Internet-Draft IANA-Maintained YANG Modules March 2022
Boucadair Expires 25 September 2022 [Page]
8407 (if approved)
Intended Status:
Standards Track
M. Boucadair

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 also relaxes a recommendation related to the extensibility for such modules.

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 working documents as Internet-Drafts. The list of current Internet-Drafts is at

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 25 September 2022.

Table of Contents

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 modules.

Section 3 updates the guidelines in [RFC8407].

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 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.

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, 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 IANA-maintained module may use identities (e.g., [RFC8675]) or typedefs (e.g., [RFC9108]). Such a decision is left to the module designers and should be made based upon specifics related to the intended use of the module. 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 typedefs 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."

For IANA-maintained modules, this recommendation takes precedence over the behavior specified in Section 4.11.1 of [RFC8407] because the extensibility concern is not applicable for such modules.

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 by IANA for generating the module (e.g., an XSLT 1.0 stylesheet in Appendix A of [RFC9108]).

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 for the comments.

7. References

7.1. Normative References

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.
Bierman, A., "Guidelines for Authors and Reviewers of Documents Containing YANG Data Models", BCP 216, RFC 8407, DOI 10.17487/RFC8407, , <>.

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, , <>.
McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB", RFC 2863, DOI 10.17487/RFC2863, , <>.
Bjorklund, M., "IANA Interface Type YANG Module", RFC 7224, DOI 10.17487/RFC7224, , <>.
Boucadair, M., Farrer, I., and R. Asati, "A YANG Data Model for Tunnel Interface Types", RFC 8675, DOI 10.17487/RFC8675, , <>.
Thaler, D. and D. Romascanu, "Guidelines and Registration Procedures for Interface Types and Tunnel Types", RFC 8892, DOI 10.17487/RFC8892, , <>.
Lhotka, L. and P. Špaček, "YANG Types for DNS Classes and Resource Record Types", RFC 9108, DOI 10.17487/RFC9108, , <>.
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, , <>.

Author's Address

Mohamed Boucadair
35000 Rennes