Augmentaiton Addition into the IETF-YANG-Library

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 6 May 2024.¶

Copyright Notice

Copyright (c) 2023 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶

Table of Contents

1. Introduction

The YANG library [RFC8525] specifies a YANG module that provides the information about the YANG models and datastores to facilitate a client application to fully utilize and understand the YANG data modelling language. To know the YANG dependencies, [RFC8525] has defined and provided the submodule list and the YANG modules deviation list. However, the YANG modules augmentation list is not provided.¶

According to [RFC7950], both augmentations and deviations are defining contents external to the model, but applying internally for the model. Therefore, it is important to know the augmentation and deviation as they are dependencies of the model, but it is also difficult because they are defined externally. When we try to use the ietf-yang-library in [RFC8525] to obtain the reverse dependencies (augmentations and deviations), the augmentation is missing. However, the augmentation and the deviation work similarly as YANG modules dependency, therefore it is resonable to document them the same way in the IETF YANG library. Besides, it will be easier to determine the reverse dependency if the augmentation is directly available, through a GET request into this new YANG model.¶

Therefore, this draft augments the ietf-yang-library to include the YANG modules augmentated information.¶

2. Motivation

When using one YANG model, it is important to make sure that all its dependencies are presented. In [RFC7950] there are four dependencies for one YANG mode:¶

• Import: the "import" statement allows a module or submodule to reference definitions defined in other modules.¶
• Include: the "include" statement is used in a module to identify each submodule that belongs to it.¶
• Augmentation: the "augment" statement defines the location in the data model hierarchy where additional nodes are inserted¶
• Deviation: the "deviation" statement defines a hierarchy of a module that the server does not implement faithfully.¶

The import and include are direct dependencies while the augmentation and deviation are reverse dependencies. To know a specific YANG model's direct dependencies, we can parse this YANG model as the dependencies are directly specified (import and include statements"). As for the reverse dependencies, since they are defined externally, we cannot parse the YANG model itself. Among all the methods for getting reverse dependency, getting the ietf-yang-library content is one of the most convenient way. However, it only provides the deviation list, not the augmentation list. It is reasonable to update it with the augmentation list, since both augmentation and deviation have similar behavior (both are invisible to the original model). A noticable difference between deviations and augmentations is that the deviations are required to understand the API contract between the client and the server.¶

Here is a typical use case: as the demand arises for YANG-based telemetry [RFC8641], there is a need for real-time knowledge of a specific YANG model's dependency list, when a specific YANG-Push message is received. The alternative, for a YANG-push receiver, to collect and store the entire module set for every single server who could be streaming data, is not always practical. Indeed, it's time consuming to request all YANG modules from the server.¶

In an open-sourced project covering Support of Versioning in YANG Notifications Subscription [I-D.ietf-netconf-yang-notifications-versioning], Support of Network Observation Timestamping in YANG Notifications [I-D.netconf-tgraf-yang-push-observation-time], among others, the purpose is to provide adequate information in the YANG push notification so that when it is received, the model and its dependency can be parsed and found automatically from the vantage point. Currently, the method used for finding model's reverse dependency is get-all-schemas, that is to retrieve all YANG modules from the device to the client's disk to enable the client fully understand the YANG model relationship. This process is heavy because dependencies are recursive; each dependency module could have another set of dependencies. Considering the telemetry real-time aspects, this extra delay in processing the dependencies through get-all-schemas is a burden.¶

The YANG module in this draft is proposed to solve the above problem. It can make the process of discovering the augmentation easier.¶

3. The "ietf-yang-library-augmentation" YANG module

This YANG module augments the ietf-yang-library module with the augmentation in the "yang-library/module-set". Note that this module only augments the ietf-yang-library defined in [RFC8525]. At the time of writing this document, most router vendors support [RFC7895], a previous revision of the IETF-YANG-LIBRARY YANG module; The module that augments [RFC7895] is provided in the appendix A.¶

module: ietf-yang-library-augmentation

  augment /yanglib:yang-library/yanglib:module-set/yanglib:module:
    +--ro augmentation*   -> /yanglib:yang-library/module-set/module/name

module: ietf-yang-library
  +--ro yang-library
  |  +--ro module-set* [name]
  |  |  +--ro name                  string
  |  |  +--ro module* [name]
  |  |  |  +--ro name                        yang:yang-identifier
  |  |  |  +--ro revision?                   revision-identifier
  |  |  |  +--ro namespace                   inet:uri
  |  |  |  +--ro location*                   inet:uri
  |  |  |  +--ro submodule* [name]
  |  |  |  |  +--ro name        yang:yang-identifier
  |  |  |  |  +--ro revision?   revision-identifier
  |  |  |  |  +--ro location*   inet:uri
  |  |  |  +--ro feature*                    yang:yang-identifier
  |  |  |  +--ro deviation*                  -> ../../module/name
  |  |  |  +--ro yanglib-aug:augmentation*   -> /yanglib:yang-library/module-set/module/name
  |  |  +--ro import-only-module* [name revision]
  |  |     +--ro name         yang:yang-identifier
  |  |     +--ro revision     union
  |  |     +--ro namespace    inet:uri
  |  |     +--ro location*    inet:uri
  |  |     +--ro submodule* [name]
  |  |        +--ro name        yang:yang-identifier
  |  |        +--ro revision?   revision-identifier
  |  |        +--ro location*   inet:uri
  |  +--ro schema* [name]
  |  |  +--ro name          string
  |  |  +--ro module-set*   -> ../../module-set/name
  |  +--ro datastore* [name]
  |  |  +--ro name      ds:datastore-ref
  |  |  +--ro schema    -> ../../schema/name
  |  +--ro content-id    string
  x--ro modules-state
     x--ro module-set-id    string
     x--ro module* [name revision]
        x--ro name                yang:yang-identifier
        x--ro revision            union
        +--ro schema?             inet:uri
        x--ro namespace           inet:uri
        x--ro feature*            yang:yang-identifier
        x--ro deviation* [name revision]
        |  x--ro name        yang:yang-identifier
        |  x--ro revision    union
        x--ro conformance-type    enumeration
        x--ro submodule* [name revision]
           x--ro name        yang:yang-identifier
           x--ro revision    union
           +--ro schema?     inet:uri

  notifications:
    +---n yang-library-update
    |  +--ro content-id    -> /yang-library/content-id
    x---n yang-library-change
       x--ro module-set-id    -> /modules-state/module-set-id

<CODE BEGINS> file "ietf-yang-library-augmentation@2023-10-27.yang"

module ietf-yang-library-augmentation {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-yang-library-augmentation";
  prefix yanglib-aug;

  import ietf-yang-library {
    prefix yanglib;
    reference
      "RFC 8525: YANG library";
  }

  organization
    "IETF NETCONF (Network Configuration) Working Group";
  contact
    "WG Web:   <https://datatracker.ietf.org/wg/netconf/>
     WG List:  <mailto:netconf@ietf.org>

     Author:   Zhuoyao Lin
               <mailto:zephyre888@gmail.com>
               Benoit Claise
               <mailto:benoit.claise@huawei.com>";

  description
    "This module augments the ietf-yang-library defined in [RFC8525] to provide the augmentation list, in order to give sufficient information about the YANG models reverse dependency. It facilitates the process of obtaining the entire dependencies of YANG model.";

  revision 2023-10-27 {
    description
      "Added list augmentation in yang-library/module-set/module to
      make the module store the entire reverse dependency information
      (augmentation and deviation).";
    reference
      "RFC XXXX: Support of augmentation in ietf-yang-library";
  }

  augment "/yanglib:yang-library/yanglib:module-set/yanglib:module" {
    description
      "Augment the augmentation from module info with the module-augmentation grouping" ;
    uses yanglib-aug:module-augmentation;
  }

  /*
   * Groupings
   */


  grouping module-augmentation {
    description
      "This grouping defines a leaf-list that contains the augmentation list.";

  leaf-list augmentation {
      type leafref {
        path "/yanglib:yang-library/yanglib:module-set/yanglib:module/yanglib:name";
      }

      description
        "List of all YANG augmentation 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 augmentation
         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 augmented.

         Robust clients may want to make sure that they handle a
         situation where a module augments itself (directly or
         indirectly) gracefully.";
    }
  }
}


<CODE ENDS>

4. Security Considerations

TBC¶

5. IANA Considerations

This document has no actions for IANA.¶

Appendix A. YANG Module augmenting RFC7895

module: ietf-yang-library-rfc7895-augmentation

  augment /yanglib:yang-library/yanglib:module-set/yanglib:module:
    +--ro augmentation*   -> /yanglib:yang-library/module-set/module/name
  augment /yanglib:modules-state/yanglib:module:
    x--ro augmentation* [name revision]
       +--ro name        -> /yanglib:modules-state/module/name
       +--ro revision    -> /yanglib:modules-state/module/revision

module: ietf-yang-library
  +--ro yang-library
  |  +--ro module-set* [name]
  |  |  +--ro name                  string
  |  |  +--ro module* [name]
  |  |  |  +--ro name                        yang:yang-identifier
  |  |  |  +--ro revision?                   revision-identifier
  |  |  |  +--ro namespace                   inet:uri
  |  |  |  +--ro location*                   inet:uri
  |  |  |  +--ro submodule* [name]
  |  |  |  |  +--ro name        yang:yang-identifier
  |  |  |  |  +--ro revision?   revision-identifier
  |  |  |  |  +--ro location*   inet:uri
  |  |  |  +--ro feature*                    yang:yang-identifier
  |  |  |  +--ro deviation*                  -> ../../module/name
  |  |  |  +--ro yanglib-aug:augmentation*   -> /yanglib:yang-library/module-set/module/name
  |  |  +--ro import-only-module* [name revision]
  |  |     +--ro name         yang:yang-identifier
  |  |     +--ro revision     union
  |  |     +--ro namespace    inet:uri
  |  |     +--ro location*    inet:uri
  |  |     +--ro submodule* [name]
  |  |        +--ro name        yang:yang-identifier
  |  |        +--ro revision?   revision-identifier
  |  |        +--ro location*   inet:uri
  |  +--ro schema* [name]
  |  |  +--ro name          string
  |  |  +--ro module-set*   -> ../../module-set/name
  |  +--ro datastore* [name]
  |  |  +--ro name      ds:datastore-ref
  |  |  +--ro schema    -> ../../schema/name
  |  +--ro content-id    string
  x--ro modules-state
     x--ro module-set-id    string
     x--ro module* [name revision]
        x--ro name                        yang:yang-identifier
        x--ro revision                    union
        +--ro schema?                     inet:uri
        x--ro namespace                   inet:uri
        x--ro feature*                    yang:yang-identifier
        x--ro deviation* [name revision]
        |  x--ro name        yang:yang-identifier
        |  x--ro revision    union
        x--ro conformance-type            enumeration
        x--ro submodule* [name revision]
        |  x--ro name        yang:yang-identifier
        |  x--ro revision    union
        |  +--ro schema?     inet:uri
        x--ro yanglib-aug:augmentation* [name revision]
           +--ro yanglib-aug:name        -> /yanglib:modules-state/module/name
           +--ro yanglib-aug:revision    -> /yanglib:modules-state/module/revision

  notifications:
    +---n yang-library-update
    |  +--ro content-id    -> /yang-library/content-id
    x---n yang-library-change
       x--ro module-set-id    -> /modules-state/module-set-id

<CODE BEGINS> file "ietf-yang-library-rfc7895-augmentation@2023-10-27.yang"

module ietf-yang-library-rfc7895-augmentation {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-yang-library-rfc7895-augmentation";
  prefix yanglib-aug;

  import ietf-yang-library {
    prefix yanglib;
        revision-date 2016-06-21;
    reference
      "RFC 8525: YANG library";
  }

  organization
    "IETF NETCONF (Network Configuration) Working Group";
  contact
    "WG Web:   <https://datatracker.ietf.org/wg/netconf/>
     WG List:  <mailto:netconf@ietf.org>

     Author:   Zhuoyao Lin
               <mailto:zephyre888@gmail.com>
               Benoit Claise
               <mailto:benoit.claise@huawei.com>";

  description
    "This module augments the ietf-yang-library defined in [RFC8525] to provide not only the deviation list, but also the augmentation list, in order to give sufficient information about the YANG models reverse dependency. It facilitates the process of obtaining the entire dependencies of YANG model.";

  revision 2023-10-27 {
    description
      "Added list augmentation in yang-library/module-set/module to
      make the module store the entire reverse dependency information
      (augmentation and deviation).";
    reference
      "RFC XXXX: Support of augmentation in ietf-yang-library";
  }

  augment "/yanglib:yang-library/yanglib:module-set/yanglib:module" {
    description
      "Augment the augmentation from module info with the module-augmentation grouping" ;
    uses yanglib-aug:module-augmentation;
  }

  augment "/yanglib:modules-state/yanglib:module" {
    description
      "Augment the augmentation from module info with the module-augmentation grouping" ;
    uses yanglib-aug:module-state-augmentation;
  }

  /*
   * Groupings
   */


  grouping module-augmentation {
    description
      "This grouping defines a leaf-list that contains the augmentation list.";

  leaf-list augmentation {
      type leafref {
        path "/yanglib:yang-library/yanglib:module-set/yanglib:module/yanglib:name";
      }

      description
        "List of all YANG augmentation 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 augmentation
         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 augmented.

         Robust clients may want to make sure that they handle a
         situation where a module augments itself (directly or
         indirectly) gracefully.";
    }
  }

  grouping module-state-augmentation {
    description
      "This grouping defines a list with keys being the module
      name and revison. The list contains the augmentation list.";

    list augmentation {
      key "name revision";
      status deprecated;

      description
        "List of YANG augmentation 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 augmentations for
         multiple modules, so the same entry MAY appear
         within multiple 'module' entries.

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

      leaf name {
        type leafref {
          path "/yanglib:modules-state/yanglib:module/yanglib:name";
        }
      }

      leaf revision {
        type leafref {
          path "/yanglib:modules-state/yanglib:module/yanglib:revision";
        }
      }
    }
  }
}


<CODE ENDS>

Authors' Addresses