Recommendations for Creating IANA-Maintained YANG Modules
draft-boucadair-netmod-iana-registries-04

netmod                                                      M. Boucadair
Internet-Draft                                                    Orange
Updates: 8407, 8126 (if approved)                       8 September 2022
Intended status: Standards Track                                        
Expires: 12 March 2023

       Recommendations for Creating IANA-Maintained YANG Modules
               draft-boucadair-netmod-iana-registries-04

Abstract

   This document provides a set of guidelines for YANG module authors
   related to the design of IANA-maintained modules.  These guidelines
   are meant to leverage existing IANA registries and use YANG as
   another format to present the content of these registries when
   appropriate.

   This document updates RFC 8407 by providing additional guidelines for
   IANA-maintained modules.  Also, this document updates RFC 8126 by
   providing additional guidelines for writing the IANA considerations
   for RFCs that specify IANA-maintained modules.  This document does
   not change anything written in RFC 8407 and RFC 8126.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on 12 March 2023.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Guidelines for IANA-Maintained Modules  . . . . . . . . . . .   3
   4.  Guidance for Writing the IANA Considerations for RFCs Defining
           IANA-Maintained Modules . . . . . . . . . . . . . . . . .   4
     4.1.  Template for IANA-Maintained Modules with Identities  . .   5
     4.2.  Template for IANA-Maintained Modules with Enumerations  .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   IANA maintains a set of registries that are key for interoperability.
   The content of these registries are usually available using various
   formats (e.g., plain text, XML).  However, there were some confusion
   in the past about whether the content of some registries is dependent
   on a specific representation format.  For example, Section 5 of
   [RFC8892] was published to clarify that MIB and YANG modules are
   merely additional formats in which the "Interface Types (ifType)" and
   "Tunnel Types (tunnelType)" registries are available.  The MIB
   [RFC2863] and YANG modules [RFC7224][RFC8675] are not separate
   registries, and the same values are always present in all formats of
   the same registry.

   Also, some YANG modules include parameters and values directly in a
   module that is not maintained by IANA while these are populated in an
   IANA registry.  Such a design is suboptimal as it creates another
   source of information that may deviate from the IANA registry as new
   values are assigned or some values are deprecated.

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   For the sake of consistency, better flexibility to support new
   values, and maintaining IANA registries as the unique authoritative
   source of information, when such an information is maintained in a
   registry, this document encourages the use of IANA-maintained
   modules.

   Section 3 updates the guidelines in [RFC8407].  Also, Section 4
   updates [RFC8407] and [RFC8126] by providing guidance for writing the
   IANA considerations for RFCs that specify IANA-maintained modules.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   This document makes use of the terms defined in Section 2 of
   [RFC8407].

3.  Guidelines for IANA-Maintained Modules

   When designing a YANG module for a functionality governed by a
   protocol for which IANA maintains a registry, it is RECOMMENDED to
   specify an IANA-maintained module that echoes the content of that
   registry.  This is superior to including that content in an IETF-
   maintained module.

   When one or multiple sub-registries are available under the same
   registry, it is RECOMMENDED to define an IANA-maintained module for
   each sub-registry.  However, module designers MAY consider defining
   one single IANA-maintained module that covers all sub-registries if
   maintaining that single module is manageable (e.g., very few values
   are present or expected to be present for each sub-registry).  An
   example of such a module is documented in Section 5.2 of [RFC9132].

   An IANA-maintained module may use identities (e.g., [RFC8675]) or
   enumerations (e.g., [RFC9108]).  The decision about which type to use
   is left to the module designers and should be made based upon
   specifics related to the intended use of the IANA-maintained module.
   For example, identities are useful if the registry entries are
   organized hierarchically, possibly including multiple inheritances.
   It is RECOMMENDED that the reasoning for the design choice is
   documented in the companion specification that registers an IANA-
   maintained module.  For example, [RFC9244] defines an IANA-maintained
   module that uses enumerations for the following reason:

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    "The DOTS telemetry module (Section 10.1) uses "enumerations" rather
     than "identities" to define units, samples, and intervals because
     otherwise the namespace identifier "ietf-dots-telemetry" must be
     included when a telemetry attribute is included (e.g., in a
     mitigation efficacy update).  The use of "identities" is thus
     suboptimal from a message compactness standpoint; one of the key
     requirements for DOTS messages."

   Designers of IANA-maintained modules MAY supply the full initial
   version of the module in a specification document that registers the
   module or only a script to be used (including by IANA) for generating
   the module (e.g., an XSLT stylesheet as in Appendix A of [RFC9108]).
   When a script is used, the Internet-Draft that defines an IANA-
   maintained module SHOULD include an appendix with the initial full
   version of the module.  Including such an appendix in pre-RFC
   versions is meant to assess the correctness of the outcome of the
   supplied script.  The authors MUST include a note to the RFC Editor
   requesting that the appendix be removed before publication as RFC.
   Initial versions of IANA-maintained modules that are published in
   RFCs may be misused despite the appropriate language to refer to the
   IANA registry to retrieve the up-to-date module.  This is problematic
   for interoperability, e.g., when values are deprecated or are
   associated with a new meaning.

      Note: [Style] provides XSLT 1.0 stylesheets and other tools for
      translating IANA registries to YANG modules.  The tools can be
      used to generate up-to-date revisions of an IANA-maintained module
      based upon the XML representation of an IANA registry.

4.  Guidance for Writing the IANA Considerations for RFCs Defining IANA-
    Maintained Modules

   In addition to the IANA considerations in Section 3.8 of [RFC8407],
   the IANA Considerations Section of an RFC that includes an IANA-
   maintained module MUST provide the required instructions for IANA to
   automatically perform the maintenance of that IANA module.  These
   instructions describe how to proceed with updates to the IANA-
   maintained module that are triggered by a change to the authoritative
   registry.  Concretely, the IANA Considerations Section SHALL at least
   provide the following information:

   *  An IANA request to add a note to the page displaying the
      information about the IANA-maintained module that new values must
      not be directly added to the module, but to an authoritative IANA
      registry.

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   *  An IANA request to add a note to the authoritative IANA registry
      to indicate that any change to the registry must be reflected into
      the corresponding IANA-maintained module.

   *  Details about the required actions (e.g., add a new "identity" or
      "enum" statement) to update the IANA-maintained module to reflect
      changes to an authoritative IANA registry.  Typically, these
      details have to include the procedure to create a new "identity"
      statement name and sub-statements ("base", "status",
      "description", and "reference") or a new "enum" statement and sub-
      statements ("value", "status", "description", and "reference").

   *  A note that unassigned or reserved values must not be present in
      the IANA-maintained module.

   *  An indication whether experimental values are included in the
      IANA-maintained module.  Absent such an indication, experimental
      values MUST NOT be listed in the IANA-maintained module.

   *  An instruction about how to generate the "revision" statement.

   A template for the IANA Considerations is provided in Section 4.1 for
   IANA-maintained modules with identities and Section 4.2 for IANA-
   maintained modules with enumerations.  Authors may modify the
   template to reflect specifics of their modules (e.g., Multiple
   registries can be listed for a single IANA-maintained module, no
   explicit description (or name) field is listed under the
   authoritative IANA registry).

   The following templates are to be considered in addition to the
   required information that is provided in Section 3.8 of [RFC8407].

4.1.  Template for IANA-Maintained Modules with Identities

   This document defines the initial version of the IANA-maintained
   "iana-foo" YANG module.  The most recent version of the YANG module
   is available from the "YANG Parameters" registry
   [IANA-YANG-PARAMETERS].

   IANA is requested to add this note to the registry:

      New values must not be directly added to the "iana-foo" YANG
      module.  They must instead be added to the "foo" registry.

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   When a value is added to the "foo" registry, a new "identity"
   statement must be added to the "iana-foo" YANG module.  The name of
   the "identity" is the lower-case of the name provided in the
   registry.  The "identity" statement should have the following sub-
   statements defined:

   "base":        Contains 'name-base-identity-defined-in-foo'.

   "status":      Include only if a registration has been deprecated or
                  obsoleted.  IANA "deprecated" maps to YANG status
                  "deprecated", and IANA "obsolete" maps to YANG status
                  "obsolete".

   "description":  Replicates the description from the registry.

   "reference":   Replicates the reference(s) from the registry with the
                  title of the document(s) added.

   Unassigned or reserved values are not present in the module.

   When the "iana-foo" YANG module is updated, a new "revision"
   statement with a unique revision date must be added in front of the
   existing revision statements.

   IANA is requested to add this note to [reference-to-the-iana-foo-
   registry]:

      When this registry is modified, the YANG module "iana-foo" must be
      updated as defined in RFCXXXX.

4.2.  Template for IANA-Maintained Modules with Enumerations

   This document defines the initial version of the IANA-maintained
   "iana-foo" YANG module.  The most recent version of the YANG module
   is available from the "YANG Parameters" registry
   [IANA-YANG-PARAMETERS].

   IANA is requested to add this note to the registry:

      New values must not be directly added to the "iana-foo" YANG
      module.  They must instead be added to the "foo" registry.

   When a value is added to the "foo" registry, a new "enum" statement
   must be added to the "iana-foo" YANG module.  The "enum" statement,
   and sub-statements thereof, should be defined:

   "enum":        Replicates a name from the registry.

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   "value":       Contains the decimal value of the IANA-assigned value.

   "status":      Is included only if a registration has been deprecated
                  or obsoleted.  IANA "deprecated" maps to YANG status
                  "deprecated", and IANA "obsolete" maps to YANG status
                  "obsolete".

   "description":  Replicates the description from the registry.

   "reference":   Replicates the reference(s) from the registry with the
                  title of the document(s) added.

   Unassigned or reserved values are not present in the module.

   When the "iana-foo" YANG module is updated, a new "revision"
   statement with a unique revision date must be added in front of the
   existing revision statements.

   IANA is requested to add this note to [reference-to-the-iana-foo-
   registry]:

      When this registry is modified, the YANG module "iana-foo" must be
      updated as defined in RFCXXXX.

5.  IANA Considerations

   This document does not require any IANA action.

6.  Security Considerations

   This document does not introduce new concerns other than those
   already discussed in Section 15 of [RFC8407].

7.  Acknowledgements

   This document is triggered by a discussion the author had with Dhruv
   Dhody and Jensen Zhang.

   Thanks to Juergen Schoenwaelder, Ladislav Lhotka, and Qin Wu for the
   discussion and valuable comments.  Special thanks to Ladislav Lhotka
   for sharing more context that led to the design documented in
   [RFC9108].

   Thanks to Andy Bierman for the comments.  Lou Berger suggested to
   include more details about IANA considerations.

8.  References

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8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8407]  Bierman, A., "Guidelines for Authors and Reviewers of
              Documents Containing YANG Data Models", BCP 216, RFC 8407,
              DOI 10.17487/RFC8407, October 2018,
              <https://www.rfc-editor.org/info/rfc8407>.

8.2.  Informative References

   [IANA-YANG-PARAMETERS]
              IANA, "YANG Parameters",
              <https://www.iana.org/assignments/yang-parameters>.

   [RFC2863]  McCloghrie, K. and F. Kastenholz, "The Interfaces Group
              MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000,
              <https://www.rfc-editor.org/info/rfc2863>.

   [RFC7224]  Bjorklund, M., "IANA Interface Type YANG Module",
              RFC 7224, DOI 10.17487/RFC7224, May 2014,
              <https://www.rfc-editor.org/info/rfc7224>.

   [RFC8675]  Boucadair, M., Farrer, I., and R. Asati, "A YANG Data
              Model for Tunnel Interface Types", RFC 8675,
              DOI 10.17487/RFC8675, November 2019,
              <https://www.rfc-editor.org/info/rfc8675>.

   [RFC8892]  Thaler, D. and D. Romascanu, "Guidelines and Registration
              Procedures for Interface Types and Tunnel Types",
              RFC 8892, DOI 10.17487/RFC8892, August 2020,
              <https://www.rfc-editor.org/info/rfc8892>.

   [RFC9108]  Lhotka, L. and P. Špaček, "YANG Types for DNS Classes and
              Resource Record Types", RFC 9108, DOI 10.17487/RFC9108,
              September 2021, <https://www.rfc-editor.org/info/rfc9108>.

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   [RFC9132]  Boucadair, M., Ed., Shallow, J., and T. Reddy.K,
              "Distributed Denial-of-Service Open Threat Signaling
              (DOTS) Signal Channel Specification", RFC 9132,
              DOI 10.17487/RFC9132, September 2021,
              <https://www.rfc-editor.org/info/rfc9132>.

   [RFC9244]  Boucadair, M., Ed., Reddy.K, T., Ed., Doron, E., Chen, M.,
              and J. Shallow, "Distributed Denial-of-Service Open Threat
              Signaling (DOTS) Telemetry", RFC 9244,
              DOI 10.17487/RFC9244, June 2022,
              <https://www.rfc-editor.org/info/rfc9244>.

   [Style]    IANA YANG, "IANA YANG",
              <https://github.com/llhotka/iana-yang>.

Author's Address

   Mohamed Boucadair
   Orange
   35000 Rennes
   France
   Email: mohamed.boucadair@orange.com

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