YANG Module Versioning Requirements
draft-verdt-netmod-yang-versioning-reqs-01

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Network Working Group                                     J. Clarke, Ed.
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Informational                          October 20, 2018
Expires: April 23, 2019

                  YANG Module Versioning Requirements
               draft-verdt-netmod-yang-versioning-reqs-01

Abstract

   This document describes the problems that can arise because of the
   YANG language module update rules, that require all updates to YANG
   module preserve strict backwards compatibility.  It also defines the
   requirements on any solution designed to solve the stated problems.
   This document does not consider possible solutions, nor endorse any
   particular solution.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on April 23, 2019.

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.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   2
     2.1.  Striving for model perfection . . . . . . . . . . . . . .   3
     2.2.  Some YANG Modules Are Not Backwards-Compatible  . . . . .   3
     2.3.  Non-Backwards-Compatible Errors . . . . . . . . . . . . .   4
     2.4.  No way to easily decide whether a change is Backwards-
           Compatible  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.5.  No good way to specify which module revision to import  .   5
     2.6.  Early Warning about Removal . . . . . . . . . . . . . . .   6
     2.7.  Clear Indication of Node Support  . . . . . . . . . . . .   6
   3.  Terminology and Conventions . . . . . . . . . . . . . . . . .   7
   4.  The Problem Statement . . . . . . . . . . . . . . . . . . . .   7
   5.  Requirements of a YANG Versioning Solution  . . . . . . . . .   9
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  11
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     10.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   This requirements document initially considers some of the existing
   YANG module update rules, then describes the problems that arise due
   to those rules embracing strict backwards compatibility, and finally
   defines requirements on any solution that may be designed to solve
   these problems by providing an alternative YANG versioning strategy.

2.  Background

   The YANG data modeling language [RFC7950] specifies strict rules for
   updating YANG modules (see section 11 "Updating a Module").  Citing a
   few of the relevant rules:

   1.  "As experience is gained with a module, it may be desirable to
       revise that module.  However, changes to published modules are
       not allowed if they have any potential to cause interoperability
       problems between a client using an original specification and a
       server using an updated specification."

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   2.  "Note that definitions contained in a module are available to be
       imported by any other module and are referenced in "import"
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