NETMOD                                                        Q. Ma, Ed.
Internet-Draft                                                    Huawei
Updates: RFC8342, RFC6241, RFC8526, RFC8040 (if                K. Watsen
         approved)                                       Watsen Networks
Intended status: Standards Track                                   Q. Wu
Expires: 12 October 2022                                         C. Feng
                                                                  Huawei
                                                             J. Lindblad
                                                           Cisco Systems
                                                           10 April 2022


                      System-defined Configuration
                     draft-ma-netmod-with-system-03

Abstract

   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.

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 12 October 2022.






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Copyright Notice

   Copyright (c) 2022 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, 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.  Static Characteristics  . . . . . . . . . . . . . . . . . . .   7
     3.1.  Read-only to Clients  . . . . . . . . . . . . . . . . . .   7
     3.2.  May Change via Software Upgrades  . . . . . . . . . . . .   8
     3.3.  No Impact to <operational>  . . . . . . . . . . . . . . .   8
   4.  Dynamic Behavior  . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Conceptual Model  . . . . . . . . . . . . . . . . . . . .   8
     4.2.  Explicit Declaration of System Configuration  . . . . . .   9
     4.3.  Servers Auto-configuring Referenced System
           Configuration . . . . . . . . . . . . . . . . . . . . . .  10
     4.4.  Modifying (overriding) System Configuration . . . . . . .  10
     4.5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .  11
       4.5.1.  Server Configuring of <running> Automatically . . . .  11
       4.5.2.  Declaring a System-defined Node in <running>
               Explicitly  . . . . . . . . . . . . . . . . . . . . .  17
       4.5.3.  Modifying a System-instantiated Leaf's Value  . . . .  20
       4.5.4.  Configuring Descendant Nodes of a System-defined
               Node  . . . . . . . . . . . . . . . . . . . . . . . .  22
   5.  The <system> Configuration Datastore  . . . . . . . . . . . .  23
   6.  The "ietf-system-datastore" Module  . . . . . . . . . . . . .  25
     6.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .  25



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     6.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .  25
     6.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  26
   7.  The "ietf-netconf-resolve-system" Module  . . . . . . . . . .  28
     7.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .  28
     7.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .  29
     7.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  32
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  34
     8.1.  The "IETF XML" Registry . . . . . . . . . . . . . . . . .  35
     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  . . . . . . . . . . . . . . . . . . . . . . . .  36
   References  . . . . . . . . . . . . . . . . . . . . . . . . . . .  36
     Normative References  . . . . . . . . . . . . . . . . . . . . .  36
     Informative References  . . . . . . . . . . . . . . . . . . . .  37
   Appendix A.  Key Use Cases  . . . . . . . . . . . . . . . . . . .  38
     A.1.  Device Powers On  . . . . . . . . . . . . . . . . . . . .  38
     A.2.  Client Commits Configuration  . . . . . . . . . . . . . .  39
     A.3.  Operator Installs Card into a Chassis . . . . . . . . . .  40
   Appendix B.  Changes between Revisions  . . . . . . . . . . . . .  41
   Appendix C.  Open Issues tracking . . . . . . . . . . . . . . . .  42
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  42

1.  Introduction

   NMDA [RFC8342] defines system configuration as the configuration that
   is supplied by the device itself and should be present in
   <operational> when it is in use.

   However, there is a desire to enable a server to better document the
   system configuration.  Clients can benefit from a standard mechanism
   to see what system configuration is available in a server.

   In some cases, the client references a system configuration which
   isn't present in the target datastore (e.g., <running>).  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.









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   In some other cases, configuration of descendant nodes of system-
   defined configuration needs to be supported.  For example, the system
   configuration may contain an almost empty physical interface, while
   the client needs to be able to add, modify, 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 servers to implement the "ietf-
   system-datastore" YANG Module.

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 as follows:

   System configuration:  Configuration that is provided by the system
      itself.  System configuration is present in <system> once it's
      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" from RFC 8342 to add "system" to the list of conventional
   configuration datastores:

   Conventional configuration datastore:  One of the following set of





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      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, 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



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   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.

   According to the NETCONF constraint enforcement model defined in the
   section 8.3 of [RFC7950], if the target datastore of the <edit-
   config>/<edit-data> or <copy-config> is "running" or "startup", 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.  If the target
   datastore of the <edit-config>/<edit-data> or <copy-config> is
   "candidate", the server's copy referenced nodes from <system> to the
   target datastore is delayed until a <commit> or <validate> operation
   takes place.

1.5.  Updates to RFC 8040

   This document extends Section 4.8 and Section 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          |
  |                |         | system configuration into <running>     |
  |                |         | automatically. This parameter can be    |
  |                |         | given in any order.                     |
  +----------------+---------+-----------------------------------------+

1.5.2.  Query Parameter URI

   To enable the 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




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2.  Kinds of System Configuration

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

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 loop-back 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 QoS function is enabled, QoS policies are automatically
   created by the system.

2.3.  Inactive-Until-Referenced

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

3.  Static Characteristics

3.1.  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 4.4).  Configuration defined in
   <system> is merged into <intended>, and present in <operational> if
   it is actively in use by the device.  Thus unless the resource is no
   longer available (e.g., the interface removed physically), there is
   no way to actually delete system configuration from a server, even if
   a client may be allowed to delete the configuration copied from



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   <system> into <running>.  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.

3.2.  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 QoS function is
   enabled, QoS-related policies are created by system.  If the system
   configuration gets changed, YANG notification (e.g., "push-change-
   update" notification) [RFC8641][RFC8639][RFC6470] 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.

3.3.  No Impact to <operational>

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

4.  Dynamic Behavior

4.1.  Conceptual Model

   This document introduces a mandatory 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.








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   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 objects.  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 objects 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.

4.2.  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



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   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.

4.3.  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>.

   If the "resolve-system" is present, 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.

   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.

4.4.  Modifying (overriding) System Configuration

   In some cases, a server may allow some parts of system configuration
   to be modified.  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 and NACM rules,
   and other server-internal restrictions.  If a system configuration
   node is non-modifiable, then writing a different value for that node
   in <running> MUST return an error.  The immutability of system
   configuration is further defined in [I-D.ma-netmod-immutable-flag].






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   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.

   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).

   While modifying (overriding) system configuration nodes may be
   supported by a server, there is no mechanism for deleting a system
   configuration node unless the resource is no longer available.  For
   example, a "mandatory true" leaf may have a value in <system> which
   can be modified (overridden) by a client setting that leaf to a value
   in <running>.  But the leaf could not be deleted.  Another example of
   this might be that system initializes a value for a particular leaf
   which is overridden by the client with intended value in <running>.
   The client may delete the leaf in <running>, but system-initialized
   value defined in <system> will be in use and appear in <operational>.

   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?

   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.

4.5.  Examples

   This section shows the 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.

4.5.1.  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 objects 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:


















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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.













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          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 destination_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;
                  }
                }
              }
            }
          }




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   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>
                      <destination_address>192.0.2.0/24</destination_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:
















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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>

   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>





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   Since the configuration of application "smtp" is not referenced by
   the client, it does not appear in <operational> but only in <system>.

4.5.2.  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:


















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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>
                      <destination_address>192.0.2.0/24</destination_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:





















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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>

   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>





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

4.5.3.  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:












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           <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:








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        <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>

4.5.4.  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:









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        <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>

5.  The <system> Configuration Datastore

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




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   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.  A device MAY
   implement the mechanism defined in this document without implementing
   the "system" datastore, which would only eliminate the ability to
   programmatically determine 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 NETCONF, RESTCONF, the
      CLI, etc, but may change itself by upgrades and/or when resource-
      conditions are met.  The datastore can be read using the standard
      NETCONF/RESTCONF protocol operations.

   *  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].




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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> 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"
           }
       }
   }



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   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@2021-05-14.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 NETMDOD (Network Modeling) Working Group";

       contact
         "WG Web:   <http://tools.ietf.org/wg/netmod/>
          WG List:  <mailto:netmod@ietf.org>
          Author: Qiufang Ma
                  <mailto:maqiufang1@huawei.com>
          Author: Chong Feng
                  <mailto:frank.fengchong@huawei.com>



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          Author: Qin Wu
                  <mailto:bill.wu@huawei.com>";

       description
        "This module defines a new YANG identity that uses the
         ds:datastore identity defined in [RFC8342].

         Copyright (c) 2021 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 Simplified
         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 2021-05-14 {
         description

           "Initial version.";
         reference
          "RFC XXXX: System-defined Configuration";
       }

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







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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 YANG library
   information with "ietf-netconf-resolve-system" 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}?



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       |     +---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

   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 objects 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:





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    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:










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   <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 resonse 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>:












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   <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@2021-05-14.yang"
    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";
       }



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

       contact
         "WG Web:   <http://tools.ietf.org/wg/netmod/>
          WG List:  <mailto:netmod@ietf.org>
          Author: Qiufang Ma
                  <mailto:maqiufang1@huawei.com>
          Author: Chong Feng
                  <mailto:frank.fengchong@huawei.com>
          Author: Qin Wu
                  <mailto:bill.wu@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) 2021 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 Simplified
           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 2021-05-14 {
         description
           "Initial version.";
         reference
           "RFC XXXX: System-defined Configuration";
       }

     augment /nc:edit-config/nc:input {



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       description
         "Allows the server to automatically configure
          referenced system configuration to make configuration
          valid.";
        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:copy-config/nc:input {
       description
         "Allows the server to automatically configure
          referenced system configuration to make configuration
          valid.";
        leaf resolve-system {
          type empty ;
          description
            "When present, the server is allowed to automatically
             configure referenced system configuration into the
             target configuration datastore.";
         }
      }

     augment /ncds:edit-data/ncds:input {
       description
         "Allows the server to automatically configure
          referenced system configuration to make configuration
          valid.";
        leaf resolve-system {
          type empty ;
          description
            "When present, the server is allowed to automatically
             configure referenced system configuration into the
             target configuration datastore.";
        }
      }
    }
   <CODE ENDS>

8.  IANA Considerations







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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
      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
      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].




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   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

         Chongfeng Xie
         China Telecom
         Beijing
         China

         Email: xiechf@chinatelecom.cn

         Jason Sterne
         Nokia

         Email: jason.sterne@nokia.com

Acknowledgements

   Thanks to Robert Wilton, Balazs Lengyel, Andy Bierman, Juergen
   Schoenwaelder, Alex Clemm, Martin Bjorklund, Timothy Carey for
   reviewing, and providing important input to, this document.

References

Normative References





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   [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>.

Informative References

   [I-D.ma-netmod-immutable-flag]
              Ma, Q., Wu, Q., and H. Li, "Immutable Metadata
              Annotation", Work in Progress, Internet-Draft, draft-ma-
              netmod-immutable-flag-00, 10 February 2022,
              <https://www.ietf.org/archive/id/draft-ma-netmod-
              immutable-flag-00.txt>.

   [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>.

   [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>.

   [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>.

   [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>.

   [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>.

   [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,
   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>







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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>
            <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>



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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>
            <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>:










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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 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

   v02 - v03

   *  Define a RESTCONF capability URI for "resolve-system" RESTCONF
      query parameter;

   *  Augment <copy-config> RPC operation to support "resolve-system"
      for input parameter;

   *  Editorial changes for clarification and explanation.  E.g.,
      definition of system configuration, is <system> always valid?
      Will the update of <system> be reflected into <running>?  Clarify
      "read-only to clients" and "modifying system configuration", non-
      deletable system configuration, etc

   v00 - v02

   *  Remove the "with-system" parameter to retrieve <running> with
      system configuration merged in.

   *  Add a new parameter named "resolve-system" to allow the server to
      populate referenced system configuration into <running>
      automatically in order to make <running> valid.

   *  Usage examples refinement.

   v02 - v00

   *  Restructure the document content based on input in the system
      defined configuration interim meeting.





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   *  Updates NMDA to define a read-only conventional configuration
      datastore called "system".

   *  Retrieval of implicit hidden system configuration via <get><get-
      config> with "with-system" parameter to support non-NMDA servers.

   *  Provide system defined configuration classification.

   *  Define Static Characteristics and dynamic behavior for system
      defined configuration.

   *  Separate "ietf-system-datastore" Module from "ietf-netconf-with-
      system" Module.

   *  Provide usage examples for dynamic behaviors.

   *  Provide usage examples for two YANG modules.

   *  Provide three use cases related to system-defined configuration
      lifecycle management.

   *  Classify the relation with <factory-default>.

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


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










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   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


   Jan Lindblad
   Cisco Systems
   Email: jlindbla@cisco.com






























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