System-Defined Configuration

Internet Engineering Task Force (IETF)                        Q. Ma, Ed.
Request for Comments: 10016                                        Q. Wu
Updates: 8342                                                     Huawei
Category: Standards Track                                        C. Feng
ISSN: 2070-1721                                           September 2026


                      System-Defined Configuration

Abstract

   The Network Management Datastore Architecture (NMDA) in RFC 8342
   defines several configuration datastores holding configuration.  The
   contents of these configuration datastores are controlled by clients.
   This document introduces the concept of a system configuration
   datastore holding configuration controlled by the system on which a
   server is running.  The system configuration can be referenced (e.g.,
   leafref) by configuration explicitly created by clients.

   This document updates RFC 8342.

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/rfc10016.

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.

Table of Contents

   1.  Introduction
     1.1.  Terminology
     1.2.  Requirements Language
     1.3.  Updates to RFC 8342
   2.  Kinds of System Configuration
     2.1.  Always Present
     2.2.  Conditionally Present
   3.  The System Configuration Datastore (<system>)
   4.  Conceptual Model of Datastores
   5.  Static Characteristics
     5.1.  Read-Only to Clients
     5.2.  No Changes to <operational>
   6.  Dynamic Behaviors
     6.1.  May Change via Software Upgrades or Resource Changes
     6.2.  Referencing System Configuration
     6.3.  Overriding System Configuration
     6.4.  Configuring Descendant Nodes of System Configuration
   7.  The "ietf-system-datastore" Module
     7.1.  Data Model Overview
     7.2.  YANG Module
     7.3.  Example Usage
   8.  IANA Considerations
     8.1.  The IETF XML Registry
     8.2.  The YANG Module Names Registry
   9.  Operational Considerations
   10. Security Considerations
     10.1.  Considerations for the "ietf-system-datastore" YANG Module
     10.2.  Considerations for System Configuration
   11. References
     11.1.  Normative References
     11.2.  Informative References
   Appendix A.  Example of Dynamic Behaviors (Informative)
     A.1.  Referencing System-Defined Nodes
     A.2.  Modifying a System-Instantiated Leaf's Value
     A.3.  Configuring Descendant Nodes of a System-Defined Node
   Appendix B.  Key Use Cases (Informative)
     B.1.  Device Powers On
     B.2.  Client Commits Configuration
     B.3.  Operator Installs Card into a Chassis
     B.4.  Client Further Commits Configuration
   Acknowledgements
   Contributors
   Authors' Addresses

1.  Introduction

   The Network Management Datastore Architecture (NMDA) [RFC8342]
   defines system configuration as the configuration that is supplied by
   the device itself and appears in <operational> when it is in use (see
   Figure 2 in [RFC8342]).

   However, there is a desire from operators to enable a server to
   better expose the system configuration, regardless of whether it is
   in use.  For example, some implementations define the system
   configuration that must be referenced to be active.  Network
   Configuration Protocol (NETCONF) / RESTCONF clients can benefit from
   a standard mechanism to retrieve what system configuration is
   available on a server.

   Some servers allow the descendant nodes of system-defined
   configuration to be configured or modified.  For example, the system
   configuration may contain an almost empty physical interface, whose
   existence in the system configuration is tied to the presence of
   particular hardware, while the client needs to be able to add,
   modify, or remove a number of descendant nodes.  Some descendant
   nodes may not be modifiable (e.g., the interface "type" set by the
   system).

   This document updates the NMDA defined in [RFC8342] with a read-only
   conventional configuration datastore called "system" to expose
   system-defined configuration.  The solution enables configuration
   explicitly created by the clients to reference nodes defined in
   <system>, override system-provided values, and configure descendant
   nodes of system-defined configuration.

   The solution defined in this document requires the use of NMDA for
   both clients and servers.  Conformance to this document requires NMDA
   servers implement the "ietf-system-datastore" YANG module
   (Section 7).

1.1.  Terminology

   This document assumes that the reader is familiar with the contents
   of [RFC6241], [RFC7950], [RFC8342], and [RFC8525] and uses
   terminologies from those documents.  The terms "device" and "server"
   are used interchangeably in this document.

   The following terms are defined in this document:

   system configuration:
      [RFC8342] defines it as "Configuration that is supplied by the
      device itself".  The definition herein refines that definition to
      represent configuration present in the system configuration
      datastore (regardless of whether it is applied or referenced).  It
      may also be referred to as "system-defined configuration" or
      "system-provided configuration" throughout this document.  The
      system configuration discussed in this document cannot be
      deletable; configuration provided by the server that is deletable
      is outside the scope of this document.

   system configuration datastore:
      This is a configuration datastore holding configuration provided
      by the system itself.  This datastore is referred to as
      "<system>".

   This document redefines the term "conventional configuration
   datastore" in Section 3 of [RFC8342] to add "system" to the list of
   conventional configuration datastores:

   conventional configuration datastore:
      One of the following set of configuration datastores: <running>,
      <startup>, <candidate>, <system>, and <intended>.  These
      datastores share a common datastore schema, and protocol
      operations allow copying data between these datastores.  The term
      "conventional" is chosen as a generic umbrella term for these
      datastores.  Note that while protocol operations allow copying
      data between conventional datastores, the read-only nature of
      datastores such as <system> and <intended> restricts clients from
      copying data into them.

   system node:
      This is an instance in the data tree that is provided by the
      system itself.  System node may also be called "system-defined
      node" or "system-provided node" throughout this document.

   referenced node:
      A referenced node is one of the following:

      *  Targets of leafref values defined via the "path" statement.

      *  Targets of "instance-identifier" type values.

      *  Nodes present in an XPath expression of "when" constraints.

      *  Nodes present in an XPath expression of "must" constraints.

      *  Nodes defined to satisfy the "mandatory true" constraints.

      *  Nodes defined to satisfy the "min-elements" constraints.

1.2.  Requirements Language

   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 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

1.3.  Updates to RFC 8342

   This document updates [RFC8342] to define a configuration datastore
   called "system" that holds system configuration (Section 3).  It also
   redefines the term "conventional configuration datastore" from
   [RFC8342] to include "system" in the list.

   To ensure the validity of <intended> when clients interact with
   system configuration (e.g., configuration provided by clients
   references system configuration) and allow the existence of system-
   defined templates and inactive system configuration, configuration in
   <running> is merged with <system> to create the contents of
   <intended> after the configuration transformations (e.g., template
   expansion or removal of inactive configuration defined in [RFC8342])
   have been performed, as described in Section 4.  Specifications in
   [RFC8342] related to the processing of system configuration are
   updated by the mechanism defined in this document.

   Additionally, this document also updates the definition of the
   "intended" origin metadata annotation identity defined in
   Section 5.3.4 of [RFC8342].  The "intended" identity of the origin
   value defined in [RFC8342] represents the origin of configuration
   provided by <intended>.  This document updates that definition as the
   origin source of configuration explicitly provided by clients and
   allows a subset of configuration in <intended> that flows from
   <system> yet is not configured or overridden explicitly in <running>
   to use "system" as its origin value.  As per Section 5.3.4 of
   [RFC8342], all configuration with the origin value being reported as
   "intended" MUST originate from <running>, which includes any
   configuration in <system> that has been copied into <running>.
   Configuration that is in <system> and not also present in <running>
   MUST be reported as origin "system" in <operational>.

2.  Kinds of System Configuration

   This document defines two types of system configuration:
   configuration that is always present and configuration that is
   conditionally present.  These types of system configuration are
   described in Sections 2.1 and 2.2, respectively.

2.1.  Always Present

   The always-present system configuration is generated in <system> when
   the device is powered on, irrespective of whether physical resources
   are present or whether a special functionality is enabled.  An
   example of an always-present system configuration is an always-
   existing loopback interface.

2.2.  Conditionally Present

   The conditionally present system configuration is generated in
   <system> based on specific conditions being met in a system.  For
   example, if a physical resource is present (e.g., an interface card
   is inserted), the system automatically detects it and loads the
   associated configuration; when the physical resource is not present
   (an interface card is removed), the system configuration will
   automatically be removed from <system>.  Another example is when a
   special functionality (e.g., a license or feature) is enabled,
   specific configuration may be created by the system.

3.  The System Configuration Datastore (<system>)

   Following guidelines for defining datastores in Appendix A of
   [RFC8342], this document introduces a new datastore resource named
   "system" that represents the system configuration.  NMDA servers
   compliant with this document MUST implement a system configuration
   datastore, and they SHOULD also implement <intended>.

   Name:  "system"

   YANG modules:  all

   YANG nodes:  all "config true" data nodes up to the root node,
      generated by the system.

   Management operations:  The datastore can be read using network
      management protocols such as NETCONF and RESTCONF, but its
      contents cannot be changed by management operations via NETCONF
      and RESTCONF protocols.

   Origin:  This document does not define any new origin identity.  The
      "system" identity of origin metadata annotation [RFC7952] is used
      to indicate the origin of a data item provided in <system>.

   Protocols:  YANG-driven management protocols, such as NETCONF and
      RESTCONF.

   Defining YANG module:  "ietf-system-datastore" (Section 7).

   The system configuration datastore does not persist across reboots.

4.  Conceptual Model of Datastores

   Clients may provide configuration nodes that reference nodes defined
   in <system>, override system-provided values, and configure
   descendant nodes of system-defined configuration in <running>, as
   detailed in Section 6.

   To ensure the validity of <intended>, configuration in <running> is
   merged with <system> to become <intended>, in which process,
   configuration appearing in <running> takes precedence over the same
   node in <system>.  Since it is unspecified how to merge configuration
   before transformations, if <system> or <running> includes
   configuration that requires further transformation (e.g., template
   expansion or removal of inactive configuration defined in [RFC8342])
   before it can be applied, configuration transformations MUST be
   performed independently on each datastore before <running> is merged
   with <system>.

   Whenever configuration in <system> changes, the server MUST also
   immediately update and validate <intended>.

   As a result, Figure 2 in Section 5 of [RFC8342] is updated with the
   below conceptual model of datastores that incorporates the system
   configuration datastore.  For completeness, this model also includes
   <factory-default> introduced in [RFC8808].

                              +-----------------+
                              |<factory-default>|
                        +-----|    (ct, ro)     |-----+
                        |     +-----------------+     |
   //"factory-reset" RPC|             |               |
                        v             |               v
                +-------------+       |         +-----------+
                | <candidate> |       |         | <startup> |
                |  (ct, rw)   |<---+  |   +---->| (ct, rw)  |
                +-------------+    |  |   |     +-----------+
                       |           |  v   |           |
 +-----------+         |        +-----------+         |
 | <system>  |         +------->| <running> |<--------+
 | (ct, ro)  |                  | (ct, rw)  |
 +-----------+                  +-----------+
      |                              |
      |                              |
      |                              | // configuration transformations,
      +--------------+---------------+ // e.g., removal of nodes marked
                     |                 // as "inactive", expansion of
                     |                 // templates
                     v
               +------------+
               | <intended> |  // subject to validation
               | (ct, ro)   |
               +------------+
                      |       // changes applied, subject to
                      |       // local factors, e.g., missing
                      |       // resources, delays
  dynamic             |
  configuration       |   +-------- learned configuration
  datastores -----+   |   +-------- default configuration
                  |   |   |
                  v   v   v
              +---------------+
              | <operational> | <-- system state
              | (ct + cf, ro) |
              +---------------+

 ct = config true; cf = config false
 rw = read-write; ro = read-only
 boxes denote named datastores

              Figure 1: Architectural Model of Datastores

   Configuration in <system> cannot be deleted by clients (e.g., a list
   entry can never be removed from <system> through protocol
   operations), even though a node defined in <system> may be overridden
   in <running>.  If the system initializes a value for a particular
   leaf that is overridden by the client with a different value in
   <running> (Section 6.3), and if the node in <running> is removed at a
   later time, the system-initialized value defined in <system> appears
   in <intended> and may come into use eventually if applied
   successfully.

   Configuration may disappear from <system> due to, e.g., resources no
   longer available.  In such cases, configuration for missing resources
   can still remain in <running> and <intended>, but it will not be
   applied and appear in <operational>.  This is further clarified in
   Section 5.3.2 of [RFC8342].

5.  Static Characteristics

5.1.  Read-Only to Clients

   The system datastore is read-only (i.e., edits towards <system>
   directly MUST be denied), though the client may be allowed to provide
   configuration that overrides the value of a system-initialized node
   (see Section 6.3).

5.2.  No Changes to <operational>

   This work does not change the definition of <operational> nor does it
   impact the contents of <operational>, as specified in [RFC8342].  It
   clarifies origin reporting, i.e., the origin of nodes sourced from
   <system> is reported as "system" unless explicitly configured or
   overridden in <running>.  <system> enables system-defined nodes to be
   defined like configuration, i.e., made visible to clients in order
   for being referenced or configurable prior to present in
   <operational>.  "config false" nodes are out of scope; hence,
   existing "config false" nodes are not impacted by this work.

6.  Dynamic Behaviors

6.1.  May Change via Software Upgrades or Resource Changes

   The contents of <system> MAY change dynamically under various
   conditions, such as license change, software upgrade, and system-
   controlled resources change (see Section 2.2).  The updates of system
   configuration may be obtained through YANG notifications [RFC8639]
   [RFC8641] (e.g., on-change notification).

   If system configuration changes (e.g., during a software upgrade),
   <running> SHOULD remain a valid configuration data tree.  Any
   mechanisms to achieve this are outside the scope of this document.

6.2.  Referencing System Configuration

   Clients may create configuration data in <running> that references
   nodes in <system>.  Some implementations may define system nodes
   solely as a convenience for clients to reference.  It is also
   possible for the clients to define their customized nodes for
   reference.

   Appendix A.1 provides an example of a client referencing system-
   defined nodes.

6.3.  Overriding System Configuration

   Although <system> is read-only, in some cases, a server may allow
   some parts of system configuration (e.g., a leaf's value) to be
   overridden (note the distinction between <system> and system
   configuration).  Overriding of system configuration is achieved by
   the client writing configuration data in <running>, which overrides
   the values of matched configuration nodes at the corresponding level
   in <system>.  Configurations defined in <running> take precedence
   over system configuration nodes in <system> if the server allows the
   nodes to be overridden (some implementations may have immutable
   system configuration that is identified by the server using an
   immutable metadata annotation; see [YANG-FLAG] for details),
   regardless of whether a system-instantiated value changes
   subsequently.

   Appendix A.2 provides an example of a client overriding a system-
   instantiated leaf's value.

6.4.  Configuring Descendant Nodes of System Configuration

   A server may also allow a client to add nodes to a list entry in
   <system> by writing those additional nodes in <running>.  Those
   additional data nodes may not exist in <system> (i.e., an addition
   rather than an override).

   Appendix A.3 provides an example of a client configuring descendant
   nodes of a system-defined node.

7.  The "ietf-system-datastore" Module

7.1.  Data Model Overview

   This YANG module defines a new YANG identity named "system", which
   uses the "ds:conventional" identity defined in [RFC8342] as its base.
   A client can discover the system configuration datastore support on
   the server by reading the YANG library information from the
   operational state datastore.

   The system datastore is defined as a conventional configuration
   datastore and shares a common datastore schema with other
   conventional datastores.

   The following diagram illustrates the relationship amongst the
   "identity" statements defined in the "ietf-system-datastore" and
   "ietf-datastores" YANG modules:

   Identities:
     +--- datastore
     |  +--- conventional
     |  |  +--- running
     |  |  +--- candidate
     |  |  +--- startup
     |  |  +--- system
     |  |  +--- intended
     |  +--- dynamic
     |  +--- operational

   The diagram above uses syntax that is similar to but not defined in
   [RFC8340].

7.2.  YANG Module

   <CODE BEGINS> file "ietf-system-datastore@2026-09-16.yang"
   module ietf-system-datastore {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-system-datastore";
     prefix sysds;

     import ietf-datastores {
       prefix ds;
       reference
         "RFC 8342: Network Management Datastore Architecture (NMDA)";
     }

     organization
       "IETF NETMOD (Network Modeling) Working Group";

     contact
       "WG Web:   <https://datatracker.ietf.org/wg/netmod/>
        WG List:  <mailto:netmod@ietf.org>

        Author: Qiufang Ma
                <mailto:maqiufang1@huawei.com>
        Author: Qin Wu
                <mailto:bill.wu@huawei.com>
        Author: Chong Feng
                <mailto:fengchongllly@gmail.com>";

     description
       "This module defines a new YANG identity that uses the
        ds:conventional identity defined in RFC 8342.

        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).

        This version of this YANG module is part of RFC 10016
        (https://www.rfc-editor.org/info/rfc10016); see the RFC
        itself for full legal notices.";

     revision 2026-09-16 {
       description
         "Initial version.";
       reference
         "RFC 10016: System-Defined Configuration";
     }

     identity system {
       base ds:conventional;
       description
         "This read-only datastore contains the configuration
          provided by the system itself.";
     }
   }
   <CODE ENDS>

7.3.  Example Usage

   The following example shows how the configuration in <system> could
   be retrieved in a NETCONF <get-data> RPC operation.  The example uses
   the "example-application" fictional data model defined in
   Appendix A.1 and the Extensible Markup Language (XML) [W3C.XML1.0]
   encoding.

   <rpc message-id="101"
        xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <get-data xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-nmda"
        xmlns:sysds="urn:ietf:params:xml:ns:yang:ietf-system-datastore">
       <datastore>sysds:system</datastore>
       <subtree-filter>
         <applications xmlns="urn:example:application"/>
       </subtree-filter>
     </get-data>
   </rpc>

   When using the RESTCONF protocol, the system configuration datastore
   can be accessed via the resource: {+restconf}/ds/ietf-system-
   datastore:system.  The following example uses an HTTP GET method to
   request "applications" configuration:

   GET /restconf/ds/ietf-system-datastore:system/\
      example-application:applications HTTP/1.1
   Host: example.com
   Accept: application/yang-data+xml

8.  IANA Considerations

8.1.  The IETF XML Registry

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

   URI:  urn:ietf:params:xml:ns:yang:ietf-system-datastore
   Registrant Contact:  The IESG
   XML:  N/A; the requested URIs are XML namespaces.

8.2.  The YANG Module Names Registry

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

   Name:  ietf-system-datastore
   Maintained by IANA?  N
   Namespace:  urn:ietf:params:xml:ns:yang:ietf-system-datastore
   Prefix:  sysds
   Reference:  RFC 10016

9.  Operational Considerations

   System configuration exists regardless of whether the server
   implements <system> or not.  The introduction of <system> provides a
   standardized way to expose system configuration within NMDA.

   NMDA clients that are not aware of <system> will continue to operate
   correctly.  They will interact only with datastores such as
   <running>, <candidate>, <intended>, and <operational> as before.  The
   presence of <system> does not change the fundamental behavior for
   such legacy clients.  Operators should be aware that to fully
   leverage the capabilities defined in this document, client
   applications need to be updated to recognize and interact with
   <system>.

10.  Security Considerations

10.1.  Considerations for the "ietf-system-datastore" YANG Module

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

   The "ietf-system-datastore" 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 and (2) have to use mutual authentication
   (e.g., Secure Shell (SSH) [RFC4252], TLS [TLS1.3], and QUIC
   [RFC9000]).

   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.

   The YANG module only defines an identity that uses the
   "ds:conventional" identity as its base.  The module by itself does
   not expose any sensitive data nodes that are writable or that contain
   read-only state, and there are no particularly sensitive RPC or
   action operations.  As such, there are no additional security issues
   related to the YANG module that need to be considered.

10.2.  Considerations for System Configuration

   The system datastore, while read-only to clients, may contain
   sensitive information such as hardware identifiers, security
   policies, and critical system resources.  Read access to sensitive
   system nodes and subtrees within the datastore MUST be controlled to
   prevent unauthorized disclosure.  Implementations are strongly
   advised to log all access attempts to sensitive system configuration
   for audit purposes.

   Furthermore, while <system> cannot be modified directly, system
   configuration may be overridden as a merging result (Section 6.3).
   An attacker may configure a leaf that shadows a sensitive node in
   <system>.  Misconfiguration in <running> could lead to unintended
   system behavior, including security policy bypass and availability
   risks.  Unauthorized modification to sensitive contents MUST be
   prevented to avoid those negative effects on the network.

11.  References

11.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC7952]  Lhotka, L., "Defining and Using Metadata with YANG",
              RFC 7952, DOI 10.17487/RFC7952, August 2016,
              <https://www.rfc-editor.org/info/rfc7952>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore Architecture
              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
              <https://www.rfc-editor.org/info/rfc8342>.

11.2.  Informative References

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC4252]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
              January 2006, <https://www.rfc-editor.org/info/rfc4252>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://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,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [RFC8525]  Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K.,
              and R. Wilton, "YANG Library", RFC 8525,
              DOI 10.17487/RFC8525, March 2019,
              <https://www.rfc-editor.org/info/rfc8525>.

   [RFC8639]  Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
              E., and A. Tripathy, "Subscription to YANG Notifications",
              RFC 8639, DOI 10.17487/RFC8639, September 2019,
              <https://www.rfc-editor.org/info/rfc8639>.

   [RFC8641]  Clemm, A. and E. Voit, "Subscription to YANG Notifications
              for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
              September 2019, <https://www.rfc-editor.org/info/rfc8641>.

   [RFC8808]  Wu, Q., Lengyel, B., and Y. Niu, "A YANG Data Model for
              Factory Default Settings", RFC 8808, DOI 10.17487/RFC8808,
              August 2020, <https://www.rfc-editor.org/info/rfc8808>.

   [RFC9000]  Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/info/rfc9000>.

   [RFC9907]  Bierman, A., Boucadair, M., Ed., and Q. Wu, "Guidelines
              for Authors and Reviewers of Documents Containing YANG
              Data Models", BCP 216, RFC 9907, DOI 10.17487/RFC9907,
              March 2026, <https://www.rfc-editor.org/info/rfc9907>.

   [TLS1.3]   Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 9846, DOI 10.17487/RFC9846, July 2026,
              <https://www.rfc-editor.org/info/rfc9846>.

   [W3C.XML1.0]
              Bray, T., Ed., Paoli, J., Ed., Sperberg-McQueen, C.M.,
              Ed., Maler, E., Ed., and F. Yergeau, Ed., "Extensible
              Markup Language (XML) 1.0 (Fifth Edition)", W3C
              Recommendation, 26 November 2008,
              <https://www.w3.org/TR/2008/REC-xml-20081126/>.  Latest
              version available at <https://www.w3.org/TR/xml/>.

   [YANG-FLAG]
              Ma, Q., Ed., Wu, Q., Lengyel, B., Ed., and H. Li, "YANG
              Metadata Annotation for Immutable Flag", Work in Progress,
              Internet-Draft, draft-ietf-netmod-immutable-flag-08, 26
              February 2026, <https://datatracker.ietf.org/doc/html/
              draft-ietf-netmod-immutable-flag-08>.

Appendix A.  Example of Dynamic Behaviors (Informative)

   This section presents some sample data models and corresponding
   contents of various datastores with different dynamic behaviors
   described in Section 6.  The XML snippets are used only for
   illustration purposes.  Note that this section does not show the
   contents of <intended> as they are related to the configuration in
   <operational>, assuming the intended configuration is applied
   successfully.  Also note that if the "origin" metadata annotation for
   configuration is unspecified in snippets, it is inherited from its
   parent node.

A.1.  Referencing System-Defined Nodes

   In this subsection, the following fictional module is used:

   module example-application {
     yang-version 1.1;
     namespace "urn:example:application";
     prefix ex-app;

     import ietf-inet-types {
       prefix inet;
     }
     container applications {
       list application {
         key "name";
         leaf name {
           type string;
         }
         leaf app-id {
           type string;
         }
         leaf protocol {
           type enumeration {
             enum tcp;
             enum udp;
           }
           mandatory true;
         }
         leaf destination-port {
           default "0";
           type inet:port-number;
         }
         leaf description {
           type string;
         }
         container security-protection {
           presence "Indicates that security protection is enabled.";
           leaf risk-level {
             type enumeration {
               enum high;
               enum low;
             }
           }
           //additional leafs for security-specific configuration...
         }
       }
     }
   }

   A fictional Access Control List (ACL) YANG module is used as follows,
   which defines a leafref for the leaf-list "application" data node to
   refer to an existing application name.

   module example-acl {
     yang-version 1.1;
     namespace "urn:example:acl";
     prefix ex-acl;

     import example-application {
       prefix ex-app;
     }

     import ietf-inet-types {
       prefix inet;
     }

     container acl {
       list acl-rule {
         key "name";
         leaf name {
           type string;
         }
         container matches {
           choice l3 {
             container ipv4 {
               leaf src-address {
                 type inet:ipv4-prefix;
               }
               leaf dst-address {
                 type inet:ipv4-prefix;
               }
             }
           }
           choice applications {
             leaf-list application {
               type leafref {
                 path "/ex-app:applications/ex-app:application"
                    + "/ex-app:name";
               }
             }
           }
         }
         leaf packet-action {
           type enumeration {
             enum forward;
             enum drop;
             enum redirect;
           }
         }
       }
     }
   }

   The server may predefine some applications as a convenience for
   clients; these applications are immediately present system
   configuration.  When the device is powered on, the system-
   instantiated application entries may be present in <system> as
   follows:

   <applications xmlns="urn:example:application">
     <application>
       <name>ftp</name>
       <app-id>001</app-id>
       <protocol>tcp</protocol>
       <destination-port>21</destination-port>
       <security-protection>
         <risk-level>low</risk-level>
       </security-protection>
     </application>
     <application>
       <name>tftp</name>
       <app-id>002</app-id>
       <protocol>udp</protocol>
       <destination-port>69</destination-port>
       <security-protection>
         <risk-level>low</risk-level>
       </security-protection>
     </application>
     <application>
       <name>smtp</name>
       <app-id>003</app-id>
       <protocol>tcp</protocol>
       <destination-port>25</destination-port>
       <security-protection>
         <risk-level>low</risk-level>
       </security-protection>
     </application>
   </applications>

   The client may also define customized applications.  Those
   applications may be present in <running> as follows:

   <applications xmlns="urn:example:application">
     <application>
       <name>my-smtp</name>
       <app-id>101</app-id>
       <protocol>tcp</protocol>
       <destination-port>2345</destination-port>
       <description>customized smtp application</description>
       <security-protection>
         <risk-level>high</risk-level>
       </security-protection>
     </application>
     <application>
       <name>my-foo</name>
       <app-id>102</app-id>
       <protocol>udp</protocol>
       <destination-port>1024</destination-port>
       <description>customized application</description>
     </application>
   </applications>

   If a client configures an ACL rule referencing some system-provided
   or customized applications, the configuration of the ACL rule may be
   shown as follows:

   <acl xmlns="urn:example:acl">
     <acl-rule>
       <name>allow-access-to-ftp-tftp</name>
       <matches>
         <ipv4>
           <src-address>198.51.100.0/24</src-address>
           <dst-address>192.0.2.0/24</dst-address>
         </ipv4>
         <application>ftp</application>
         <application>tftp</application>
         <application>my-smtp</application>
       </matches>
       <packet-action>forward</packet-action>
     </acl-rule>
   </acl>

   As different entries of application configuration in <system> and
   <running> are merged to create <intended>, and there are no merging
   conflicts in the contents between <system> and <running>,
   <operational> might contain the configuration of applications with
   the values of origin reflecting the source of entries as follows:

   <applications xmlns="urn:example:application"
                 xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
                 or:origin="or:intended">
     <application>
       <name>my-smtp</name>
       <app-id>101</app-id>
       <protocol>tcp</protocol>
       <destination-port>2345</destination-port>
       <description>customized smtp application</description>
       <security-protection>
         <risk-level>high</risk-level>
       </security-protection>
     </application>
     <application>
       <name>my-foo</name>
       <app-id>102</app-id>
       <protocol>udp</protocol>
       <destination-port>1024</destination-port>
       <description>customized application</description>
     </application>
     <application or:origin="or:system">
       <name>ftp</name>
       <app-id>001</app-id>
       <protocol>tcp</protocol>
       <destination-port>21</destination-port>
       <security-protection>
         <risk-level>low</risk-level>
       </security-protection>
     </application>
     <application or:origin="or:system">
       <name>tftp</name>
       <app-id>002</app-id>
       <protocol>udp</protocol>
       <destination-port>69</destination-port>
       <security-protection>
         <risk-level>low</risk-level>
       </security-protection>
     </application>
     <application or:origin="or:system">
       <name>smtp</name>
       <app-id>003</app-id>
       <protocol>tcp</protocol>
       <destination-port>25</destination-port>
       <security-protection>
         <risk-level>low</risk-level>
       </security-protection>
     </application>
   </applications>

A.2.  Modifying a System-Instantiated Leaf's Value

   This subsection uses the following fictional interface YANG module:

   module example-interface {
     yang-version 1.1;
     namespace "urn:example:interface";
     prefix ex-if;

     import ietf-inet-types {
       prefix inet;
     }

     container interfaces {
       list interface {
         key "name";
         leaf name {
           type string;
         }
         leaf description {
           type string;
         }
         leaf mtu {
           type uint32;
         }
         leaf-list ip-address {
           type inet:ip-address;
         }
       }
     }
   }

   Suppose the system provides an always-present loopback interface
   (named "lo0") with an MTU value "65536", a default IPv4 address of
   "127.0.0.1", and a default IPv6 address of "::1".  The configuration
   of the "lo0" interface may be present in <system> as follows:

   <interfaces xmlns="urn:example:interface">
     <interface>
       <name>lo0</name>
       <mtu>65536</mtu>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
     </interface>
   </interfaces>

   A client modifies the value of MTU to 9216 by adding the following
   configuration into <running>:

   <interfaces xmlns="urn:example:interface">
     <interface>
       <name>lo0</name>
       <mtu>9216</mtu>
     </interface>
   </interfaces>

   Since the MTU value provided by the client takes precedence over the
   system-provided value, and the "origin" value of configuration
   provided by the client is set to "intended", the configuration of
   interfaces that is present in <operational> may be as follows:

   <interfaces xmlns="urn:example:interface"
               xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
               or:origin="or:intended">
     <interface>
       <name>lo0</name>
       <mtu>9216</mtu>
       <ip-address or:origin="or:system">127.0.0.1</ip-address>
       <ip-address or:origin="or:system">::1</ip-address>
     </interface>
   </interfaces>

A.3.  Configuring Descendant Nodes of a System-Defined Node

   Based on the example in Appendix A.2, imagine the client further adds
   the description node of a "lo0" interface in <running> as follows:

   <interfaces xmlns="urn:example:interface">
     <interface>
       <name>lo0</name>
       <description>loopback</description>
     </interface>
   </interfaces>

   The configuration of interface "lo0" is present in <operational> as
   follows:

   <interfaces xmlns="urn:example:interface"
               xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
               or:origin="or:intended">
     <interface>
       <name>lo0</name>
       <description>loopback</description>
       <mtu>9216</mtu>
       <ip-address or:origin="or:system">127.0.0.1</ip-address>
       <ip-address or:origin="or:system">::1</ip-address>
     </interface>
   </interfaces>

Appendix B.  Key Use Cases (Informative)

   This section updates the "Interface Example" supplied in Appendix C.3
   of [RFC8342].

   This section provides several use cases related to how <system>
   interacts with other datastores (e.g., <candidate>, <running>,
   <intended>, and <operational>).  The following fictional interface
   data model is used:

   module example-interface-management {
     yang-version 1.1;
     namespace "urn:example:interfacemgmt";
     prefix ex-ifm;

     import ietf-inet-types {
       prefix inet;
     }

     container interfaces {
       list interface {
         key "name";
         leaf name {
           type string;
         }
         leaf type {
           type enumeration {
             enum ethernet;
             enum atm;
             enum loopback;
           }
         }
         leaf enabled {
           type boolean;
           default "true";
         }
         leaf-list ip-address {
           type inet:ip-address;
         }
         leaf speed {
           when "../type = 'ethernet'";
           type enumeration {
             enum 10Mb;
             enum 100Mb;
           }
         }
         leaf description {
           type string;
         }
       }
     }
   }

   For each use case, corresponding sample configuration in <running>,
   <system>, <intended>, and <operational> is shown.  The XML snippets
   are used only for illustration purposes.

B.1.  Device Powers On

   When the device is powered on, assume the system provides an always-
   present loopback interface named "lo0" that is not explicitly
   configured in <running>.  As a result, no interface configuration
   appears in <running>, and the content of <system> is as follows:

   <interfaces xmlns="urn:example:interfacemgmt">
     <interface>
       <name>lo0</name>
       <type>loopback</type>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
       <description>system-defined interface</description>
     </interface>
   </interfaces>

   In this case, the configuration of loopback interface is only present
   in <system>, and the configuration of interface in <intended> would
   be identical to the one in <system> shown above.

   In addition, <operational> will show the system-provided loopback
   interface.  Note that <operational> also includes the default value
   specified in the YANG module:

   <interfaces xmlns="urn:example:interfacemgmt"
               xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
               or:origin="or:system">
     <interface>
       <name>lo0</name>
       <type>loopback</type>
       <enabled or:origin="or:default">true</enabled>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
       <description>system-defined interface</description>
     </interface>
   </interfaces>

B.2.  Client Commits Configuration

   If a client creates an interface "et-0/0/0" but the interface does
   not physically exist at this point, the content of <running> appears
   as follows:

   <interfaces xmlns="urn:example:interfacemgmt">
     <interface>
       <name>et-0/0/0</name>
       <ip-address>192.168.10.10</ip-address>
       <description>pre-provisioned interface</description>
     </interface>
   </interfaces>

   And the content of <system> remains unchanged, only containing the
   "lo0" loopback interface since the interface "et-0/0/0" is not
   physically present:

   <interfaces xmlns="urn:example:interfacemgmt">
     <interface>
       <name>lo0</name>
       <type>loopback</type>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
       <description>system-defined interface</description>
     </interface>
   </interfaces>

   The content of <intended> represents the merged data of <system> and
   <running>:

   <interfaces xmlns="urn:example:interfacemgmt">
     <interface>
       <name>lo0</name>
       <type>loopback</type>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
       <description>system-defined interface</description>
     </interface>
     <interface>
       <name>et-0/0/0</name>
       <ip-address>192.168.10.10</ip-address>
       <description>pre-provisioned interface</description>
     </interface>
   </interfaces>

   Since the interface named "et-0/0/0" does not exist, the associated
   configuration is not present in <operational>, which appears as
   follows:

   <interfaces xmlns="urn:example:interfacemgmt"
               xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
               or:origin="or:intended">
     <interface or:origin="or:system">
       <name>lo0</name>
       <type>loopback</type>
       <enabled or:origin="or:default">true</enabled>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
       <description>system-defined interface</description>
     </interface>
   </interfaces>

B.3.  Operator Installs Card into a Chassis

   When the interface is installed by the operator, the system will
   detect it and generate the associated conditionally present interface
   configuration in <system>.  The content of <running> remains
   unchanged:

   <interfaces xmlns="urn:example:interfacemgmt">
     <interface>
       <name>et-0/0/0</name>
       <ip-address>192.168.10.10</ip-address>
       <description>pre-provisioned interface</description>
     </interface>
   </interfaces>

   And <system> might appear as follows:

   <interfaces xmlns="urn:example:interfacemgmt">
     <interface>
       <name>lo0</name>
       <type>loopback</type>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
       <description>system-defined interface</description>
     </interface>
     <interface>
       <name>et-0/0/0</name>
       <type>ethernet</type>
       <description>system-defined interface</description>
     </interface>
   </interfaces>

   Then, <intended> contains the merged configuration of <system> and
   <running>:

   <interfaces xmlns="urn:example:interfacemgmt">
     <interface>
       <name>lo0</name>
       <type>loopback</type>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
       <description>system-defined interface</description>
     </interface>
     <interface>
       <name>et-0/0/0</name>
       <type>ethernet</type>
       <ip-address>192.168.10.10</ip-address>
       <description>pre-provisioned interface</description>
     </interface>
   </interfaces>

   And the content of <operational> appears as follows:

   <interfaces xmlns="urn:example:interfacemgmt"
               xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
               or:origin="or:intended">
     <interface or:origin="or:system">
       <name>lo0</name>
       <type>loopback</type>
       <enabled or:origin="or:default">true</enabled>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
       <description>system-defined interface</description>
     </interface>
     <interface>
       <name>et-0/0/0</name>
       <type or:origin="or:system">ethernet</type>
       <enabled or:origin="or:default">true</enabled>
       <ip-address>192.168.10.10</ip-address>
       <description>pre-provisioned interface</description>
     </interface>
   </interfaces>

B.4.  Client Further Commits Configuration

   If the client further sets the speed of interface "et-0/0/0" in
   <running>:

   <interfaces xmlns="urn:example:interfacemgmt">
     <interface>
       <name>et-0/0/0</name>
       <speed>10Mb</speed>
     </interface>
   </interfaces>

   The content of <system> remains unchanged:

   <interfaces xmlns="urn:example:interfacemgmt">
     <interface>
       <name>lo0</name>
       <type>loopback</type>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
       <description>system-defined interface</description>
     </interface>
     <interface>
       <name>et-0/0/0</name>
       <type>ethernet</type>
       <description>system-defined interface</description>
     </interface>
   </interfaces>

   And the content of <intended>, which represents the merged result of
   <running> and <system>, is as follows:

   <interfaces xmlns="urn:example:interfacemgmt">
     <interface>
       <name>lo0</name>
       <type>loopback</type>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
       <description>system-defined interface</description>
     </interface>
     <interface>
       <name>et-0/0/0</name>
       <type>ethernet</type>
       <ip-address>192.168.10.10</ip-address>
       <speed>10Mb</speed>
       <description>pre-provisioned interface</description>
     </interface>
   </interfaces>

   And <operational> would appear as follows:

   <interfaces xmlns="urn:example:interfacemgmt"
              xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
              or:origin="or:intended">
    <interface or:origin="or:system">
      <name>lo0</name>
      <type>loopback</type>
      <enabled or:origin="or:default">true</enabled>
      <ip-address>127.0.0.1</ip-address>
      <ip-address>::1</ip-address>
      <description>system-defined interface</description>
    </interface>
    <interface>
      <name>et-0/0/0</name>
      <type or:origin="or:system">ethernet</type>
      <enabled or:origin="or:default">true</enabled>
      <ip-address>192.168.10.10</ip-address>
      <speed>10Mb</speed>
      <description>pre-provisioned interface</description>
    </interface>
   </interfaces>

Acknowledgements

   The authors would like to thank the following for discussions and
   providing input to this document: Balázs Lengyel, Robert Wilton,
   Jürgen Schönwälder, Andy Bierman, Martin Björklund, Mohamed
   Boucadair, Michal Vaško, Alexander Clemm, and Timothy Carey.

Contributors

   Kent Watsen
   Watsen Networks
   Email: kent+ietf@watsen.net


   Jan Lindblad
   Cisco Systems
   Email: jlindbla@cisco.com


   Jason Sterne
   Nokia
   Email: jason.sterne@nokia.com


   Chongfeng Xie
   China Telecom
   Beijing
   China
   Email: xiechf@chinatelecom.cn


Authors' Addresses

   Qiufang Ma (editor)
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing
   Jiangsu, 210012
   China
   Email: maqiufang1@huawei.com


   Qin Wu
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing
   Jiangsu, 210012
   China
   Email: bill.wu@huawei.com


   Chong Feng
   Email: fengchongllly@gmail.com