to change protocols depends on exercising the extension
   and version negotiation mechanisms that support change.  Protocols
   that don't use these mechanisms can find that deploying changes can
   be difficult and costly.

Status of This Memo

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   This Internet-Draft will expire on January 9, 2020.

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   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Implementations of Protocols are Imperfect  . . . . . . . . .   3
     2.1.  Good Protocol Design is Not Itself Sufficient . . . . . .   3
     2.2.  Multi-Party Interactions and Middleboxes  . . . . . . . .   5
   3.  Retaining Viable Protocol Evolution Mechanisms  . . . . . . .   6
     3.1.  Examples of Active Use  . . . . . . . . . . . . . . . . .   7
     3.2.  Dependency is Better  . . . . . . . . . . . . . . . . . .   7
     3.3.  Unused Extension Points Become Unusable . . . . . . . . .   8
   4.  Defensive Design Principles for Protocols . . . . . . . . . .   9
     4.1.  Active Use  . . . . . . . . . . . . . . . . . . . . . . .   9
     4.2.  Cryptography  . . . . . . . . . . . . . . . . . . . . . .   9
     4.3.  Grease  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     4.4.  Invariants  . . . . . . . . . . . . . . . . . . . . . . .  11
     4.5.  Effective Feedback  . . . . . . . . . . . . . . . . . . .  11
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   7.  Informative References  . . . . . . . . . . . . . . . . . . .  12
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  15
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   A successful protocol [SUCCESS] will change in ways that allow it to
   continue to fulfill the needs of its users.  New use cases,
   conditions and constraints on the deployment of a protocol can render
   a protocol that does not change obsolete.

   Usage patterns and requirements for a protocol shift over time.  In
   response, implementations might adjust usage patterns within the
   constraints of the protocol, the protocol could be extended, or a
   replacement protocol might be developed.  Experience with Internet-
   scale protocol deployment shows that each option comes with different
   costs.  [TRANSITIONS] examines the problem of protocol evolution more
   broadly.

   This document examines the specific conditions that determine whether
   protocol maintainers have the ability to design and deploy new or
   modified protocols.  Section 2 highlights some historical issues with
   difficulties in transitions to new protocol features.  Section 3
   argues that ossified protocols are more difficult to update and
   successful protocols make frequent use of new extensions and code-
   points.  Section 4 outlines several strategies that might aid in
   ensuring that protocol changes remain possible over time.

   The experience that informs this document is predominantly at
   "higher" layers of the network stack, in protocols that operate at

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