Constrained YANG Module Library
draft-veillette-core-yang-library-04

Internet Engineering Task Force                        M. Veillette, Ed.
Internet-Draft                                   Trilliant Networks Inc.
Intended status: Standards Track                          I. Petrov, Ed.
Expires: September 30, 2019                                       Acklio
                                                          March 29, 2019

                    Constrained YANG Module Library
                  draft-veillette-core-yang-library-04

Abstract

   This document describes a constrained version of the YANG library
   that provides information about the YANG modules, datastores, and
   datastore schemas used by a constrained network management server
   (e.g., a CORECONF server).

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 30, 2019.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology and Notation  . . . . . . . . . . . . . . . . . .   2
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Tree diagram  . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Major differences between ietf-constrained-yang-library
           and ietf-yang-library . . . . . . . . . . . . . . . . . .   4
   4.  YANG Module "ietf-constrained-yang-library" . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     5.1.  YANG Module Registry  . . . . . . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  13
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   There is a need for a standard mechanism to expose which YANG
   modules, datastores and datastore schemas are in use by a constrained
   network management server.  This document defines the YANG module
   'ietf-constrained-yang-library' that provides this information.

   YANG module 'ietf-constrained-yang-library' shares the same data
   model and objectives as 'ietf-yang-library', only datatypes and
   mandatory requirements have been updated to minimize its size to
   allow its implementation by Constrained Nodes and/or Constrained
   Networks as defined by [RFC7228].  To review the list of objectives
   and proposed data model, please refer to [RFC8525] section 2 and 3.

2.  Terminology and Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   The following terms are defined in [RFC7950]: client, deviation,
   feature, module, submodule and server.

   The following term is defined in [I-D.ietf-core-sid]: YANG Schema
   Item iDentifier (SID).

   The following terms are defined in [RFC8525]: YANG library and YANG
   library checksum.

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3.  Overview

   The conceptual model of the YANG library is depicted in Figure 1.

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

              Figure 1: Conceptual model of the YANG library

   It's expected that most constrained network management servers have
   one datastore (e.g. a unified datastore).  However, some servers may
   have multiples datastore as described by NMDA [RFC8342].  The YANG
   library data model supports both cases.

   In this model, every datastore has an associated datastore schema,
   which is the union of module sets, which is a collection of modules.
   Multiple datastores may refer to the same datastore schema and
   individual datastore schemas may share module sets.

   For each module, the YANG library provides:

   o  the YANG module identifier (i.e.  SID)

   o  its revision

   o  its list of submodules

   o  its list of imported modules

   o  its set of features and deviations

   YANG module namespace and location are also supported, but their
   implementation is not recommended for constrained servers.

3.1.  Tree diagram

   The tree diagram of YANG module ietf-constrained-yang-library is
   provided below.  This graphical representation of a YANG module is
   defined in [RFC8340].

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   module: ietf-constrained-yang-library
     +--ro yang-library
        +--ro module-set* [index]
        |  +--ro index                 uint8
        |  +--ro module* [identifier]
        |  |  +--ro identifier    sid:sid
        |  |  +--ro revision?     revision-identifier
        |  |  +--ro namespace?    inet:uri
        |  |  +--ro location*     inet:uri
        |  |  +--ro submodule* [identifier]
        |  |  |  +--ro identifier    sid:sid
        |  |  |  +--ro revision?     revision-identifier
        |  |  |  +--ro location*     inet:uri
        |  |  +--ro feature*      sid:sid
        |  |  +--ro deviation*    -> ../../module/identifier
        |  +--ro import-only-module* [identifier revision]
        |     +--ro identifier    sid:sid
        |     +--ro revision      union
        |     +--ro namespace?    inet:uri
        |     +--ro location*     inet:uri
        |     +--ro submodule* [identifier]
        |        +--ro identifier    sid:sid
        |        +--ro revision?     revision-identifier
        |        +--ro location*     inet:uri
        +--ro schema* [index]
        |  +--ro index         uint8
        |  +--ro module-set*   -> ../../module-set/index
        +--ro datastore* [identifier]
        |  +--ro identifier    ds:datastore-ref
        |  +--ro schema        -> ../../schema/index
        +--ro checksum      binary

     notifications:
       +---n yang-library-update
          +--ro checksum    -> /yang-library/checksum

3.2.  Major differences between ietf-constrained-yang-library and ietf-
      yang-library

   The list of changes between the reference data model 'ietf-yang-
   library' and its constrained version 'ietf-constrained-yang-library'
   are listed below:

   o  module-set 'name' and schema 'name' are implemented using an 8
      bits unsigned integer and renamed 'index'.

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   o  module 'name', submodule 'name' and datastore 'name' are
      implemented using a SID (i.e. an unsigned integer) and renamed
      'identifier'.

   o  'feature' and 'deviation' are implemented using a SID (i.e. an
      unsigned integer).

   o  'revision' fields are implemented using a 4 bytes binary string.

   o  the mandatory requirement of the 'namespace' fields is removed,
      and implementation is not recommended.  SIDs used by constrained
      devices and protocols don't require namespaces.

   o  the implementation of the 'location' fields are not recommended,
      the use of the module SID as the handle to retrieve the associated
      YANG module is proposed instead.

4.  YANG Module "ietf-constrained-yang-library"

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

<CODE BEGINS> file "ietf-constrained-yang-library@2019-03-28.yang"
module ietf-constrained-yang-library {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-constrained-yang-library";
  prefix "yanglib";

  // RFC Ed.: update ietf-core-sid reference.

  import ietf-sid-file {
    prefix sid;
    reference "I-D.ietf-core-sid";
  }
  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 (NMDA).";
  }

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

  contact
    "WG Web:   <http://datatracker.ietf.org/wg/core/>

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     WG List:  <mailto:core@ietf.org>

     WG Chair: Carsten Bormann
               <mailto:cabo@tzi.org>

     WG Chair: Jaime Jimenez
               <mailto:jaime.jimenez@ericsson.com>

     Editor:   Michel Veillette
               <mailto:michel.veillette@trilliantinc.com>";

  description
    "This module provides information about the YANG modules,
     datastores, and datastore schemas implemented by a constrained
     network 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 reference.

  revision 2019-03-28 {
    description
      "Second revision.";
    reference
      "[I-D.veillette-core-yang-library]  Constrained YANG Module Library";
  }

  revision 2018-09-21 {
    description
      "Initial revision.";
    reference
      "[I-D.veillette-core-yang-library]  Constrained YANG Module Library";
  }

  /*
   * Typedefs
   */

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  typedef revision-identifier {
    type binary {
      length "4";
    }
    description
      "Revision date encoded as a binary string, each nibble representing
       a digit of the of revision date. For example, revision 2018-09-21
       is encoded as 0x20 0x18 0x09 0x21.";
  }

  /*
   * Groupings
   */

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

    leaf identifier {
      type sid:sid;
      mandatory true;
      description
        "SID assigned to this module or submodule.";
    }
    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 is present in the model to keep the alignment with
         'ietf-yang-library'. Support of this leaf in constrained
         devices is not necessarily required, nor expected. It is
         recommended that clients used the module or sub-module SID

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         as the handle used to retrieve the corresponding YANG module";
    }
  }

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

    leaf-list feature {
      type sid:sid;
      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 {
        path "../../module/identifier";
      }
      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 index {
      type uint8;
      description
        "An arbitrary number assigned of the module set.";
    }
    list module {
      key "identifier";
      description
        "An entry in this list represents a module implemented by the

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         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;
        description
          "The XML namespace identifier for this module.
           This leaf is present in the model to keep the alignment
           with 'ietf-yang-library'. Support of this leaf in
           constrained devices is not required, nor expected.";
      }

      uses location-leaf-list;

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

      uses implementation-parameters;
    }
    list import-only-module {
      key "identifier 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 identifier {
        type sid:sid;
        description
          "The YANG module name.";
      }
      leaf revision {
        type union {

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          type revision-identifier;
          type string {
            length 0;
          }
        }
        description
          "The YANG module revision date.";
      }
      leaf namespace {
        type inet:uri;
        description
          "The XML namespace identifier for this module.
           This leaf is present in the model to keep the alignment
           with 'ietf-yang-library'. Support of this leaf in
           constrained devices is not required, nor expected.";
      }

      uses location-leaf-list;

      list submodule {
        key "identifier";
        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 index;
      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;
    }

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    list schema {
      key "index";
      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 index {
        type uint8;
        description
          "An arbitrary reference number assigned to the schema.";
      }
      leaf-list module-set {
        type leafref {
          path "../../module-set/index";
        }
        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 "identifier";
      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 identifier {
        type ds:datastore-ref;
        description
          "The identity of the datastore.";
      }
      leaf schema {
        type leafref {
          path "../../schema/index";

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        }
        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.";

    uses yang-library-parameters;

    leaf checksum {
      type binary;
      mandatory true;
      description
        "A server-generated checksum or digest 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/checksum', has
         changed.";
    }
  }

  /*
   * Notifications
   */

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

    leaf checksum {
      type leafref {
        path "/yanglib:yang-library/yanglib:checksum";
      }
      mandatory true;
      description

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        "Contains the YANG library checksum or digest for the updated
         YANG library at the time the notification is generated.";
    }
  }
}
<CODE ENDS>

5.  IANA Considerations

5.1.  YANG Module Registry

   This document registers one YANG module in the YANG Module Names
   registry [RFC7950].

   name: ietf-constrained-yang-library

   namespace: urn:ietf:params:xml:ns:yang:ietf-constrained-yang-library

   prefix: lib

   reference: RFC XXXX

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

6.  Security Considerations

   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 to these data nodes.

   Specifically, the 'module' list may help an attacker to identify the
   server capabilities and server implementations with known bugs.
   Server vulnerabilities may be specific to particular modules, module
   revisions, module features, or even module deviations.  This
   information is included in each module entry.  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 to identify server
   implementations with such a defect, in order to launch a denial of
   service attack on these devices.

7.  Acknowledgments

   The YANG module defined by this memo have been derived from an
   already existing YANG module, ietf-yang-library [RFC8525], we will
   like to thanks to the authors of this YANG module.  A special thank
   also to Andy Bierman for his initial recommendations for the creation
   of this YANG module.

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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>.

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,
              <https://www.rfc-editor.org/info/rfc7228>.

   [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>.

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

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

   [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>.

8.2.  Informative References

   [I-D.ietf-core-sid]
              Veillette, M., Pelov, A., and I. Petrov, "YANG Schema Item
              iDentifier (SID)", draft-ietf-core-sid-06 (work in
              progress), March 2019.

Authors' Addresses

   Michel Veillette (editor)
   Trilliant Networks Inc.
   610 Rue du Luxembourg
   Granby, Quebec  J2J 2V2
   Canada

   Email: michel.veillette@trilliantinc.com

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   Ivaylo Petrov (editor)
   Acklio
   1137A avenue des Champs Blancs
   Cesson-Sevigne, Bretagne  35510
   France

   Email: ivaylo@ackl.io

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