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Versions: (draft-veillette-core-cool-library) 00 01

Internet Engineering Task Force                        M. Veillette, Ed.
Internet-Draft                                   Trilliant Networks Inc.
Intended status: Standards Track                           July 24, 2017
Expires: January 25, 2018


                    Constrained YANG Module Library
                  draft-veillette-core-yang-library-01

Abstract

   This document describes a YANG library that provides information
   about all the YANG modules used by a constrained network management
   server (e.g., a CoAP Management Interface (CoMI) server).  Simple
   caching mechanisms are provided to allow clients to minimize
   retrieval of this information.

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 January 25, 2018.

Copyright Notice

   Copyright (c) 2017 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.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Major differences between ietf-constrained-yang-library
           and ietf-yang-library . . . . . . . . . . . . . . . . . .   3
   2.  Terminology and Notation  . . . . . . . . . . . . . . . . . .   3
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Tree diagram  . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Description . . . . . . . . . . . . . . . . . . . . . . .   4
       3.2.1.  modules-state . . . . . . . . . . . . . . . . . . . .   5
       3.2.2.  modules-state/module-set-id . . . . . . . . . . . . .   5
       3.2.3.  modules-state/module  . . . . . . . . . . . . . . . .   5
   4.  YANG Module "ietf-constrained-yang-library" . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
     5.1.  YANG Module Registry  . . . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   The YANG library specified in this document is available to clients
   of a given server to discover the YANG modules supported by this
   constrained network management server.  A CoMI server provides a link
   to this library in the /mod.uri resource.  The following YANG module
   information is provided to client applications to fully utilize the
   YANG data modeling language:

   o  module list: The list of YANG modules implemented by a server,
      each module is identified by its assigned YANG Schema Item
      iDentifier (SID) and revision.

   o  submodule list: The list of YANG submodules included by each
      module, each submodule is identified by its assigned SID and
      revision.

   o  feature list: The list of features supported by the server, each
      feature is identified by its assigned SID.

   o  deviation list: The list of YANG modules used for deviation
      statements associated with each YANG module, each module is
      identified by its assigned SID and revision.






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

   YANG module ietf-constrained-yang-library targets the same
   functionality and shares the same approach as YANG module ietf-yang-
   library.  The following changes with respect to ietf-yang-library are
   specified to make ietf-constrained-yang-library compatible with SID
   [I-D.ietf-core-yang-cbor] used by CoMI [I-D.ietf-core-comi] and to
   improve its applicability to constrained devices and networks.

   o  YANG module ietf-constrained-yang-library extends the caching
      mechanism supported by ietf-yang-library to multiple servers.
      This is accomplished by supporting the identityref datatype for
      "module-set-id".  This enables the use of a managed identifier
      (i.e. a SID) to identify a specific assembly of YANG modules,
      deviations and features implemented by a group of constrained
      servers.

   o  Modules, sub-modules, deviations and features are identified using
      a numerical value (SID) instead of a string (yang-identifier).

   o  The "namespace" leaf, not required for SIDs, but mandatory in
      ietf-yang-library is not included in ietf-constrained-yang-
      library.

   o  Schemas can be located using the already available module or sub-
      module identifier (SID) and revision.  For this reason, support of
      module and sub-module schema URIs have been removed.

   o To minimize their size, each revision date is encoded in binary.

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]:

   o  module

   o  submodule

   o  feature

   o  deviation

   The following terms are defined in [I-D.ietf-core-yang-cbor]:



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   o  YANG Schema Item iDentifier (SID)

   The following terms are defined in [I-D.ietf-core-comi]:

   o  client

   o  server

   The following terms are used within this document:

   o  library: a collection of YANG modules used by a server.

3.  Overview

   The "ietf-constrained-yang-library" module provides information about
   the YANG library used by a given server.  This module is defined
   using YANG version 1 as defined by [RFC7950], but it supports the
   description of YANG modules written in any revision of YANG.

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 [I-D.ietf-netmod-yang-tree-diagrams].

   module: ietf-constrained-yang-library
      +--ro modules-state
         +--ro module-set-id    union
         +--ro module* [sid revision]
            +--ro sid                 sid
            +--ro revision            revision
            +--ro feature*            sid
            +--ro deviation* [sid revision]
            |  +--ro sid         sid
            |  +--ro revision    revision
            +--ro conformance-type    enumeration
            +--ro submodule* [sid revision]
               +--ro sid         sid
               +--ro revision    revision
   notifications:
      +---n yang-library-change
         +--ro module-set-id    -> /modules-state/module-set-id

3.2.  Description







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3.2.1.  modules-state

   This mandatory container specifies the module set identifier and the
   list of modules supported by the server.

3.2.2.  modules-state/module-set-id

   This mandatory leaf contains an identifier representing the current
   set of modules and submodules used by a server.  This identifier is
   server-specific when implemented as unit32 or can be used by multiple
   servers when implemented as identityref.  The value of this leaf MUST
   change whenever the set of modules and submodules in the library
   changes.  There is no requirement that the same set always results in
   the same 'module-set-id' value.

   This leaf allows a client to fetch the module list once, cache it,
   and only re-fetch it if the value of this leaf has been changed.

   If the value of this leaf changes, the server also generates a 'yang-
   library-change' notification, with the new value of 'module-set-id'.

3.2.3.  modules-state/module

   This mandatory list contains one entry for each YANG module supported
   by the server.  There MUST be an entry in this list for each revision
   of each YANG module that is used by the server.  It is possible for
   multiple revisions of the same module to be imported, in addition to
   an entry for the revision that is implemented by the server.

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@2017-01-20.yang"
   module ietf-constrained-yang-library {
     namespace
       "urn:ietf:params:xml:ns:yang:ietf-constrained-yang-library";
     prefix "lib";

     organization
       "IETF CORE (Constrained RESTful Environments) Working Group";

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

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




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        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 contains the list of YANG modules and submodules
       implemented by a server.

        Copyright (c) 2016 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.: replace XXXX with actual RFC number and remove
     // this note.

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

     revision 2017-01-20 {
       description
         "Initial revision.";
       reference
         "RFC XXXX: Constrained YANG Module Library.";
     }

     /*
      * Typedefs
      */

     typedef revision {
       type binary {
         length "4";
       }
       description



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         "Revision date encoded as a binary string as follow:
         - First byte = Year divided by 100
         - Second byte = Year modulo 100 (0 to 99)
         - Third byte = Month (1 = January to 12 = december)
         - Forth byte = Day (1 to 31)";
     }

     typedef sid {
       type uint64;
       description
         "Identifier assigned to different YANG items such as
         data nodes, RPCs and actions, notifications, modules,
         sub-modules, features and deviations.";
     }

     /*
      * Groupings
      */

     grouping identification-info {
       description
         "YANG modules and submodules identification information.";

       leaf sid {
         type sid;
         mandatory true;
         description
           "SID assigned to this module or submodule.";
       }

       leaf revision {
         type revision;
         description
           "Revision date assigned to this module or submodule.
           A zero-length binary string is used if no revision statement
           is present in the YANG module or submodule.";
       }
     }

     identity module-set {
         description
           "Base identity from which shared module-set identifiers
           are derived.";
       }

     /*
      * Operational state data nodes
      */



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     container modules-state {
       config false;
       description
         "Contains information about the different data models
         implemented by the server.";

       leaf module-set-id {
         type union {
           type uint32;
           type identityref {
             base "lib:module-set";
           }
         }
         mandatory true;
         description
           "Identifier representing the current set of modules
           and submodules listed in the 'module' list. This
           identifier is server-specific when implemented as
           unit32 or shared between multiple servers when
           implemented as identityref. The server MUST change
           the value of this leaf each time the content of the
           'module' list instance change.";
       }

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

         uses identification-info;

         leaf-list feature {
           type sid;
           description
             "List of YANG features from this module that are
             supported by the server, regardless whether
             they are defined in the module or in any included
             submodules.";
         }

         list deviation {
           key "sid revision";
           description
             "List of 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



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             same entry MAY appear within multiple 'module' entries.

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

           uses identification-info;
         }

         leaf conformance-type {
           type enumeration {
             enum implement {
               value 0;
               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
                 particular module, 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.";
             }
             enum import {
               value 1;
               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 MAY
                 exist. This can occur if multiple modules import the
                 same module, but specify different revision-dates in
                 the import statements.";
             }
           }
           mandatory true;
           description
             "Indicates the type of conformance the server is claiming
             for the YANG module identified by this entry.";
         }




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         list submodule {
           key "sid revision";
           description
             "Each entry represents one submodule within the
              parent module.";
           uses identification-info;
         }
       }
     }

     /*
      * Notifications
      */

     notification yang-library-change {
       description
         "Generated when the set of modules and submodules supported
         by the server has changed.";

       leaf module-set-id {
         type leafref {
           path "/lib:modules-state/lib:module-set-id";
         }
         mandatory true;
         description
           "Contains the module-set-id value representing the
           set of modules and submodules supported by the server
           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




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

6.  Security Considerations

   This YANG module is designed to be accessed via the CoMI protocol
   [I-D.ietf-core-comi].  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 identify server
   implementations with such a defect, in order to launch a denial of
   service attack on the device.

7.  Acknowledgments

   The YANG module defined by this memo have been derived from an
   already existing YANG module, ietf-yang-library [RFC7895], 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.

8.  References

8.1.  Normative References

   [I-D.ietf-core-comi]
              Veillette, M., Stok, P., Pelov, A., and A. Bierman, "CoAP
              Management Interface", draft-ietf-core-comi-01 (work in
              progress), July 2017.

   [I-D.ietf-core-yang-cbor]
              Veillette, M., Pelov, A., Somaraju, A., Turner, R., and A.
              Minaburo, "CBOR Encoding of Data Modeled with YANG",
              draft-ietf-core-yang-cbor-04 (work in progress), February
              2017.

   [I-D.ietf-netmod-yang-tree-diagrams]
              Bjorklund, M. and L. Berger, "YANG Tree Diagrams", draft-
              ietf-netmod-yang-tree-diagrams-01 (work in progress), June
              2017.



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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

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

8.2.  Informative References

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

Author's Address

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

   Phone: +14503750556
   Email: michel.veillette@trilliantinc.com


























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