



Network Working Group                                         A. Bierman
Internet-Draft                                                 YumaWorks
Obsoletes: 7895 (if approved)                               M. Bjorklund
Intended status: Standards Track                          Tail-f Systems
Expires: April 20, 2019                                 J. Schoenwaelder
                                                       Jacobs University
                                                               K. Watsen
                                                        Juniper Networks
                                                               R. Wilton
                                                           Cisco Systems
                                                        October 17, 2018


                              YANG Library
                    draft-ietf-netconf-rfc7895bis-07

Abstract

   This document describes a YANG library that provides information
   about the YANG modules, datastores, and datastore schemas used by a
   network management server.  Simple caching mechanisms are provided to
   allow clients to minimize retrieval of this information.  This
   version of the YANG library supports the Network Management Datastore
   Architecture by listing all datastores supported by a network
   management server and the schema that is used by each of these
   datastores.

   This document obsoletes RFC 7895.

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 http://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 April 20, 2019.






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Copyright Notice

   Copyright (c) 2018 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Objectives  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  YANG Library Data Model . . . . . . . . . . . . . . . . . . .   5
   4.  YANG Library YANG Module  . . . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  22
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  22
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  23
   Appendix A.  Summary of Changes from RFC 7895 . . . . . . . . . .  24
   Appendix B.  Example YANG Library Instance for a Basic Server . .  25
   Appendix C.  Example YANG Library Instance for an Advanced Server  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  31

1.  Introduction

   There is a need for a standard mechanism to expose which YANG modules
   [RFC7950], datastores and datastore schemas [RFC8342] are in use by a
   network management server.

   This document defines the YANG module "ietf-yang-library" that
   provides this information.  This version of the YANG library is
   compatible with the Network Management Datastore Architecture (NMDA)
   [RFC8342].  The previous version of the YANG library, defined in
   [RFC7895], is not compatible with the NMDA since it assumes that all
   datastores have exactly the same schema.  This is not necessarily
   true in the NMDA since dynamic configuration datastores may have
   their own datastore schema.  Furthermore, the operational state




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   datastore may support non-configurable YANG modules in addition to
   the YANG modules supported by conventional configuration datastores.

   The old YANG library definitions have been retained (for backwards
   compatibility reasons) but the definitions have been marked as
   deprecated.  For backwards compatibility, an NMDA-supporting server
   SHOULD populate the deprecated "/modules-state" tree in a backwards-
   compatible manner.  The new "/yang-library" tree would be ignored by
   legacy clients, while providing all the data needed for NMDA-aware
   clients, which would themselves ignore the "/modules-state" tree.
   The recommended approach to populate "/modules-state" is to report
   the schema for YANG modules that are configurable via conventional
   configuration datastores and for which config false data nodes are
   returned via a NETCONF <get> operation, or equivalent.

   The YANG library information can be different on every server and it
   can change at runtime or across a server reboot.  If a server
   implements multiple network management protocols to access the
   server's datastores, then each such protocol may have its own
   conceptual instantiation of the YANG library.

   If a large number of YANG modules are utilized by a server, then the
   YANG library contents can be relatively large.  Since the YANG
   library contents changes very infrequently, it is important that
   clients be able to cache the YANG library contents and easily
   identify whether their cache is out of date.

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 following terms are defined in [RFC7950]:

   o  module

   o  submodule

   o  data node

   This document uses the phrase "implementing a module" as defined in
   [RFC7950] Section 5.6.5.

   The following terms are defined in [RFC8342]:




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   o  datastore

   o  datastore schema

   o  configuration

   o  configuration datastore

   o  conventional configuration

   o  conventional configuration datastore

   o  operational state

   o  operational state datastore

   o  dynamic configuration datastore

   o  client and server

   The following terms are used within this document:

   o  YANG library: A collection of YANG modules, submodules,
      datastores, and datastore schemas used by a server.

   o  YANG library content identifier: A server-generated identifier of
      the contents of the YANG library.

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

2.  Objectives

   The following information is needed by a client application (for each
   YANG module in the library) to fully utilize the YANG data modeling
   language:

   o  name: The name of the YANG module.

   o  revision: If defined in the YANG module or submodule, the revision
      is derived from the most recent revision statement within the
      module or submodule.

   o  submodule list: The name, and if defined, revision of each
      submodule used by the module must be identified.

   o  feature list: The name of each YANG feature supported by the
      server, in a given datastore schema, must be identified.



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   o  deviation list: The name of each YANG module with deviation
      statements affecting a given YANG module, in a given datastore
      schema, must be identified.

   In addition, the following information is needed by a client
   application for each datastore supported by a server:

   o  identity: The YANG identity for the datastore.

   o  schema: The schema (i.e., the set of modules) implemented by the
      datastore.

   In order to select one out of several possible data model designs,
   the following criteria were used:

   1.  The information must be efficient for a client to consume.  Since
       the size of the YANG library can be quite large, it should be
       possible for clients to cache the YANG library information.

   2.  A dynamic configuration datastore must be able to implement a
       module or feature that is not implemented in the conventional
       configuration datastores.

   3.  It must be possible to not implement a module or feature in
       <operational>, even if it is implemented in some other datastore.
       This is required for transition purposes; a server that wants to
       implement <operational> should not have to implement all modules
       at once.

   4.  A given module can only be implemented in one revision in all
       datastores.  If a module is implemented in more than one
       datastore, the same revision is implemented in all these
       datastores.

   5.  Multiple revisions can be used for import, if import-by revision
       is used.

   6.  It must be possible to use the YANG library by schema mount
       [I-D.ietf-netmod-schema-mount].

3.  YANG Library Data Model

   The "ietf-yang-library" YANG module provides information about the
   modules, submodules, datastores, and datastore schemas supported by a
   server.  All data nodes in "ietf-yang-library" are "config false",
   and thus only accessible in the operational state datastore.





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   +-----------+
   | datastore |
   +-----------+
        |
        | has a
        V
   +-----------+            +--------+                +------------+
   | datastore |  union of  | module |  consists of   | modules +  |
   |  schema   |----------->|  set   |--------------->| submodules |
   +-----------+            +--------+                +------------+

                                 Figure 1

   The conceptual model of the YANG library is depicted in Figure 1.
   Following the NMDA, every datastore has an associated datastore
   schema.  A datastore schema is a union of module sets and every
   module set is a collection of modules and submodules, including the
   modules and submodules used for imports.  Note that multiple
   datastores may refer to the same datastore schema.  Furthermore, it
   is possible that individual datastore schemas share module sets.  A
   common use case is the operational state datastore schema which is a
   superset of the schema used by conventional configuration datastores.

   Below is the YANG Tree Diagram for the "ietf-yang-library" module,
   excluding the deprecated "modules-state" tree:


























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   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 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

     notifications:
       +---n yang-library-update
          +--ro content-id    -> /yang-library/content-id

   The "/yang-library" container holds the entire YANG library.  The
   container has the following child nodes:

   o  The "/yang-library/module-set" contains entries representing
      module sets.  The list "/yang-library/module-set/module"
      enumerates the modules that belong to the module set.  A module is
      listed together with its submodules (if any), a set of features,
      and any deviation modules.  The list "/yang-library/module-set/
      import-only-module" lists all modules (and their submodules) used
      only for imports.  The assignment of a module to a module-set is
      at the server's discretion.  This revision of the YANG library




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      attaches no semantics as to which module-set a module is listed
      in.

   o  The "/yang-library/schema" list contains an entry for each
      datastore schema supported by the server.  All conventional
      configuration datastores use the same "schema" list entry.  A
      dynamic configuration datastore may use a different datastore
      schema from the conventional configuration datastores, and hence
      may require a separate "schema" entry.  A "schema" entry has a
      leaf-list of references to entries in the "module-set" list.  The
      schema consists of the union of all modules in all referenced
      module sets.

   o  The "/yang-library/datastore" list contains one entry for each
      datastore supported by the server, and it identifies the datastore
      schema associated with a datastore via a reference to an entry in
      the "schema" list.  Each supported conventional configuration
      datastore has a separate entry, pointing to the same "schema" list
      element.

   o  The "/yang-library/content-id" leaf contains the YANG library
      content identifier, which is an implementation-specific identifier
      representing the current information in the YANG library on a
      specific server.  The value of this leaf MUST change whenever the
      information in the YANG library changes.  There is no requirement
      that the same information always results in the same "content-id"
      value.  This leaf allows a client to fetch all schema information
      once, cache it, and only refetch it if the value of this leaf has
      been changed.  If the value of this leaf changes, the server also
      generates a "yang-library-update" notification.

   Note that for a NETCONF server implementing the NETCONF extensions to
   support the NMDA [I-D.ietf-netconf-nmda-netconf], a change of the
   YANG library content identifier results in a new value for the :yang-
   library:1.1 capability defined in [I-D.ietf-netconf-nmda-netconf].
   Thus, if such a server implements NETCONF notifications [RFC5277],
   and the notification "netconf-capability-change" [RFC6470], a
   "netconf-capability-change" notification is generated whenever the
   YANG library content identifier changes.

4.  YANG Library YANG Module

   The "ietf-yang-library" YANG module imports definitions from
   "ietf-yang-types" and "ietf-inet-types" defined in [RFC6991] and from
   "ietf-datastores" defined in [RFC8342].  While the YANG module is
   defined using YANG version 1.1, the YANG library supports the YANG
   modules written in any version of YANG.




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

   <CODE BEGINS> file "ietf-yang-library@2018-10-16.yang"

   module ietf-yang-library {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-yang-library";
     prefix "yanglib";

     import ietf-yang-types {
       prefix yang;
       reference "RFC 6991: Common YANG Data Types.";
     }
     import ietf-inet-types {
       prefix inet;
       reference "RFC 6991: Common YANG Data Types.";
     }
     import ietf-datastores {
       prefix ds;
       reference "RFC 8342: Network Management Datastore Architecture.";
     }

     organization
       "IETF NETCONF (Network Configuration) Working Group";

     contact
       "WG Web:   <http://tools.ietf.org/wg/netconf/>
        WG List:  <mailto:netconf@ietf.org>

        Author:   Andy Bierman
                  <mailto:andy@yumaworks.com>

        Author:   Martin Bjorklund
                  <mailto:mbj@tail-f.com>

        Author:   Juergen Schoenwaelder
                  <mailto:j.schoenwaelder@jacobs-university.de>

        Author:   Kent Watsen
                  <mailto:kwatsen@juniper.net>

        Author:   Rob Wilton
                  <mailto:rwilton@cisco.com>";

     description
       "This module provides information about the YANG modules,
        datastores, and datastore schemas used by a network



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        management server.

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

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

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

     // RFC Ed.: update the date below with the date of RFC publication
     // and remove this note.
     // RFC Ed.: replace XXXX with actual RFC number and remove this
     // note.
     revision 2018-10-16 {
       description
         "Added support for multiple datastores according to the
          Network Management Datastore Architecture (NMDA).";
       reference
         "RFC XXXX: YANG Library.";
     }
     revision 2016-04-09 {
       description
         "Initial revision.";
       reference
         "RFC 7895: YANG Module Library.";
     }

     /*
      * Typedefs
      */

     typedef revision-identifier {
       type string {
         pattern '\d{4}-\d{2}-\d{2}';
       }
       description
         "Represents a specific date in YYYY-MM-DD format.";
     }

     /*
      * Groupings
      */



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     grouping module-identification-leafs {
       description
         "Parameters for identifying YANG modules and submodules.";

       leaf name {
         type yang:yang-identifier;
         mandatory true;
         description
           "The YANG module or submodule name.";
       }
       leaf revision {
         type revision-identifier;
         description
           "The YANG module or submodule revision date.  If no revision
            statement is present in the YANG module or submodule, this
            leaf is not instantiated.";
       }
     }

     grouping location-leaf-list {
       description
         "Common location leaf list parameter for modules and
          submodules.";

       leaf-list location {
         type inet:uri;
         description
           "Contains a URL that represents the YANG schema
            resource for this module or submodule.

            This leaf will only be present if there is a URL
            available for retrieval of the schema for this entry.";
       }
     }

     grouping module-implementation-parameters {
       description
         "Parameters for describing the implementation of a module.";

       leaf-list feature {
         type yang:yang-identifier;
         description
           "List of all YANG feature names from this module that are
            supported by the server, regardless whether they are defined
            in the module or any included submodule.";
       }
       leaf-list deviation {
         type leafref {



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           path "../../module/name";
         }
         description
           "List of all YANG deviation modules used by this server to
            modify the conformance of the module associated with this
            entry.  Note that the same module can be used for deviations
            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 deviated.

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

     grouping module-set-parameters {
       description
         "A set of parameters that describe a module set.";

       leaf name {
         type string;
         description
           "An arbitrary name of the module set.";
       }
       list module {
         key "name";
         description
           "An entry in this list represents a module implemented by the
            server, as per RFC 7950 section 5.6.5, with a particular set
            of supported features and deviations.";
         reference
           "RFC 7950: The YANG 1.1 Data Modeling Language.";

         uses module-identification-leafs;

         leaf namespace {
           type inet:uri;
           mandatory true;
           description
             "The XML namespace identifier for this module.";
         }

         uses location-leaf-list;

         list submodule {



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           key "name";
           description
             "Each entry represents one submodule within the
              parent module.";
           uses module-identification-leafs;
           uses location-leaf-list;
         }

         uses module-implementation-parameters;
       }
       list import-only-module {
         key "name revision";
         description
           "An entry in this list indicates that the server imports
            reusable definitions from the specified revision of the
            module, but does not implement any protocol accessible
            objects from this revision.

            Multiple entries for the same module name MAY exist.  This
            can occur if multiple modules import the same module, but
            specify different revision-dates in the import statements.";

         leaf name {
           type yang:yang-identifier;
           description
             "The YANG module name.";
         }
         leaf revision {
           type union {
             type revision-identifier;
             type string {
               length 0;
             }
           }
           description
             "The YANG module revision date.
              A zero-length string is used if no revision statement
              is present in the YANG module.";
         }
         leaf namespace {
           type inet:uri;
           mandatory true;
           description
             "The XML namespace identifier for this module.";
         }

         uses location-leaf-list;




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         list submodule {
           key "name";
           description
             "Each entry represents one submodule within the
              parent module.";

           uses module-identification-leafs;
           uses location-leaf-list;
         }
       }
     }

     grouping yang-library-parameters {
       description
         "The YANG library data structure is represented as a grouping
          so it can be reused in configuration or another monitoring
          data structure.";

       list module-set {
         key name;
         description
           "A set of modules that may be used by one or more schemas.

            A module set does not have to be referentially complete,
            i.e., it may define modules that contain import statements
            for other modules not included in the module set.";

         uses module-set-parameters;
       }

       list schema {
         key "name";
         description
           "A datastore schema that may be used by one or more
            datastores.

            The schema must be valid and referentially complete, i.e.,
            it must contain modules to satisfy all used import
            statements for all modules specified in the schema.";

         leaf name {
           type string;
           description
             "An arbitrary name of the schema.";
         }
         leaf-list module-set {
           type leafref {
             path "../../module-set/name";



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           }
           description
             "A set of module-sets that are included in this schema.
              If a non import-only module appears in multiple module
              sets, then the module revision and the associated features
              and deviations must be identical.";
         }
       }

       list datastore {
         key "name";
         description
           "A datastore supported by this server.

            Each datastore indicates which schema it supports.

            The server MUST instantiate one entry in this list per
            specific datastore it supports.

            Each datstore entry with the same datastore schema SHOULD
            reference the same schema.";

         leaf name {
           type ds:datastore-ref;
           description
             "The identity of the datastore.";
         }
         leaf schema {
           type leafref {
             path "../../schema/name";
           }
           mandatory true;
           description
             "A reference to the schema supported by this datastore.
              All non import-only modules of the schema are implemented
              with their associated features and deviations.";
         }
       }
     }

     /*
      * Top-level container
      */

     container yang-library {
       config false;
       description
         "Container holding the entire YANG library of this server.";



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       uses yang-library-parameters;

       leaf content-id {
         type string;
         mandatory true;
         description
           "A server-generated identifier of the contents of the
            'yang-library' tree.  The server MUST change the value of
            this leaf if the information represented by the
            'yang-library' tree, except 'yang-library/content-id', has
            changed.";
       }
     }

     /*
      * Notifications
      */

     notification yang-library-update {
       description
         "Generated when any YANG library information on the
          server has changed.";

       leaf content-id {
         type leafref {
           path "/yanglib:yang-library/yanglib:content-id";
         }
         mandatory true;
         description
           "Contains the YANG library content identifier for the updated
            YANG library at the time the notification is generated.";
       }
     }

     /*
      * Legacy groupings
      */

     grouping module-list {
       status deprecated;
       description
         "The module data structure is represented as a grouping
          so it can be reused in configuration or another monitoring
          data structure.";

       grouping common-leafs {
         status deprecated;
         description



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           "Common parameters for YANG modules and submodules.";

         leaf name {
           type yang:yang-identifier;
           status deprecated;
           description
             "The YANG module or submodule name.";
         }
         leaf revision {
           type union {
             type revision-identifier;
             type string {
               length 0;
             }
           }
           status deprecated;
           description
             "The YANG module or submodule revision date.
              A zero-length string is used if no revision statement
              is present in the YANG module or submodule.";
         }
       }
       grouping schema-leaf {
         status deprecated;
         description
           "Common schema leaf parameter for modules and submodules.";
         leaf schema {
           type inet:uri;
           description
             "Contains a URL that represents the YANG schema
              resource for this module or submodule.

              This leaf will only be present if there is a URL
              available for retrieval of the schema for this entry.";
         }
       }

       list module {
         key "name revision";
         status deprecated;
         description
           "Each entry represents one revision of one module
            currently supported by the server.";

         uses common-leafs {
           status deprecated;
         }
         uses schema-leaf {



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           status deprecated;
         }

         leaf namespace {
           type inet:uri;
           mandatory true;
           status deprecated;
           description
             "The XML namespace identifier for this module.";
         }
         leaf-list feature {
           type yang:yang-identifier;
           status deprecated;
           description
             "List of YANG feature names from this module that are
              supported by the server, regardless whether they are
              defined in the module or any included submodule.";
         }
         list deviation {
           key "name revision";
           status deprecated;
           description
             "List of YANG deviation 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 deviations for
              multiple modules, so the same entry MAY appear
              within multiple 'module' entries.

              The deviation module MUST be present in the 'module'
              list, with the same name and revision values.
              The 'conformance-type' value will be 'implement' for
              the deviation module.";
           uses common-leafs {
             status deprecated;
           }
         }
         leaf conformance-type {
           type enumeration {
             enum implement {
               description
                 "Indicates that the server implements one or more
                  protocol-accessible objects defined in the YANG module
                  identified in this entry.  This includes deviation
                  statements defined in the module.

                  For YANG version 1.1 modules, there is at most one
                  module entry with conformance type 'implement' for a



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                  particular module name, since YANG 1.1 requires that
                  at most one revision of a module is implemented.

                  For YANG version 1 modules, there SHOULD NOT be more
                  than one module entry for a particular module name.";
             }
             enum import {
               description
                 "Indicates that the server imports reusable definitions
                  from the specified revision of the module, but does
                  not implement any protocol accessible objects from
                  this revision.

                  Multiple module entries for the same module name MAY
                  exist. This can occur if multiple modules import the
                  same module, but specify different revision-dates in
                  the import statements.";
             }
           }
           mandatory true;
           status deprecated;
           description
             "Indicates the type of conformance the server is claiming
              for the YANG module identified by this entry.";
         }
         list submodule {
           key "name revision";
           status deprecated;
           description
             "Each entry represents one submodule within the
              parent module.";
           uses common-leafs {
             status deprecated;
           }
           uses schema-leaf {
             status deprecated;
           }
         }
       }
     }

     /*
      * Legacy operational state data nodes
      */

     container modules-state {
       config false;
       status deprecated;



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       description
         "Contains YANG module monitoring information.";

       leaf module-set-id {
         type string;
         mandatory true;
         status deprecated;
         description
           "Contains a server-specific identifier representing
            the current set of modules and submodules.  The
            server MUST change the value of this leaf if the
            information represented by the 'module' list instances
            has changed.";
       }

       uses module-list {
         status deprecated;
       }
     }

     /*
      * Legacy notifications
      */

     notification yang-library-change {
       status deprecated;
       description
         "Generated when the set of modules and submodules supported
          by the server has changed.";
       leaf module-set-id {
         type leafref {
           path "/yanglib:modules-state/yanglib:module-set-id";
         }
         mandatory true;
         status deprecated;
         description
           "Contains the module-set-id value representing the
            set of modules and submodules supported at the server
            at the time the notification is generated.";
       }
     }

   }

   <CODE ENDS>






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5.  IANA Considerations

   RFC 7895 previously registered one URI in the IETF XML registry
   [RFC3688].  This document takes over this registration entry made by
   RFC 7895 and changes the Registrant to the IESG according to
   Section 4 in [RFC3688].

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

     Registrant Contact: The IESG.

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

   RFC 7895 previously registered one YANG module in the "YANG Module
   Names" registry [RFC6020] as follows:

     name:         ietf-yang-library
     namespace:    urn:ietf:params:xml:ns:yang:ietf-yang-library
     prefix:       yanglib
     reference:    RFC 7895

   This document takes over this registration entry made by RFC 7895.

6.  Security Considerations

   The YANG module specified in this document defines a schema for data
   that is accessed by 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 NETCONF access control model [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.

   Some of the readable data nodes 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 these data nodes.  These are the subtrees and data
   nodes and their sensitivity/vulnerability:

   The "/yang-library" subtree of the YANG library may help an attacker
   identify the server capabilities and server implementations with
   known bugs since the set of YANG modules supported by a server may
   reveal the kind of device and the manufacturer of the device.



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   Although some of this information may be available to all NETCONF
   users via the NETCONF <hello> message (or similar messages in other
   management protocols), this YANG module potentially exposes
   additional details that could be of some assistance to an attacker.
   Server vulnerabilities may be specific to particular modules, module
   revisions, module features, or even module deviations.  For example,
   if a particular operation on a particular data node is known to cause
   a server to crash or significantly degrade device performance, then
   the module list information will help an attacker identify server
   implementations with such a defect, in order to launch a denial-of-
   service attack on the device.

7.  Acknowledgments

   Contributions to this material by Andy Bierman are based upon work
   supported by the The Space & Terrestrial Communications Directorate
   (S&TCD) under Contract No.  W15P7T-13-C-A616.  Any opinions, findings
   and conclusions or recommendations expressed in this material are
   those of the author(s) and do not necessarily reflect the views of
   The Space & Terrestrial Communications Directorate (S&TCD).

8.  References

8.1.  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>.

   [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>.




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   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
              RFC 6991, DOI 10.17487/RFC6991, July 2013,
              <https://www.rfc-editor.org/info/rfc6991>.

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

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

   [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>.

   [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>.

   [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>.

8.2.  Informative References

   [I-D.ietf-netconf-nmda-netconf]
              Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "NETCONF Extensions to Support the Network
              Management Datastore Architecture", draft-ietf-netconf-
              nmda-netconf-07 (work in progress), October 2018.

   [I-D.ietf-netconf-nmda-restconf]
              Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "RESTCONF Extensions to Support the Network
              Management Datastore Architecture", draft-ietf-netconf-
              nmda-restconf-05 (work in progress), October 2018.

   [I-D.ietf-netmod-schema-mount]
              Bjorklund, M. and L. Lhotka, "YANG Schema Mount", draft-
              ietf-netmod-schema-mount-11 (work in progress), August
              2018.



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   [RFC5277]  Chisholm, S. and H. Trevino, "NETCONF Event
              Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008,
              <https://www.rfc-editor.org/info/rfc5277>.

   [RFC6470]  Bierman, A., "Network Configuration Protocol (NETCONF)
              Base Notifications", RFC 6470, DOI 10.17487/RFC6470,
              February 2012, <https://www.rfc-editor.org/info/rfc6470>.

   [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>.

   [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>.

   [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>.

   [RFC8345]  Clemm, A., Medved, J., Varga, R., Bahadur, N.,
              Ananthakrishnan, H., and X. Liu, "A YANG Data Model for
              Network Topologies", RFC 8345, DOI 10.17487/RFC8345, March
              2018, <https://www.rfc-editor.org/info/rfc8345>.

   [RFC8348]  Bierman, A., Bjorklund, M., Dong, J., and D. Romascanu, "A
              YANG Data Model for Hardware Management", RFC 8348,
              DOI 10.17487/RFC8348, March 2018, <https://www.rfc-
              editor.org/info/rfc8348>.

   [RFC8349]  Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for
              Routing Management (NMDA Version)", RFC 8349,
              DOI 10.17487/RFC8349, March 2018, <https://www.rfc-
              editor.org/info/rfc8349>.

Appendix A.  Summary of Changes from RFC 7895

   This document updates [RFC7895] in the following ways:

   o  Renamed document title from "YANG Module Library" to "YANG
      Library".






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   o  Added a new top-level "/yang-library" container to hold the entire
      YANG library providing information about module sets, schemas, and
      datastores.

   o  Refactored the "/modules-state" container into a new
      "/yang-library/module-set" list.

   o  Added a new "/yang-library/schema" list and a new "/yang-library/
      datastore" list.

   o  Added a set of new groupings as replacements for the deprecated
      groupings.

   o  Added a "yang-library-update" notification as a replacement for
      the deprecated "yang-library-change" notification.

   o  Deprecated the "/modules-state" tree.

   o  Deprecated the "/module-list" grouping.

   o  Deprecated the "/yang-library-change" notification.

Appendix B.  Example YANG Library Instance for a Basic Server

   The following example shows the YANG Library of a basic server
   implementing the "ietf-interfaces" [RFC8343] and "ietf-ip" [RFC8344]
   modules in the <running>, <startup>, and <operational> datastores and
   the "ietf-hardware" [RFC8348] module in the <operational> datastore.

   Newlines in leaf values are added for formatting reasons.

   <yang-library
       xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library"
       xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">

     <module-set>
       <name>config-modules</name>
       <module>
         <name>ietf-interfaces</name>
         <revision>2018-01-09</revision> <!-- RFC Ed. update this -->
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-interfaces
         </namespace>
       </module>
       <module>
         <name>ietf-ip</name>
         <revision>2018-01-09</revision> <!-- RFC Ed. update this -->
         <namespace>



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           urn:ietf:params:xml:ns:yang:ietf-ip
         </namespace>
       </module>
       <import-only-module>
         <name>ietf-yang-types</name>
         <revision>2013-07-15</revision>
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-yang-types
         </namespace>
       </import-only-module>
       <import-only-module>
         <name>ietf-inet-types</name>
         <revision>2013-07-15</revision>
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-inet-types
         </namespace>
       </import-only-module>
     </module-set>

     <module-set>
       <name>state-modules</name>
       <module>
         <name>ietf-hardware</name>
         <revision>2018-12-18</revision> <!-- RFC Ed. update this -->
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-hardware
         </namespace>
       </module>
       <import-only-module>
         <name>ietf-inet-types</name>
         <revision>2013-07-15</revision>
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-inet-types
         </namespace>
       </import-only-module>
       <import-only-module>
         <name>ietf-yang-types</name>
         <revision>2013-07-15</revision>
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-yang-types
         </namespace>
       </import-only-module>
       <import-only-module>
         <name>iana-hardware</name>
         <revision>2017-12-18</revision> <!-- RFC Ed. update this -->
         <namespace>
           urn:ietf:params:xml:ns:yang:iana-hardware
         </namespace>



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       </import-only-module>
     </module-set>

     <schema>
       <name>config-schema</name>
       <module-set>config-modules</module-set>
     </schema>
     <schema>
       <name>state-schema</name>
       <module-set>config-modules</module-set>
       <module-set>state-modules</module-set>
     </schema>

     <datastore>
       <name>ds:startup</name>
       <schema>config-schema</schema>
     </datastore>
     <datastore>
       <name>ds:running</name>
       <schema>config-schema</schema>
     </datastore>
     <datastore>
       <name>ds:operational</name>
       <schema>state-schema</schema>
     </datastore>

     <content-id>75a43df9bd56b92aacc156a2958fbe12312fb285</content-id>
   </yang-library>

Appendix C.  Example YANG Library Instance for an Advanced Server

   The following example extends the preceding Basic Server YANG Library
   example, by using modules from [RFC8345] and [RFC8349], to illustrate
   a slightly more advanced server that:

   o  Has a module with features only enabled in <operational>; the
      "ietf-routing module" is supported in <running>, <startup>, and
      <operational>, but the "multiple-ribs" and "router-id" features
      are only enabled in <operational>.  Hence the "router-id" leaf may
      be read but not configured.

   o  Supports a dynamic configuration datastore "example-ds-ephemeral",
      with only the "ietf-network" and "ietf-network-topology" modules
      configurable via a notional dynamic configuration protocol.

   o  Shows an example of datastore specific deviations.  The module
      "example-vendor-hardware-deviations" is included in the schema for




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      <operational> to remove data nodes that cannot be supported by the
      server.

   o  Shows how module-sets can be used to organize related modules
      together.

   <yang-library
       xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library"
       xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores"
       xmlns:ex-ds-eph="urn:example:ds-ephemeral">

     <module-set>
       <name>config-state-modules</name>
       <module>
         <name>ietf-interfaces</name>
         <revision>2018-01-09</revision> <!-- RFC Ed. update this -->
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-interfaces
         </namespace>
       </module>
       <module>
         <name>ietf-ip</name>
         <revision>2018-01-09</revision> <!-- RFC Ed. update this -->
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-ip
         </namespace>
       </module>
       <module>
         <name>ietf-routing</name>
         <revision>2018-01-25</revision> <!-- RFC Ed. update this -->
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-routing
         </namespace>
       </module>
       <import-only-module>
         <name>ietf-yang-types</name>
         <revision>2013-07-15</revision>
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-yang-types
         </namespace>
       </import-only-module>
       <import-only-module>
         <name>ietf-inet-types</name>
         <revision>2013-07-15</revision>
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-inet-types
         </namespace>
       </import-only-module>



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     </module-set>

     <module-set>
       <name>config-only-modules</name>
       <module>
         <name>ietf-routing</name>
         <revision>2018-01-25</revision> <!-- RFC Ed. update this -->
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-routing
         </namespace>
       </module>
     </module-set>

     <module-set>
       <name>dynamic-config-state-modules</name>
       <module>
         <name>ietf-network</name>
         <revision>2017-12-18</revision> <!-- RFC Ed. update this -->
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-network
         </namespace>
       </module>
       <module>
         <name>ietf-network-topology</name>
         <revision>2017-12-18</revision> <!-- RFC Ed. update this -->
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-network-topology
         </namespace>
       </module>
       <import-only-module>
         <name>ietf-inet-types</name>
         <revision>2013-07-15</revision>
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-inet-types
         </namespace>
       </import-only-module>
     </module-set>

     <module-set>
       <name>state-only-modules</name>
       <module>
         <name>ietf-hardware</name>
         <revision>2018-12-18</revision> <!-- RFC Ed. update this -->
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-hardware
         </namespace>
         <deviation>example-vendor-hardware-deviations</deviation>
       </module>



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       <module>
         <name>ietf-routing</name>
         <revision>2018-01-25</revision> <!-- RFC Ed. update this -->
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-routing
         </namespace>
         <feature>multiple-ribs</feature>
         <feature>router-id</feature>
       </module>
       <module>
         <name>example-vendor-hardware-deviations</name>
         <revision>2018-01-31</revision>
         <namespace>
           urn:example:example-vendor-hardware-deviations
         </namespace>
       </module>
       <import-only-module>
         <name>ietf-inet-types</name>
         <revision>2013-07-15</revision>
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-inet-types
         </namespace>
       </import-only-module>
       <import-only-module>
         <name>ietf-yang-types</name>
         <revision>2013-07-15</revision>
         <namespace>
           urn:ietf:params:xml:ns:yang:ietf-yang-types
         </namespace>
       </import-only-module>
       <import-only-module>
         <name>iana-hardware</name>
         <revision>2017-12-18</revision> <!-- RFC Ed. update this -->
         <namespace>
           urn:ietf:params:xml:ns:yang:iana-hardware
         </namespace>
       </import-only-module>
     </module-set>

     <schema>
       <name>config-schema</name>
       <module-set>config-state-modules</module-set>
       <module-set>config-only-modules</module-set>
     </schema>
     <schema>
       <name>dynamic-config-schema</name>
       <module-set>dynamic-config-state-modules</module-set>
     </schema>



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     <schema>
       <name>state-schema</name>
       <module-set>config-state-modules</module-set>
       <module-set>dynamic-config-state-modules</module-set>
       <module-set>state-only-modules</module-set>
     </schema>

     <datastore>
       <name>ds:startup</name>
       <schema>config-schema</schema>
     </datastore>
     <datastore>
       <name>ds:running</name>
       <schema>config-schema</schema>
     </datastore>
     <datastore>
       <name>ex-ds-eph:ds-ephemeral</name>
       <schema>dynamic-config-schema</schema>
     </datastore>
     <datastore>
       <name>ds:operational</name>
       <schema>state-schema</schema>
     </datastore>

     <content-id>14782ab9bd56b92aacc156a2958fbe12312fb285</content-id>
   </yang-library>

Authors' Addresses

   Andy Bierman
   YumaWorks

   Email: andy@yumaworks.com


   Martin Bjorklund
   Tail-f Systems

   Email: mbj@tail-f.com


   Juergen Schoenwaelder
   Jacobs University

   Email: j.schoenwaelder@jacobs-university.de






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   Kent Watsen
   Juniper Networks

   Email: kwatsen@juniper.net


   Robert Wilton
   Cisco Systems

   Email: rwilton@cisco.com









































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