



Network Configuration                                     R. Wilton, Ed.
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                               H. Keller
Expires: 3 September 2026                              Deuetsche Telekom
                                                               B. Claise
                                                          Everything OPS
                                                                E. Aries
                                                                 Juniper
                                                              J. Cumming
                                                                   Nokia
                                                                 T. Graf
                                                                Swisscom
                                                            2 March 2026


             YANG Datastore Telemetry (YANG Push version 2)
                  draft-wilton-netconf-yang-push-2-00

Abstract

   YANG Push version 2 is a YANG datastore telemetry solution, as an
   alternative lightweight specification to the Subscribed Notifications
   and YANG Push solution, specifically optimized for the efficient
   observability of operational data.

About This Document

   This note is to be removed before publishing as an RFC.

   The latest revision of this draft can be found at
   https://rgwilton.github.io/draft-yp-observability/draft-wilton-
   netconf-yp-observability.html.  Status information for this document
   may be found at https://datatracker.ietf.org/doc/draft-wilton-
   netconf-yang-push-2/.

   Discussion of this document takes place on the Network Configuration
   Working Group mailing list (mailto:netconf@ietf.org), which is
   archived at https://mailarchive.ietf.org/arch/browse/netconf/.
   Subscribe at https://www.ietf.org/mailman/listinfo/netconf/.

   Source for this draft and an issue tracker can be found at
   https://github.com/rgwilton/draft-yp-observability.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.




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Copyright Notice

   Copyright (c) 2026 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Document Status . . . . . . . . . . . . . . . . . . . . . . .   5
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Background and Motivation for YANG Push v2  . . . . . . .   6
     3.2.  Complexities in Modelling the Operational State
           Datastore . . . . . . . . . . . . . . . . . . . . . . . .   8
     3.3.  Complexities for Consumers of YANG Push Data  . . . . . .   8
       3.3.1.  Combined periodic and on-change subscription  . . . .   9
     3.4.  Relationships to existing RFCs and Internet Drafts  . . .   9
       3.4.1.  RFC 8639 and RFC 8641 . . . . . . . . . . . . . . . .  10
       3.4.2.  I-D.draft-ietf-netconf-notif-envelope and RFC 5277  .  10
       3.4.3.  RFC 9196 and
               I-D.draft-netana-netconf-yp-transport-capabilities  .  10
       3.4.4.  I-D.draft-ietf-netconf-https-notif and
               I-D.draft-ietf-netconf-udp-notif  . . . . . . . . . .  11
       3.4.5.  
   4.  YANG Push v2 Overview . . . . . . . . . . . . . . . . . . . .  11
   5.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .  13
   6.  Subscription paths and selection filters  . . . . . . . . . .  15
     6.1.  _YPath_ definition  . . . . . . . . . . . . . . . . . . .  16



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     6.2.  The "filters" Container . . . . . . . . . . . . . . . . .  17
     6.3.  Decomposing Subscription Filters  . . . . . . . . . . . .  18
   7.  Datastore Event Streams . . . . . . . . . . . . . . . . . . .  19
     7.1.  Notification Envelope . . . . . . . . . . . . . . . . . .  20
     7.2.  Event Records . . . . . . . . . . . . . . . . . . . . . .  22
     7.3.  Types of subscription event monitoring  . . . . . . . . .  23
     7.4.  Periodic events . . . . . . . . . . . . . . . . . . . . .  24
     7.5.  On-Change events  . . . . . . . . . . . . . . . . . . . .  25
       7.5.1.  On-Change Notifiable Datastore Nodes  . . . . . . . .  26
       7.5.2.  On-Change Considerations  . . . . . . . . . . . . . .  27
     7.6.  Combined periodic and on-change subscriptions . . . . . .  27
     7.7.  Streaming Update Examples . . . . . . . . . . . . . . . .  28
   8.  Receivers, Transports, and Encodings  . . . . . . . . . . . .  29
     8.1.  Receivers . . . . . . . . . . . . . . . . . . . . . . . .  29
       8.1.1.  Receivers for Configured Subscriptions  . . . . . . .  30
       8.1.2.  Receivers for Dynamic Subscriptions . . . . . . . . .  32
       8.1.3.  Receiver Session States and State Machine . . . . . .  32
     8.2.  Transports  . . . . . . . . . . . . . . . . . . . . . . .  33
       8.2.1.  Requirements for YANG Push v2 Transport
               Specifications  . . . . . . . . . . . . . . . . . . .  34
     8.3.  Encodings . . . . . . . . . . . . . . . . . . . . . . . .  35
   9.  Setting up and Managing Subscriptions . . . . . . . . . . . .  36
     9.1.  Common Subscription Parameters  . . . . . . . . . . . . .  36
       9.1.1.  Subscription States . . . . . . . . . . . . . . . . .  37
       9.1.2.  Creating Subscriptions  . . . . . . . . . . . . . . .  39
       9.1.3.  Modifying Subscriptions . . . . . . . . . . . . . . .  40
       9.1.4.  Terminating Subscriptions . . . . . . . . . . . . . .  41
     9.2.  Subscription Lifecycle Notifications  . . . . . . . . . .  42
       9.2.1.  "subscription-started"  . . . . . . . . . . . . . . .  43
       9.2.2.  "subscription-modified" . . . . . . . . . . . . . . .  44
       9.2.3.  "subscription-terminated" . . . . . . . . . . . . . .  45
       9.2.4.  "update-completed"  . . . . . . . . . . . . . . . . .  46
     9.3.  Configured Subscriptions  . . . . . . . . . . . . . . . .  47
       9.3.1.  Creating a Configured Subscription  . . . . . . . . .  48
       9.3.2.  Modifying a Configured Subscription . . . . . . . . .  49
       9.3.3.  Deleting a Configured Subscription  . . . . . . . . .  49
       9.3.4.  Resetting a Configured Subscription . . . . . . . . .  49
     9.4.  Dynamic Subscriptions . . . . . . . . . . . . . . . . . .  50
       9.4.1.  Establishing a Dynamic Subscription . . . . . . . . .  51
       9.4.2.  Modifying a Dynamic Subscription  . . . . . . . . . .  52
       9.4.3.  Deleting a Dynamic Subscription . . . . . . . . . . .  53
       9.4.4.  Killing a Dynamic Subscription  . . . . . . . . . . .  54
       9.4.5.  RPC Failures  . . . . . . . . . . . . . . . . . . . .  55
   10. Robustness, Reliability, and Subscription Monitoring  . . . .  56
     10.1.  Robustness and Reliability . . . . . . . . . . . . . . .  56
     10.2.  Subscription Monitoring  . . . . . . . . . . . . . . . .  57
     10.3.  Publisher Capacity . . . . . . . . . . . . . . . . . . .  57
   11. Conformance and Capabilities  . . . . . . . . . . . . . . . .  58



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     11.1.  Capabilities . . . . . . . . . . . . . . . . . . . . . .  58
     11.2.  Subscription Content Versioning  . . . . . . . . . . . .  60
   12. Distributed Notifications - Multiple Publishing Processes . .  61
   13. Core YANG Push v2 YANG Data Model . . . . . . . . . . . . . .  63
     13.1.  ietf-yang-push-2 YANG tree . . . . . . . . . . . . . . .  63
     13.2.  ietf-yang-push-2 YANG Model  . . . . . . . . . . . . . .  65
   14. Configured Subscription YANG Data Model . . . . . . . . . . .  89
     14.1.  ietf-yang-push-2-config YANG tree  . . . . . . . . . . .  91
     14.2.  ietf-yang-push-2-config YANG Model . . . . . . . . . . .  93
   15. Capabilities YANG Data Model  . . . . . . . . . . . . . . . . 104
     15.1.  ietf-yang-push-2-capabilities YANG tree  . . . . . . . . 104
     15.2.  ietf-yang-push-2-capabilities YANG Model . . . . . . . . 105
   16. Security Considerations . . . . . . . . . . . . . . . . . . . 111
     16.1.  Use of YANG Push v2 with NACM  . . . . . . . . . . . . . 111
     16.2.  Receiver Authorization . . . . . . . . . . . . . . . . . 112
     16.3.  YANG Module Security Considerations  . . . . . . . . . . 113
   17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 114
     17.1.  Namespace URI registrations  . . . . . . . . . . . . . . 114
   18. YANG Module Name registrations  . . . . . . . . . . . . . . . 115
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 115
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . . 116
   References  . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
     Normative References  . . . . . . . . . . . . . . . . . . . . . 116
     Informative References  . . . . . . . . . . . . . . . . . . . . 118
   Appendix A.  Functional changes between YANG Push v2 and YANG
           Push  . . . . . . . . . . . . . . . . . . . . . . . . . . 122
     A.1.  Removed Functionality . . . . . . . . . . . . . . . . . . 122
     A.2.  Changed Functionality . . . . . . . . . . . . . . . . . . 123
     A.3.  Added Functionality . . . . . . . . . . . . . . . . . . . 125
   Appendix B.  Subscription Errors (from RFC 8641)  . . . . . . . . 125
     B.1.  RPC Failures  . . . . . . . . . . . . . . . . . . . . . . 125
     B.2.  Failure Notifications . . . . . . . . . . . . . . . . . . 127
   Appendix C.  Examples . . . . . . . . . . . . . . . . . . . . . . 127
     C.1.  Example of periodic update messages . . . . . . . . . . . 128
     C.2.  Example of an on-change-update notification using the new
           style update message  . . . . . . . . . . . . . . . . . . 130
     C.3.  Example of an on-change-delete notification using the new
           style update message  . . . . . . . . . . . . . . . . . . 132
       C.3.1.  Update message with single deleted data node  . . . . 132
       C.3.2.  Update message with multiple on-change deletes  . . . 133
     C.4.  NETCONF Dynamic Subscription RPC examples . . . . . . . . 134
       C.4.1.  Successful periodic subscription  . . . . . . . . . . 134
       C.4.2.  Failed periodic subscription  . . . . . . . . . . . . 135
       C.4.3.  "delete-subscription" RPC . . . . . . . . . . . . . . 137
     C.5.  Distributed Notifications Subscription  . . . . . . . . . 137
   Appendix D.  Summary of Open Issues & Potential Enhancements  . . 140
     D.1.  Issues related to general IETF process  . . . . . . . . . 140
     D.2.  Issue related to Terminology/Definitions  . . . . . . . . 140



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     D.3.  Issues related to YANG Push v2 Overview . . . . . . . . . 140
     D.4.  Issues related to Subscription Paths and Selection
            Filters  . . . . . . . . . . . . . . . . . . . . . . . . 140
     D.5.  Issues related to Datastore Event Streams & message
            format . . . . . . . . . . . . . . . . . . . . . . . . . 141
     D.6.  Issues related to Receivers, Transports, & Encodings  . . 141
       D.6.1.  Issues related to Transports: . . . . . . . . . . . . 141
     D.7.  Issues related to Setting up & Managing Subscriptions . . 141
       D.7.1.  Issues related to the configuration model:  . . . . . 141
       D.7.2.  Issues related to dynamic subscriptions:  . . . . . . 141
     D.8.  Issues related to Subscription Lifecycle  . . . . . . . . 141
     D.9.  Issues related to Performance, Reliability & Subscription
            Monitoring . . . . . . . . . . . . . . . . . . . . . . . 142
       D.9.1.  Issues/questions related to operational data: . . . . 142
     D.10. Issues related to Conformance and Capabilities  . . . . . 142
     D.11. Issues related to the YANG Modules  . . . . . . . . . . . 143
     D.12. Issues related to the Security Considerations (& NACM
            filtering) . . . . . . . . . . . . . . . . . . . . . . . 143
     D.13. Issues related to the IANA  . . . . . . . . . . . . . . . 143
     D.14. Issues related to the Appendixes  . . . . . . . . . . . . 143
       D.14.1.  Examples related issues/questions: . . . . . . . . . 143
     D.15. Summary of closed/resolved issues . . . . . . . . . . . . 144
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 145

1.  Document Status

   _RFC Editor: If present, please remove this section before
   publication._ _RFC Editor: Please replace 'RFC XXXX' with the RFC
   number for this RFC._

   Based on the feedback received during the IETF 121 NETCONF session,
   this document has currently been written as a self-contained
   lightweight protocol and document replacement for [RFC8639] and
   [RFC8641], defining a separate configuration data model.

   *The comparison between YANG Push and YANG Push v2 is now in
   Appendix A.*

   *Open issues are either now being tracked inline in the text or in
   Appendix D for the higher level issues.*

2.  Conventions

   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.



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   All _YANG tree diagrams_ used in this document follow the notation
   defined in [RFC8340].

3.  Introduction

   [I-D.ietf-nmop-yang-message-broker-integration] describes an
   architecture for how YANG datastore telemetry, e.g., [RFC8641], can
   be integrated effectively with message brokers, e.g., [Kafka], that
   forms part of a wider architecture for a _Network Anomaly Detection
   Framework_, specified in
   [I-D.ietf-nmop-network-anomaly-architecture].

   This document specifies "YANG Push v2", an lightweight alternative to
   Subscribed Notifications [RFC8639] and YANG Push [RFC8641].  YANG
   Push v2 is a separate YANG datastore telemetry solution, which can be
   implemented independently or, if desired, alongside [RFC8639] and
   [RFC8641].

   At a high level, YANG Push v2 is designed to solve a similar set of
   requirements as YANG Push, and it reuses a significant subset of the
   ideas and base solution from YANG Push.  YANG Push v2 defines a
   separate data model to allow concurrent implementation of both
   protocols and to facilitate more significant changes in behavior, but
   many of the data nodes are taken from YANG Push and have the same, or
   very similar definitions.

   The following sections give the background for the solution, and
   highlight the key ways that this specification differs from the
   specifications that it is derived from.

3.1.  Background and Motivation for YANG Push v2

   A push based telemetry solution, as described both in this document
   and also the YANG Push solution described by [RFC8639] and [RFC8641],
   is beneficial because it allows operational data to be exported by
   publishers more immediately and efficiently compared to legacy poll
   based mechanisms, such as SNMP [RFC3411].  Some further background
   information on the general motivations for push based telemetry,
   which equally apply here, can be found in the _Motivation_ (section
   1.1) of [RFC8639] and the Introduction (section 1) of [RFC8641].  The
   remainder of this section is focused on the reasons why a new
   lightweight version of YANG Push has been specified, and what
   problems is aims to solve.








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   Early implementation efforts of the
   [I-D.ietf-nmop-yang-message-broker-integration] architecture hit
   issues with using either of the two common YANG datastore telemetry
   solutions that have been specified, i.e., [gNMI] or YANG Push
   [RFC8641].

   gNMI is specified by the OpenConfig Industry Consortium.  It is more
   widely implemented, but operators report that some inter-operability
   issues between device implementations cause problems.  Many of the
   OpenConfig protocols and data models are also expected to evolve more
   rapidly than IETF protocols and models - that are expected to have a
   more gradual pace of evolution once an RFC has been published.

   YANG Push [RFC8641] was standardized by the IETF in 2019, but market
   adoption has been rather slow.  During 2023/2024, when vendors
   started implementing, or considering implementing, YANG Push, it was
   seen that some design choices for how particular features have been
   specified in the solution make it expensive and difficult to write
   performant implementations, particularly when considering the
   complexities and distributed nature of operational data.  In
   addition, some design choices of how the data is encoded (e.g., YANG
   Patch [RFC8072]) make more sense when considering changes in
   configuration data but less sense when the goal is to export a subset
   of the operational data off the device in an efficient fashion for
   both devices (publishers) and clients (receivers).

   Hence, during 2024, the vendors and operators working towards YANG
   telemetry solutions agreed to a plan to implement a subset of
   [RFC8639] and [RFC8641], including common agreements of features that
   are not needed and would not be implemented, and deviations from the
   standards for some aspects of encoding YANG data.  In addition, the
   implementation efforts identified the minimal subset of functionality
   needed to support the initial telemetry use cases, and areas of
   potential improvement and optimization to the overall YANG Push
   telemetry solution (which has been written up as a set of small
   internet drafts that augment or extend the base YANG Push solution).

   Out of this work, consensus was building to specify a cut down
   version of Subscribed Notifications [RFC8639] and YANG Push [RFC8641]
   that is both more focussed on the operational telemetry use case and
   is also easier to implement, achieved by relaxing some of the
   constraints on consistency on the device, and removing, or
   simplifying some of the operational features.  This has resulted in
   this specification, YANG Push v2.

   The implementation efforts also gave rise to potential improvements
   to the protocol and encoding of notification messages.




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3.2.  Complexities in Modelling the Operational State Datastore

   The YANG abstraction of a single datastore of related consistent data
   works very well for configuration that has a strong requirement to be
   self consistent, and that is always updated, and validated, in a
   transactional way.  But for producers of telemetry data, the YANG
   abstraction of a single operational datastore is not really possible
   for devices managing a non-trivial quantity of operational data.

   Some systems may store their operational data in a single logical
   database, yet it is less likely that the operational data can always
   be updated in a transactional way, and often for memory efficiency
   reasons such a database does not store individual leaves, but instead
   semi-consistent records of data at a container or list entry level.

   For other systems, the operational information may be distributed
   across multiple internal nodes (e.g., linecards), and potentially
   many different process daemons within those distributed nodes.  Such
   systems generally do not, and cannot, exhibit full consistency
   [Consistency] of the operational data (which would require
   transactional semantics across all daemons and internal nodes), only
   offering an eventually consistent [EventualConsistency] view of the
   data instead.

   In practice, many network devices will manage their operational data
   as a combination of some data being stored in a central operational
   datastore, and other, higher scale, and potentially more frequently
   changing data (e.g., statistics or FIB information) being stored
   elsewhere in a more memory efficient and performant way.

3.3.  Complexities for Consumers of YANG Push Data

   For the consumer of the telemetry data, there is a requirement to
   associate a schema with the instance-data that will be provided by a
   subscription.  One approach is to fetch and build the entire schema
   for the device, e.g., by fetching YANG library, and then use the
   subscription XPath to select the relevant subtree of the schema that
   applies only to the subscription.  The problem with this approach is
   that if the schema ever changes, e.g., after a software update, then
   it is reasonably likely of some changes occurring with the global
   device schema even if there are no changes to the schema subtree
   under the subscription path.  Hence, it would be helpful to identify
   and version the schema associated with a particular subscription
   path, and also to encoded the instance data relatively to the
   subscription path rather than as an absolute path from the root of
   the operational datastore.





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   *TODO More needs to be added here, e.g., encoding, on-change
   considerations.  Splitting subscriptions up.*

   This document proposes a new opt-in YANG-Push encoding format to use
   instead of the "push-update" and "push-change-update" notifications
   defined in [RFC8641].

   1.  To allow the device to split a subscription into smaller child
       subscriptions for more efficient independent and concurrent
       processing.  I.e., reusing the ideas from
       [I-D.ietf-netconf-distributed-notif].  However, all child
       subscriptions are still encoded from the same subscription point.

3.3.1.  Combined periodic and on-change subscription

   Sometimes it is helpful to have a single subscription that covers
   both periodic and on-change notifications.

   There are two ways in which this may be useful:

   1.  For generally slow changing data (e.g., a device's physical
       inventory), then on-change notifications may be most appropriate.
       However, in case there is any lost notification that isn't always
       detected, for any reason, then it may also be helpful to have a
       slow cadence periodic backup notification of the data (e.g., once
       every 24 hours), to ensure that the management systems should
       always eventually converge on the current state in the network.

   2.  For data that is generally polled on a periodic basis (e.g., once
       every 10 minutes) and put into a time series database, then it
       may be helpful for some data trees to also get more immediate
       notifications that the data has changed.  Hence, a combined
       periodic and on-change subscription, would facilitate more
       frequent notifications of changes of the state, to reduce the
       need of having to always wait for the next periodic event.

   Hence, this document allows a single subscription to be configured as
   both periodic and on-change.

3.4.  Relationships to existing RFCs and Internet Drafts

   This document, specifying YANG Push v2, is intended to be a
   lightweight alternative for [RFC8639] and [RFC8641], but that also
   incorporates various extensions since those RFCs were written.  Often
   substantial parts of those documents and models have been
   incorporated almost verbatim, but modified to fit the YANG Push v2
   functionality and module structure.




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   Hence, the authors of this draft would like to sincerely thank and
   acknowledge the very significant effort put into those RFCs and
   drafts by authors, contributors and reviewers.  In particular, We
   would like to thank the listed authors of these documents: Eric Voit,
   Alex Clemm, Alberto Gonzalez Prieto, Einar Nilsen-Nygaard, Ambika
   Prasad Tripathy, Balazs Lengyel, Alexander Clemm, Benoit Claise, Qin
   Wu, Qiufang Ma, Alex Huang Feng, Thomas Graf, Pierre Francois.

3.4.1.  RFC 8639 and RFC 8641

   This document is primarily intended to be a lightweight alternative
   for [RFC8639] and [RFC8641], but it intentionally reuses substantial
   parts of the design and data model of those RFCs.

   YANG Push v2 is defined using a separate module namespace, and hence
   can be implemented independently or, if desired, alongside [RFC8639]
   and [RFC8641], and the various extensions to YANG Push.

   A more complete description of the main differences in YANG Push v2
   compares to [RFC8639] and [RFC8641] is given in Appendix A.

3.4.2.  [I-D.draft-ietf-netconf-notif-envelope] and RFC 5277

   All of the notifications defined in this specification, i.e., both
   the datastore update message and subscription lifecycle update
   notifications (Section 9.2) depend upon and use the notification
   envelope format defined in [I-D.draft-ietf-netconf-notif-envelope].

   As such, this specification does not make any use of the notification
   format defined in [RFC5277], but this does not prevent
   implementations using [RFC5277] format notifications for other YANG
   notifications, e.g., for the "NETCONF" event stream defined in
   [RFC5277].

3.4.3.  RFC 9196 and
        [I-D.draft-netana-netconf-yp-transport-capabilities]

   This document uses the capabilities concepts defined in [RFC9196].

   In particular, it augments into the ietf-system-capabilities YANG
   module, but defines an equivalent alternative capability structure
   for the ietf-notification-capabilities YANG module, which defines the
   capabilities for YANG Push [RFC8641].

   The generic transport capabilities defined in
   [I-D.draft-netana-netconf-yp-transport-capabilities] have been
   incorporated into the ietf-yang-push-2 YANG module, to augment YANG
   Push v2 transport capabilities and to use the different identities.



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3.4.4.  [I-D.draft-ietf-netconf-https-notif] and
        [I-D.draft-ietf-netconf-udp-notif]

   The ietf-yang-push-2 YANG module has subsumed and extended the
   _receivers_ data model defined in the ietf-subscribed-notif-receivers
   YANG module defined in [I-D.draft-ietf-netconf-https-notif].

   The overall YANG Push v2 solution anticipates and requires new bis
   versions of both of these transports documents that augment into the
   _receivers/receiver/transport-type_ choice statement, and also
   augment the transport identity defined in the ietf-yang-push-2 data
   model.

3.4.5.  [I-D.draft-ietf-netconf-distributed-notif]

   This document reuses the work from
   [I-D.draft-ietf-netconf-distributed-notif], but with some changes to
   work with the YANG Push v2 data models.  This is described in
   Section 12.

4.  YANG Push v2 Overview

   This document specifies a lightweight telemetry solution that
   provides a subscription service for updates to the state and changes
   in state from a chosen datastore.

   Subscriptions specify when notification messages (also referred to as
   _updates_) should be sent, what data to include in the update
   records, and where those notifications should be sent.

   A YANG Push v2 subscription comprises:

   *  a target datastore for the subscription, where the monitored
      subscription data is logically sourced from.

   *  a set of selection filters to choose which datastore nodes from
      the target datastore the subscription is monitoring or sampling,
      as described in Section 6.

   *  a choice of how update event notifications for the datastore's
      data nodes are triggered.  I.e., either periodic sampling of the
      current state, on-change event-driven, or both.  These are
      described in Section 7.3.

   *  a choice of encoding of the messages, e.g., JSON, or CBOR.

   *  a receiver to which datastore updates and subscription
      notifications are sent, as described in Section 8.1;



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      -  for configured subscriptions, the receivers parameters are
         configured, and specify transport, receiver, and encoding
         parameters.

      -  for dynamic subscriptions, the receiver uses the same transport
         session on which the dynamic subscription has been created.

   If a subscription is valid and acceptable to the publisher, and if a
   suitable connection can be made to the receiver associated with a
   subscription, then the publisher will enact the subscription,
   periodically sampling or monitoring changes to the chosen datastore's
   data nodes that match the selection filter.  Push updates are
   subsequently sent by the publisher to the receiver, as per the terms
   of the subscription.

   Subscriptions may be set up in two ways: either through configuration
   - or YANG RPCs to create and manage dynamic subscriptions.  These two
   mechanisms are described in Section 9.

   Changes to the state of subscription are notified to receivers as
   subscription lifecycle notifications.  These are described in
   Section 9.2.

   Security access control mechanisms, e.g., NACM {RFC8341}} can be used
   to ensure the receivers only get access to the information for which
   they are allowed.  This is further described in Section 16.

   While the functionality defined in this document is transport
   agnostic, transports like the Network Configuration Protocol
   (NETCONF) [RFC6241] or RESTCONF [RFC8040] can be used to configure or
   dynamically signal subscriptions.  In the case of configured
   subscription, the transport used for carrying the subscription
   notifications is entirely independent from the protocol used to
   configure the subscription, and other transports, e.g.,
   [I-D.draft-ietf-netconf-udp-notif] defines a simple UDP based
   transport for Push notifications.  Transport considerations are
   described in Section 8.2. *TODO the reference to draft-ietf-netconf-
   udp-notif isn't right, it wouldn't be that draft, but a -bis version
   of it.  James is querying whether we need this at all*

   *TODO Introduce capabilities and operational monitoring*










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   This document defines a YANG data model, that includes RPCs and
   notifications, for configuring and managing subscriptions and
   associated configuration, and to define the format of a _update_
   notification message.  The YANG model is defined in Section 13.2 and
   associated tree view in Section 13.1.  The YANG data model defined in
   this document conforms to the Network Management Datastore
   Architecture defined in [RFC8342].

5.  Definitions

   This document reuses the terminology defined in [RFC7950], [RFC8341],
   [RFC8342], [RFC8639] and [RFC8641].

   The following terms are taken from [RFC8342]:

   *  _Datastore_: A conceptual place to store and access information.
      A datastore might be implemented, for example, using files, a
      database, flash memory locations, or combinations thereof.  A
      datastore maps to an instantiated YANG data tree.

   *  _Client_: An entity that can access YANG-defined data on a server,
      over some network management protocol.

   *  _Configuration_: Data that is required to get a device from its
      initial default state into a desired operational state.  This data
      is modeled in YANG using "config true" nodes.  Configuration can
      originate from different sources.

   *  _Configuration datastore_: A datastore holding configuration.

   The following terms are taken from [RFC8639]:

   *  _Configured subscription_: A subscription installed via
      configuration into a configuration datastore.

   *  _Dynamic subscription_: A subscription created dynamically by a
      subscriber via a Remote Procedure Call (RPC).

   *  _Event_: An occurrence of something that may be of interest.
      Examples include a configuration change, a fault, a change in
      status, crossing a threshold, or an external input to the system.

   *  _Event occurrence time_: A timestamp matching the time an
      originating process identified as when an event happened.

   *  _Event record_: A set of information detailing an event.





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   *  _Event stream_: A continuous, chronologically ordered set of
      events aggregated under some context.

   *  _Event stream filter_: Evaluation criteria that may be applied
      against event records in an event stream.  Event records pass the
      filter when specified criteria are met.

   *  _Notification message_: Information intended for a receiver
      indicating that one or more events have occurred.

   *  _Publisher_: An entity responsible for streaming notification
      messages per the terms of a subscription.

   *  _Receiver_: A target to which a publisher pushes subscribed event
      records.  For dynamic subscriptions, the receiver and subscriber
      are the same entity.

   *  _Subscriber_: A client able to request and negotiate a contract
      for the generation and push of event records from a publisher.
      For dynamic subscriptions, the receiver and subscriber are the
      same entity.

   The following terms are taken from [RFC8641]:

   *  _Datastore node_: A node in the instantiated YANG data tree
      associated with a datastore.  In this document, datastore nodes
      are often also simply referred to as "objects".

   *  _Datastore node update_: A data item containing the current value
      of a datastore node at the time the datastore node update was
      created, as well as the path to the datastore node.

   *  _Datastore subscription_: A subscription to a stream of datastore
      node updates.

   *  _Datastore subtree_: A datastore node and all its descendant
      datastore nodes.

   *  _On-change subscription_: A datastore subscription with updates
      that are triggered when changes in subscribed datastore nodes are
      detected.

   *  _Periodic subscription_: A datastore subscription with updates
      that are triggered periodically according to some time interval.

   *  _Selection filter_: Evaluation and/or selection criteria that may
      be applied against a targeted set of objects.




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   *  _Update record_: A representation of one or more datastore node
      updates.  In addition, an update record may contain which type of
      update led to the datastore node update (e.g., whether the
      datastore node was added, changed, or deleted).  Also included in
      the update record may be other metadata, such as a subscription id
      of the subscription for which the update record was generated.  In
      this document, update records are often also simply referred to as
      "updates".

   *  _Update trigger_: A mechanism that determines when an update
      record needs to be generated.

   *  _YANG-Push_: The subscription and push mechanism for datastore
      updates that is specified in [RFC8641].

   This document introduces the following terms:

   *  _Subscription_: A registration with a publisher, stipulating the
      information the receiver wishes to have pushed from the publisher
      without the need for further solicitation.

   *  _Subscription Identifier_: A numerical identifier for a configured
      or dynamic subscription.  Also referred to as the subscription-id.

   *  _YANG-Push-Lite_: The light weight subscription and push mechanism
      for datastore updates that is specified in this document. *Add
      comment*

   This document also uses the terminology from
   [I-D.ietf-netconf-distributed-notif] in Section 12 and the related
   examples in Appendix C.5.

6.  Subscription paths and selection filters

   A key part of a subscription is to select which data nodes should be
   monitored, and so a subscription must specify both the selection
   filters and the datastore against which these selection filters will
   be applied.  This information is used to choose, and subsequently
   push, _update_ notifications from the publisher's datastore(s) to the
   subscription's receiver.

   Filters can either be defined inline within a configured subscription
   (Figure 21), a dynamic subscription's _establish-subscription_ RPC
   (Figure 14), or as part of the _datastore-telemetry/filters_
   container (Figure 1) which can then be referenced from a configured
   or dynamic subscription.





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   The following selection filter types are included in the YANG Push v2
   data model and may be applied against a datastore:

   *  _YPaths_: A list of basic YANG path selection filters that defines
      a path to a subtree of data nodes in the data tree, with some
      simple constraints on keys.  See Section 6.1.

   *  _subtree_: A subtree selection filter identifies one or more
      datastore subtrees.  When specified, _update_ records will only
      include the datastore nodes of selected datastore subtree(s).  The
      syntax and semantics correspond to those specified in [RFC6241],
      Section 6.

   *  _XPaths_: A list of _XPath_ ([XPATH]) selection filter
      expressions.  When specified, updates will only come from the
      selected datastore nodes that match the node set associated with
      the XPath expression.

   These filters are used as selectors that define which data nodes fall
   within the scope of a subscription.  A publisher MUST support YPath
   filters, and MAY also support subtree or XPath filters.

   For both YPath and XPath based filters, each filter may define a list
   of path expressions.  Each of these filter path expressions MAY be
   processed by the publisher independently, and if two or more filter
   path expressions end up selecting overlapping data nodes then the
   publisher MAY notify duplicate values for those data nodes, but the
   encoded data that is returned MUST always be syntactically valid,
   i.e., as per section 5.3 of [RFC8342].

6.1.  _YPath_ definition

   A _YPath_ represents a simple path into a YANG schema tree, where
   some of the list key values may be constrained.

   It is encoded in the similar format to the YANG JSON encoding for
   instance-identifier, section 6.11 of [RFC7951], except with more
   flexibility on the keys, in that keys may be left-out or be bound to
   a regular expression filter.

   The rules for constructing a YPath are:

   *  A YPath is a sequence of data tree path segment separated by a '/'
      character.  If the path starts with a '/' then it is absolute path
      from the root of the schema, otherwise it is a relative path,
      where the context of the relative path must be declared.





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   *  Constraints on key values may be specified within a single pair of
      '[' ']' brackets, where:

      -  keys may be given in any order, and may be omitted, in which
         case they match any value.  Key matches are separated by a
         comma (,) with optional space character either side.

      -  key match is given by _<key>=<value>_, with optional space
         characters either side of the equals (=), and value is
         specified as:

         o  '<value>', for an exact match of the key's value.  Single
            quote characters (') must be escaped with a backslash (\).

         o  r'<reg-expr>', for a regex match of the key value using
            [RFC9485], and where the regular-expression is a full match
            of the string, i.e, it implicit anchors to the start and end
            of the value.

   Some examples of YPaths:

   *  _/ietf-interfaces:interfaces/interface[name='eth0']/ietf-ip:ipv6/
      ip_ - which identifies is 'ipv6/ip' data node in the ietf-ip
      module for the 'eth0' interface.

   *  _/ietf-interfaces:interfaces/interface[name=r'eth.*']/ietf-
      ip:ipv6/ip_ - which identifies all interfaces with a name that
      start with "eth".

   *  _/example:multi-keys-list[first-key='foo', second-key=r'bar.*']_ -
      which identifies all entries in the 'multi-keys-list, where the
      first-key matches foo, and the second-key starts with bar.

   *  _/ietf-interfaces:interfaces/interface_ - which identifies the
      _interface_ list data node in the ietf-interfaces module for all
      interfaces.  I.e., the interface list 'name' key is unrestricted.

   *  _/ietf-interfaces:interfaces/interface[]_ - alternative form of
      the previous YPath.

6.2.  The "filters" Container

   The "filters" container maintains a list of all datastore
   subscription filters that persist outside the lifecycle of a single
   subscription.  This enables predefined filters that may be referenced
   by more than one configured or dynamic subscription.





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   Below is a tree diagram for the "filters" container.  All objects
   contained in this tree are described in the YANG module in
   Section 13.

   module: ietf-yang-push-2-config
     +--rw datastore-telemetry!
        +--rw filters
           +--rw filter* [name]
              +--rw name             string
              +--rw (filter)
                 +--:(path)
                 |  +--rw path       ypath
                 +--:(subtree)
                 |  +--rw subtree    <anydata>
                 +--:(xpath)
                    +--rw xpath      yang:xpath1.0 {yp2:xpath}?

     augment /yp2:subscription-started/yp2:target:
       +-- filter-ref?   filter-ref
     augment /yp2:subscription-modified/yp2:target:
       +-- filter-ref?   filter-ref

                                  Figure 1

6.3.  Decomposing Subscription Filters

   In order to address the issues described in Section 3.2, YANG Push v2
   allows for publishers to send subtrees of data nodes in separate
   _update_ notifications, rather than requiring that the subscription
   data be returned as a single datastore _update_ notification covering
   all data nodes matched by the subscription filter.  This better
   facilitates publishers that internally group some of their
   operational data fields together into larger structures for
   efficiency, and avoids publishers or receivers having to consume
   potentially very large notification messages.  For example, each
   entry in the _/ietf-interfaces:interface/interface_ list could be
   represented as an object of data internally within the publisher.  In
   essence, a client specified subscription filter can be decomposed by
   a publisher into more specific non-overlapping filters that are then
   used to return the data.

   In particular:









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   1.  A Publisher MAY decompose a client specified subscription filter
       path into a set of non-overlapping subscription filter paths that
       collectively cover the same data.  The publisher is allowed to
       return data for each of these decomposed subscription filter
       paths in separate _update_ notification messages, each with
       separate, perhaps more precise, _observation-time_ timestamps,
       but all using the same notification _event-time_.

   2.  A Publisher MAY split large lists into multiple separate update
       messages, each with separate _observation-time_ timestamps, but
       all using the same notification _event-time_.  E.g., if a device
       has 10,000 entries in a list, it may return them in a single
       response, or it may split them into multiple smaller messages,
       perhaps for 500 interfaces at a time.

   To ensure that clients can reasonably process data returned via
   decomposed filters then:

   1.  _update_ notifications MUST indicate the precise subtree of data
       that the update message is updating or replacing, i.e., so a
       receiver can infer that data nodes no longer being notified by
       the publisher have been deleted:

       *  if we support splitting list entries in multiple updates, then
          something like a _more_data_ flag is needed to indicate that
          the given update message is not complete.

7.  Datastore Event Streams

   In YANG Push v2, a subscription, based on the selected filters, will
   generate a ordered stream of datastore _update_ records that is
   referred to as an event stream.  Each subscription logically has a
   different event stream of update records, even if multiple
   subscriptions use the same filters to select datastore nodes.

   As YANG-defined event records are created by a system, they may be
   assigned to one or more streams.  The event record is distributed to
   a subscription's receiver where (1) a subscription includes the
   identified stream and (2) subscription filtering does not exclude the
   event record from that receiver.

   Access control permissions may be used to silently exclude event
   records from an event stream for which the receiver has no read
   access.  See [RFC8341], Section 3.4.6 for an example of how this
   might be accomplished.  Note that per Section 2.7 of this document,
   subscription state change notifications are never filtered out.
   *TODO, filtering and NACM filtering should be dependent on whether it
   is a configured or dynamic subscription.*



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   If subscriber permissions change during the lifecycle of a
   subscription and event stream access is no longer permitted, then the
   subscription MUST be terminated. *TODO, check this*

   Event records SHALL be sent to a receiver in the order in which they
   were generated.  I.e., the publisher MUST not reorder the events when
   enqueuing notifications on the transport session, but there is no
   guarantee of delivery order.

   Event records MUST NOT be sent before a _subscription-started_
   notification (Section 9.2.1) or after a _subscription-terminated_
   notification (Section 9.2.3).

7.1.  Notification Envelope

   All notifications in the event stream MUST be encoded using
   [I-D.draft-ietf-netconf-notif-envelope] to wrap the notification
   message, and MUST include the _event-time_, _hostname_, and
   _sequence-number_ leafs in all messages.  The _publisher-id_ MAY be
   excluded in it matches the default value (0), otherwise it MUST be
   included.

   The following example illustrates a fully encoded _update_
   notification that includes the notification envelope and additional
   meta-data fields.  The _update_ notification, i.e., as defined via
   the _notification_ statement in the yang-push-lite YANG module, is
   carried in the _contents_ anydata data node.

   The _event-time_ field is used to correlate separate _update_
   messages that collectively represent individual parts of the same
   update (e.g., where the source data is being obtained from multiple
   producers).



















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   {
     "ietf-yp-notification:envelope": {
       "event-time": "2024-10-10T08:00:05.22Z",
       "hostname": "example-router",
       "sequence-number": 3219,
       "contents": {
         "ietf-yang-push-2:update": {
           "id": 1011,
           "path-prefix": "/ietf-interfaces:interfaces",
           "snapshot-type": "periodic",
           "observation-time": "2024-10-10T08:00:05.11Z",
           "updates": [
             {
               "target-path": "interface",
               "replace-by": {
                 "interface": [
                   {
                     "name": "eth0",
                     "type": "iana-if-type:ethernetCsmacd",
                     "enabled": true,
                     "oper-status": "up",
                     "admin-status": "up"
                   },
                   {
                     "name": "eth1",
                     "type": "iana-if-type:ethernetCsmacd",
                     "enabled": true,
                     "oper-status": "up",
                     "admin-status": "up"
                   }
                 ]
               }
             }
           ]
         }
       }
     }
   }

      Figure 2: Example of update notification including notification
                                  envelope










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7.2.  Event Records

   A single _update_ record is used for all datastore notifications.  It
   is used to report the current state of a set of data nodes at a given
   target path for either periodic, on-change, or resync notifications,
   and also for on-change notifications to indicate that the data node
   at the given target path has been deleted.

   The schema for this notifications is given in the following tree
   diagram:

       +---n update
       |  +--ro id?                 subscription-id
       |  +--ro path-prefix?        string
       |  +--ro snapshot-type       enumeration
       |  +--ro observation-time?   yang:date-and-time
       |  +--ro updates* [target-path]
       |  |  +--ro target-path          string
       |  |  +--ro (data)?
       |  |     +--:(merge)
       |  |     |  +--ro merge?         <anydata>
       |  |     +--:(replaced-by)
       |  |     |  +--ro replaced-by?   <anydata>
       |  |     +--:(deleted)
       |  |        +--ro deleted?       empty
       |  +--ro complete?           boolean

                      Figure 3: 'update' notification

   The normative definitions for the notifications fields are given in
   the YANG module in Section 13.  The fields can be informatively
   summarized as:

   *  _id_ - identifies the subscription the notification relates to.

   *  _path-prefix_ - identifies the absolute instance-data path to
      which all target-paths are data are encoded relative to.

   *  _snapshot-type_ - this indicates what type of event causes the
      update message to be sent.  I.e., a periodic collection, an on-
      change event, or a resync collection.

   *  _observation-time_ - the time that the data was sampled, or when
      the on-change event occurred that caused the message to be
      published.

   *  _target-path_ - identifies the data node that is being acted on by
      the _merge_, _replace-by_, or _deleted_ data.



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   *  _data_ - A choice representing the action taken and the updated
      data, which is one of the following:

      -  _merge_ - identifies the data node that the receiver should
         merge with their current view of that data node.  I.e., all
         descendant data nodes reporting values should replace those
         held by the receiver, but the absence of a decendent data node
         does not imply that it no longer exists and hence should be
         deleted.

      -  _replaced-by_ - identifies the data node that replaces the copy
         of that data node in the receiver's state.  Any descendent data
         nodes not present in the update no longer exist and hence
         should be implicitly deleted in the receiver's current state.

      -  _deleted_ - indicates that the data node no longer exists and
         should be deleted in the receivers state.  This field _MUST
         NOT_ be sent in an _on-change_ update message.

   *  _complete_ - if present, this flag indicates whether the
      notification is complete or whether more messages as part of the
      same update will follow.  The default value for the flag depends
      on the _snapshot-type_.  For _on-change_ events, the messages are
      assumed to be completed until the _complete_ leaf is set to false.
      For other type of events (e.g., periodic), the messages are
      assumed to be incomplete unless the _complete_ leaf is set to
      true.  Setting this flag to true is semantically equivalent to the
      server sending a separate _update-complete_ notification.

   As per the structure of the _update_ notification, a single
   notification MAY provide updates for multiple target-paths.

7.3.  Types of subscription event monitoring

   Subscription can either be based on sampling the requested data on a
   periodic cadence or being notified when the requested data changes.
   In addition, this specification allows for subscriptions that both
   notify on-change and also with a periodic cadence, which can help
   ensure that the system eventually converges on the right state, even
   if on-change notification were somehow lost or mis-processed anywhere
   in the data processing pipeline.

   The schema for the update-trigger container is given in the following
   tree diagram:







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   module: ietf-yang-push-2-config
     +--rw datastore-telemetry!
        +--rw subscriptions
           +--rw subscription* [id]
              +--rw update-trigger
                 +--rw periodic!
                 |  +--rw period         centiseconds
                 |  +--rw anchor-time?   yang:date-and-time
                 +--rw on-change! {on-change}?
                    +--rw sync-on-start?   boolean

     augment /yp2:subscription-started/yp2:target:
       +-- filter-ref?   filter-ref
     augment /yp2:subscription-modified/yp2:target:
       +-- filter-ref?   filter-ref

                    Figure 4: 'update-trigger' container

   The normative definitions for the update-trigger fields are given in
   the _ietf-yang-push-2_ YANG module in Section 13.  They are also
   described in the following sections.

7.4.  Periodic events

   In a periodic subscription, the data included as part of an update
   record corresponds to data that could have been read using a
   retrieval operation.  Only the state that exists in the system at the
   time that it is being read is reported, periodic updates never
   explicitly indicate whether any data-nodes or list entries have been
   deleted.  Instead, receivers must infer deletions by the absence of
   data during a particular collection event.

   Where possible, publishers SHOULD use the _replaced-by_ data node to
   represent the new data since it provides clients with simple explicit
   semantics.  Publishers MAY use the _merge_ data node when they cannot
   determine whether the data being published in the update is complete.

   For periodic subscriptions, triggered updates will occur at the
   boundaries of a specified time interval.  These boundaries can be
   calculated from the periodic parameters:

   *  a _period_ that defines the duration between push updates.

   *  an _anchor-time_; update intervals fall on the points in time that
      are a multiple of a _period_ from an _anchor-time_.  If an
      _anchor-time_ is not provided, then the publisher chooses a
      suitable anchor-time, e.g., perhaps the time that the subscription
      was first instantiated by the publisher.



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   The anchor time and period are particularly useful, in fact required,
   for when the collected telemetry data is being stored in a time-
   series database and the subscription is setup to ensure that each
   collection is placed in a separate time-interval bucket.

   Periodic update notifications are expected, but not required, to use
   a single _target-path_ per _update_ notification.

7.5.  On-Change events

   In an on-change subscription, _update_ records indicate updated
   values or when a monitored data node or list node has been deleted.
   An _update_ record is sent whenever a change in the subscribed
   information is detected.  In the case that data nodes have been
   changed then the _update_ record SHOULD only report the state that
   has changed (included any required list keys), but MAY include
   additional unchanged data nodes if the publisher is unable to
   optimize the on-change update message.

   Each entry in the _updates_ list identifies a data node (i.e., list
   entry, container, leaf or leaf-list), via the _target-path_ that
   either has changes is state or has been deleted.

   A delete of a specific individual data node or subtree may be
   notified in two different ways:

   *  if the data that is being deleted is below the _target-path_ then
      the delete is implicit by the publisher returning the current data
      node subtree with the delete data nodes missing.  I.e., the
      receiver must implicitly infer deletion.

   *  if the data node is being deleted at the target path.  E.g., if an
      interface is deleted then an entire list entry related to that
      interface may be removed.  In this case, the _target path_
      identifies the list entry that is being deleted, but the data
      returned is just an empty object {}, which replaces all the
      existing data for that object in the receiver. *TODO, is this
      better as a delete flag, or separate delete list?*

   On-change subscriptions also support the following additional
   parameters:

   *  _sync-on-start_ defines whether or not a complete snapshot of all
      subscribed data is sent at the start of a subscription.  Such
      early synchronization establishes the frame of reference for
      subsequent updates.  For each data node covered by an on-change
      with sync-on-start subscription, then an _sync-on-start_ _update_
      notification containing the current state MUST be sent before any



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      on-change _update_ notifications for those same data nodes.
      However, _sync-on-start_ and _on-change_ _update_ notifications
      may be interleaved for different data-nodes under the
      subscription.  Unsolicited _sync-on-start update_ notifications
      MUST NOT be sent, they MUST only be sent after a subscription has
      started.

7.5.1.  On-Change Notifiable Datastore Nodes

   Publishers are not required to support on-change notifications for
   all data nodes, and they may not be able to generate on-change
   updates for some data nodes.  Possible reasons for this include:

   *  the value of the datastore node changes frequently (e.g., the in-
      octets counter as defined in [RFC8343]),

   *  small object changes that are frequent and meaningless (e.g., a
      temperature gauge changing 0.1 degrees),

   *  or no implementation is available to generate a notification when
      the source variable for a particular data node has changed.

   In addition, publishers are not required to notify every change or
   value for an on-change monitored data node.  Instead, publishers MAY
   limit the rate at which changes are reported for a given data node,
   i.e., effectively deciding the interval at which an underlying value
   is sampled.  If a data node changes value and then reverts back to
   the original value within a sample interval then the publisher MAY
   not detect the change and it would go unreported.  However, if the
   data node changes to a new value after it has been sampled, then the
   change and latest state MUST be reported to the receiver.  In
   addition, if a client was to query the value (e.g., through a NETCONF
   get-data RPC) then they MUST see the same observed value as would be
   notified.

   To give an example, if the interface link state reported by hardware
   is changing state hundreds of times per second, then it would be
   entirely reasonable to limit those interface state changes to a much
   lower cadence, e.g., perhaps every 100 milliseconds.  In the
   particular case of interfaces, there may also be data model specific
   forms of more advanced dampening that are more appropriate, e.g.,
   that notify interface down events immediately, but rate limit how
   quickly the interface is allowed to transition to up state, which
   overall acts as a limit on the rate at which the interface state may
   change, and hence also act as a limit on the rate at which on-change
   notifications could be generated.





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   The information about what nodes support on-change notifications is
   reported using capabilities operational data model.  This is further
   described in Section 11.

7.5.2.  On-Change Considerations

   On-change subscriptions allow receivers to receive updates whenever
   changes to targeted objects occur.  As such, on-change subscriptions
   are particularly effective for data that changes infrequently but for
   which applications need to be quickly notified, with minimal delay,
   whenever a change does occur.

   On-change subscriptions tend to be more difficult to implement than
   periodic subscriptions.  Accordingly, on-change subscriptions may not
   be supported by all implementations or for every object.

   Whether or not to accept or reject on-change subscription requests
   when the scope of the subscription contains objects for which on-
   change is not supported is up to the publisher implementation.  A
   publisher MAY accept an on-change subscription even when the scope of
   the subscription contains objects for which on-change is not
   supported.  In that case, updates are sent only for those objects
   within the scope of the subscription that do support on-change
   updates, whereas other objects are excluded from update records, even
   if their values change.  In order for a subscriber to determine
   whether objects support on-change subscriptions, objects are marked
   accordingly on a publisher.  Accordingly, when subscribing, it is the
   responsibility of the subscriber to ensure that it is aware of which
   objects support on-change and which do not.  For more on how objects
   are so marked, see Section 3.10. *TODO Is this paragraph and the one
   below still the right choice for YANG Push v2?*

   Alternatively, a publisher MAY decide to simply reject an on-change
   subscription if the scope of the subscription contains objects for
   which on-change is not supported.  In the case of a configured
   subscription, the publisher MAY keep the subscription in _inactive_
   state.

7.6.  Combined periodic and on-change subscriptions

   A single subscription may created to generate notifications both when
   changes occur and on a periodic cadence.  Such subscriptions are
   equivalent to having separate periodic and on-change subscriptions on
   the same path, except that they share the same subscription-id and
   filter paths.






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7.7.  Streaming Update Examples

   Figure 5 provides an example of a notification message for a
   subscription tracking the operational status of interface (per
   [RFC8343]).  This notification message is encoded using JSON
   [RFC7951].

   {
     "ietf-yang-push-2:update": {
       "id": "interfaces",
       "path-prefix": "/ietf-interfaces:interfaces/interface",
       "snapshot-type": "periodic",
       "observation-time": "2024-10-10T08:00:05.11Z",
       "updates": [
         {
           "target-path": "",
           "merge": {
             "interface": [
               {
                 "name": "eth0",
                 "type": "iana-if-type:ethernetCsmacd",
                 "enabled": true,
                 "ietf-interfaces:oper-status": "up",
                 "ietf-interfaces:admin-status": "up"
               },
               {
                 "name": "eth1",
                 "type": "iana-if-type:ethernetCsmacd",
                 "enabled": true,
                 "ietf-interfaces:oper-status": "up",
                 "ietf-interfaces:admin-status": "up"
               }
             ]
           }
         }
       ],
       "complete": false
     }
   }

                 Figure 5: Example periodic update message

   Figure 6 provides an example of an on-change notification message for
   the same subscription.







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   {
     "ietf-yang-push-2:update": {
       "id": "interfaces",
       "path-prefix": "/ietf-interfaces:interfaces",
       "snapshot-type": "on-change-update",
       "observation-time": "2025-10-10T08:16:06.11Z",
       "updates": [
         {
           "target-path": "interface[name='eth0']",
           "replaced-by": {
             "name": "eth0",
             "type": "iana-if-type:ethernetCsmacd",
             "enabled": false,
             "ietf-interfaces:oper-status": "down"
           }
         },
         {
           "target-path": "interface[name='eth1']",
           "replaced-by": {
             "name": "eth1",
             "type": "iana-if-type:ethernetCsmacd",
             "enabled": false,
             "ietf-interfaces:oper-status": "down"
           }
         }
       ]
     }
   }

                 Figure 6: Example on-change update message

8.  Receivers, Transports, and Encodings

8.1.  Receivers

   Every subscription is associated with a receiver, which identifies
   the destination host, transport and encoding settings, where all
   notifications for a subscription are sent.

   For configured subscriptions there is no explicit association with an
   existing transport session, and hence the properties associated with
   the receiver are explicitly configured, as described in
   Section 8.1.1.

   For dynamic subscriptions, the receiver, and most associated
   properties are implicit from the session on which the dynamic
   subscription was initiated, as described in Section 8.1.2.




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8.1.1.  Receivers for Configured Subscriptions

   For configured subscriptions, receivers are configured independently
   from the subscriptions and then referenced from the subscription
   configuration.

   Below is a tree diagram for _datastore-telemetry/receivers_
   container.  All objects contained in this tree are described in the
   YANG module in Section 13.2.

   These parameters identify how to connect to each receiver.  For each
   subscription, the publisher uses the referenced receiver
   configuration to establish transport connectivity to the receiver.

   module: ietf-yang-push-2-config
     +--rw datastore-telemetry!
        +--rw receivers
           +--rw receiver* [name]
              +--rw name                      string
              +--rw encoding                  yp2:encoding
              +--rw dscp?                     inet:dscp
              +---x reset
              +--rw (notification-message-origin)?
              |  +--:(interface-originated)
              |  |  +--rw source-interface?   if:interface-ref
              |  |          {interface-designation}?
              |  +--:(address-originated)
              |     +--rw source-vrf?         leafref {supports-vrf}?
              |     +--rw source-address?     inet:ip-address-no-zone
              +--rw (transport-type)

     augment /yp2:subscription-started/yp2:target:
       +-- filter-ref?   filter-ref
     augment /yp2:subscription-modified/yp2:target:
       +-- filter-ref?   filter-ref

             Figure 7: datastore-telemetry/receivers container

   Each configured receiver has the following associated properties:

   *  a _name_ to identify and reference the receiver in the
      subscription configuration.

   *  a _transport_, which identifies the transport protocol to use for
      all connections to the receiver.






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      -  any transport-specific related parameters, some of which may be
         mandatory, others optional to specify, e.g., DSCP.  There are
         likely to be various data nodes related to establishing
         appropriate security and encryption.

   *  an _encoding_ to encode all YANG notification messages to the
      receiver, i.e., see Section 8.3.

   *  optional parameters to identify where traffic should egress the
      publisher:

      -  a _source-interface_, identifying the egress interface to use
         from the publisher, implicitly choosing the source IP address
         and VRF.

      -  a _source-vrf_, identifying the Virtual Routing and Forwarding
         (VRF) instance on which to reach receivers.  This VRF is a
         network instance as defined in [RFC8529].  Publisher support
         for VRFs is optional and advertised using the _supports-vrf_
         feature.

      -  a _source-address_ address, identifying the IP address to
         source notification messages from.

      If none of the above parameters are set, the publisher MAY choose
      which interface(s) and address(es) to source subscription
      notifications from.

   This specification is transport independent, e.g., see Section 8.2,
   and thus the YANG module defined in Section 13.2 cannot directly
   define and expose these transport parameters.  Instead, receiver-
   specific transport connectivity parameters MUST be configured via
   transport-specific augmentations to the YANG choice node _/datastore-
   telemetry/receivers/receiver/transport-type_.

   A publisher supporting configured subscriptions clearly must support
   at least one YANG data model that augments transport connectivity
   parameters onto _/datastore-telemetry/receivers/receiver/transport-
   type_.  For an example of a similar such augmentation (but for YANG
   Push), see [I-D.draft-ietf-netconf-udp-notif]. *TODO, this reference
   and text will need to be updated to a UDP-notif bis document, that
   augments the new YANG Push v2 receiver path.*









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8.1.2.  Receivers for Dynamic Subscriptions

   For dynamic subscriptions, each subscription has a single receiver
   that is implicit from the host that initiated the _establish-
   subscription_ RPC, reusing the same transport session for all the
   subscription notifications.

   Hence most receiver parameters for a dynamic subscription, e.g.,
   related to the transport, are implicitly determined and cannot be
   explicitly controlled.

   Dynamic subscriptions MUST specify an encoding (see Section 8.3) and
   MAY specify DSCP Marking (see Section 8.2.1.1) for the telemetry
   notifications in the _establish-subscription_ RPC (see Figure 14).

8.1.3.  Receiver Session States and State Machine

   Each subscription will need to establish a subscription to the
   specified receiver.  Multiple subscriptions may share one or more
   transport sessions to the same receiver.

   A receiver in YANG Push v2 can be in one of the following states:

   *  *Configured*: The receiver has been configured on the publisher,
      but the receiver is not referenced by any valid subscriptions and
      hence there is no attempt to establish a connection to the
      receiver.

   *  *Connecting*: The receiver has at least one associated
      subscription and the publisher is attempting to establish a
      transport session and complete any required security exchanges,
      but this process has not yet succeeded.

   *  *Active*: The receiver has at least one associated subscription, a
      transport session has been established (if required), security
      exchanges have successfully completed, and the publisher is able
      to send notifications to the receiver.

   The state transitions for a receiver are illustrated below:












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                       .-------------------.
                       |                   |
                       |    Configured     |
                       |                   |
                       '-------------------'
                               |  ^
     Receiver is referenced by |  |  No configured subscriptions
     1 or more subscriptions   |  |  reference the receiver
                               v  |
                       .-------------------.
                       |                   |
                       |    Connecting     |
                       |                   |
                       '-------------------'
                               |  ^
     Transport and/or security |  |  Transport or security session
     has been established.     |  |  has been lost or failed.
                               v  |
                       .-------------------.
                       |                   |
                       |      Active       |
                       |                   |
                       '-------------------'

                  Figure 8: Receiver Session State Diagram

   This state model allows implementations and operators to clearly
   distinguish between receivers that are simply configured, those that
   are in the process of connecting, and those that are actively being
   used.

   If the configuration has changed such that there were previously
   connections to a receiver, but that receiver is no longer referenced
   by valid subscriptions, then the publisher MUST close any associated
   transport sessions to the receiver, but MAY delay the closing for a
   short period of time (no more than 15 minutes) to potentially allow
   existing transport session to be reused by new subscriptions.

8.2.  Transports

   This document describes a transport-agnostic mechanism for
   subscribing to YANG datastore telemetry.  Hence, separate
   specifications are required to define transports that support YANG
   Push v2.  The requirements for these transport specifications are
   documented in the following section:






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8.2.1.  Requirements for YANG Push v2 Transport Specifications

   This section provides requirements for any transport specifications
   supporting the YANG Push v2 solution presented in this document.

   The transport specification MUST provide YANG modules, to be
   implemented by publishers implementing the YANG Push configuration
   model in Section 14, that:

   *  augments the _datastore-telemetry/receivers/transport-type_ choice
      statement with a container that both identifies the transport and
      contains all transport specific parameters.

   *  augments _/sysc:system-capabilities/transport/transport-
      capabilities/_ container with any transport specific capabilities
      or options (conditional on a YANG _when_ statement).  Note,
      encodings for a given transport are advertised directly via the
      ietf-yang-push-2-capabilities YANG Model Section 15.2.

   Using a secure transport is RECOMMENDED.  Thus, any transport
   specification MUST provide a mechanism to ensure secure communication
   between the publisher and receiver in a hostile environment, e.g.,
   through the use of transport layer encryption.  Transport
   specifications MAY also specify a mechanism for unencrypted
   communications, which can be used when transport layer security is
   not required, e.g., if the transport session is being secured via
   another mechanism, or when operating within a controlled environment
   or test lab.

   Any transport specification SHOULD support mutual receiver and
   publisher authentication at the transport layer.

   The transport selected by the subscriber to reach the publisher
   SHOULD be able to support multiple "establish-subscription" requests
   made in the same transport session.

   The transport specification MUST specifying how multiple
   subscriptions referencing the same receiver are to be handled at the
   transport layer.  The transport specification MAY require separate
   transport sessions per subscription to a given receiver, or it MAY
   allow multiple subscriptions to the same receiver to be multiplexed
   over a shared transport session.

   A specification for a transport built upon this document can choose
   whether to use the same logical channel for the RPCs and the event
   records.  However, the _update_ records and the subscription state
   change notifications MUST be sent on the same transport session.




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   The transport specification MAY specify a keepalive mechanism to keep
   the transport session alive.  There is no YANG Push v2 protocol or
   application level keepalive mechanism.

   *TODO, do we need to mention anything about transport session
   timeouts, e.g., which would cause a subscription to be terminated.
   What about buffering?  Is that a transport consideration?*

   Additional transport requirements may be dictated by the choice of
   transport used with a subscription.

8.2.1.1.  DSCP Marking

   YANG Push v2 supports _dscp_ marking to differentiate prioritization
   of notification messages during network transit.

   A receiver with a _dscp_ leaf results in a corresponding
   Differentiated Services Code Point (DSCP) marking [RFC2474]} being
   placed in the IP header of any resulting _update_ notification
   messages and subscription state change notifications.  A publisher
   MUST respect the DSCP markings for subscription traffic egressing
   that publisher.

   The transport specification MUST specify if there are any particular
   quality-of-service or class-of-service considerations related to
   handling DSCP settings associated with the subscription.

8.3.  Encodings

   The _update_ notification (Section 7.2) and subscription lifecycle
   notifications (Section 9.2) can be encoded in any format that has a
   definition for encoding YANG data.  For a given subscription, all
   notification messages are encoded using the same encoding.

   Some IETF standards for YANG encodings known at the time of
   publication are:

   *  JSON, defined in [RFC7951]

   *  CBOR, defined in [RFC9254], and [RFC9595] for using compressed
      schema identifiers (YANG SIDs)

   *  XML, defined in [RFC7950]

   To maximize interoperability, all implementations are RECOMMENDED to
   support both JSON and CBOR encodings (using regular YANG
   identifiers).  Constrained platforms may not be able to support JSON
   and hence may choose to only support CBOR encoding.  JSON encoding



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   may not be supported in the scenario that another encoding becomes
   the defacto standard (e.g., as JSON has largely replaced XML as the
   defacto choice for text based encoding).  Support for the XML
   encoding and/or CBOR encoding using YANG SIDs is OPTIONAL.

   Encodings are defined in the _ietf-yang-push-2.yang_ as YANG
   identities that derive from the _encoding_ base identity.  Additional
   encodings can be defined by defining and implementing new identities
   that derive from the _encoding_ base identity, and also advertising
   those identities as part of the ietf-yang-push-2-capabilities YANG
   module's transport capabilities Section 15.2.

9.  Setting up and Managing Subscriptions

   Subscriptions can be set up and managed in two ways:

   1.  Configured Subscriptions - a subscription created and principally
       controlled by configuration.

   2.  Dynamic Subscriptions - a subscription created and principally
       controlled via YANG RPCs from a telemetry receiver.

   Conformant implementations MUST implement at least one of the two
   mechanisms above for establishing and maintaining subscriptions, but
   they MAY choose to only implement a single mechanism.

   The core behavior for both configured and dynamic subscription is the
   same, with the key differentiation being how they are provisioned,
   and how the transport is setup.  This next section describes the
   functionality that is common to both types of subscription, followed
   by the sections that describe the specifics and differences between
   the two ways of managing subscriptions.

9.1.  Common Subscription Parameters

   All subscriptions require the following state to be instantiated:

   *  an _id_ to identify the subscription.

   *  the _target_ for the subscription, comprising:

      -  the target datastore, as per [RFC8342]

      -  a set of selection filters to choose which datastore nodes the
         subscription is monitoring or sampling, as described in
         Section 6.





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   *  the _update-trigger_ to indicate when _update_ notifications are
      generated:

      -  _periodic_, for the publisher to send updated copies of the
         state on a periodic basis

      -  _on-change_, for the publisher to send state updates when the
         internal state changes, i.e., event driven.

   *  receiver, transport, and encoding parameters, as per Section 8.1.
      How these are provided differs for configured vs dynamic
      subscriptions and is further explained in the sections below.

   Subscription ids MUST be unique across all configured and dynamic
   subscriptions.  Configured subscription take precedence over dynamic
   subscription, so:

   *  attempts to create a dynamic subscription with a subscription id
      that conflicts with any other subscription id (configured or
      dynamic) MUST fail,

   *  configuring a subscription, assuming it passes configuration
      validation, replaces any dynamic subscriptions with the same
      subscription id.  Thus, causing the dynamic subscription to be
      immediately terminated (see Section 9.1.4).

   *  subscription ids starting with dyn- are reserved for the publisher
      to use for automatically allocate subscription ids for dynamic
      subscriptions when the client has choosen not to provide one in
      the _establish-subscription_ RPC.

9.1.1.  Subscription States

   YANG Push v2 has a small set of simple states for a subscription on a
   publisher.  These states are intended to help clients easily
   determine the health and status of a subscription.

   *  *Invalid*: a subscription that is invalid for any reason.  E.g.,
      the subscription references an invalid filter expression for the
      current device schema.  Normally, invalid configurations should be
      rejected by the system, whether due to subscription configuration
      or _establish-subscription_ RPC, and hence this state should
      rarely be seen.

   *  *Inactive*: a valid subscription, but one that is not active
      because it has no associated receiver.  This state is unlikely to
      be seen for dynamic subscriptions.




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   *  *Connecting*: a subscription that is valid, and has appropriate
      receiver configuration, but the publisher has not managed to
      successfully connect to the receiver yet, and hence has not sent a
      _subscription-started_ notification.  Transport security failures
      would be in this state.

   *  *Active*: a valid subscription, connected to the receiver, that
      has sent a _subscription-stated_ notification and is generating
      _update_ notifications, as per the terms of the subscription
      update policy.

   *  *Terminated*: represents a subscription that has finished.
      Subscriptions would only be expected to transiently be in this
      state and hence it would not normally be reported.  Terminated
      dynamic subscriptions, or unconfigured subscriptions, should
      quickly be removed from the operational state of the device.
      Terminated

   Below is a state diagram illustrating the states, and the likely
   changes between states.  However, this is not a formal state machine
   and publishers can move between arbitrary states based on changes to
   subscription properties, the system, connectivity to receivers, or
   resource constraints on the system.  New subscriptions should choose
   an appropriate starting state, e.g., either Inactive or Invalid.



























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                     .-------------------.         .-------------------.
                     |                   |         |                   |
                     |    Inactive       | <------>|     Invalid       |
                     |                   |         |                   |
                     '-------------------'         '-------------------'
                               ^
                               |
                               v
                     .-------------------.
                     |                   |
                     |    Connecting     |
                     |                   |
                     '-------------------'
                               ^
                               |
                               v
                     .-------------------.
                     |                   |
                     |    Active         |
                     |                   |
                     '-------------------'


                     .-------------------.
                     |                   |
                     |    Terminated     |
                     |                   |
                     '-------------------'

              Figure 9: Publisher's States for a Subscription

9.1.2.  Creating Subscriptions

   After a subscription is successfully established, the publisher
   immediately sends a _subscription-started_ subscription state change
   notification to the receiver.  It is quite possible that upon
   configuration, reboot, or even steady-state operations, a transport
   session may not be currently available to the receiver.

   With active configured subscriptions, it is allowable to buffer event
   records even after a _subscription-started_ has been sent.  However,
   if events are lost (rather than just delayed) due to buffer capacity
   being reached, a _subscription-terminated_ notification MUST be sent,
   followed by a new _subscription-started_ notification.  These
   notifications indicate an event record discontinuity has occurred.
   *TODO, do we always want this behaviour or is it transport specific?*





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9.1.3.  Modifying Subscriptions

   The parameters associated with a subscription MAY be modified by
   client _modify-subscription_ RPC or through configuration.

   If the subscription is in _Active_ state, and hence a _subscription-
   started_ notification has been enqueued to the receiver, then any
   subscription parameter changes are handled as per the following sub-
   sections.  If the subscription is not yet in _Active_ state then any
   transport changes associated with the receiver must be made, but
   otherwise the new parameters would be notified in the _subscription-
   started_ notification.

9.1.3.1.  Modifications requiring subscription-terminated notification

   Changes to any of following parameters MUST terminate the
   subscription, as per Section 9.1.4, before recreating it, clearing
   and reinitializing any associated statistics, as per Section 9.1.2:

   1.  the subcription _id_

   2.  the _encoding_

   3.  any _receiver_ settings that change the encoding, transport,
       transport security, or receiver destination address/port

   4.  the update-trigger to enable _sync-on-start_.

   5.  if the _sync-in-start option_ is enabled, then any changes to the
       subscription-filter (inline or referenced) or YANG schema
       (_schema-id_) associated with the subscription. _TODO, Why?
       Should a subscription-modifies message resend the sync-on-start
       data anyway?_

   The _subscription-terminated_ notification MUST be sent using the old
   _encoding_ and _receiver_ settings before the subscription parameters
   were changed.  The _subscription-started_ notification MUST be sent
   using the updated subscription parameters.

9.1.3.2.  Modifications allowing subscription-modified notification

   If changes to a subscription only include changes to the following
   parameters then they SHOULD be handled via a _subscription-modified_
   notification, but MAY be handled as described above.  This applies
   for changes to:

   1.  the subscription target _filter_ (inline, referring to a
       different named filter, or changing the referenced filter).



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   2.  the YANG schema (_schema-id_) associated with subscription target
       filter,

   3.  the _update-trigger_, unless _sync-on-start_ is enabled.

   4.  the _description_ field,

   5.  any other fields that are included in a _subscription-started_
       notification message, unless the definition of those fields
       explicitly specifies different behavior.

9.1.3.3.  Modifications requiring no lifecycle notification

   Changes to any of the following subscription parameters do not need
   to be notified to the client:

   1.  _dscp_ settings.

   2.  _source-address_, _source-interface_, _source-vrf_, or the source
       port.

   3.  any other settings not reported in the _subscription-started_
       notification message.

9.1.4.  Terminating Subscriptions

   Subscriptions MUST be terminated by the publisher due to any of the
   following circumstances:

   1.  The subscription has been unconfigured.

   2.  Some subscription, receiver, transport or encoding configuration
       has been removed, e.g., receiver configuration, such that there
       is no longer the sufficient minimum information to maintain the
       subscription.

   3.  A dynamic subscription has been terminated via a _delete-
       subscription_ or _kill-subscription_ YANG RPC.

   4.  Transport connectivity to the receiver has been lost, either due
       to network issues, or a failure in the security session state.

   5.  The publisher does not have sufficient resources to honor the
       terms of the subscription, i.e., it is generating too many
       _update_ notifications, or attempting to send too much data.






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   6.  The subscription parameters have changed in such a way, i.e., as
       defined in Section 9.1.3.1, that needs the subscription to be
       reset by terminating and recreating it.

   7.  The _reset_ RPC is invoked on a configured subscription, or on
       the referenced receiver associated with a configured
       subscription.

   In addition, from a receiver's perspective, if transport connectivity
   is lost, then that is equivalent to terminating the subscription via
   a _subscription-terminated_ notification.

   If possible, the publisher MUST try and close the subscription
   gracefully by generating a _subscription-terminated_ notification to
   the receiver before closing any sessions to any receivers that have
   no remaining subscriptions.  Publishers MAY complete their current
   collection if one is in progress before generating the _subscription-
   terminated_ notification.  Obviously, if transport connectivity to a
   receiver has been lost then neither of these two actions is possible.

   The publisher MUST NOT generate any further events, e.g., _update_
   notifications, related to the subscription after the _subscription-
   terminated_ notification has been generated.  In addition, receivers
   SHOULD ignore any messages received outside of an active
   subscription, i.e., either before a _subscription-started_
   notification or after a _subscription-terminated_ notification.

   If the publisher accepts the request, which it MUST, if the
   subscription-id matches a dynamic subscription established in the
   same transport session, then it should stop the subscription and send
   a _subscription-terminated_ notification.

9.2.  Subscription Lifecycle Notifications

   In addition to sending event records to receivers, a publisher also
   sends subscription lifecycle state change notifications when
   lifecycle events related to subscription management occur.

   Subscription state change notifications are generated per
   subscription, and are injected into the steam of _update_ messages
   for that that subscription.  These notifications MUST NOT be dropped
   or filtered.

   Future extensions, or implementations MAY augment additional fields
   into the notification structures.  Receivers MUST silently ignore
   unexpected fields.





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   The complete set of subscription state change notifications is
   described in the following subsections:

9.2.1.  "subscription-started"

   The subscription started notification is sent to a receiver to
   indicate that a subscription is active and they may start to receive
   _update_ records from the publisher.

   The _subscription-started_ notification is sent for any of these
   reasons:

   1.  A new subscription (configured or dynamic) has been started.

   2.  The properties of a configured subscription has been changed,
       i.e., as specified in Section 9.1.3.1, that requires a
       _subscription-terminated_ notification to be sent followed by a
       _subscription-started_ notification, presuming that the new
       subscription parameters are valid.

   3.  A configured subscription previously failed, and was terminated.
       After the publisher has successfully re-established a connection
       to the receiver and is ready to send datastore event records
       again.

   Below is the tree diagram for the _subscription-started_
   notification.  All data nodes contained in this tree diagram are
   described in the YANG module in Section 13.2.























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       +---n subscription-started
       |  +--ro id                    subscription-id
       |  +--ro description?          string
       |  +--ro target
       |  |  +--ro datastore?                 identityref
       |  |  +--ro (filter)
       |  |  |  +--:(path)
       |  |  |  |  +--ro path                 ypath
       |  |  |  +--:(subtree)
       |  |  |  |  +--ro subtree              <anydata>
       |  |  |  +--:(xpath)
       |  |  |     +--ro xpath                yang:xpath1.0 {yp2:xpath}?
       |  |  +--ro schema-id?                 string
       |  |  +--ro yang-library-content-id?
       |  |          -> /yanglib:yang-library/content-id
       |  +--ro update-trigger
       |  |  +--ro periodic!
       |  |  |  +--ro period         centiseconds
       |  |  |  +--ro anchor-time?   yang:date-and-time
       |  |  +--ro on-change! {on-change}?
       |  |     +--ro sync-on-start?   boolean
       |  +--ro message-publishers
       |     +--ro publisher-id*   uint32

         Figure 10: subscription-started Notification Tree Diagram

9.2.2.  "subscription-modified"

   The _subscription-modified_ notification is sent to a receiver to
   indicate that some parameters associated with an active subscription
   have changed, as per Section 9.1.3.2.

   Below is the tree diagram for the _subscription-modified_
   notification.  Other than the notification name and the _reason_
   leaf, the parameters for a _subscription-modified_ notification are
   the same as for the _subscription-started_ notification.  Robust
   receivers are expected to handle _subscription-started_ and
   _subscription-modified_ notifications equivalently.

   All data nodes contained in this tree diagram are described in the
   YANG module in Section 13.2.










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       +---n subscription-modified
       |  +--ro id                    subscription-id
       |  +--ro description?          string
       |  +--ro target
       |  |  +--ro datastore?                 identityref
       |  |  +--ro (filter)
       |  |  |  +--:(path)
       |  |  |  |  +--ro path                 ypath
       |  |  |  +--:(subtree)
       |  |  |  |  +--ro subtree              <anydata>
       |  |  |  +--:(xpath)
       |  |  |     +--ro xpath                yang:xpath1.0 {yp2:xpath}?
       |  |  +--ro schema-id?                 string
       |  |  +--ro yang-library-content-id?
       |  |          -> /yanglib:yang-library/content-id
       |  +--ro update-trigger
       |  |  +--ro periodic!
       |  |  |  +--ro period         centiseconds
       |  |  |  +--ro anchor-time?   yang:date-and-time
       |  |  +--ro on-change! {on-change}?
       |  |     +--ro sync-on-start?   boolean
       |  +--ro message-publishers
       |  |  +--ro publisher-id*   uint32
       |  +--ro reason                subscription-change

         Figure 11: subscription-modified Notification Tree Diagram

9.2.3.  "subscription-terminated"

   For a receiver, this notification indicates that no further event
   records for an active subscription should be expected from the
   publisher unless and until a new _subscription-started_ notification
   is received.

   A _subscription-terminated_ notification SHOULD only be sent by a
   publisher to a receiver if a _subscription-started_ notification was
   previously sent.

   The subscription terminated notification may be sent to a receiver
   for any of these reasons:

   1.  A subscription has been stopped, either due to the change/removal
       of some configuration, or an RPC has been invoked to delete or
       kill a dynamic subscription.







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   2.  The properties of a subscription have been changed, i.e., as
       specified in Section 9.1.3.1, that requires a _subscription-
       terminated_ notification to be sent followed by a _subscription-
       started_ notification, presuming that the new subscription
       parameters are valid.

   3.  A subscription has failed for any reason, e.g.,:

       *  The publisher is no longer able to honor the subscription, due
          to resource constraints, or the filter is no longer valid.

       *  Any transport level buffer to the receiver has become full,
          and the hence the publisher is dropping _update_
          notifications.

   Below is a tree diagram for "subscription-terminated".  All objects
   contained in this tree are described in the YANG module in
   Section 13.2.

       +---n subscription-terminated
       |  +--ro id        subscription-id
       |  +--ro reason    identityref
       +---n update
       |  +--ro id?                 subscription-id
       |  +--ro path-prefix?        string
       |  +--ro snapshot-type       enumeration
       |  +--ro observation-time?   yang:date-and-time

        Figure 12: subscription-terminated Notification Tree Diagram

   *TODO Augmenting extra fields is better for clients?* The _reason_
   data node identityref indicates why a subscription has been
   terminated, and could be extended with further reasons in future.  I
   suggest that we change this to an enum with an optional description
   field.**

9.2.4.  "update-completed"

   *TODO, this description needs to be updated*.

   This notification indicates that all of the event records prior to
   the current time have been passed to a receiver.  It is sent before
   any notification messages containing an event record with a timestamp
   later than (1) the subscription's start time.

   After the _update-complete_ notification has been sent, additional
   event records will be sent in sequence as they arise naturally on the
   publisher.



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   Below is a tree diagram for _update-complete_.  All objects contained
   in this tree are described in the YANG module in Section 4.

       +---n update-complete
          +--ro id?   subscription-id

            Figure 13: update-complete Notification Tree Diagram

9.3.  Configured Subscriptions

   Configured subscriptions allow the management of subscriptions via
   configuration so that a publisher can send notification messages to a
   receiver.

   This document specifies the ietf-yang-push-2-config YANG module
   Section 14.2 that defines an configuration model for configuring
   subscriptions.  Support for this YANG module is OPTIONAL and is
   advertised using the normal YANG mechanisms, e.g., [RFC8525]. *TODO,
   do we also advertise support via capabilities, i.e., issue 16
   (https://github.com/rgwilton/draft-yp-observability/issues/16)*

   In addition to the common subscription parameters described in
   Section 9.1, a configured subscription also includes:

   *  the receiver for the subscription, as described in Section 8.1.
      The referenced receiver specifies all transport, receiver, and
      encoding parameters.

   Configured subscriptions have several characteristics distinguishing
   them from dynamic subscriptions, such as:

   *  configured subscriptions are created, modified or deleted, by any
      configuration client with write permission on the subscription
      configuration.

   *  configured subscription may reference a filter rather than define
      it inline as part of the subscription.  Even for a referenced
      filter, the _subscription-started_ and _subscription-modified_
      notifications always include the filter specification inline in
      the notification.

   *  The lifetime of a configured subscription is tied to the
      configuration.  I.e., if a valid and complete configuration exists
      for a subscription, then the publisher MUST attempt to connect to
      the receiver and honor the requirements of the subscription.  In
      particular:





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      -  If the configuration is altered or removed then the
         subscription will similarly be altered or removed.

      -  If the device reboots, then the configured subscription will
         obviously end, but once the subscription configuration has been
         processed after boot up, then the subscription will be
         recreated again, assuming the subscription configuration is
         still valid.

      -  If the publisher detects that transport connectivity to the
         receiver is broken, then any subscriptions using that transport
         are terminated, but the publisher MUST periodically attempt to
         re-establish connection to the receiver and re-activate any
         configured subscriptions to that receiver.

   *  The lifetime of any transport session(s) to receiver(s) are also
      tied to the subscription configuration, but in a way that depends
      on the behavior of the Yang Push 2 transport specificiation, i.e.,

      -  For YANG Push transports that specify a separate transport
         session for each subscription to the same receiver then a new
         transport session is established whenever a valid subscription
         is configured and the transport session MUST be closed if the
         subscription configuration is removed or changed such that the
         subscription is no longer valid.

      -  For YANG Push transports that specify a shared transport
         session for all subscriptions to the same receiver then a new
         transport session is established for the first valid configured
         subscription.  Note, if there are no active subscriptions for a
         given receiver then any transport session(s) associated with
         that receiver MUST be closed, but that MAY be after a short
         delay.

   *  Other than the _reset_ YANG Action, described in Section 9.3.4,
      there are no YANG RPCs to dynamically create, modify, or delete a
      configured subscription, any alterations MUST be done via changes
      to the configuration.

9.3.1.  Creating a Configured Subscription

   Configured subscriptions are those created via changes to the
   publisher's configuration, e.g., using the YANG module defined in
   Section 14, or an equivalent configuration mechanism, such as a
   command-line interface, or alternative YANG configuration model.

   After the configuration change has been accepted by the system, then
   the subscription is updated, as per Section 9.1.2.



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   *TODO, to see an example of subscription creation using configuration
   operations over NETCONF, see Appendix A.*

9.3.2.  Modifying a Configured Subscription

   Configured subscriptions can be modified due to configuration changes
   in the subscription configuration or referenced configuration, i.e.,
   filters or receivers.  After the configuration change has been
   accepted by the system, then the subscription is updated, as per
   Section 9.1.3.

9.3.3.  Deleting a Configured Subscription

   Configured subscriptions can be deleted via configuration.  After the
   configuration change has been accepted by the system the subscription
   is terminated, as per Section 9.1.4.

9.3.4.  Resetting a Configured Subscription

   Configured subscriptions are generally expected to self-monitor and
   automatically reconnect to the receiver if they experience network or
   transport issues.  However, the data model also defines explicit YANG
   _actions_ to either: (i) reset a single subscription, or (ii) reset
   all subscriptions and the transports(s) associated with a specific
   configured receiver instance.

   These reset actions primarily act at the subscription application
   layer, but may be useful if a receiver or collector determines that a
   configured subscription is not behaving correctly, and wishes to
   force a reset of the subscription without modifying the configuration
   associated with the subscription or forcing a configuration change on
   the publisher device.

   The reset action on a subscription is handled equivalently to
   removing and re-adding the subscription configuration.  I.e., the
   subscription MUST be terminated, as per Section 9.1.4 before being
   recreated, as per Section 9.1.2.  The reset action also resets
   (terminated and re-establishes) any subscription specific transport
   session that is not shared with any other subscriptions.  Any
   counters associated with the subscription are also re-initialized in
   a manner that is consistent with a client unconfiguring and then
   reconfiguring the subscription.

   The reset action on a receiver is handled equivalently to removing
   and re-adding the receiver configuration for the receiver that has
   been reset.  Specifically, every subscription referencing the
   receiver MUST be terminated, as per Section 9.1.4 before being
   recreated, as per Section 9.1.2.  Any transport sessions tied to the



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   subscriptions referencing the reset receiver MUST also be terminated
   and re-established.  Any counters associated with the receiver are
   also re-initialized in a manner that is consistent with a client
   unconfiguring and then reconfiguring the receiver configuration.

9.4.  Dynamic Subscriptions

   Dynamic subscriptions are where a subscriber initiates a subscription
   negotiation with a publisher via a YANG RPC [RFC7950].

   Support for dynamic subscriptions is OPTIONAL, with its availability
   advertised via the _dynamic_ YANG feature in the ietf-yang-push-2
   YANG module Section 13.2, and also via the capabilities module
   Section 15.2.

   Dynamic subscription differ from configured subscription in the
   following ways:

   *  Dynamic subscription reuse the same transport session on which the
      _establish-subscription_ RPC was received to send back any
      notifications, and so the transport and receiver do not need to be
      specified and each dynamic subscription can always only have a
      single receiver.

   *  The publisher MUST reply to the _establish-subscription_ RPC
      before sending the _subscription-started_ or any _update_
      notifications for this subscription.

   *  The lifetime of a dynamic subscription is bound by the transport
      session used to establish it.  If the transport session fails then
      the dynamic subscription MUST be terminated.

   *  Dynamic subscriptions can either be terminated by the client that
      established the subscription sending a _delete-subscription_ YANG
      RPC on the same transport session, or any client with sufficient
      access permissions invoking the _kill-subscription_ YANG RPC.

   *  A publisher MAY terminate a dynamic subscription at any time,
      i.e., due to internal constraints of the publisher.

   *  If a dynamic subscription is terminated for any reason, then the
      client is responsible for re-establishing the subscription if it
      is still required.








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   *  If the publisher cannot honor the terms of a dynamic subscription
      then the subscription MUST be terminated. *TODO, is this a SHOULD
      or MUST, do we want some leeway for temporary issues?  E.g., allow
      some buffering.  Also, this effectively applies to config
      subscriptions as well and hence should move.*

9.4.1.  Establishing a Dynamic Subscription

   The _establish-subscription_ RPC allows a subscriber to request the
   creation of a subscription.

   In addition to the common subscription parameters described in
   Section 9.1, the _establish-subscription_ YANG RPC:

   *  includes the _encoding_ to be used for all YANG Push v2
      notifications

   *  optionally includes DSCP settings to use for the transport.

   The DSCP code point settings for all subscription using the same
   transport session MUST be the same.  Attempts to invoke _establish-
   subscription_ with a different DSCP code point MUST be rejected.

   If the publisher can satisfy the _establish-subscription_ request, it
   replies with a numeric identifier for the subscription and then
   immediately starts streaming notification messages.

   A dynamic subscription request MUST be declined if a publisher
   determines that it may be unable to provide update records meeting
   the terms of an _establish-subscription_ RPC request.

   Below is a tree diagram for _establish-subscription_ YANG RPC.  All
   objects contained in this tree are described in the YANG module in
   Section 13.2.

















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       +---x establish-subscription {dynamic}?
       |  +---w input
       |  |  +---w id?               subscription-id
       |  |  +---w description?      string
       |  |  +---w target
       |  |  |  +---w datastore?       identityref
       |  |  |  +---w (filter)
       |  |  |     +--:(path)
       |  |  |     |  +---w path       ypath
       |  |  |     +--:(subtree)
       |  |  |     |  +---w subtree    <anydata>
       |  |  |     +--:(xpath)
       |  |  |        +---w xpath      yang:xpath1.0 {yp2:xpath}?
       |  |  +---w update-trigger
       |  |  |  +---w periodic!
       |  |  |  |  +---w period         centiseconds
       |  |  |  |  +---w anchor-time?   yang:date-and-time
       |  |  |  +---w on-change! {on-change}?
       |  |  |     +---w sync-on-start?   boolean
       |  |  +---w encoding          encoding
       |  |  +---w dscp?             inet:dscp
       |  +--ro output
       |     +--ro id    subscription-id

                 Figure 14: establish-subscription YANG RPC

   A publisher MAY reject the "establish-subscription" RPC for many
   reasons, as described in *TODO* (Section 2.4.6)?

9.4.2.  Modifying a Dynamic Subscription

   The _modify-subscription_ RPC allows a subscriber to request the
   modification of parameters associated with a dynamic subscription.
   It uses the same parameters as the _establish-subscription_ RPC
   defined in Section 9.4.1, except that the _id_ leaf is mandatory.

   If the modification to the subscription is accepted by the publisher
   then it is processed as per Section 9.1.3, otherwise an error is
   returned to the _modify-subscription_ RPC and the subscription is
   left unmodified.

   The publisher MUST reply to the _modify-subscription_ RPC before
   sending any subscription lifecycle notifications, i.e., a pair of
   _subscription-terminated_/_subscription-started_ notifications, or
   a_subscription-modified_ notification.






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   Below is a tree diagram for the _modify-subscription_ YANG RPC.  All
   objects contained in this tree are described in the YANG module in
   Section 13.2.

       +---x modify-subscription {dynamic}?
       |  +---w input
       |     +---w id                subscription-id
       |     +---w description?      string
       |     +---w target
       |     |  +---w datastore?       identityref
       |     |  +---w (filter)
       |     |     +--:(path)
       |     |     |  +---w path       ypath
       |     |     +--:(subtree)
       |     |     |  +---w subtree    <anydata>
       |     |     +--:(xpath)
       |     |        +---w xpath      yang:xpath1.0 {yp2:xpath}?
       |     +---w update-trigger
       |     |  +---w periodic!
       |     |  |  +---w period         centiseconds
       |     |  |  +---w anchor-time?   yang:date-and-time
       |     |  +---w on-change! {on-change}?
       |     |     +---w sync-on-start?   boolean
       |     +---w dscp?             inet:dscp

                  Figure 15: modify-subscription YANG RPC

   A publisher MAY reject the "modify-subscription" RPC for various
   reasons, as described in *TODO*.

9.4.3.  Deleting a Dynamic Subscription

   The _delete-subscription_ operation permits canceling an existing
   dynamic subscription that was established on the same transport
   session connecting to the subscriber.

   The publisher responds to the request in the following way:

   *  If the identifier matches a _dynamic_ subscription created on the
      same transport session then it MUST terminate the subscription, as
      per Section 9.1.4.










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      The publisher MAY reply back to the client before the subscription
      has been terminated, i.e., it may act asynchronously with respect
      to the delete request, however, the publisher MUST allow the
      client to create a new subscription using the same subscription id
      immediately after either the RPC operation completes or the
      _subscription-terminated_ notification (Section 9.2.3) has been
      transmitted.

   *  Otherwise, the request is failed with an "unknown subscription"
      error message.

   Below is the tree diagram for the _delete-subscription_ RPC.  All
   objects contained in this tree are described in the YANG module in
   Section 13.2.

       +---x delete-subscription {dynamic}?
       |  +---w input
       |     +---w id    subscription-id

                  Figure 16: delete-subscription YANG RPC

9.4.4.  Killing a Dynamic Subscription

   The _kill-subscription_ RPC operation permits a client, that has the
   required access permissions, to forcibly terminate any arbitrary
   dynamic subscription, identified by subscription id, including those
   not associated with the transport session used for the _kill-
   subscription_ RPC.  The subscription is terminated as per
   Section 9.1.4.

   The publisher MAY reply back to the client before the subscription
   has been terminated, i.e., it may act asynchronously with respect to
   the delete request, however, the publisher MUST allow the client to
   create a new subscription using the same subscription id immediately
   after the _subscription-terminated_ notification (Section 9.2.3) has
   been transmitted.

   Below is the tree diagram for the _kill-subscription_ RPC.  All
   objects contained in this tree are described in the YANG module in
   Section 13.2.

       +---x kill-subscription {dynamic}?
          +---w input
             +---w id    subscription-id

                   Figure 17: kill-subscription YANG RPC





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9.4.5.  RPC Failures

   *TODO, we should see if we can simplify how errors are reported.*

   Whenever an RPC is unsuccessful, the publisher returns relevant
   information as part of the RPC error response.  Transport-level error
   processing MUST be done before the RPC error processing described in
   this section.  In all cases, RPC error information returned by the
   publisher will use existing transport-layer RPC structures, such as
   those seen with NETCONF (Appendix A of [RFC6241]) or RESTCONF
   (Section 7.1 of [RFC8040]).  These structures MUST be able to encode
   subscription-specific errors identified below and defined in this
   document's YANG data model.

   As a result of this variety, how subscription errors are encoded in
   an RPC error response is transport dependent.  Valid errors that can
   occur for each RPC are as follows:

     establish-subscription         modify-subscription
     ----------------------         ----------------------
     dscp-unavailable               filter-unsupported
     encoding-unsupported           insufficient-resources
     filter-unsupported             no-such-subscription
     insufficient-resources

     delete-subscription            kill-subscription
     ----------------------         ----------------------
     no-such-subscription           no-such-subscription

   To see a NETCONF-based example of an error response from the list
   above, see the "no-such-subscription" error response illustrated in
   [RFC8640], Figure 10.

   There is one final set of transport-independent RPC error elements
   included in the YANG data model defined in this document: three yang-
   data structures that enable the publisher to provide to the receiver
   any error information that does not fit into existing transport-layer
   RPC structures.  These structures are:

   1.  "establish-subscription-stream-error-info": This MUST be returned
       with the leaf "reason" populated if an RPC error reason has not
       been placed elsewhere in the transport portion of a failed
       "establish-subscription" RPC response.  This MUST be sent if
       hints on how to overcome the RPC error are included.







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   2.  "modify-subscription-stream-error-info": This MUST be returned
       with the leaf "reason" populated if an RPC error reason has not
       been placed elsewhere in the transport portion of a failed
       "modify-subscription" RPC response.  This MUST be sent if hints
       on how to overcome the RPC error are included.

   3.  "delete-subscription-error-info": This MUST be returned with the
       leaf "reason" populated if an RPC error reason has not been
       placed elsewhere in the transport portion of a failed "delete-
       subscription" or "kill-subscription" RPC response.

10.  Robustness, Reliability, and Subscription Monitoring

10.1.  Robustness and Reliability

   It is important for clients to have confidence that the telemetry
   data that they receive is correct and complete.  The design of YANG
   Push v2 achieves this in several ways:

   *  the _complete_ flag in the _update_ notification, or the
      equivalent _update-complete_ notification, are used to signal when
      all data for a periodic collection event has been enqueued by the
      publisher.  This allows clients to delete stale information and
      monitor the performance and behavior of the publisher.

   *  publishers use buffers when enqueuing traffic on to a transport to
      a receiver, but if that buffer becomes full then the transport
      specification indicates whether update messages should be dropped,
      or the subscription should be terminated.  In that case that a
      dynamic subscription is terminated, the client may attempt to re-
      created the subscription.  For configured subscriptions that have
      been terminated, the publisher should attempt to periodically
      recreate the subscription or reconnect the receiver.

   *  the _notification envelope_ structure, Section 7.1, used for all
      YANG Push notifications contains a monotonically increasing
      _sequence-number_ field that allows for lost messages in an end-
      to-end data pipeline spanning multiple transport hops to be
      detected, allowing appropriate mitigation steps to be taken.  For
      example, see figure 1 in
      [I-D.ietf-nmop-network-anomaly-architecture].

   *  the protocol relies on transport protocols that are either
      reliable, e.g., TCP or HTTP, or unreliable transports that employ
      mechanisms for clients to detect when losses at the transport
      layer have occurred, e.g., the _message id_ in
      [I-D.draft-ietf-netconf-udp-notif] (*TODO fix reference to bis
      version, once that becomes available*).



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   *  finally, if a publisher is not able to honor the expectation for a
      subscription for any reason, then the publisher always has the
      option to terminate the subscription.  It can then subsequently
      refuse to handle new subscriptions if it does not have sufficient
      resources to handle the subscription.

10.2.  Subscription Monitoring

   In the operational state datastore, the _datastore-telemetry_
   container maintains operational state for all configured and dynamic
   subscriptions.

   Both configured and dynamic subscriptions are represented in the list
   _ietf-yang-push-2-config:datastore-telemetry/subscriptions/
   subscription_.  Dynamic subscriptions are only present in the list
   when they are active, and are removed as soon as they are terminated.
   Whereas, configured subscriptions are always present in the list when
   they are configured, regardless of whether they are active.

   The operational state is important for monitoring the health of
   subscriptions, receivers, and the overall telemetry subsystem.

   This includes:

   *TODO, update the YANG model with more useful operational data, and
   mostly this section should briefly summarize and refer to the YANG
   model.  We should also consider what indications to include from
   filters that cause a larger amount of internal work but don't
   generate a large number of transmitted notifications.*

   *  per subscription status and counters

   *  per receiver status and counters

   *  maybe some indication of the overall load on the telemetry
      subsystem, but we need to consider how useful that actually is,
      and whether just monitoring the device CPU load and general
      performance would be a better indication.

10.3.  Publisher Capacity

   A publisher SHOULD reject a request for a subscription if it is
   unlikely that the publisher will be able to fulfill the terms of that
   subscription request.

   Whether or not a subscription can be supported will be determined by
   a combination of several factors, such as the subscription update
   trigger (on-change or periodic), the period in which to report



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   changes (one-second periods will consume more resources than one-hour
   periods), the amount of data in the datastore subtree that is being
   subscribed to, the number and combination of other subscriptions that
   are concurrently being serviced, and the overall load from other
   services running on the publisher.

   It is entirely possible that a subscription may be reasonable at the
   time that it is created, but other changes to configuration or
   operational data or load in the system means that the subscription
   can no longer be honored.

   TODO - Do we allow servers to reduce the period of the subscription
   to allow it to be kept active?  E.g., with a subscription
   modification notification?  E.g., see issue 41
   (https://github.com/rgwilton/draft-yp-observability/issues/41)

11.  Conformance and Capabilities

   The normative text in this document already indicates which parts of
   the specification must or should be implemented for a compliant YANG
   Push v2 implementation via the use of [RFC2119] language.  It also
   sets out some additional related requirements, e.g., on transports
   Section 8.2, that add in additional functionality.

   Some parts of this specification are optional to implement.  Some of
   these optional parts can be identified through the use of YANG
   Library [RFC8525] specifying the list of implemented YANG modules and
   YANG features.  But, the broader approach adopted by this
   specification is via extending the ietf-system-capabilities YANG
   module specified in [RFC9196] to make capability information
   available as standard YANG described operational data.

11.1.  Capabilities

   Publishers SHOULD implement the ietf-system-capabilities YANG module,
   defined in [RFC9196], and the ietf-yang-push-2-capabilities YANG
   module, defined in Section 15.2) that augments ietf-system-
   capabilities.

   The ietf-yang-push-2-capabilities module contains capabilities to
   indicate what types of subscriptions and transports may be
   configured, along with acceptable subscription parameter for given
   subtrees.

   The schema tree for the ietf-system-capabilities augmented by ietf-
   yang-push-2-capabilities is given below.





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   module: ietf-system-capabilities
     +--ro system-capabilities
        +--ro datastore-capabilities* [datastore]
        |  +--ro datastore
        |  |       -> /yanglib:yang-library/datastore/name
        |  +--ro per-node-capabilities* []
        |     +--ro (node-selection)?
        |     |  +--:(node-selector)
        |     |     +--ro node-selector?
        |     |             nacm:node-instance-identifier
        |     +--ro notc:subscription-capabilities
        |     |  +--ro notc:max-nodes-per-update?               uint32
        |     |  +--ro notc:periodic-notifications-supported?
        |     |  |       notification-support
        |     |  +--ro (notc:update-period)?
        |     |  |  +--:(notc:minimum-update-period)
        |     |  |  |  +--ro notc:minimum-update-period?        uint32
        |     |  |  +--:(notc:supported-update-period)
        |     |  |     +--ro notc:supported-update-period*      uint32
        |     |  +--ro notc:on-change-supported?
        |     |  |       notification-support {yp:on-change}?
        |     |  +--ro notc:minimum-dampening-period?           uint32
        |     |  |       {yp:on-change}?
        |     |  +--ro notc:supported-excluded-change-type*     union
        |     |          {yp:on-change}?
        |     +--ro yp2ca:datastore-telemetry
        |        +--ro yp2ca:periodic-notifications-supported?
        |        |       notification-support
        |        +--ro (yp2ca:update-period)?
        |        |  +--:(yp2ca:minimum-update-period)
        |        |  |  +--ro yp2ca:minimum-update-period?        uint32
        |        |  +--:(yp2ca:supported-update-period)
        |        |     +--ro yp2ca:supported-update-period*      uint32
        |        +--ro yp2ca:on-change-supported?
        |                notification-support
        +--ro notc:subscription-capabilities
        |  +--ro notc:max-nodes-per-update?               uint32
        |  +--ro notc:periodic-notifications-supported?
        |  |       notification-support
        |  +--ro (notc:update-period)?
        |  |  +--:(notc:minimum-update-period)
        |  |  |  +--ro notc:minimum-update-period?        uint32
        |  |  +--:(notc:supported-update-period)
        |  |     +--ro notc:supported-update-period*      uint32
        |  +--ro notc:on-change-supported?
        |  |       notification-support {yp:on-change}?
        |  +--ro notc:minimum-dampening-period?           uint32
        |  |       {yp:on-change}?



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        |  +--ro notc:supported-excluded-change-type*     union
        |  |       {yp:on-change}?
        |  +--ro inotenv:notification-metadata
        |     +--ro inotenv:notification-envelope?   boolean
        |     +--ro inotenv:metadata
        |        +--ro inotenv:hostname-sequence-number?   boolean
        +--ro yp2ca:datastore-telemetry
        |  +--ro yp2ca:periodic-notifications-supported?
        |  |       notification-support
        |  +--ro (yp2ca:update-period)?
        |  |  +--:(yp2ca:minimum-update-period)
        |  |  |  +--ro yp2ca:minimum-update-period?        uint32
        |  |  +--:(yp2ca:supported-update-period)
        |  |     +--ro yp2ca:supported-update-period*      uint32
        |  +--ro yp2ca:on-change-supported?
        |  |       notification-support
        |  +--ro yp2ca:transport
        |     +--ro yp2ca:transport-capability* [transport-protocol]
        |        +--ro yp2ca:transport-protocol    identityref
        |        +--ro yp2ca:security-protocol?    identityref
        |        +--ro yp2ca:encoding-format*      identityref
        +--ro yp2ca:distributed-notifications-supported?   boolean

      Figure 18: YANG tree for ietf-system-capabilities with ietf-yl-
                      lite-capabilities augmentations.

   *TODO, do we need additional capabilities, as per Issue 18
   (https://github.com/rgwilton/draft-yp-observability/issues/18)*

11.2.  Subscription Content Versioning

   Many receivers will want to know what the schema is associated with a
   subscription and whether that schema has changed, e.g., due to a
   changing in software on the publisher.

   Various mechanisms are available to help receivers or collectors
   learn or monitor the schema associated with a subscription:

   1.  The device schema is available in the YANG library module ietf-
       yang-library.yang as defined in [RFC8525].  YANG library also
       provides a simple "yang-library-change" notification that informs
       the subscriber that the library has changed, or alternatively,
       the publisher may support an on-change telemetry subscription to

   Content Schema Identification

   YANG Module Synchronization




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   To make subscription requests, the subscriber needs to know the YANG
   datastore schemas used by the publisher.  These schemas are available
   in the YANG library module ietf-yang-library.yang as defined in
   [RFC8525].  The receiver is expected to know the YANG library
   information before starting a subscription.

   The set of modules, revisions, features, and deviations can change at
   runtime (if supported by the publisher implementation).  For this
   purpose, the YANG library provides a simple "yang-library-change"
   notification that informs the subscriber that the library has
   changed.  In this case, a subscription may need to be updated to take
   the updates into account.  The receiver may also need to be informed
   of module changes in order to process updates regarding datastore

   *TODO, this section should be updated so that a subscription is
   restarted if the schema that it is using changes, and to incorporate
   ideas to fingerprint the subscription schema in the subscription-
   started notification.*

12.  Distributed Notifications - Multiple Publishing Processes

   Distributed notifications is the concept of allowing subscriptions to
   be served from multiple different agent publisher processes on the
   same device.  As a simple example, an implementation could choose to
   have separate publishing processes for each linecard in a network
   device, so that data that is local to that linecard can be published
   directly from the linecard, perhaps directly from the linecard data
   interfaces, without been sent to a Management Processor card that
   could act a bottleneck.

   The YANG Push 2 specification supports distributed notifications as
   described in [I-D.ietf-netconf-distributed-notif], and using the
   terminology defined therewithin, but with some differences due to the
   different YANG data models, which are described below.

   It is OPTIONAL for YANG Push 2 publishers to support multiple
   publisher agents since they always have the option of handling all
   subscriptions from a single publisher process on each server.
   Receivers and consumers of YANG Push 2 subscription data MUST
   accommodate servers that publish their data from multiple Message
   Publishing processes, e.g., they may need to correlate the update-
   complete notification across multiple publishing processes.

   Publishers serving a subscription MUST only send the data for a given
   YANG data node from a single Message Publisher process.  Publishers
   MAY change which Message Publisher process is sending the data for a
   given YANG data node over time, e.g., to load-balance work.




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   The differences for supporting [I-D.ietf-netconf-distributed-notif]
   with YANG Push 2 are:

   *  the publisher-id leaf, that identities the Message Publisher ID of
      the publishing process, is augmented in the envelope notification
      [I-D.draft-ietf-netconf-notif-envelope] rather than the _push-
      update_ and _push-change-update_ messages.  This means that all
      messages sent by any Message Publishers (e.g., including
      Subscription Lifecyle Notifications) will indicate which Message
      Publisher sent the message.

   *  the publisher-id leaf has a default value of 0.  The publisher-id
      of 0 is reserved for the Publisher Parent process and MUST NOT be
      allocated to any Publisher Agent processes, since that allows for
      the publisher-id leaf to be omitted from notification messages
      sent from the Publisher Parent.

   *  the _subscription-started_ and _subscription-modified_
      notifications have a _message-publishers/publisher-id_ leaf-list
      that identifies all Message Publishers that will send messages as
      part of the subscription.  This leaf-list defaults to a single
      entry of 0, so MAY be ommitted if there is only a single Message
      Publisher and it has an publisher-id of 0.

      -  As per [I-D.ietf-netconf-distributed-notif], the list of
         Message Publishers serving an active subscription can change
         during the lifetime of the subscription and the Publisher
         Parent MUST send a _subscription-modified_ notification of any
         change in publisher-ids.

      -  Yang Push 2 does not return the list of publisher-ids as part
         of the establish-subscription response output because the
         dynamic subscription will receive a _subscription-started_
         notification instead, which also provides a more robust
         mechanism consistent with configured subscriptions.

   *  the _subscriptions/subscription_ has a _message-publishers/
      publisher-id_ leaf-list to report the current list of Message
      Publishers associated with a subscription.

   *  A capability flag is used to indicate whether the server might use
      distributed notifications.

   *  the _update-complete_ notifications, or the equivalent _complete_
      leaf as part of an _update_ notification are generated per Message
      Publisher process, and are scoped as such.  I.e., this may require
      clients to count and correlate update complete indications across
      Message Publishers for a given subscription.



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13.  Core YANG Push v2 YANG Data Model

13.1.  ietf-yang-push-2 YANG tree

   This section shows the full tree output for ietf-yang-push-2 YANG
   module.

   Note, this output does not include support for any transport
   configuration, and for any implementation that supports configured
   subscriptions using this YANG module then at least one transport
   would expect to be configurable.

   module: ietf-yang-push-2

     rpcs:
       +---x establish-subscription {dynamic}?
       |  +---w input
       |  |  +---w id?               subscription-id
       |  |  +---w description?      string
       |  |  +---w target
       |  |  |  +---w datastore?       identityref
       |  |  |  +---w (filter)
       |  |  |     +--:(path)
       |  |  |     |  +---w path       ypath
       |  |  |     +--:(subtree)
       |  |  |     |  +---w subtree    <anydata>
       |  |  |     +--:(xpath)
       |  |  |        +---w xpath      yang:xpath1.0 {yp2:xpath}?
       |  |  +---w update-trigger
       |  |  |  +---w periodic!
       |  |  |  |  +---w period         centiseconds
       |  |  |  |  +---w anchor-time?   yang:date-and-time
       |  |  |  +---w on-change! {on-change}?
       |  |  |     +---w sync-on-start?   boolean
       |  |  +---w encoding          encoding
       |  |  +---w dscp?             inet:dscp
       |  +--ro output
       |     +--ro id    subscription-id
       +---x modify-subscription {dynamic}?
       |  +---w input
       |     +---w id                subscription-id
       |     +---w description?      string
       |     +---w target
       |     |  +---w datastore?       identityref
       |     |  +---w (filter)
       |     |     +--:(path)
       |     |     |  +---w path       ypath
       |     |     +--:(subtree)



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       |     |     |  +---w subtree    <anydata>
       |     |     +--:(xpath)
       |     |        +---w xpath      yang:xpath1.0 {yp2:xpath}?
       |     +---w update-trigger
       |     |  +---w periodic!
       |     |  |  +---w period         centiseconds
       |     |  |  +---w anchor-time?   yang:date-and-time
       |     |  +---w on-change! {on-change}?
       |     |     +---w sync-on-start?   boolean
       |     +---w dscp?             inet:dscp
       +---x delete-subscription {dynamic}?
       |  +---w input
       |     +---w id    subscription-id
       +---x kill-subscription {dynamic}?
          +---w input
             +---w id    subscription-id

     notifications:
       +---n subscription-started
       |  +--ro id                    subscription-id
       |  +--ro description?          string
       |  +--ro target
       |  |  +--ro datastore?                 identityref
       |  |  +--ro (filter)
       |  |  |  +--:(path)
       |  |  |  |  +--ro path                 ypath
       |  |  |  +--:(subtree)
       |  |  |  |  +--ro subtree              <anydata>
       |  |  |  +--:(xpath)
       |  |  |     +--ro xpath                yang:xpath1.0 {yp2:xpath}?
       |  |  +--ro schema-id?                 string
       |  |  +--ro yang-library-content-id?
       |  |          -> /yanglib:yang-library/content-id
       |  +--ro update-trigger
       |  |  +--ro periodic!
       |  |  |  +--ro period         centiseconds
       |  |  |  +--ro anchor-time?   yang:date-and-time
       |  |  +--ro on-change! {on-change}?
       |  |     +--ro sync-on-start?   boolean
       |  +--ro message-publishers
       |     +--ro publisher-id*   uint32
       +---n subscription-modified
       |  +--ro id                    subscription-id
       |  +--ro description?          string
       |  +--ro target
       |  |  +--ro datastore?                 identityref
       |  |  +--ro (filter)
       |  |  |  +--:(path)



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       |  |  |  |  +--ro path                 ypath
       |  |  |  +--:(subtree)
       |  |  |  |  +--ro subtree              <anydata>
       |  |  |  +--:(xpath)
       |  |  |     +--ro xpath                yang:xpath1.0 {yp2:xpath}?
       |  |  +--ro schema-id?                 string
       |  |  +--ro yang-library-content-id?
       |  |          -> /yanglib:yang-library/content-id
       |  +--ro update-trigger
       |  |  +--ro periodic!
       |  |  |  +--ro period         centiseconds
       |  |  |  +--ro anchor-time?   yang:date-and-time
       |  |  +--ro on-change! {on-change}?
       |  |     +--ro sync-on-start?   boolean
       |  +--ro message-publishers
       |  |  +--ro publisher-id*   uint32
       |  +--ro reason                subscription-change
       +---n subscription-terminated
       |  +--ro id        subscription-id
       |  +--ro reason    identityref
       +---n update
       |  +--ro id?                 subscription-id
       |  +--ro path-prefix?        string
       |  +--ro snapshot-type       enumeration
       |  +--ro observation-time?   yang:date-and-time
       |  +--ro updates* [target-path]
       |  |  +--ro target-path          string
       |  |  +--ro (data)?
       |  |     +--:(merge)
       |  |     |  +--ro merge?         <anydata>
       |  |     +--:(replaced-by)
       |  |     |  +--ro replaced-by?   <anydata>
       |  |     +--:(deleted)
       |  |        +--ro deleted?       empty
       |  +--ro complete?           boolean
       +---n update-complete
          +--ro id?   subscription-id

          Figure 19: YANG tree for YANG Push v2 Module Tree Output

13.2.  ietf-yang-push-2 YANG Model

   This module imports typedefs from [RFC6991], [RFC8343], [RFC8341],
   [RFC8529], and [RFC8342].  It references [RFC6241], [XPATH] ("XML
   Path Language (XPath) Version 1.0"), [RFC7049], [RFC8259], [RFC7950],
   [RFC7951], and [RFC7540].





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   This YANG module imports typedefs from [RFC6991], identities from
   [RFC8342], and the "sx:structure" extension from [RFC8791].  It also
   references [RFC6241], [XPATH], and [RFC7950].

   <CODE BEGINS> file "ietf-yang-push-2.yang#0.1.0"
   module ietf-yang-push-2 {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-yang-push-2";
     prefix yp2;

     import ietf-inet-types {
       prefix inet;
       reference
         "RFC 6991: Common YANG Data Types";
     }
     import ietf-netconf-acm {
       prefix nacm;
       reference
         "RFC 8341: Network Configuration Access Control Model";
     }
     import ietf-yang-structure-ext {
       prefix sx;
       reference
         "RFC 8525: YANG Data Structure Extensions";
     }
     import ietf-yang-types {
       prefix yang;
       reference
         "RFC 6991: Common YANG Data Types";
     }
     import ietf-datastores {
       prefix ds;
       reference
         "RFC 8342: Network Management Datastore Architecture (NMDA)";
     }
     import ietf-yang-library {
       prefix yanglib;
       reference
         "RFC 8525: YANG Library";
     }
     import ietf-yp-notification {
       prefix iypn;
       reference
        "draft-ietf-netconf-notif-envelope: Extensible YANG Model for
         YANG-Push Notifications

         TODO: RFC Editor please replace with latest draft/RFC version
        at publication time.";



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     }

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

        Author:  Robert Wilton
                 <mailto:rwilton@cisco.com>";
     description
       "This module contains YANG specifications for YANG-Push
        version 2, a simplified version of the YANG-Push [RFC 8641]
        protocol.

        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.

        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).

        This version of this YANG module is part of RFC XXXX
        (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
        for full legal notices.";

     revision 2025-08-03 {
       description
         "Initial revision.";
       reference
         "XXXX: YANG Datastore Telemetry (YANG Push version 2)";
     }

     /*
      * FEATURES
      */

     feature dynamic {
       description



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         "This feature indicates that dynamic establishment of
          subscriptions is
          supported.";
     }

     feature on-change {
       description
         "This feature indicates that on-change triggered subscriptions
          are supported.";
     }

     feature subtree {
       description
         "This feature indicates support for YANG subtree filtering.";
       reference
         "RFC 6241: Network Configuration Protocol (NETCONF),
                    Section 6";
     }

     feature xpath {
       description
         "This feature indicates support for XPath filtering.";
       reference
         "XML Path Language (XPath) Version 1.0
          (https://www.w3.org/TR/1999/REC-xpath-19991116)";
     }

     /*
      * IDENTITIES
      */
     /* Identities for RPC and notification errors */

     identity delete-subscription-error {
       description
         "Base identity for the problem found while attempting to
          fulfill either a 'delete-subscription' RPC request or a
          'kill-subscription' RPC request.";
     }

     identity establish-subscription-error {
       description
         "Base identity for the problem found while attempting to
          fulfill an 'establish-subscription' RPC request.";
     }

     identity subscription-terminated-reason {
       description
         "Base identity for the problem condition communicated to a



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          receiver as part of a 'subscription-terminated'
          notification.";
     }

     identity dscp-unavailable {
       base establish-subscription-error;
       description
         "The publisher is unable to mark notification messages with
          prioritization information in a way that will be respected
          during network transit.";
     }

     identity encoding-unsupported {
       base establish-subscription-error;
       description
         "Unable to encode notification messages in the desired
          format.";
     }

     identity filter-unavailable {
       base subscription-terminated-reason;
       description
         "Referenced filter does not exist.  This means a receiver is
          referencing a filter that doesn't exist or to which it
          does not have access permissions.";
     }

     identity filter-unsupported {
       base establish-subscription-error;
       description
         "Cannot parse syntax in the filter.  This failure can be from
          a syntax error or a syntax too complex to be processed by the
          publisher.";
     }

     identity insufficient-resources {
       base establish-subscription-error;
       description
         "The publisher does not have sufficient resources to support
          the requested subscription.  An example might be that
          allocated CPU is too limited to generate the desired set of
          notification messages.";
     }

     identity no-such-subscription {
       base delete-subscription-error;
       base subscription-terminated-reason;
       description



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         "Referenced subscription doesn't exist.  This may be as a
          result of a nonexistent subscription ID, an ID that belongs to
          another subscriber, or an ID for a configured subscription.";
     }

     identity stream-unavailable {
       base subscription-terminated-reason;
       description
         "Not a subscribable event stream.  This means the referenced
          event stream is not available for subscription by the
          receiver.";
     }

     identity suspension-timeout {
       base subscription-terminated-reason;
       description
         "Termination of a previously suspended subscription.  The
          publisher has eliminated the subscription, as it exceeded a
          time limit for suspension.";
     }

     identity unsupportable-volume {
       base subscription-terminated-reason;
       description
         "The publisher does not have the network bandwidth needed to
          get the volume of generated information intended for a
          receiver.";
     }

     identity conflicting-identifier {
       base subscription-terminated-reason;
       description
         "The subscription identifier conflicts with another
          subscription.

          This can prevent a dynamic subscription from being
          established, or cause a dynamic subscription to be terminated
          if a configured subscription with the same id is created.";

       // TODO - Should there be separate error codes for creating a
       // subscription vs terminating an existing one?
     }


     /* Identities for encodings */

     identity configurable-encoding {
       description



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         "If a transport identity derives from this identity, it means
          that it supports configurable encodings.  An example of a
          configurable encoding might be a new identity such as
          'encode-cbor'.  Such an identity could use
          'configurable-encoding' as its base.  This would allow a
          dynamic subscription encoded in JSON (RFC 8259) to request
          that notification messages be encoded via the Concise Binary
          Object Representation (CBOR) (RFC 7049).  Further details for
          any specific configurable encoding would be explored in a
          transport document based on this specification.

          TODO - Clear up this text or use YANG-CBOR reference";
       reference
         "RFC 8259: The JavaScript Object Notation (JSON) Data
                    Interchange Format
          RFC 7049: Concise Binary Object Representation (CBOR)";
     }

     identity encoding {
       description
         "Base identity to represent data encodings.";
     }

     identity json {
       base encoding;
       description
         "Encode data using JSON as described in RFC 7951.";
       reference
         "RFC 7951: JSON Encoding of Data Modeled with YANG";
     }

     identity xml {
       base encoding;
       description
         "Encode data using XML as described in RFC 7950.";
       reference
         "RFC 7950: The YANG 1.1 Data Modeling Language";
     }

     identity cbor {
       base encoding;
       description
         "Encode data using CBOR as described in RFC 9245,
          without using YANG SIDs";
       reference
         "RFC 9245: Encoding of Data Modeled with YANG in the
          Concise Binary Object Representation (CBOR).";
     }



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     identity cbor-sids {
       base encoding;
       description
         "Encode data using JSON as described in RFC 7951, using YANG
          SIDs.";
       reference
         "RFC 9245: Encoding of Data Modeled with YANG in the
          Concise Binary Object Representation (CBOR).

          RFC 9595: YANG Schema Item iDentifier (YANG SID).";
     }

     /* Identities for transports */

     identity transport {
       description
         "An identity that represents the underlying mechanism for
          passing notification messages.";
     }


     /*
      * TYPEDEFs
      */

     typedef ypath {
       type string {
         length "1..max";
       }
       description
         "A type for YANG instance data paths.";
     }

     typedef encoding {
       type identityref {
         base encoding;
       }
       description
         "Specifies a data encoding, e.g., for a data subscription.";
     }

     typedef subscription-id {
      type string {
         length "1..64";
         pattern '[A-Za-z0-9._-]+';
       }
       description
         "A used friendly string identifier for a subscription.";



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     }

     typedef transport {
       type identityref {
         base transport;
       }
       description
         "Specifies the transport used to send notification messages
          to a receiver.";
     }

   // TODO - Consider changes to list keys or reordering of
   //        user-ordered lists.

     typedef centiseconds {
       type uint32;
       description
         "A period of time, measured in units of 0.01 seconds.";
     }

     typedef subscription-type {
       type enumeration {
         enum configured {
           description
             "A subscription that is created and managed via
              configuration.";
         }
         enum dynamic {
           description
             "A subscription that is created and managed via RPC
              primitives.";
         }
       }
       description
         "Indicate the type of subscription.";
     }

     typedef subscription-status {
       type enumeration {
         enum invalid {
           description
             "The subscription as a whole is unsupportable with its
             current parameters.";
         }
         enum inactive {
           description
             "The subscription is supportable with its current
             parameters, but it is not currently connected to a



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             receiver";
         }
         enum active {
           description
             "The subscription is actively running, and is connected
              to at least one receiver.

              A subscription-started notification must have been sent
              for a subscription to be in this state, and the receiver
              will receive update notifications, as per the
              update-trigger selection.";
         }
       }
       description
         "Indicates the status of a subscription";
     }

     typedef subscription-change {
       type enumeration {
         enum new-subscription {
           description
             "This is a new subscription.";
         }
         enum deleted {
           description
             "The subscription has been unconfigured or deleted via
              a delete-subscription RPC";
         }
         enum killed {
           description
             "A dynamic subscription has been killed via a
              kill-subscription RPC";
         }
         enum receiver-added {
           description
             "A new receiver has been added to a configured
              subscription, and has connected successfully.";
         }
         enum receiver-removed {
           description
             "A receiver has been removed from a configured
              subscription, or has become disconnected.";
         }
         enum config-changed {
           description
             "The subscription configuration has been changed,
              requiring the subscription to be restarted.";
         }



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       }

       description
         "Indicates the reason why a subscription has changed.";
     }

     /*
      * GROUPINGS
      */

     grouping dscp {
       description
         "This grouping describes QoS information concerning a
          subscription.  This information is passed to lower layers
          for transport prioritization and treatment.";
       leaf dscp {
         type inet:dscp;
         default "0";
         description
           "The desired network transport priority level.  This is the
            priority set on notification messages encapsulating the
            results of the subscription.  This transport priority is
            shared for all receivers of a given subscription.";
       }
     }

     grouping publishers {
       description
         "Grouping describes the list of publisher-ids";
       leaf-list publisher-id {
         type uint32;
         default 0;
         config false;
         description
           "Identifies the software process which publishes notification
           messages (e.g., processor 1 on line card 1). This field
           is used to notify the receiver which publisher processes
           are going to publish. The identifiers are locally unique to
           the Network Node.";
       }
     }

     grouping filter-choice {
       description
         "This grouping defines the types of selectors for objects
          from a datastore.";
       choice filter {
         mandatory true;



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         description
           "The content filter specification for this request.";

         leaf path {
           type ypath;
           mandatory true;
           description
             "A basic path filter that allows wildcard, regex, or
              fixed value for list keys.  Each format is TODO";
         }
         anydata subtree {
           //if-feature "yp2:subtree";
           mandatory true;
           description
             "This parameter identifies the portions of the
              target datastore to retrieve.";
           reference
             "RFC 6241: Network Configuration Protocol (NETCONF),
                        Section 6";
         }
         leaf xpath {
           if-feature "yp2:xpath";
           type yang:xpath1.0;
           mandatory true;
           description
             "This parameter contains an XPath expression identifying
              the portions of the target datastore to retrieve.

              If the expression returns a node set, all nodes in the
              node set are selected by the filter.  Otherwise, if the
              expression does not return a node set, the filter
              doesn't select any nodes.

              The expression is evaluated in the following XPath
              context:

              o  The set of namespace declarations is the set of prefix
                 and namespace pairs for all YANG modules implemented
                 by the server, where the prefix is the YANG module
                 name and the namespace is as defined by the
                 'namespace' statement in the YANG module.

                 If the leaf is encoded in XML, all namespace
                 declarations in scope on the 'stream-xpath-filter'
                 leaf element are added to the set of namespace
                 declarations.  If a prefix found in the XML is
                 already present in the set of namespace declarations,
                 the namespace in the XML is used.



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              o  The set of variable bindings is empty.

              o  The function library is comprised of the core
                 function library and the XPath functions defined in
                 Section 10 in RFC 7950.

              o  The context node is the root node of the target
                 datastore.";
           reference
             "XML Path Language (XPath) Version 1.0
              (https://www.w3.org/TR/1999/REC-xpath-19991116)
              RFC 7950: The YANG 1.1 Data Modeling Language,
                        Section 10";
         }
       }
     }

     grouping update-policy {
       description
         "This grouping describes the susbcription update policy";

       container update-trigger {
         description
           "This container describes all conditions under which
            subscription update messages are generated";

         container periodic {
           presence "indicates a periodic subscription";
           description
             "The publisher is requested to periodically notify the
               receiver regarding the current values of the datastore
               as defined by the selection filter.";
           leaf period {
             type centiseconds;
             mandatory true;
             description
               "Duration of time that should occur between periodic
                 push updates, in units of 0.01 seconds.";
           }
           leaf anchor-time {
             type yang:date-and-time;
             description
               "Designates a timestamp before or after which a series
                 of periodic push updates are determined.  The next
                 update will take place at a point in time that is a
                 multiple of a period from the 'anchor-time'.
                 For example, for an 'anchor-time' that is set for the
                 top of a particular minute and a period interval of a



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                 minute, updates will be sent at the top of every
                 minute that this subscription is active.";
           }
         }
         container on-change {
           if-feature "on-change";
           presence "indicates an on-change subscription";
           description
             "The publisher is requested to notify the receiver
               regarding changes in values in the datastore subset as
               defined by a selection filter.";

           leaf sync-on-start {
             type boolean;
             default "true";
             description
               "When this object is set to 'false', (1) it restricts an
                on-change subscription from sending 'push-update'
                notifications and (2) pushing a full selection per the
                terms of the selection filter MUST NOT be done for
                this subscription.  Only updates about changes
                (i.e., only 'push-change-update' notifications)
                are sent.  When set to 'true' (the default behavior),
                in order to facilitate a receiver's synchronization,
                a full update is sent, via a 'push-update' notification,
                when the subscription starts.  After that,
                'push-change-update' notifications are exclusively sent,
                unless the publisher chooses to resync the subscription
                via a new 'push-update' notification.";
           }
         }
       }
     }

     grouping subscription-id {
       description
         "This grouping describes the subscription identifier.";

       leaf id {
         type subscription-id;
         mandatory true;
         description
           "The unique identifier for the subscription.";
       }
     }

     grouping client-subscription-id {
       description



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         "This grouping describes a subscription identifier that
          cannot start with 'dyn-', which is reserved for dynamically
          created subscriptions.";

       leaf id {
         type subscription-id {
           pattern "dyn-.*" {
             modifier "invert-match";
           }
         }
         description
           "A identifier for the subscription, that MUST be unique
           across all configured and dynamic subscriptions.

           MUST NOT start with 'dyn-' which is reserved for
           dynamic subscriptions created by the publisher.";
       }
     }

     grouping subscription-schema {
       description
         "This grouping describes schema information related to a
          subscription.";

       leaf schema-id {
         type string;
         description
           "Indicates the version of the YANG schema used for this
           subscription.  The schema-id MUST change if the schema
           associated with the subscription changes.  The schema-id
           MAY change if the device schema changes, even if the
           change does not affect the subscription.";
       }

       leaf yang-library-content-id {
         type leafref {
           path "/yanglib:yang-library/yanglib:content-id";
         }
         description
           "Contains the YANG library content identifier.";
       }
     }

     grouping subscription-common {
       description
         "Common settings that are shared between dynamic and
          configured subscriptions.";




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       leaf description {
         type string {
           length "1..1000";
         }
         description
           "Open text allowing a configuring entity to embed the
            originator or other specifics of this subscription.";
       }

       container target {
         description
           "Identifies the source of information against which a
            subscription is being applied as well as specifics on the
            subset of information desired from that source.";
         leaf datastore {
           type identityref {
             base ds:datastore;
           }
           default "ds:operational";
           description
             "Datastore from which to retrieve data, defaults to
              operational";
         }

         uses filter-choice;
       }

       uses update-policy;
     }


     /*
      * RPCs
      */

     rpc establish-subscription {
       if-feature "dynamic";
       description
         "This RPC allows a subscriber to create (and possibly
          negotiate) a subscription on its own behalf.  If successful,
          the subscription remains in effect for the duration of the
          subscriber's association with the publisher or until the
          subscription is terminated.  If an error occurs or the
          publisher cannot meet the terms of a subscription, an RPC
          error is returned, and the subscription is not created.
          In that case, the RPC reply's 'error-info' MAY include
          suggested parameter settings that would have a higher
          likelihood of succeeding in a subsequent



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          'establish-subscription' request.";
       input {
         uses client-subscription-id {
           refine id {
             description
               "A optional identifier for a dynamic
                subscription, that must be unique across all
                configured and dynamic subscriptions.

                MUST NOT start with 'dyn-'.

                If not provided, the publisher MUST generate a unique
                identifier for the subscription, with an identifier
                that starts with 'dyn-', which is returned to the
                client in the RPC reply.";
           }
         }
         uses subscription-common;

         leaf encoding {
           type encoding;
           mandatory true;
           description
             "The encoding to use for the subscription notifications.";
         }

         uses dscp;

       }
       output {
         leaf id {
           type subscription-id;
           mandatory true;
           description
             "Identifier used for this subscription.";
         }
       }
     }

     rpc modify-subscription {
       if-feature "dynamic";
       description
         "This RPC allows a subscriber to modify a dynamic
          subscription's parameters.  If successful, the changed
          subscription parameters remain in effect for the duration of
          the subscription, until the subscription is again modified, or
          until the subscription is terminated.  In the case of an error
          or an inability to meet the modified parameters, the



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          subscription is not modified and the original subscription
          parameters remain in effect.";
       input {
         uses subscription-id;
         uses subscription-common;

         uses dscp;

       }
       //output {
         // leaf id {
         //   type subscription-id;
         //   mandatory true;
         //   description
         //     "Identifier used for this subscription.";
         // }
       //}
     }

     sx:structure establish-subscription-stream-error-info {
       container establish-subscription-stream-error-info {
         description
           "If any 'establish-subscription' RPC parameters are
            unsupportable against the event stream, a subscription
            is not created and the RPC error response MUST indicate the
            reason why the subscription failed to be created.  This
            yang-data MAY be inserted as structured data in a
            subscription's RPC error response to indicate the reason for
            the failure.  This yang-data MUST be inserted if hints are
            to be provided back to the subscriber.";
         leaf reason {
           type identityref {
             base establish-subscription-error;
           }
           description
             "Indicates the reason why the subscription has failed to
              be created to a targeted event stream.";
         }
         leaf filter-failure-hint {
           type string;
           description
             "Information describing where and/or why a provided
              filter was unsupportable for a subscription.  The
              syntax and semantics of this hint are
              implementation specific.";
         }
       }
     }



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     rpc delete-subscription {
       if-feature "dynamic";
       description
         "This RPC allows a subscriber to delete a subscription that
          was previously created by that same subscriber using the
          'establish-subscription' RPC.

          Only subscriptions that were created using
          'establish-subscription' from the same origin as this RPC
          can be deleted via this RPC. // TODO - Why same origin?

          If an error occurs, the server replies with an 'rpc-error'
          where the 'error-info' field MAY contain a
          'delete-subscription-error-info' structure.";
       input {
         leaf id {
           type subscription-id;
           mandatory true;
           description
             "The name of the dynamic subscription to be deleted.";
         }
       }
     }

     rpc kill-subscription {
       if-feature "dynamic";
       nacm:default-deny-all;
       description
         "This RPC allows an operator to delete a dynamic subscription
          without restrictions on the originating subscriber or
          underlying transport session.

          Only dynamic subscriptions, i.e., those that were created
          using 'establish-subscription', may be deleted via this RPC.

          If an error occurs, the server replies with an 'rpc-error'
          where the 'error-info' field MAY contain a
          'delete-subscription-error-info' structure.";
       input {
         leaf id {
           type subscription-id;
           mandatory true;
           description
             "The name of the dynamic subscription to be deleted.";
         }
       }
     }




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     sx:structure delete-subscription-error-info {
       container delete-subscription-error-info {
         description
           "If a 'delete-subscription' RPC or a 'kill-subscription' RPC
            fails, the subscription is not deleted and the RPC error
            response MUST indicate the reason for this failure.  This
            yang-data MAY be inserted as structured data in a
            subscription's RPC error response to indicate the reason
            for the failure.";
         leaf reason {
           type identityref {
             base delete-subscription-error;
           }
           mandatory true;
           description
             "Indicates the reason why the subscription has failed to be
              deleted.";
         }
       }
     }

     /*
      * NOTIFICATIONS
      */

     grouping subscription-update-common {
       description
         "Data nodes common to both subscription-started and
          subscription-modified notifications.";

       uses subscription-id;
       uses subscription-common {
         augment "target" {
           description
             "Augments fields to identify the target schema.";
           uses subscription-schema;
         }
       }
       container message-publishers {
         description
           "Holds the publisher-ids for all processes currently
            associated with the subscription";
           uses yp2:publishers;
       }
     }

     notification subscription-started {
       description



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         "This notification indicates that a subscription has started
          and notifications will now be sent.";
          uses subscription-update-common;
     }

     notification subscription-modified {
       description
         "This notification indicates that subscription paramaters have
          changed.";
       uses subscription-update-common;

       leaf reason {
         type subscription-change;
         mandatory true;
         description
           "Gives a hint for the message recipient as to why the
            notification has been sent.";
       }
     }

     notification subscription-terminated {
       description
         "This notification indicates that a subscription has been
          terminated.";
       uses subscription-id;
       leaf reason {
         type identityref {
           base subscription-terminated-reason;
         }
         mandatory true;
         description
           "Identifies the condition that resulted in the
            termination.";
       }
     }

     notification update {
       description
         "This notification contains a push update that in turn
          contains data subscribed to via a subscription.  In the case
          of a periodic subscription, this notification is sent for
          periodic updates.  It can also be used for synchronization
          updates of an on-change subscription.  This notification
          shall only be sent to receivers of a subscription.";
       leaf id {
         type subscription-id;
         description
           "The identifier of the subscription that is the source of



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            this notification.";
       }

       leaf path-prefix {
         type string;
         description
           "Specifies the common prefix that all other paths and data
            are encoded relative to.

            TODO - This should be a JSONified instance data path.";
       }

       leaf snapshot-type {
         type enumeration {
           enum "periodic" {
             description
               "The update message is due to a periodic update.";
           }
           enum "on-change-update" {
             description
               "The update message is due to an on-change update.  This
                means that one or more fields have changed under the
                snapshot path.

                TODO - Split this into a on-change-delete msg?";
           }
           enum "on-change-delete" {
             description
               "The update message is due to an on-change event where
                the data node at the target path has been delete.";
           }
           enum "resync" {
             description
               "This indicates that the update is to resynchronize the
                state, e.g., after a subscription started notification.

                Ideally, the resync message SHOULD be the first
                notification sent when a subscription has started, but
                it is not gauranteed or required to be the first
                (e.g., if an on-change event occurs).

                These messages can be used to ensure that all state
                has been sent to the client, and can be used to purge
                stale data.

                TODO - In the distributed notification case, need a
                notification to indicate that all child subscriptions
                have been sent.";



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           }
         }
         mandatory true;
         description
           "This indicates the type of notification message that is
            being sent.";
       }

       leaf observation-time {
         type yang:date-and-time;
         description
           "The time that the update was observed by the publisher.";
       }

       list updates {
         key "target-path";
         description
           "This list contains the updated data.  It constitutes a
            snapshot at the time of update of the set of data that has
            been subscribed to.  The snapshot corresponds to the same
            snapshot that would be returned in a corresponding 'get'
            operation with the same selection filter parameters
            applied.";

         leaf target-path {
           type string;
           description
             "The target path of the data that is being replaced, i.e.,
              updated or deleted.  The path is given relative to the
              path-prefix.";
         }

         choice data {
           description
             "This choice indicates the type of update that is being
              performed at the target path.";
           anydata merge {
             description
               "This contains the updated data that is to be merged with
               the existing data at the target path.  It constitutes a
               snapshot at the time of update of the set of data that
               has been subscribed to.  The snapshot corresponds to the
               same snapshot that would be returned in a corresponding
               'get' operation with the same selection filter parameters
               applied.

               The snapshot is encoded relative to the combined path
               defined by the common path-prefix and target-path";



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           }
           anydata replaced-by {
             description
               "This contains the updated data that is to replace all
               existing data at the target path.   It constitutes a
               snapshot at the time of update of the set of data that
               has been subscribed to.  The snapshot corresponds to the
               same snapshot that would be returned in a corresponding
               'get' operation with the same selection filter parameters
               applied.

               The snapshot is encoded relative to the combined path
               defined by the common path-prefix and target-path";
           }
           leaf deleted {
             type empty;
             description
               "This indicates that the data at the target path has been
                deleted.";
           }
         }
       }

       leaf complete {
         type boolean;
         default "false";
         description
           "This flag indicates that this is the last
            notification in a series of notifications that together
            constitute a complete snapshot of the subscribed data at
            the event-time.

            The 'update-complete' notification MAY be used as an
            alternative to setting this flag, and is semantically
            equivalent.";
       }
     }

     notification update-complete {
       description
         "This notification indicates the end of a periodic collection
          or resync event for an on-change subscription, and can be used
          to indicate that the receiver has a complete snapshot of the
          subscribed data at the event-time, and hence the client MAY
          use this as a signal that it can purge stale state
          information.

          Alternatively, the 'complete' flag in the update



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          notification MAY be used instead of sending this notification
          as a separate message, and both are semantically equivalent.";
       leaf id {
         type subscription-id;
         description
           "The name of the subscription that is the source of
             this notification.";
       }
     }

     sx:augment-structure "/iypn:envelope" {
       leaf publisher-id {
         type uint32;
         default 0;
         description
           "Identifies the software process which publishes notification
            messages (e.g., processor 1 on line card 1). This field
            is used to notify the receiver which publisher process
            published which message. The identifier is locally unique to
            the Network Node.";
       }
     }
   }
   <CODE ENDS>

                  Figure 20: YANG module ietf-yang-push-2

14.  Configured Subscription YANG Data Model

   This document specifies the ietf-yang-push-2-config YANG module
   Section 14.2 that defines an NMDA [RFC8342] compatible YANG data
   model for configuring subscriptions.  Support for this YANG module is
   OPTIONAL and is advertised using the normal mechanisms, e.g.,
   [RFC8525].

   Below is a tree diagram for the "subscriptions" container.  All
   objects contained in this tree are described in the YANG module in
   Section 13.2.  In the operational datastore [RFC8342], the
   "subscription" list contains entries both for configured and dynamic
   subscriptions.

   module: ietf-yang-push-2-config
     +--rw datastore-telemetry!
        +--rw subscriptions
           +--rw subscription* [id]
              +--rw id                                  subscription-id
              +--rw description?                        string
              +--rw target



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              |  +--rw datastore?          identityref
              |  +--rw (filter)
              |     +--:(path)
              |     |  +--rw path          ypath
              |     +--:(subtree)
              |     |  +--rw subtree       <anydata>
              |     +--:(xpath)
              |     |  +--rw xpath         yang:xpath1.0 {yp2:xpath}?
              |     +--:(by-reference)
              |        +--rw filter-ref    filter-ref
              +--rw update-trigger
              |  +--rw periodic!
              |  |  +--rw period         centiseconds
              |  |  +--rw anchor-time?   yang:date-and-time
              |  +--rw on-change! {on-change}?
              |     +--rw sync-on-start?   boolean
              +--rw receiver
              |       -> /datastore-telemetry/receivers/receiver/name
              +--ro status?
              |       yp2:subscription-status
              +--ro type?
              |       yp2:subscription-type
              +--ro encoding?                           yp2:encoding
              +--ro message-publishers
              |  +--ro publisher-id*   uint32
              +--ro last-sequence-number?
              |       yang:zero-based-counter64
              +--ro last-notification-time?
              |       yang:date-and-time
              +--ro last-periodic-collection-time?
              |       yang:date-and-time
              +--ro last-on-change-notification-time?
              |       yang:date-and-time
              +--ro statistics
              |  +--ro started-notifications?
              |  |       yang:zero-based-counter64
              |  +--ro terminated-notifications?
              |  |       yang:zero-based-counter64
              |  +--ro update-notifications?
              |  |       yang:zero-based-counter64
              |  +--ro periodic-collections?
              |  |       yang:zero-based-counter64
              |  +--ro excluded-events?
              |  |       yang:zero-based-counter64
              |  +--ro receiver-disconnects?
              |          yang:zero-based-counter64
              +---x reset




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     augment /yp2:subscription-started/yp2:target:
       +-- filter-ref?   filter-ref
     augment /yp2:subscription-modified/yp2:target:
       +-- filter-ref?   filter-ref

              Figure 21: subscriptions container Tree Diagram

   An overview of the behavior for configured subscriptions is specified
   in Section 9.3, with further details specified in the ietf-yang-push-
   2-config YANG module.

14.1.  ietf-yang-push-2-config YANG tree

   This section shows the full tree output for ietf-yang-push-2-config
   YANG module.

   Note, this output does not include support for any transport
   configuration, and for any implementation that supports configured
   subscriptions using this YANG module then at least one transport
   would expect to be configurable.

   module: ietf-yang-push-2-config
     +--rw datastore-telemetry!
        +--rw filters
        |  +--rw filter* [name]
        |     +--rw name             string
        |     +--rw (filter)
        |        +--:(path)
        |        |  +--rw path       ypath
        |        +--:(subtree)
        |        |  +--rw subtree    <anydata>
        |        +--:(xpath)
        |           +--rw xpath      yang:xpath1.0 {yp2:xpath}?
        +--rw subscriptions
        |  +--rw subscription* [id]
        |     +--rw id                                  subscription-id
        |     +--rw description?                        string
        |     +--rw target
        |     |  +--rw datastore?          identityref
        |     |  +--rw (filter)
        |     |     +--:(path)
        |     |     |  +--rw path          ypath
        |     |     +--:(subtree)
        |     |     |  +--rw subtree       <anydata>
        |     |     +--:(xpath)
        |     |     |  +--rw xpath         yang:xpath1.0 {yp2:xpath}?
        |     |     +--:(by-reference)
        |     |        +--rw filter-ref    filter-ref



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        |     +--rw update-trigger
        |     |  +--rw periodic!
        |     |  |  +--rw period         centiseconds
        |     |  |  +--rw anchor-time?   yang:date-and-time
        |     |  +--rw on-change! {on-change}?
        |     |     +--rw sync-on-start?   boolean
        |     +--rw receiver
        |     |       -> /datastore-telemetry/receivers/receiver/name
        |     +--ro status?
        |     |       yp2:subscription-status
        |     +--ro type?
        |     |       yp2:subscription-type
        |     +--ro encoding?                           yp2:encoding
        |     +--ro message-publishers
        |     |  +--ro publisher-id*   uint32
        |     +--ro last-sequence-number?
        |     |       yang:zero-based-counter64
        |     +--ro last-notification-time?
        |     |       yang:date-and-time
        |     +--ro last-periodic-collection-time?
        |     |       yang:date-and-time
        |     +--ro last-on-change-notification-time?
        |     |       yang:date-and-time
        |     +--ro statistics
        |     |  +--ro started-notifications?
        |     |  |       yang:zero-based-counter64
        |     |  +--ro terminated-notifications?
        |     |  |       yang:zero-based-counter64
        |     |  +--ro update-notifications?
        |     |  |       yang:zero-based-counter64
        |     |  +--ro periodic-collections?
        |     |  |       yang:zero-based-counter64
        |     |  +--ro excluded-events?
        |     |  |       yang:zero-based-counter64
        |     |  +--ro receiver-disconnects?
        |     |          yang:zero-based-counter64
        |     +---x reset
        +--rw receivers
           +--rw receiver* [name]
              +--rw name                      string
              +--rw encoding                  yp2:encoding
              +--rw dscp?                     inet:dscp
              +---x reset
              +--rw (notification-message-origin)?
              |  +--:(interface-originated)
              |  |  +--rw source-interface?   if:interface-ref
              |  |          {interface-designation}?
              |  +--:(address-originated)



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              |     +--rw source-vrf?         leafref {supports-vrf}?
              |     +--rw source-address?     inet:ip-address-no-zone
              +--rw (transport-type)

     augment /yp2:subscription-started/yp2:target:
       +-- filter-ref?   filter-ref
     augment /yp2:subscription-modified/yp2:target:
       +-- filter-ref?   filter-ref

      Figure 22: YANG tree for YANG Push v2 Config Module Tree Output

14.2.  ietf-yang-push-2-config YANG Model

   This module has import dependencies on [RFC6991], [RFC8343], and
   [RFC8529], and ietf-yang-push-lite.yang (this RFC).  In addition,
   this YANG module references [BCP14] ([RFC2119] [RFC8174]), and
   [RFC8529].

   <CODE BEGINS> file "ietf-yang-push-2-config.yang#0.1.0"
   module ietf-yang-push-2-config {
     yang-version 1.1;
     namespace
       "urn:ietf:params:xml:ns:yang:ietf-yang-push-2-config";
     prefix yp2co;

     import ietf-inet-types {
       prefix inet;
       reference
         "RFC 6991: Common YANG Data Types";
     }
     import ietf-interfaces {
       prefix if;
       reference
         "RFC 8343: A YANG Data Model for Interface Management";
     }
     import ietf-network-instance {
       prefix ni;
       reference
         "RFC 8529: YANG Data Model for Network Instances";
     }
     import ietf-yang-types {
       prefix yang;
       reference
         "RFC 6991: Common YANG Data Types";
     }
     import ietf-yang-push-2 {
       prefix yp2;
       reference



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         "RFC XXXX: YANG Datastore Telemetry (YANG Push version 2)";
     }

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

        Author:  Robert Wilton
                 <mailto:rwilton@cisco.com>";
     description
       "This module contains YANG specifications for YANG-Push version 2
        configuration and operational state model.

        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.

        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).

        This version of this YANG module is part of RFC XXXX
        (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
        for full legal notices.";

     revision 2025-08-03 {
       description
         "Initial revision.";
       reference
         "XXX: YANG Datastore Telemetry (YANG Push version 2)";
     }

     /*
      * FEATURES
      */

     feature interface-designation {
       description



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         "This feature indicates that a publisher supports sourcing all
          receiver interactions for a configured subscription from a
          single designated egress interface.";
     }

     feature supports-vrf {
       description
         "This feature indicates that a publisher supports VRF
          configuration for configured subscriptions.  VRF support for
          dynamic subscriptions does not require this feature.";
       reference
         "RFC 8529: YANG Data Model for Network Instances,
                    Section 6";
     }

     /*
      * TYPEDEFs
      */

     typedef filter-ref {
       type leafref {
         path "/datastore-telemetry/filters/filter/name";
       }
       description
         "This type is used to reference a selection filter.";
     }

     /*
      * GROUPINGS
      */
     grouping filter-ref {
       description
         "This grouping is used to reference a selection filter.";
       leaf filter-ref {
         type filter-ref;
         mandatory true;
         description
           "References an existing selection filter that is to be
           applied to the subscription.";
       }
     }

     /*
      * DATA NODES
      */

     container datastore-telemetry {
       presence "Enables datastore telemetry";



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       description
       "YANG Push v2 Datastore Telemetry Configuration and State.";
       container filters {
         description
           "Contains a list of configurable filters that can be applied
            to subscriptions.  This facilitates the reuse of complex
            filters once defined.";

         list filter {
           key "name";
           description
             "A list of preconfigured filters that can be applied
             to datastore subscriptions.";
           leaf name {
             type string {
               length "1..64";
               pattern '[A-Za-z0-9._-]+';
             }
             description
               "A unique name to identify the selection filters.";
           }
           uses yp2:filter-choice;
         }
       }
       container subscriptions {
         description
           "Contains the list of currently active subscriptions, i.e.,
           subscriptions that are currently in effect, used for
           subscription management and monitoring purposes.  This
           includes subscriptions that have been set up via
           RPC primitives as well as subscriptions that have been
           established via configuration.";
         list subscription {
           key "id";
           description
             "The identity and specific parameters of a subscription.
             Subscriptions in this list can be created using a control
             channel or RPC or can be established through configuration.

             If the 'kill-subscription' RPC or configuration operations
             are used to delete a subscription, a
             'subscription-terminated' message is sent to any active or
             suspended receivers.";

           uses yp2:client-subscription-id;
           uses yp2:subscription-common;

           leaf receiver {



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             type leafref {
               path "/datastore-telemetry/receivers/receiver/name";
             }
             mandatory true;
             description
               "Identifies the receiver for a subscription.";
           }

           // leaf status {
           //   type enumeration {
           //     enum disconnected {
           //       description
           //         "This subscription does not have an active session
           //           with the receiver, and it is not trying to
           //           connect.

           //         E.g., this state may be reported if the
           //         subscription is not valid, or has not been started
           //         yet.";
           //     }
           //     enum connecting {
           //       description
           //         "The publisher is trying to establish a session
           //           with the receiver for this subscription.

           //           For a session less transport, this state may be
           //           used to indicate that there is no route to the
           //           receiver.

           //           A receiver in connecting state may indicate that
           //           the transport or associated security session
           //           could not be established, and the publisher is
           //         periodically trying to establish the connection.";
           //     }
           //     enum active {
           //       description
           //         "The publisher has successfully connected (if over
           //           a session based transport) to the receiver for
           //           this subscription, and the publisher is able to
           //           send notifications to the receiver.";
           //     }
           //   }
           //   config false;
           //   description
           //     "Specifies the connection status of the receiver for
           //       this subscription.";
           // }




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           leaf status {
             type yp2:subscription-status;
             config false;
             description
               "The presence of this leaf indicates that the
                subscription originated from configuration, not through
                a control channel or RPC.  The value indicates the state
                of the subscription as established by the publisher.";
           }

           leaf type {
             type yp2:subscription-type;
             default "configured";
             config false;
             description
               "Whether the subscription is configured or dynamic.";
           }

           leaf encoding {
             type yp2:encoding;
             config false;
             description
               "The type of encoding for notification messages.";
           }

           container message-publishers {
             config false;
             description
               "Holds the publisher-ids for all processes
                currently associated with the subscription";
               uses yp2:publishers;
           }

           leaf last-sequence-number {
             type yang:zero-based-counter64;
             config false;
             description
               "The envelope sequence number for the last notification
                sent for this subscription.

                The sequence number is initialized to zero when the
                subscription first becomes active and the first
                subscription-started notification is sent.";
           }

           leaf last-notification-time {
             type yang:date-and-time;
             config false;



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             description
               "The notification envelope event-time timestamp of the
                last notification sent for this subscription.

                The timestamp is initialized to the time when the
                subscription first becomes active and the first
                subscription-started notification is sent.";
           }

           leaf last-periodic-collection-time {
             type yang:date-and-time;
             config false;
             description
               "The event-time timestamp of the last completed periodic
                collection or resynchronization collection for this
                subscription, and used as the event-time in the
                notification header.

                The timestamp is initialized to the time when the
                subscription first becomes active and the first
                subscription-started notification is sent.";
           }

           leaf last-on-change-notification-time {
             type yang:date-and-time;
             config false;
             description
               "The notification envelope event-time timestamp of the
                last on-change notification sent for this subscription.

                The timestamp is initialized to the time when the
                subscription first becomes active and the first
                subscription-started notification is sent.";
           }

           container statistics {
             config false;
             description
               "Statistics related to the number of messages generated
                for this subscription.";

             leaf started-notifications {
               type yang:zero-based-counter64;
               config false;
               description
                 "The number of subscription-started notifications
                  sent for this subscription since the subscription
                  list entry was created and the configuration



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                  was applied by the publisher.";
             }

             leaf terminated-notifications {
               type yang:zero-based-counter64;
               config false;
               description
                 "The number of subscription-terminated notifications
                  sent for this subscription since the subscription
                  list entry was created and the configuration
                  was applied by the publisher.";
             }

             leaf update-notifications {
               type yang:zero-based-counter64;
               config false;
               description
                 "The number of update records generated for the
                  subscription, to be queued to one of more active
                  receivers.

                  The count is re-initialized to 0 when the
                  subscription first becomes active and the
                  subscription-started notification is sent.

                  The count is incremented even if the update
                  record has been generated, but is not queued to
                  any receiver.";
             }

             leaf periodic-collections {
               type yang:zero-based-counter64;
               config false;
               description
                 "The number of periodic collections completed for
                  the subscription.

                  The count is re-initialized to 0 when the
                  subscription first becomes active and the
                  subscription-started notification is sent.

                  The count is incremented even if the update
                  record has been generated, but is not queued to
                  any receiver.";
             }

             leaf excluded-events {
               type yang:zero-based-counter64;



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               config false;
               description
                 "The number of event records explicitly removed via
                 either an event stream filter or an access control
                 filter so that they are not passed to a receiver.
                 This count is set to zero each time
                 'sent-event-records' is initialized.";
             }

             leaf receiver-disconnects {
               type yang:zero-based-counter64;
               config false;
               description
                 "The number of times that the receiver has been
                   disconnected since the subscription
                   receiver entry was created and the configuration
                   was applied by the publisher";
             }
           }

           action reset {
             description
               "Reset the subscription.

                This action will cause a new subscription-started
                message to be sent for the subscription";
           }
         }
       }
       container receivers {
         description
           "A container for all instances of configured receivers.";

         list receiver {
           key "name";

           leaf name {
             type string {
               length "1..64";
               pattern '[A-Za-z0-9._-]+';
             }
             description
               "An arbitrary but unique name for this receiver
               instance.";
           }

           leaf encoding {
     /*        when 'not(../transport) or derived-from(../transport,



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             "yp2:configurable-encoding")';*/
             type yp2:encoding;
             mandatory true;
             description
               "The type of encoding for notification messages.  For a
                dynamic subscription, if not included as part of an
                'establish-subscription' RPC, the encoding will be
                populated with the encoding used by that RPC.  For a
                configured subscription, if not explicitly configured,
                the encoding will be the default encoding for an
                underlying transport.";
           }

           uses yp2:dscp;

           action reset {
             description
               "Resets all configured subscriptions that reference
                this receiver.

                This action is similar to invoking the 'reset' action
                on all subscriptions that reference this receiver
                configuration.";
           }

           choice notification-message-origin {
             description
               "Identifies the egress interface on the publisher
               from which notification messages are to be sent.";
             case interface-originated {
               description
                 "When notification messages are to egress a specific,
                 designated interface on the publisher.";
               leaf source-interface {
                 if-feature "interface-designation";
                 type if:interface-ref;
                 description
                   "References the interface for notification
                    messages.";
               }
             }
             case address-originated {
               description
                 "When notification messages are to depart from a
                 publisher using a specific originating address and/or
                 routing context information.";
               leaf source-vrf {
                 if-feature "supports-vrf";



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                 type leafref {
                   path
                     '/ni:network-instances/ni:network-instance/'
                     + 'ni:name';
                 }
                 description
                   "VRF from which notification messages should egress a
                   publisher.";
               }
               leaf source-address {
                 type inet:ip-address-no-zone;
                 description
                   "The source address for the notification messages.
                   If a source VRF exists but this object doesn't, a
                   publisher's default address for that VRF must
                   be used.";
               }
             }
           }

           choice transport-type {
             mandatory true;
             description
               "Choice of different types of transports used to
                send notifications.  The 'case' statements must
                be augmented in by other modules.";
           }

           description
             "A list of all receiver instances.";
         }
       }
     }

     augment "/yp2:subscription-started/yp2:target" {

       description
         "Allow a subscription-started notification to include a
          referenced named filter";
       uses filter-ref {
         refine "filter-ref" {
           mandatory false;
         }
       }
     }

     augment "/yp2:subscription-modified/yp2:target" {




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       description
         "Allow a subscription-modified notification to include a
          referenced named filter";
       uses filter-ref {
         refine "filter-ref" {
           mandatory false;
         }
       }
     }

     augment "/datastore-telemetry/subscriptions/subscription/"
           + "target/filter" {

       description
         "Augment the subscription filter to allow
          referencing a filter configured separately.";

       case by-reference {
         description
           "Incorporates a filter that has been configured
            separately.";
         uses filter-ref;
       }
     }
   }
   <CODE ENDS>

               Figure 23: YANG module ietf-yang-push-2-config

15.  Capabilities YANG Data Model

15.1.  ietf-yang-push-2-capabilities YANG tree

   This section shows the tree output for ietf-yang-push-2-capabilities
   YANG module, which augments the ietf-system-capabilities YANG module
   [RFC9196].















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   module: ietf-yang-push-2-capabilities

     augment /sysc:system-capabilities:
       +--ro datastore-telemetry
       |  +--ro periodic-notifications-supported?   notification-support
       |  +--ro (update-period)?
       |  |  +--:(minimum-update-period)
       |  |  |  +--ro minimum-update-period?        uint32
       |  |  +--:(supported-update-period)
       |  |     +--ro supported-update-period*      uint32
       |  +--ro on-change-supported?                notification-support
       |  +--ro transport
       |     +--ro transport-capability* [transport-protocol]
       |        +--ro transport-protocol    identityref
       |        +--ro security-protocol?    identityref
       |        +--ro encoding-format*      identityref
       +--ro distributed-notifications-supported?   boolean
     augment /sysc:system-capabilities/sysc:datastore-capabilities
               /sysc:per-node-capabilities:
       +--ro datastore-telemetry
          +--ro periodic-notifications-supported?   notification-support
          +--ro (update-period)?
          |  +--:(minimum-update-period)
          |  |  +--ro minimum-update-period?        uint32
          |  +--:(supported-update-period)
          |     +--ro supported-update-period*      uint32
          +--ro on-change-supported?                notification-support

   Figure 24: YANG tree for YANG Push v2 Capabilities Module Tree Output

15.2.  ietf-yang-push-2-capabilities YANG Model

   This module imports typedefs from the yang-push-lite YANG module.

   This module augments the ietf-system-capabilities YANG module
   [RFC9196].

   <CODE BEGINS> file "ietf-yang-push-2-capabilities.yang#0.1.0"
   module ietf-yang-push-2-capabilities {
     yang-version 1.1;
     namespace
       "urn:ietf:params:xml:ns:yang:ietf-yang-push-2-capabilities";
     prefix yp2ca;

     import ietf-system-capabilities {
       prefix sysc;
       reference
         "RFC 9196: YANG Modules Describing Capabilities for Systems



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          and Datastore Update Notifications";
     }
     import ietf-yang-push-2 {
       prefix yp2;
       reference
         "RFC XXX: YANG Datastore Telemetry (YANG Push version 2)";
     }

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

        Author:  Robert Wilton
                 <mailto:rwilton@cisco.com>";
     description
       "This module contains YANG specifications for YANG-Push lite.

        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.

        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).

        This version of this YANG module is part of RFC XXXX
        (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
        for full legal notices.";

     revision 2024-11-11 {
       description
         "Initial revision.";
       reference
         "XXX: YANG Datastore Telemetry (YANG Push version 2)";
     }

     /*
      * IDENTITIES



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      */

     identity security-protocol {
       description
         "Identity for security protocols.";
     }

     identity tls12 {
       base security-protocol;
       description
         "Indicates TLS Protocol Version 1.2. TLS 1.2 is obsolete,
          and thus it is NOT RECOMMENDED to enable this feature.";
       reference
         "RFC 5246: The Transport Layer Security (TLS) Protocol
                    Version 1.2";
     }

     identity tls13 {
       base security-protocol;
       description
         "Indicates TLS Protocol Version 1.3.";
       reference
         "RFC 8446: The Transport Layer Security (TLS)
                    Protocol Version 1.3";
     }

     identity dtls12 {
       base security-protocol;
       description
         "Indicates DTLS Protocol Version 1.2. TLS 1.2 is obsolete,
          and thus it is NOT RECOMMENDED to enable this feature.";
       reference
         "RFC 6347: The Datagram Transport Layer Security (TLS) Protocol
                    Version 1.2";
     }

     identity dtls13 {
       base security-protocol;
       description
         "Indicates DTLS Protocol Version 1.3.";
       reference
         "RFC 9147: The Datagram Transport Layer Security (TLS)
                    Protocol Version 1.3";
     }

     identity ssh {
       base security-protocol;
       description



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         "Indicates SSH.";
     }


     grouping yp2-capabilities {
       description
         "Capabilities related to YANG Push Lite subscriptions
          and notifications";
       container datastore-telemetry {
         description
           "Capabilities related to YANG Push List subscriptions
            and notifications";
         typedef notification-support {
           type bits {
             bit config-changes {
               description
                 "The publisher is capable of sending
                  notifications for 'config true' nodes for the
                  relevant scope and subscription type.";
             }
             bit state-changes {
               description
                 "The publisher is capable of sending
                  notifications for 'config false' nodes for the
                  relevant scope and subscription type.";
             }
           }
           description
             "Type for defining whether 'on-change' or
              'periodic' notifications are supported for all data nodes,
              'config false' data nodes, 'config true' data nodes, or
              no data nodes.

              The bits config-changes or state-changes have no effect
              when they are set for a datastore or for a set of nodes
              that does not contain nodes with the indicated config
              value.  In those cases, the effect is the same as if no
              support was declared.  One example of this is indicating
              support for state-changes for a candidate datastore that
              has no effect.";
         }

         leaf periodic-notifications-supported {
           type notification-support;
           description
             "Specifies whether the publisher is capable of
              sending 'periodic' notifications for the selected
              data nodes, including any subtrees that may exist



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              below them.";
           reference
             "RFC 8641: Subscription to YANG Notifications for
              Datastore Updates, 'periodic' subscription concept";
         }
         choice update-period {
           description
             "Supported update period value or values for
              'periodic' subscriptions.";
           leaf minimum-update-period {
             type uint32;
             units "centiseconds";
             description
               "Indicates the minimal update period that is
                supported for a 'periodic' subscription.

                A subscription request to the selected data nodes with
                a smaller period than what this leaf specifies is
                likely to result in a 'period-unsupported' error.";
           }
           leaf-list supported-update-period {
             type uint32;
             units "centiseconds";
             description
               "Supported update period values for a 'periodic'
                subscription.

                A subscription request to the selected data nodes with a
                period not included in the leaf-list will result in a
                'period-unsupported' error.";
           }
         }
         leaf on-change-supported {
           type notification-support;
           description
             "Specifies whether the publisher is capable of
              sending 'on-change' notifications for the selected
              data nodes and the subtree below them.";
         }
       }
     }

     grouping yp2-transport-capabilities {
       description
         "Capabilities related to transports supporting Yang Push Lite";
       container transport {
         description
           "Specifies capabilities related to YANG-Push transports.";



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         list transport-capability {
           key "transport-protocol";
           description
             "Indicates a list of capabilities related to notification
                     transport.";
           leaf transport-protocol {
             type identityref {
               base yp2:transport;
             }
             description
               "Indicates supported transport protocol for YANG-Push.";
           }
           leaf security-protocol {
             type identityref {
               base security-protocol;
             }
             description
               "Indicates transport security protocol.";
           }
           leaf-list encoding-format {
             type identityref {
               base yp2:encoding;
             }
             description
               "Indicates supported encoding formats.";
           }
         }
       }
     }

     // YANG Push Lite Capabilities
     augment "/sysc:system-capabilities" {
       description
         "Adds system level capabilities for YANG Push Lite";
       uses yp2-capabilities;

       leaf distributed-notifications-supported {
         type boolean;
         description
           "Indicates whether the server supports distributed
             notifications and may source message from different
             Message Publishers.";
       }
     }

     augment "/sysc:system-capabilities/yp2ca:datastore-telemetry" {
       description
         "Adds system level Yang Push Lite transport capabilities";



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       uses yp2-transport-capabilities;
     }

     augment "/sysc:system-capabilities/sysc:datastore-capabilities"
           + "/sysc:per-node-capabilities" {
       description
         "Add datastore and node-level capabilities";
       uses yp2-capabilities;
     }
   }
   <CODE ENDS>

            Figure 25: YANG module ietf-yang-push-2-capabilities

16.  Security Considerations

   With configured subscriptions, one or more publishers could be used
   to overwhelm a receiver.  To counter this, notification messages
   SHOULD NOT be sent to any receiver that does not support this
   specification.  Receivers that do not want notification messages need
   only terminate or refuse any transport sessions from the publisher.

   When a receiver of a configured subscription gets a new
   "subscription-started" message for a known subscription where it is
   already consuming events, it may indicate that an attacker has done
   something that has momentarily disrupted receiver connectivity. *TODO
   - Do we still want this paragraph?*.

   For dynamic subscriptions, implementations need to protect against
   malicious or buggy subscribers that may send a large number of
   "establish-subscription" requests and thereby use up system
   resources.  To cover this possibility, operators SHOULD monitor for
   such cases and, if discovered, take remedial action to limit the
   resources used, such as suspending or terminating a subset of the
   subscriptions or, if the underlying transport is session based,
   terminating the underlying transport session.

   Using DNS names for configured subscription's receiver "name" lookups
   can cause situations where the name resolves differently than
   expected on the publisher, so the recipient would be different than
   expected.

16.1.  Use of YANG Push v2 with NACM

   *TODO, do we even need this section?*






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   This specification MAY be used with access control tools, such as
   NACM [RFC8341].  Please refer to that specification for normative
   guidance of how NACM applies.

   For informative purposes, please note that NACM can be used:

   *  NACM can be used to control access to the data nodes and RPCs
      defined in the YANG modules defined in this document.

   *  NACM can be used to control access to the data included in the
      YANG _update_ notifications.

16.2.  Receiver Authorization

   *TODO Relax when access control must be checked.*

   *TODO Consider if this is the best place in the document, but this
   text needs to be updated regardless.*

   A receiver of subscription data MUST only be sent updates for which
   it has proper authorization.  A publisher MUST ensure that no
   unauthorized data is included in push updates.  To do so, it needs to
   apply all corresponding checks applicable at the time of a specific
   pushed update and, if necessary, silently remove any unauthorized
   data from datastore subtrees.  This enables YANG data that is pushed
   based on subscriptions to be authorized in a way that is equivalent
   to a regular data retrieval ("get") operation.

   Each "push-update" and "push-change-update" MUST have access control
   applied, as depicted in Figure 5.  This includes validating that read
   access is permitted for any new objects selected since the last
   notification message was sent to a particular receiver.  A publisher
   MUST silently omit data nodes from the results that the client is not
   authorized to see.  To accomplish this, implementations SHOULD apply
   the conceptual authorization model of [RFC8341], specifically
   Section 3.2.4, extended to apply analogously to data nodes included
   in notifications, not just <rpc-reply> messages sent in response to
   <get> and <get-config> requests.

                        +-----------------+      +--------------------+
     push-update or --> | datastore node  |  yes | add datastore node |
    push-change-update  | access allowed? | ---> | to update record   |
                        +-----------------+      +--------------------+

                 Figure 26: Access Control for Push Updates






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   A publisher MUST allow for the possibility that a subscription's
   selection filter references nonexistent data or data that a receiver
   is not allowed to access.  Such support permits a receiver the
   ability to monitor the entire lifecycle of some datastore tree
   without needing to explicitly enumerate every individual datastore
   node.  If, after access control has been applied, there are no
   objects remaining in an update record, then the effect varies given
   if the subscription is a periodic or on-change subscription.  For a
   periodic subscription, an empty "push-update" notification MUST be
   sent, so that clients do not get confused into thinking that an
   update was lost.  For an on-change subscription, a "push-update"
   notification MUST NOT be sent, so that clients remain unaware of
   changes made to nodes they don't have read-access for.

   A publisher MAY choose to reject an "establish-subscription" request
   that selects nonexistent data or data that a receiver is not allowed
   to access.  The error identity "unchanging-selection" SHOULD be
   returned as the reason for the rejection.  In addition, a publisher
   MAY choose to terminate a dynamic subscription or suspend a
   configured receiver when the authorization privileges of a receiver
   change or the access controls for subscribed objects change.  In that
   case, the publisher SHOULD include the error identity "unchanging-
   selection" as the reason when sending the "subscription-terminated"
   or "subscription-suspended" notification, respectively.  Such a
   capability enables the publisher to avoid having to support
   continuous and total filtering of a subscription's content for every
   update record.  It also reduces the possibility of leakage of access-
   controlled objects.

   If read access into previously accessible nodes has been lost due to
   a receiver permissions change, this SHOULD be reported as a patch
   "delete" operation for on-change subscriptions.  If not capable of
   handling such receiver permission changes with such a "delete",
   publisher implementations MUST force dynamic subscription re-
   establishment or configured subscription reinitialization so that
   appropriate filtering is installed.

16.3.  YANG Module Security Considerations

   This section is modeled after the template described in Section 3.7.1
   of [I-D.draft-ietf-netmod-rfc8407bis].

   The "ietf-yang-push-2" YANG module defines a data model that is
   designed to be accessed via YANG-based management protocols, such as
   NETCONF [RFC6241] and RESTCONF [RFC8040].  These protocols have to
   use a secure transport layer (e.g., SSH [RFC4252], TLS [RFC8446], and
   QUIC [RFC9000]) and have to use mutual authentication.




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   The Network Configuration Access Control Model (NACM) [RFC8341]
   provides the means to restrict access for particular NETCONF or
   RESTCONF users to a pre-configured subset of all available NETCONF or
   RESTCONF protocol operations and content.

   There are a number of data nodes defined in this YANG module that are
   writable/creatable/deletable (i.e., "config true", which is the
   default).  All writable data nodes are likely to be reasonably
   sensitive or vulnerable in some network environments.  Write
   operations (e.g., edit-config) and delete operations to these data
   nodes without proper protection or authentication can have a negative
   effect on network operations.  The following subtrees and data nodes
   have particular sensitivities/vulnerabilities:

   *  There are no particularly sensitive writable data nodes.

   Some of the readable data nodes 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, get-config, or
   notification) to these data nodes.  Specifically, the following
   subtrees and data nodes have particular sensitivities/
   vulnerabilities:

   *  There are no particularly sensitive readable data nodes.

   Some of the RPC or action operations in this YANG module may be
   considered sensitive or vulnerable in some network environments.  It
   is thus important to control access to these operations.
   Specifically, the following operations have particular sensitivities/
   vulnerabilities:

   *  kill-subscription - this RPC operation allows the caller to kill
      any dynamic subscription, even those created via other users, or
      other transport sessions.

17.  IANA Considerations

17.1.  Namespace URI registrations

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










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       +===========================================================+
       | URI                                                       |
       +===========================================================+
       | urn:ietf:params:xml:ns:yang:ietf-yang-push-2              |
       +-----------------------------------------------------------+
       | urn:ietf:params:xml:ns:yang:ietf-yang-push-2-config       |
       +-----------------------------------------------------------+
       | urn:ietf:params:xml:ns:yang:ietf-yang-push-2-capabilities |
       +-----------------------------------------------------------+

                    Table 1: Namespace URI registrations

   For all registrations:

   *  Registrant Contact: The IESG.

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

18.  YANG Module Name registrations

   This document registers the following YANG modules in the "YANG
   Module Names" registry [RFC6020]:

     +==================+===================================+========+
     | Name             | Namespace                         | Prefix |
     +==================+===================================+========+
     | ietf-yang-push-2 | urn:ietf:params:xml:ns:yang:ietf- | ypl    |
     |                  | yang-push-2                       |        |
     +------------------+-----------------------------------+--------+
     | ietf-yang-push-  | urn:ietf:params:xml:ns:yang:ietf- | yplco  |
     | 2-config         | yang-push-2-config                |        |
     +------------------+-----------------------------------+--------+
     | ietf-yang-push-  | urn:ietf:params:xml:ns:yang:ietf- | yplca  |
     | 2-capabilities   | yang-push-2-capabilities          |        |
     +------------------+-----------------------------------+--------+

                  Table 2: YANG Module Name Registrations

   For all registration the reference is "RFC XXXX".

Acknowledgments

   This initial draft is early work is based on discussions with various
   folk, particularly Thomas Graf, Holger Keller, Dan Voyer, Nils
   Warnke, and Alex Huang Feng; but also wider conversations that
   include: Benoit Claise, Pierre Francois, Paolo Lucente, Jean
   Quilbeuf, among others.




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   In addition, as described in the introduction, the authors would like
   to acknowledge that this work builds on work of others, such as,
   Subscribed Notifications, YANG Push, and various extensions to that
   work.

Contributors

   The following individuals have actively contributed to this draft and
   the YANG Push Solution.

   *  Dan Voyer

References

Normative References

   [BCP14]    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/rfc/rfc8174>.

   [I-D.draft-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-04, 6 February 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              notif-envelope-04>.

   [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/rfc/rfc2119>.

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              DOI 10.17487/RFC2474, December 1998,
              <https://www.rfc-editor.org/rfc/rfc2474>.

   [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/rfc/rfc6241>.

   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
              RFC 6991, DOI 10.17487/RFC6991, July 2013,
              <https://www.rfc-editor.org/rfc/rfc6991>.




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   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/rfc/rfc7950>.

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,
              <https://www.rfc-editor.org/rfc/rfc7951>.

   [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/rfc/rfc8174>.

   [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/rfc/rfc8340>.

   [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/rfc/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/rfc/rfc8342>.

   [RFC8525]  Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K.,
              and R. Wilton, "YANG Library", RFC 8525,
              DOI 10.17487/RFC8525, March 2019,
              <https://www.rfc-editor.org/rfc/rfc8525>.

   [RFC8529]  Berger, L., Hopps, C., Lindem, A., Bogdanovic, D., and X.
              Liu, "YANG Data Model for Network Instances", RFC 8529,
              DOI 10.17487/RFC8529, March 2019,
              <https://www.rfc-editor.org/rfc/rfc8529>.

   [RFC8791]  Bierman, A., Björklund, M., and K. Watsen, "YANG Data
              Structure Extensions", RFC 8791, DOI 10.17487/RFC8791,
              June 2020, <https://www.rfc-editor.org/rfc/rfc8791>.

   [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/rfc/rfc9196>.







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   [RFC9254]  Veillette, M., Ed., Petrov, I., Ed., Pelov, A., Bormann,
              C., and M. Richardson, "Encoding of Data Modeled with YANG
              in the Concise Binary Object Representation (CBOR)",
              RFC 9254, DOI 10.17487/RFC9254, July 2022,
              <https://www.rfc-editor.org/rfc/rfc9254>.

   [RFC9485]  Bormann, C. and T. Bray, "I-Regexp: An Interoperable
              Regular Expression Format", RFC 9485,
              DOI 10.17487/RFC9485, October 2023,
              <https://www.rfc-editor.org/rfc/rfc9485>.

   [RFC9595]  Veillette, M., Ed., Pelov, A., Ed., Petrov, I., Ed.,
              Bormann, C., and M. Richardson, "YANG Schema Item
              iDentifier (YANG SID)", RFC 9595, DOI 10.17487/RFC9595,
              July 2024, <https://www.rfc-editor.org/rfc/rfc9595>.

   [RFC9911]  Schönwälder, J., Ed., "Common YANG Data Types", RFC 9911,
              DOI 10.17487/RFC9911, December 2025,
              <https://www.rfc-editor.org/rfc/rfc9911>.

Informative References

   [Consistency]
              Wikipedia, "Consistency (database systems)",
              <https://en.wikipedia.org/wiki/
              Consistency_(database_systems)>.

   [EventualConsistency]
              Rouse, M., "Eventual Consistency",
              <https://www.techopedia.com/definition/29165/eventual-
              consistency>.

   [gNMI]     OpenConfig, "gRPC Network Management Interface (gNMI)",
              <https://github.com/openconfig/reference/blob/master/rpc/
              gnmi/gnmi-specification.md>.

   [I-D.draft-ietf-netconf-distributed-notif]
              Zhou, T., Zheng, G., Voit, E., Graf, T., and P. Francois,
              "Subscription to Notifications in a Distributed
              Architecture", Work in Progress, Internet-Draft, draft-
              ietf-netconf-distributed-notif-18, 28 February 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              distributed-notif-18>.








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   [I-D.draft-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.draft-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-25, 28 January 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              udp-notif-25>.

   [I-D.draft-ietf-netmod-rfc8407bis]
              Bierman, A., Boucadair, M., and Q. Wu, "Guidelines for
              Authors and Reviewers of Documents Containing YANG Data
              Models", Work in Progress, Internet-Draft, draft-ietf-
              netmod-rfc8407bis-28, 5 June 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
              rfc8407bis-28>.

   [I-D.draft-netana-netconf-yp-transport-capabilities]
              Wu, Q., Ma, Q., Feng, A. H., and T. Graf, "YANG
              Notification Transport Capabilities", Work in Progress,
              Internet-Draft, draft-netana-netconf-yp-transport-
              capabilities-01, 17 January 2025,
              <https://datatracker.ietf.org/doc/html/draft-netana-
              netconf-yp-transport-capabilities-01>.

   [I-D.ietf-netconf-distributed-notif]
              Zhou, T., Zheng, G., Voit, E., Graf, T., and P. Francois,
              "Subscription to Notifications in a Distributed
              Architecture", Work in Progress, Internet-Draft, draft-
              ietf-netconf-distributed-notif-18, 28 February 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              distributed-notif-18>.

   [I-D.ietf-nmop-network-anomaly-architecture]
              Graf, T., Du, W., Francois, P., and A. H. Feng, "A
              Framework for a Network Anomaly Detection Architecture",
              Work in Progress, Internet-Draft, draft-ietf-nmop-network-
              anomaly-architecture-07, 18 January 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-nmop-
              network-anomaly-architecture-07>.





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   [I-D.ietf-nmop-yang-message-broker-integration]
              Graf, T. and A. Elhassany, "An Architecture for YANG-Push
              to Message Broker Integration", Work in Progress,
              Internet-Draft, draft-ietf-nmop-yang-message-broker-
              integration-11, 28 February 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-nmop-
              yang-message-broker-integration-11>.

   [I-D.tgraf-netconf-notif-sequencing]
              Graf, T., Quilbeuf, J., and A. H. Feng, "Support of
              Hostname and Sequencing in YANG Notifications", Work in
              Progress, Internet-Draft, draft-tgraf-netconf-notif-
              sequencing-06, 29 June 2024,
              <https://datatracker.ietf.org/doc/html/draft-tgraf-
              netconf-notif-sequencing-06>.

   [I-D.tgraf-netconf-yang-push-observation-time]
              Graf, T., Claise, B., and A. H. Feng, "Support of
              Observation Timestamp in YANG-Push Notifications", Work in
              Progress, Internet-Draft, draft-tgraf-netconf-yang-push-
              observation-time-03, 14 December 2024,
              <https://datatracker.ietf.org/doc/html/draft-tgraf-
              netconf-yang-push-observation-time-03>.

   [Kafka]    Apache.org, "Apache Kafka", <https://kafka.apache.org/>.

   [RFC3411]  Harrington, D., Presuhn, R., and B. Wijnen, "An
              Architecture for Describing Simple Network Management
              Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
              DOI 10.17487/RFC3411, December 2002,
              <https://www.rfc-editor.org/rfc/rfc3411>.

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

   [RFC4252]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
              January 2006, <https://www.rfc-editor.org/rfc/rfc4252>.

   [RFC5277]  Chisholm, S. and H. Trevino, "NETCONF Event
              Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008,
              <https://www.rfc-editor.org/rfc/rfc5277>.

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



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   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <https://www.rfc-editor.org/rfc/rfc7049>.

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,
              <https://www.rfc-editor.org/rfc/rfc7540>.

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

   [RFC8072]  Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch
              Media Type", RFC 8072, DOI 10.17487/RFC8072, February
              2017, <https://www.rfc-editor.org/rfc/rfc8072>.

   [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/rfc/rfc8259>.

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

   [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/rfc/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/rfc/rfc8639>.

   [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/rfc/rfc8640>.

   [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/rfc/rfc8641>.







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   [RFC9000]  Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/rfc/rfc9000>.

   [XPATH]    W3C, "XML Path Language (XPath) Version 1.0",
              <https://www.w3.org/TR/1999/REC-xpath-19991116/>.

Appendix A.  Functional changes between YANG Push v2 and YANG Push

   This non-normative section highlights the significant functional
   changes where the YANG Push v2 implementation differs from YANG Push.
   However, the main body of this document, from Section 4 onwards,
   provides the normative definition of the YANG Push v2 specification,
   except for any text or sections that explicitly indicate that they
   are informative rather being normative.

   _Note to reviewers: If you notice mistakes in this section during
   development of the document and solution then please point them out
   to the authors and the working group._ *(RFC editor, please remove
   this paragraph prior to publication)*

A.1.  Removed Functionality

   This section lists functionality specified in [RFC8639] and YANG Push
   which is not specified in YANG Push v2.

   *  Negotiation and hints of failed subscriptions.

   *  The RPC to modify an existing dynamic subscription, instead the
      subscription must be terminated and re-established.

   *  The ability to suspend and resume a dynamic subscription.  Instead
      a dynamic subscription is terminated if the device cannot reliably
      fulfill the subscription or a receiver is too slow causing the
      subscription to be back pressured.

   *  Specifying a subscription stop time, and the corresponding
      subscription-completed notification have been removed.

   *  Replaying of buffered event records are not supported, for both
      configured and dynamic subscriptions.  The nearest equivalent is
      requesting a sync-on-start replay when the subscription transport
      session comes up which will reply the current state.

   *  QoS weighting and dependency between subscriptions has been
      removed due to the complexity of implementation.




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   *  Support for reporting subscription error hints has been removed.
      The device SHOULD reject subscriptions that are likely to overload
      the device, but more onus is placed on the operator configuring
      the subscriptions or setting up the dynamic subscriptions to
      ensure that subscriptions are reasonable, as they would be
      expected to do for any other configuration.

   *  The "subscription-state-notif" extension has been removed.

   *  The YANG Patch format [RFC8072] is no longer used for on-change
      subscriptions.

   *  Support for multiple receivers for a configured subscription.

A.2.  Changed Functionality

   This section documents behavior that exists in both YANG Push and
   YANG Push v2, but the behavior differs between the two:

   *  All YANG Push v2 notifications messages use
      [I-D.draft-ietf-netconf-notif-envelope] rather than [RFC5277] used
      by YANG Push [RFC8641].

   *  There is a lot more alignment in data model, behavior, and state
      machined in YANG Push v2, aiming to minimize differences.

   *  Changes to handling receivers:

      -  Receivers are always configured separately from the
         subscription and are referenced.

      -  Transport and Encoding parameters are configured as part of a
         receiver definition, and are used by all subscriptions directed
         towards a given receiver.

      -  Encoding is now a mandatory parameter under a receiver and
         dynamic subscription (rather than specifying a default).

      -  Invoking the _reset_ RPC operation on a receiver requires and
         forces a reset of any transport sessions associated with that
         receiver.  Previously, the sessions would not be reset if they
         were used by other subscriptions.

      -  YANG Push v2 only supports a single receiver per subscription.







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   *  Periodic and on-change message uses a common _update_ notification
      message format, allowing for the messages to be processed by
      clients in a similar fashion and to support combined periodic and
      on-change subscriptions.

   *  Changes related to the configuration model:

      -  Subscriptions are identified by a string identifier rather than
         a numeric identifier.  The prefix 'dyn-' is reserved for
         publisher allocated dyanmic subscription ids.  Clients may
         provide the id to be used for dynamic subscriptions.  There is
         changed handling for conflicting subscription-ids between
         configured and dynamic.

      -  Purpose has been renamed to Description (since it is a more
         generic term), limited to 1k characters, but also available for
         dynamic subscriptions.

   *  On-change dampening:

      -  Client configurable on-change dampening has been removed.

      -  However, YANG Push v2 allows a publisher to limit the rate at
         which a data node is sampled for on-change notifications.  See
         Section 7.5.1 for further details.

   *  Dynamic subscriptions are no longer mandatory to implement, either
      or both of Configured and Dynamic Subscriptions may be implemented
      in YANG Push v2.

   *  The solution focuses solely on datastore subscriptions that each
      have their own event stream.  Filters cannot be applied to the
      event stream, only to the set of datastore data nodes that are
      monitored by the subscription.

   *  The lifecycle events of when a subscription-started or
      subscription-terminated may be sent differs from
      [RFC8639]/[RFC8641]:

      -  Subscription-started notifications are also sent for dynamic
         subscriptions.

   *  Some of the requirements on transport have been relaxed.

   *  The encoding identities have been extended with CBOR encodings,
      and the "encoding-" prefix has been removed (so that there is a
      better on the wire representation).




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   *  YANG Push v2 allows for a publisher to provide an eventually
      consistent distributed view of the operational datastore, rather
      than a fully consistent datastore where on-change updates are sent
      as logic diffs to that datastore.

A.3.  Added Functionality

   *  Device capabilities are reported via XXX and additional models
      that augment that data model.

   *  A new _update_ message:

      -  Covers both on-change and periodic events.

      -  Allows multiple updates to be sent in a single message (e.g.,
         for on-change).

      -  Allows for a common path prefix to be specified, with any paths
         and encoded YANG data to be encoded relative to the common path
         prefix.

   *  An _update-complete_ notification has been defined to inform
      collectors when a subscription's periodic collection cycle is
      complete.

   *  Support for {I-D.ietf-netconf-distributed-notif}} has been added
      to the base YANG Push v2 specification, as described in
      Section 12.

   *  TODO - More operational data on the subscription load and
      performance.

   *  All YANG Push v2 configuration is under a new _datastore-
      telemetry_ presence container

Appendix B.  Subscription Errors (from RFC 8641)

B.1.  RPC Failures

   Rejection of an RPC for any reason is indicated via an RPC error
   response from the publisher.  Valid RPC errors returned include both
   (1) existing transport-layer RPC error codes, such as those seen with
   NETCONF in [RFC6241] and (2) subscription-specific errors, such as
   those defined in the YANG data model.  As a result, how subscription
   errors are encoded in an RPC error response is transport dependent.






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   References to specific identities in the ietf-subscribed-
   notifications YANG module [RFC8639] or the ietf-yang-push YANG module
   may be returned as part of the error responses resulting from failed
   attempts at datastore subscription.  For errors defined as part of
   the ietf-subscribed-notifications YANG module, please refer to
   [RFC8639].  The errors defined in this document, grouped per RPC, are
   as follows:

         establish-subscription          modify-subscription
         ---------------------------     ---------------------
          cant-exclude                    period-unsupported
          datastore-not-subscribable      update-too-big
          on-change-unsupported           sync-too-big
          on-change-sync-unsupported      unchanging-selection
          period-unsupported
          update-too-big                 resync-subscription
          sync-too-big                   ----------------------------
          unchanging-selection            no-such-subscription-resync
                                          sync-too-big

   There is one final set of transport-independent RPC error elements
   included in the YANG data model.  These are the four yang-data
   structures for failed datastore subscriptions:

   1.  yang-data "establish-subscription-error-datastore": This MUST be
       returned if information identifying the reason for an RPC error
       has not been placed elsewhere in the transport portion of a
       failed "establish-subscription" RPC response.  This MUST be sent
       if hints are included.

   2.  yang-data "modify-subscription-error-datastore": This MUST be
       returned if information identifying the reason for an RPC error
       has not been placed elsewhere in the transport portion of a
       failed "modify-subscription" RPC response.  This MUST be sent if
       hints are included.

   3.  yang-data "sn:delete-subscription-error": This MUST be returned
       if information identifying the reason for an RPC error has not
       been placed elsewhere in the transport portion of a failed
       "delete-subscription" or "kill-subscription" RPC response.

   4.  yang-data "resync-subscription-error": This MUST be returned if
       information identifying the reason for an RPC error has not been
       placed elsewhere in the transport portion of a failed "resync-
       subscription" RPC response.






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B.2.  Failure Notifications

   A subscription may be unexpectedly terminated or suspended
   independently of any RPC or configuration operation.  In such cases,
   indications of such a failure MUST be provided.  To accomplish this,
   a number of errors can be returned as part of the corresponding
   subscription state change notification.  For this purpose, the
   following error identities are introduced in this document, in
   addition to those that were already defined in [RFC8639]:

     subscription-terminated        subscription-suspended
     ---------------------------    ----------------------
     datastore-not-subscribable     period-unsupported
     unchanging-selection           update-too-big
                                     synchronization-size

Appendix C.  Examples

   Notes on examples:

   *  To allow for programmatic validation, most notification examples
      in this section exclude the mandatory notification envelope and
      associated metadata defined in
      [I-D.draft-ietf-netconf-notif-envelope].  Only the full
      notification example in Section 7.1 includes the notification
      header.

   *  These notification message examples are given using a JSON
      encoding, but could be encoded using XML or CBOR.

   *  Some additional meta data fields, e.g., like those defined in
      [I-D.tgraf-netconf-notif-sequencing] would also likely be
      included, but have also been excluded to allow for slightly more
      concise examples.

   *  The examples include the
      [I-D.tgraf-netconf-yang-push-observation-time] field for the
      existing YANG-Push Notification format, and the proposed
      equivalent "observation-time" leaf for the new update notification
      format.

   *  All these examples are created by hand, may contain errors, and
      may not parse correctly.








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C.1.  Example of periodic update messages

   In this example, a subscription is for _/ietf-interfaces:interfaces/
   interface_.  However, for efficiency reasons, the publisher is
   internally returning the data from two different data providers.

   Of note:

   *  The first periodic message is published for the entries in the _/
      ietf-interfaces:interface/interfaces_ list, but doesn't contain
      the data in the _statistics_ child container.

   *  the _path-prefix_ is to the subscription subtree, since the device
      will never return data outside of the subscription subtree.

   *  the _target-path_ is elided because the data is returned at the
      subscription point. **TODO, or should it actually be to the
      element above? **

































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   {
     "ietf-yang-push-2:update": {
       "id": "interfaces",
       "path-prefix": "/ietf-interfaces:interfaces/interface",
       "snapshot-type": "periodic",
       "observation-time": "2024-10-10T08:00:05.11Z",
       "updates": [
         {
           "target-path": "",
           "merge": {
             "interface": [
               {
                 "name": "eth0",
                 "type": "iana-if-type:ethernetCsmacd",
                 "enabled": true,
                 "ietf-interfaces:oper-status": "up",
                 "ietf-interfaces:admin-status": "up"
               },
               {
                 "name": "eth1",
                 "type": "iana-if-type:ethernetCsmacd",
                 "enabled": true,
                 "ietf-interfaces:oper-status": "up",
                 "ietf-interfaces:admin-status": "up"
               }
             ]
           }
         }
       ],
       "complete": false
     }
   }

           Figure 27: Example periodic update for interfaces list

   For the second notification related to the same subscription:

   *  the second periodic message is published for only the statistics
      associated with the interfaces.

   *  as above, the _path-prefix_ is still to the subscription subtree.

   *  the second notification uses a separate observation-time, but
      would use the same event-time in the notification header so that
      the two messages can be correlated to the same periodic collection
      event.





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   *  the second periodic message has set the _complete_ flag to
      indicate that it is the last notification as part of the periodic
      collection.  A separate _update-complete_ notification could have
      been sent instead.

   {
     "ietf-yang-push-2:update": {
       "id": "interfaces",
       "path-prefix": "/ietf-interfaces:interfaces/interface",
       "snapshot-type": "periodic",
       "observation-time": "2024-10-10T08:00:05.21Z",
       "updates": [
         {
           "target-path": "",
           "merge": {
             "ietf-interfaces:interface": [
               {
                 "name": "eth0",
                 "statistics": {
                   "in-octets": 123456,
                   "out-octets": 654321
                 }
               },
               {
                 "name": "eth1",
                 "statistics": {
                   "in-octets": 789012,
                   "out-octets": 210987
                 }
               }
             ]
           }
         }
       ]
     }
   }

        Figure 28: Example periodic update for interface statistics

C.2.  Example of an on-change-update notification using the new style
      update message

   If the subscription is for on-change notifications, or periodic-and-
   on-change-notifications, then, if the interface state changed
   (specifically if the 'state' leaf of the interface changed state),
   and if the device was capable of generating on-change notifications,
   then you may see the following message.  A few points of notes here:




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   *  The on-change notification contains *all* of the state at the
      "target-path"

      -  Not present in the below example, but if the notification
         excluded some state under an interfaces list entry (e.g., the
         line-state leaf) then this would logically represent the
         implicit deletion of that field under the given list entry.

      -  In this example it is restricted to a single interface.  It
         could also publish an on-change notification for all
         interfaces, by indicating a target-path without any keys
         specified.  TODO - Can it represent notifications for a subset
         of interfaces?

   *  The schema of the change message is exactly the same as for the
      equivalent periodic message.  It doesn't use the YANG Patch format
      [RFC8072] for on-change messages.

   *  The "observation time" leaf represents when the system first
      observed the on-change event occurring.

   *  The on-change event doesn't differentiate the type of change to
      operational state.  The on-change-update snapshot type is used to
      indicate the creation of a new entry or some update to some
      existing state.  Basically, the message can be thought of as the
      state existing with some current value.

























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   <CODE BEGINS> file "on-change-msg.json"
   {
     "ietf-yp-notification:envelope": {
       "event-time": "2024-09-27T14:16:30.973Z",
       "hostname": "example-router",
       "sequence-number": 454,
       "contents": {
         "ietf-yp-ext:update": {
           "id": 1,
           "subscription-path":
             "Cisco-IOS-XR-pfi-im-cmd-oper:interfaces",
           "target-path":
             "Cisco-IOS-XR-pfi-im-cmd-oper:interfaces/interfaces/
             interface[interface=GigabitEthernet0/0/0/0]",
           "snapshot-type": "on-change-update"
           "observation-time": "2024-09-27T14:16:30.973Z",
           "datastore-snapshot": {
             "interfaces": {
               "interface": [
                 {
                   "interface-name": "GigabitEthernet0/0/0/0",
                   "interface": "GigabitEthernet0/0/0/0",
                   "state": "im-state-up",
                   "line-state": "im-state-up"
                 }
               ]
             }
           }
         }
       }
     }
   }
   <CODE ENDS>

          Figure 29: Example YANG Push v2 on-change update message

C.3.  Example of an on-change-delete notification using the new style
      update message

C.3.1.  Update message with single deleted data node

   If the interface was deleted, and if the system was capable of
   reporting on-change events for the delete event, then an on-change
   delete message would be encoded as per the following message.

   Of note:

   *  The ietf-yp-notification:envelope has been elided



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   *  The deleted data is identified by the target node in the _updates/
      target-path_ element.

   *  The observation time represents the time at which the delete event
      occurred, e.g., perhaps when the system processed a configuration
      change.

   {
     "ietf-yang-push-2:update": {
       "id": "interfaces",
       "snapshot-type": "on-change-delete",
       "observation-time": "2025-10-10T08:16:15.11Z",
       "updates": [
         {
           "target-path": "/ietf-interfaces:interfaces/interface[name='eth0']",
           "deleted": [null]
         }
       ]
     }
   }

          Figure 30: Example YANG Push v2 on-change delete message

C.3.2.  Update message with multiple on-change deletes

   This follow example illustrates how a single update notification
   message can contain multiple on-change delete events for different
   data nodes.  In this example, two separate interfaces are being
   deleted.

   Of note:

   *  The ietf-yp-notification:envelope has been elided

   *  _prefix-path_ is used to shorten the target-paths, the full paths
      can be constructed concatenating the _prefix-path_ with each
      _target-path_ in the _updates_ list.

   *  all delete events share a common observation-time of when the
      delete events occurred.  If it is necessary to identify separate
      observation times then the publisher would send separate messages.

   *  data node subtrees that are deleted (list entries in this case)
      are identified by separate entries in the _updates_ list.







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   {
     "ietf-yang-push-2:update": {
       "id": "interfaces",
       "path-prefix": "/ietf-interfaces:interfaces",
       "snapshot-type": "on-change-delete",
       "observation-time": "2025-10-10T08:16:16.11Z",
       "updates": [
         {
           "target-path": "interface[name='eth0']"
         },
         {
           "target-path": "interface[name='eth1']"
         }
       ]
     }
   }

          Figure 31: Example YANG Push v2 on-change delete message

C.4.  NETCONF Dynamic Subscription RPC examples

   The examples in this section illustrate NETCONF RPCs for establishing
   and deleting dynamic subscriptions using YANG Push v2.  The examples
   include one successfully establishing a subscription, and a second to
   illustrate how errors are returned if a request to establish the
   subscription fails.  Examples of the _update_ and subscription
   lifecycle notifications have been given in the previous section.

C.4.1.  Successful periodic subscription

   The subscriber sends an "establish-subscription" RPC with the
   parameters listed in Section 9.4.1 An example might look like:



















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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-yp-lite">
       <name>if-stats-sub</name>
       <description>Subscribe to interface statistics</description>
       <target>
         <datastore xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
           ds:operational
         </datastore>
         <path>/ietf-interfaces:interfaces/interface/statistics</path>
       </target>
       <update-trigger>
         <periodic>
           <period>3000</period>
         </periodic>
       </update-trigger>
       <encoding>json</encoding>
     </establish-subscription>
   </netconf:rpc>

        Figure 32: Example establish-subscription RPC for interface
                                 statistics

   If a publisher is happy to accept the subscription, then it returns a
   positive response that includes the "id" of the accepted
   subscription.  For example,

   <rpc-reply
   message-id="101" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <id xmlns="urn:ietf:params:xml:ns:yang:ietf-yp-lite">52</id>
   </rpc-reply>

       Figure 33: Example establish-subscription RPC successful reply

   Once established, the publisher would send a _subscription-started_
   notification message followed by _update_ notification messages at
   the requested periodic cadence.

C.4.2.  Failed periodic subscription

   A subscription can be rejected for multiple reasons, including the
   lack of authorization to establish a subscription, no capacity to
   serve the subscription at the publisher, or the inability of the
   publisher to select datastore content at the requested cadence.

   If a request is rejected because the publisher is not able to serve
   it, the publisher SHOULD include in the returned error hints that
   help a subscriber understand what subscription parameters might have



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   been accepted for the request.  These hints would be included in the
   yang-data structure "establish-subscription-error-datastore".
   However, even with these hints, there are no guarantees that
   subsequent requests will in fact be accepted.

   The specific parameters to be returned as part of the RPC error
   response depend on the specific transport that is used to manage the
   subscription.  For NETCONF, those parameters are defined in
   [RFC8640].  For example, for the following NETCONF request:

     <rpc message-id="101"
         xmlns="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:on-change>
         </yp:on-change>
       </establish-subscription>
     </rpc>

         Figure 12: "establish-subscription" Request: Example 2

   A publisher that cannot serve on-change updates but can serve
   periodic updates might return the following NETCONF response:


















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 <rpc-reply message-id="101"
   xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"
   xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
   <rpc-error>
     <error-type>application</error-type>
     <error-tag>operation-failed</error-tag>
     <error-severity>error</error-severity>
     <error-path>/yp:periodic/yp:period</error-path>
     <error-info>
       <yp:establish-subscription-error-datastore>
         <yp:reason>yp:on-change-unsupported</yp:reason>
       </yp:establish-subscription-error-datastore>
     </error-info>
   </rpc-error>
 </rpc-reply>

       Figure 13: "establish-subscription" Error Response: Example 2

C.4.3.  "delete-subscription" RPC

   To stop receiving updates from a subscription and effectively delete
   a subscription that had previously been established using an
   "establish-subscription" RPC, a subscriber can send a "delete-
   subscription" RPC, which takes as its only input the subscription's
   "id".  This RPC is unmodified from [RFC8639].

C.5.  Distributed Notifications Subscription

   This simple example illustrates how messages may look like when using
   distributed notifications, as described in Section 12.  This example
   is for a very simple periodic subscription to the ietf-interfaces
   YANG data model.

   The first message is a subscription started message that indicates
   that there are 2 additional _Publisher Agents_ with publisher-ids of
   4 and 7, e.g., perhaps representing a device with two linecards
   inserted into slots 4 and 7, each with their owner separate Message
   Publisher process.  This message has a publisher-id of 0 because it
   is sent by the Publisher Parent, which, because this field has the
   default value, could have been elided from the message.











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   {
     "ietf-yp-notification:envelope": {
       "event-time": "2025-10-10T08:00:05.22Z",
       "hostname": "example-router",
       "sequence-number": 23,
       "ietf-yang-push-2:publisher-id": 0
       "contents": {
         "ietf-yang-push-2:subscription-started": {
           "id": "interfaces",
           "target": {
             "datastore": "ietf-datastores:operational",
             "path": "/ietf-interfaces:interfaces"
           },
           "update-trigger": {
             "periodic": {
               "period": 3000,
               "anchor-time": "2025-01-01T00:00:00.00Z"
             }
           },
           "message-publishers": {
             "publisher-id" = [0, 4, 7]
           }
         }
       }
     }
   }

      Figure 34: Example distributed notification subscription started
                                  message

   The second message is an example of a periodic update message sent
   from one of the Publisher Agents on the linecard.  In this case the
   message is sent from the publisher agent on linecard 4, and it has
   set the _complete_ leaf to indicate that the message represents all
   data for that periodic collection from that publisher.
















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   {
     "ietf-yp-notification:envelope": {
       "event-time": "2025-10-10T08:00:05.22Z",
       "hostname": "example-router",
       "sequence-number": 18,
       "ietf-yang-push-2:publisher-id": 4
       "contents": {
         "ietf-yang-push-2:update": {
           "id": 1011,
           "snapshot-type": "periodic",
           "observation-time": "2025-10-10T08:00:05.11Z",
           "updates": [
             {
               "target-path": "ietf-interfaces:interfaces/interface",
               "merge": {
                 "ietf-interfaces:interfaces": {
                   "ietf-interfaces:interface": [
                     {
                       "name": "eth4/0",
                       "type": "iana-if-type:ethernetCsmacd",
                       "enabled": true,
                       "ietf-interfaces:oper-status": "up",
                       "ietf-interfaces:admin-status": "up"
                     },
                     {
                       "name": "eth4/1",
                       "type": "iana-if-type:ethernetCsmacd",
                       "enabled": true,
                       "ietf-interfaces:oper-status": "down",
                       "ietf-interfaces:admin-status": "up"
                     }
                   ]
                 }
               }
             }
           ],
           complete = true
         }
       }
     }
   }

         Figure 35: Example distributed notification update message

   Not shown here, but because there were 3 publisher-ids listed in the
   subscription-started message means that each Message Publisher must
   send at least one message for each periodic subscription returning
   any data associated with the subscription from that Message Publisher



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   and also indicating that the periodic collection is complete by
   either setting complete = true or sending an _update-complete_
   notification.

Appendix D.  Summary of Open Issues & Potential Enhancements

   This temporary section lists open issues and enhancements that
   require further discussion by the authors, or the WG.  Once adopted,
   it is anticipated that tracking the open issues would move to github.

   The issues are ordered/grouped by the sections in the current
   document.  I.e., to make it easier to review/update sections of the
   document.

D.1.  Issues related to general IETF process

   1.  If this work progresses we will need simple bis versions of the
       transports document so that they augment into the new data model
       paths.  Drafts that would need to be updated as documented in
       Section 3.4.  Issue 27 (https://github.com/rgwilton/draft-yp-
       observability/issues/27)

   2.  Do we need to fold in any text from RFC 8640? and RESTCONF?
       Issue 26 (https://github.com/rgwilton/draft-yp-observability/
       issues/26)

D.2.  Issue related to Terminology/Definitions

   1.  Should we use the object terminology?  Tracked as editorial, in
       Issue 15 (https://github.com/rgwilton/draft-yp-observability/
       issues/15)

D.3.  Issues related to YANG Push v2 Overview

   None currently.

D.4.  Issues related to Subscription Paths and Selection Filters

   1.  This draft introduces a new simple yang path (ypath) format that
       is like a JSON instance data path, that all implementations MUST
       support.  Issue 29 (https://github.com/rgwilton/draft-yp-
       observability/issues/29)

   2.  Advertising subscription schema: Issue 11
       (https://github.com/rgwilton/draft-yp-observability/issues/11)






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D.5.  Issues related to Datastore Event Streams & message format

   1.  Agree format and usage of _update_ notification.  Issue 32
       (https://github.com/rgwilton/draft-yp-observability/issues/32)

D.6.  Issues related to Receivers, Transports, & Encodings

D.6.1.  Issues related to Transports:

   1.  James: We also need to add some text into security section.

       *  Rob: Is this transport specific, or related to application
          layer authorization?

   2.  What is the rules/restrictions for subscription receiver
       instances vs transport sessions?  E.g., is this entirely down to
       the transport to define.

D.7.  Issues related to Setting up & Managing Subscriptions

D.7.1.  Issues related to the configuration model:

   1.  YP Lite is somewhat different (separate namespace, separate
       receivers, no event filters, some config has moved to a separate
       receivers list).  See the data model and Appendix A.  Note some
       of these apply or impact dynamic subscriptions as well.  Issue 30
       (https://github.com/rgwilton/draft-yp-observability/issues/30)

D.7.2.  Issues related to dynamic subscriptions:

   1.  Do we want to change how RPC errors are reported?  E.g., change
       the RPC ok response to indicate whether the subscription was
       successfully created or not, or included extra error information.
       Note NETCONF and RESTCONF already define how errors are encoded
       in XML and JSON (for RESTCONF only), is it possible to unify this
       so we don't need large extra separate documents.

D.8.  Issues related to Subscription Lifecycle

   1.  Should subscription-started notification include a fingerprint of
       the schema that is covered by the subscription that would
       guaranteed to change if the subscription changes?  Issue 11
       (https://github.com/rgwilton/draft-yp-observability/issues/11)








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   2.  If a subscription references a filter, then should that be
       included inline in the subscription started notification (as per
       the RFC 8641 text), or should it indicate that it is a referenced
       filter?  Issue 20 (https://github.com/rgwilton/draft-yp-
       observability/issues/20)

   3.  Is a publisher allowed to arbitrarily send a sync-on-start
       resync, e.g., if it detects data loss, or should it always just
       terminate and reinitialize the subscription?  Issue 22
       (https://github.com/rgwilton/draft-yp-observability/issues/22)

   4.  Should we have a YANG Action to reset a receiver or a
       subscription?  E.g., discussed in Section 9.3.4.  Issue 24
       (https://github.com/rgwilton/draft-yp-observability/issues/24)

   5.  Should we support configurable subscription-level keepalives?
       Issue 14 (https://github.com/rgwilton/draft-yp-observability/
       issues/14)

D.9.  Issues related to Performance, Reliability & Subscription
      Monitoring

D.9.1.  Issues/questions related to operational data:

   1.  Should we define some additional operational data to help
       operators check that the telemetry infrastructure is performing
       correctly, to get an approximation of the load, etc.

       *  Rob: probably, but lower priority.

       *  Tracked by Issue 31 (https://github.com/rgwilton/draft-yp-
          observability/issues/31)

   2.  Should dynamic subscriptions use the same receivers structure as
       for configured subscriptions, or should they be inline in the
       configured subscription?  Also tracked by Issue 31
       (https://github.com/rgwilton/draft-yp-observability/issues/31)

D.10.  Issues related to Conformance and Capabilities

   1.  Do we advertise that conformance via capabilities and/or YANG
       features (both for configured and dynamic subscriptions)?

   2.  For on-change, should a subscription be rejected (or not brought
       up) if there are no on-change notifiable nodes?






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   3.  Further work and discussion is required for advertising
       capabilities for filter paths.  E.g., listing all of the paths
       that support on-change could be a very long list.  Related, does
       the draft need to advertise at what points a publisher would
       decompose a higher subscription into more specific subscriptions.

   All tracked via Issue 18 (https://github.com/rgwilton/draft-yp-
   observability/issues/18)

D.11.  Issues related to the YANG Modules

   None open.

D.12.  Issues related to the Security Considerations (& NACM filtering)

   1.  Need to consider how NACM applies to YANG Push v2, which may
       differ for dynamic vs configured subscription, but generally we
       want the permissions to be checked when the subscription is
       created rather than each time a path is accessed.

   2.  Where should this be in the document (current it in the security
       considerations section)

   3.  Do we want to retain the the current text in Section 7
       introduction related to terminating a subscription if permissions
       change?

   4.  Also note, text was removed from the transport section related to
       RPC authorization, and which should be moved to an application
       (rather than transport) layer security mechanism.

   All tracked via Issue 33 (https://github.com/rgwilton/draft-yp-
   observability/issues/33)

D.13.  Issues related to the IANA

   None open.

D.14.  Issues related to the Appendixes

D.14.1.  Examples related issues/questions:

   1.  Not a question, but a note that many examples need to be updated
       to reflect the data models currently in the draft.







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D.15.  Summary of closed/resolved issues

   This appendix is only intended while the authors/WG are working on
   the document, and should be deleted prior to WG LC.

   1.   Rename subscription-terminated to subscription-stopped (Change
        rejected 21 Feb 25, unnecessary renaming.)

   2.   MUST use envelope, hostname and sequence-number (and event-time)
        (Decided 21 Feb 25)

   3.   Don't mandate configured or dynamic subscriptions, allow
        implementations to implement one or both of them.  (Decided 21
        Feb 25)

   4.   Dynamic subscriptions require the encoding to be specified.
        (Decided 21 Feb 25)

   5.   DSCP settings are only specified under the receiver (for
        configured subscriptions) (Decided 21 Feb 25)

   6.   Config and dynamic subscriptions should be aligned as much as
        possible.

   7.   If subscription parameters change then force subscription down
        and up again, issue 14 (https://github.com/rgwilton/draft-yp-
        observability/issues/14)

   8.   No RPC to modify a dynamic subscription, use delete-subscription
        then create-subscription.

   9.   Lifecycle messages are sent per subscription rather than per
        receiver, and we only support a single receiver per
        subscription.

   10.  Encoding is set per subscription, and we don't allow different
        per-receiver encodings for a subscription with more than one
        receiver.  issue 17 (https://github.com/rgwilton/draft-yp-
        observability/issues/17)

   11.  We have a updated-completed flag/notification to allow deleted
        data to be implicitly detected.  Something similar may be added
        to gNMI.  issue 12 (https://github.com/rgwilton/draft-yp-
        observability/issues/12)







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   12.  We use a string identifier to uniquely identify a subscription
        rather than a numeric id.  Reserve 'dyn-' for server allocated
        dynamic subscription ids.  Agreed config/dynamic conflict
        policy.  Restricted names for fitler-id and receiver name.
        Don't use a union type (could be added in future).  (Dec 8th)

   13.  Draft renamed from Yang Push Lite to Yang Push 2.  (Dec 8th)

   14.  ietf-yp2-config no longer augments dynamic subscriptions with a
        reference to a configured filter issue 19
        (https://github.com/rgwilton/draft-yp-observability/issues/19)

   15.  Publisher MUST NOT send more notifications after a subscription
        terminated message Issue 13 (https://github.com/rgwilton/draft-
        yp-observability/issues/13).

   16.  on-change notifications SHOULD send a minimal update but MAY
        send additional unchanged fields.

Authors' Addresses

   Robert Wilton (editor)
   Cisco Systems
   Email: rwilton@cisco.com


   Holger Keller
   Deuetsche Telekom
   Email: Holger.Keller@telekom.de


   Benoit Claise
   Everything OPS
   Email: benoit@everything-ops.net


   Ebben Aries
   Juniper
   Email: exa@juniper.net


   James Cumming
   Nokia
   Email: james.cumming@nokia.com


   Thomas Graf
   Swisscom



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   Email: Thomas.Graf@swisscom.com


















































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