Network Working Group                                         A. Bierman
Internet-Draft                                                 YumaWorks
Intended status: Standards Track                            M. Bjorklund
Expires: April 20, June 17, 2016                                    Tail-f Systems
                                                               K. Watsen
                                                        Juniper Networks
                                                        October 18,
                                                       December 15, 2015

                          YANG Module Library
                   draft-ietf-netconf-yang-library-02
                   draft-ietf-netconf-yang-library-03

Abstract

   This document describes a YANG library, which provides information
   about all the YANG modules used by a device to represent management
   and protocol information.  A YANG library can be shared by multiple
   protocols within the same device.  Simple caching mechanisms are
   needed 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 April 20, June 17, 2016.

Copyright Notice

   Copyright (c) 2015 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
       1.1.1.  NETCONF . . . . . . . . . . . . . . . . . . . . . . .   3
       1.1.2.  YANG  . . . . . . . . . . . . . . . . . . . . . . . .   3
       1.1.3.  Terms . . . . . . . . . . . . . . . . . . . . . . . .   3
       1.1.4.  Tree Diagrams . . . . . . . . . . . . . . . . . . . .   4
   2.  YANG Module Library . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  modules . . . . . . . . . . . . . . . . . . . . . . . . .   4   5
       2.1.1.  modules/module-set-id . . . . . . . . . . . . . . . .   5
       2.1.2.  modules/yang-protocol . . . . . . . . . . . . . . . .   5
       2.1.3.  modules/module  . . . . . . . . . . . . . . . . . . .   5
     2.2.  YANG Library Module . . . . . . . . . . . . . . . . . . .   5   6
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10  12
     3.1.  YANG Module Registry  . . . . . . . . . . . . . . . . . .  10  12
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  11  12
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11  13
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .  11  13
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  12  13
     A.1.  01  v02 to 02 v03  . . . . . . . . . . . . . . . . . . . . . . . .  12  13
     A.2.  00  v01 to 01 v02  . . . . . . . . . . . . . . . . . . . . . . . .  12  14
     A.3.  v00 to v01  . . . . . . . . . . . . . . . . . . . . . . .  14
     A.4.  draft-ietf-netconf-restconf-03 to 00 v00 . . . . . . . . . .  12  14
   Appendix B.  Open Issues  . . . . . . . . . . . . . . . . . . . .  12  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12  14

1.  Introduction

   There is a need for standard mechanisms to identify the YANG modules
   and submodules that are in use by a server that utilizes YANG-based
   data abstractions.  If a large number of YANG modules are utilized by
   the server, then the YANG library information needed can be
   relatively large.  This information changes very infrequently, so it
   is important that clients be able to cache the YANG library and
   easily identify if their cache is out-of-date.

   YANG library information can be different on every server, and can
   change at run-time or across a server reboot.  Typically, a firmware
   upgrade is required to change the set of YANG modules used by a
   server.

   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 mandatory YANG module name MUST be unique within a YANG
      library.

   o  revision: Each YANG module and submodule within the library has a
      revision.  This is derived from the most recent revision statement
      within the module or submodule.  If no such revision statement
      exists, the module's or submodule's revision is the empty string.

   o  submodule list: The name and revision of each submodule used by
      the module MUST be identified.

   o  feature list: The name of each YANG feature supported by the
      server MUST be identified.

   o  deviation list: The name of each YANG module used for deviation
      statements SHOULD be identified.

1.1.  Terminology

   The keywords "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].

1.1.1.  NETCONF

   The following terms are defined in [RFC6241]:

   o  client

   o  server

1.1.2.  YANG

   The following terms are defined in [RFC6020]:

   o  module

   o  submodule

1.1.3.  Terms

   The following terms are used within this document:

   o  YANG library: a collection of YANG modules and submodules used by
      a server

1.1.4.  Tree Diagrams

   A simplified graphical representation of the data model is used in
   this document.  The meaning of the symbols in these diagrams is as
   follows:

   o  Brackets "[" and "]" enclose list keys.

   o  Abbreviations before data node names: "rw" means configuration
      data (read-write) and "ro" state data (read-only).

   o  Symbols after data node names: "?" means an optional node, "!"
      means a presence container, and "*" denotes a list and leaf-list.

   o  Parentheses enclose choice and case nodes, and case nodes are also
      marked with a colon (":").

   o  Ellipsis ("...") stands for contents of subtrees that are not
      shown.

2.  YANG Module Library

   The "ietf-yang-library" module provides information about the YANG
   library used by a server.

   YANG Tree Diagram for "ietf-yang-library" module:

   +--ro modules
      +--ro module-set-id    string
      +--ro yang-protocol*   identityref
      +--ro module* [name revision]
         +--ro name                   yang:yang-identifier
         +--ro revision               union
         +--ro schema?                inet:uri
         +--ro namespace              inet:uri
         +--ro feature*               yang:yang-identifier
         +--ro deviation* [name revision]
         |  +--ro name        yang:yang-identifier
         |  +--ro revision    union
         +--ro conformance            enumeration
         +--ro submodules
         |  +--ro submodule* [name revision]
         |     +--ro name        yang:yang-identifier
         |     +--ro revision    union
         |     +--ro schema?     inet:uri
         +--ro restricted-protocol*   identityref

2.1.  modules

   This mandatory container holds the identifiers for the YANG data
   model modules supported by the server.

2.1.1.  modules/module-set-id

   This mandatory leaf contains a unique implementation-specific
   identifier representing the current set of modules and submodules.
   This can for example be a checksum of all modules and submodules.

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

2.1.2.  modules/yang-protocol

   This leaf-list identifies the YANG-based protocols that are using the
   YANG library.  It allows an operator to be aware that multi-protocol
   conflicts could potentially occur on a managed device.

   A corresponding leaf-list called 'restricted-protocol' is defined in
   the module entry to identify modules that are not supported by one or
   more protocols.

2.1.3.  modules/module
   This mandatory list contains one entry for each YANG data model
   module supported by the server.  There MUST be an entry in this list
   for every YANG module that is used by the server.

2.2.  YANG Library Module

   The "ietf-yang-library" module defines monitoring information for the
   YANG modules used by a server.

   The "ietf-yang-types" and "ietf-inet-types" modules from [RFC6991]
   are used by this module for some type definitions.

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

   <CODE BEGINS> file "ietf-yang-library@2015-10-18.yang"

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

     import ietf-yang-types {
       prefix yang;
     }
     import ietf-inet-types {
       prefix inet;
     }

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

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

        WG Chair: Mehmet Ersue
                  <mailto:mehmet.ersue@nsn.com>

        WG Chair: Mahesh Jethanandani
                  <mailto:mjethanandani@gmail.com>

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

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

        Editor:   Kent Watsen
                  <mailto:kwatsen@juniper.net>";

     description
       "This module contains monitoring information about the YANG
        modules and submodules that are used within a YANG-based
        server.

        Copyright (c) 2015 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.: remove this note
     // Note: extracted from draft-ietf-netconf-yang-library-02.txt draft-ietf-netconf-yang-library-03.txt

     // RFC Ed.: update the date below with the date of RFC publication
     // and remove this note.
     revision 2015-10-18 2015-12-08 {
       description
         "Initial revision.";
       reference
         "RFC XXXX: YANG Module Library.";
     }

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

     identity yang-protocol {
       description
        "The base for all YANG-based protocol identifiers.";
     }
     identity netconf1.0 {
       base yang-protocol;
       description "Version 1.0 of the NETCONF protocol";
       reference "RFC 4271";
     }

     identity netconf1.1 {
       base yang-protocol;
       description "Version 1.1 of the NETCONF protocol";
       reference "RFC 6241";
     }

     identity restconf1.0 {
       base yang-protocol;
       description "Version 1.0 of the RESTCONF protocol";
       reference "draft-ietf-netconf-restconf";
     }

     grouping module module-list {
       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 {
         description
           "Common parameters for YANG modules and submodules.";

         leaf name {
           type yang:yang-identifier;
           description
             "The YANG module or submodule name.";
         }
         leaf revision {
           type union {
             type revision-identifier;
             type string { length 0; }
           }
           description
             "The YANG module or submodule revision date.
              An empty string is used if no revision statement
              is present in the YANG module or submodule.";
         }
       }

       grouping schema-leaf {
         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";
         description
           "Each entry represents one module currently
            supported by the server.";

         uses common-leafs;
         uses schema-leaf;

         leaf namespace {
           type inet:uri;
           mandatory true;
           description
             "The XML namespace identifier for this module.";
         }
         leaf-list feature {
           type yang:yang-identifier;
           description
             "List of YANG feature names from this module that are
              supported by the server.";
         }
         list deviation {
           key "name revision";
           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.

              If the deviation module is available for download
              from the server then a 'module' entry for that module
              will exist, with the same name and revision values.
              The 'conformance' value will be 'implement' for
              the deviation module.";
           uses common-leafs;

         }
         leaf conformance {
           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 1.1 modules, there MUST NOT be more than one
                  module entry with conformance 'implement' for a
                  particular module name.

                  For YANG 1.1 modules that use the import statement
                  without specifying a revision date, the implemented
                  revision of the imported module MUST be used.
                  If the imported module is not implemented, then
                  the most recent revision of the imported module
                  used by the server (and contained in the module list)
                  MUST be used.

                  For YANG 1.0 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.

                  For import statements that do not specify a revision
                  date, the most recent revision in the library SHOULD
                  be used by the server.";
             }
           }
           mandatory true;
           description
             "Indicates the type of conformance the server is claiming
              for the YANG module identified by this entry.";
         }
         container submodules {
           description
             "Contains information about all the submodules used
              by the parent module entry";

           list submodule {
             key "name revision";
             description
               "Each entry represents one submodule within the
                parent module.";
             uses common-leafs;
             uses schema-leaf;
           }
         }
         leaf-list restricted-protocol {
           type identityref {
             base yang-protocol;
           }
           description
            "Identifies a protocol that does not use the module
             described by this module instance.";
         }
       } // list module
     }  // grouping module

     container modules {
       config false;
       description
         "Contains YANG module monitoring information.";

       leaf module-set-id {
         type string;
         mandatory true;
         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.";
       }

       leaf-list yang-protocol {
         type identityref {
           base yang-protocol;
         }
         description
          "Identifies a protocol that is using modules described
           in this library.  There SHOULD be one instance of
           this object for each protocol for each YANG-based
           protocol using this library.";
       }

       uses module; module-list;
     }

   }

   <CODE ENDS>

3.  IANA Considerations

3.1.  YANG Module Registry

   This document registers one URI in the IETF XML registry [RFC3688].
   Following the format in RFC 3688, the following registration is
   requested to be made.

     URI: urn:ietf:params:xml:ns:yang:ietf-yang-library
     Registrant Contact: The NETMOD WG of the IETF.
     XML: N/A, the requested URI is an XML namespace.

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

   name:         ietf-yang-library
   namespace:    urn:ietf:params:xml:ns:yang:ietf-yang-library
   prefix:       yanglib
   // RFC Ed.: replace XXXX with RFC number and remove this note
   reference:    RFC XXXX

4.  Security Considerations

   The YANG module defined in this memo is designed to be accessed via
   the NETCONF protocol [RFC6241].  The lowest NETCONF layer is the
   secure transport layer and the mandatory-to-implement secure
   transport is SSH [RFC6242].

   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:

   o  /modules/module: The module list used in a server implementation
      may help an attacker 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.

5.  Acknowledgements

   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).

6.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, June 2011.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, June 2011.

   [RFC6991]  Schoenwaelder, J., "Common YANG Data Types", RFC 6991,
              July 2013.

Appendix A.  Change Log

    -- RFC Ed.: remove this section before publication.

A.1.  01  v02 to v03

   o  added yang-protocol identity
   o  added identities for NETCONF and RESTCONF protocols

   o  added yang-protocol leaf-list to 02 /modules

   o  added restricted-protocol leaf-list to /modules/module

A.2.  v01 to v02

   o  clarify 'implement' conformance for YANG 1.1 modules

A.2.  00

A.3.  v00 to 01 v01

   o  change conformance leaf to enumeration

   o  filled in security considerations section

A.3.

A.4.  draft-ietf-netconf-restconf-03 to 00 v00

   o  moved ietf-yang-library from RESTCONF draft to new draft

Appendix B.  Open Issues

    -- RFC Ed.: remove this section before publication.

   The YANG Library issue tracker can be found here:

   https://github.com/netconf-wg/yang-library/issues [1]

Authors' Addresses

   Andy Bierman
   YumaWorks

   Email: andy@yumaworks.com

   Martin Bjorklund
   Tail-f Systems

   Email: mbj@tail-f.com

   Kent Watsen
   Juniper Networks

   Email: kwatsen@juniper.net