Network Working Group C. Hopps
Internet-Draft Deutsche Telekom
Updates: rfc6087bis (if approved) L. Berger
Intended status: Standards Track LabN Consulting, L.L.C.
Expires: September 7, 2018 D. Bogdanovic
March 6, 2018

YANG Module Tags


This document provides for the association of tags with YANG modules. The expectation is for such tags to be used to help classify and organize modules. A method for defining, reading and writing a modules tags is provided. Tags may be standardized and assigned during module definition; assigned by implementations; or dynamically defined and set by users. This document provides guidance to future model writers and, as such, this document updates [I-D.ietf-netmod-rfc6087bis].

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Table of Contents

1. Introduction

The use of tags for classification and organization is fairly ubiquitous not only within IETF protocols, but in the internet itself (e.g., #hashtags). Tags can be usefully standardized, but they can also serve as a non-standardized mechanism available for users to define themselves. Our solution provides for both cases allowing for the most flexibility. In particular, tags may be standardized as well as assigned during module definition; assigned by implementations; or dynamically defined and set by users.

This document defines a module which provides a list of module entries to allow for adding or removing of tags as well as viewing the set of tags associated with a module.

This document also defines an IANA registry for tag prefixes as well as a set of globally assigned tags.

Section 7 provides guidelines for authors of YANG data models. This section updates [I-D.ietf-netmod-rfc6087bis].

2. Conventions Used in This Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

Note that lower case versions of these key words are used in section Section 7 where guidance is provided to future document authors.

3. Tag Prefixes

All tags have a prefix indicating who owns their definition. An IANA registry is used to support standardizing tag prefixes. Currently 3 prefixes are defined with all others reserved.

3.1. IETF Standard Tags

An IETF standard tag is a tag that has the prefix "ietf:". All IETF standard tags are registered with IANA in a registry defined later in this document.

3.2. Vendor Tags

A vendor tag is a tag that has the prefix "vendor:". These tags are defined by the vendor that implements the module, and are not standardized; however, it is recommended that the vendor consider including extra identification in the tag name to avoid collisions (e.g., vendor:super-duper-company:...).

3.3. Local Tags

A local tag is any tag that has the prefix "local:". These tags are defined by the local user/administrator and will never be standardized.

3.4. Reserved Tags

Any tag not starting with the prefix "ietf:", "vendor:" or "local:" is reserved for future standardization.

4. Tag Management

Tags can become associated with a module in a number of ways. Tags may be defined and associated at model design time, at implementation time, or via user administrative control. As the main consumer of tags are users, users may also remove any tag, no matter how the tag became associated with a module.

4.1. Module Definition Association

A module definition SHOULD indicate a set of tags to be automatically added by the module implementer. These tags MUST be standard tags (Section 3.1). This does imply that new modules may also drive the addition of new standard tags to the IANA registry.

4.2. Implementation Association

An implementation MAY include additional tags associated with a module. These tags may be standard or vendor specific tags.

4.3. Administrative Tagging

Tags of any kind can be assigned and removed with normal configuration mechanisms.

Implementations MUST ensure that a modules tag list is consistent across any location from which the list is accessible. So if a user adds a tag through configuration that tag should also be seen when using any augmentation that exposes the modules tag list.

5. Tags Module Structure

5.1. Tags Module Tree

The tree associated with the tags module is:

module: ietf-module-tags
    +--rw module-tags* [name]
       +--rw name          yang:yang-identifier
       +--rw tag*          string
       +--rw masked-tag*   string

5.2. Tags Module

<CODE BEGINS> file "ietf-module-tags@2018-03-06.yang"
module ietf-module-tags {
  yang-version "1";
  namespace "urn:ietf:params:xml:ns:yang:ietf-module-tags";
  prefix "mtags";

  import ietf-yang-types {
    prefix yang;

  organization "IETF NetMod Working Group (NetMod)";

    "NetMod Working Group - <>";

    "This module describes a tagging mechanism for yang module.
     Tags may be IANA assigned or privately defined types.";

  revision "2018-03-06" {
      "Initial revision.";
    reference "TBD";

  list module-tags {
    key "name";

      "A list of modules and their associated tags";

    leaf name {
        type yang:yang-identifier;
        mandatory true;
            "The YANG module or submodule name.";

    leaf-list tag {
        type string;

            "A tag associated with the module. See the IANA 'YANG Module
             Tag Prefix' registry for reserved prefixes and the IANA
             'YANG Module IETF Tag' registry for IETF standard tags.

             The operational view of this list will contain all
             user-configured tags as well as any predefined tags that
             have not been masked by the user using the masked-tag leaf
             list below.";

    leaf-list masked-tag {
        type string;

            "The list of tags that should not be associated with this
             module. This user can remove (mask) predefined tags by
             adding them to this list. It is not an error to add tags to
             this list that are not predefined for the module.";

6. Other Classifications

It's worth noting that a different yang module classification document exists [RFC8199]. That document is classifying modules in only a logical manner and does not define tagging or any other mechanisms. It divides yang modules into 2 categories (service or element) and then into one of 3 origins: standard, vendor or user. It does provide a good way to discuss and identify modules in general. This document defines standard tags to support [RFC8199] style classification.

7. Guidelines to Model Writers

This section updates [I-D.ietf-netmod-rfc6087bis].

7.1. Define Standard Tags

        module example-module {
            "[Text describing the module...]

            RFC<this document> TAGS:
            The following tags MUST be included by an implementation:
                 - ietf:some-required-tag:foo
                 - ...
            The following tags SHOULD be included by an implementation:
                 - ietf:some-recommended-tag:bar
                 - ...
            The following tags MAY be included by an implementation:
                 - ietf:some-optional-tag:baz
                 - ...


A module SHOULD indicate, in the description statement of the module, a set of tags that are to be associated with it. This description should also include the appropriate conformance statement or statements, using [RFC2119] language for each tag.

One SHOULD only include conformance text if there will be tags listed (i.e., there's no need to indicate an empty set).

The module writer may use existing standard tags, or use new tags defined in the model definition, as appropriate. New tags should be assigned in the IANA registry defined below, see Section 8.2 below.

8. IANA Considerations

8.1. YANG Module Tag Prefix Registry

This registry allocates tag prefixes. All YANG module tags SHOULD begin with one of the prefixes in this registry.

The allocation policy for this registry is Specification Required [RFC5226].

 prefix    description
 --------  ---------------------------------------------------
 ietf:     IETF Standard Tag allocated in the IANA YANG Module
           IETF Tag Registry.
 vendor:   Non-standardized tags allocated by the module implementer.
 local:    Non-standardized tags allocated by and for the user.

The initial values for this registry are as follows.

Other SDOs (standard organizations) wishing to standardize their own set of tags could allocate a top level prefix from this registry.

8.2. YANG Module IETF Tag Registry

This registry allocates prefixes that have the standard prefix "ietf:". New values should be well considered and not achievable through a combination of already existing standard tags.

The allocation policy for this registry is IETF Review [RFC5226].

The initial values for this registry are as follows.

[Editor's note: many of these tags may move to [I-D.ietf-rtgwg-device-model] if/when that document is refactored to use tags.]

IETF Module Tag Registry
Tag Description Reference
ietf:rfc8199:element A module for a network element. [RFC8199]
ietf:rfc8199:service A module for a network service. [RFC8199]
ietf:rfc8199:standard A module defined by a standards organization. [RFC8199]
ietf:rfc8199:vendor A module defined by a vendor. [RFC8199]
ietf:rfc8199:user A module defined by the user. [RFC8199]
ietf:device:hardware A module relating to device hardware (e.g., inventory). [This document]
ietf:device:software A module relating to device software (e.g., installed OS). [This document]
ietf:device:qos A module for managing quality of service. [This document]
ietf:protocol A module representing a protocol. [This document]
ietf:system-management A module relating to system management (e.g., a system management protocol). [This document]
ietf:network-service A module relating to network service (e.g., a network service protocol). [This document]
ietf:oam A module representing Operations, Administration, and Maintenance. [This document]
ietf:routing A module related to routing. [This document]
ietf:routing:rib A module related to routing information bases. [This document]
ietf:routing:igp An interior gateway protocol module. [This document]
ietf:routing:egp An exterior gateway protocol module. [This document]
ietf:signaling A module representing control plane signaling. [This document]
ietf:lmp A module representing a link management protocol. [This document]

9. References

9.1. Normative References

[I-D.ietf-netmod-rfc6087bis] Bierman, A., "Guidelines for Authors and Reviewers of YANG Data Model Documents", Internet-Draft draft-ietf-netmod-rfc6087bis-18, February 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 5226, DOI 10.17487/RFC5226, May 2008.
[RFC8199] Bogdanovic, D., Claise, B. and C. Moberg, "YANG Module Classification", RFC 8199, DOI 10.17487/RFC8199, July 2017.

9.2. Informative References

[I-D.ietf-rtgwg-device-model] Lindem, A., Berger, L., Bogdanovic, D. and C. Hopps, "Network Device YANG Logical Organization", Internet-Draft draft-ietf-rtgwg-device-model-02, March 2017.

Authors' Addresses

Christan Hopps Deutsche Telekom EMail:
Lou Berger LabN Consulting, L.L.C. EMail:
Dean Bogdanovic EMail: