Support of Versioning in YANG Notifications Subscription

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Table of Contents

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.¶

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.¶

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 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.¶

{
  "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"
      }
    }
  }
}

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

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

<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-07, 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 {
    leaf revision {
      type rev:revision-date-or-label;
      config true;
      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 {
    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" {
    uses ypm:yang-push-module-version-config;
  }
  augment "/sn:modify-subscription/sn:input/sn:target" {
    uses ypm:yang-push-module-version-config;
  }

  // Subscription notifications
  augment "/sn:subscription-started/sn:target" {
    uses ypm:yang-push-module-version;
  }
  augment "/sn:subscription-modified/sn:target" {
    uses ypm:yang-push-module-version;
  }

  // Subscription container
  augment "/sn:subscriptions/sn:subscription/sn:target" {
    uses ypm:yang-push-module-version;
  }
}

<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.¶

Authors' Addresses