NETMOD Working Group                                               Q. Wu
Internet-Draft                                                 B. Claise
Updates: 8407 (if approved)                                       Huawei
Intended status: Standards Track                                  P. Liu
Expires: 31 October 2022                                           Z. Du
                                                            China Mobile
                                                            M. Boucadair
                                                                  Orange
                                                           29 April 2022


                     Data Node Tags in YANG Modules
                     draft-ietf-netmod-node-tags-07

Abstract

   This document defines a method to tag data nodes that are associated
   with operation and management data in YANG modules.  This method for
   tagging YANG data nodes is meant to be used for classifying data
   nodes or instance of data nodes from different YANG modules and
   identifying their characteristic data.  Tags may be registered as
   well as assigned during the definition of the module, assigned by
   implementations, or dynamically defined and set by users.

   This document also provides guidance to future YANG data model
   writers; as such, this document updates RFC 8407.

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 31 October 2022.

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
   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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Data Classification and Fetching using Data Node Tags . . . .   4
   4.  Data Node Tag Values  . . . . . . . . . . . . . . . . . . . .   7
     4.1.  IETF Tags . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  Vendor Tags . . . . . . . . . . . . . . . . . . . . . . .   7
     4.3.  User Tags . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.4.  Reserved Tags . . . . . . . . . . . . . . . . . . . . . .   8
   5.  Data Node Tag Management  . . . . . . . . . . . . . . . . . .   8
     5.1.  Module Design Tagging . . . . . . . . . . . . . . . . . .   8
     5.2.  Implementation Tagging  . . . . . . . . . . . . . . . . .  10
     5.3.  User Tagging  . . . . . . . . . . . . . . . . . . . . . .  10
   6.  Data Node Tags Module Structure . . . . . . . . . . . . . . .  10
     6.1.  Data Node Tags Module Tree  . . . . . . . . . . . . . . .  10
   7.  YANG Module . . . . . . . . . . . . . . . . . . . . . . . . .  10
   8.  Guidelines to Model Writers . . . . . . . . . . . . . . . . .  14
     8.1.  Define Standard Tags  . . . . . . . . . . . . . . . . . .  14
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
     9.1.  YANG Data Object Tag Prefixes Registry  . . . . . . . . .  15
     9.2.  IETF YANG Data Object Tags Registry . . . . . . . . . . .  16
     9.3.  Updates to the IETF XML Registry  . . . . . . . . . . . .  18
     9.4.  Updates to the YANG Module Names Registry . . . . . . . .  18
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  18
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   12. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  19
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     13.2.  Informative References . . . . . . . . . . . . . . . . .  20
   Appendix A.  Example: Additional Auxiliary Data Property
           Information . . . . . . . . . . . . . . . . . . . . . . .  22
   Appendix B.  Instance Level Tunnel Tagging Example  . . . . . . .  22
   Appendix C.  NETCONF Example  . . . . . . . . . . . . . . . . . .  24
   Appendix D.  Non-NMDA State Module  . . . . . . . . . . . . . . .  25
   Appendix E.  Targeted Data Fetching Example . . . . . . . . . . .  28
   Appendix F.  Changes between Revisions  . . . . . . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  32




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1.  Introduction

   The use of tags for classification and organization purposes is
   fairly ubiquitous, not only within IETF protocols, but globally in
   the Internet (e.g., "#hashtags").  For the specific case of YANG data
   models, a module tag is defined as a string that is associated with a
   module name at the module level [RFC8819].

   Many data models have been specified by various Standards Developing
   Organizations (SDOs) and the Open Source community, and it is likely
   that many more will be specified.  These models cover many of the
   networking protocols and techniques.  However, data nodes defined by
   these technology-specific data models might represent only a portion
   of fault, configuration, accounting, performance, and security
   (FCAPS) management information ([FCAPS]) at different levels and
   network locations, but also categorised in various different ways.
   Furthermore, there is no consistent classification criteria or
   representations for a specific service, feature, or data source.

   This document defines data node tags and shows how they may be
   associated with data nodes within a YANG module, which:

   *  Provide dictionary meaning for specific targeted data nodes.

   *  Indicate a relationship between data nodes within the same YANG
      module or from different YANG modules.

   *  Identify key performance metric related data nodes and the
      absolute XPath expression identifying the element path to the
      nodes.

   The data node tags can be used by a NETCONF [RFC6241] or RESTCONF
   [RFC8040]client to classify data nodes of instance of these data
   nodes from different YANG modules and identify characteristic data.
   In addition, these tags can provide input, instructions, or
   indications to selection filters and filter queries of configuration
   or operational state on a server based on these data node tags (e.g.,
   return specific data containing operational state related to
   performance management).  NETCONF clients can discover data nodes or
   instances of data nodes with data node tags supported by a NETCONF
   server by means of the <get-schema> operation (Section 3.1 of
   [RFC6022]).  The data node tag information can also be queried using
   the model defined in Section 6.1.  Similar to YANG module tags
   defined in [RFC8819], these data node tags may be registered or
   assigned during the module definition, assigned by implementations,
   or dynamically defined and set by users.





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   This document defines a YANG module [RFC7950] that augments the
   module tag model [RFC8819] and provides a list of data node instance
   entries to add or remove data node tags as well as to view the set of
   data node tags associated with specific data nodes or instance of
   data nodes within YANG modules.

   This document defines three extension statements to indicate data
   node 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 and a
   set of globally assigned tags (Section 9).

   Section 8 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].

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.

   The meanings of the symbols in tree diagrams are defined in
   [RFC8340].

3.  Data Classification and Fetching using Data Node Tags

   Among data node tags, the 'opm' (object, property, metric) tags can
   be used to classify collected data, indicate relationships between
   data nodes, and capture YANG-modelled performance metrics data
   associated with data nodes of instances of data nodes.  An example is
   depicted in Figure 1.














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                         .------.
                         |Object|
                         | Tag  |
                         '--+--'
                            |
                  +---------V--------+    contain
                  | YANG Data Node   <----------------+
                  |        1         |                |
                  +--^-------------^-+                |
                     |contain      |contain           |
                     |             |                  |
         +-----------+---+ +- -----+-------+    +-----+---------+
         | YANG Data Node| | YANG Data Node|    | YANG Data Node|
         |     2         | |      3        |    |      4        |
         +--^------------+ +^-----^--------+    +^-----^------^-+
            |               |     |              |     |      |
        .---+---.           |  .--+--.           |  .--+--.   |
       |Property |          | |Metric |          | |Metric |  |
       |   Tag   |          | |  Tag  |          | | Tag   |  |
       '---------'          | '-------'          | '-------'  |
                            |                    |            |
                         .--+--.              .--+--.     .---+---.
                        |Metric |            |Metric |   || Multi ||
                        | Type  |            | Type  |   ||Metric ||
                        | Tag   |            |  Tag  |   ||Source ||
                        '-------'            '-------'   \\  Tag  //
                                                           '-----'

        Figure 1: The Relation between Object, Property, and Metric

   In Figure 1.

   Data nodes that contain other data nodes can be one of type
   'container', 'leaf-list', or 'list' and are tagged with the 'object'
   tag.

   A Data node tagged with the 'property' tag is a 'leaf' node.

   Data nodes tagged with the 'metric' tag can be one of 'container',
   'leaf-list', 'list', or 'leaf' data node.

   A data node may be associated with one single 'object' tag, or one
   single 'property' tag, or one single 'metric' tag.  The data node
   tagged with the 'metric' tag also can have one or multiple MetricType
   tags and/or one single multi-source tag.






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   The use of 'opm' tags is meant to help filter discrete categories of
   YANG data objects scattered across the same or different YANG modules
   that are supported by a device and capture all network performance
   data or all property data in a single view of the data.  In the
   example shown in Figure 2, the 'tunnel-svc' data node is a list node
   defined in a 'example-tunnel-pm' module and can be seen as the root
   object for property tagged data node (e.g., 'tunnel-svc'/'create-
   time') and metric tagged data node (e.g., 'tunnel-svc'/'avg-
   latency').  The 'name', 'create-time', and 'modified-time' are
   property tagged data node under 'tunnel-svc' list.  The 'avg-latency'
   and 'packet-loss' metrics are metric tagged data nodes under 'tunnel-
   svc' list node.  Consider the 'tunnel-svc' data node and the 'tunnel-
   svc/name' data node as an example: the 'tunnel-svc' data node has one
   single 'object' tag (i.e., 'ietf:object'), while the 'tunnel-svc/
   name' data node has one single 'property' data node tag (i.e.,
   'ietf:property').  In addition, not all metric data node need to be
   tagged (e.g., define specific categories, such as loss-related metric
   data nodes need to be tagged with a metric-type tag which can further
   reduce amount data to be fetched).

 +------------------------+--------------------------------+-----------+
 |      Data              |  Object    Property     Metric |  Multi-   |
 |      Node              |   Tag        Tag         Tag   |Source Tag |
 +------------------------+--------------------------------+-----------+
 |                        |  ietf:                         |           |
 |tunnel-svc              |  object                        |           |
 |                        |            ietf:               |           |
 |tunnel-svc/name         |            property            |           |
 |                        |            ietf:               |           |
 |tunnel-svc/create-time  |            property            |           |
 |                        |            ietf:               |           |
 |tunnel-svc/modified-time|            property            |           |
 |                        |                                |           |
 |tunnel-svc/avg-latency  |                        ietf:   | non-agg   |
 |                        |                        metric  |           |
 |tunnel-svc/packet-loss  |                        ietf:   | non-agg   |
 |                        |                        metric  |           |
 |tunnel-svc/min-latency  |                        ietf:   | non-agg   |
 |                        |                        metric  |           |
 |tunnel-svc/max-latency  |                        ietf:   | non-agg   |
 |                        |                        metric  |           |
 +------------------------+--------------------------------+-----------+

         Figure 2: Example of OPM Tags Used in the YANG Module







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   If data objects in YANG modules are adequately tagged and learnt by
   the client from a server, the client can retrieve paths to all
   targeted data nodes and then use an XPath query defined in
   [RFC8639][RFC8641] to list all tagged data nodes which reflect the
   network characteristics.

4.  Data Node Tag Values

   All data node tags (except in some cases of user tags as described in
   Section 4.3) begin with a prefix indicating who owns their
   definition.  An IANA registry (Section 9.1) is used to register data
   node tag prefixes.  Initially, three prefixes are defined.

   No further structure is imposed by this document on the value
   following the registered prefix, and the value can contain any YANG
   type 'string' characters except carriage returns, newlines, tabs, and
   spaces.

   Except for the conflict-avoiding prefix, this document is
   purposefully not specifying any structure on (i.e., restricting) the
   tag values.  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.

4.1.  IETF Tags

   An IETF tag is a data node tag that has the prefix "ietf:".

   All IETF data node tags are registered with IANA in the registry
   defined in Section 9.2.

4.2.  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 registered with IANA.  However, it is RECOMMENDED that the
   vendor includes extra identification in the tag to avoid collisions,
   such as using the enterprise or organization name following the
   "vendor:" prefix (e.g., vendor:entno:vendor-defined-classifier).

4.3.  User Tags

   User tags are defined by a user/administrator and are not registered
   by IANA.





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   Any tag with the prefix "user:" is a user tag.  Furthermore, any tag
   that does not contain a colon (":", i.e., has no prefix) is also a
   user tag.  Users are not required to use the "user:" prefix; however,
   doing so is RECOMMENDED.

4.4.  Reserved Tags

   Section 9.1 describes the IANA registry of tag prefixes.  Any prefix
   not included in that registry is reserved for future use, but tags
   starting with such a prefix are still valid tags.

5.  Data Node Tag Management

   Tags may be associated with a data node within a YANG module in a
   number of ways.  Typically, tags may be defined and associated at the
   module design time, at implementation time without the need of a live
   server, or via user administrative control.  As the main consumers of
   data node tags are users, users may also remove any tag from a live
   server, no matter how the tag became associated with a data node
   within a YANG module.

5.1.  Module Design Tagging

   A data node definition MAY indicate a set of data node tags to be
   added by a module's implementer.  These design time tags are
   indicated using a set of extension statements which include:

   opm-tag extension statement:  Classifies management and operation
      data into object, property, and metric three categories.  Three
      values (object, property and metric) are assigned to the 'opm-tag'
      tag.

      Data nodes that contain other data nodes can be one of type
      'container', 'leaf-list', and 'list' and are tagged with the
      'object' tag value.  A data node tagged with the 'property' tag
      value is a 'leaf' node.  Data node tagged with the 'metric' tag
      value can be one of 'container', 'leaf-list', 'list', or 'leaf'
      data node.  A data node contains one single 'object' tag, one
      single 'property' tag, or one single 'metric' tag.  Both 'object'
      tag value and 'property' tag value are not inherited down the
      containment hierarchy, e.g., if a container is marked with a
      'object ' tag value, all its contained leaves don't inherit the
      tag value.  The 'metric' tag value is inherited down the
      containment hierarchy if Data nodes tagged with the 'metric' tag
      is one of 'container', 'leaf-list', 'list'.






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      A data node tagged with the 'metric' tag also can have one or
      multiple Metric type tag and/or one single multi-source tag.  See
      the examples depicted in Figure 2 and Figure 4.

   metric-type extension statement:  Provides metric related data nodes
      classifications (e.g., loss, jitter, delay, counter, gauge,
      summary, unknown) for data nodes tagged with the 'metric' tag.
      Data nodes tagged with the 'metric-type' tag can be one of
      'container', 'leaf-list', 'list', or 'leaf' data node.  The
      'metric-type' tag is inherited down the containment hierarchy if
      Data nodes tagged with the 'metric-type' tag is one of
      'container', 'leaf-list', 'list'.  Figure 6 provides a list of
      possbile values for the 'metric-type' tag.

   multi-source-tag extension statement:  Identifies multi-source
      aggregation type for data nodes tagged with the 'metric' tag.  Two
      values (i.e., aggregated, non-aggregated) are assigned to 'multi-
      source-tag' tag.

      The 'aggregated' multi-source aggregation type allows a large
      number of measurements on metric subobjects from different sources
      of the same type (e.g., line card, each subinterface of aggregated
      Ethernet interface) to be combined into aggregated statistics and
      report as one metric subobject.

      The 'non-aggregated' multi-source aggregation type allows
      measurement from each source of the same type (e.g., line card,
      each subinterface of aggregated Ethernet interface) to be reported
      separately.

      Data nodes tagged with the 'multi-source-tag' tag can be one of
      'container', 'leaf-list', 'list', or 'leaf' data node.  The
      'multi-source-tag' tag is inherited down the containment hierarchy
      if Data nodes tagged with the 'multi-source-tag' tag is one of
      'container', 'leaf-list', 'list'.

   Among these extension statements, the 'metric-type' and 'multi-
   source-tag' extension statements are context information that can be
   used to correlate data nodes from the different modules.

   If the data node is defined in an IETF Standards Track document, the
   data node tags MUST be IETF Tags (Section 4.1).  Thus, new data nodes
   can drive the addition of new IETF tags to the IANA registry defined
   in Section 9.2, and the IANA registry can serve as a check against
   duplication.






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5.2.  Implementation Tagging

   An implementation MAY include additional tags associated with data
   nodes within a YANG module.  These tags SHOULD be IETF ((i.e.,
   registered) ) or vendor tags.

5.3.  User Tagging

   data node tags of any kind, with or without a prefix, can be assigned
   and removed by the user from a server using normal configuration
   mechanisms.  In order to remove a data node tag from the operational
   datastore, the user adds a matching "masked-tag" entry for a given
   data node within the 'ietf-data-node-tags' module.

6.  Data Node Tags Module Structure

6.1.  Data Node Tags Module Tree

   The tree associated with the "ietf-data-node-tags" module is as
   follows:

   module: ietf-data-node-tags
   augment /tags:module-tags/tags:module:
     +--rw data-node-tags
        +--rw data-node* [ni-id]
           +--rw ni-id        nacm:node-instance-identifier
           +--rw tag*         tags:tag
           +--rw masked-tag*  tags:tag
           +--rw extended-tag-type?   identityref

             Figure 3: YANG Module Data Node Tags Tree Diagram

7.  YANG Module

   This module imports types from [RFC8819],[RFC8341].

   <CODE BEGINS> file "ietf-data-node-tags@2022-02-04.yang"
   module ietf-data-node-tags {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-data-node-tags";
     prefix ntags;

     import ietf-netconf-acm {
       prefix nacm;
       reference
       "RFC 8341: Network Configuration Access Control
                  Model";
     }



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     import ietf-module-tags {
       prefix tags;
       reference
       "RFC 8819: YANG Module Tags ";
     }

     organization
       "IETF NetMod Working Group (NetMod)";
     contact
      "WG Web:  <https://datatracker.ietf.org/wg/netmod/>
       WG List: <mailto:netmod@ietf.org>

       Editor: Qin Wu
               <mailto:bill.wu@huawei.com>

       Editor: Benoit Claise
               <mailto:benoit.claise@huawei.com>

       Editor: Peng Liu
               <mailto:liupengyjy@chinamobile.com>

       Editor: Zongpeng Du
               <mailto:duzongpeng@chinamobile.com>

       Editor: Mohamed Boucadair
               <mailto:mohamed.boucadair@orange.com>";
      // RFC Ed.: replace XXXX with actual RFC number and
      // remove this note.
     description
       "This module describes a mechanism associating data node
        tags with YANG data node within YANG modules. Tags may be IANA
        assigned or privately defined.

        Copyright (c) 2022 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 Revised 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).

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

      // RFC Ed.: update the date below with the date of RFC publication



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      // and RFC number and remove this note.
     revision 2022-02-04 {
       description
         "Initial revision.";
       reference
         "RFC XXXX: data node Tags in YANG Modules";
     }
     identity other-data-property {
      description
        "Base identity for data property type.";
     }
     extension opm-tag {
       argument tag;
       description
         "The argument 'tag' is of type 'tag'. This extension statement
          is used by module authors to indicate the opm tags that should
          be added automatically by the system. 'opm-tag' is used to
          classify operation and management data nodes into the three
          categories, object, property, and metric. A data node
          tagged with 'object' tag can be one of container, leaf-list, or
          list. A data node tagged is with the 'property' tag is a leaf
          node. The data node tagged with the 'metric' tag can be one of
          container, leaf-list, list, or leaf. A data nodes tagged
          with either property tag or metric tag are child nodes
          belonging to a specific root data node. Each data node may
          contain one single 'object' tag, or one single 'property' tag,
          or one single 'metric' tag (these tags are mutually
          exclusive). As such,  the origin of the value for the
          pre-defined tags should be set to 'system'.";
     }

     extension metric-type {
       argument tag;
       description
         "The argument 'tag' is of type 'tag'. The metric type can be
          used to provide metric data node classification
          (e.g., loss, jitter, packet loss, counter, gauge,
          summary, unknown) within a YANG module.The initial values of
          the 'metric-type' tag is defined in section 9.2, additional
          metric-type tag value can be added in the future.";
     }

     extension multi-source-tag {
       argument tag;
       description
         "The argument 'tag' is of type 'tag'. The multi-source-tag can
         be used to identify multi-source aggregation type
         (e.g., aggregated,  non-aggregated) related to a metric



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         subobject.

         The 'aggregated' multi-source aggregation type allows a large
         number of measurements on metric subobjects from different
         sources of the same type (e.g., line card, each subinterface of
         an aggregated Ethernet interface) to be combined into
         aggregated statistics and reported as one metric subobject
         value.

         The 'non-aggregated'multi-source aggregation type allows
         measurement from each source of the same type (e.g., line
         card, each subinterface of an aggregated Ethernet interface) to
         be reported separately.";
      }

     augment "/tags:module-tags/tags:module" {
       description
         "Augment the Module Tags module with data node tag
          attributes.";
       container data-node-tags {
         description
           "Contains the list of data nodes and their associated data
            object tags.";
         list data-node {
           key "ni-id";
           description
             "Includes a list of data nodes and their associated data
              object tags.";
           leaf ni-id {
             type nacm:node-instance-identifier;
             mandatory true;
             description
               "The YANG data node name.";
           }
          leaf-list tag {
             type tags:tag;
             description
               "Lists the tags associated with the data node within
                the YANG  module.

                See the IANA 'YANG data node Tag Prefixes' registry
                for reserved prefixes and the IANA 'IETF YANG Data
                Object Tags' registry for IETF tags.

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

                1) System tags (i.e., tags of 'system' origin) are



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                   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.";
             reference
               "RFC XXXX: data node Tags in YANG Data
                          Modules, Section 9";
           }
           leaf-list masked-tag {
             type tags:tag;
             description
               "The list of tags that should not be associated with the
                data node within the YANG module. The user can remove
                (mask) tags from the operational state datastore by
                adding them to this list. It is not an error to add tags
                to this list that are not associated with the data
                object within YANG  module, but they have no operational
                effect.";
           }
          leaf extended-tag-type {
            type identityref {
            base other-data-property;
          }
         description
         "Type of the extended tag. The extended tag type doesn't include opm tag,
          metric-type tag and multi-source tag three types defined in
          this document. The specific extended tag type and associated auxiliary data
          are defined in the data node tags extension module.";
          }
         }
       }
     }
   }
   <CODE ENDS>

8.  Guidelines to Model Writers

   This section updates [RFC8407] by providing text that may be regarded
   as a new subsection to Section 4 of that document.  It does not
   change anything already present in [RFC8407].

8.1.  Define Standard Tags

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





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   module example-module-A {
     //...
     import ietf-data-node-tags { prefix ntags; }

     container top {
       ntags:opm-tag "ietf:object";
       list X {
         leaf foo {
            ntags:opm-tag "ietf:property";
         }
         leaf bar {
           ntags:opm-tag "ietf:metric";
         }
       }
     }
     // ...
   }

                  Figure 4: An Example of Data Object Tag

   The module writer can use existing standard data node tags, or use
   new data node tags defined in the data node definition, as
   appropriate.  For IETF standardized modules, new data node tags MUST
   be assigned in the IANA registry defined in Section 9.2.

9.  IANA Considerations

9.1.  YANG Data Object Tag Prefixes Registry

   This document requests IANA to create "YANG data node Tag Prefixes"
   subregistry in "YANG data node Tag" 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
   [RFC8126].  The Reference and Assignee values should be sufficient to
   identify and contact the organization that has been allocated the
   prefix.  There is no specific guidance for the Designated Expert and
   there is a presumption that a code point should be granted unless
   there is a compelling reason to the contrary.

   The initial values for this registry are as follows:








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  +----------+----------------------------------+-----------+----------+
  | Prefix   | Description                      | Reference | Assignee |
  +----------+----------------------------------+-----------+----------+
  | ietf:    | IETF Tags allocated in the IANA  | [This     | IETF     |
  |          | IETF YANG data node Tags         | document] |          |
  |          | registry                         |           |          |
  |          |                                  |           |          |
  | vendor:  | Non-registered tags allocated by | [This     | IETF     |
  |          | the module's implementer.        | document] |          |
  |          |                                  |           |          |
  | user:    | Non-registered tags allocated by | [This     | IETF     |
  |          | and for the user.                | document] |          |
  +----------+----------------------------------+-----------+----------+

                            Figure 5: Table 1

   Other standards organizations (SDOs) wishing to allocate their own
   set of tags should request the allocation of a prefix from this
   registry.

9.2.  IETF YANG Data Object Tags Registry

   This document requests IANA to create "IETF OPM Tags","IETF Metric
   Type Tags","IETF Multiple Source Tags" three subregistries in "YANG
   data node Tag" registry.  These 3 subregistries appear below "YANG
   data node Tag Prefixes" registry.

   Three subregistries allocate tags that have the registered prefix
   "ietf:".  New values should be well considered and not achievable
   through a combination of already existing IETF tags.

   The allocation policy for these three subregistries is IETF Review
   [RFC8126].  The Designated Expert is expected to verify that IANA
   assigned tags conform to Net-Unicode as defined in [RFC5198], and
   shall not need normalization.

   The initial values for these three subregistries are as follows:

   +----------------------------+--------------------------+-----------+
   | OPM Tag                    | Description              | Reference |
   +----------------------------+--------------------------+-----------+
   | ietf:object                |Represents Root object    | [This     |
   |                            |containing other data     | document] |
   |                            |objects (e.g., interfaces)|           |
   |                            |                          |           |
   | ietf:property              |Represents a property     | [This     |
   |                            |data node(e.g., ifindex)  | document] |
   |                            |associated with a specific|           |



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   |                            |root object (e.g.,        |           |
   |                            |interfaces)               |           |
   |                            |                          |           |
   | ietf:metric                |Represent metric data     | [This     |
   |                            |object(e.g., ifstatistics)| document] |
   |                            |associated with specific  |           |
   |                            |root object(e.g.,         |           |
   |                            |interfaces)               |           |
   +----------------------------+--------------------------+-----------+
   +----------------------------+--------------------------+-----------+
   | Metric Type Tag            | Description               | Reference |
   +----------------------------+--------------------------+-----------+
   | ietf:delay                 |Represents the delay metric           |
   |                            |group to which the metric | [This     |
   |                            |data nodes belong to.     | document] |
   |                            |                          |           |
   | ietf:jitter                |Represents the jitter metric [This    |
   |                            |group to which the metric |document]  |
   |                            |data nodes belong to.     |           |
   |                            |                          |           |
   | ietf:loss                  |Represents the loss metric| [This     |
   |                            |group to which the metric | document] |
   |                            |data nodes belong to.     |           |
   |                            |                          |           |
   | ietf:counter               |Represents any metric value           |
   |                            |associated with a metric  |           |
   |                            |data node that monotonically[This     |
   |                            |increases over time,      | document] |
   |                            |starting from zero.       |           |
   |                            |                          |           |
   | ietf:gauge                 |Represents current        |           |
   |                            |measurements associated   | [This     |
   |                            |with a metric data node   |document]  |
   |                            |that may increase,        |           |
   |                            |decrease or stay constant.|           |
   |                            |                          |           |
   | ietf:summary               |Represents the metric value [This     |
   |                            |associated with a metric  | document] |
   |                            |data node that measures   |           |
   |                            |distributions of discrete |           |
   |                            |events without knowing    |           |
   |                            |predefined range.         |           |
   |                            |                          |           |
   | ietf:unknown               |Represents the metric value [This     |
   |                            |associated with metric    | document] |
   |                            |data node that can not    |           |
   |                            |determine the type of metric.         |
   +----------------------------+--------------------------+-----------+



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   +----------------------------+--------------------------+-----------+
   | Multiple Source Tag        | Description              | Reference |
   +----------------------------+--------------------------+-----------+
   |ietf:agg                    |Relates to multiple sources [This     |
   |                            |aggregation type (i.e.,   | document] |
   |                            |aggregated statistics)    |           |
   |                            |                          |           |
   |ietf:non-agg                |Relates to multiple sources [This     |
   |                            |aggregation type (i.e.,   | document] |
   |                            |non-aggregated statistics)|           |
   +----------------------------+--------------------------+-----------+

                          Figure 6: Table 2

9.3.  Updates to the IETF XML Registry

   This document registers the following namespace URI in the "ns"
   subregistry within the "IETF XML Registry" [RFC3688]:

      URI: urn:ietf:params:xml:ns:yang:ietf-data-node-tags
      Registrant Contact: The IESG.
      XML: N/A; the requested URI is an XML namespace.

9.4.  Updates to the YANG Module Names Registry

   This document registers the following YANG module in the YANG Module
   Names registry [RFC6020] within the "YANG Parameters" registry:

      name: ietf-data-node-tags
      namespace: urn:ietf:params:xml:ns:yang:ietf-data-node-tags
      prefix: ntags
      reference: RFC XXXX
      maintained by IANA: N

10.  Security Considerations

   The YANG module specified in this document defines schema for data
   that is designed to be accessed via network management protocols such
   as NETCONF [RFC6241] or RESTCONF [RFC8040].  The lowest NETCONF layer
   is the secure transport layer, and the mandatory-to-implement secure
   transport is Secure Shell (SSH) [RFC6242].  The lowest RESTCONF layer
   is HTTPS, and the mandatory-to-implement secure transport is TLS
   [RFC8446].

   The Network Configuration Access Control Model (NACM) [RFC8341]
   provides the means to restrict access for particular NETCONF or
   RESTCONF users to a preconfigured subset of all available NETCONF or
   RESTCONF protocol operations and content, e.g., the presence of tags



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   may reveal information about the way in which data nodes are used and
   therefore providing access to private information or revealing an
   attack vector should be restricted.  Note that appropriate privilege
   and security levels need to be applied to the addition and removal of
   user tags to ensure that a user receives the correct data.

   This document adds the ability to associate data node tag with data
   nodes or instances of data nodes within the 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 data node tag meta-data may define various actions to be
   taken based on the data node 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, including the potential for a tag to get 'masked' by another
   user.

11.  Acknowledgements

   The authors would like to thank Ran Tao for his major contributions
   to the initial modeling and use cases.

   The authors would also like to acknowledge the comments and
   suggestions received from Juergen Schoenwaelder, Andy Bierman, Lou
   Berger,Jaehoon Paul Jeong, Wei Wang, Yuan Zhang, Ander Liu, YingZhen
   Qu, Boyuan Yan, Adrian Farrel, and Mahesh Jethanandani.

12.  Contributors

         Liang Geng
         Individual
         32 Xuanwumen West St, Xicheng District
         Beijing  10053

13.  References

13.1.  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>.

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



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   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [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>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [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>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [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>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8819]  Hopps, C., Berger, L., and D. Bogdanovic, "YANG Module
              Tags", RFC 8819, DOI 10.17487/RFC8819, January 2021,
              <https://www.rfc-editor.org/info/rfc8819>.

13.2.  Informative References

   [FCAPS]    International Telecommunication Union, "X.700 : Management
              framework for Open Systems Interconnection (OSI) for CCITT
              applications",  , September 1992,
              <http://www.itu.int/rec/T-REC-X.700-199209-I/en>.





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   [RFC5198]  Klensin, J. and M. Padlipsky, "Unicode Format for Network
              Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,
              <https://www.rfc-editor.org/info/rfc5198>.

   [RFC6022]  Scott, M. and M. Bjorklund, "YANG Module for NETCONF
              Monitoring", RFC 6022, DOI 10.17487/RFC6022, October 2010,
              <https://www.rfc-editor.org/info/rfc6022>.

   [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>.

   [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>.

   [RFC8639]  Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
              E., and A. Tripathy, "Subscription to YANG Notifications",
              RFC 8639, DOI 10.17487/RFC8639, September 2019,
              <https://www.rfc-editor.org/info/rfc8639>.

   [RFC8641]  Clemm, A. and E. Voit, "Subscription to YANG Notifications
              for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
              September 2019, <https://www.rfc-editor.org/info/rfc8641>.

   [RFC8792]  Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
              "Handling Long Lines in Content of Internet-Drafts and
              RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
              <https://www.rfc-editor.org/info/rfc8792>.

   [RFC9195]  Lengyel, B. and B. Claise, "A File Format for YANG
              Instance Data", RFC 9195, DOI 10.17487/RFC9195, February
              2022, <https://www.rfc-editor.org/info/rfc9195>.

   [RFC9196]  Lengyel, B., Clemm, A., and B. Claise, "YANG Modules
              Describing Capabilities for Systems and Datastore Update
              Notifications", RFC 9196, DOI 10.17487/RFC9196, February
              2022, <https://www.rfc-editor.org/info/rfc9196>.



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Appendix A.  Example: Additional Auxiliary Data Property Information

   This section gives an example of how Auxiliary Data Property Module
   could be defined.  It demonstrates how auxiliary data property
   configuration parameters can be conditionally augmented to the
   generic data node list.  The example is not intended as a complete
   module for Auxiliary Data Property configuration.

  module ex-auxiliary-data-property {
    yang-version 1.1;
     namespace "http://example.com/auxiliary-data-property";
     prefix "dp";

     import ietf-module-tags {
       prefix tags;
     }
     import ietf-data-node-tags {
       prefix ntags;
     }
     identity critical {
      base ntags:other-data-property;
      description
      "Identity for critical data node tag type.";
     }
     augment "/tags:module-tags/tags:module/ntags:data-node-tags/ntags:data-node" {
       when 'derived-from-or-self(ntags:extended-tag-type, "dp:critical")';
       leaf value {
         type string;
           description
           "The auxiliary information corresponding
            to data node instance tagged with 'critical'
            extended tag type.";
       }
       // other auxiliary data property config params, etc.
     }
   }

Appendix B.  Instance Level Tunnel Tagging Example

   In the example shown in Figure 2,the 'tunnel-svc' data node is a list
   node defined in a 'example-tunnel-pm' module and has 7 child nodes:
   'name','create-time','modified-time','average-latency','packet-
   loss','min-latency','max-latency' leaf node.  In these child nodes,
   the 'name' leaf node is the key leaf for the 'tunnel-svc' list.
   Following is the tree diagram [RFC8340] for the "example-tunnel-pm"
   module:





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           +--rw tunnel-svc* [name]
           |   +--rw name                      string
           |   +--ro create-time               yang:date-and-time
           |   +--ro modified-time             yang:date-and-time
           |   +--ro average-latency           yang:gauge64
           |   +--ro packet-loss               yang:counter64
           |   +--ro min-latency               yang:gauge64
           |   +--ro max-latency               yang:gauge64

   To help identify specific data for a customer, users tags on specific
   instances of the data nodes are created as follows:

   <rpc message-id="103"
        xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <edit-data xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-nmda"
                xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
       <datastore>ds:running</datastore>
       <config>
       <module-tag>
        <module>
        <name>example-tunnel-pm</name>
         <data-node-tags xmlns="urn:ietf:params:xml:ns:yang:ietf-data-node-tags">
         <data-node>
           <ni-id>
            /tp:tunnel-svc[name='foo']/tp:packet-loss
           </ni-id>
           <tag>user:customer1_example_com</tag>
           <tag>ietf:critical</tag>
         </data-node>
         <data-node>
           <ni-id>
             /tp:tunnel-svc[name='bar']/tp:modified-time
          </ni-id>
           <tag>user:customer2_example_com</tag>
         </data-node>
       </data-node-tags>
      </module>
      </module-tag>
       </config>
     </edit-data>
   </rpc>

   Note that the 'ietf:critical' tag is addtional new tag value that
   needs to be allocated from "IETF Metric Type Tags" subregistry in
   section 9.2.






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Appendix C.  NETCONF Example

   The following is a NETCONF example result from a query of the data
   node tags list.  For the sake of brevity only a few module and
   associated data node results are provided.  The example uses the
   folding defined in [RFC8792].

 =============== NOTE: '\' line wrapping per RFC 8792 ================

 <ns0:data 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-interfaces</t:name>
        <s:data-node-tags xmlns:s="urn:ietf:params:xml:ns:yang:ietf-\
        data-node-tags">
         <s:data-node>
          <s:ni-id>/if:interfaces/if:interface</s:ni-id>
          <s:tag>ietf:object</s:tag>
         </s:data-node>
        <s:data-node>
         <s:ni-id>/if:interfaces/if:interface/if:last-change</\
        s:ni-id>
         <s:tag>ietf:property</s:tag>
        </s:data-node>
         <s:data-node>
          <s:ni-id>
           /if:interfaces/if:interface/if:statistics/if:in-errors
          </s:ni-id>
          <s:tag>ietf:metric</s:tag>
          <s:tag>ietf:loss</s:tag>
          <s:tag>ietf:non-agg</s:tag>
         </s:data-node>
       </s:data-node-tags>
     </t:module>
     <t:module>
        <t:ni-id>ietf-ip</t:ni-id>
        <s:data-node-tags xmlns:s="urn:ietf:params:xml:ns:yang:ietf\
      -data-node-tags">
        <s:data-node>
          <s:ni-id>/if:interfaces/if:interface/ip:ipv4</s:ni-id>
          <s:tag>ietf:object</s:tag>
        </s:data-node>
        <s:data-node>
          <s:ni-id>/if:interfaces/if:interface/ip:ipv4/ip:enable\
        </s:ni-id>
          <s:tag>ietf:property</s:tag>
        </s:data-node>
         <s:data-node>



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         <s:ni-id>/if:interfaces/if:interface/ip:ipv4/ip:mtu</s:ni-id>
         <s:tag>ietf:metric</s:tag>
         <s:tag>ietf:non-agg</s:tag>
        </s:data-node>
       </s:data-node-tags>
     </t:module>
   </t:module-tags>
 </ns0:data>

                 Figure 7: Example NETCONF Query Output

Appendix D.  Non-NMDA State Module

   As per [RFC8407], the following is a non-NMDA module to support
   viewing the operational state for non-NMDA compliant servers.

   <CODE BEGINS> file "ietf-data-node-tags-state@2022-02-03.yang"
   module ietf-data-node-tags-state {
     yang-version 1.1;
     namespace
           "urn:ietf:params:xml:ns:yang:ietf-data-node-tags-state";
     prefix ntags-s;

     import ietf-netconf-acm {
       prefix nacm;
       reference
       "RFC 8341: Network Configuration Access Control
                  Model";
     }
     import ietf-module-tags {
       prefix tags;
     }
     import ietf-module-tags-state {
       prefix tags-s;
       reference
       "RFC 8819: YANG Module Tags ";
     }
     organization
       "IETF NetMod Working Group (NetMod)";

     contact
      "WG Web: <https://datatracker.ietf.org/wg/netmod/>
       WG List:<mailto:netmod@ietf.org>

       Editor: Qin Wu
               <mailto:bill.wu@huawei.com>

       Editor: Benoit Claise



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               <mailto:benoit.claise@huawei.com>

       Editor: Peng Liu
               <mailto:liupengyjy@chinamobile.com>

       Editor: Zongpeng Du
               <mailto:duzongpeng@chinamobile.com>

       Editor: Mohamed Boucadair
               <mailto:mohamed.boucadair@orange.com>";
      // RFC Ed.: replace XXXX with actual RFC number and
      // remove this note.
     description
       "This module describes a mechanism associating data node
        tags with YANG data node within YANG modules. Tags may be
        IANA assigned or privately defined.

        Copyright (c) 2022 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).

        This version of this YANG module is part of RFC XXXX
        (https://datatracker.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 2022-02-04 {
       description
         "Initial revision.";
       reference
         "RFC XXXX: Data node Tags in YANG Data
                    Modules";
     }
     identity other-data-property {
      description
        "Base identity for data property type.";
     }
     augment "/tags-s:module-tags-state/tags-s:module" {
       description
         "Augments the Module Tags module with data node tag
          attributes.";



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       container data-node-tags {
         config false;
         status deprecated;
         description
           "Contains the list of data nodes and their
            associated self describing tags.";
         list data-node {
           key "ni-id";
           status deprecated;
           description
             "Lists the data nodes and their associated self
              describing tags.";
           leaf ni-id {
             type nacm:node-instance-identifier;
             mandatory true;
             status deprecated;
             description
               "The YANG data node name.";
           }
           leaf-list tag {
             type tags:tag;
             status deprecated;
             description
               "Tags associated with the data node within the
                YANG module. See the IANA 'YANG data node Tag
                Prefixes' registry for reserved prefixes and the
                IANA 'IETF YANG data node Tags'registry for
                IETF tags.

                The 'operational' state 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.";
             reference
               "RFC XXXX: Data node Tags in YANG Data
                          Modules, Section 9";
           }
           leaf-list masked-tag {
             type tags:tag;
             status deprecated;
             description
               "The list of tags that should not be associated with the
                data node within the YANG module. The user can remove
                (mask) tags from the operational state datastore by



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                adding them to this list. It is not an error to add
                tags to this list that are not associated with the
                data node within YANG module, but they have no
                operational effect.";
           }
          leaf extended-tag-type {
            type identityref {
            base other-data-property;
          }
         description
         "Type of the extended tag. The extended tag type doesn't
          include opm tag, metric-type tag and multi-source tag three
          types defined in this document. The specific extended tag
          type and associated auxiliary data are defined in the data
          node tags extension module.";
          }
         }
       }
     }
   }
   <CODE ENDS>

Appendix E.  Targeted Data Fetching Example

   The following provides targeted data node collection example which
   helps reduce amount of data to be fetched.  The subscription "id"
   values of 22 used below is just an example.  In production, the
   actual values of "id" might not be small integers.

   +-----------+                        +-----------+
   | Subscriber|                        | Publisher |
   +-----+-----+                        +-----+-----+
         |                                    |
         |    data Node Tagging Fetching      |
         |    (ni-id, opm-tag = metric)       |
         |<-----------------------------------+
         |                                    |
         |     establish-subscription         |
         +----------------------------------->|
         |                                    |
         |       RPC Reply: OK, id = 22       |
         |<-----------------------------------+
         |                                    |
         |    Notification Message (for 22)   |
         |<-----------------------------------+
         |                                    |





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   The subscriber fetches data node tag information from the provider
   using 'get-schema' operation.  The data node tag information instruct
   the receiver to subscribe tagged data node (e.g., performance metric
   data nodes) using standard subscribed notification mechanism
   [RFC8639].

   Figure 8 illustrates the retrieval of the list of available target
   data nodes using the YANG instance file format [RFC9195]:

 =============== NOTE: '\' line wrapping per RFC 8792 ================

 <?xml version="1.0" encoding="UTF-8"?>
 <instance-data-set xmlns=\
 "urn:ietf:params:xml:ns:yang:ietf-yang-instance-data">
   <name>acme-router-notification-capabilities</name>
   <content-schema>
     <module>ietf-system-capabilities@2020-03-23</module>
     <module>ietf-notification-capabilities@2020-03-23</module>
     <module>ietf-data-export-capabilities@2020-03-23</module>
   </content-schema>
   <!-- revision date, contact, etc. -->
   <description>Defines the notification capabilities of an
     acme-router.The router only has running, and operational
     datastores. Every change can be reported on-change from
     running, but only config=true nodes and some config=false data
     from operational. Statistics are not reported based on timer
     based trigger and counter threshold based trigger.
   </description>
   <content-data>
     <t:module-tags xmlns:t="urn:ietf:params:xml:ns:yang:ietf-\
        module-tags">
        <t:module>
           <t:name>ietf-interfaces</t:name>
           <s:data-node-tags xmlns:s="urn:ietf:params:xml:ns:yang:ietf-\
        data-node-tags">
            <s:data-node>
             <s:ni-id>/if:interfaces/if:interface/if:in-errors</s:ni-id>
             <s:opm-tag>ietf:metric</s:opm-tag>
             <s:metric-type>ietf:loss</s:metric-type>
            </s:data-node>
            </s:data-node-tags>
       </t:module>
   </content-data>
 </instance-data-set>

               Figure 8: List of Available Target Objects





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   With data node tag information carried in the <get-schema> operation,
   the subscriber identifies targeted data node and associated data path
   to the datastore node and sends a standard establish-subscription RPC
   [RFC8639] to subscribe tagged data nodes that are interests to the
   client application from the publisher.  Alternatively, the subscriber
   can query data node tag list from somewhere (e.g., the network
   device, or offline document) using ietf-data-node-tags module defined
   in this document and fetch tagged data nodes and associated data path
   to the datastore node and sends a standard establish-subscription RPC
   [RFC8639] to subscribe tagged data nodes that are interests to the
   client application from the publisher.

   =============== NOTE: '\' line wrapping per RFC 8792 ================

    <netconf:rpc message-id="101"
        xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
      <establish-subscription
          xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifica\
   tions"
          xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
        <yp:datastore
             xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
          ds:operational
        </yp:datastore>
        <yp:datastore-xpath-filter
            xmlns:ex="https://example.com/sample-data/1.0">
          /if:interfaces/if:interface/if:statistics/if:in-errors
        </yp:datastore-xpath-filter>
        <yp:periodic>
          <yp:period>500</yp:period>
        </yp:periodic>
      </establish-subscription>
    </netconf:rpc>


   The publisher returns specific object types of operational state
   (e.g., in-errors statistics data) subscribed by the client.

Appendix F.  Changes between Revisions

   Editorial Note (To be removed by RFC Editor)

   v06 - v07

   *  Update use case in section 3 to remove object and subobject
      concept and massive related words.

   *  Change the title into Data Node Tags in YANG Modules.



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   *  Update Model Tag design in section 5.1 based on Balazs's comments.

   *  Add Instance level tunnel tagging example in the Appendix.

   *  Add 'type' parameter in the base model and add one more model
      extension example in the Appendix.

   *  Other Appendix Updates.

   v05 - v06

   *  Additional Editorial changes;

   *  Use the folding defined in [RFC8792].

   v04 - v05

   *  Add user tag formating clarification;

   *  Provide guidance to the Designated Expert for evaluation of YANG
      data node Tag registry and YANG data node Tag prefix registry.

   *  Update the figure 1 and figure 2 with additional tags.

   *  Security section enhancement for user tag managment.

   *  Change data node name into name in the module.

   *  Other Editorial changes to address Adrian's comments and comments
      during YANG docotor review.

   *  Open issue: Are there any risks associated with an attacker adding
      or removing tags so that a requester gets the wrong data?

   v03 - v04

   *  Remove histogram metric type tag from metric type tags.

   *  Clarify the object tag and property tag,metric tag are mutual
      exlusive.

   *  Clarify to have two optional node tags (i.e.,object tag and
      property tag) to indicate relationship between data nodes.

   *  Update targeted data node collection example.

   v02 - v03




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   *  Additional Editorial changes.

   *  Security section enhancement.

   *  Nits fixed.

   v01 - v02

   *  Clarify the relation between data node, object tag, property tag
      and metric tag in figure 1 and figure 2 and related description;

   *  Change Metric Group into Metric Type in the YANG model;

   *  Add 5 metric types in section 7.2;

   v00 - v01

   *  Merge data node tag use case section into introduction section as
      a subsection;

   *  Add one glossary section;

   *  Clarify the relation between data node, object tag, property tag
      and metric tag in data node Tags Use Case section;

   *  Add update to RFC8407 in the front page.

Authors' Addresses

   Qin Wu
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing
   Jiangsu, 210012
   China
   Email: bill.wu@huawei.com


   Benoit Claise
   Huawei
   De Kleetlaan 6a b1
   1831 Diegem
   Belgium
   Email: benoit.claise@huawei.com







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   Peng Liu
   China Mobile
   32 Xuanwumen West St, Xicheng District
   Beijing
   Email: liupengyjy@chinamobile.com


   Zongpeng Du
   China Mobile
   32 Xuanwumen West St, Xicheng District
   Beijing
   Email: duzongpeng@chinamobile.com


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
































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