NETMOD                                                        Q. Ma, Ed.
Internet-Draft                                                     Q. Wu
Updates: 8342, 6241, 8526, 8040 (if approved)                     Huawei
Intended status: Standards Track                                 C. Feng
Expires: 24 August 2024                                 21 February 2024


                      System-defined Configuration
                   draft-ietf-netmod-system-config-05

Abstract

   This document defines how a management client and server handle YANG-
   modeled configuration data that is defined by the server itself.  The
   system-defined configuration can be referenced (e.g. leafref) by
   configuration explicitly created by a client.

   The Network Management Datastore Architecture (NMDA) defined in RFC
   8342 is updated with a read-only conventional configuration datastore
   called "system" to hold system-defined configuration.

   As an alternative to clients explicitly copying referenced system-
   defined configuration into the target configuration datastore (e.g.,
   <running>) so that the datastore is valid, a "resolve-system"
   parameter is defined to allow the server acting as a "system client"
   to copy referenced system nodes automatically.  This solution enables
   clients manipulating the target configuration datastore (e.g.,
   <running>) to reference nodes defined in <system>, override system-
   provided values, and configure descendant nodes of system-defined
   configuration.

   This document updates RFC 8342, RFC 6241, RFC 8526 and RFC 8040.

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."




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   This Internet-Draft will expire on 24 August 2024.

Copyright Notice

   Copyright (c) 2024 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   5
     1.3.  Updates to RFC 8342 . . . . . . . . . . . . . . . . . . .   5
     1.4.  Updates to RFC 6241 and RFC 8526  . . . . . . . . . . . .   6
     1.5.  Updates to RFC 8040 . . . . . . . . . . . . . . . . . . .   6
       1.5.1.  Query Parameter . . . . . . . . . . . . . . . . . . .   6
       1.5.2.  Query Parameter URI . . . . . . . . . . . . . . . . .   7
   2.  Kinds of System Configuration . . . . . . . . . . . . . . . .   7
     2.1.  Immediately-Active  . . . . . . . . . . . . . . . . . . .   7
     2.2.  Conditionally-Active  . . . . . . . . . . . . . . . . . .   7
     2.3.  Inactive-Until-Referenced . . . . . . . . . . . . . . . .   8
   3.  The System Configuration Datastore (<system>) . . . . . . . .   8
   4.  Static Characteristics of <system>  . . . . . . . . . . . . .   9
     4.1.  Read-only to Clients  . . . . . . . . . . . . . . . . . .   9
     4.2.  May Change via Software Upgrades or Resource Changes  . .   9
     4.3.  No Impact to <operational>  . . . . . . . . . . . . . . .  10
   5.  Dynamic Behaviors . . . . . . . . . . . . . . . . . . . . . .  10
     5.1.  Conceptual Model of Datastores  . . . . . . . . . . . . .  10
     5.2.  Explicit Declaration of System Configuration  . . . . . .  12
     5.3.  Servers Auto-configuring Referenced System Configuration
           ("resolve-system" parameter)  . . . . . . . . . . . . . .  12
     5.4.  Modifying (Overriding) System Configuration . . . . . . .  14
     5.5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .  14
       5.5.1.  Server Configuring of <running> Automatically . . . .  14
       5.5.2.  Declaring a System-defined Node in <running>
               Explicitly  . . . . . . . . . . . . . . . . . . . . .  20
       5.5.3.  Modifying a System-instantiated Leaf's Value  . . . .  21
       5.5.4.  Configuring Descendant Nodes of a System-defined
               Node  . . . . . . . . . . . . . . . . . . . . . . . .  22



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   6.  The "ietf-system-datastore" Module  . . . . . . . . . . . . .  23
     6.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .  23
     6.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .  24
     6.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  25
   7.  The "ietf-netconf-resolve-system" Module  . . . . . . . . . .  27
     7.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .  27
     7.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .  28
     7.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  28
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  31
     8.1.  The "IETF XML" Registry . . . . . . . . . . . . . . . . .  31
     8.2.  The "YANG Module Names" Registry  . . . . . . . . . . . .  31
     8.3.  NETCONF Capability URN Registry . . . . . . . . . . . . .  31
     8.4.  RESTCONF Capability URN Registry  . . . . . . . . . . . .  32
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  32
     9.1.  Regarding the "ietf-system-datastore" YANG Module . . . .  32
     9.2.  Regarding the "ietf-netconf-resolve-system" YANG
           Module  . . . . . . . . . . . . . . . . . . . . . . . . .  32
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  32
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  33
   References  . . . . . . . . . . . . . . . . . . . . . . . . . . .  33
     Normative References  . . . . . . . . . . . . . . . . . . . . .  33
     Informative References  . . . . . . . . . . . . . . . . . . . .  34
   Appendix A.  Key Use Cases  . . . . . . . . . . . . . . . . . . .  36
     A.1.  Device Powers On  . . . . . . . . . . . . . . . . . . . .  36
     A.2.  Client Commits Configuration  . . . . . . . . . . . . . .  37
     A.3.  Operator Installs Card into a Chassis . . . . . . . . . .  38
   Appendix B.  Changes between Revisions  . . . . . . . . . . . . .  39
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  40

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
   (Figure 2 in [RFC8342]).

   However, there is a desire to enable a server to better structure and
   expose the system configuration.  NETCONF/RESTCONF clients can
   benefit from a standard mechanism to retrieve what system
   configuration is available on a server.

   Some servers allow the NETCONF/RESTCONF client to reference a system-
   defined node which isn't present in the target datastore (e.g.,
   <running>).  The absence of the system configuration in the datastore
   can render the datastore invalid from the perspective of a client or
   offline tools (e.g., missing leafref targets).  This document
   describes several approaches to bring the datastore to a valid state
   and satisfy referential integrity constraints.



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   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, 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 Network Management Datastore Architecture
   (NMDA) defined in RFC 8342 with a read-only conventional
   configuration datastore called "system" to hold system-defined
   configuration.

   As an alternative to clients explicitly copying referenced system-
   defined configuration into the target configuration datastore (e.g.,
   <running>) so that the datastore is valid, a "resolve-system"
   parameter is defined to allow the server acting as a "system client"
   to copy referenced system nodes automatically.  This solution enables
   clients manipulating the target configuration datastore (e.g.,
   <running>) to reference nodes defined in <system>, override system-
   provided values, and configure descendant nodes of system-defined
   configuration.

   If a system-defined node is referenced, it refers to one of the
   following cases throughout this document:

   *  It is present in a leafref "path" statement and referred as the
      leafref value

   *  It is used as an "instance-identifier" type value

   *  It is present in an XPath expression of "when" or "must"
      constraints

   *  It is defined to satisfy the "mandatory" constraints

   *  It is defined to exactly satisfy the "min-element" constraints

   Conformance to this document requires the NMDA servers to implement
   the "ietf-system-datastore" YANG module (Section 6).

1.1.  Terminology

   This document assumes that the reader is familiar with the contents
   of [RFC6241], [RFC7950], [RFC8342], [RFC8407], and [RFC8525] and uses
   terminologies from those documents.

   The following terms are defined in this document:




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   System configuration:  Configuration that is provided by the system
      itself.  System configuration is present in the system
      configuration datastore (regardless of whether it is applied or
      referenced) and appears in <intended> unless explicitly
      overridden.  System configuration that is considered active
      appears in <operational> with origin="system".  It is a different
      and separate concept from factory default configuration defined in
      RFC 8808 (which represents a preset initial configuration that is
      used to initialize the configuration of a server).


   System configuration datastore:  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.


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 RFC 8342 to define a configuration datastore
   called "system" to hold system configuration (Section 3), it also
   redefines the term "conventional configuration datastore" from
   [RFC8342] to add "system" to the list of conventional configuration
   datastores.

   Configuration in <running> is merged into <system> to create the
   contents of <intended> after the configuration transformations to
   <running> (e.g., template expansion, removal of inactive
   configuration defined in [RFC8342]) have been performed.  This
   document updates the definition of "intended" origin metadata



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   annotation identity to allow a subset of configuration provided by
   <intended> to use "system" as origin value as it flows into
   <operational>.  Applied system configuration appears in <operational>
   with origin value being reported as "system" (Section 5.1).

1.4.  Updates to RFC 6241 and RFC 8526

   This document augments <edit-config> and <edit-data> RPC operations
   defined in [RFC6241] and [RFC8526] respectively, with a new
   additional input parameter "resolve-system" to allow the server to
   copy referenced system nodes into target datastore automatically
   without the client doing so explicitly.  The <copy-config> RPC
   operation defined in [RFC6241] is also augmented to support "resolve-
   system" parameter (Section 5.3).

   This document defines a NETCONF protocol capability to indicate
   support for this parameter.  NETCONF server that supports "resolve-
   system" parameter MUST advertise the following capability identifier:

   urn:ietf:params:netconf:capability:resolve-system:1.0

1.5.  Updates to RFC 8040

   This document extends Sections 4.8 and 9.1.1 of [RFC8040] to add a
   new query parameter "resolve-system" and corresponding query
   parameter capability URI.

1.5.1.  Query Parameter

   The "resolve-system" parameter controls whether to allow a server to
   copy any referenced system-defined configuration automatically
   without the client doing so explicitly.  This parameter is only
   allowed with no values carried.  If this parameter has any unexpected
   value, then a "400 Bad Request" status-line is returned.

  +----------------+---------+-----------------------------------------+
  | Name           | Methods | Description                             |
  +----------------+---------+-----------------------------------------+
  |resolve-system  | POST,   | resolve any references not resolved by  |
  |                | PUT     | the client and copy referenced          |
  |                | PATCH   | system configuration into <running>     |
  |                |         | automatically. This parameter can be    |
  |                |         | given in any order.                     |
  +----------------+---------+-----------------------------------------+

           Figure 1: RESTCONF "resolve-system" Query Parameter





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1.5.2.  Query Parameter URI

   To enable a RESTCONF client to discover if the "resolve-system" query
   parameter is supported by the server, the following capability URI is
   defined, which is advertised by the server if supported, using the
   "ietf-restconf-monitoring" module defined in RFC 8040:

   urn:ietf:params:restconf:capability:resolve-system:1.0

2.  Kinds of System Configuration

   There are three types of system configurations defined in this
   document: immediately-active system configuration, conditionally-
   active system configuration, and inactive-until-referenced system
   configuration.

   Active system configuration refers to system configuration that is
   currently in use.  As per definition of the operational state
   datastore in [RFC8342], if system configuration is inactive, it does
   not appear in <operational>.  However, system configuration is
   present in <system> once it is generated, regardless of whether it is
   active or not.

2.1.  Immediately-Active

   Immediately-active refers to system configuration which is generated
   in <system> and applied immediately when the device is powered on
   (e.g., a loopback interface), irrespective of physical resource
   present or not, a special functionality enabled or not.

2.2.  Conditionally-Active

   System configuration which is generated in <system> and applied based
   on specific conditions being met in a system, e.g., if a physical
   resource is present (e.g., insert interface card), the system will
   automatically detect it and load associated configuration; when the
   physical resource is not present (remove interface card), the system
   configuration will be automatically cleared.  Another example is when
   a special functionality is enabled, e.g., when a QoS feature is
   enabled, related QoS policies are automatically created by the
   system.










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2.3.  Inactive-Until-Referenced

   There are some system configuration predefined (e.g., application
   ids, anti-x signatures, trust anchor certs, etc.) as a convenience
   for the clients, which must be referenced to be active.  The clients
   can also define their own configurations for their unique
   requirements.  Inactive-until-referenced system configuration is
   generated in <system> immediately when the device is powered on, but
   it is not active until being referenced.

3.  The System Configuration Datastore (<system>)

   NMDA servers compliant with this document MUST implement a system
   configuration datastore, and they SHOULD also implement <intended>.

   Following guidelines for defining datastores in the appendix A of
   [RFC8342], this document introduces a new datastore resource named
   'system' that represents the system configuration.

   *  Name: "system"

   *  YANG modules: all

   *  YANG nodes: all "config true" data nodes up to the root of the
      tree, generated by the system

   *  Management operations: The content of the datastore is set by the
      server in an implementation dependent manner.  The content can not
      be changed by management operations via protocols such as NETCONF,
      RESTCONF, but may change itself by license change, device upgrade
      and/or system-controlled resources change.  The datastore can be
      read using the standard network management protocols such as
      NETCONF and RESCTCONF.

   *  Origin: This document does not define any new origin identity when
      it interacts with <intended> and flows into <operational>.  The
      "system" origin Metadata Annotation [RFC7952] is used to indicate
      the origin of a data item is system, which is achieved by updating
      the definition of "intended" origin metadata annotation in
      [RFC8342].

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

   *  Defining YANG module: "ietf-system-datastore".






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   The datastore's content is defined by the server and read-only to
   clients.  Upon the content is created or changed, it will be merged
   into <intended>.  Unlike <factory-default> [RFC8808], it MAY change
   dynamically, e.g., depending on factors like license change, device
   upgrade or system-controlled resources change (e.g., HW available).
   The system configuration datastore doesn't persist across reboots;
   <factory-reset> RPC operation defined in [RFC8808] can reset it to
   its factory default configuration without including configuration
   generated due to the system update or client-enabled functionality.

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

4.  Static Characteristics of <system>

4.1.  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
   override the value of a system-initialized node (see Section 5.4).

4.2.  May Change via Software Upgrades or Resource Changes

   System configuration may change dynamically, e.g., depending on
   factors like license change, device upgrade, or system-controlled
   resources (e.g., HW available) change.  In some implementations, when
   a QoS feature is enabled, QoS-related policies are created by the
   system.  The updates of system configuration may be obtained through
   YANG notifications (e.g., on-change notification)
   [RFC6470][RFC8639][RFC8641].

   If system configuration changes (e.g., due to device upgrade),
   <running> MAY become invalid.  The server behaviors of migrating
   updated system data into <running> is beyond the scope of this
   document.  That said, the following gives a list of examples of
   server implementations that might be possible:

   *  Servers migrate system configuration update into <running> with
      the clients' awareness to keep <running> valid

   *  Servers don't migrate any system configuration update into
      <running> and clients are responsible to correct the configuration
      in <running> if it becomes invalid

   *  Servers rejects the operation to change system configuration
      (e.g., device upgrade fails) and needs the client to correct the
      configuration in <running> as a prerequisite to ensure validity



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4.3.  No Impact to <operational>

   This work intends to have no impact to <operational>.  System
   configuration appears in <operational> with origin value being
   reported as "system" if not configured or overridden explicitly in
   <running>.  This document enables a subset of those system generated
   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.

5.  Dynamic Behaviors

5.1.  Conceptual Model of Datastores

   This document introduces a datastore named "system" which is used to
   hold all three types of system configurations defined in Section 2.

   When the device is powered on, immediately-active system
   configuration is generated in <system> and active immediately, but
   inactive-until-referenced system configuration only becomes active if
   referenced by client-defined configuration.  However, conditionally-
   active system configuration will only be created and active when
   specific conditions on system resources are met.

   All above three types of system configurations appear in <system>.
   Clients MAY reference nodes defined in <system>, override system-
   provided values, and configure descendant nodes of system-defined
   configuration, by copying or writing intended configurations into the
   target configuration datastore (e.g., <running>).

   To ensure the validity of <intended>, configuration in <running> is
   merged into <system> to become <intended>, in which process,
   configuration appearing in <running> takes precedence over the same
   node in <system>; additional nodes to a list entry or new list/leaf-
   list entries appearing in <running> extends the list entry or the
   whole list/leaf-list defined in <system> if the server allows the
   list/leaf-list to be updated.  If <running> includes configuration
   that requires further transformation (e.g., template expansion,
   removal of inactive configuration defined in [RFC8342]) before it can
   be applied, configuration transformations MUST be performed before
   <running> is merged into <system>.  If a server implements
   <intended>, <system> MUST be merged into <intended>.

   As a result, Figure 2 in Section 5 of RFC 8342 is updated with the
   below conceptual model of datastores which incorporates the system
   configuration datastore.




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               +-------------+                 +-----------+
               | <candidate> |                 | <startup> |
               |  (ct, rw)   |<---+       +--->| (ct, rw)  |
               +-------------+    |       |    +-----------+
                      |           |       |           |
        +-----------+ |         +-----------+         |
        | <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 2: Architectural Model of Datastores

   The "intended" identity of origin value defined in RFC 8342 to
   represent the origin of configuration provided by <intended>, this
   document updates its definition as origin source of configuration
   explicitly provided by <running>, 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.  Configuration copied from <system> into <running>
   has its origin value reported as "intended" when it flows into
   <operational>.



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   Configuration in <system> is non-deletable to clients, even though a
   client may delete a copied system node from <running>.  If system
   initializes a value for a particular leaf which is overridden by the
   client with a different value in <running>, the client may delete it
   in <running>, in which case system-initialized value defined in
   <system> may still be in use and appear in <operational>.

   Any deletable system-provided configuration that is populated as part
   of <running> by the system at boot up, without being part of the
   contents of a <startup> datastore, must be defined in <factory-
   default> [RFC8808], which is used to initialize <running> when the
   device is first-time powered on or reset to its factory default
   condition.

5.2.  Explicit Declaration of System Configuration

   It is possible for a client to explicitly declare system
   configuration nodes in the target datastore (e.g., <running>) with
   the same values as in <system>, by configuring a node (list/leaf-list
   entry, leaf, etc.) in the target datastore (e.g., <running>) that
   matches the same node and value in <system>.

   The explicit configuration of system-defined nodes in the target
   datastore (e.g., <running>) can be useful, for example, when the
   client does not want a "system client" to have a role or not support
   the "resolve-system" parameter but needs the datastore to be
   referentially complete.  The client can explicitly declare (i.e.,
   configure in the datastore like <running>) the list entries (with at
   least the keys) that are referenced elsewhere in <running>.  The
   client does not necessarily need to declare all the contents of the
   list entry (i.e. the descendant nodes), only the parts that are
   required to make the datastore appear valid.

5.3.  Servers Auto-configuring Referenced System Configuration
      ("resolve-system" parameter)

   This document defines a new parameter "resolve-system" to the input
   for the <edit-config>, <edit-data>, and <copy-config> operations.
   Clients that are aware of the "resolve-system" parameter MAY use this
   parameter to avoid the requirement to provide a referentially
   complete configuration in <running>.

   The "resolve-system" parameter is optional and has no value.  If it
   is present, and the server supports this capability, the server MUST
   copy referenced system nodes into the target datastore (e.g.,
   <running>) without the client doing the copy/paste explicitly, to
   resolve any references not resolved by the client.  The server acting
   as a "system client" like any other remote clients copies the



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   referenced system-defined nodes when triggered by the "resolve-
   system" parameter.  Legacy clients interacting with servers that
   support this parameter don't see any changes in <edit- config>/<edit-
   data> and <copy-config> behaviors.

   The server's copy referenced nodes from <system> to the target
   datastore MUST be enforced at the end of the <edit-config>/<edit-
   data> or <copy-config> operations during the validation processing,
   regardless of which target datastore it is.

   The server may automatically configure the list entries (with at
   least the keys) in the target datastore (e.g., <running>) that are
   referenced elsewhere by the clients.  Similarly, not all the contents
   of the list entry (i.e., the descendant nodes) are necessarily copied
   by the server - only the parts that are required to make
   configuration valid.

   There is no distinction between the configuration in the target
   datastore (e.g., <running>) automatically configured by the server
   and the one explicitly declared by the client, e.g., a read back of
   the datastore (i.e., <get>, <get-config> or <get-data> operation)
   returns automatically configured nodes.

   Note that even an auto-configured node is allowed to be deleted from
   the target datastore by the client, the system may automatically
   configure the deleted node again to make configuration valid, when a
   "resolve-system" parameter is carried.  It is also possible that the
   operation request (e.g., <edit-config>) may not succeed due to
   incomplete referential integrity.

   Support for the "resolve-system" parameter is OPTIONAL.  Servers not
   supporting NMDA [RFC8342] MAY also implement this parameter without
   implementing the system configuration datastore, which would only
   eliminate the ability to expose the system configuration via protocol
   operations.  If a server implements <system>, referenced system
   configuration is copied from <system> into the target datastore
   (e.g., <running>) when the "resolve-system" parameter is used;
   otherwise it is an implementation decision where to copy referenced
   system configuration into the target datastore (e.g., <running>).

   If the "resolve-system" parameter is not given by the client, the
   server should not modify <running> in any way otherwise not specified
   by the client.  Not using capitalized "SHOULD NOT" in the previous
   sentence is intentional.  The intention is to bring awareness to the
   general need to not surprise clients with unexpected changes.  It is
   desirable for clients to always opt into using mechanisms having
   server-side changes.  This document enables a client to opt into this
   behavior using the "resolve-system" parameter.  An example of this



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   type of opt-in behavior can also be found in RFC 7317, which enables
   a client to opt into its behavior using a "$0$" prefix (see
   ianach:crypt-hash type defined in [RFC7317]).

   Implementation specifics are beyond the scope of this document,
   however, due to the extra complexity brought by the "resolve-system"
   parameter, clients should be aware that it would cost a reasonable
   amount of time for the server to resolve reference, retrieve and copy
   the referenced system configuration from <system>, which could take
   multiple rounds since some errors may depend on the resolution of
   previous ones.

5.4.  Modifying (Overriding) System Configuration

   In some cases, a server may allow some parts of system configuration
   to be modified.  Modification of system configuration is achieved by
   the client writing configuration to <running> that overrides the
   system configuration.  Configurations defined in <running> take
   precedence over system configuration nodes in <system> if the server
   allows the nodes to be modified.

   For instance, descendant nodes in a system-defined list entry may be
   modifiable or not, even if some system configuration has been copied
   into <running> earlier.  If a system node is non-modifiable, then
   writing a different value for that node MUST return an error.  The
   immutability of system configuration is defined in
   [I-D.ma-netmod-immutable-flag].

   A server may also allow a client to add data 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).

5.5.  Examples

   This section presents some sample data models and corresponding
   contents of various datastores with different dynamical behaviors
   above.  The XML snippets are used only for examples.

5.5.1.  Server Configuring of <running> Automatically

   In this subsection, the following fictional module is used:









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

     import ietf-inet-types {
       prefix "inet";
     }
     container applications {
       list application {
         key "name";
         leaf name {
           type string;
         }
         leaf protocol {
           type enumeration {
             enum tcp;
             enum udp;
           }
         }
         leaf destination-port {
           type inet:port-number;
         }
       }
     }
   }

   The server may predefine some applications as a convenience for the
   clients.  These predefined configurations are active only after being
   referenced by other configurations, which fall into the "inactive-
   until-referenced" system configuration as defined in Section 2.  The
   system-instantiated application entries may be present in <system> as
   follows:


















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   <applications xmlns="urn:example:application">
     <application>
       <name>ftp</name>
       <protocol>tcp</protocol>
       <destination-port>21</destination-port>
     </application>
     <application>
       <name>tftp</name>
       <protocol>udp</protocol>
       <destination-port>69</destination-port>
     </application>
     <application>
       <name>smtp</name>
       <protocol>tcp</protocol>
       <destination-port>25</destination-port>
     </application>
   </applications>

   The client may also define its customized applications.  Suppose the
   configuration of applications is present in <running> as follows:

   <applications xmlns="urn:example:application">
     <application>
       <name>my-app-1</name>
       <protocol>tcp</protocol>
       <destination-port>2345</destination-port>
     </application>
     <application>
       <name>my-app-2</name>
       <protocol>udp</protocol>
       <destination-port>69</destination-port>
     </application>
   </applications>

   A fictional 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 "acl";

     import example-application {
       prefix "app";
     }

     import ietf-inet-types {



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       prefix "inet";
     }

     container acl {
       list acl_rule {
         key "name";
         leaf name {
           type string;
         }
         container matches {
           choice l3 {
             container ipv4 {
               leaf source_address {
                 type inet:ipv4-prefix;
               }
               leaf dest_address {
                 type inet:ipv4-prefix;
               }
             }
           }
           choice applications {
             leaf-list application {
               type leafref {
               path "/app:applications/app:application/app:name";
               }
             }
           }
         }
         leaf packet_action {
           type enumeration {
             enum forward;
             enum drop;
             enum redirect;
           }
         }
       }
     }
   }


   If a client configures an ACL rule referencing system provided
   applications which are not present in <running>, take NETCONF
   protocol for example, the client may issue an <edit-config> operation
   with the parameter "resolve-system" as follows:







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   <rpc message-id="101"
        xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <edit-config>
       <target>
         <running/>
       </target>
       <config>
         <acl xmlns="urn:example:acl">
           <acl_rule>
             <name>allow_access_to_ftp_tftp</name>
             <matches>
               <ipv4>
                 <source_address>198.51.100.0/24</source_address>
                 <dest_address>192.0.2.0/24</dest_address>
               </ipv4>
               <application>ftp</application>
               <application>tftp</application>
               <application>my-app-1</application>
             </matches>
             <packet_action>forward</packet_action>
           </acl_rule>
         </acl>
       </config>
       <resolve-system/>
     </edit-config>
   </rpc>

   The following gives the configuration of applications in <running>
   which is returned in the response to a follow-up retrieval operation:






















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   <applications xmlns="urn:example:application">
     <application>
       <name>my-app-1</name>
       <protocol>tcp</protocol>
       <destination-port>2345</destination-port>
     </application>
     <application>
       <name>my-app-2</name>
       <protocol>udp</protocol>
       <destination-port>69</destination-port>
     </application>
     <application>
       <name>ftp</name>
     </application>
     <application>
       <name>tftp</name>
     </application>
   </applications>


   And the configuration of applications is present in <operational> as
   follows:

   <applications xmlns="urn:example:application"
                 xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
                 or:origin="or:intended">
     <application>
       <name>my-app-1</name>
       <protocol>tcp</protocol>
       <destination-port>2345</destination-port>
     </application>
     <application>
       <name>my-app-2</name>
       <protocol>udp</protocol>
       <destination-port>69</destination-port>
     </application>
     <application>
       <name>ftp</name>
       <protocol or:origin="or:system">tcp</protocol>
       <destination-port or:origin="or:system">21</destination-port>
     </application>
     <application>
       <name>tftp</name>
       <protocol or:origin="or:system">udp</protocol>
       <destination-port or:origin="or:system">69</destination-port>
     </application>
   </applications>




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   Since the configuration of application "smtp" is not referenced by
   the client, and the server treats application "smtp" configuration as
   "inactive-until-referenced", it does not appear in <operational> but
   only in <system>.

5.5.2.  Declaring a System-defined Node in <running> Explicitly

   It's also possible for a client to explicitly declare the system-
   defined configurations that are referenced instead of using the
   "resolve-system" parameter.  For instance, in the above example, the
   client MAY also explicitly configure the following system defined
   applications "ftp" and "tftp" only with the list key "name" before
   referencing:

   <applications xmlns="urn:example:application">
     <application>
       <name>ftp</name>
     </application>
     <application>
       <name>tftp</name>
     </application>
   </applications>

   Then the client configures the following ACL rule referencing
   applications "ftp" and "tftp" as follows:

   <acl xmlns="urn:example:acl">
     <acl_rule>
       <name>allow_access_to_ftp_tftp</name>
       <matches>
         <ipv4>
           <source_address>198.51.100.0/24</source_address>
           <dest_address>192.0.2.0/24</dest_address>
         </ipv4>
         <application>ftp</application>
         <application>tftp</application>
         <application>my-app-1</application>
       </matches>
       <packet_action>forward</packet_action>
     </acl_rule>
   </acl>

   Once the data is written to <running>, it makes no difference whether
   it is explicitly declared by the client or automatically copied by
   the server.  The configuration for applications in <running> and
   <operational> would be identical to the ones in Section 5.5.1.





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5.5.3.  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 "exif";

     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 a loopback interface (named "lo0") with a
   MTU value "65536", a default IPv4 address of "127.0.0.1", and a
   default IPv6 address of "::1".  The configuration of "lo0" interface
   is 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>





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   A client modifies the value of MTU to 65535 and adds the following
   configuration into <running>:

   <interfaces xmlns="urn:example:interface">
     <interface>
       <name>lo0</name>
       <mtu>65535</mtu>
     </interface>
   </interfaces>

   Then the configuration of interfaces 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>
       <mtu>65535</mtu>
       <ip-address or:origin="or:system">127.0.0.1</ip-address>
       <ip-address or:origin="or:system">::1</ip-address>
     </interface>
   </interfaces>

5.5.4.  Configuring Descendant Nodes of a System-defined Node

   In the above example, image the client further configures 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:













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   <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>65535</mtu>
       <ip-address or:origin="or:system">127.0.0.1</ip-address>
       <ip-address or:origin="or:system">::1</ip-address>
     </interface>
   </interfaces>

6.  The "ietf-system-datastore" Module

6.1.  Data Model Overview

   This YANG module defines a new YANG identity named "system" that uses
   the "ds:datastore" identity defined in [RFC8342].  A client can
   discover the system configuration datastore support on the server by
   reading the YANG library information from the operational state
   datastore.  Note that no new origin identity is defined in this
   document, the "or:system" origin Metadata Annotation [RFC7952] is
   used to indicate the origin of a data item is system.  Support for
   the "origin" annotation is identified with the feature "origin"
   defined in [RFC8526].

   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].








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6.2.  Example Usage

   This section gives an example of data retrieval from <system>.  The
   fictional YANG module used following are from Appendix C.2 of
   [RFC8342].

   container bgp {
     leaf local-as {
       type uint32;
     }
     leaf peer-as {
       type uint32;
     }
     list peer {
       key name;
       leaf name {
         type inet:ip-address;
       }
       leaf local-as {
         type uint32;
         description
           "... Defaults to ../local-as.";
       }
       leaf peer-as {
         type uint32;
         description
           "... Defaults to ../peer-as.";
       }
       leaf local-port {
         type inet:port;
       }
       leaf remote-port {
         type inet:port;
         default 179;
       }
       leaf state {
         config false;
         type enumeration {
           enum init;
           enum established;
           enum closing;
         }
       }
     }
   }

   All the messages are presented in a protocol-independent manner.
   JSON is used to not imply a preferred encoding in this document.



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   Suppose the following BGP peer configuration is added to <running>:

   {
       "bgp": {
           "local-as": "64501",
           "peer-as": "64502",
           "peer": {
               "name": "2001:db8::2:3",
               "local-as": "64501",
               "peer-as": "64502"
           }
       }
   }

   The local port and remote port are used when the BGP peer connection
   is established.  Since both are not supplied explicitly in <running>
   and <intended>, the default value for "bgp/peer/remote-port" is used,
   and there is no default statement for "bgp/peer/local-port", the
   system will select a value for it.  So the contents of <system> are
   shown as follows:

   {
       "bgp": {
           "peer": {
               "name": "2001:db8::2:3",
               "local-port": "60794"
           }
       }
   }

6.3.  YANG Module

   <CODE BEGINS> file "ietf-system-datastore@2024-02-21.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 NETDOD (Network Modeling) Working Group";
     contact



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       "WG Web:   https://datatracker.ietf.org/wg/netmod/
        WG List:  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:fengchonglly@gmail.com>";
     description
       "This module defines a new YANG identity that uses the
        ds:datastore identity defined in [RFC8342].

        Copyright (c) 2024 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 HHHH
        (https://www.rfc-editor.org/info/rfcHHHH); see the RFC
        itself for full legal notices.

        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.";

     revision 2024-02-21 {
       description
         "Initial version.";
       reference
         "RFC XXXX: System-defined Configuration";
     }

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



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   <CODE ENDS>

7.  The "ietf-netconf-resolve-system" Module

   This YANG module is optional to implement.

7.1.  Data Model Overview

   This YANG module augments NETCONF <edit-config>, <edit-data> and
   <copy-config> operations with a new parameter "resolve-system" in the
   input parameters.  If the "resolve-system" parameter is present, the
   server will copy the referenced system configuration into target
   datastore automatically.  A NETCONF client can discover the "resolve-
   system" parameter support on the server by checking the server's
   capabilities included in the <hello> message.

   The following tree diagram [RFC8340] illustrates the "ietf-netconf-
   resolve-system" module:

   module: ietf-netconf-resolve-system
     augment /nc:edit-config/nc:input:
       +---w resolve-system?   empty
     augment /nc:copy-config/nc:input:
       +---w resolve-system?   empty
     augment /ncds:edit-data/ncds:input:
       +---w resolve-system?   empty

   The following tree diagram [RFC8340] illustrates "edit-config",
   "copy-config" and "edit-data" rpcs defined in "ietf-netconf" and
   "ietf-netconf-nmda" respectively, augmented by "ietf-netconf-resolve-
   system" YANG module:

     rpcs:
       +---x edit-config
       |  +---w input
       |     +---w target
       |     |  +---w (config-target)
       |     |     +--:(candidate)
       |     |     |  +---w candidate?   empty {candidate}?
       |     |     +--:(running)
       |     |        +---w running?     empty {writable-running}?
       |     +---w default-operation?   enumeration
       |     +---w test-option?         enumeration {validate}?
       |     +---w error-option?        enumeration
       |     +---w (edit-content)
       |     |   +--:(config)
       |     |   |  +---w config?        <anyxml>
       |     |   +--:(url)



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       |     |     +---w url?           inet:uri {url}?
       |     +---w resolve-system?      empty
       +---x copy-config
       |  +---w input
       |     +---w target
       |     |  +---w (config-target)
       |     |     +--:(candidate)
       |     |     |  +---w candidate?   empty {candidate}?
       |     |     +--:(running)
       |     |     |  +---w running?     empty {writable-running}?
       |     |     +--:(startup)
       |     |     |  +---w startup?     empty {startup}?
       |     |     +--:(url)
       |     |        +---w url?         inet:uri {url}?
       |     +---w source
       |     |  +---w (config-source)
       |     |     +--:(candidate)
       |     |     |  +---w candidate?   empty {candidate}?
       |     |     +--:(running)
       |     |     |  +---w running?     empty
       |     |     +--:(startup)
       |     |     |  +---w startup?     empty {startup}?
       |     |     +--:(url)
       |     |     |  +---w url?         inet:uri {url}?
       |     |     +--:(config)
       |     |        +---w config?      <anyxml>
       |     +---w resolve-system?       empty
       +---x edit-data
          +---w input
             +---w datastore            ds:datastore-ref
             +---w default-operation?   enumeration
             +---w (edit-content)
             |  +--:(config)
             |  |  +---w config?        <anydata>
             |  +--:(url)
             |     +---w url?           inet:uri {nc:url}?
             +---w resolve-system?      empty

7.2.  Example Usage

   Please refer to Section 5.5.1 for example usage of the "resolve-
   system" parameter.

7.3.  YANG Module

   <CODE BEGINS> file "ietf-netconf-resolve-system@2024-02-21.yang"





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   module ietf-netconf-resolve-system {
     yang-version 1.1;
     namespace
       "urn:ietf:params:xml:ns:yang:ietf-netconf-resolve-system";
     prefix ncrs;

     import ietf-netconf {
       prefix nc;
       reference
         "RFC 6241: Network Configuration Protocol (NETCONF)";
     }
     import ietf-netconf-nmda {
       prefix ncds;
       reference
         "RFC 8526: NETCONF Extensions to Support the Network
          Management Datastore Architecture";
     }

     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:fengchonglly@gmail.com>";
     description
       "This module defines an extension to the NETCONF protocol
        that allows the NETCONF client to control whether the server
        is allowed to copy referenced system configuration
        automatically without the client doing so explicitly.

         Copyright (c) 2024 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 HHHH
         (https://www.rfc-editor.org/info/rfcHHHH); see the RFC



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         itself for full legal notices.

         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.";

     revision 2024-02-21 {
       description
         "Initial version.";
       reference
         "RFC XXXX: System-defined Configuration";
     }

     grouping resolve-system-grouping {
       description
         "Define the resolve-system parameter grouping.";
       leaf resolve-system {
         type empty;
         description
           "When present, the server is allowed to automatically
            configure referenced system configuration into the
            target configuration datastore.";
       }
     }

     augment "/nc:edit-config/nc:input" {
       description
         "Allows the server to automatically configure
          referenced system configuration to make configuration
          valid.";
       uses resolve-system-grouping;
     }

     augment "/nc:copy-config/nc:input" {
       description
         "Allows the server to automatically configure
          referenced system configuration to make configuration
          valid.";
       uses resolve-system-grouping;
     }

     augment "/ncds:edit-data/ncds:input" {
       description
         "Allows the server to automatically configure
          referenced system configuration to make configuration



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          valid.";
       uses resolve-system-grouping;
     }
   }

   <CODE ENDS>

8.  IANA Considerations

8.1.  The "IETF XML" Registry

   This document registers two XML namespace URNs in the 'IETF XML
   registry', following the format defined in [RFC3688].

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

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

8.2.  The "YANG Module Names" Registry

   This document registers two module names in the 'YANG Module Names'
   registry, defined in [RFC6020].

      name: ietf-system-datastore
      prefix: sys
      namespace: urn:ietf:params:xml:ns:yang:ietf-system-datatstore
      maintained by IANA: N
      RFC: XXXX // RFC Ed.: replace XXXX and remove this comment


      name: ietf-netconf-resolve-system
      prefix: ncrs
      namespace: urn:ietf:params:xml:ns:yang:ietf-netconf-resolve-system
      maintained by IANA: N
      RFC: XXXX // RFC Ed.: replace XXXX and remove this comment

8.3.  NETCONF Capability URN Registry

   This document registers the following capability identifier URN in
   the 'Network Configuration Protocol (NETCONF) Capability URNs'
   registry:

   urn:ietf:params:netconf:capability:resolve-system:1.0




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8.4.  RESTCONF Capability URN Registry

   This document registers a capability in the 'RESTCONF Capability
   URNs' registry [RFC8040]:

 Index            Capability Identifier
 -----------------------------------------------------------------------
 :resolve-system  urn:ietf:params:restconf:capability:resolve-system:1.0

9.  Security Considerations

9.1.  Regarding the "ietf-system-datastore" YANG Module

   The YANG module defined in this document extends the base operations
   for NETCONF [RFC6241] and RESTCONF [RFC8040].  The lowest NETCONF
   layer is the secure transport layer, and the mandatory-to-implement
   secure transport is Secure Shell (SSH) [RFC6242].  The lowest
   RESTCONF layer is HTTPS, and the mandatory-to-implement secure
   transport is TLS [RFC8446].

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

9.2.  Regarding the "ietf-netconf-resolve-system" YANG Module

   The YANG module defined in this document extends the base operations
   for NETCONF [RFC6241] and [RFC8526].  The lowest NETCONF layer is the
   secure transport layer, and the mandatory-to-implement secure
   transport is Secure Shell (SSH) [RFC6242].  The lowest RESTCONF layer
   is HTTPS, and the mandatory-to-implement secure transport is TLS
   [RFC8446].

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

   The security considerations for the base NETCONF protocol operations
   (see Section 9 of [RFC6241] apply to the new extended RPC operations
   defined in this document.

10.  Contributors







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         Kent Watsen
         Watsen Networks

         Email: kent+ietf@watsen.net

         Jan Lindblad
         Cisco Systems

         Email: jlindbla@cisco.com

         Chongfeng Xie
         China Telecom
         Beijing
         China

         Email: xiechf@chinatelecom.cn

         Jason Sterne
         Nokia

         Email: jason.sterne@nokia.com

Acknowledgements

   The authors would like to thank for following for discussions and
   providing input to this document (ordered by first name): Alex Clemm,
   Andy Bierman, Balazs Lengyel, Juergen Schoenwaelder, Martin
   Bjorklund, Mohamed Boucadair, Robert Wilton and Timothy Carey.

References

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>.

   [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>.

   [RFC6470]  Bierman, A., "Network Configuration Protocol (NETCONF)
              Base Notifications", RFC 6470, DOI 10.17487/RFC6470,
              February 2012, <https://www.rfc-editor.org/info/rfc6470>.





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   [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>.

   [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>.

   [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>.

   [RFC8526]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "NETCONF Extensions to Support the Network
              Management Datastore Architecture", RFC 8526,
              DOI 10.17487/RFC8526, March 2019,
              <https://www.rfc-editor.org/info/rfc8526>.

   [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>.

Informative References

   [I-D.ma-netmod-immutable-flag]
              Ma, Q., Wu, Q., Lengyel, B., and H. Li, "YANG Metadata
              Annotation for Immutable Flag", Work in Progress,
              Internet-Draft, draft-ma-netmod-immutable-flag-09, 22
              October 2023, <https://datatracker.ietf.org/doc/html/
              draft-ma-netmod-immutable-flag-09>.

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






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   [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>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [RFC7317]  Bierman, A. and M. Bjorklund, "A YANG Data Model for
              System Management", RFC 7317, DOI 10.17487/RFC7317, August
              2014, <https://www.rfc-editor.org/info/rfc7317>.

   [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>.

   [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>.

   [RFC8407]  Bierman, A., "Guidelines for Authors and Reviewers of
              Documents Containing YANG Data Models", BCP 216, RFC 8407,
              DOI 10.17487/RFC8407, October 2018,
              <https://www.rfc-editor.org/info/rfc8407>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [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>.

   [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>.









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Appendix A.  Key Use Cases

   Following provides three use cases related to system-defined
   configuration lifecycle management.  The simple interface data model
   defined in Appendix C.3 of [RFC8342] is used.  For each use case,
   corresponding sample configuration in <running>, <system>, <intended>
   and <operational> are shown.  The XML snippets are used only for
   examples.

A.1.  Device Powers On

   <running>:

   No configuration for interfaces appears in <running>;

   <system>:

   <interfaces>
     <interface>
       <name>lo0</name>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
     </interface>
   </interfaces>

   <intended>:

   <interfaces>
     <interface>
       <name>lo0</name>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
     </interface>
   </interfaces>

   <operational>:

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






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A.2.  Client Commits Configuration

   If a client creates an interface "et-0/0/0" but the interface does
   not physically exist at this point:

   <running>:

   <interfaces>
     <interface>
       <name>et-0/0/0</name>
       <description>Test interface</description>
     </interface>
   </interfaces>

   <system>:

   <interfaces>
     <interface>
       <name>lo0</name>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
     </interface>
   </interfaces>

   <intended>:

   <interfaces>
     <interface>
       <name>lo0</name>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
     </interface>
     <interface>
       <name>et-0/0/0</name>
       <description>Test interface</description>
     </interface>
   </interfaces>

   <operational>:

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



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A.3.  Operator Installs Card into a Chassis

   <running>:

   <interfaces>
     <interface>
       <name>et-0/0/0</name>
       <description>Test interface</description>
     </interface>
   </interfaces>

   <system>:

   <interfaces>
     <interface>
       <name>lo0</name>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
     </interface>
     <interface>
       <name>et-0/0/0</name>
       <mtu>1500</mtu>
     </interface>
   </interfaces>

   <intended>:

   <interfaces>
     <interface>
       <name>lo0</name>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
     </interface>
     <interface>
       <name>et-0/0/0</name>
       <description>Test interface</description>
       <mtu>1500</mtu>
     </interface>
   </interfaces>

   <operational>:










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   <interfaces xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
               or:origin="or:intended">
     <interface or:origin="or:system">
       <name>lo0</name>
       <ip-address>127.0.0.1</ip-address>
       <ip-address>::1</ip-address>
     </interface>
     <interface>
       <name>et-0/0/0</name>
       <description>Test interface</description>
       <mtu or:origin="or:system">1500</mtu>
     </interface>
   </interfaces>

Appendix B.  Changes between Revisions

   v04 - v05

   *  Explicitly state that system configuration copied from <system>
      into <running> have its origin value being reported as "intended"
      and update the examples accordingly to reflect it

   *  Update the definition of "intended" origin identity in 8342 to
      allow a subset of configuration in <intended> to use "system" as
      origin value

   *  State server behaviors of migrating updated system data into
      <running> is beyond the scope of this document, and give a couple
      of implementation examples

   *  Remove the related statement which mandates referenced system
      configuration must be copied into <running>

   *  Refine usage examples (e.g., fix validation errors, remove
      redundancy)

   v03 - v04

   *  Add some implementation consideration for "resolve-system"
      parameter

   *  Define a NETCONF capability identifier for "resolve-system"
      parameter so that the client can discover if it is supported by
      the server.

   *  state servers may upgrade copied system configuration in <running>
      as well during device upgrade or licensing change.




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   v02 - v03

   *  remove the merge mechanism related comments, as discussed in
      https://github.com/netconf-wg/netconf-next/issues/19

   *  Editorial changes

   v01 - v02

   *  Define referenced system configuration

   *  better clarify "resolve-system" parameter

   *  update Figure 2 in NMDA RFC

   *  Editorial changes

   v00 - v01

   *  Clarify why client's explicit copy is not preferred but cannot be
      avoided if resolve-system parameter is not defined

   *  Clarify active system configuration

   *  Update the timing when the server's auto copy should be enforced
      if a resolve-system parameter is used

   *  Editorial changes

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




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   Feng Chong
   Email: fengchongllly@gmail.com

















































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