RFC 10035: YANG Library: Addition of the augmented-by List

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 https://www.rfc-editor.org/info/rfc10035.¶

Copyright Notice

Copyright (c) 2026 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.¶

1. Introduction

The YANG library [RFC8525] provides information about the data models supported by a server. This is presented as an inventory of YANG modules. It helps a client by listing all datastores supported by a network management server and the schema that is used by each of these datastores.¶

According to Sections 4.2.8 and 5.6.3 of [RFC7950], "augment" defines additional nodes to a module, while a "deviation" changes (i.e., adds, modifies, or deletes) properties (sub-statements) of another module's schema nodes. They provide crucial information about the YANG data model composition, and this is referred to as "reverse dependency" in this document: this means the behavior of a schema node depends on external modifications, creating a backward flow from the augmenting and/or deviation module to the base module.¶

It is difficult to obtain the YANG schema tree (defined in Section 3 of [RFC7950]) without obtaining and parsing all the YANG modules from a management server. The deviation list defined in the YANG library enables clients to obtain a module reverse dependency without having to get and parse all YANG modules. However, the augmentation list is not defined in the YANG library.¶

Since both augmentation and deviation work as YANG module dependencies, it is reasonable to document them the same way in the YANG library. Having both augmentation and deviation directly available in the YANG library provides a convenient solution for determining the reverse dependencies.¶

This document specifies a YANG module that augments the YANG library to include the YANG module augmentation information. It updates [RFC8525] by modifying the list in Section 2 to also include the augmented-by list.¶

One specific requirement with the implementation of this augmented-by YANG module specification is that the modules and the augmented-by modules are required to be listed in the same module-set. Note that a similar requirement already applies for the YANG deviations.¶

2. Motivation

When using YANG modules, it is necessary to make sure that all of their dependencies are present. [RFC7950] identifies four types of dependencies between YANG modules:¶

• 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.¶
• Augment: the "augment" statement defines the location in the data model hierarchy where additional nodes are inserted.¶
• Deviation: the "deviation" statement defines a fragment of a module that the server does not implement.¶

The "import" and "include" statements are direct dependencies that can be obtained by parsing a YANG module's source code, while the "augment" and "deviation" statements are reverse dependencies that are defined in another module.¶

For the reverse dependencies, since they are defined externally, it is not possible to discover them by parsing the YANG module. The current way to discover the reverse dependencies is to query all YANG modules from the server and parse them. This is a lengthy process, which must be repeated for each client that requires this information.¶

According to the definition of the "ietf-yang-library" module in [RFC8525], the "deviation" list identifies the name of each YANG module with deviation statements affecting the given YANG module. Since deviations and augmentations work similarly, if the YANG library could directly report all reverse dependencies, including augmentations, it would provide a much more convenient solution to find all module dependencies, as compared to obtaining and parsing all modules. In addition, to avoid causing problems in devices, for instance, falsely referring to modules in the wrong module-set, this document requires that the base modules and the augmentations be listed in the same module-set.¶

The YANG library only provides the deviation list, without augmentations. With augmentations being more widely used and defined, and with use cases to automate network management, augmentations become essential information for clients to better understand the network management server module relationships. Thus, the YANG library should be extended to also provide the augmentation information.¶

3. Use Cases

  "datastore-contents": {
    "ietf-interfaces:interfaces": [
    {
      "interface": {
        "name": "eth0",
        "type": "iana-if-type:ethernetCsmacd",
        "oper-status": "up",
        "speed": "1000000",
        "ietf-ip:ipv4": {
          "enabled": true,
          "forwarding": true
        }
      }
    }
    ]
  }

4. The "ietf-yang-library-augmentedby" YANG Module

module: ietf-yang-library-augmentedby

  augment /yanglib:yang-library/yanglib:module-set/yanglib:module:
    +--ro augmented-by*   -> ../../yanglib:module/name
  augment /yanglib:modules-state/yanglib:module:
    x--ro augmented-by*   -> ../../yanglib:module/name

<CODE BEGINS> file "ietf-yang-library-augmentedby@2026-08-26.yang"

module ietf-yang-library-augmentedby {
  yang-version 1.1;
  namespace
    "urn:ietf:params:xml:ns:yang:ietf-yang-library-augmentedby";
  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>

     Authors:  Zhuoyao Lin
               <mailto:zephyre888@gmail.com>
               Benoit Claise
               <mailto:benoit@everything-ops.net>
               Ignacio Dominguez Martinez-Casanueva
               <mailto:i.domingumar@gmail.com>";
  description
    "This module augments the 'ietf-yang-library' module defined in
     RFC 8525 to provide not only the deviation list, but also
     the augmented-by list, in order to give sufficient
     information about the YANG module's reverse dependency.  It
     facilitates the process of obtaining all the
     dependencies of YANG module.

     The key words '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 (RFC 2119) (RFC 8174) when, and only when,
     they appear in all capitals, as shown here.

     Copyright (c) 2026 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 Revised BSD License
     set forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (https://trustee.ietf.org/license-info).

     All revisions of IETF and IANA published modules can be found
     at the YANG Parameters registry group
     (https://www.iana.org/assignments/yang-parameters).

     This version of this YANG module is part of RFC 10035; see
     the RFC itself for full legal notices.";

  revision 2026-08-26 {
    description
      "Initial revision.";
    reference
      "RFC 10035: YANG Library: Addition of the augmented-by List";
  }

  augment "/yanglib:yang-library/yanglib:module-set/yanglib:module" {
    description
      "Adds augmented-by leaf-list to the list of modules of a
       module set";
    leaf-list augmented-by {
      type leafref {
        path "../../yanglib:module/yanglib:name";
      }
      description
        "Leaf-list of the augmentations used by this server to
         modify the schema tree of the module associated with
         this entry.  Note that the same module can be used for
         augmented-by 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 and MUST NOT
         be referenced in the import-only list.

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

  augment "/yanglib:modules-state/yanglib:module" {
    status deprecated;
    description
      "Adds augmented-by leaf-list to the list of modules of a
       module set";
    leaf-list augmented-by {
      type leafref {
        path "../../yanglib:module/yanglib:name";
      }
      status deprecated;
      description
        "Leaf-list of the augmentations used by this server to
         modify the schema tree of the module associated with
         this entry.  Note that the same module can be used for
         augmented-by 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 and MUST NOT
         be referenced in the import-only list.

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

<CODE BEGINS> file "example_yanglib_result1.xml"

<!-- NOTE: '\' line wrapping per RFC 8792 -->
<yang-library xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
  <content-id>1</content-id>
  <module-set>
    <name>module-set1</name>
    <module>
      <name>A</name>
      <revision>2026-08-19</revision>
      <namespace>urn:ietf:params:xml:ns:yang:A</namespace>
      <augmented-by
      xmlns="urn:ietf:params:xml:ns:yang:\
      ietf-yang-library-augmentedby">B</augmented-by>
      <augmented-by
      xmlns="urn:ietf:params:xml:ns:yang:\
      ietf-yang-library-augmentedby">C</augmented-by>
    </module>
    <module>
      <name>B</name>
      <revision>2026-08-19</revision>
      <namespace>urn:ietf:params:xml:ns:yang:B</namespace>
    </module>
    <module>
      <name>C</name>
      <revision>2026-08-19</revision>
      <namespace>urn:ietf:params:xml:ns:yang:C</namespace>
    </module>
  </module-set>
</yang-library>
<modules-state xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
    <module-set-id>0</module-set-id>
</modules-state>


<CODE ENDS>

<CODE BEGINS> file "example_yanglib_result2.xml"

<!-- NOTE: '\' line wrapping per RFC 8792 -->
<yang-library xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
  <content-id>1</content-id>
  <module-set>
    <name>module-set1</name>
    <module>
      <name>A</name>
      <revision>2026-08-19</revision>
      <namespace>urn:ietf:params:xml:ns:yang:A</namespace>
      <augmented-by
      xmlns="urn:ietf:params:xml:ns:yang:\
      ietf-yang-library-augmentedby">B</augmented-by>
    </module>
    <module>
      <name>B</name>
      <revision>2026-08-19</revision>
      <namespace>urn:ietf:params:xml:ns:yang:B</namespace>
      <augmented-by
      xmlns="urn:ietf:params:xml:ns:yang:\
      ietf-yang-library-augmentedby">C</augmented-by>
    </module>
    <module>
      <name>C</name>
      <revision>2026-08-19</revision>
      <namespace>urn:ietf:params:xml:ns:yang:C</namespace>
    </module>
  </module-set>
</yang-library>
<modules-state xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
  <module-set-id>0</module-set-id>
</modules-state>


<CODE ENDS>

5. Operational Considerations

With the implementation of augmented-by, the base modules and the augmented-by modules are required to be listed in the same module-set.¶

Note that the reverse dependency will increase the size of the "ietf-yang-library" instance on the server. Also, the "ietf-yang-library" instance, and therefore the augmented-by instance, should be updated when new YANG modules are onboarded.¶

A YANG example with the expected augmented-by result is provided in Section 4.2.2.¶

6. Security Considerations

This section is modeled after the template described in Section 3.7.1 of [RFC9907].¶

The "ietf-yang-library-augmentedby" YANG module defines a data model that is designed to be accessed via YANG-based management protocols, such as the Network Configuration Protocol (NETCONF) [RFC6241] and RESTCONF [RFC8040]. These YANG-based management protocols (1) have to use a secure transport layer (e.g., Secure Shell (SSH) [RFC4252], TLS [RFC9846], and QUIC [RFC9000]) and (2) have to use mutual authentication.¶

The Network Configuration Access Control Model (NACM) [RFC8341] provides the means to restrict access for particular NETCONF or RESTCONF users to a preconfigured subset of all available NETCONF or RESTCONF protocol operations and content.¶

There are no writable ("config true") data nodes defined in this YANG module.¶

This YANG module defines only readable ("config false") data nodes. 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. Specifically, the following subtrees and data nodes have particular sensitivities/vulnerabilities:¶

• /yang-library/module-set/module/augmented-by¶

• /modules-state/module/augmented-by (modules-state is deprecated)¶

These nodes expose the augmentation relationships among modules implemented by a server. Unauthorized read access could help an attacker identify implementation structure, optional features, or software components present on a server, which might then be used to target known platform vulnerabilities. Therefore, access control policies SHOULD restrict read access to authorized users only.¶

There are no RPCs or action operations defined in this module. Therefore, there are no particularly sensitive RPC or action operations.¶

This module uses groupings from the "ietf-yang-library" YANG module defined in [RFC8525], which defines nodes that may be considered sensitive or vulnerable in network environments. Since this document augments the "ietf-yang-library" YANG module defined in [RFC8525], the Security Considerations of [RFC8525] apply here as well. Refer to Section 6 of [RFC8525] for information as to which nodes may be considered sensitive or vulnerable in network environments.¶

7. IANA Considerations

IANA has registered the following URI in the "ns" registry within the "IETF XML Registry" registry group [RFC3688]:¶

URI:

urn:ietf:params:xml:ns:yang:ietf-yang-library-augmentedby¶

Registration Contact:

The IESG¶

XML:

N/A, the requested URI is an XML namespace.¶

IANA has registered the following YANG module in the "YANG Module Names" registry [RFC6020] within the "YANG Parameters" registry group:¶

Name:

ietf-yang-library-augmentedby¶

Maintained by IANA?

N¶

Namespace:

urn:ietf:params:xml:ns:yang:ietf-yang-library-augmentedby¶

Prefix:

yanglib-aug¶

Reference:

RFC 10035¶

Appendix A. Full Tree View of "ietf-yang-library"

The following is the YANG tree diagram [RFC8340] for the "ietf-yang-library" module after adding augmentation from the "ietf-yang-library-augmentedby" module. The RPCs and notifications are included as well.¶

[NOTE: '\' line wrapping per RFC 8792]
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:augmented-by*
                                     -> ../../yanglib: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:augmented-by*\
          -> ../../yanglib:module/name

  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

Authors' Addresses