Network Working Group A. Bierman
Internet-Draft YumaWorks
Obsoletes: rfc7895 (if approved) M. Bjorklund
Intended status: Standards Track Tail-f Systems
Expires: December 2, 2017 K. Watsen
Juniper Networks
May 31, 2017

YANG Module Library


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 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

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This Internet-Draft will expire on December 2, 2017.

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 ( 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

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so it is important that clients be able to cache the YANG library contents and easily identify whether their cache is out of date.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:

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]:

The following terms are defined in [RFC7950]:

The following terms are used within this document:

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:

1.3. Summary of Changes from RFC 7895

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

This document updates the "ietf‑yang‑library" module in RFC 7895 in the following ways:

2. YANG Module Library

The "ietf‑yang‑library" module provides information about the modules 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 datastores
    |  +--ro datastore*   identityref
    +--ro modules-state
       +--ro module-set-id    string
       +--ro module* [name revision]
          +--ro name                yang:yang-identifier
          +--ro revision            union
          +--ro datastore*          identityref
          +--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. datastores

This mandatory container holds the identifiers of the datastores supported by the server.

2.2. modules-state

[DISCUSS: should the above be renamed to "modules" per NMDA guidelines?]

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

2.2.1. 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.

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 [RFC7950], a change of the "module‑set‑id" value results in a new value for the :yang-library capability defined in [RFC7950]. 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.

2.2.2. 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.

2.3. YANG Library Module

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

The modules "ietf‑yang‑types" and "ietf‑inet‑types" from [RFC6991] and the module "ietf‑datastores" from [I-D.ietf-netmod-revised-datastores] 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@2017-04-21.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;
  import ietf-datastores {
    prefix ds;

    "IETF NETCONF (Network Configuration) Working Group";

    "WG Web:   <>
     WG List:  <>

     Editor:   Andy Bierman

     Editor:   Martin Bjorklund

     Editor:   Kent Watsen

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

     Copyright (c) 2017 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

     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 RFC publication
  // and remove this note.
  revision 2017-04-29 {
      "Updated to add support for indicating which datastores
       a server supports and, on a per-module basis,  which
       datastores the module is accessible in.";
      "RFC XXXX: YANG Module Library.";

  revision 2016-06-21 {
      "Initial revision.";
      "RFC 7895: YANG Module Library.";

   * Typedefs

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

   * Groupings

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

    grouping common-leafs {
        "Common parameters for YANG modules and submodules.";

      leaf name {
        type yang:yang-identifier;
          "The YANG module or submodule name.";
      leaf revision {
        type union {
          type revision-identifier;
          type string { length 0; }
          "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 {
        "Common schema leaf parameter for modules and submodules.";

      leaf schema {
        type inet:uri;
          "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";
        "Each entry represents one revision of one module
         currently supported by the server.";

      uses common-leafs;

      leaf-list datastore {
        type identityref {
          base ds:datastore;
          "The datastores in which this module is supported.";

      uses schema-leaf;

      leaf namespace {
        type inet:uri;
        mandatory true;
          "The XML namespace identifier for this module.";
      leaf-list feature {
        type yang:yang-identifier;
          "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";
          "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;
      leaf conformance-type {
        type enumeration {
          enum implement {
              "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 {
              "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;
          "Indicates the type of conformance the server is claiming
           for the YANG module identified by this entry.";
      list submodule {
        key "name revision";
          "Each entry represents one submodule within the
           parent module.";
        uses common-leafs;
        uses schema-leaf;

   * Operational state data nodes

  container datastores {
    config false;
      "Identifies which datastores are supported by this server.";
    leaf-list datastore {
      type identityref {
        base ds:datastore;
        "A datastore supported by this server.";

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

    leaf module-set-id {
      type string;
      mandatory true;
        "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 {
      "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;
        "Contains the module-set-id value representing the
         set of modules and submodules supported at the server at
         the time the notification is generated.";



3. IANA Considerations

3.1. YANG Module Registry

RFC 7895 previously registered one URI in the IETF XML registry [RFC3688]. Following the format in RFC 3688, the following registration was 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 takes over this registration entry made by RFC 7895.

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.

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:

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. References

6.1. Normative References

[I-D.ietf-netmod-revised-datastores] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K. and R. Wilton, "Network Management Datastore Architecture", Internet-Draft draft-ietf-netmod-revised-datastores-02, May 2017.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004.
[RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011.
[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011.
[RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration Protocol (NETCONF) Access Control Model", RFC 6536, DOI 10.17487/RFC6536, March 2012.
[RFC6991] Schoenwaelder, J., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, July 2013.
[RFC7895] Bierman, A., Bjorklund, M. and K. Watsen, "YANG Module Library", RFC 7895, DOI 10.17487/RFC7895, June 2016.
[RFC7950] Bjorklund, M., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016.

6.2. Informative References

[RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008.
[RFC6470] Bierman, A., "Network Configuration Protocol (NETCONF) Base Notifications", RFC 6470, DOI 10.17487/RFC6470, February 2012.

Authors' Addresses

Andy Bierman YumaWorks EMail:
Martin Bjorklund Tail-f Systems EMail:
Kent Watsen Juniper Networks EMail: