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Support of Versioning in YANG Notifications Subscription
draft-tgraf-netconf-yang-notifications-versioning-02

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Document Type
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
Authors Thomas Graf , Benoît Claise , Alex Huang Feng
Last updated 2023-01-13
Replaced by draft-netconf-yang-notifications-versioning, draft-ietf-netconf-yang-notifications-versioning
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draft-tgraf-netconf-yang-notifications-versioning-02
Network Working Group                                            T. Graf
Internet-Draft                                                  Swisscom
Intended status: Standards Track                               B. Claise
Expires: 18 July 2023                                             Huawei
                                                           A. Huang Feng
                                                               INSA-Lyon
                                                         14 January 2023

        Support of Versioning in YANG Notifications Subscription
          draft-tgraf-netconf-yang-notifications-versioning-02

Abstract

   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.

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.

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 18 July 2023.

Copyright Notice

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

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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Extend the Datastore Selection  . . . . . . . . . . . . . . .   3
   3.  Extend the Subscription State Change Notifications  . . . . .   4
   4.  The "ietf-yang-push-revision" Module  . . . . . . . . . . . .   5
     4.1.  Data Model Overview . . . . . . . . . . . . . . . . . . .   5
     4.2.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  10
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   In order to process the received YANG push notification messages
   described in section 3.7 of [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.

   This specification applies to the YANG push configured subscriptions
   defined in Section 2.5 of [RFC8639], where a publisher is configured
   to stream notification out of band, as opposed to dynamic
   subscriptions defined in Section 2.4 of [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.

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

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

   The YANG notifications subscription mechanism defined in [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.

   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.

2.  Extend the Datastore Selection

   The YANG notifications subscription OPTIONALLY can be restricted to
   the following YANG module revision for future capabilities:

   latest:  Restricts the subscription to the latest YANG module
      revision.

   revision:  Restricts the subscription to a specific YANG module
      revision.  Example: "2014-05-08".

   latest-compatible-semversion:  Restricts the subscription to the
      latest compatible YANG module semantic version referenced to.
      Example: "2.0.0".

   If nothing is specified, latest YANG module version is implied.

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3.  Extend the Subscription State Change Notifications

   Besides the Subscription ID and the xpath or sub-tree filter
   reference as described in Section 2.7 of [RFC8639], the following
   metadata objects are part of a "subscription-started" or
   "subscription-modified" subscription state change notification.

   revision:  Describes the YANG module revision as specified in
      Section 7.1.9 of [RFC6020] for the related streamed content.

   revision-label:  Describes the YANG module semantic version as
      specified in [I-D.ietf-netmod-yang-semver] for the related
      streamed content.

   Figure 1 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 [RFC8343]).
   This subscription state change notification message is encoded XML
   [W3C.REC-xml-20081126] over the Network Configuration Protocol
   (NETCONF) as per [RFC8640].

<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>

        Figure 1: XML Push Example for a subscription-modified
                         notification message

   Figure 2 provides an example of a JSON encoded, [RFC8259],
   subscription state change notification message over HTTPS-based
   [I-D.ietf-netconf-https-notif] or UDP-based
   [I-D.ietf-netconf-udp-notif] transport for the same subscription.

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   {
     "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"
         }
       }
     }
   }

          Figure 2: JSON Push Example for a subscription-modified
                            notification message

4.  The "ietf-yang-push-revision" Module

4.1.  Data Model Overview

   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.

4.1.1.  Tree View

   The following is the YANG tree diagram [RFC8340] for the ietf-yang-
   push-revision YANG module

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   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

4.1.2.  Full Tree View

   The following is the YANG tree diagram [RFC8340] for the ietf-yang-
   push-revision augmentation within the ietf-subscribed-notifications,
   including the RPCs and notifications.

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)?

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        |  |  |  +--:(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)

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    |  |  |  |  |     +---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

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    +---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

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    |  |  +--:(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

4.2.  YANG Module

   The YANG module has two leaves augmenting the model of Subscription
   to YANG Notifications [RFC8639].

   <CODE BEGINS> file "ietf-yang-push-revision@2023-01-12.yang"
   module ietf-yang-revisions {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-yang-revisions";
     prefix rev;

     organization
       "IETF NETMOD (Network Modeling) Working Group";
     contact
       "WG Web:   <https://datatracker.ietf.org/wg/netmod/>
        WG List:  <mailto:netmod@ietf.org>

        Author:   Joe Clarke
                 <mailto:jclarke@cisco.com>

        Author:   Reshad Rahman
                 <mailto:reshad@yahoo.com>

        Author:   Robert Wilton
                 <mailto:rwilton@cisco.com>

        Author:   Balazs Lengyel
                 <mailto:balazs.lengyel@ericsson.com>

        Author:   Jason Sterne
                 <mailto:jason.sterne@nokia.com>";
     description

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       "This YANG 1.1 module contains definitions and extensions to
        support updated YANG revision handling.

        Copyright (c) 2002 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.

        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.";
     // RFC Ed.: update the date below with the date of RFC publication
     // and remove this note.
     // RFC Ed.: replace XXXX (inc above) with actual RFC number and
     // remove this note.

     revision 2022-11-29 {
       rev:label "1.0.0-draft-ietf-netmod-yang-module-versioning-08";
       description
         "Initial version.";
       reference
         "XXXX: Updated YANG Module Revision Handling";
     }

     typedef revision-date {
       type string {
         pattern '[0-9]{4}-(1[0-2]|0[1-9])-(0[1-9]|[1-2][0-9]|3[0-1])';
       }
       description
         "A date associated with a YANG revision.

          Matches dates formatted as YYYY-MM-DD.";
       reference
         "RFC 7950: The YANG 1.1 Data Modeling Language";
     }

     typedef revision-label {
       type string {

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         length "1..255";
         pattern '[a-zA-Z0-9,\-_.+]+';
         pattern '[0-9]{4}-[0-9]{2}-[0-9]{2}' {
           modifier "invert-match";
           error-message
             "The revision-label must not match a revision-date.";
         }
       }
       description
         "A label associated with a YANG revision.

          Alphanumeric characters, comma, hyphen, underscore, period
          and plus are the only accepted characters. MUST NOT match
          revision-date or pattern similar to a date.";
       reference
         "XXXX: Updated YANG Module Revision Handling;
          Section 3.3, Revision label";
     }

     typedef revision-date-or-label {
       type union {
         type revision-date;
         type revision-label;
       }
       description
         "Represents either a YANG revision date or a revision label";
     }

     extension non-backwards-compatible {
       description
         "This statement is used to indicate YANG module revisions that
          contain non-backwards-compatible changes.

          The statement MUST only be a substatement of the 'revision'
          statement.  Zero or one 'non-backwards-compatible' statements
          per parent statement is allowed.  No substatements for this
          extension have been standardized.

          If a revision of a YANG module contains changes, relative to
          the preceding revision in the revision history, that do not
          conform to the backwards-compatible module update rules
          defined in RFC-XXX, then the 'non-backwards-compatible'
          statement MUST be added as a substatement to the revision
          statement.

          Conversely, if a revision does not contain a
          'non-backwards-compatible' statement then all changes,
          relative to the preceding revision in the revision history,

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          MUST be backwards-compatible.

          A new module revision that only contains changes that are
          backwards-compatible SHOULD NOT include the
          'non-backwards-compatible' statement.  An example of when an
          author might add the 'non-backwards-compatible' statement is
          if they believe a change could negatively impact clients even
          though the backwards compatibility rules defined in RFC-XXXX
          classify it as a backwards-compatible change.

          Add, removing, or changing a 'non-backwards-compatible'
          statement is a backwards-compatible version change.";
       reference
         "XXXX: Updated YANG Module Revision Handling;
          Section 3.2,
          non-backwards-compatible revision extension statement";
     }

     extension label {
       argument revision-label;
       description
         "The revision label can be used to provide an additional
          versioning identifier associated with a module or submodule
          revision.  One such scheme that could be used is [XXXX:
          ietf-netmod-yang-semver].

          The format of the revision label argument MUST conform to the
          pattern defined for the revision label typedef in this module.

          The statement MUST only be a substatement of the revision
          statement.  Zero or one revision label statements per parent
          statement are allowed.  No substatements for this extension
          have been standardized.

          Revision labels MUST be unique amongst all revisions of a
          module or submodule.

          Adding a revision label is a backwards-compatible version
          change.  Changing or removing an existing revision label in
          the revision history is a non-backwards-compatible version
          change, because it could impact any references to that
          revision label.";
       reference
         "XXXX: Updated YANG Module Revision Handling;
          Section 3.3, Revision label";
     }

     extension revision-label-scheme {

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       argument revision-label-scheme-base;
       description
         "The revision label scheme specifies which revision label
          scheme the module or submodule uses.

          The mandatory revision-label-scheme-base argument MUST be an
          identity derived from revision-label-scheme-base.

          This extension is only valid as a top-level statement, i.e.,
          given as as a substatement to 'module' or 'submodule'.  No
          substatements for this extension have been standardized.

          This extension MUST be used if there is a revision label
          statement in the module or submodule.

          Adding a revision label scheme is a backwards-compatible
          version change.  Changing a revision label scheme is a
          non-backwards-compatible version change, unless the new
          revision label scheme is backwards-compatible with the
          replaced revision label scheme.  Removing a revision label
          scheme is a non-backwards-compatible version change.";
       reference
         "XXXX: Updated YANG Module Revision Handling;
          Section 3.3.1, Revision label scheme extension statement";
     }

     extension recommended-min {
       argument revision-date-or-label;
       description
         "Recommends the revision of the module that may be imported to
          one that matches or is derived from the specified
          revision-date or revision label.

          The argument value MUST conform to the
          'revision-date-or-label' defined type.

          The statement MUST only be a substatement of the import
          statement.  Zero, one or more 'recommended-min' statements per
          parent statement are allowed.  No substatements for this
          extension have been standardized.

          If specified multiple times, then any module revision that
          satisfies at least one of the 'recommended-min' statements is
          an acceptable recommended revision for import.

          A particular revision of an imported module adheres to an
          import's 'recommended-min' extension statement if the imported
          module's revision history contains a revision statement with a

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          matching revision date or revision label.

          Adding, removing or updating a 'recommended-min' statement to
          an import is a backwards-compatible change.";
       reference
         "XXXX: Updated YANG Module Revision Handling; Section 4,
          Recommending a minimum revision for module imports";
     }

     identity revision-label-scheme-base {
       description
         "Base identity from which all revision label schemes are
          derived.";
       reference
         "XXXX: Updated YANG Module Revision Handling;
          Section 3.3.1, Revision label scheme extension statement";
     }
   }
   <CODE ENDS>

5.  Security Considerations

   The security considerations for the YANG notifications subscription
   mechanism are described in [RFC8641].  This documents adds no
   additional security considerations.

6.  IANA Considerations

   This document has no IANA actions.

7.  Acknowledgements

   The authors would like to thank xxx for their review and valuable
   comments.

8.  References

8.1.  Normative References

   [I-D.ietf-netmod-yang-module-versioning]
              Wilton, R., Rahman, R., Lengyel, B., Clarke, J., and J.
              Sterne, "Updated YANG Module Revision Handling", Work in
              Progress, Internet-Draft, draft-ietf-netmod-yang-module-
              versioning-07, 24 October 2022,
              <https://www.ietf.org/archive/id/draft-ietf-netmod-yang-
              module-versioning-07.txt>.

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   [I-D.ietf-netmod-yang-semver]
              Clarke, J., Wilton, R., Rahman, R., Lengyel, B., Sterne,
              J., and B. Claise, "YANG Semantic Versioning", Work in
              Progress, Internet-Draft, draft-ietf-netmod-yang-semver-
              08, 24 October 2022, <https://www.ietf.org/archive/id/
              draft-ietf-netmod-yang-semver-08.txt>.

   [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>.

   [RFC6020]  Bjorklund, M., Ed. and RFC Publisher, "YANG - A Data
              Modeling Language for the Network Configuration Protocol
              (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [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>.

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

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

8.2.  Informative References

   [I-D.ietf-netconf-https-notif]
              Jethanandani, M. and K. Watsen, "An HTTPS-based Transport
              for YANG Notifications", Work in Progress, Internet-Draft,
              draft-ietf-netconf-https-notif-13, 4 November 2022,
              <https://www.ietf.org/archive/id/draft-ietf-netconf-https-
              notif-13.txt>.

   [I-D.ietf-netconf-udp-notif]
              Zheng, G., Zhou, T., Graf, T., Francois, P., Feng, A. H.,
              and P. Lucente, "UDP-based Transport for Configured
              Subscriptions", Work in Progress, Internet-Draft, draft-
              ietf-netconf-udp-notif-08, 12 September 2022,
              <https://www.ietf.org/archive/id/draft-ietf-netconf-udp-
              notif-08.txt>.

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   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

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

   [RFC8343]  Bjorklund, M. and RFC Publisher, "A YANG Data Model for
              Interface Management", RFC 8343, DOI 10.17487/RFC8343,
              March 2018, <https://www.rfc-editor.org/info/rfc8343>.

   [RFC8640]  Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
              E., and A. Tripathy, "Dynamic Subscription to YANG Events
              and Datastores over NETCONF", RFC 8640,
              DOI 10.17487/RFC8640, September 2019,
              <https://www.rfc-editor.org/info/rfc8640>.

   [W3C.REC-xml-20081126]
              Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
              F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
              Edition)", World Wide Web Consortium Recommendation REC-
              xml-20081126, November 2008,
              <https://www.w3.org/TR/2008/REC-xml-20081126>.

Authors' Addresses

   Thomas Graf
   Swisscom
   Binzring 17
   CH-8045 Zurich
   Switzerland
   Email: thomas.graf@swisscom.com

   Benoit Claise
   Huawei
   Email: benoit.claise@huawei.com

   Alex Huang Feng
   INSA-Lyon
   Lyon
   France
   Email: alex.huang-feng@insa-lyon.fr

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