draft-tgraf-netconf-yang-notifications-versioning-03.xml

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<?rfc tocdepth="2"?>
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<rfc category="std"
     docName="draft-tgraf-netconf-yang-notifications-versioning-03"
     ipr="trust200902">
  <front>
    <title abbrev="YANG Notifications Versioning">Support of Versioning in
    YANG Notifications Subscription</title>

    <author fullname="Thomas Graf" initials="T" surname="Graf">
      <organization>Swisscom</organization>

      <address>
        <postal>
          <street>Binzring 17</street>

          <city>Zurich</city>

          <code>8045</code>

          <country>Switzerland</country>
        </postal>

        <email>thomas.graf@swisscom.com</email>
      </address>
    </author>

    <author fullname="Benoit Claise" initials="B" surname="Claise">
      <organization>Huawei</organization>

      <address>
        <email>benoit.claise@huawei.com</email>
      </address>
    </author>

    <author fullname="Alex Huang Feng" initials="A." surname="Huang Feng">
      <organization>INSA-Lyon</organization>

      <address>
        <postal>
          <street/>

          <city>Lyon</city>

          <region/>

          <code/>

          <country>France</country>
        </postal>

        <phone/>

        <facsimile/>

        <email>alex.huang-feng@insa-lyon.fr</email>

        <uri/>
      </address>
    </author>

    <date day="17" month="January" year="2023"/>

    <abstract>
      <t>This document extends the YANG notifications subscription mechanism
      to specify the YANG module semantic version at the subscription. Then, a
      new extension with the revision and the semantic version of the YANG
      push subscription state change notification is proposed.</t>
    </abstract>

    <note title="Requirements Language">
      <t>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
      <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only when,
      they appear in all capitals, as shown here.</t>
    </note>
  </front>

  <middle>
    <section anchor="Introduction" title="Introduction">
      <t>In order to process the received YANG push notification messages
      described in section 3.7 of <xref target="RFC8641"/> at the YANG push
      receiver, a semantic reference to the YANG module and the XPath or
      subtree is needed to determine the data types for each field and which
      part of the YANG module the metrics are expose from.</t>

      <t>This specification applies to the YANG push configured subscriptions
      defined in Section 2.5 of <xref target="RFC8639"/>, where a publisher is
      configured to stream notification out of band, as opposed to dynamic
      subscriptions defined in Section 2.4 of <xref target="RFC8639"/>, where
      the subscriber can initiate and modify the subscription dynamically
      in-band. In the latter case, the subscriber knows already all the
      subscriber YANG-related information, which it has to know in order to
      configure the subscription.</t>

      <t>This semantic reference is available when the subscription is being
      establish as described in Section 3.6 of <xref target="RFC8641"/> and
      being streamed from the publisher to receiver with the subscription
      state change notifications described in Section 2.7 of <xref
      target="RFC8639"/> where for each subscription a locally unique
      subscription ID described in Section 4.3.2 of <xref target="RFC8641"/>
      is being issued and streamed as metadata with the notification message
      in the YANG push message header.</t>

      <t>The semantics can change between different YANG module revisions. The
      YANG module version statement is specified in Section 7.1.2 of <xref
      target="RFC6020"/> and states that the newer revision needs to be
      backward compatible to the previous revision. Section 3.1 of <xref
      target="I-D.ietf-netmod-yang-module-versioning"/> specifies that newer
      semantic versions introduced in <xref
      target="I-D.ietf-netmod-yang-semver"/> MAY not be backward compatible to
      the previous version when indicated with non-backwards-compatible
      keyword.</t>

      <t>The YANG notifications subscription mechanism defined in <xref
      target="RFC8641"/> does not allow to specify the YANG module revision.
      When a network node is upgraded, the subscribed YANG module revision MAY
      have updated and might, consequently, break the data processing pipeline
      since the YANG push receiver may not be aware of this change.</t>

      <t>This documents extends the current YANG notifications subscription
      mechanism to allow to subscribe to a specific revision or latest YANG
      module semantic version to which the YANG module version needs to be
      backward compatible to. The subscription state change
      "subscription-started" and "subscription-modified" notification messages
      are also extended to include the revision and semantic version.</t>
    </section>

    <section anchor="Datastore-Selection"
             title="Extend the Datastore Selection">
      <t>The YANG notifications subscription OPTIONALLY can be restricted to
      the following YANG module revision for future capabilities:</t>

      <dl>
        <dt>latest:</dt>

        <dd>Restricts the subscription to the latest YANG module
        revision.</dd>
      </dl>

      <dl>
        <dt>revision:</dt>

        <dd>Restricts the subscription to a specific YANG module revision.
        Example: "2014-05-08".</dd>
      </dl>

      <dl>
        <dt>latest-compatible-semversion:</dt>

        <dd>Restricts the subscription to the latest compatible YANG module
        semantic version referenced to. Example: "2.0.0".</dd>
      </dl>

      <t>If nothing is specified, latest YANG module version is implied.</t>
    </section>

    <section anchor="Streaming-Update"
             title="Extend the Subscription State Change Notifications">
      <t>Besides the Subscription ID and the xpath or sub-tree filter
      reference as described in Section 2.7 of <xref target="RFC8639"/>, the
      following metadata objects are part of a "subscription-started" or
      "subscription-modified" subscription state change notification.</t>

      <dl>
        <dt>revision:</dt>

        <dd>Describes the YANG module revision as specified in Section 7.1.9
        of <xref target="RFC6020"/> for the related streamed content.</dd>
      </dl>

      <dl>
        <dt>revision-label:</dt>

        <dd>Describes the YANG module semantic version as specified in <xref
        target="I-D.ietf-netmod-yang-semver"/> for the related streamed
        content.</dd>
      </dl>

      <t><xref target="subscription_modified_example_xml_fig"/> provides an
      example of a "subscription-modified" subscription state change
      notification message with the YANG revision, revision label and
      datastore-xpath-filter for tracking the operational status of a single
      Ethernet interface (per <xref target="RFC8343"/>). This subscription
      state change notification message is encoded XML <xref
      target="W3C.REC-xml-20081126"/> over the Network Configuration Protocol
      (NETCONF) as per <xref target="RFC8640"/>.</t>

      <figure anchor="subscription_modified_example_xml_fig"
              title="XML Push Example for a subscription-modified notification message">
        <artwork><![CDATA[
<notification xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
  <eventTime>2023-01-03T10:00:00Z</eventTime>
  <subscription-modified
      xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
    <id>101</id>
    <revision>2014-05-08</revision>
    <revision-label>1.0.0</revision-label>
    <stream-xpath-filter xmlns:int="urn:ietf:params:xml:ns:yang:ietf-interfaces">
      /int:interfaces
    </stream-xpath-filter>
    <stream>NETCONF</stream>
  </subscription-modified>
</notification>
        ]]></artwork>
      </figure>

      <t><xref target="subscription_modified_example_json_fig"/> provides an
      example of a JSON encoded, <xref target="RFC8259"/>, subscription state
      change notification message over HTTPS-based <xref
      target="I-D.ietf-netconf-https-notif"/> or UDP-based <xref
      target="I-D.ietf-netconf-udp-notif"/> transport for the same
      subscription.</t>

      <figure anchor="subscription_modified_example_json_fig"
              title="JSON Push Example for a subscription-modified notification message">
        <artwork><![CDATA[
{
  "ietf-restconf:notification" : {
    "eventTime": "2023-01-03T10:00:00Z",
    "ietf-subscribed-notifications:subscription-modified": {
      "id": 101,
      "revision": "2014-05-08",
      "revision-label": "1.0.0",
      "stream-xpath-filter": "/ietf-interfaces:interfaces",
      "stream": {
         "ietf-netconf-subscribed-notifications" : "NETCONF"
      }
    }
  }
} 
        ]]></artwork>
      </figure>
    </section>

    <section anchor="YANG-push-revision-module"
             title="The &quot;ietf-yang-push-revision&quot; Module">
      <section anchor="YANG-revision-model" title="Data Model Overview">
        <t>This YANG module augments the "ietf-yang-push" module with the
        revision and revision-label in the "subscription-started" and
        "subscription-modified" subscription state change notifications and
        the ability to define the "revision" and "revision-label" in the
        "establish-subscription" and "modify-subscription" RPCs in the
        datastore push subscription.</t>

        <section anchor="Tree View" title="Tree View">
          <t>The following is the YANG tree diagram <xref target="RFC8340"/>
          for the ietf-yang-push-revision YANG module</t>

          <t><figure>
              <artwork><![CDATA[
module: ietf-yang-push-revision

  augment /sn:establish-subscription/sn:input/sn:target:
    +--rw revision?         rev:revision-date-or-label
    +-- revision-label?   ysver:version
  augment /sn:modify-subscription/sn:input/sn:target:
    +--rw revision?         rev:revision-date-or-label
    +-- revision-label?   ysver:version
  augment /sn:subscription-started/sn:target:
    +--ro revision          rev:revision-date-or-label
    +-- revision-label?   ysver:version
  augment /sn:subscription-modified/sn:target:
    +--ro revision          rev:revision-date-or-label
    +-- revision-label?   ysver:version
  augment /sn:subscriptions/sn:subscription/sn:target:
    +--ro revision          rev:revision-date-or-label
    +--rw revision-label?   ysver:version
]]></artwork>
            </figure></t>
        </section>

        <section anchor="Full Tree View" title="Full Tree View">
          <t>The following is the YANG tree diagram <xref target="RFC8340"/>
          for the ietf-yang-push-revision augmentation within the
          ietf-subscribed-notifications, including the RPCs and
          notifications.</t>

          <t><figure>
              <artwork><![CDATA[
pyang -f tree ietf-yang-push-revision.yang ietf-yang-revisions.yang ietf-subscribed-notifications@2019-09-09.yang 
ietf-yang-push-revision.yang:118 (at ietf-yang-push-revision.yang:88): error: cannot augment with mandatory node "revision"
module: ietf-subscribed-notifications
  +--ro streams
  |  +--ro stream* [name]
  |     +--ro name                        string
  |     +--ro description?                string
  |     +--ro replay-support?             empty {replay}?
  |     +--ro replay-log-creation-time    yang:date-and-time {replay}?
  |     +--ro replay-log-aged-time?       yang:date-and-time {replay}?
  +--rw filters
  |  +--rw stream-filter* [name]
  |     +--rw name                           string
  |     +--rw (filter-spec)?
  |        +--:(stream-subtree-filter)
  |        |  +--rw stream-subtree-filter?   <anydata> {subtree}?
  |        +--:(stream-xpath-filter)
  |           +--rw stream-xpath-filter?     yang:xpath1.0 {xpath}?
  +--rw subscriptions
     +--rw subscription* [id]
        +--rw id                                         subscription-id
        +--rw (target)
        |  +--:(stream)
        |  |  +--rw (stream-filter)?
        |  |  |  +--:(by-reference)
        |  |  |  |  +--rw stream-filter-name             stream-filter-ref
        |  |  |  +--:(within-subscription)
        |  |  |     +--rw (filter-spec)?
        |  |  |        +--:(stream-subtree-filter)
        |  |  |        |  +--rw stream-subtree-filter?   <anydata> {subtree}?
        |  |  |        +--:(stream-xpath-filter)
        |  |  |           +--rw stream-xpath-filter?     yang:xpath1.0 {xpath}?
        |  |  +--rw stream                               stream-ref
        |  |  +--ro replay-start-time?                   yang:date-and-time {replay}?
        |  |  +--rw configured-replay?                   empty {configured,replay}?
        |  +--:(ypm:revision)
        |  |  +--ro ypm:revision                         rev:revision-date-or-label
        |  +--:(ypm:revision-label)
        |     +--rw ypm:revision-label?                  ysver:version
        +--rw stop-time?                                 yang:date-and-time
        +--rw dscp?                                      inet:dscp {dscp}?
        +--rw weighting?                                 uint8 {qos}?
        +--rw dependency?                                subscription-id {qos}?
        +--rw transport?                                 transport {configured}?
        +--rw encoding?                                  encoding
        +--rw purpose?                                   string {configured}?
        +--rw (notification-message-origin)? {configured}?
        |  +--:(interface-originated)
        |  |  +--rw source-interface?                    if:interface-ref {interface-designation}?
        |  +--:(address-originated)
        |     +--rw source-vrf?                          -> /ni:network-instances/network-instance/name {supports-vrf}?
        |     +--rw source-address?                      inet:ip-address-no-zone
        +--ro configured-subscription-state?             enumeration {configured}?
        +--rw receivers
           +--rw receiver* [name]
              +--rw name                      string
              +--ro sent-event-records?       yang:zero-based-counter64
              +--ro excluded-event-records?   yang:zero-based-counter64
              +--ro state                     enumeration
              +---x reset {configured}?
                 +--ro output
                    +--ro time    yang:date-and-time

  rpcs:
    +---x establish-subscription
    |  +---w input
    |  |  +---w (target)
    |  |  |  +--:(stream)
    |  |  |  |  +---w (stream-filter)?
    |  |  |  |  |  +--:(by-reference)
    |  |  |  |  |  |  +---w stream-filter-name             stream-filter-ref
    |  |  |  |  |  +--:(within-subscription)
    |  |  |  |  |     +---w (filter-spec)?
    |  |  |  |  |        +--:(stream-subtree-filter)
    |  |  |  |  |        |  +---w stream-subtree-filter?   <anydata> {subtree}?
    |  |  |  |  |        +--:(stream-xpath-filter)
    |  |  |  |  |           +---w stream-xpath-filter?     yang:xpath1.0 {xpath}?
    |  |  |  |  +---w stream                               stream-ref
    |  |  |  |  +---w replay-start-time?                   yang:date-and-time {replay}?
    |  |  |  +--:(ypm:revision)
    |  |  |  |  +---w ypm:revision?                        rev:revision-date-or-label
    |  |  |  +--:(ypm:revision-label)
    |  |  |     +---w ypm:revision-label?                  ysver:version
    |  |  +---w stop-time?                                 yang:date-and-time
    |  |  +---w dscp?                                      inet:dscp {dscp}?
    |  |  +---w weighting?                                 uint8 {qos}?
    |  |  +---w dependency?                                subscription-id {qos}?
    |  |  +---w encoding?                                  encoding
    |  +--ro output
    |     +--ro id                            subscription-id
    |     +--ro replay-start-time-revision?   yang:date-and-time {replay}?
    +---x modify-subscription
    |  +---w input
    |     +---w id                                         subscription-id
    |     +---w (target)
    |     |  +--:(stream)
    |     |  |  +---w (stream-filter)?
    |     |  |     +--:(by-reference)
    |     |  |     |  +---w stream-filter-name             stream-filter-ref
    |     |  |     +--:(within-subscription)
    |     |  |        +---w (filter-spec)?
    |     |  |           +--:(stream-subtree-filter)
    |     |  |           |  +---w stream-subtree-filter?   <anydata> {subtree}?
    |     |  |           +--:(stream-xpath-filter)
    |     |  |              +---w stream-xpath-filter?     yang:xpath1.0 {xpath}?
    |     |  +--:(ypm:revision)
    |     |  |  +---w ypm:revision?                        rev:revision-date-or-label
    |     |  +--:(ypm:revision-label)
    |     |     +---w ypm:revision-label?                  ysver:version
    |     +---w stop-time?                                 yang:date-and-time
    +---x delete-subscription
    |  +---w input
    |     +---w id    subscription-id
    +---x kill-subscription
       +---w input
          +---w id    subscription-id

  notifications:
    +---n replay-completed {replay}?
    |  +--ro id    subscription-id
    +---n subscription-completed {configured}?
    |  +--ro id    subscription-id
    +---n subscription-modified
    |  +--ro id                                         subscription-id
    |  +--ro (target)
    |  |  +--:(stream)
    |  |  |  +--ro (stream-filter)?
    |  |  |  |  +--:(by-reference)
    |  |  |  |  |  +--ro stream-filter-name             stream-filter-ref
    |  |  |  |  +--:(within-subscription)
    |  |  |  |     +--ro (filter-spec)?
    |  |  |  |        +--:(stream-subtree-filter)
    |  |  |  |        |  +--ro stream-subtree-filter?   <anydata> {subtree}?
    |  |  |  |        +--:(stream-xpath-filter)
    |  |  |  |           +--ro stream-xpath-filter?     yang:xpath1.0 {xpath}?
    |  |  |  +--ro stream                               stream-ref
    |  |  |  +--ro replay-start-time?                   yang:date-and-time {replay}?
    |  |  +--:(ypm:revision)
    |  |  |  +--ro ypm:revision                         rev:revision-date-or-label
    |  |  +--:(ypm:revision-label)
    |  |     +--ro ypm:revision-label?                  ysver:version
    |  +--ro stop-time?                                 yang:date-and-time
    |  +--ro dscp?                                      inet:dscp {dscp}?
    |  +--ro weighting?                                 uint8 {qos}?
    |  +--ro dependency?                                subscription-id {qos}?
    |  +--ro transport?                                 transport {configured}?
    |  +--ro encoding?                                  encoding
    |  +--ro purpose?                                   string {configured}?
    +---n subscription-resumed
    |  +--ro id    subscription-id
    +---n subscription-started {configured}?
    |  +--ro id                                         subscription-id
    |  +--ro (target)
    |  |  +--:(stream)
    |  |  |  +--ro (stream-filter)?
    |  |  |  |  +--:(by-reference)
    |  |  |  |  |  +--ro stream-filter-name             stream-filter-ref
    |  |  |  |  +--:(within-subscription)
    |  |  |  |     +--ro (filter-spec)?
    |  |  |  |        +--:(stream-subtree-filter)
    |  |  |  |        |  +--ro stream-subtree-filter?   <anydata> {subtree}?
    |  |  |  |        +--:(stream-xpath-filter)
    |  |  |  |           +--ro stream-xpath-filter?     yang:xpath1.0 {xpath}?
    |  |  |  +--ro stream                               stream-ref
    |  |  |  +--ro replay-start-time?                   yang:date-and-time {replay}?
    |  |  |  +--ro replay-previous-event-time?          yang:date-and-time {replay}?
    |  |  +--:(ypm:revision)
    |  |  |  +--ro ypm:revision                         rev:revision-date-or-label
    |  |  +--:(ypm:revision-label)
    |  |     +--ro ypm:revision-label?                  ysver:version
    |  +--ro stop-time?                                 yang:date-and-time
    |  +--ro dscp?                                      inet:dscp {dscp}?
    |  +--ro weighting?                                 uint8 {qos}?
    |  +--ro dependency?                                subscription-id {qos}?
    |  +--ro transport?                                 transport {configured}?
    |  +--ro encoding?                                  encoding
    |  +--ro purpose?                                   string {configured}?
    +---n subscription-suspended
    |  +--ro id        subscription-id
    |  +--ro reason    identityref
    +---n subscription-terminated
       +--ro id        subscription-id
       +--ro reason    identityref

]]></artwork>
            </figure></t>
        </section>
      </section>

      <section anchor="YANG-revision-module" title="YANG Module">
        <t>The YANG module has two leaves augmenting the model of <xref
        target="RFC8639">Subscription to YANG Notifications</xref>.</t>

        <t><figure>
            <artwork><![CDATA[
<CODE BEGINS> file "ietf-yang-push-revision@2023-01-12.yang"
module ietf-yang-push-revision {
  yang-version 1.1;
  namespace
    "urn:ietf:params:xml:ns:yang:ietf-yang-push-revision";
  prefix ypm;
  import ietf-subscribed-notifications {
    prefix sn;
    reference
      "RFC 8639: Subscription to YANG Notifications";
  }
  import ietf-yang-revisions {
    prefix rev;
    reference
      "RFC XXXX: draft-ietf-netmod-yang-module-versioning-06, Updated YANG
      Module Revision Handling";
  }
  import ietf-yang-semver {
    prefix ysver;
    reference
      "RFC XXXX: draft-ietf-netmod-yang-semver-08, YANG Semantic Versioning";
  }

  organization "IETF NETCONF (Network Configuration) Working Group";
  contact
    "WG Web:   <http:/tools.ietf.org/wg/netconf/>
     WG List:  <mailto:netconf@ietf.org>

     Authors:  Thomas Graf
               <mailto:thomas.graf@swisscom.com>
               Benoit Claise
               <mailto:benoit.claise@huawei.com>
               Alex Huang Feng
               <mailto:alex.huang-feng@insa-lyon.fr>";

  description
    "Defines YANG push event notification header with the revision and
    the revision-label. Adds the support of the revision and
    revision-label selection in the YANG push subscription RPCs.

    Copyright (c) 2023 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 XXXX; see the RFC
    itself for full legal notices.";

  revision 2023-01-12 {
    description
      "First revision";
    reference
      "RFC XXXX: Support of Versioning in YANG Notifications Subscription";
  }

  feature yang-push-revision-supported {
    description
      "This feature indicates the YANG Subscription Notifications supports
      the revision and revision-label defined in this YANG module.";
  }

  grouping yang-push-module-version-config {
    description
      "This grouping combines the revision and revision-label leaves, with 
       the revison being configurable.";
    leaf revision {
      type rev:revision-date-or-label;
      description
        "This references the YANG module revision to be sent in the subscription.";
    }
    leaf revision-label {
      type ysver:version;
      description
        "This references the YANG module semversion to be sent in the subscription.";
    }
  }

  grouping yang-push-module-version {
    description
      "This grouping combines the revision and revision-label leaves, with 
       the revison being non configurable.";
    leaf revision {
      type rev:revision-date-or-label;
      config false;
      mandatory true;
      description
        "This references the YANG module revision of the sent notification message.";
    }
    leaf revision-label {
      type ysver:version;
      description
        "This references the YANG module semversion of the sent notification message.";
    }
  }

  // Subscription parameters
  augment "/sn:establish-subscription/sn:input/sn:target" {
    description
      "Augment the establish-subscription RPC from the ietf-subscribed-notifications 
      YANG module with the yang-push-module-version-config grouping.";
    uses ypm:yang-push-module-version-config;
  }
  augment "/sn:modify-subscription/sn:input/sn:target" {
  description
      "Augment the modify-subscription RPC from the ietf-subscribed-notifications 
      YANG module with the yang-push-module-version-config grouping.";
          uses ypm:yang-push-module-version-config;
  }

  // Subscription notifications
  augment "/sn:subscription-started/sn:target" {
  description
      "Augment the subscription-started RPC from the ietf-subscribed-notifications 
      YANG module with the yang-push-module-version grouping.";
    uses ypm:yang-push-module-version;
  }
  augment "/sn:subscription-modified/sn:target" {
  description
      "Augment the subscription-modified RPC from the ietf-subscribed-notifications 
      YANG module with the yang-push-module-version grouping.";
    uses ypm:yang-push-module-version;
  }

  // Subscription container
  augment "/sn:subscriptions/sn:subscription/sn:target" {
  description
      "Augment the subscriptions RPC from the ietf-subscribed-notifications 
      YANG module with the yang-push-module-version grouping.";
    uses ypm:yang-push-module-version;
  }
}
<CODE ENDS>]]></artwork>
          </figure></t>
      </section>
    </section>

    <section anchor="Security" title="Security Considerations">
      <t>The security considerations for the YANG notifications subscription
      mechanism are described in <xref target="RFC8641"/>. This documents adds
      no additional security considerations.</t>
    </section>

    <section anchor="IANA_Considerations" title="IANA Considerations">
      <t>This document has no IANA actions.</t>
    </section>

    <section anchor="Acknowledgements" title="Acknowledgements">
      <t>The authors would like to thank xxx for their review and valuable
      comments.</t>
    </section>
  </middle>

  <back>
    <references title="Normative References">
      <?rfc include='reference.RFC.2119'?>

      <?rfc include='reference.RFC.6020'?>

      <?rfc include='reference.RFC.8174'?>

      <?rfc include='reference.RFC.8639'?>

      <?rfc include='reference.RFC.8641'?>

      <?rfc include='reference.I-D.ietf-netmod-yang-module-versioning'?>

      <?rfc include='reference.I-D.ietf-netmod-yang-semver'?>
    </references>

    <references title="Informative References">
      <?rfc include='reference.RFC.8259'?>

      <?rfc include='reference.RFC.8340'?>

      <?rfc include='reference.RFC.8343'?>

      <?rfc include='reference.RFC.8640'?>

      <?rfc include='reference.I-D.ietf-netconf-https-notif'?>

      <?rfc include='reference.I-D.ietf-netconf-udp-notif'?>

      <reference anchor="W3C.REC-xml-20081126"
                 derivedAnchor="W3C.REC-xml-20081126" quoteTitle="true"
                 target="https://www.w3.org/TR/2008/REC-xml-20081126">
        <front>
          <title>Extensible Markup Language (XML) 1.0 (Fifth Edition)</title>

          <author fullname="Tim Bray" initials="T." surname="Bray">
            <organization showOnFrontPage="true"/>
          </author>

          <author fullname="Jean Paoli" initials="J." surname="Paoli">
            <organization showOnFrontPage="true"/>
          </author>

          <author fullname="Michael Sperberg-McQueen" initials="M."
                  surname="Sperberg-McQueen">
            <organization showOnFrontPage="true"/>
          </author>

          <author fullname="Eve Maler" initials="E." surname="Maler">
            <organization showOnFrontPage="true"/>
          </author>

          <author fullname="Francois Yergeau" initials="F." surname="Yergeau">
            <organization showOnFrontPage="true"/>
          </author>

          <date month="November" year="2008"/>
        </front>

        <refcontent>World Wide Web Consortium Recommendation
        REC-xml-20081126</refcontent>
      </reference>
    </references>
  </back>
</rfc>