Augmented-by Addition to the YANG Library
draft-ietf-netconf-yang-library-augmentedby-17

NETCONF                                                           Z. Lin
Internet-Draft                                                    Huawei
Updates: 8525 (if approved)                                    B. Claise
Intended status: Standards Track                          Everything OPS
Expires: 22 August 2026                         I. D. Martinez-Casanueva
                                                              Telefonica
                                                        18 February 2026

               Augmented-by Addition to the YANG Library
             draft-ietf-netconf-yang-library-augmentedby-17

Abstract

   "YANG Library" specifies the YANG module "ietf-yang-library" that
   provides information about the YANG modules, datastores, and
   datastore schemas used by a network management server.

   This document augments the "ietf-yang-library" to provide the
   augmented-by list.  It facilitates the process of obtaining all
   dependencies between YANG modules, by querying the network management
   server's YANG library.  This document updates RFC 8525, as the lists
   in Section 2 is modified to also include augmented-by list.

Discussion Venues

   This note is to be removed before publishing as an RFC.

   Source for this draft and an issue tracker can be found at
   https://github.com/Zephyre777/draft-lincla-netconf-yang-library-
   augmentation.

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 22 August 2026.

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Copyright Notice

   Copyright (c) 2026 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 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
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Data Mesh Architecture  . . . . . . . . . . . . . . . . .   6
     3.2.  Data Catalog  . . . . . . . . . . . . . . . . . . . . . .   8
   4.  The "ietf-yang-library-augmentedby" YANG module . . . . . . .   9
     4.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .   9
       4.1.1.  Tree Structure  . . . . . . . . . . . . . . . . . . .   9
       4.1.2.  YANG ietf-yang-library-augmentedby Module . . . . . .   9
     4.2.  Implementation Instructions . . . . . . . . . . . . . . .  12
       4.2.1.  The scope of augmented-by . . . . . . . . . . . . . .  12
       4.2.2.  Examples  . . . . . . . . . . . . . . . . . . . . . .  12
   5.  Operational Considerations  . . . . . . . . . . . . . . . . .  16
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .  16
     6.1.  Netopeer2 at IETF119 Hackathon  . . . . . . . . . . . . .  16
     6.2.  Netopeer2 at IETF120 Hackathon  . . . . . . . . . . . . .  16
     6.3.  Libyangpush Find-dependency . . . . . . . . . . . . . . .  16
     6.4.  Device Implementations  . . . . . . . . . . . . . . . . .  17
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  19
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  19
   Appendix A.  Full Tree View of ietf-yang-library  . . . . . . . .  22
   Appendix B.  Changes  . . . . . . . . . . . . . . . . . . . . . .  23
     B.1.  draft-lincla-netconf-yang-library-augmentation: Changes
            from 00 to 01  . . . . . . . . . . . . . . . . . . . . .  23
     B.2.  draft-lincla-netconf-yang-library-augmentedby version
            00 . . . . . . . . . . . . . . . . . . . . . . . . . . .  23

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     B.3.  draft-lincla-netconf-yang-library-augmentedby: Changes from
            00 to 01 . . . . . . . . . . . . . . . . . . . . . . . .  23
     B.4.  draft-lincla-netconf-yang-library-augmentedby: Changes from
            01 to 02 . . . . . . . . . . . . . . . . . . . . . . . .  24
     B.5.  draft-ietf-netconf-yang-library-augmentedby version 00  .  24
     B.6.  draft-ietf-netconf-yang-library-augmentedby: Changes from
            00 to 01 . . . . . . . . . . . . . . . . . . . . . . . .  24
     B.7.  draft-ietf-netconf-yang-library-augmentedby: Changes from
            01 to 02 . . . . . . . . . . . . . . . . . . . . . . . .  24
     B.8.  draft-ietf-netconf-yang-library-augmentedby: Changes from
            02 to 03 . . . . . . . . . . . . . . . . . . . . . . . .  25
     B.9.  draft-ietf-netconf-yang-library-augmentedby: Changes from
            03 to 04 . . . . . . . . . . . . . . . . . . . . . . . .  25
     B.10. draft-ietf-netconf-yang-library-augmentedby: Changes from
            04 to 05 . . . . . . . . . . . . . . . . . . . . . . . .  25
     B.11. draft-ietf-netconf-yang-library-augmentedby: Changes from
            05 to 06 . . . . . . . . . . . . . . . . . . . . . . . .  25
     B.12. draft-ietf-netconf-yang-library-augmentedby: Changes from
            06 to 07 . . . . . . . . . . . . . . . . . . . . . . . .  26
     B.13. draft-ietf-netconf-yang-library-augmentedby: Changes from
            07 to 08 . . . . . . . . . . . . . . . . . . . . . . . .  26
     B.14. draft-ietf-netconf-yang-library-augmentedby: Changes from
            08 to 09 . . . . . . . . . . . . . . . . . . . . . . . .  26
     B.15. draft-ietf-netconf-yang-library-augmentedby: Changes from
            09 to 10 . . . . . . . . . . . . . . . . . . . . . . . .  26
     B.16. draft-ietf-netconf-yang-library-augmentedby: Changes from
            10 to 11 . . . . . . . . . . . . . . . . . . . . . . . .  26
     B.17. draft-ietf-netconf-yang-library-augmentedby: Changes from
            12 to 13 . . . . . . . . . . . . . . . . . . . . . . . .  26
     B.18. draft-ietf-netconf-yang-library-augmentedby: Changes from
            13 to 14 . . . . . . . . . . . . . . . . . . . . . . . .  27
     B.19. draft-ietf-netconf-yang-library-augmentedby: Changes from
            14 to 15 . . . . . . . . . . . . . . . . . . . . . . . .  27
     B.20. draft-ietf-netconf-yang-library-augmentedby: Changes from
            15 to 16 . . . . . . . . . . . . . . . . . . . . . . . .  27
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

1.  Introduction

   The YANG library [RFC8525] provides information about the data models
   supported by a server.  This is presented as an inventory of YANG
   modules.  It helps a client with listing all datastores supported by
   a network management server and the schema that is used by each of
   these datastores.

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   According to Sections 4.2.8 and 5.6.3 of [RFC7950], augment defines
   additional nodes to a module while deviations change (add, modify,
   delete) properties (sub-statements) to other module's schema nodes.
   They provide crucial information about the YANG data model
   composition, and is referred to as reverse dependency in this
   document: this means the behavior of a schema node depends on
   external modifications, creating flow backward from the augmenting/
   deviation module to the base module.

   It is difficult to obtain the YANG schema tree (defined in Section 3
   in [RFC7950]) without obtaining and parsing all the YANG modules from
   a management server.  The deviation list defined in YANG library
   enables clients to obtain a module reverse dependency without having
   to get and parse all YANG modules.  However, the augmentation list is
   not defined in it.

   Since both augmentation and deviation work as YANG module
   dependencies, it is reasonable to document them the same way in the
   YANG library.  Having both augmentation and deviation directly
   available in the YANG library provides a convenient solution for
   determining the reverse dependencies.

   This document specifies a YANG module that augments the YANG library
   to include the YANG module augmentation information.  It updates RFC
   8525, as the lists in Section 2 is modified to also include
   augmented-by list.

   One specific requirement with the implementation of this augmented-by
   YANG module specification is, the modules and the augmented-by
   modules require to be listed in the same module-set.  Note that a
   similar requirement already applies for the YANG deviations.

1.1.  Requirements Language

   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.

1.2.  Terminology

   The terminology from [RFC8525] is used in this document

   The term "client" is used as defined in [RFC6241] for NETCONF and
   [RFC8040] for RESTCONF.

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   The term "YANG schema tree" is used as defined in Section 3 of
   [RFC7950]

   The term Network Management Datastore Architecture (NMDA) is used as
   defined in [RFC8342]

   Tree diagrams in this document use the notations defined in [RFC8340]
   .

   This document defines the following term:

   *  Reverse Dependency: is the dependency YANG modules that provide
      external modification to the behavior of a base YANG module, by
      inserting additional nodes (augment) or deviating existing nodes
      (deviation).

2.  Motivation

   When using YANG modules, it is necessary to make sure that all its
   dependencies are present.  [RFC7950] identifies four types of
   dependencies between YANG modules:

   *  Import: the "import" statement allows a module or submodule to
      reference definitions defined in other modules.

   *  Include: the "include" statement is used in a module to identify
      each submodule that belongs to it.

   *  Augment: the augmentation defines the location in the data model
      hierarchy where additional nodes are inserted.

   *  Deviation: the "deviation" statement defines a fragment of a
      module that the server does not implement.

   "import" and "include" are direct dependencies which can be obtained
   by parsing a YANG module source code, while the augmentation and
   deviation are reverse dependencies which are defined in another
   module.

   For the reverse dependencies, since they are defined externally, it
   is not possible to discover them by parsing the YANG module.  The
   current way to discover the reverse dependencies is to query all YANG
   modules from the server and parse them.  This is a lengthy process,
   which must be repeated for each client that requires this
   information.

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   According to the definition of the module ietf-yang-library defined
   in [RFC8525], the "deviation" list describes that a module is
   deviated by which other modules.  Since deviations and augmentations
   work similarly, if the YANG library could directly report all reverse
   dependencies, including augmentations, it would provide a much
   convenient solution to find module all dependencies, compared to
   obtaining and parsing all modules.  In addition, to avoid causing
   problems in devices, for instance, falsely referring to modules in
   the wrong module-set, this document requires that the base modules
   and the augmentations be listed in the same module-set.

   The YANG library only provides the deviation list, without
   augmentations.  With augmentations being more widely used and
   defined, and with use cases to automate network management,
   augmentations become essential information for clients to better
   understand the network management server module relationships.  Thus,
   the YANG library should be extended to also provide the augmentation
   information.

3.  Use Cases

3.1.  Data Mesh Architecture

   As the demand for YANG-based telemetry [RFC8641] arises, there is a
   need for real-time knowledge of a specific YANG module's dependency
   list when a specific YANG-Push notification for a given subscription
   is received.

   Some YANG-Push receivers will collect the information in advance of
   the telemetry collection, storing the entire module set for every
   single server who could be streaming data.  However, this approach is
   not always practical in case of Configured Subscriptions [RFC8639]
   where the YANG-Push receiver is not configuring the subscriptions
   itself and in case of UDP transport [I-D.ietf-netconf-udp-notif].
   See figure 1 in An Architecture for YANG-Push to Message Broker
   Integration [I-D.ietf-nmop-yang-message-broker-integration] for more
   details.

   This architecture relies on the information of YANG dependencies in
   this specification to solve the problem of missing YANG semantics
   when notifications are transformed or indexed in Time Series
   Database.

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   Prior to the implementation of this specification, the method used
   for obtaining modules and finding module dependencies is to retrieve
   the full set of supported YANG modules from the network device,
   triggered by parsing the <subscription-started> message for each new
   YANG-Push subscription, because the YANG-push receiver would not know
   which YANG-Push publisher sends the subscribed YANG content until the
   first notification is received.

   By using the provided augmentedby information in this specification,
   the YANG-Push receiver can directly obtain the YANG reverse
   dependencies for the specific YANG module(s) in the subscription by
   querying the server, saving collection and processing time at the
   YANG-Push receiver, by querying dependencies only for the required
   modules, and therefore helping with the real-time aspects of network
   observability.

   Following is an example YANG-Push message of this use case received
   from within a subscription to YANG module "ietf-interfaces":

     "datastore-contents": {
       "ietf-interfaces:interfaces": [
       {
         "interface": {
           "name": "eth0",
           "type": "iana-if-type:ethernetCsmacd",
           "oper-status": "up",
           "speed": "1000000",
           "ietf-ip:ipv4": {
             "enabled": true,
             "forwarding": true
           }
         }
       }
       ]
     }

   To correctly interpret the semantics of this message, both the "ietf-
   interfaces" and "ietf-ip" YANG modules are required.  Knowing only
   that the subscribed YANG module is "ietf-interfaces" is therefore
   insufficient, but that is currently the only dependency information
   exposed by the subscription information.  In this case, a mechanism
   is needed to discover all relevant dependency modules, especially
   reverse dependencies (refer to "ietf-ip" in this example) so that
   every YANG module referenced in the pushed data can be reliably
   identified.

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3.2.  Data Catalog

   Finding the YANG modules implemented by a network management server
   is paramount for configuring and monitoring the status of a network.
   However, since the inception of YANG the network industry has defined
   large number of YANG modules developed by SDOs, open-source
   communities, and network vendors.  This heterogeneity of YANG
   modules, that vary from one network device/service model to another,
   makes the management of a multi-vendor network a big challenge for
   operators.  [Martinez-Casanueva2023].

   In this regard, a data catalog provides a registry of the datasets
   exposed by remote data sources for consumers to discover data of
   interest.  Besides the location of the dataset (i.e., the data
   source), the data catalog registers additional metadata such as the
   data model (or schema) followed in the dataset or even related terms
   defined in a business glossary.

   Data catalog solutions typically implement collectors that ingest
   metadata from the data sources themselves and external metadata
   sources.  For example, a Kafka Schema Registry is a metadata source
   that provides metadata about the data model followed by some data
   stored in a Kafka topic.

   In this sense, a YANG-enabled network device can be considered as
   another kind of data source, which the Data Catalog can pull metadata
   from.  For instance, the data catalog can include a connector that
   fetches metadata about the YANG modules implemented by the network
   device.  Combining this metadata with others such as the business
   concept "interface", would enable data consumers to discover which
   datasets related to the concept "interface" are exposed by the
   network device.

   Network devices that implement YANG library expose metadata about
   which YANG modules are implemented, and which are only imported.
   However, what a data consumer needs at the end are the YANG modules
   implemented by the device, hence, the combination of implemented YANG
   modules with other YANG modules that might deviate or augment the
   formers.

   Consider a network device that implements the "ietf-interfaces"
   module [RFC8343] and the "ietf-ip" module [RFC8344], where the latter
   augments the former.  For a data catalog to collect this metadata, a
   connector would retrieve YANG library data from the target device.
   However, the current version of YANG library would not satisfy the
   use case as it would tell that the device implements both "ietf-
   interfaces" and "ietf-ip" modules, but will miss the augment
   dependency between them.

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   A workaround is in combination with the YANG library data to
   additionally obtain both YANG modules and process them to discover
   that there is an augment dependency.  This adds extra burden on the
   connector, which is forced to combine multiple metadata collection
   mechanisms.  This process could be softened by extending YANG library
   to also capture augment dependencies, similarly to deviation
   dependencies.

4.  The "ietf-yang-library-augmentedby" YANG module

4.1.  Data Model Overview

4.1.1.  Tree Structure

   The following is the YANG tree diagram for module "ietf-yang-library-
   augmentedby".

   module: ietf-yang-library-augmentedby

     augment /yanglib:yang-library/yanglib:module-set/yanglib:module:
       +--ro augmented-by*   -> ../../yanglib:module/name
     augment /yanglib:modules-state/yanglib:module:
       +--ro augmented-by*   -> ../../yanglib:module/name

   This YANG module augments the ietf-yang-library module by adding the
   augmented-by leaf-list in the "yang-library/module-set" and "yang-
   library/modules-state".  The name of list "augmented-by" indicates by
   which modules that the current module is being directly augmented.

   The "yang-library/modules-state" is augmented despite its
   "deprecated" state to cope with the situation when container
   "modules-state" is used for compatibility reason with ietf-yang-
   library defined in [RFC7895].  Both the NMDA[RFC8342] and non-NMDA
   compliant additions are defined in the same YANG module for
   simplicity for users and implementors.

   For the scope of "augmented-by", this document only considers the
   direct augmentation relationship.  The recursive result of
   augmentation or transitive dependency for module specified along the
   XPath, is out of the scope of this draft.  Section 4.2 has given the
   implementation instructions.

4.1.2.  YANG ietf-yang-library-augmentedby Module

   This YANG module imports and augments the "ietf-yang-library"
   [RFC8525].

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   <CODE BEGINS> file "ietf-yang-library-augmentedby@2025-05-28.yang"
   module ietf-yang-library-augmentedby {
     yang-version 1.1;
     namespace
       "urn:ietf:params:xml:ns:yang:ietf-yang-library-augmentedby";
     prefix yanglib-aug;

     import ietf-yang-library {
       prefix yanglib;
       reference
         "RFC 8525: YANG Library";
     }

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

        Authors:  Zhuoyao Lin
                  <mailto:zhuoyao.lin1@huawei-partners.com>
                  Benoit Claise
                  <mailto:benoit@everything-ops.net>
                  Ignacio Dominguez Martinez-Casanueva
                  <mailto:ignacio.dominguezmartinez@telefonica.com>";
     description
       "This module augments the ietf-yang-library defined in
        RFC8525 to provide not only the deviation list, but also
        the augmented-by list, in order to give sufficient
        information about the YANG modules reverse dependency. It
        facilitates the process of obtaining the entire
        dependencies of YANG module.

        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 (RFC 2119)
        (RFC 8174) when, and only when, they appear in all
        capitals, as shown here.

        Copyright (c) 2026 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

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        (https://trustee.ietf.org/license-info).

        All revisions of IETF and IANA published modules can be found
        at the YANG Parameters registry group
        (https://www.iana.org/assignments/yang-parameters).

        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";

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

     // replace 'date-revision' with the module publication date
     // the format is (YYYY-MM-DD)

     revision 2025-05-28 {
       description
         "Initial revision.";
       reference
         "RFC XXXX: Augmented-by Addition to the YANG Library (Note to the
         RFC-Editor: Please replace this with RFC plus the RFC number when this
         document can be published.)";
     }

     grouping augmented-by {
       description
         "Provides augmented-by leaf-list from module info with the
          module-augmented-by grouping";
       leaf-list augmented-by {
         type leafref {
           path "../../yanglib:module/yanglib:name";
         }
         description
           "Leaf-list of the augmentations used by this server to
            modify the schema tree of the module associated with
            this entry.  Note that the same module can be used for
            augmented-by for multiple modules, so the same
            entry MAY appear within multiple 'module' entries.

            This reference MUST NOT (directly or indirectly)
            refer to the module being augmented, and MUST NOT
            be referenced in the import-only list.

            Robust clients may want to make sure that they handle a
            situation where a module augments itself (directly or
            indirectly) gracefully.";
       }
     }

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     augment "/yanglib:yang-library/yanglib:module-set/yanglib:module" {
       description
         "Augments the augmented-by leaf-list from module info with the
          augmented-by grouping.";
       uses augmented-by;
     }

     augment "/yanglib:modules-state/yanglib:module" {
       status deprecated;
       description
         "Augments the augmented-by leaf-list from module info with the
          augmented-by grouping.";
       uses augmented-by;
     }
   }
   <CODE ENDS>

4.2.  Implementation Instructions

4.2.1.  The scope of augmented-by

   This section explains the scope of augmented-by.

   The "augmented-by" leaf-list should only consider those YANG modules
   that directly augment the YANG module in question in the "ietf-yang-
   library", and the augmenting and augmented modules must be defined in
   the same module-set.

   The "direct augment" is identified by the relationship between the
   augment module and the target node's parent module that it augments
   to.  Only the direct parent module of the target node is augmented,
   and the rest of the parent modules defined in the schema tree are
   only indirect dependencies but not augmented modules.  (Refer to
   "Target node" definition in Section 7.17 of [RFC7950])

   In the case when a YANG application requires recursive dependency or
   specific schema tree dependency, the search logic should be
   implemented by the application itself.

4.2.2.  Examples

   This section provides two module-set examples and their corresponding
   ietf-yang-library-augmentedby query results to explain the definition
   of "direct augment" stated in Section 4.2.1.

   The two scenarios are provided with the same three YANG modules
   (Module A, B, and C) defined in the module-set, however the
   relationships among them are different.  All three YANG modules are

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   defined in the same module-set name 'module-set1' to be able to
   augment or be augmented by the others.  Otherwise, the YANG
   validation should fail.

4.2.2.1.  Example 1

   Relationships among Module A, Module B and Module C in this example
   are following:

   *  Module A is the base module with container "foo-a"

   *  Module B augments "/A:foo-a" with container "foo-b"

   *  Module C augments "/A:foo-a" with leaf "leaf-c"

   The ietf-yang-library-augmentedby query result is:

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   <CODE BEGINS> file "example_yanglib_result1.xml"
   <yang-library xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
     <content-id>1</content-id>
     <module-set>
       <name>module-set1</name>
       <module>
         <name>A</name>
         <revision>2024-02-29</revision>
         <namespace>urn:ietf:params:xml:ns:yang:A</namespace>
         <augmented-by
         xmlns="urn:ietf:params:xml:ns:yang:
         ietf-yang-library-augmentedby">B</augmented-by>
         <augmented-by
         xmlns="urn:ietf:params:xml:ns:yang:
         ietf-yang-library-augmentedby">C</augmented-by>
       </module>
       <module>
         <name>B</name>
         <revision>2024-02-29</revision>
         <namespace>urn:ietf:params:xml:ns:yang:B</namespace>
       </module>
       <module>
         <name>C</name>
         <revision>2024-02-29</revision>
         <namespace>urn:ietf:params:xml:ns:yang:C</namespace>
       </module>
     </module-set>
   </yang-library>
   <modules-state xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
       <module-set-id>0</module-set-id>
   </modules-state>
   <CODE ENDS>

   In this example, both Module B and Module C directly augment the
   container "foo-a".  Therefore, both B and C are listed as "augmented-
   by" modules for Module A.

4.2.2.2.  Example 2

   Relationships among Module A, Module B and Module C in this example
   are following:

   *  Module A is the base module with container "foo-a"

   *  Module B augments "/A:foo-a" with container "foo-b"

   *  Module C augments "/A:foo-a/B:foo-b" with leaf "leaf-c"

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   The ietf-yang-library-augmentedby query result is:

   <CODE BEGINS>
   file "example_yanglib_result2.xml"
   <yang-library xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
     <content-id>1</content-id>
     <module-set>
       <name>module-set1</name>
       <module>
         <name>A</name>
         <revision>2025-06-18</revision>
         <namespace>urn:ietf:params:xml:ns:yang:A</namespace>
         <augmented-by
         xmlns="urn:ietf:params:xml:ns:yang:
         ietf-yang-library-augmentedby">B</augmented-by>
       </module>
       <module>
         <name>B</name>
         <revision>2025-06-18</revision>
         <namespace>urn:ietf:params:xml:ns:yang:B</namespace>
         <augmented-by
         xmlns="urn:ietf:params:xml:ns:yang:
         ietf-yang-library-augmentedby">C</augmented-by>
       </module>
       <module>
         <name>C</name>
         <revision>2025-06-18</revision>
         <namespace>urn:ietf:params:xml:ns:yang:C</namespace>
       </module>
     </module-set>
   </yang-library>
   <modules-state xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
     <module-set-id>0</module-set-id>
   </modules-state>
   <CODE ENDS>

   In this example, although the augment XPath statement used by Module
   C is rooted from the container "foo-a" defined in Module A, the node
   that Module C directly augments is the container "foo-b" defined in
   Module B.  As a result, Module C is not considered to directly
   augment Module A and therefore does not appear in the "augmented-by"
   leaf-list of Module A.  Only Module B, which directly augments the
   container "foo-a", is listed as an "augmented-by" module for Module
   A.

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5.  Operational Considerations

   With the implementation of augmented-by, the base modules and the
   augmented-by modules require to be listed in the same module-set.

   Note that the reverse dependency will increase the size of the ietf-
   yang-library instance on the server.  Also, the ietf-yang-library
   instance, and therefore the augmented-by, should be updated when new
   YANG modules are onboarded".

   A YANG example with the expected augmented-by result is provided in
   Section 4.2.2.

6.  Implementation Status

   Note to the RFC-Editor: Please remove this section before publishing.

6.1.  Netopeer2 at IETF119 Hackathon

   Zhuoyao Lin did the prototype implementation of the augmented-by list
   feature of this draft and demonstrated it based on Netopeer2 in IETF
   119 Hackathon.

   Netopeer2 is a NETCONF server & client implementation developed by
   CESNET.  Source code is here: [NTP17].  The actual feature is
   implemented by extending the libyang [LY16] and sysrepo [SR16] which
   are the base libraries for Netopeer2 to support populating the
   augmented-by list.

6.2.  Netopeer2 at IETF120 Hackathon

   Zhuoyao Lin did a docker image of netopeer2 that integrates the
   augmented-by feauture in sysrepo and libyang.  The result is
   presented at IETF 120 hackathon.

   The source code can be obtained here: [NP24]

6.3.  Libyangpush Find-dependency

   Zhuoyao Lin did an implementation of find-dependency based on the
   ietf-yang-library with augmented-by feature in the YANG-Push message
   parser library libyangpush.  The result is presented in IETF 120
   hackathon.

   The source code can be obtained here: [NP24]

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6.4.  Device Implementations

   This section introduced the device implementations status [NA25] of
   this document from vendors like Huawei, Cisco, 6Wind.

   The list of Router Images supporting (upcoming and already
   implemented) the ietf-yang-library-augmentedby YANG module proposed
   in this document is following:

   *  Huawei VRP R025C00 for NE8000 and NE40 (2025-10-15).
      https://support.huawei.com/

   *  Cisco IOS XR 25.3.1 (2025-08-31). https://software.cisco.com/

   *  Huawei VRP R024C10 for MA5800T-X17 (2025-06-30).
      https://support.huawei.com/

   *  6WIND VSR 3.10. https://www.6wind.com/

7.  Security Considerations

   This section follows the guidelines in Section 3.7 of
   [I-D.ietf-netmod-rfc8407bis].

   The "ietf-yang-library-augmentedby" YANG module defines a data model
   that is designed to be accessed via YANG-based management protocols,
   such as NETCONF [RFC6241] and RESTCONF [RFC8040].  These YANG-based
   management protocols require the use of a secure transport layer
   (e.g., SSH [RFC4252], TLS [I-D.ietf-tls-rfc8446bis], and QUIC
   [RFC9000]) and require mutual authentication.

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

   There are no writable ("config true") data nodes defined in this YANG
   module.

   This YANG module defines only readable ("config false") data nodes.
   Some of these readable data nodes may be considered sensitive or
   vulnerable in some network environments.  It is important to control
   read access (e.g., via get, get-config, or notification) to these
   data nodes.

   Specifically, the following readable data nodes contain potentially
   sensitive information:

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   *  /yang-library/module-set/module/augmented-by

   *  /modules-state/module/augmented-by (modules-state is deprecated)

   These nodes expose the augmentation relationships among modules
   implemented by a server.  Unauthorized read access could help an
   attacker identify implementation structure, optional features, or
   software components present on a server, which might then be used to
   target known platform vulnerabilities.  Therefore, access control
   policies SHOULD restrict read access to authorized users only.

   There are no RPCs or action operations defined in this module.
   Therefore, there are no particularly sensitive RPC or action
   operations.

   This module uses groupings from the ietf-yang-library YANG module
   defined in [RFC8525], which defines nodes that may be considered
   sensitive or vulnerable in network environments.  Since this document
   augments the ietf-yang-library YANG module defined in [RFC8525], the
   Section 6 Security Considerations of [RFC8525] apply here as well.
   Refer to that Section for information as to which nodes may be
   considered sensitive or vulnerable in network environments.

8.  IANA Considerations

   This document registers one 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-yang-library-augmentedby

   Registration Contact: The IESG.

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

   This document registers one YANG module in the "YANG Module Names"
   registry [RFC6020]

   Name: ietf-yang-library-augmentedby

   Namespace: urn:ietf:params:xml:ns:yang:ietf-yang-library-augmentedby

   Prefix: yanglib-aug

   Reference: RFC-to-be (Note to the RFC-Editor: Please replace this
   with RFC plus the RFC number when this document can be published.)

   Maintained by IANA: N

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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>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 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 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>.

   [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>.

   [RFC8525]  Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K.,
              and R. Wilton, "YANG Library", RFC 8525,
              DOI 10.17487/RFC8525, March 2019,
              <https://www.rfc-editor.org/info/rfc8525>.

9.2.  Informative References

   [I-D.ietf-netconf-udp-notif]
              Feng, A. H., Francois, P., Zhou, T., Graf, T., and P.
              Lucente, "UDP-based Transport for Configured
              Subscriptions", Work in Progress, Internet-Draft, draft-
              ietf-netconf-udp-notif-25, 28 January 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              udp-notif-25>.

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   [I-D.ietf-netmod-rfc8407bis]
              Bierman, A., Boucadair, M., and Q. Wu, "Guidelines for
              Authors and Reviewers of Documents Containing YANG Data
              Models", Work in Progress, Internet-Draft, draft-ietf-
              netmod-rfc8407bis-28, 5 June 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
              rfc8407bis-28>.

   [I-D.ietf-nmop-yang-message-broker-integration]
              Graf, T., "An Architecture for YANG-Push to Apache Kafka
              Integration", Work in Progress, Internet-Draft, draft-
              ietf-nmop-yang-message-broker-integration, 3 July 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-nmop-
              yang-kafka-integration>.

   [I-D.ietf-tls-rfc8446bis]
              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", Work in Progress, Internet-Draft, draft-
              ietf-tls-rfc8446bis-14, 13 September 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-tls-
              rfc8446bis-14>.

   [LY16]     Vasko, M., "libyang", BSD-3-Clause license, November 2016,
              <https://github.com/CESNET/libyang.git>.

   [Martinez-Casanueva2023]
              Martinez-Casanueva, I. D., Gonzalez-Sanchez, D., Bellido,
              L., Fernandez, D., and D. R. Lopez, "Toward Building a
              Semantic Network Inventory for Model-Driven Telemetry",
              DOI 10.1109/MCOM.001.2200222, March 2023,
              <https://doi.org/10.1109/MCOM.001.2200222>.  IEEE
              Communications Magazine

   [NA25]     "IETF YANG-Push - Implementations", <https://www.network-
              analytics.org/yp/implementations.html>.

   [NP24]     Lin, Z., "Netopeer2-docker-ietf120", July 2024,
              <https://github.com/network-
              analytics/libyangpush/tree/feature/draft_augmentedby>.

   [NTP17]    Vasko, M., "Netopeer2", BSD-3-Clause license, May 2017,
              <https://github.com/CESNET/netopeer2>.

   [RFC4252]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
              January 2006, <https://www.rfc-editor.org/info/rfc4252>.

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   [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>.

   [RFC7895]  Bierman, A., Bjorklund, M., and K. Watsen, "YANG Module
              Library", RFC 7895, DOI 10.17487/RFC7895, June 2016,
              <https://www.rfc-editor.org/info/rfc7895>.

   [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>.

   [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>.

   [RFC8343]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
              <https://www.rfc-editor.org/info/rfc8343>.

   [RFC8344]  Bjorklund, M., "A YANG Data Model for IP Management",
              RFC 8344, DOI 10.17487/RFC8344, March 2018,
              <https://www.rfc-editor.org/info/rfc8344>.

   [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>.

   [RFC9000]  Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/info/rfc9000>.

   [SR16]     Vasko, M., "sysrepo", BSD-3-Clause license, January 2016,
              <https://github.com/sysrepo/sysrepo.git>.

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Appendix A.  Full Tree View of ietf-yang-library

   The following is the YANG tree diagram [RFC8340] for module ietf-
   yang-library after adding augmentation from module ietf-yang-library-
   augmentedby.  The RPCs and notifications are included as well.

  module: ietf-yang-library
    +--ro yang-library
    |  +--ro module-set* [name]
    |  |  +--ro name                  string
    |  |  +--ro module* [name]
    |  |  |  +--ro name                        yang:yang-identifier
    |  |  |  +--ro revision?                   revision-identifier
    |  |  |  +--ro namespace                   inet:uri
    |  |  |  +--ro location*                   inet:uri
    |  |  |  +--ro submodule* [name]
    |  |  |  |  +--ro name        yang:yang-identifier
    |  |  |  |  +--ro revision?   revision-identifier
    |  |  |  |  +--ro location*   inet:uri
    |  |  |  +--ro feature*                    yang:yang-identifier
    |  |  |  +--ro deviation*                  -> ../../module/name
    |  |  |  +--ro yanglib-aug:augmented-by*
                                       -> ../../yanglib:module/name
    |  |  +--ro import-only-module* [name revision]
    |  |     +--ro name         yang:yang-identifier
    |  |     +--ro revision     union
    |  |     +--ro namespace    inet:uri
    |  |     +--ro location*    inet:uri
    |  |     +--ro submodule* [name]
    |  |        +--ro name        yang:yang-identifier
    |  |        +--ro revision?   revision-identifier
    |  |        +--ro location*   inet:uri
    |  +--ro schema* [name]
    |  |  +--ro name          string
    |  |  +--ro module-set*   -> ../../module-set/name
    |  +--ro datastore* [name]
    |  |  +--ro name      ds:datastore-ref
    |  |  +--ro schema    -> ../../schema/name

    |  +--ro content-id       string
    x--ro modules-state
       x--ro module-set-id    string
       x--ro module* [name revision]
          x--ro name                yang:yang-identifier
          x--ro revision            union
          +--ro schema?             inet:uri
          x--ro namespace           inet:uri

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          x--ro feature*            yang:yang-identifier
          x--ro deviation* [name revision]
          |  x--ro name        yang:yang-identifier
          |  x--ro revision    union
          x--ro conformance-type    enumeration
          x--ro submodule* [name revision]
          |  x--ro name        yang:yang-identifier
          |  x--ro revision    union
          |  +--ro schema?     inet:uri
          +--ro yanglib-aug:augmented-by*   -> ../../yanglib:module/name

    notifications:
      +---n yang-library-update
      |  +--ro content-id    -> /yang-library/content-id
      x---n yang-library-change
         x--ro module-set-id    -> /modules-state/module-set-id

Appendix B.  Changes

   Note to the RFC-Editor: Please remove this section before publishing.

B.1.  draft-lincla-netconf-yang-library-augmentation: Changes from 00 to
      01

   The list name has been updated from "augmentation" to "augmented-by",
   in order to represent the usage clearly.

   The leafref has been changed from absolute path "/yanglib:yang-
   libraray/yanglib:module-set/yanglib:module/yanglib:name" to relative
   path "../../yanglib:module/yanglib:name".  The YANG validation in the
   appendix B shows that this path can work as expected.

   Section 5 Implementation and section 6 Changes has been added.

B.2.  draft-lincla-netconf-yang-library-augmentedby version 00

   Updated the Use case content in Section 3.1.  Add explanation: the
   scope of use case "Data Mesh Architecture" is limited to configured
   subscription.

   Updated Implementation status content.

B.3.  draft-lincla-netconf-yang-library-augmentedby: Changes from 00 to
      01

   Updated affiliations

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   Update content of Section 3.1 Data Mesh use case.  Explain the
   limitation of applying get-all-schemas solution under the background
   of using UDP-notif of configured subscription, and how the feature
   proposed in the draft can improve the solution.

   Full review of document.  Nits and refinement of sections.

B.4.  draft-lincla-netconf-yang-library-augmentedby: Changes from 01 to
      02

   Rewrite Section 2 Motivation.

   Update Section 6 Changes's subsection title.

   Update the Section 7 security consideration and section 8 IANA
   Considerations.

   Added in the appendix the Impact Analysis of ietf-yang-library and
   proposal for the RFC8525bis draft.

B.5.  draft-ietf-netconf-yang-library-augmentedby version 00

   Resubmitted the draft name from:

   draft-lincla-netconf-yang-library-augmentedby-02

   to:

   draft-ietf-netconf-yang-library-augmentedby-00

B.6.  draft-ietf-netconf-yang-library-augmentedby: Changes from 00 to 01

   Correct the yanglint validation invalid example.

   Updated the explaination to the yanglint validation example
   principle.

   Delete Section "ietf-yang-library Impact Analysis, as an evaluation
   for RFC8525bis".  The idea of updating the RFC8525 is paused.

B.7.  draft-ietf-netconf-yang-library-augmentedby: Changes from 01 to 02

   Update and rephrase the Introduction section.

   Add Section 4.2 Implementation Instructions.  Address in
   Section 4.2.1 that the definition of "augmented-by" only consider the
   direct augment.  A YANG example for explaining this purpose has been
   put into Section 4.2.2.

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   Draft refinement.

   Reference update.

B.8.  draft-ietf-netconf-yang-library-augmentedby: Changes from 02 to 03

   Merge review comment from Thomas.

B.9.  draft-ietf-netconf-yang-library-augmentedby: Changes from 03 to 04

   Update module content ietf-yang-library-augmentedby: Organise the
   augmentation content to grouping; Add augmentation to modules-state
   container.

   Appendix B is deleted.

B.10.  draft-ietf-netconf-yang-library-augmentedby: Changes from 04 to
       05

   Update ietf-yang-library-augmentedby module revision.

B.11.  draft-ietf-netconf-yang-library-augmentedby: Changes from 05 to
       06

   Merged Jean, Thomas and Alex's editorial feedback.

   Merged Andy's review.

   Changed contents are listed following:

   *  Section 1: Rewrite introduction.  Added definition for 'reverse
      dependency'.  Avoid possible misleading expression about reverse
      dependency and external dependency.

   *  Section 2: Editorial Changes.

   *  Section 3: Merged editorial feedback from Alex, mainly for
      Section 3.1.

   *  Section 4: Move the full tree diagram to appendix A; Correct the
      YANG file date; Update the description statement in YANG module to
      provide implementation instructions information; Improve the text
      of implementation instruction and the direct augment example.

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   *  Appendix: For Appendix A: The ietf-yang-library full tree view has
      been moved to Appendix A.  For Appendix B: The yanglint validation
      example has been moved from Appendix A to Appendix B.  The invalid
      yanglint example has been removed.  Set up texted has been added
      before the validation example.

B.12.  draft-ietf-netconf-yang-library-augmentedby: Changes from 06 to
       07

   Change the reference in IANA Consideration to 'RFC-to-be'.

B.13.  draft-ietf-netconf-yang-library-augmentedby: Changes from 07 to
       08

   Merged Per's review and comments.

B.14.  draft-ietf-netconf-yang-library-augmentedby: Changes from 08 to
       09

   Updated YANG module's line length and spacing.  Corrected the
   "author" to "authors".

   Corrected typo.

   Added section 5 Operational Considerations to explain that the base
   and augmentedby modules should be in the same module-set.

B.15.  draft-ietf-netconf-yang-library-augmentedby: Changes from 09 to
       10

   Corrected the typo of 'requires'.

   Moved RFC8525 reference to Nomative References section.

B.16.  draft-ietf-netconf-yang-library-augmentedby: Changes from 10 to
       11

   Mentioned in the title that this document updates RFC8525.

B.17.  draft-ietf-netconf-yang-library-augmentedby: Changes from 12 to
       13

   Updated draft according to the AD review.

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Internet-Draft        Augmented-by for YANG Library        February 2026

B.18.  draft-ietf-netconf-yang-library-augmentedby: Changes from 13 to
       14

   Resolving nits.

B.19.  draft-ietf-netconf-yang-library-augmentedby: Changes from 14 to
       15

   Improved the examples, based on the designated expert review.

B.20.  draft-ietf-netconf-yang-library-augmentedby: Changes from 15 to
       16

   Address Med's DISCUSS.

Acknowledgments

   The author would like to thank Jan Lindblad and Jean Quilbeuf for
   their help during the design of the YANG module, and Thomas Graf, Rob
   Wilton, Andy Bierman, Jean Quilbeuf, Alex Huang Feng, Per Andersson,
   Mahesh Jethanandani, and Med Boucadair for their valuable review and
   comments.

Authors' Addresses

   Zhuoyao Lin
   Huawei
   Townsend Street, 4th Floor George's Court
   Dublin
   Ireland
   Email: zhuoyao.lin1@huawei-partners.com

   Benoit Claise
   Everything OPS
   Email: benoit@everything-ops.net

   Ignacio Dominguez Martinez-Casanueva
   Telefonica
   Ronda de la Comunicacion, S/N
   Madrid 28050
   Spain
   Email: ignacio.dominguezmartinez@telefonica.com

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