Subscription to Notifications in a Distributed Architecture
draft-ietf-netconf-distributed-notif-16

NETCONF                                                          T. Zhou
Internet-Draft                                                  G. Zheng
Intended status: Standards Track                                  Huawei
Expires: 23 April 2026                                           E. Voit
                                                           Cisco Systems
                                                                 T. Graf
                                                                Swisscom
                                                             P. Francois
                                                               INSA-Lyon
                                                         20 October 2025

      Subscription to Notifications in a Distributed Architecture
                draft-ietf-netconf-distributed-notif-16

Abstract

   This document describes extensions to the YANG notifications
   subscription to allow metrics being published directly from
   processors on line cards to target receivers, while subscription is
   still maintained at the route processor in a distributed forwarding
   system.

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 23 April 2026.

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Copyright Notice

   Copyright (c) 2025 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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminologies . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Motivation and Solution Overview  . . . . . . . . . . . . . .   4
   4.  Solution Detail . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Subscription Decomposition  . . . . . . . . . . . . . . . . .   7
   6.  Publication Composition . . . . . . . . . . . . . . . . . . .   7
   7.  Subscription State Change Notifications . . . . . . . . . . .   8
   8.  Publisher Configurations  . . . . . . . . . . . . . . . . . .   8
   9.  YANG Tree . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   10. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . .   9
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   12. Implementation Status . . . . . . . . . . . . . . . . . . . .  12
     12.1.  Huawei VRP . . . . . . . . . . . . . . . . . . . . . . .  12
     12.2.  6WIND VSR  . . . . . . . . . . . . . . . . . . . . . . .  12
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  13
   14. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  13
   15. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   16. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     16.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     16.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  15
     A.1.  Dynamic Subscription  . . . . . . . . . . . . . . . . . .  15
     A.2.  Configured Subscription . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

1.  Introduction

   The mechanism to support a subscription of a continuous and
   customized stream of updates from a YANG datastore [RFC8342] is
   defined in [RFC8639] and [RFC8641].  Requirements for Subscription to
   YANG Datastores are defined in [RFC7923].

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   By streaming YANG-Push notifications from publishers to receivers,
   much better performance and fine-grained sampling can be achieved
   than with a polling-based mechanism.  In a distributed forwarding
   system, the packet forwarding is delegated to multiple processors on
   line cards.  To not to overwhelm the route processor resources, it is
   not uncommon that data records are published directly from processors
   on line cards to target receivers to further increase efficiency on
   the routing system.

   This document complements the general subscription requirements
   defined in Section 4.2.1 of [RFC7923] by the paragraph: A
   Subscription Service MAY support the ability to export from multiple
   software processes on a single routing system and expose the
   information which software process produced which message.

2.  Terminologies

   The following terms are defined in [RFC8639] and are not redefined
   here:

   Subscriber

   Publisher

   Receiver

   Subscription

   The following terms are defined in [RFC9196] and are not redefined
   here:

   Capability

   In addition, this document defines the following terms:

   Global Subscription: The Subscription requested by the subscriber.
   It may be decomposed into multiple Component Subscriptions.

   Component Subscription: The Subscription that defines a data source
   which is managed and controlled by a single Publisher.

   Global Capability: The overall subscription capability that the group
   of Publishers can expose to the Subscriber as defined in [RFC9196]
   for the distributed system.  This includes which YANG nodes can be
   subscribed at which minimum-update-period for periodical
   subscriptions respectively which minimum-dampening-period for on-
   change subscriptions.

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   Component Capability: The subscription capability that each Publisher
   exposes to the Publisher Master.  This includes which YANG nodes with
   which minimum-update-period for periodical subscriptions respectively
   which minimum-dampening-period for on-change subscriptions can be
   subscribed on which Component.

   Publisher Master: The component of a Publisher that interacts with
   the Subscriber to deal with the Global Subscription.  It decomposes
   the Global Subscription to multiple Component Subscriptions and
   interacts with the Publisher Agents.

   Publisher Agent: The component of a Publisher that interacts with the
   Publisher Master to deal with the Component Subscription and pushing
   the data to the Receiver.

   Node: Is the network node which contains one or more Publishers that
   obtains the data from the YANG datastore and pushes it to the
   Receiver.

   Message Publisher: The Publisher that pushes the message to the
   Receiver.

   Message Publisher ID: A 32-bit identifier of the publishing process
   that is locally unique to the publisher Node.  With this identifier
   the publishing process from where the message was published from can
   be uniquely identified.  Receivers SHOULD use the transport session
   and the Publisher ID field to separate different publisher streams
   originating from the same network Node.

3.  Motivation and Solution Overview

   In distributed forwarding systems much YANG data is subscribed to
   processors on line cards and published from the route processor,
   creating an unnecessary overhead at the route processor and a
   potential bottleneck.

   This document proposes that subscribed YANG data can be published
   from processors on line cards while for such Subscriptions the route
   processor is only involved in maintaining and decomposing the
   Subscription, which includes notifying the Receiver which
   Subscription is being published from which line card processor with
   subscription state change notifications.

   To enable Receivers to detect notification message loss when
   publishers share a transport session, the Message Publisher ID in the
   transport message header of the YANG notification message is
   introduced.  In case of UDP transport, this is described in
   Section 3.2 of [I-D.ietf-netconf-udp-notif].  With unique sequence-

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   numbers per publishing process described in Section 3.4.1 of
   [I-D.ietf-netconf-notif-envelope], each message can uniquely be
   identified, loss recognized and related to a transport session and
   publishing process.

4.  Solution Detail

   Figure 1 below shows the distributed data export framework.

   A collector usually includes two components,

   *  the Subscriber generates the subscription instructions to express
      what and how the Receiver wants to receive the data;

   *  the Receiver is the target for the data publication.

   For one subscription, there can be one or more Receivers.  And the
   Subscriber does not necessarily share the same IP address as the
   Receivers.

   In this framework, the Publisher pushes messages to the Receiver
   according to the subscription.  The Publisher is either in the Master
   or Agent role.  The Publisher Master knows all the capabilities that
   his Agents can provide and exposes the Global Capability to the
   collector.  The Subscriber maintains the Global Subscription at the
   Publisher Master and disassembles the Global Subscription to multiple
   Component Subscriptions, depending which source data is needed.  The
   Component Subscriptions are then distributed to the corresponding
   Publisher Agents on route and processors on line cards.

   Publisher Agents collects metrics according to the Component
   Subscription, add its metadata, encapsulates, and pushes messages.
   Messages may require segmentation depending on the amount of YANG
   data subscribed and maximum transmission unit of the interface where
   the message is published from.  The Receiver then reassembles packets
   and decapsulates notifications accordingly.

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                +-----------------------------------------+
                |        Collector        |-------------+ |
                |                        +------------+ | |
                |      +------------+    || Receiver  | | |
                |      | Subscriber |    |--------------+ |
                |      +-----^-+----+    +------^-----^   |
                |            | |                |     |   |
                +-----------------------------------------+
                   Global    | | Global         |     |
                   Capability| | Subscription   |     |
                +-----------------------------------------+
                |            | |                |     |   |
                |            | |   Subscription |     |   |
                |            | |  State Changes |     |   |
                |            | |                |     |   |
                |   +--------+-v-------------------+  |   |
                |   |       Publisher(Master)      |  |   |
                |   +--------^-+-------------------+  |   |
                |            | |                      |   |
                |            | |                      |   |
                |  Component | | Component       Push |   |
                |  Capability| | Subscription         |   |
                |   +--------+-v-------------------+  |   |
                |   |       Publisher(Agent)       +--+   |
                |   +------------------------------+      |
                |                                         |
                |            Network Node                 |
                +-----------------------------------------+

              Figure 1: The Distributed Data Export Framework

   Publisher Master and Publisher Agents interact with each other in
   several ways:

   *  Publisher Agents need to register at the Master at the beginning
      of their process life cycle.

   *  Contracts are created and maintained throughout the subscription
      lifecycle between the Publisher Master and each Agent on the
      Component Capability, and the format for notification data
      structure.

   *  The Publisher Master relays the component subscriptions to the
      Publisher Agents.

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   *  The Publisher Agents announce the status of their Component
      Subscriptions to the Publisher Master.  The status of the overall
      subscription is maintained by the Publisher Master.  The Publisher
      Master is responsible for notifying the subscriber in case of
      problems with the Component Subscriptions.

   The technical mechanisms or protocols used for the coordination of
   operational information between Publisher Master and Agent is out of
   scope of this document.

5.  Subscription Decomposition

   The Collector can only subscribe to the Master.  This requires the
   Publisher Master to:

   1.  expose the Global Capability that can be served by multiple
       Publisher Agents;

   2.  disassemble the Global Subscription to multiple Component
       Subscriptions, and distribute them to the Publisher Agents of the
       corresponding metric sources from the YANG schema tree so that
       they do not overlap; How the subscription is being distributed is
       implementation specific and not part of this document.

   3.  notify changes related to the existing subscriptions to the
       different Publisher Agents.

   And the Publisher Agent to:

   *  Inherit the Global Subscription properties from Publisher Master
      for its Component Subscription;

   *  share the same life-cycle as the Global Subscription;

   *  share the same Subscription ID as the Global Subscription.

6.  Publication Composition

   The Publisher Agent collects data and encapsulates the packets per
   Component Subscription.  The format and structure of the data records
   are defined by the YANG schema, so that the decomposition at the
   Receiver can benefit from the structured and hierarchical data
   records.

   The Receiver can associate the YANG data records with Subscription ID
   [RFC8639] to the subscribed subscription.  Additionally, it can use
   the Message Publisher ID to determine the corresponding publisher
   process.

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   For the dynamic subscription, the output of the "establish-
   subscription" RPC defined in [RFC8639] MUST include a list of Message
   Publisher IDs to indicate how the Global Subscription is decomposed
   into several Component Subscriptions.

   The "subscription-started" and "subscription-modified" notification
   defined in [RFC8639] and "push-update" and "push-change-update"
   notification defined in [RFC8641] MUST also include a list of Message
   Publisher IDs to notify the current Publishers for the corresponding
   Global Subscription.

7.  Subscription State Change Notifications

   In addition to sending event records to Receivers, the Master MUST
   also send subscription state change notifications [RFC8639] when
   events related to subscription management have occurred.  All the
   subscription state change notifications MUST be delivered by the
   Master.

   When the subscription decomposition result changed, the
   "subscription-modified" notification MUST be sent to indicate the new
   list of Publisher Agents.

8.  Publisher Configurations

   This document assumes that all Publisher Agents are preconfigured to
   push data.  The actual working Publisher Agents are selected based on
   the subscription decomposition result.

   All Publisher Agents share the same source IP address for data
   export.  For connectionless data transport such as UDP based
   transport [I-D.ietf-netconf-udp-notif] the same Layer 4 source port
   for data export can be used.  For connection based data transport
   such as HTTPS based transport [I-D.ietf-netconf-https-notif], each
   Publisher Agent MUST be able to acknowledge packet retrieval from
   Receivers, and therefore requires a dedicated Layer 4 source port per
   software process.

   The specific configuration on transports is described in the
   responsible documents.

9.  YANG Tree

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   module: ietf-distributed-notif

     augment /sn:subscriptions/sn:subscription:
       +--ro message-publisher-id*   uint32
     augment /sn:subscription-started:
       +--ro message-publisher-id*   uint32
     augment /sn:subscription-modified:
       +--ro message-publisher-id*   uint32
     augment /sn:establish-subscription/sn:output:
       +--ro message-publisher-id*   uint32
     augment /yp:push-update:
       +--ro message-publisher-id?   uint32
     augment /yp:push-change-update:
       +--ro message-publisher-id?   uint32

      Figure 2: YANG tree diagram for 'ietf-distributed-notif' module.

10.  YANG Module

   <CODE BEGINS> file "ietf-distributed-notif@2025-04-12.yang"
   module ietf-distributed-notif {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-distributed-notif";
     prefix dn;

     import ietf-subscribed-notifications {
       prefix sn;
     }
     import ietf-yang-push {
       prefix yp;
       reference
         "RFC 8641: Subscription to YANG Notifications for Datastore
         Updates";
     }

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

        Authors:  Guangying Zheng
                  <mailto:zhengguangying@huawei.com>
                  Tianran Zhou
                  <mailto:zhoutianran@huawei.com>
                  Thomas Graf
                  <mailto:thomas.graf@swisscom.com>
                  Pierre Francois

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                  <mailto:pierre.francois@insa-lyon.fr>
                  Eric Voit
                  <mailto:evoit@cisco.com>";
     description
       "Defines augmentation for ietf-subscribed-notifications to
        enable the distributed publication with single subscription.

        Copyright (c) 2025 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).

        All revisions of IETF and IANA published modules can be found
        at the YANG Parameters registry
        (https://www.iana.org/assignments/yang-parameters).

        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";

     revision 2025-04-12 {
       description
         "Initial version";
       reference
         "RFC XXXX: Subscription to Distributed Notifications";
     }

     grouping message-publisher-id {
       description
         "Provides a reusable leaf of the message-publisher-id.";
       leaf message-publisher-id {
         type uint32;
         config false;
         description
           "Identifies the software process which publishes the
            message (e.g., processor 1 on line card 1). This field
            is used to notify the receiver which publisher process
            published which message.";
       }
     }

     grouping message-publisher-ids {
       description
         "Provides a reusable leaf-list of message-publisher-id-list.";

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       leaf-list message-publisher-id {
         type uint32;
         config false;
         description
           "Identifies the software process which publishes the
            message (e.g., processor 1 on line card 1). This field
            is used to notify the receiver which publisher processes
            are going to publish.";
       }
     }

     augment "/sn:subscriptions/sn:subscription" {
       description
         "This augmentation allows the Message
          Publisher ID to be exposed for a subscription.";
       uses message-publisher-ids;
     }

     augment "/sn:subscription-started" {
       description
         "This augmentation adds the Message Publisher ID to the
          subscription-started subscription change notifications.";
       uses message-publisher-ids;
     }

     augment "/sn:subscription-modified" {
       description
         "This augmentation adds the Message Publisher ID to the
          subscription-modified subscription change notifications.";
       uses message-publisher-ids;
     }

     augment "/sn:establish-subscription/sn:output" {
       description
         "This augmentation adds the Message Publisher ID to the
          dynamic establish-subscription output.";
       uses message-publisher-ids;
     }

     augment "/yp:push-update" {
       description
         "This augmentation adds the Message Publisher ID in the
          push-update notification.";
       uses message-publisher-id;
     }

     augment "/yp:push-change-update" {
       description

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         "This augmentation adds the Message Publisher ID in the
          push-change-update notification.";
       uses message-publisher-id;
     }
   }
   <CODE ENDS>

11.  IANA Considerations

   This document registers the following namespace URI in the IETF XML
   Registry [RFC3688]:

      URI: urn:ietf:params:xml:ns:yang:ietf-distributed-notif

      Registrant Contact: The IESG.

      XML: N/A; the requested URI is an XML namespace.

   This document registers the following YANG module in the YANG Module
   Names registry [RFC3688]:

      Name: ietf-distributed-notif

      Namespace: urn:ietf:params:xml:ns:yang:ietf-distributed-notif

      Prefix: dn

      Reference: RFC XXXX

12.  Implementation Status

   Note to the RFC-Editor: Please remove this section before publishing.

12.1.  Huawei VRP

   Huawei implemented the Subscription Decomposition described in this
   document for a YANG-Push publisher on UDP-based Transport for
   Configured Subscriptions [I-D.ietf-netconf-udp-notif] in their VRP
   platform.

12.2.  6WIND VSR

   6WIND implemented the Subscription Decomposition described in this
   document for a YANG-Push publisher on UDP-based Transport for
   Configured Subscriptions [I-D.ietf-netconf-udp-notif] in their VSR
   platform.

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13.  Security Considerations

   The YANG module specified in this document defines a schema for data
   that is designed to be accessed via network management protocols such
   as NETCONF [RFC6241] or 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 layer is
   HTTPS, and the mandatory-to-implement secure transport is TLS
   [RFC8446].

   The NETCONF Access Control Model (NACM) [RFC8341] provides the means
   to restrict access particulary for NETCONF or RESTCONF users to a
   preconfigured subset of all available NETCONF or RESTCONF protocol
   operations and content.

   The new data nodes introduced in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control read access (e.g., via get-config or
   notification) to this data nodes.  These are the subtrees and data
   nodes and their sensitivity/vulnerability:

   *  /subscriptions/subscription/message-publisher-ids

   The entries in the two lists above will show where subscribed
   resources might be located on the publishers.  Access control MUST be
   set so that only someone with proper access permissions has the
   ability to access this resource.

   Other Security Considerations is the same as those discussed in
   [RFC8639].

14.  Contributors

      Alexander Clemm
      Futurewai
      2330 Central Expressway
      Santa Clara
      California
      United States of America
      Email: ludwig@clemm.org

15.  Acknowledgements

   We thank Kent Watsen, Mahesh Jethanandani, Martin Bjorklund, Tim
   Carey, Qin Wu, Robert Wilton, Benoit Claise, Alex Huang Feng Camilo
   Cardona and Juergen Schoenwaelder for their constructive suggestions
   for improving this document.

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16.  References

16.1.  Normative References

   [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>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [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>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

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

   [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>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [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>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [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>.

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   [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>.

   [RFC9196]  Lengyel, B., Clemm, A., and B. Claise, "YANG Modules
              Describing Capabilities for Systems and Datastore Update
              Notifications", RFC 9196, DOI 10.17487/RFC9196, February
              2022, <https://www.rfc-editor.org/info/rfc9196>.

16.2.  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-15, 1 February 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              https-notif-15>.

   [I-D.ietf-netconf-notif-envelope]
              Feng, A. H., Francois, P., Graf, T., and B. Claise,
              "Extensible YANG Model for YANG-Push Notifications", Work
              in Progress, Internet-Draft, draft-ietf-netconf-notif-
              envelope-02, 17 June 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              notif-envelope-02>.

   [I-D.ietf-netconf-udp-notif]
              Feng, A. H., Francois, P., Zhou, T., Graf, T., and P.
              Lucente, "UDP-based Transport for Configured
              Subscriptions", Work in Progress, Internet-Draft, draft-
              ietf-netconf-udp-notif-23, 14 October 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              udp-notif-23>.

   [RFC7923]  Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements
              for Subscription to YANG Datastores", RFC 7923,
              DOI 10.17487/RFC7923, June 2016,
              <https://www.rfc-editor.org/info/rfc7923>.

Appendix A.  Examples

   This appendix is non-normative.

A.1.  Dynamic Subscription

   Figure 3 shows a typical dynamic subscription to the network Node
   with distributed data export capability.

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   +-------------+                 +-------------+ +-------------+
   | Subscriber/ |                 |  Publisher  | |  Publisher  |
   | Receiver    |                 |  (Master)   | |  (Agent)    |
   +-------------+                 +------+------+ +------+------+
          |                               |               |
          | establish-subscription        |               |
          +------------------------------>+ component     |
          |                               | subscription  |
          | RPC Reply: OK, id #22         +-------------->+
          | Message Publisher ID [#1,#2]  |               |
          +<------------------------------+               |
          |                               |               |
          | notif-mesg, id #22            |               |
          | Message Publisher ID #1       |               |
          +<------------------------------+               |
          |                               |               |
          | notif-mesg, id#22             |               |
          | Message Publisher ID #2       |               |
          +<----------------------------------------------+
          |                               |               |
          | modify-subscription (id#22)   |               |
          +------------------------------>+ component     |
          |                               | subscription  |
          | RPC Reply: OK, id #22         +-------------->+
          +<------------------------------+               |
          |                               |               |
          | subscription-modified, id#22  |               |
          | Message Publisher ID [#1]     |               |
          +<------------------------------+               |
          |                               |               |
          | notif-mesg, id #22            |               |
          | Message Publisher ID  #1      |               |
          +<------------------------------+               |
          |                               |               |
          |                               |               |
          +                               +               +

                Figure 3: Call Flow for Dynamic Subscription

   A "establish-subscription" RPC request as per [RFC8641] is sent to
   the Master with a successful response.  An example of using NETCONF:

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   <netconf:rpc message-id="101"
      xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
    <establish-subscription
       xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
       xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
      <yp:datastore
           xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
        ds:operational
      </yp:datastore>
      <yp:datastore-xpath-filter
          xmlns:ex="https://example.com/sample-data/1.0">
        /ex:foo
      </yp:datastore-xpath-filter>
      <yp:periodic>
        <yp:period>500</yp:period>
      </yp:periodic>
     </establish-subscription>
    </netconf:rpc>

                 Figure 4: "establish-subscription" Request

   As the network Node is able to fully satisfy the request, the request
   is given a subscription ID of 22.  The response as in Figure 5
   indicates that the subscription is decomposed into two component
   subscriptions which will be published by two message Message
   Publisher ID: #1 and #2.

   <rpc-reply message-id="101"
     xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <id
      xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
        22
     </id>
     <message-publisher-id
      xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
        1
     </message-publisher-id>
     <message-publisher-id
      xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
        2
     </message-publisher-id>
   </rpc-reply>

          Figure 5: "establish-subscription" Positive RPC Response

   Then, both Publishers send notifications with the corresponding piece
   of data to the Receiver.

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   The subscriber may invoke the "modify-subscription" RPC for a
   subscription it previously established.  The RPC has no difference to
   the single publisher case as in [RFC8641].  Figure 6 provides an
   example where a subscriber attempts to modify the period and
   datastore XPath filter of a subscription using NETCONF.

        <rpc message-id="102"
          xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
       <modify-subscription
           xmlns=
             "urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
           xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
         <id>22</id>
         <yp:datastore
             xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
           ds:operational
         </yp:datastore>
         <yp:datastore-xpath-filter
             xmlns:ex="https://example.com/sample-data/1.0">
           /ex:bar
         </yp:datastore-xpath-filter>
         <yp:periodic>
           <yp:period>250</yp:period>
         </yp:periodic>
        </modify-subscription>
     </rpc>

                  Figure 6: "modify-subscription" Request

   If the modification is successfully accepted, the "subscription-
   modified" subscription state notification is sent to the subscriber
   by the Master.  The notification, Figure 7 for example, indicates the
   modified subscription is decomposed into one component subscription
   which will be published by message Message Publisher ID #1.

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 <notification
       xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
 <eventTime>2007-09-01T10:00:00Z</eventTime>
 <subscription-modified
       xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
       xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
     <id>22</id>
     <yp:datastore
         xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
       ds:operational
     </yp:datastore>
     <yp:datastore-xpath-filter
         xmlns:ex="https://example.com/sample-data/1.0">
       /ex:bar
     </yp:datastore-xpath-filter>
     <yp:periodic>
         <yp:period>250</yp:period>
     </yp:periodic>
     <message-publisher-id
     xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
        1
     </message-publisher-id>
   </subscription-modified>
 </notification>

   Figure 7: "subscription-modified" Subscription State Notification

A.2.  Configured Subscription

   Figure 8 shows a typical configured subscription to the network Node
   with distributed data export capability.

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   +-------------+                 +-------------+ +-------------+
   | Receiver    |                 |  Publisher  | |  Publisher  |
   |             |                 |  (Master)   | |  (Agent)    |
   +------+------+                 +------+------+ +------+------+
          |                               |               |
          | subscription-started, id#39   |               |
          | Message Publisher ID [#1,#2]  |               |
          +<------------------------------+               |
          |                               |               |
          | notif-mesg, id#39             |               |
          | Message Publisher ID #1       |               |
          +<------------------------------+               |
          |                               |               |
          | notif-mesg, id#39             |               |
          | Message Publisher ID #2       |               |
          +<----------------------------------------------+
          |                               |               |
          |                               |               |
          |                               |               |

              Figure 8: Call Flow for Configured Subscription

   Before starting to push data, the "subscription-started" subscription
   state notification is sent to the Receiver.  The following example
   assumes the NETCONF transport has already established.  The
   notification indicates that the configured subscription is decomposed
   into two component subscriptions which will be published by two
   message Message Publisher IDs: #1 and #2.

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 <notification xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
   <eventTime>2007-09-01T10:00:00Z</eventTime>
   <subscription-started
       xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
       xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
     <identifier>39</identifier>
     <yp:datastore
         xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
     ds:operational
     </yp:datastore>
     <yp:datastore-xpath-filter
         xmlns:ex="https://example.com/sample-data/1.0">
       /ex:foo
     </yp:datastore-xpath-filter>
     <yp:periodic>
         <yp:period>250</yp:period>
     </yp:periodic>
     <message-publisher-ids
     xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications>
        1
     </message-publisher-ids>
     <message-publisher-ids
     xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications>
        2
     </message-publisher-ids>
   </subscription-started>
 </notification>

    Figure 9: "subscription-started" Subscription State Notification

   Then, both Publishers send notifications with the corresponding data
   record to the Receiver.

Authors' Addresses

   Tianran Zhou
   Huawei
   156 Beiqing Rd., Haidian District
   Beijing
   China
   Email: zhoutianran@huawei.com

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   Guangying Zheng
   Huawei
   101 Yu-Hua-Tai Software Road
   Nanjing
   Jiangsu,
   China
   Email: zhengguangying@huawei.com

   Eric Voit
   Cisco Systems
   United States of America
   Email: evoit@cisco.com

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

   Pierre Francois
   INSA-Lyon
   Lyon
   France
   Email: pierre.francois@insa-lyon.fr

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