Augmented-by Addition into the IETF-YANG-Library
draft-ietf-netconf-yang-library-augmentedby-01

NETCONF                                                           Z. Lin
Internet-Draft                                                 B. Claise
Intended status: Standards Track                                  Huawei
Expires: 24 April 2025                          I. D. Martinez-Casanueva
                                                              Telefonica
                                                         21 October 2024

            Augmented-by Addition into the IETF-YANG-Library
             draft-ietf-netconf-yang-library-augmentedby-01

Abstract

   This document augments the ietf-yang-library to provide the
   augmented-by list.  It facilitates the process of obtaining the
   entire dependencies between YANG modules, by directly querying the
   server's YANG module.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   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 24 April 2025.

Copyright Notice

   Copyright (c) 2024 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
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Data Mesh Telemetry Architecture  . . . . . . . . . . . .   5
     3.2.  Data Catalog  . . . . . . . . . . . . . . . . . . . . . .   7
   4.  The "ietf-yang-library-augmentedby" YANG module . . . . . . .   9
     4.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .   9
       4.1.1.  Tree View . . . . . . . . . . . . . . . . . . . . . .   9
       4.1.2.  Full Tree View  . . . . . . . . . . . . . . . . . . .   9
       4.1.3.  YANG Module . . . . . . . . . . . . . . . . . . . . .  10
   5.  Implementation Status . . . . . . . . . . . . . . . . . . . .  12
     5.1.  Netopeer2 at IETF119 Hackathon  . . . . . . . . . . . . .  12
     5.2.  Netopeer2 at IETF120 Hackathon  . . . . . . . . . . . . .  13
     5.3.  Libyangpush Find-dependency . . . . . . . . . . . . . . .  13
   6.  Changes . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     6.1.  draft-lincla-netconf-yang-library-augmentation: Changes
           from 00 to 01 . . . . . . . . . . . . . . . . . . . . . .  13
     6.2.  draft-lincla-netconf-yang-library-augmentedby version
           00  . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     6.3.  draft-lincla-netconf-yang-library-augmentedby: Changes from
           00 to 01  . . . . . . . . . . . . . . . . . . . . . . . .  14
     6.4.  draft-lincla-netconf-yang-library-augmentedby: Changes from
           01 to 02  . . . . . . . . . . . . . . . . . . . . . . . .  14
     6.5.  draft-ietf-netconf-yang-library-augmentedby version 00  .  14
     6.6.  draft-ietf-netconf-yang-library-augmentedby: Changes from
           00 to 01  . . . . . . . . . . . . . . . . . . . . . . . .  14
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  17
   Appendix A.  YANG module validation with yanglint . . . . . . . .  21
     A.1.  A valid ietf-yang-library data example  . . . . . . . . .  21
     A.2.  An invalid ietf-yang-library data example . . . . . . . .  22
   Appendix B.  YANG Module augmenting RFC7895 . . . . . . . . . . .  23
     B.1.  Tree View for YANG module augmenting RFC7895  . . . . . .  23

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     B.2.  Full Tree View for ietf-yang-library with augmentation to
           RFC7895 . . . . . . . . . . . . . . . . . . . . . . . . .  24
     B.3.  YANG module augmenting RFC7895  . . . . . . . . . . . . .  24
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  27
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

1.  Introduction

   The YANG Library [RFC8525] specifies a YANG module that provides the
   information about the YANG modules and datastores to facilitate a
   client application to fully utilize and understand the YANG data
   modelling language.  To know the YANG dependencies, [RFC8525] has
   defined and provided the submodule list and the YANG modules
   deviation list.  However, the YANG modules augmentation is not
   provided.

   According to [RFC7950], both augmentations and deviations are
   defining contents external to the model, but applying internally for
   the model.  It is important to know the augmentation and deviation as
   they are dependencies between modules, but it is also difficult
   because they are defined externally.  When we try to use the ietf-
   yang-library in [RFC8525] to obtain the reverse dependencies (i.e.,
   augmentations and deviations), the augmentations are not defined in
   it.

   However, both the augmentation and the deviation work as YANG module
   dependencies.  Therefore, it is reasonable to document them the same
   way in the IETF YANG Library.  Besides, it will be easier to
   determine the reverse dependency if the augmentation is directly
   available in the YANG Library.

   This draft augments the ietf-yang-library YANG module to include the
   YANG module augmentation information.

1.1.  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 terminology from [RFC8525] is used in this document

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

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2.  Motivation

   When using a YANG module, it is necessary to make sure that all its
   dependencies are presented.  [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.

   *  Augmentation: the "augment" statement 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.

   The import and include are direct dependencies while the augmentation
   and deviation are reverse dependencies.  To know the direct
   dependencies of specific YANG module, we can parse this YANG module
   as the dependencies are directly specified (import and include
   statements").

   As for the reverse dependencies, since they are defined externally,
   we cannot parse the YANG module itself to discover them.  The current
   way to discover the reverse denpendencies is to query all YANG
   modules from the server and to parse them.  This is a lenthy process,
   which must be repeated for each client that requires that
   information.

   According to the definition of module ietf-yang-library defined in
   [RFC8525], in the schema of a module in YANG library, the deviation
   is provided to tell this module is deviated by which other modules.
   If YANG library can directly report all reverse dependencies, it
   could provide a much easier and light-weight solution to find module
   entire dependency, compared to getting and parsing all modules.

   Right now, the YANG Library only provides the deviation list, but not
   the augmentation.  With augmentation being more widly used and
   defined, and with some use cases arise as the requirement of automate
   network management, the augmentation becomes essential information to
   be learnt by client what has been additionally implemented, and for
   it to better understand the device module relationship.  Thus, the
   YANG Library should be extended to also provide the augmentation
   information.

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   The implementation is not difficult since both augmentation and
   deviation have similar way of working (both are applied to the
   original module but invisible to them).

3.  Use Cases

   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 is received.

   The alternative for a YANG-Push receiver is to collect and store the
   entire module set for every single server who could be streaming
   data.  This approach is not always practical due to the following
   reasons:

   *  For a YANG-Push collector => we never know in advance which
      telemetry content will be received and from whom.

   *  Querying all the YANG modules is time consuming => we lose the
      real-time.

   This section introduces two use cases that reflect the motivation for
   extending YANG Library.  One targets solving dependency problems in a
   data mesh telemetry system while the other aims at building a data
   catalog that makes YANG module information easily accessible.

3.1.  Data Mesh Telemetry Architecture

   A network analytics architecture that integrates YANG-Push and Kafka
   is proposed and is continuously growing and gaining influence, refer
   to the draft: An Architecture for YANG-Push to Apache Kafka
   Integration [I-D.ietf-nmop-yang-message-broker-integration-03].  This
   open-source project encompasses contributions such as Support of
   Versioning in YANG Notifications Subscription
   [I-D.ietf-netconf-yang-notifications-versioning] or Support of
   Network Observation Timestamping in YANG Notifications
   [I-D.netconf-tgraf-yang-push-observation-time], among others.

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   The purpose of this project is to provide adequate information in the
   YANG-Push notification so that when it is received, the module and
   its dependency can be parsed and found automatically from the vantage
   point.  The architecture relies on the information of YANG module and
   their dependency to realize, as one of its main goals is to solve the
   problem of missing YANG semantics when data is received in Time
   Series Database in the end.  To solve the problem, a schema registry
   is introduced to store YANG modules and all their relationships
   (direct and reverse dependencies).  The schema is obtained by the
   NETCONF <get-schema> of the subscribed YANG module, which is obtained
   by parsing the <subscription-started> message of each YANG-Push
   subscription.

   The scope of this draft is limited to configured subscriptions as
   defined in Section 2.5 of [RFC8639], as opposed to dynamic
   subscription defined in Section 2.4 of [RFC8639].  Configured
   subscriptions are configured by a YANG client on the YANG server via
   the supported network protocol.  In this scenario, once the
   subscription is set up, the YANG-Push notification (or event record)
   is sent over the connections specified by the transport and receiver
   of the configured subscription.  This technique differs from dynamic
   subscriptions, where the notification messages are sent over the
   session that has been used to establish the subscription.

   Section 3 of draft
   [I-D.ietf-nmop-yang-message-broker-integration-03], defines a
   separate network orchestrator and data collector in its architecture,
   which means subscription and data collection are done separately.
   Therefore, only configured subscription, with which user can
   configure the subscription from one YANG client and receive the
   telemetry data in another YANG collector indicated in the
   subscription, could work with this architecture.

   As a method for massively streaming telemetry data, the UDP-based
   Transport for configured Subscription defined in draft
   [I-D.ietf-netconf-udp-notif](UDP-notif) has been applied in
   [I-D.ietf-nmop-yang-message-broker-integration-03] as the transport
   method and streaming message type.  With the same spirit as applying
   the configured subscription, the UDP-notif has introduced more
   flexibility into the architecture by defining useful metadata in the
   message content such as the receiver address, port etc.  In this way,
   at the same time when the Data Mesh architecture is handling massive
   data, it has the ability to trace the publisher of each message.

   By explaining the above, we have gone back to the beginning of this
   section, where we explained the schema registry, that contains the
   YANG modules concerned in each YANG-Push subscription which are
   obtained by NETCONF <get-schema> operation.  UDP-notif has provided

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   the ability to know the publisher of message.  Therefore, an
   independent process containing multiple <get-schema> operations is
   launched after each new YANG-Push subscription module has been known.
   However, the complexity still remains at:

   *  How we are going to find dependency of the YANG modules (so that
      the YANG-Push subscription message has the complete module
      dependencies for its set of YANG modules)?

   *  How do we conduct <get-schema>?

   Currently, the method used for obtaining modules and finding module
   dependencies is "get-all-schemas", where the YANG client retrieves
   all YANG modules from the network device to enable later the client
   can fully understand and utilize all modules and module dependencies
   of device.  This process is very heavy because in a real situation,
   each device may implement hundreds of YANG modules, requiring up to
   several minutes to complete, in the worse cases.  Besides, the need
   of parsing all YANG modules and finding all the dependencies adds a
   small extra delay.  Applying this method to obtain YANG module will
   make the operation very costly, since after each subscribed module is
   learned, "get-all-schemas" needs to be re-performed.

   Therefore, considering the telemetry real-time aspects, this extra
   delay in collecting (and processing) the dependencies through a get-
   all-schemas approach is not ideal.

   It's more efficient to get dependencies only for the required modules
   in the telemetry.

   By using the provided the augmentation information in ietf-yang-
   library, the collector can directly obtain the YANG reverse
   dependencies by fetching the contents of YANG Library, saving
   collection (and processing time) at the collector, and therefore
   helping with the near real-time aspects of the closed loop action.

3.2.  Data Catalog

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

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   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 also external metadata
   sources.  For example, a Kafka Schema Registry is a metadata source
   that provides metadata about the data models 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 these metadata with other 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.

   Coming back to the example of datasets related to the "interface"
   concept, say we have 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 these
   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.

   The current workaround to this limitation is to, in combination with
   the YANG Library data, additionally fetch 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, in a similar fashion to deviation dependencies.

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

   This YANG module augments the ietf-yang-library module by adding the
   augmented-by list in the "yang-library/module-set".  The name
   "augmented-by" indicates the modules by which the current module is
   being augmented.  Note that this module only augments the ietf-yang-
   library defined in [RFC8525].  At the time of writing this document,
   most vendors support [RFC7895], a previous revision of the ietf-yang-
   library YANG module; The module that augments [RFC7895] is provided
   in the Appendix B.

4.1.  Data Model Overview

4.1.1.  Tree View

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

   module: ietf-yang-library-augmentedby

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

4.1.2.  Full Tree View

   The following is the YANG tree diagram[RFC8340] for the ietf-yang-
   library with the augmentation defined in module ietf-yang-library-
   augmentedby, including the RPCs and notifications.

   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

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     |  |     +--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
           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

     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

4.1.3.  YANG Module

   The YANG module source code of ietf-yang-library-augmentedby in which
   augmentation to the ietf-yang-library of [RFC8525] is defined.

   <CODE BEGINS> file "ietf-yang-library-augmentedby@2023-10-27.yang"
   module ietf-yang-library-augmentedby {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-yang-library-augmentedby";
     prefix yanglib-aug;

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     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>

        Author:   Zhuoyao Lin
                  <mailto:zhuoyao.lin1@huawei-parteners.com>
                  Benoit Claise
                  <mailto:benoit.claise@huawei.com>
                  IGNACIO DOMINGUEZ MARTINEZ-CASANUEVA
                  <matilto: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) 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; see the
        RFC itself for full legal notices.  ";

     revision 2023-10-27 {
       description

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         "Added list augmented-by in yang-library/module-set/module to
         make the module store the entire reverse dependency information
         (augmented-by and deviation).";
       reference
         "RFC XXXX: Support of augmentedby in ietf-yang-library";
     }

     augment "/yanglib:yang-library/yanglib:module-set/yanglib:module" {
       description
         "Augment the augmented-by 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 augmentation used by this server to
            modify the conformance 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.

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

5.  Implementation Status

   Note to the RFC-Editor: Please remove this section before publishing
   (This follows the template in RFC7942).

5.1.  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.

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   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.

5.2.  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]

5.3.  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]

6.  Changes

6.1.  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 A shows that this path can work as expected.

   Section 5 Implementation and section 6 Changes has been added.

6.2.  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.

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

   Updated affiliations

   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.

6.4.  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.

6.5.  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

6.6.  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.

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7.  Security Considerations

   The YANG module specified in this document defines a 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.

   The readable node defined in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control read access(e.g., via get, get-config, or
   notification) to this data node.  The following is the explanation to
   data node's sensitivity/vulnerability:

   The "augmented-by" node in this YANG module could reveal all modules
   that are augmenting one module.  It could help attacker identify the
   relationship between modules and server implementations known bugs.
   Server vulnerabilities may include but not restricted to: 1.  Too
   many augmented-by records causes buffer overflow. 2.  The augmented-
   by node help identify through the inter-relation of modules how to
   cause the server to crash or significantly degrade device
   performance.

8.  IANA Considerations

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

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

   Registration Contact: The NETCONF WG of the IETF.

   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

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   prefix: yanglib-aug

   reference: [I-D.lincla-netconf-yang-library-augmentedby]

9.  References

9.1.  Normative References

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

   [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>.

   [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>.

   [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>.

   [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>.

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   [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>.

   [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>.

   [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>.

   [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>.

   [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>.

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

9.2.  Informative References

   [I-D.bjorklund-netmod-structural-mount-02]
              Bjorklund, M., "YANG Structural Mount", Work in Progress,
              Internet-Draft, draft-bjorklund-netmod-structural-mount-
              02, 26 February 2016,
              <https://datatracker.ietf.org/doc/html/draft-bjorklund-
              netmod-structural-mount-02>.

   [I-D.clacla-netmod-model-catalog-03]
              Clarke, J. and B. Claise, "YANG module for
              yangcatalog.org", Work in Progress, Internet-Draft, draft-
              clacla-netmod-model-catalog-03, 3 April 2018,
              <https://datatracker.ietf.org/doc/html/draft-clacla-
              netmod-model-catalog-03>.

   [I-D.ietf-netconf-udp-notif]
              Zheng, G., Zhou, T., Graf, T., Francois, P., Feng, A. H.,
              and P. Lucente, "UDP-based Transport for Configured
              Subscriptions", Work in Progress, Internet-Draft, draft-

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              ietf-netconf-udp-notif-14, 4 July 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              udp-notif-14>.

   [I-D.ietf-netconf-yang-notifications-versioning]
              Graf, T., Claise, B., and A. H. Feng, "Support of
              Versioning in YANG Notifications Subscription", Work in
              Progress, Internet-Draft, draft-ietf-netconf-yang-
              notifications-versioning-05, 16 June 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              yang-notifications-versioning-05>.

   [I-D.ietf-netmod-module-tags-00]
              Hopps, C., Berger, L., and D. Bogdanovic, "YANG Module
              Tags", Work in Progress, Internet-Draft, draft-ietf-
              netmod-module-tags-00, 6 March 2018,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
              module-tags-00>.

   [I-D.ietf-netmod-rfc6087bis]
              Bierman, A., "Guidelines for Authors and Reviewers of
              Documents Containing YANG Data Models", Work in Progress,
              Internet-Draft, draft-ietf-netmod-rfc6087bis-20, 13 March
              2018, <https://datatracker.ietf.org/doc/html/draft-ietf-
              netmod-rfc6087bis-20>.

   [I-D.ietf-netmod-yang-module-versioning-10]
              Wilton, R., Rahman, R., Lengyel, B., Clarke, J., and J.
              Sterne, "Updated YANG Module Revision Handling", Work in
              Progress, Internet-Draft, draft-ietf-netmod-yang-module-
              versioning-10, 17 October 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
              yang-module-versioning-10>.

   [I-D.ietf-netmod-yang-module-versioning-12]
              Wilton, R., Rahman, R., Lengyel, B., Clarke, J., and J.
              Sterne, "Updated YANG Module Revision Handling", Work in
              Progress, Internet-Draft, draft-ietf-netmod-yang-module-
              versioning-12, 24 June 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
              yang-module-versioning-12>.

   [I-D.ietf-netmod-yang-packages-03]
              Wilton, R., Rahman, R., Clarke, J., Sterne, J., and B. Wu,
              "YANG Packages", Work in Progress, Internet-Draft, draft-
              ietf-netmod-yang-packages-03, 4 March 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
              yang-packages-03>.

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   [I-D.ietf-netmod-yang-semver]
              Clarke, J., Wilton, R., Rahman, R., Lengyel, B., Sterne,
              J., and B. Claise, "YANG Semantic Versioning", Work in
              Progress, Internet-Draft, draft-ietf-netmod-yang-semver-
              17, 2 July 2024, <https://datatracker.ietf.org/doc/html/
              draft-ietf-netmod-yang-semver-17>.

   [I-D.ietf-nmop-yang-message-broker-integration-03]
              Graf, T., "An Architecture for YANG-Push to Apache Kafka
              Integration", Work in Progress, Internet-Draft, draft-
              ietf-nmop-yang-message-broker-integration-03, 3 July 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-nmop-
              yang-kafka-integration/03>.

   [I-D.ietf-opsawg-collected-data-manifest-04]
              Claise, B., Quilbeuf, J., Lopez, D., Martinez-Casanueva,
              I. D., and T. Graf, "A Data Manifest for Contextualized
              Telemetry Data", Work in Progress, Internet-Draft, draft-
              ietf-opsawg-collected-data-manifest-04, 8 July 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-opsawg-
              collected-data-manifest-04>.

   [I-D.jouqui-netmod-yang-full-include-02]
              Quilbeuf, J., Claise, B., and T. Joubert, "YANG Full
              Embed", Work in Progress, Internet-Draft, draft-jouqui-
              netmod-yang-full-include-02, 5 July 2024,
              <https://datatracker.ietf.org/doc/html/draft-jouqui-
              netmod-yang-full-include-02>.

   [I-D.lincla-netconf-yang-library-augmentedby]
              Lin, Z., Claise, B., and I. D. Martinez-Casanueva,
              "Augmented-by Addition into the IETF-YANG-Library", Work
              in Progress, Internet-Draft, draft-lincla-netconf-yang-
              library-augmentedby-01, 5 July 2024,
              <https://datatracker.ietf.org/doc/html/draft-lincla-
              netconf-yang-library-augmentedby-01>.

   [I-D.netconf-tgraf-yang-push-observation-time]
              Graf, T., Claise, B., and A. H. Feng, "Support of Network
              Observation Timestamping in YANG Notifications", Work in
              Progress, Internet-Draft, draft-netconf-tgraf-yang-push-
              observation-time-00, 6 July 2023,
              <https://datatracker.ietf.org/doc/html/draft-netconf-
              tgraf-yang-push-observation-time-00>.

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   [I-D.rwilton-netmod-yang-packages-00]
              Wilton, R., "YANG Packages", Work in Progress, Internet-
              Draft, draft-rwilton-netmod-yang-packages-00, 20 December
              2018, <https://datatracker.ietf.org/doc/html/draft-
              rwilton-netmod-yang-packages-00>.

   [I-D.wilton-netmod-yang-ver-selection-01]
              Wilton, R., Rahman, R., and J. Clarke, "YANG Schema
              Version Selection", Work in Progress, Internet-Draft,
              draft-wilton-netmod-yang-ver-selection-01, 2 November
              2019, <https://datatracker.ietf.org/doc/html/draft-wilton-
              netmod-yang-ver-selection-01>.

   [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

   [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>.

   [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>.

   [RFC8528]  Bjorklund, M. and L. Lhotka, "YANG Schema Mount",
              RFC 8528, DOI 10.17487/RFC8528, March 2019,
              <https://www.rfc-editor.org/info/rfc8528>.

   [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>.

   [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.  YANG module validation with yanglint

   This section gives a few examples that the user can try themselves
   with yanglint.  This is created to prove the syntax correctness.  The
   examples shoud be used with YANG modules ietf-yang-library and ietf-
   yang-libarary-augmentedby as schemas.

   The examples provided are ietf-yang-library 'yang-library' data xml
   file containing the augmented-by field.

   The valid example should pass the validation while the invalid one
   will not.  The difference is that in the invalid example, the module
   in one module-set has augmented module in another module-set, which
   is illegal according to the ietf-yang-library definition.

A.1.  A valid ietf-yang-library data example

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   <CODE BEGINS> file "example_valid.xml"
   <yang-library xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
     <content-id>1</content-id>
     <module-set>
       <name>ms1</name>
       <module>
         <name>module1</name>
         <revision>2024-02-29</revision>
         <namespace>urn:ietf:params:xml:ns:yang:module1</namespace>
         <augmented-by
         xmlns="urn:ietf:params:xml:ns:yang:
         ietf-yang-library-augmentedby">module2</augmented-by>
         <augmented-by
         xmlns="urn:ietf:params:xml:ns:yang:
         ietf-yang-library-augmentedby">module3</augmented-by>
       </module>
       <module>
         <name>module2</name>
         <revision>2024-02-29</revision>
         <namespace>urn:ietf:params:xml:ns:yang:module2</namespace>
       </module>
       <module>
         <name>module3</name>
         <revision>2024-02-29</revision>
         <namespace>urn:ietf:params:xml:ns:yang:module3</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>

A.2.  An invalid ietf-yang-library data example

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   <CODE BEGINS> file "example_invalid.xml"
   <yang-library xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
     <content-id>1</content-id>
     <module-set>
       <name>ms1</name>
       <module>
         <name>module1</name>
         <revision>2024-02-29</revision>
         <namespace>urn:ietf:params:xml:ns:yang:module1</namespace>
         <augmented-by
         xmlns="urn:ietf:params:xml:ns:yang:
         ietf-yang-library-augmentedby">module3</augmented-by>
         <augmented-by
         xmlns="urn:ietf:params:xml:ns:yang:
         ietf-yang-library-augmentedby">module2</augmented-by>
       </module>
       <module>
         <name>module3</name>
         <revision>2024-02-29</revision>
         <namespace>urn:ietf:params:xml:ns:yang:module3</namespace>
       </module>
     </module-set>
     <module-set>
       <name>ms2</name>
       <module>
         <name>module2</name>
         <revision>2024-02-29</revision>
         <namespace>urn:ietf:params:xml:ns:yang:module2</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>

Appendix B.  YANG Module augmenting RFC7895

   This section defines the ietf-yang-library-rfc7895-augmentedby that
   augments the ietf-yang-library defined in [RFC7895].  The module-
   state/module list of this YANG module version is also defined in the
   [RFC8525] version though deprecated.

B.1.  Tree View for YANG module augmenting RFC7895

   The following is the YANG tree diagram for ietf-yang-library-
   rfc7895-augmentedby augmenting RFC7895.

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   module: ietf-yang-library-rfc7895-augmentedby

     augment /yanglib:modules-state/yanglib:module:
       x--ro augmentedby* [name revision]
          +--ro name        -> /yanglib:modules-state/module/name
          +--ro revision    -> /yanglib:modules-state/module/revision

B.2.  Full Tree View for ietf-yang-library with augmentation to RFC7895

   The following is the full YANG tree diagram of ietf-yang-library-
   rfc7895-augmentedby augmenting ietf-yang-library defined in RFC7895.

   module: ietf-yang-library
     +--ro modules-state
        +--ro module-set-id    string
        +--ro module* [name revision]
           +--ro name                        yang:yang-identifier
           +--ro revision                    union
           +--ro schema?                     inet:uri
           +--ro namespace                   inet:uri
           +--ro feature*                    yang:yang-identifier
           +--ro deviation* [name revision]
           |  +--ro name        yang:yang-identifier
           |  +--ro revision    union
           +--ro conformance-type            enumeration
           +--ro submodule* [name revision]
           |  +--ro name        yang:yang-identifier
           |  +--ro revision    union
           |  +--ro schema?     inet:uri
           x--ro yanglib-aug:augmented-by* [name revision]
              +--ro yanglib-aug:name
                           -> /yanglib:modules-state/module/name
              +--ro yanglib-aug:revision
                           -> /yanglib:modules-state/module/revision

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

B.3.  YANG module augmenting RFC7895

   The YANG module that augments the ietf-yang-library RFC7895.

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   <CODE BEGINS>
     file "ietf-yang-library-rfc7895-augmentedby@2023-10-27.yang"
   module ietf-yang-library-rfc7895-augmentedby {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-yang-library-rfc7895-augmentedby";
     prefix yanglib-aug;

     import ietf-yang-library {
       prefix yanglib;
       revision-date 2016-06-21;
       reference
         "RFC 7895: YANG Module Library.";
     }

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

        Author:   Zhuoyao Lin
                  <mailto:zhuoyao.lin1@huawei-partners.com>
        Author:   Benoit Claise
                  <mailto:benoit.claise@huawei.com>
        Author:   IGNACIO DOMINGUEZ MARTINEZ-CASANUEVA
                  <matilto:ignacio.dominguezmartinez@telefonica.com>";

     description
        "This document augments the ietf-yang-library to provide the
        augmented-by list. It facilitates the process of obtaining
        the entire dependencies between YANG modules, by directly
        querying the server's 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) 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

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        (https://trustee.ietf.org/license-info).
        This version of this YANG module is part of RFC XXXX; see the
        RFC itself for full legal notices.  ";

     revision 2023-10-27 {
       description
         "Added list augmentedby in yang-library/modules-state/module to
         make the module store the entire reverse dependency information
         (augmentedby and deviation).";
       reference
         "RFC XXXX: Support of augmentedby in ietf-yang-library
             defined in RFC7895";
     }

     augment "/yanglib:modules-state/yanglib:module" {
       description
         "Augment the augmentedby from module info with the
         module-augmented-by grouping" ;
       uses yanglib-aug:module-state-augmented-by;
     }

     /*
      * Groupings
      */

     grouping module-state-augmented-by {
       description
         "This grouping defines a list with keys being the module
         name and revison. The list contains the augmented-by list.";

       list augmented-by {
         key "name revision";
         status deprecated;

         description
           "List of YANG augmented-by module names and revisions
            used by this server to modify the conformance 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.

            The augment module MUST be present in the 'module'
            list, with the same name and revision values.
            The 'conformance-type' value will be 'implement' for
            the augment module.";

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         leaf name {
           type leafref {
             path "/yanglib:modules-state/yanglib:module/yanglib:name";
           }
           description
             "Identifies a given module in the YANG Library by
             its name.";
         }

         leaf revision {
           type leafref {
             path "/yanglib:modules-state/yanglib:module/yanglib:revision";
           }
           description
             "Revision of the module";
         }
       }
     }
   }
   <CODE ENDS>

Contributors

   The following people all contributed to creating this document:

Acknowledgements

   The author would like to thanks Jan Lindblad and Jean Quilbeuf for
   his help during the design of the YANG module.

Authors' Addresses

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

   Benoit Claise
   Huawei
   Email: benoit.claise@huawei.com

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

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