Network Working Group                                           C. Hopps
Internet-Draft                                                 L. Berger
Updates: RFC8407 (if approved)                                   LabN Consulting, L.L.C.
Updates: 8407 (if approved)                                    L. Berger
Intended status: Standards Track                           D. Bogdanovic                   LabN Consulting, LLC.
Expires: August 19, September 3, 2019                                 D. Bogdanovic
                                                          Volta Networks
                                                       February 15,
                                                           March 2, 2019

                            YANG Module Tags
                    draft-ietf-netmod-module-tags-05
                    draft-ietf-netmod-module-tags-06

Abstract

   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 also provides guidance to
   future model writers and, writers, as such, this document updates [RFC8407]. RFC8407.

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 https://datatracker.ietf.org/drafts/current/.

   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 August 19, September 3, 2019.

Copyright Notice

   Copyright (c) 2019 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
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Some possible use cases of YANG module tags . . . . . . .   3
   2.
     1.2.  Conventions Used in This Document . . . . . . . . . . . . . .   4
   3.
   2.  Tag Values  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.
     2.1.  IETF Standard Tags  . . . . . . . . . . . . . . . . . . .   4
     3.2.
     2.2.  Vendor Tags . . . . . . . . . . . . . . . . . . . . . . .   4
     3.3.
     2.3.  User Tags . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.4.   5
     2.4.  Reserved Tags . . . . . . . . . . . . . . . . . . . . . .   4
   4.   5
   3.  Tag Management  . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.   5
     3.1.  Module Definition Association Tagging . . . . . . . . . . . . . . . .   5
     4.2.
     3.2.  Implementation Association Tagging  . . . . . . . . . . . . . . . . .   5
     4.3.  Administrative
     3.3.  User Tagging  . . . . . . . . . . . . . . . . . . . . . .   5
   5.
   4.  Tags Module Structure . . . . . . . . . . . . . . . . . . . .   5
     5.1.
     4.1.  Tags Module Tree  . . . . . . . . . . . . . . . . . . . .   5
     5.2.  Tags
     4.2.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .   5
   6.   6
   5.  Other Classifications . . . . . . . . . . . . . . . . . . . .   8
   7.
   6.  Guidelines to Model Writers . . . . . . . . . . . . . . . . .   8
     7.1.
     6.1.  Define Standard Tags  . . . . . . . . . . . . . . . . . .   8
   8.
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     8.1.
     7.1.  YANG Module Tag Prefix Prefixes Registry . . . . . . . . . . . . .   9
     8.2.
     7.2.  YANG Module Tags Registry . . . . . . . . . . . . . . . .  10
     7.3.  Updates to the IETF Tag XML Registry  . . . . . . . . . . . .  11
     7.4.  Updates to the YANG Module Names Registry . . . . . . . .  11
   8.  Security Considerations . . . . . . . .   9 . . . . . . . . . . .  12
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11  12
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  11  12
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  11  12
   Appendix A.  Acknowledgements  Examples . . . . . . . . . . . . . . . . . .  11
   Appendix B.  Example . . . .  13
   Appendix B.  Acknowledgements . . . . . . . . . . . . . . . . . .  12  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12  14

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). "#hashtags").  One benefit of using tags for organization over
   a rigid structure is that it is more flexible and can more easily
   adapt over time as technologies evolve.  Tags can be usefully
   standardized, but they can also serve as a non-standardized mechanism
   available for users to define themselves.  This document provides a
   mechanism to define tags and associate them with YANG modules in a
   flexible manner.  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 YANG module [RFC7950] 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 defines an extension statement to be used to indicate
   tags that SHOULD be added by the module implementation automatically
   (i.e., outside of configuration).

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

   Section 7 6 provides guidelines for authors of YANG data models.

   This document updates [RFC8407].

   The YANG data model in this document conforms to the Network
   Management Datastore Architecture defined in [RFC8342].

1.1.  Some possible use cases of YANG module tags

   During this documents progression there were requests for example
   uses of module tags.  The following are a few example use cases for
   tags.  This list is certainly not exhaustive.

   One example use of tags would be to help filter different discrete
   categories of YANG modules supported by a device.  E.g., if modules
   are suitably tagged, then an XPath query can be used to list all of
   the vendor modules supported by a device.

   Tags can also be used to help coordination when multiple semi-
   independent clients are interacting with the same devices.  E.g., one
   management client could mark that some modules should not be used
   because they have not been verified to behave correctly, so that
   other management clients avoid querying the data associated with
   those modules.

   Tag classification is useful for users searching module repositories
   (e.g.  YANG catalog).  A query restricted to the 'ietf:routing'
   module tag could be used to return only the IETF YANG modules
   associated with routing.  Without tags, a user would need to know the
   name of all the IETF routing protocol YANG modules.

   Future management protocol extensions could allow for filtering
   queries of configuration or operational state on a server based on
   tags.  E.g., return all operational state related to system-
   management.

2.

1.2.  Conventions Used in This Document

   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
   [RFC2119] [RFC8174] when, and only when, they appear in all capitals,
   as shown here.

3.

2.  Tag Values

   All tags SHOULD begin with a prefix indicating who owns their
   definition.  An IANA registry is used to support standardizing tag
   prefixes.
   prefixes Section 7.1.  Currently 3 prefixes are defined with all
   others reserved.  No further structure is imposed by this document on
   the value following the standard prefix, and the value can contain
   any yang type 'string' characters except carriage-returns, newlines
   and tabs.

3.1.

   Again, except for the conflict-avoiding prefix, this document is not
   specifying any structure on (i.e., restricting) the tag values on
   purpose.  The intent is to avoid arbitrarily restricting the values
   that designers, implementers and users can use.  As a result of this
   choice, designers, implementers, and users are free to add or not add
   any structure they may require to their own tag values.

2.1.  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. document Section 7.2.

2.2.  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 include
   extra identification in the tag to avoid collisions such as using the
   enterpise or organization name follwing the "vendor:" prefix (e.g.,
   vendor:example.com:vendor-defined-classifier).

3.3.

2.3.  User Tags

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

3.4.

2.4.  Reserved Tags

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

4.

3.  Tag Management

   Tags can become associated with a module in a number of ways.  Tags
   may be defined and associated at module 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.

3.1.  Module Definition Association Tagging

   A module definition can MAY indicate a set of tags to be added by the
   module implementer.  These design time tags are indicated using the
   module-tag extension statement.

   If the module definition is IETF standards track, the tags MUST also
   be IETF standard tags
   (Section 3.1). Section 2.1.  Thus, new modules can drive the addition of new
   standard tags to the IANA registry, and the IANA registry can serve
   as a check against duplication.

4.2.

3.2.  Implementation Association Tagging

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

4.3.  Administrative

3.3.  User Tagging

   Tags of any kind can be assigned and removed by the user using normal
   configuration mechanisms.

5.

4.  Tags Module Structure

5.1.

4.1.  Tags Module Tree

   The tree associated with the "ietf-module-tags" module follows.  The
   meaning of the symbols can be found in [RFC8340].

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

5.2.  Tags

4.2.  YANG Module

   <CODE BEGINS> file "ietf-module-tags@2019-02-15.yang" "ietf-module-tags@2019-03-02.yang"
   module ietf-module-tags {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-module-tags";
     prefix tags;

     import ietf-yang-types {
       prefix yang;
     }

     organization
       "IETF NetMod Working Group (NetMod)";
     contact
       "NetMod Working Group - <netmod@ietf.org>";

     // RFC Ed.: replace XXXX with actual RFC number and
     // remove this note.

     description
       "This module describes a mechanism associating tags with YANG
        modules. Tags may be IANA assigned or privately defined.

        Copyright (c) 2018 IETF Trust and the persons identified as
        authors of the code. All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject to
        the license terms contained in, the Simplified BSD License set
        forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (https://trustee.ietf.org/license-info).

        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 version of this YANG module is part of RFC XXXX
        (https://tools.ietf.org/html/rfcXXXX); see the RFC itself for
        full legal notices.";

     // RFC Ed.: update the date below with the date of RFC publication
     // and RFC number and remove this note.

     revision 2018-10-17 2019-03-02 {
       description
         "Initial revision.";
       reference "RFC XXXX: YANG Module Tags";
     }

     typedef tag {
       type string {
         length "1..max";
         pattern '[a-zA-Z_][a-zA-Z0-9\-_]*:[\S ]+';
       }
       description
         "A tag value is composed of a standard prefix followed by any
          type 'string' value that does not include carriage return,
          newline or tab characters.";
     }

     extension module-tag {
       argument tag;
       description
         "The argument 'tag' is of type 'tag'. This extension statement
          is used by module authors to indicate the tags that SHOULD be
          added automatically by the system. As such the origin of the
          value for the pre-defined tags should be set to 'system'.";
     }

     container module-tags {
       description
         "Contains the list of modules and their associated tags";
       list module {
         key "name";
         description
           "A list of modules and their associated tags";
         leaf name {
           type yang:yang-identifier;
           mandatory true;
           description
             "The YANG module name.";
         }
         leaf-list tag {
           type tag;
           description
             "Tags associated with the module. See the IANA 'YANG Module
              Tag Prefix' Prefixes' registry for reserved prefixes and the IANA
              'YANG Module IETF Tag' Tags' registry for IETF standard tags.

              The 'operational' state [RFC8342] view of this list is
              constructed using the following steps:

              1) System tags (i.e., tags of 'system' origin) are added.
              2) User configured tags (i.e., tags of 'intended' origin)
              are added.
              3) Any tag that is equal to a masked-tag is removed.";
         }
         leaf-list masked-tag {
           type tag;
           description
             "The list of tags that should not be associated with this
              module. The user can remove (mask) tags from the
              operational state datastore [RFC8342] by adding them to
              this list. It is not an error to add tags to this list
              that are not associated with the module, but they have no
              operational effect.";
         }
       }
     }
   }
   <CODE ENDS>

6.

5.  Other Classifications

   It is worth noting that a different YANG module classification
   document exists [RFC8199].  That document only classifies modules in
   a logical manner and does not define tagging or any other mechanisms.
   It divides YANG modules into two categories (service or element) and
   then into one of three 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.

6.  Guidelines to Model Writers

   This section updates [RFC8407].

7.1.

6.1.  Define Standard Tags

   A module MAY indicate, using module-tag extension statements, a set
   of tags that are to be automatically associated with it (i.e., not
   added through configuration).

   module example-module {
             ...
     //...
     import module-tags { prefix tags; }

     tags:module-tag "ietf:some-new-tag";
     tags:module-tag "ietf:some-other-tag";
     // ...
   }

   The module writer can use existing standard tags, or use new tags
   defined in the model definition, as appropriate.  For standardized
   modules new tags MUST be assigned in the IANA registry defined below,
   see Section 8.2 below.

8. 7.2.

7.  IANA Considerations

8.1.

7.1.  YANG Module Tag Prefix Prefixes Registry

   This

   IANA is asked to create a new registry allocates tag prefixes.  All YANG module "YANG Module Tag Prefixes"
   grouped under a new "Protocol" category named "YANG Module Tags".

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

   Prefix entries in this registry should be short strings consisting of
   lowercase ASCII alpha-numeric characters and a final ":" character.

   The allocation policy for this registry is Specification Required
   [RFC5226].
   [RFC8126].

   The initial values for this registry are as follows.

    prefix    description
    --------  ---------------------------------------------------

   +---------+---------------------------------------------------------+
   | Prefix  | Description                                             |
   +---------+---------------------------------------------------------+
   | ietf:   | IETF Standard Tag allocated in the IANA YANG Module
              IETF Tag Registry.     |
   |         | Tags registry.                                          |
   |         |                                                         |
   | vendor: | Non-standardized tags allocated by the module           |
   |         | implementer.                                            |
   |         |                                                         |
   | user:   | Non-standardized tags allocated by and for the user.    |
   +---------+---------------------------------------------------------+

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

8.2.

7.2.  YANG Module IETF Tag Tags Registry

   IANA is asked to create a new registry "YANG Module Tags" grouped
   under a new "Protocol" category "YANG Module Tags".  This registry
   should be included below "YANG Module Tag Prefixes" when listed on
   the same page.

   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]. [RFC8126].

   The initial values for this registry are as follows.

   +----------------------------+--------------------------+-----------+
   | Tag                        | Description              | Reference |
   +----------------------------+--------------------------+-----------+
   | ietf:network-element-class |  A module for a [RFC8199] network        | [RFC8199] |
   |                            | element.                 |           |
   |                            |                          |           |
   | ietf:network-service-class |  A module for a [RFC8199] network        | [RFC8199] |
   |                            | service.                 |           |
   |                            |                          |           |
   | ietf:sdo-defined-class     |  A module Module is defined by a   | [RFC8199] |
   |                            | standards organization.  |           |
   |                            |                          |           |
   | ietf:vendor-defined-class  |  A module Module is defined by a   | [RFC8199] |
   |                            | vendor.                  |           |
   |                            |                          |           |
   | ietf:user-defined-class    | A module Module is defined by the | [RFC8199] |
   |                            | user.                    |           |
   |                            |                          |           |
   | ietf:hardware              |   A module relating Relates to hardware      | [This     |
   |                            |     hardware (e.g.,      | document] |
   |                            | inventory).       | document] |
   |                            |                          |           |
   | ietf:software              |   A module relating Relates to software      | [This     |
   |                            |     software (e.g., installed OS).    | document] |
   |                            |      installed OS).                          |           |
   | ietf:protocol              | Represents a protocol    | [This     |
   |          ietf:qos                            |  A module for managing (often combined with     |   [This document] |
   |                            |   quality of service. another tag to refine).  | document]           |
   |                            |                          |           |
   |       ietf:protocol ietf:qos                   | A module representing a Relates to quality of    | [This     |
   |                            |        protocol. service.                 | document] |
   |                            |                          |           |
   |   ietf:system-management ietf:network-service-app   |   A module relating Relates to a network     | [This     |
   |                            | system management (e.g., service application      | document] |
   |                            |   a system management    |           |
   |                            | protocol such as syslog, (e.g., an NTP server,    |           |
   |                            |  TACAC+, SNMP, netconf, DNS server, DHCP server, |           |
   |                            |          ...). etc).                    |           |
   |                            |                          |           |
   |    ietf:network-service ietf:system-management     |   A module relating Relates to system        | [This     |
   |                            | network service management (e.g., a      | document] |
   |                            | network service protocol system management        |           |
   |                            | protocol such as an NTP server, syslog, |           |
   |                            | DNS server, DHCP server, TACAC+, SNMP, netconf,   |           |
   |                            |          etc). ...).                    |           |
   |                            |                          |           |
   | ietf:oam                   |  A module representing   |   [This   |
   |                            | Relates to Operations,   | document] [This     |
   |                            | Administration, and      | document] |
   |                            | Maintenance (e.g., BFD). |           |
   |                            |                          |           |
   | ietf:routing               |   A module related Relates to routing.      | [This     |
   |                            |         routing.                          | document] |
   |                            |                          |           |
   | ietf:signaling             |  A module representing Relates to control plane | [This     |
   |                            | control plane signaling.               | document] |
   |                            |                          |           |
   |          ietf:lmp ietf:link-management       | A module representing a Relates to link          | [This     |
   |                            |     link management management.              | document] |
   |                            |        protocol.         |           |
   +----------------------------+--------------------------+-----------+

                     Table 1:

7.3.  Updates to the IETF Module Tag XML Registry

9.  References

9.1.  Normative

   This document registers a URI in the "IETF XML Registry" [RFC3688].
   Following the format in [RFC3688], the following registration has
   been made:

   URI:  urn:ietf:params:xml:ns:yang:ietf-module-tags

   Registrant Contact:  The IESG.

   XML:  N/A; the requested URI is an XML namespace.

7.4.  Updates to the YANG Module Names Registry

   This document registers one YANG module in the "YANG Module Names"
   registry [RFC6020].  Following the format in [RFC6020], the following
   registration has been made:

   name:  ietf-module-tags

   namespace:  urn:ietf:params:xml:ns:yang:ietf-module-tags

   prefix:  tags
   reference:  RFC XXXX (RFC Ed.: replace XXX with actual RFC number and
      remove this note.)

8.  Security Considerations

   The YANG module defined in this memo is designed to be accessed via
   the NETCONF protocol [RFC6241].  The lowest NETCONF layer is the
   secure transport layer and the mandatory-to-implement secure
   transport is SSH [RFC6242].

   This document adds the ability to associate tag meta-data with YANG
   modules.  This document does not define any actions based on these
   associations, and none are yet defined, and therefore it does not by
   itself introduce any new security considerations.

   Users of the tag-meta data may define various actions to be taken
   based on the tag meta-data.  These actions and their definitions are
   outside the scope of this document.  Users will need to consider the
   security implications of any actions they choose to define.

9.  References

9.1.  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>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <https://www.rfc-editor.org/info/rfc5226>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [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",

9.2.  Informative References

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 216, 81, RFC 8407, 3688,
              DOI 10.17487/RFC8407, 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2018,
              <https://www.rfc-editor.org/info/rfc8407>.

9.2.  Informative References 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [RFC8199]  Bogdanovic, D., Claise, B., and C. Moberg, "YANG Module
              Classification", RFC 8199, DOI 10.17487/RFC8199, July
              2017, <https://www.rfc-editor.org/info/rfc8199>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore Architecture
              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
              <https://www.rfc-editor.org/info/rfc8342>.

Appendix A.  Acknowledgements

   Special thanks to Robert Wilton

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

Appendix B.  Example A.  Examples

   The following is a fictional example result from a query of the
   module tags list.  For the sake of brevity only a few module results
   are imagined.

     {
       "ietf-module-tags:module-tags": {
         "module": [
           {
             "name": "ietf-bfd",
             "tag": [
               "ietf:network-element-class",
               "ietf:oam",
               "ietf:protocol",
               "ietf:sdo-defined-class"
             ]
           },
           {
             "name": "ietf-isis",
             "tag": [
               "ietf:network-element-class",
               "ietf:protocol",
               "ietf:routing"
               "ietf:sdo-defined-class",
             ]
           },
           {
             "name": "ietf-ssh-server",
             "tag": [
               "ietf:network-element-class",
               "ietf:protocol",
               "ietf:sdo-defined-class",
               "ietf:system-management"
             ]
           }
         ]
       }
     }

<ns0:config xmlns:ns0="urn:ietf:params:xml:ns:netconf:base:1.0">
  <t:module-tags xmlns:t="urn:ietf:params:xml:ns:yang:ietf-module-tags">
    <t:module>
      <t:name>ietf-bfd</t:name>
      <t:tag>ietf:network-element-class</t:tag>
      <t:tag>ietf:oam</t:tag>
      <t:tag>ietf:protocol</t:tag>
      <t:tag>ietf:sdo-defined-class</t:tag>
    </t:module>
    <t:module>
      <t:name>ietf-isis</t:name>
      <t:tag>ietf:network-element-class</t:tag>
      <t:tag>ietf:protocol</t:tag>
      <t:tag>ietf:sdo-defined-class</t:tag>
      <t:tag>ietf:routing</t:tag>
    </t:module>
    <t:module>
      <t:name>ietf-ssh-server</t:name>
      <t:tag>ietf:network-element-class</t:tag>
      <t:tag>ietf:protocol</t:tag>
      <t:tag>ietf:sdo-defined-class</t:tag>
      <t:tag>ietf:system-management</t:tag>
    </t:module>
  </t:module-tags>
</ns0:config>

Appendix B.  Acknowledgements

   Special thanks to Robert Wilton for his help improving the
   introduction and providing the example use cases.

Authors' Addresses

   Christan

   Christian Hopps
   LabN Consulting, L.L.C.

   Email: chopps@chopps.org

   Lou Berger
   LabN Consulting, L.L.C. LLC.

   Email: lberger@labn.net
   Dean Bogdanovic
   Volta Networks

   Email: ivandean@gmail.com