netmod                                                      M. Boucadair
Internet-Draft                                                    Orange
Updates: 8407 (if approved)                                25 March 2022
Intended status: Standards Track
Expires: 26 September 2022

       Recommendations for Creating IANA-Maintained YANG Modules


   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 just
   another format to present the content of these registries.

   This document updates RFC 8407 by providing additional guidelines for
   IANA-maintained modules.  It does not change anything written in RFC

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
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 26 September 2022.

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   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights
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   extracted from this document must include Revised BSD License text as
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Guidelines for IANA-Maintained Registries . . . . . . . . . .   3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

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.

   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

   Section 3 updates the guidelines in [RFC8407].

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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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

3.  Guidelines for IANA-Maintained Registries

   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 final decision is left to the
   module designers and should be made based upon specifics related to
   the intended use of the module.  It is worth mentioning that
   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 document that registers the module.  For
   example, [I-D.ietf-dots-telemetry] defines an IANA-maintained module
   that uses enumerations for the following reason:

    "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."

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   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.  IANA Considerations

   This document does not require any IANA action.

5.  Security Considerations

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

6.  Acknowledgements

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

   Thanks to Juergen Schoenwaelder and Ladislav Lhotka for the
   discussion and valuable comments.  Special thanks to Ladislav Lhotka
   for sharing more context that led to the design documented in

7.  References

7.1.  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,

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   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

   [RFC8407]  Bierman, A., "Guidelines for Authors and Reviewers of
              Documents Containing YANG Data Models", BCP 216, RFC 8407,
              DOI 10.17487/RFC8407, October 2018,

7.2.  Informative References

              Boucadair, M., Reddy.K, T., Doron, E., Chen, M., and J.
              Shallow, "Distributed Denial-of-Service Open Threat
              Signaling (DOTS) Telemetry", Work in Progress, Internet-
              Draft, draft-ietf-dots-telemetry-25, 21 March 2022,

   [RFC2863]  McCloghrie, K. and F. Kastenholz, "The Interfaces Group
              MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000,

   [RFC7224]  Bjorklund, M., "IANA Interface Type YANG Module",
              RFC 7224, DOI 10.17487/RFC7224, May 2014,

   [RFC8675]  Boucadair, M., Farrer, I., and R. Asati, "A YANG Data
              Model for Tunnel Interface Types", RFC 8675,
              DOI 10.17487/RFC8675, November 2019,

   [RFC8892]  Thaler, D. and D. Romascanu, "Guidelines and Registration
              Procedures for Interface Types and Tunnel Types",
              RFC 8892, DOI 10.17487/RFC8892, August 2020,

   [RFC9108]  Lhotka, L. and P. Špaček, "YANG Types for DNS Classes and
              Resource Record Types", RFC 9108, DOI 10.17487/RFC9108,
              September 2021, <>.

   [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,

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   [Style]    IANA YANG, "IANA YANG",

Author's Address

   Mohamed Boucadair
   35000 Rennes

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