GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc7895

Internet Engineering Task Force (IETF) A. Bierman Request for Comments: 7895 YumaWorks Category: Standards Track M. Bjorklund ISSN: 2070-1721 Tail-f Systems

                                                             K. Watsen
                                                      Juniper Networks
                                                             June 2016
                        YANG Module Library

Abstract

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

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7895.

Copyright Notice

 Copyright (c) 2016 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.

Bierman, et al. Standards Track [Page 1] RFC 7895 YANG Library June 2016

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   1.2.  Tree Diagrams . . . . . . . . . . . . . . . . . . . . . .   3
 2.  YANG Module Library . . . . . . . . . . . . . . . . . . . . .   4
   2.1.  modules-state . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.1.  modules-state/module-set-id . . . . . . . . . . . . .   4
     2.1.2.  modules-state/module  . . . . . . . . . . . . . . . .   5
   2.2.  YANG Library Module . . . . . . . . . . . . . . . . . . .   5
 3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   3.1.  YANG Module Registry  . . . . . . . . . . . . . . . . . .  11
 4.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
 5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
   5.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
   5.2.  Informative References  . . . . . . . . . . . . . . . . .  12
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  13
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1. Introduction

 There is a need for standard mechanisms to identify the YANG modules
 and submodules that are in use by a server that implements YANG data
 models.  If a large number of YANG modules are utilized by the
 server, then the YANG library contents needed can be relatively
 large.  This information changes very infrequently, so it is
 important that clients be able to cache the YANG library contents and
 easily identify whether their cache is out of date.
 YANG library information can be different on every server and can
 change at runtime or across a server reboot.
 If the server implements multiple protocols to access the YANG-
 defined data, each such protocol has its own conceptual instantiation
 of the YANG library.
 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: 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 zero-length
    string.

Bierman, et al. Standards Track [Page 2] RFC 7895 YANG Library June 2016

 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 MUST 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].
 The following terms are defined in [RFC6241]:
 o  client
 o  server
 The following terms are defined in [YANG1.1]:
 o  module
 o  submodule
 The following terms are used within this document:
 o  YANG library: A collection of YANG modules and submodules used by
    a server.

1.2. 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.

Bierman, et al. Standards Track [Page 3] RFC 7895 YANG Library June 2016

 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.  This module is defined using YANG version
 1, but it supports the description of YANG modules written in any
 revision of YANG.
 Following is the YANG Tree Diagram for the "ietf-yang-library"
 module:
    +--ro modules-state
       +--ro module-set-id    string
       +--ro module* [name revision]
          +--ro name                yang:yang-identifier
          +--ro revision            union
          +--ro schema?             inet:uri
          +--ro namespace           inet:uri
          +--ro feature*            yang:yang-identifier
          +--ro deviation* [name revision]
          |  +--ro name        yang:yang-identifier
          |  +--ro revision    union
          +--ro conformance-type    enumeration
          +--ro submodule* [name revision]
             +--ro name        yang:yang-identifier
             +--ro revision    union
             +--ro schema?     inet:uri

2.1. modules-state

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

2.1.1. modules-state/module-set-id

 This mandatory leaf contains a unique implementation-specific
 identifier representing the current set of modules and submodules on
 a specific server.  The value of this leaf MUST change whenever the
 set of modules and submodules in the YANG library changes.  There is
 no requirement that the same set always results in the same "module-
 set-id" value.

Bierman, et al. Standards Track [Page 4] RFC 7895 YANG Library June 2016

 This leaf allows a client to fetch the module list 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-change" notification, with the new value of
 "module-set-id".
 Note that for a NETCONF server that implements YANG 1.1 [YANG1.1], a
 change of the "module-set-id" value results in a new value for the
 :yang-library capability defined in [YANG1.1].  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
 "module-set-id" changes.

2.1.2. modules-state/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 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.

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.
 <CODE BEGINS> file "ietf-yang-library@2016-06-21.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;
   }

Bierman, et al. Standards Track [Page 5] RFC 7895 YANG Library June 2016

   organization
     "IETF NETCONF (Network Configuration) Working Group";
   contact
     "WG Web:   <https://datatracker.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) 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 7895; see
      the RFC itself for full legal notices.";
   revision 2016-06-21 {
     description
       "Initial revision.";
     reference
       "RFC 7895: YANG Module Library.";
   }

Bierman, et al. Standards Track [Page 6] RFC 7895 YANG Library June 2016

   /*
    * Typedefs
    */
   typedef revision-identifier {
     type string {
       pattern '\d{4}-\d{2}-\d{2}';
     }
     description
       "Represents a specific date in YYYY-MM-DD format.";
   }
   /*
    * Groupings
    */
   grouping 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.
            A zero-length 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.";

Bierman, et al. Standards Track [Page 7] RFC 7895 YANG Library June 2016

       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 revision of 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, regardless of whether they are
            defined in the module or any included submodule.";
       }
       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.
            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;

Bierman, et al. Standards Track [Page 8] RFC 7895 YANG Library June 2016

       }
       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
                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;
         description
           "Indicates the type of conformance the server is claiming
            for the YANG module identified by this entry.";
       }
       list submodule {
         key "name revision";
         description
           "Each entry represents one submodule within the
            parent module.";
         uses common-leafs;
         uses schema-leaf;
       }
     }
   }

Bierman, et al. Standards Track [Page 9] RFC 7895 YANG Library June 2016

   /*
    * Operational state data nodes
    */
   container modules-state {
     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.";
     }
     uses module-list;
   }
   /*
    * 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 "/yanglib:modules-state/yanglib:module-set-id";
       }
       mandatory true;
       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>

Bierman, et al. Standards Track [Page 10] RFC 7895 YANG Library June 2016

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 has been
 made.
   URI: urn:ietf:params:xml:ns:yang:ietf-yang-library
   Registrant Contact: The NETCONF WG of the IETF.
   XML: N/A, the requested URI is an XML namespace.
 This document registers one YANG module in the "YANG Module Names"
 registry [RFC6020].
   name:         ietf-yang-library
   namespace:    urn:ietf:params:xml:ns:yang:ietf-yang-library
   prefix:       yanglib
   reference:    RFC 7895

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].  The NETCONF access control model
 [RFC6536] provides the means to restrict access for particular
 NETCONF users to a pre-configured subset of all available NETCONF
 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:
 o  /modules-state/module: The module list used in a server
    implementation may help an attacker identify the server
    capabilities and server implementations with known bugs.  Although
    some of this information may be available to all 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.  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

Bierman, et al. Standards Track [Page 11] RFC 7895 YANG Library June 2016

    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. References

5.1. 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,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
            DOI 10.17487/RFC3688, January 2004,
            <http://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,
            <http://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,
            <http://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,
            <http://www.rfc-editor.org/info/rfc6242>.
 [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
            Protocol (NETCONF) Access Control Model", RFC 6536,
            DOI 10.17487/RFC6536, March 2012,
            <http://www.rfc-editor.org/info/rfc6536>.
 [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
            RFC 6991, DOI 10.17487/RFC6991, July 2013,
            <http://www.rfc-editor.org/info/rfc6991>.

5.2. Informative References

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

Bierman, et al. Standards Track [Page 12] RFC 7895 YANG Library June 2016

 [RFC6470]  Bierman, A., "Network Configuration Protocol (NETCONF)
            Base Notifications", RFC 6470, DOI 10.17487/RFC6470,
            February 2012, <http://www.rfc-editor.org/info/rfc6470>.
 [YANG1.1]  Bjorklund, M., "The YANG 1.1 Data Modeling Language", Work
            in Progress, draft-ietf-netmod-rfc6020bis-12, April 2016.

Acknowledgements

 Contributions to this material by Andy Bierman are based upon work
 supported by the Space & Terrestrial Communications Directorate
 (S&TCD) under Contract No. W15P7T-13-C-A616.  Any opinions, findings,
 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).

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

Bierman, et al. Standards Track [Page 13]

/data/webs/external/dokuwiki/data/pages/rfc/rfc7895.txt · Last modified: 2016/06/30 17:31 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki