Skip to main content

System-defined Configuration
draft-ietf-netmod-system-config-01

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft whose latest revision state is "Active".
Authors Qiufang Ma , Qin Wu , Chong Feng
Last updated 2023-01-04
Replaces draft-ma-netmod-with-system
RFC stream Internet Engineering Task Force (IETF)
Formats
Additional resources Mailing list discussion
Stream WG state WG Document
Document shepherd (None)
IESG IESG state I-D Exists
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD (None)
Send notices to (None)
draft-ietf-netmod-system-config-01
NETMOD                                                        Q. Ma, Ed.
Internet-Draft                                                     Q. Wu
Updates: RFC8342, RFC6241, RFC8526, RFC8040 (if                  C. Feng
         approved)                                                Huawei
Intended status: Standards Track                          4 January 2023
Expires: 8 July 2023

                      System-defined Configuration
                   draft-ietf-netmod-system-config-01

Abstract

   This document updates Network Management Datastore Architecture
   (NMDA) to define a read-only conventional configuration datastore
   called "system" to hold system-defined configurations.  To avoid
   clients' explicit copy/paste of referenced system-defined
   configuration into the target configuration datastore (e.g.,
   <running>), a "resolve-system" parameter is defined to allow the
   server acting as a "system client" to copy referenced system-defined
   nodes automatically.  This solution enables clients manipulating the
   target configuration datastore (e.g., <running>) to reference nodes
   defined in <system>, override values of configurations defined in
   <system>, and configure descendant nodes of system-defined nodes.

   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."

   This Internet-Draft will expire on 8 July 2023.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Ma, et al.                 Expires 8 July 2023                  [Page 1]
Internet-Draft        System-defined Configuration          January 2023

   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  . . . . . . . . . . . .   5
     1.5.  Updates to RFC 8040 . . . . . . . . . . . . . . . . . . .   6
       1.5.1.  Query Parameter . . . . . . . . . . . . . . . . . . .   6
       1.5.2.  Query Parameter URI . . . . . . . . . . . . . . . . .   6
   2.  Kinds of System Configuration . . . . . . . . . . . . . . . .   7
     2.1.  Immediately-Active  . . . . . . . . . . . . . . . . . . .   7
     2.2.  Conditionally-Active  . . . . . . . . . . . . . . . . . .   7
     2.3.  Inactive-Until-Referenced . . . . . . . . . . . . . . . .   7
   3.  The <system> Configuration Datastore  . . . . . . . . . . . .   7
   4.  Static Characteristics of the <system> Configuration
           Datastore . . . . . . . . . . . . . . . . . . . . . . . .   9
     4.1.  Read-only to Clients  . . . . . . . . . . . . . . . . . .   9
     4.2.  May Change via Software Upgrades  . . . . . . . . . . . .   9
     4.3.  No Impact to <operational>  . . . . . . . . . . . . . . .   9
   5.  Dynamic Behavior  . . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  Conceptual Model of Datastores  . . . . . . . . . . . . .   9
     5.2.  Explicit Declaration of System Configuration  . . . . . .  11
     5.3.  Servers Auto-configuring Referenced System
           Configuration . . . . . . . . . . . . . . . . . . . . . .  11
     5.4.  Modifying (overriding) System Configuration . . . . . . .  12
     5.5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .  13
       5.5.1.  Server Configuring of <running> Automatically . . . .  13
       5.5.2.  Declaring a System-defined Node in <running>
               Explicitly  . . . . . . . . . . . . . . . . . . . . .  18
       5.5.3.  Modifying a System-instantiated Leaf's Value  . . . .  21
       5.5.4.  Configuring Descendant Nodes of a System-defined
               Node  . . . . . . . . . . . . . . . . . . . . . . . .  23
   6.  The "ietf-system-datastore" Module  . . . . . . . . . . . . .  24
     6.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .  25
     6.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .  25
     6.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  26
   7.  The "ietf-netconf-resolve-system" Module  . . . . . . . . . .  27
     7.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .  28

Ma, et al.                 Expires 8 July 2023                  [Page 2]
Internet-Draft        System-defined Configuration          January 2023

     7.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .  29
     7.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  32
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  34
     8.1.  The "IETF XML" Registry . . . . . . . . . . . . . . . . .  34
     8.2.  The "YANG Module Names" Registry  . . . . . . . . . . . .  35
     8.3.  RESTCONF Capability URN Registry  . . . . . . . . . . . .  35
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  35
     9.1.  Regarding the "ietf-system-datastore" YANG Module . . . .  35
     9.2.  Regarding the "ietf-netconf-resolve-system" YANG
           Module  . . . . . . . . . . . . . . . . . . . . . . . . .  36
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  36
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  37
   References  . . . . . . . . . . . . . . . . . . . . . . . . . . .  37
     Normative References  . . . . . . . . . . . . . . . . . . . . .  37
     Informative References  . . . . . . . . . . . . . . . . . . . .  38
   Appendix A.  Key Use Cases  . . . . . . . . . . . . . . . . . . .  39
     A.1.  Device Powers On  . . . . . . . . . . . . . . . . . . . .  39
     A.2.  Client Commits Configuration  . . . . . . . . . . . . . .  40
     A.3.  Operator Installs Card into a Chassis . . . . . . . . . .  41
   Appendix B.  Changes between Revisions  . . . . . . . . . . . . .  42
   Appendix C.  Open Issues tracking . . . . . . . . . . . . . . . .  42
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  42

1.  Introduction

   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.

   In some cases, the NETCONF/RESTCONF client references a system
   configuration which isn't present in the target datastore (e.g.,
   <running>), thus the configuration is considered invalid.  To
   facilitate manipulation of the client configuration, having to copy
   the entire contents of the system configuration into the target
   datastore should be avoided or reduced when possible while ensuring
   that all referential integrity constraints are satisfied.

Ma, et al.                 Expires 8 July 2023                  [Page 3]
Internet-Draft        System-defined Configuration          January 2023

   In some other cases, configuration of descendant nodes of system-
   defined configuration needs to be supported.  For example, the system
   configuration contains 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.,
   "name" and "type" set by the system).

   This document updates NMDA [RFC8342] to define a read-only
   conventional configuration datastore called "system" to hold system-
   defined configurations.  To avoid clients' explicit copy/paste of
   referenced system-defined configuration into the target configuration
   datastore (e.g., <running>), a "resolve-system" parameter has been
   defined to allow the server acting as a "system client" to copy
   referenced system-defined nodes automatically.  The solution enables
   clients manipulating the target configuration datastore (e.g.,
   <running>) to overlay and reference nodes defined in <system>,
   override values of configurations defined in <system>, and configure
   descendant nodes of system-defined nodes.

   Conformance to this document requires 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:

   System configuration:  Configuration that is provided by the system
      itself.  System configuration is present in <system> once it is
      created (regardless of being applied by the device), and appears
      in <intended> which is subject to validation.  Applied system
      configuration also appears in <operational> with origin="system".

   System configuration datastore:  A configuration datastore holding
      the complete 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

Ma, et al.                 Expires 8 July 2023                  [Page 4]
Internet-Draft        System-defined Configuration          January 2023

      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, it also redefines the
   term "conventional configuration datastore" from RFC 8342 to add
   "system" to the list of conventional configuration datastores.  The
   contents of <system> datastore are read-only to clients but may
   change dynamically.  The <system> aware client may retrieve all three
   types of system configuration defined in Section 2, reference nodes
   defined in <system>, override values of configurations defined in
   <system>, and configure descendant nodes of system-defined nodes.

   The server will merge <running> and <system> to create <intended>.
   As always, system configuration will appear in <operational> with
   origin="system" when it is in use.

   The <system> datastore makes system configuration visible to clients
   in order for being referenced or configurable prior to present in
   <operational>.

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".  The <copy-config> RPC
   operation defined in [RFC6241] is also augmented to support "resolve-
   system" parameter.

   The "resolve-system" parameter is optional and has no value.  When it
   is provided and the server detects that there is a reference to a
   system-defined node during the validation, the server will
   automatically copy the referenced system configuration into the
   validated datastore to make the configuration valid without the

Ma, et al.                 Expires 8 July 2023                  [Page 5]
Internet-Draft        System-defined Configuration          January 2023

   client doing so explicitly.  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, regardless of which target
   datastore it is.

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
   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.                     |
  +----------------+---------+-----------------------------------------+

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

   Comment: Should we define a similar capability identifier for NETCONF
   protocol?

Ma, et al.                 Expires 8 July 2023                  [Page 6]
Internet-Draft        System-defined Configuration          January 2023

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 configuration that is in use by
   a device.  As per definition of the operational state datastore in
   [RFC8342], if system configuration is inactive, it should 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 system configurations are those 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 configurations which are 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 pre-provisioned
   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.

2.3.  Inactive-Until-Referenced

   There are some system configurations 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 configurations are
   generated in <system> immediately when the device is powered on, but
   they are not applied and active until being referenced.

3.  The <system> Configuration Datastore

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

Ma, et al.                 Expires 8 July 2023                  [Page 7]
Internet-Draft        System-defined Configuration          January 2023

   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 upgrades and/or when resource-
      conditions are met.  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> datastore and flows into
      <operational>.  The "system" origin Metadata Annotation [RFC7952]
      is used to indicate the origin of a data item is system.

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

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

   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> datastore.  Unlike <factory-default>[RFC8808], it MAY
   change dynamically, e.g., depending on factors like device upgrade or
   system-controlled resources change (e.g., HW available).  The
   <system> datastore doesn't persist across reboots; the contents of
   <system> will be lost upon reboot and recreated by the system with
   the same or changed contents.  <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.  The <system> configuration datastore must
   always be valid, as defined in Section 8.1 of [RFC7950].

Ma, et al.                 Expires 8 July 2023                  [Page 8]
Internet-Draft        System-defined Configuration          January 2023

4.  Static Characteristics of the <system> Configuration Datastore

4.1.  Read-only to Clients

   The <system> configuration datastore is a read-only configuration
   datastore (i.e., edits towards <system> directly MUST be denied),
   though the client may be allowed to override the value of a system-
   initialized data node (see Section 5.4).

4.2.  May Change via Software Upgrades

   System configuration may change dynamically, e.g., depending on
   factors like device upgrade or if 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.  If the
   system configuration gets changed, YANG notifications (e.g., "push-
   change-update" notification) [RFC6470][RFC8639][RFC8641] can be used
   to notify the client.  Any update of the contents in <system> will
   not cause the automatic update of <running>, even if some of the
   system configuration has already been copied into <running>
   explicitly or automatically before the update.

4.3.  No Impact to <operational>

   This work intends to have no impact to <operational>.  System
   configuration will appear in <operational> with "origin=system".
   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 Behavior

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 will be generated in <system> and applied immediately
   but inactive-until-referenced system configuration only becomes
   active if it is referenced by client-defined configuration.  While
   conditionally-active system configuration will be created and
   immediately applied if the condition on system resources is met when
   the device is powered on or running.

Ma, et al.                 Expires 8 July 2023                  [Page 9]
Internet-Draft        System-defined Configuration          January 2023

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

   The server will merge <running> and <system> to create <intended>, in
   which process, the data node appears in <running> takes precedence
   over the same node in <system> if the server allows the node to be
   modifiable; additional nodes to a list entry or new list/leaf-list
   entries appear 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.  In addition, the <intended> configuration datastore
   represents the configuration after all configuration transformation
   to <system> are performed (e.g., system-defined template expansion,
   removal of inactive system configuration).  If a server implements
   <intended>, <system> MUST be merged into <intended>.

   Servers MUST enforce that configuration references in <running> are
   resolved within the <running> datastore and ensure that <running>
   contains any referenced system configuration.  Clients MUST either
   explicitly copy system-defined nodes into <running> or use the
   "resolve-system" parameter.  The server MUST enforce that the
   referenced system nodes configured into <running> by the client is
   consistent with <system>.  Note that <system> aware clients know how
   to discover what nodes exist in <system>.  How clients unaware of the
   <system> datastore can find appropriate configurations is beyond the
   scope of this document.

   No matter how the referenced system configurations are copied into
   <running>, the nodes copied into <running> would always be returned
   after a read of <running>, regardless if the client is <system>
   aware.

   Configuration defined in <system> is present in <operational> if it
   is actively in use by the device, even if a client may delete the
   configuration copied from <system> into <running>.  For example,
   system initializes a value for a particular leaf which is overridden
   by the client with a different value in <running>.  The client may
   delete that node in <running>, in which case system-initialized value
   defined in <system> can be still in use and appear in <operational>.
   Any deletable system-provided configuration 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.

Ma, et al.                 Expires 8 July 2023                 [Page 10]
Internet-Draft        System-defined Configuration          January 2023

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>.

   This explicit configuration of system-defined nodes in <running> can
   be useful, for example, when the client doesn't want a "system
   client" to have a role or hasn't implemented the "resolve-system"
   parameter.  The client can explicitly declare (i.e., configure in
   <running>) the list entries (with at least the keys) for any system
   configuration list entries 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 <running> appear valid.

5.3.  Servers Auto-configuring Referenced System Configuration

   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>.

   Non-NMDA servers MAY 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" is present, and the server supports this
   capability, the server MUST copy relevant referenced system-defined
   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 referenced system-defined nodes
   when triggered by the "resolve-system" parameter.

   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

Ma, et al.                 Expires 8 July 2023                 [Page 11]
Internet-Draft        System-defined Configuration          January 2023

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

   The server may automatically configure the list entries (with at
   least the keys) in the target datastore (e.g., <running>) for any
   system configuration list entries 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 the <running> valid.  A read
   back of <running> (i.e., <get>, <get-config> or <get-data> operation)
   returns those automatically copied nodes.

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, list keys in system configuration can't be changed by a
   client, but other descendant nodes in a list entry may be modifiable
   or non-modifiable.  Leafs and leaf-lists outside of lists may also be
   modifiable or non-modifiable.  Even if some system configuration has
   been copied into <running> earlier, whether it is modifiable or not
   in <running> follows general YANG constraints and NACM rules, and
   other server-internal restrictions.  If a system configuration node
   is non-modifiable, then writing a different value for that node MUST
   return an error.  The immutability of system configuration is further
   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).

   Comment 1: What if <system> contains a set of values for a leaf-list,
   and a client configures another set of values for that leaf-list in
   <running>, will the set of values in <running> completely replace the
   set of values in <system>?  Or the two sets of values are merged
   together?

Ma, et al.                 Expires 8 July 2023                 [Page 12]
Internet-Draft        System-defined Configuration          January 2023

   Comment 2: how "ordered-by user" lists and leaf-lists are merged?  Do
   the <running> values go before or after, or is this a case where a
   full-replace is needed.

5.5.  Examples

   This section shows some examples of server-configuring of <running>
   automatically, declaring a system-defined node in <running>
   explicitly, modifying a system-instantiated leaf's value and
   configuring descendant nodes of a system-defined node.  For each
   example, the corresponding XML snippets are provided.

5.5.1.  Server Configuring of <running> Automatically

   In this subsection, the following fictional module is used:

            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;
                  }
                }
              }
            }

Ma, et al.                 Expires 8 July 2023                 [Page 13]
Internet-Draft        System-defined Configuration          January 2023

   The server may predefine some applications as a convenience for the
   clients.  These predefined configurations are applied 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:

           <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.

Ma, et al.                 Expires 8 July 2023                 [Page 14]
Internet-Draft        System-defined Configuration          January 2023

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

            import example-application {
              prefix "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 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;
                  }
                }
              }
            }
          }

Ma, et al.                 Expires 8 July 2023                 [Page 15]
Internet-Draft        System-defined Configuration          January 2023

   If a client configures an ACL rule referencing system predefined
   nodes which are not present in <running>, the client may issue an
   <edit-config> operation with the parameter "resolve-system" as
   follows:

          <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>

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

Ma, et al.                 Expires 8 July 2023                 [Page 16]
Internet-Draft        System-defined Configuration          January 2023

           <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>

   Then 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 or:origin="or:system">
            <name>ftp</name>
            <protocol>tcp</protocol>
            <destination-port>21</destination-port>
          </application>
          <application or:origin="or:system">
            <name>tftp</name>
            <protocol>udp</protocol>
            <destination-port>69</destination-port>
          </application>
        </applications>

Ma, et al.                 Expires 8 July 2023                 [Page 17]
Internet-Draft        System-defined Configuration          January 2023

   Since the configuration of application "smtp" is not referenced by
   the client, 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.  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:

             <rpc message-id="101"
                  xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
                <edit-config>
                  <target>
                    <running/>
                  </target>
                  <config>
                    <applications xmlns="urn:example:application">
                      <application>
                        <name>ftp</name>
                      </application>
                      <application>
                        <name>tftp</name>
                      </application>
                    </applications>
                  </config>
                </edit-config>
              </rpc>

   Then the client issues an <edit-config> operation to configure an ACL
   rule referencing applications "ftp" and "tftp" without the parameter
   "resolve-system" as follows:

Ma, et al.                 Expires 8 July 2023                 [Page 18]
Internet-Draft        System-defined Configuration          January 2023

          <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>
            </edit-config>
          </rpc>

   Then following gives the configuration of applications in <running>
   which is returned in the response to a follow-up <get-config>
   operation, all the configuration of applications are explicitly
   configured by the client:

Ma, et al.                 Expires 8 July 2023                 [Page 19]
Internet-Draft        System-defined Configuration          January 2023

           <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>

   Then 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>

Ma, et al.                 Expires 8 July 2023                 [Page 20]
Internet-Draft        System-defined Configuration          January 2023

   Since the application names "ftp" and "tftp" are explicitly
   configured by the client, they take precedence over the values in
   <system>, the "origin" attribute will be set to "intended".

5.5.3.  Modifying a System-instantiated Leaf's Value

   In this subsection, we will use this fictional QoS data model:

          module example-qos-policy {
            yang-version 1.1;
            namespace "urn:example:qos";
            prefix "qos";

            container qos-policies {
               list policy {
                 key "name";
                 leaf name {
                 type string;
               }
                 list queue {
                   key "queue-id";
                     leaf queue-id {
                       type int32 {
                         range "1..32";
                       }
                     }
                     leaf maximum-burst-size {
                       type int32 {
                         range "0..100";
                       }
                     }
                   }
                 }
               }
             }

   Suppose a client creates a qos policy "my-policy" with 4 system
   instantiated queues(1~4).  The configuration of qos-policies is
   present in <system> as follows:

Ma, et al.                 Expires 8 July 2023                 [Page 21]
Internet-Draft        System-defined Configuration          January 2023

           <qos-policies xmlns="urn:example:qos">
             <name>my-policy</name>
             <queue>
               <queue-id>1</queue-id>
               <maximum-burst-size>50</maximum-burst-size>
             </queue>
             <queue>
               <queue-id>2</queue-id>
               <maximum-burst-size>60</maximum-burst-size>
             </queue>
             <queue>
               <queue-id>3</queue-id>
               <maximum-burst-size>70</maximum-burst-size>
             </queue>
             <queue>
               <queue-id>4</queue-id>
               <maximum-burst-size>80</maximum-burst-size>
             </queue>
           </qos-policies>

   A client modifies the value of maximum-burst-size to 55 in queue-id
   1:

           <rpc message-id="101"
                xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
             <edit-config>
               <target>
                 <running/>
               </target>
               <config>
                 <qos-policies xmlns="urn:example:qos">
                   <name>my-policy</name>
                   <queue>
                     <queue-id>1</queue-id>
                     <maximum-burst-size>55</maximum-burst-size>
                   </queue>
                 </qos-policies>
               </config>
             </edit-config>
           </rpc>

   Then, the configuration of qos-policies is present in <operational>
   as follows:

Ma, et al.                 Expires 8 July 2023                 [Page 22]
Internet-Draft        System-defined Configuration          January 2023

        <qos-policies  xmlns="urn:example:qos"
                       xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
                       or:origin="or:intended">
          <name>my-policy</name>
          <queue>
            <queue-id>1</queue-id>
            <maximum-burst-size>55</maximum-burst-size>
          </queue>
          <queue or:origin="or:system">
            <queue-id>2</queue-id>
            <maximum-burst-size>60</maximum-burst-size>
          </queue>
           <queue or:origin="or:system">
            <queue-id>3</queue-id>
            <maximum-burst-size>70</maximum-burst-size>
          </queue>
           <queue or:origin="or:system">
            <queue-id>4</queue-id>
            <maximum-burst-size>80</maximum-burst-size>
          </queue>
        </qos-policies>

5.5.4.  Configuring Descendant Nodes of a System-defined Node

   This subsection also uses the fictional interface YANG module defined
   in Appendix C.3 of [RFC8342].  Suppose the system provides a loopback
   interface (named "lo0") with 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>
           <interface>
             <name>lo0</name>
             <ip-address>127.0.0.1</ip-address>
             <ip-address>::1</ip-address>
           </interface>
         </interfaces>

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

Ma, et al.                 Expires 8 July 2023                 [Page 23]
Internet-Draft        System-defined Configuration          January 2023

        <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>

   Later on, the client further configures the description node of a
   "lo0" interface as follows:

        <rpc message-id="101"
             xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
          <edit-config>
            <target>
              <running/>
            </target>
            <config>
              <interfaces>
                <interface>
                  <name>lo0</name>
                  <description>loopback</description>
                </interface>
              </interfaces>
            </config>
          </edit-config>
        </rpc>

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

          <interfaces xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"
                      or:origin="or:intended">
            <interface>
              <name>lo0</name>
              <description>loopback</description>
              <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

Ma, et al.                 Expires 8 July 2023                 [Page 24]
Internet-Draft        System-defined Configuration          January 2023

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> 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].

6.2.  Example Usage

   This section gives an example of data retrieval from <system>.  The
   YANG module used are shown in Appendix C.2 of [RFC8342].  All the
   messages are presented in a protocol-independent manner.  JSON is
   used only for its conciseness.

   Suppose the following data is added to <running>:

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

Ma, et al.                 Expires 8 July 2023                 [Page 25]
Internet-Draft        System-defined Configuration          January 2023

   REQUEST (a <get-data> or GET request sent from the NETCONF or
   RESTCONF client):

   Datastore: <system>
   Target:/bgp

   An example of RESTCONF request:

         GET /restconf/ds/system/bgp HTTP/1.1
         Host: example.com
         Accept: application/yang-data+xml

   RESPONSE ("local-port" leaf value is supplied by the system):

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

6.3.  YANG Module

   <CODE BEGINS> file "ietf-system-datastore@2023-01-05.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
       "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>

Ma, et al.                 Expires 8 July 2023                 [Page 26]
Internet-Draft        System-defined Configuration          January 2023

        Author: Chong Feng
                <mailto:frank.fengchong@huawei.com>";
     description
       "This module defines a new YANG identity that uses the
        ds:datastore identity defined in [RFC8342].

        Copyright (c) 2022 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 2023-01-05 {
       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.";
     }
   }

   <CODE ENDS>

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

   This YANG module is optional to implement.

Ma, et al.                 Expires 8 July 2023                 [Page 27]
Internet-Draft        System-defined Configuration          January 2023

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 YANG library
   information with "ietf-netconf-resolve-system" YANG module included
   from the operational state datastore.

   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)
       |     |     +---w url?           inet:uri {url}?
       |     +---w resolve-system?      empty
       +---x copy-config
       |  +---w input
       |     +---w target

Ma, et al.                 Expires 8 July 2023                 [Page 28]
Internet-Draft        System-defined Configuration          January 2023

       |     |  +---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

   This section gives an example of an <edit-config> request to
   reference system-defined data nodes which are not present in
   <running> with a "resolve-system" parameter.  A retrieval of
   <running> to show the auto-copied referenced system configurations
   after the <edit-config> request is also given.  The YANG module used
   is shown as follows, leafrefs refer to an existing name and address
   of an interface:

Ma, et al.                 Expires 8 July 2023                 [Page 29]
Internet-Draft        System-defined Configuration          January 2023

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

      container interfaces {
        list interface {
          key name;
          leaf name {
            type string;
          }
          leaf description {
            type string;
          }
          leaf mtu {
            type uint16;
          }
          leaf ip-address {
            type inet:ip-address;
          }
        }
      }
      container default-address {
        leaf ifname {
          type leafref {
            path "../../interfaces/interface/name";
          }
        }
        leaf address {
          type leafref {
            path "../../interfaces/interface[name = current()/../ifname]"
               + "/ip-address";
          }
        }
      }
    }

   Image that the system provides a loopback interface (named "lo0")
   with a predefined MTU value of "1500" and a predefined IP address of
   "127.0.0.1".  The <system> datastore shows the following
   configuration of loopback interface:

Ma, et al.                 Expires 8 July 2023                 [Page 30]
Internet-Draft        System-defined Configuration          January 2023

   <interfaces xmlns="urn:example:interfacemgmt">
     <interface>
       <name>lo0</name>
       <mtu>1500</mtu>
       <ip-address>127.0.0.1</ip-address>
     </interface>
   </interfaces>

   The client sends an <edit-config> operation to add the configuration
   of default-address with a "resolve-system" parameter:

  <rpc xmlns="urn:ietf:params:xml:ns:netconf:base:1.0" message-id="101">
    <edit-config>
      <target>
        <running/>
      </target>
      <config>
        <default-address xmlns="urn:example:interfacemgmt">
          <if-name>lo0</if-name>
          <address>127.0.0.1</address>
        </default-address>
      </config>
     <resolve-system/>
    </edit-config>
  </rpc>

   Since the "resolve-system" parameter is provided, the server will
   resolve any leafrefs to system configurations and copy the referenced
   system-defined nodes into <running> automatically with the same value
   (i.e., the name and ip-address data nodes of lo0 interface) in
   <system> at the end of <edit-config> operation constraint
   enforcement.  After the processing, a positive response is returned:

   <rpc-reply message-id="101"
        xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <ok/>
   </rpc-reply>

   Then the client sends a <get-config> operation towards <running>:

Ma, et al.                 Expires 8 July 2023                 [Page 31]
Internet-Draft        System-defined Configuration          January 2023

   <rpc message-id="101"
        xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <get-config>
       <source>
         <running/>
       </source>
       <filter type="subtree">
         <interfaces xmlns="urn:example:interfacemgmt"/>
       </filter>
     </get-config>
   </rpc>

   Given that the referenced interface "name" and "ip-address" of lo0
   are configured by the server, the following response is returned:

   <rpc-reply message-id="101"
        xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <data>
       <interfaces xmlns="urn:example:interfacemgmt">
         <interface>
           <name>lo0</name>
           <ip-address>127.0.0.1</ip-address>
         </interface>
       </interfaces>
     </data>
   </rpc-reply>

7.3.  YANG Module

   <CODE BEGINS> file "ietf-netconf-resolve-system@2023-01-05.yang"

  =============== NOTE: '\' line wrapping per RFC 8792 ================

  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";

Ma, et al.                 Expires 8 July 2023                 [Page 32]
Internet-Draft        System-defined Configuration          January 2023

    }

    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:frank.fengchong@huawei.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) 2022 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 2023-01-05 {
      description
        "Initial version.";
      reference
        "RFC XXXX: System-defined Configuration";
    }

Ma, et al.                 Expires 8 July 2023                 [Page 33]
Internet-Draft        System-defined Configuration          January 2023

    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
         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].

Ma, et al.                 Expires 8 July 2023                 [Page 34]
Internet-Draft        System-defined Configuration          January 2023

      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.  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].

Ma, et al.                 Expires 8 July 2023                 [Page 35]
Internet-Draft        System-defined Configuration          January 2023

   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

         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

Ma, et al.                 Expires 8 July 2023                 [Page 36]
Internet-Draft        System-defined Configuration          January 2023

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. and RFC Publisher, "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.,
              Bierman, A., Ed., and RFC Publisher, "Network
              Configuration Protocol (NETCONF)", RFC 6241,
              DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

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

   [RFC7950]  Bjorklund, M., Ed. and RFC Publisher, "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., Watsen, K., and RFC Publisher,
              "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040,
              January 2017, <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              Wilton, R., and RFC Publisher, "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.,
              Wilton, R., and RFC Publisher, "NETCONF Extensions to
              Support the Network Management Datastore Architecture",
              RFC 8526, DOI 10.17487/RFC8526, March 2019,
              <https://www.rfc-editor.org/info/rfc8526>.

Ma, et al.                 Expires 8 July 2023                 [Page 37]
Internet-Draft        System-defined Configuration          January 2023

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

   [RFC8641]  Clemm, A., Voit, E., and RFC Publisher, "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 Extension
              and Metadata Annotation for Immutable Flag", Work in
              Progress, Internet-Draft, draft-ma-netmod-immutable-flag-
              04, 20 October 2022,
              <https://datatracker.ietf.org/doc/html/draft-ma-netmod-
              immutable-flag-04>.

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

   [RFC8174]  Leiba, B. and RFC Publisher, "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>.

   [RFC8407]  Bierman, A. and RFC Publisher, "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>.

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

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

Ma, et al.                 Expires 8 July 2023                 [Page 38]
Internet-Draft        System-defined Configuration          January 2023

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,
   snippets of <running>, <system>, <intended> and <operational> are
   shown.

A.1.  Device Powers On

   <running>:

   No configuration for "lo0" 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>

Ma, et al.                 Expires 8 July 2023                 [Page 39]
Internet-Draft        System-defined Configuration          January 2023

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>
            <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>
          <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>

Ma, et al.                 Expires 8 July 2023                 [Page 40]
Internet-Draft        System-defined Configuration          January 2023

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>
            <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>
          <interface>
        </interfaces>

   <operational>:

Ma, et al.                 Expires 8 July 2023                 [Page 41]
Internet-Draft        System-defined Configuration          January 2023

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

Appendix B.  Changes between Revisions

   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

Appendix C.  Open Issues tracking

   *  Should the "with-origin" parameter be supported for <intended>?

Authors' Addresses

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

Ma, et al.                 Expires 8 July 2023                 [Page 42]
Internet-Draft        System-defined Configuration          January 2023

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

   Feng Chong
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing
   Jiangsu, 210012
   China
   Email: frank.fengchong@huawei.com

Ma, et al.                 Expires 8 July 2023                 [Page 43]