Network Working Group T. Graf Internet-Draft Swisscom Intended status: Standards Track B. Claise Expires: 16 August 2026 Huawei A. Huang-Feng INSA-Lyon 12 February 2026 Support of Versioning in YANG Notifications Subscription draft-ietf-netconf-yang-notifications-versioning-11 Abstract This document extends the YANG-Push Subscription mechanism to enforce that particular revisions or semantic versions are used when configuring or establishing a Subscription. It also extends the YANG-Push Subscription state change Notifications with additional context regarding the YANG schema associated with the Subscription. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 16 August 2026. Copyright Notice Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved. Graf, et al. Expires 16 August 2026 [Page 1] Internet-Draft YANG Notifications Versioning February 2026 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2. Subscription Policy Extension . . . . . . . . . . . . . . . . 4 3. Subscription State Change Notification Extension . . . . . . 8 4. Discovering "ietf-yang-push-revision" Support . . . . . . . . 10 5. The "ietf-yang-push-revision" Module . . . . . . . . . . . . 11 5.1. Data Model Overview . . . . . . . . . . . . . . . . . . . 12 5.2. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 22 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 6.1. IETF XML Registry . . . . . . . . . . . . . . . . . . . . 28 6.2. YANG Module Name . . . . . . . . . . . . . . . . . . . . 28 7. Operational Considerations . . . . . . . . . . . . . . . . . 28 8. Implementation Status . . . . . . . . . . . . . . . . . . . . 29 8.1. Huawei VRP . . . . . . . . . . . . . . . . . . . . . . . 29 8.2. 6WIND VSR . . . . . . . . . . . . . . . . . . . . . . . . 30 8.3. Cisco IOS XR . . . . . . . . . . . . . . . . . . . . . . 30 9. Security Considerations . . . . . . . . . . . . . . . . . . . 30 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 31 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 31 11.1. Normative References . . . . . . . . . . . . . . . . . . 31 11.2. Informative References . . . . . . . . . . . . . . . . . 33 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34 1. Introduction In order to process the YANG-Push Notification messages described in Section 3.7 of [RFC8641] at the YANG-Push Receiver, the Publisher's instance of ietf-yang-library [RFC8525] needs to be queried each time a Subscription state change Notification, as described in Section 2.7 of [RFC8639], is being received to understand whether the YANG module(s) semantic has changed. To notify the Receiver whether the YANG module(s) semantic has changed, a semantic reference to the YANG modules and the XPath or subtree in the Subscription state change Notifications is needed. Graf, et al. Expires 16 August 2026 [Page 2] Internet-Draft YANG Notifications Versioning February 2026 This specification is primarily aimed for YANG-Push Configured Subscription, as defined in Section 2.5 of [RFC8639], since the schema of a YANG-Push Publisher datastore could change after a Configured Subscription has been established and the 'subscription- started' Notification has already been sent to the Receiver. Without the mechanism described in Section 2 and Section 3, a subscriber is unable to control the supported YANG module revision or version nor would the YANG-Push Receiver be notified of changes in YANG module revision or version in the YANG-Push Subscription. Although this mechanism is primarily designed for YANG-Push Configured Subscriptions, the extensions defined in Section 3 for 'subscription- started' are also applicable to Dynamic Subscriptions as defined in Section 2.4 of [RFC8639]. This semantic reference is available when the Subscription is established as described in Section 2.4 and 2.5 of [RFC8639] and being streamed from the Publisher to the Receiver with the Subscription state change Notifications, as described in Section 2.7 of [RFC8639]. For each Subscription, a locally unique Subscription ID, as described in Section 4.3.2 of [RFC8641], is issued and streamed as metadata with the Notification message in the YANG-Push message header. The YANG module version statement is specified in Section 7.1.2 of [RFC7950] and states that the newer revision needs to be backward compatible to the previous revision. Section 3.1 of [I-D.ietf-netmod-yang-module-versioning] specifies that newer semantic versions introduced in [I-D.ietf-netmod-yang-semver] MAY not be backward compatible to the previous version when indicated with non-backwards-compatible keyword. The YANG Notifications Subscription mechanism defined in [RFC8641] does not include the YANG module revision. Hence, when a network node is upgraded, the subscribed YANG module revision might have changed, and might consequently break the data processing pipeline since the YANG-Push Receiver may not be aware of this change. This document extends the current YANG Notifications Subscription mechanism to allow Subscriptions to a specific revision or latest YANG module semantic version to which the YANG module version needs to be backward compatible to. Graf, et al. Expires 16 August 2026 [Page 3] Internet-Draft YANG Notifications Versioning February 2026 The Subscription state change 'subscription-started' and 'subscription-modified' Notification messages are also extended to include the YANG module revision, version, and YANG library content- id. Changes in the revision and version fields allow a YANG-Push Receiver to detect whenever the subscribed YANG module has changed. Changes in yang-library-content-id indicates that YANG module(s) on the network management Server of the YANG-Push Publisher has or have changed. 1.1. Terminology 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. The terms "subscriber", "subscription", "dynamic subscription", "configured subscription", "publisher", "receiver" and "notification message" are used as defined in [RFC8639]. The terms "client", and "server" are used as defined in [RFC8342]. The terms "YANG library" and "YANG library content identifier" are used as defined in [RFC8525]. 2. Subscription Policy Extension The ability to configure or establish a Dynamic Subscription can be constrained to particular module versions or revisions using the following fields that are defined in the 'ietf-yang-push-revision' YANG module: module: Restricts the Subscription to one or more YANG module names on the Subscription path with revision and version together for the related streamed content. revision: Restricts the Subscription to a specific YANG module revision. Example: "2014-05-08". version: Restricts the Subscription to the latest compatible YANG module semantic version referenced to. Example: "2.0.0". Graf, et al. Expires 16 August 2026 [Page 4] Internet-Draft YANG Notifications Versioning February 2026 When a NETCONF client creates or modifies a Subscription, either by updating the Subscription configuration or by invoking the 'establish-subscription' or 'modify-subscription' RPCs, and the NETCONF server does not support the specified revision or version in the request, the server MUST return an RPC reply containing an element as defined in Section 4.3 of [RFC6241], with the error information populated as follows: * an "error-type" node of "application". * an "error-tag" node whose value is a string that corresponds to an identity associated with the error. +===================================+==================+ | Error identity | Uses "error-tag" | +===================================+==================+ | revision-unsupported | invalid-value | +-----------------------------------+------------------+ | version-unsupported | invalid-value | +-----------------------------------+------------------+ | incompatible-revision-and-version | invalid-value | +-----------------------------------+------------------+ Table 1: General Subscription Error Identities and Associated "error-tag" Use Figure 1 provides an example of a Dynamic periodic YANG-Push "establish-subscription" RPC call with YANG revision and datastore- xpath-filter. Figure 2 shows the response when the RPC has been accepted by the NETCONF Server and Figure 3 the error sent by the NETCONF Server when the revision is not supported. Graf, et al. Expires 16 August 2026 [Page 5] Internet-Draft YANG Notifications Versioning February 2026 ds:operational /ex:foo foo 2023-09-17 500 Figure 1: Dynamic YANG-Push subscription 52 Figure 2: RPC Example for a positive establish-subscription response Graf, et al. Expires 16 August 2026 [Page 6] Internet-Draft YANG Notifications Versioning February 2026 application operation-failed error ypr:revision-unsupported Figure 3: RPC Example for an error establish-subscription response Figure 4 provides an example of configured periodic YANG-Push Subscription with YANG revision and datastore-xpath-filter. =============== NOTE: '\' line wrapping per RFC 8792 ================ 53 ds:operational /if:interfaces Graf, et al. Expires 16 August 2026 [Page 7] Internet-Draft YANG Notifications Versioning February 2026 ietf-interfaces 2018-02-20 unt:udp-notif encode-json subscription-specific-receiver-def global-udp-notif-receiver-def 6000 global-udp-notif-receiver-def
192.0.5.1
12345 true Figure 4: Configured YANG-Push subscription The YANG-Push Publisher MUST NOT send Notifications if the 'revision' or 'version' of the YANG module name in the Subscription policy configuration does not match with the YANG library [RFC8525]. 3. Subscription State Change Notification Extension Besides the Subscription ID and the xpath or subtree filter reference as described in Section 2.7 of [RFC8639], the following metadata objects are part of a 'subscription-started' or 'subscription- modified' Subscription state change Notifications. module: Describes the YANG module names from the Subscription path Graf, et al. Expires 16 August 2026 [Page 8] Internet-Draft YANG Notifications Versioning February 2026 for the related streamed content. revision: Describes the YANG module revision as specified in Section 7.1.9 of [RFC7950] for the related streamed content. version: Describes the YANG module semantic version as specified in [I-D.ietf-netmod-yang-semver] for the related streamed content. yang-library-content-id: Contains the YANG library content identifier [RFC8525] which is an implementation-specific identifier representing the current information in the YANG library on a specific Server. Figure 5 provides an example of a 'subscription-modified' Subscription state change Notification message with the YANG module name, revision, version and datastore-xpath-filter for tracking the operational status of a single Ethernet interface (per [RFC8343]). This Subscription state change Notification message is encoded in XML [W3C.REC-xml-20081126] over the Network Configuration Protocol (NETCONF) as per [RFC8640]. 2023-01-03T10:00:00Z 101 /int:interfaces NETCONF ietf-interfaces 2018-02-20 2.0.0 1 Figure 5: XML Push Example for a subscription-modified Notification message Figure 6 provides an example of a JSON encoded, [RFC8259], Subscription state change Notification message over HTTPS-based [I-D.ietf-netconf-https-notif] or UDP-based [I-D.ietf-netconf-udp-notif] transport for the same Subscription. Graf, et al. Expires 16 August 2026 [Page 9] Internet-Draft YANG Notifications Versioning February 2026 { "ietf-restconf:notification" : { "eventTime": "2023-01-03T10:00:00Z", "ietf-subscribed-notifications:subscription-modified": { "id": 101, "stream-xpath-filter": "/ietf-interfaces:interfaces", "stream": "NETCONF", "ietf-yang-push-revision:module-version": [ { "name": "ietf-interfaces", "revision": "2018-02-20", "version": "2.0.0", } ], "ietf-yang-push-revision:yang-library-content-id": "1", } } } Figure 6: JSON Push Example for a subscription-modified Notification message 4. Discovering "ietf-yang-push-revision" Support A Client can discover whether the Server supports the 'ietf-yang- push-revision' model through the capabilities model defined in [RFC9196]. This document extends the 'ietf-notification- capabilities' model [RFC9196] with: * A leaf 'yang-push-module-revision-supported', stating that the YANG-Push Subscription state change Notifications are extended with 'revision', 'version' and 'yang-library-content-id' extensions. The YANG models defined in Section 5.2 augments the 'ietf- notification-capabilities' model with the leaf listed above. Graf, et al. Expires 16 August 2026 [Page 10] Internet-Draft YANG Notifications Versioning February 2026 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 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 ypr:yang-push-module-revision-supported? boolean This model can be retrieved via a NETCONF RPC. 5. The "ietf-yang-push-revision" Module Graf, et al. Expires 16 August 2026 [Page 11] Internet-Draft YANG Notifications Versioning February 2026 5.1. Data Model Overview This 'ietf-yang-push-revision' YANG module augments the 'ietf- subscribed-notifications' module with the 'name', 'revision', 'version' and 'yang-library-content-id' in the 'subscription-started' and 'subscription-modified' Subscription state change Notifications and the ability to define the 'revision' and 'version' in the 'establish-subscription' and 'modify-subscription' RPCs in the datastore push Subscription. 5.1.1. Tree View The following is the YANG tree diagram [RFC8340] for the 'ietf-yang- push-revision' YANG module Graf, et al. Expires 16 August 2026 [Page 12] Internet-Draft YANG Notifications Versioning February 2026 module: ietf-yang-push-revision augment /sn:establish-subscription/sn:input: +---w module-version-subs* [name] +---w name yang:yang-identifier +---w (revision-version)? +--:(revision) | +---w revision? rev:revision-date +--:(version) +---w version? ysver:version augment /sn:modify-subscription/sn:input: +---w module-version-subs* [name] +---w name yang:yang-identifier +---w (revision-version)? +--:(revision) | +---w revision? rev:revision-date +--:(version) +---w version? ysver:version augment /sn:subscription-started: +--ro module-version* [name] | +--ro name yang:yang-identifier | +--ro revision rev:revision-date | +--ro version? ysver:version +--ro yang-library-content-id? -> /yanglib:yang-library/content-id augment /sn:subscription-modified: +--ro module-version* [name] | +--ro name yang:yang-identifier | +--ro revision rev:revision-date | +--ro version? ysver:version +--ro yang-library-content-id? -> /yanglib:yang-library/content-id augment /sn:subscriptions/sn:subscription: +--rw module-version-subs* [name] +--rw name yang:yang-identifier +--rw (revision-version)? +--:(revision) | +--rw revision? rev:revision-date +--:(version) +--rw version? ysver:version augment /sysc:system-capabilities/notc:subscription-capabilities: +--ro yang-push-module-revision-supported? boolean 5.1.2. Full Tree View The following is the YANG tree diagram [RFC8340] for the 'ietf-yang- push-revision' augmentation within the 'ietf-subscribed- notifications', including the RPCs and Notifications. Graf, et al. Expires 16 August 2026 [Page 13] Internet-Draft YANG Notifications Versioning February 2026 module: ietf-subscribed-notifications +--ro streams | +--ro stream* [name] | +--ro name string | +--ro description? string | +--ro replay-support? empty {replay}? | +--ro replay-log-creation-time yang:date-and-time | | {replay}? | +--ro replay-log-aged-time? yang:date-and-time | {replay}? +--rw filters | +--rw stream-filter* [name] | | +--rw name string | | +--rw (filter-spec)? | | +--:(stream-subtree-filter) | | | +--rw stream-subtree-filter? {subtree}? | | +--:(stream-xpath-filter) | | +--rw stream-xpath-filter? yang:xpath1.0 {xpath}? | +--rw yp:selection-filter* [filter-id] | +--rw yp:filter-id string | +--rw (yp:filter-spec)? | +--:(yp:datastore-subtree-filter) | | +--rw yp:datastore-subtree-filter? | | {sn:subtree}? | +--:(yp:datastore-xpath-filter) | +--rw yp:datastore-xpath-filter? yang:xpath1.0 | {sn:xpath}? +--rw subscriptions +--rw subscription* [id] +--rw id | subscription-id +--rw (target) | +--:(stream) | | +--rw (stream-filter)? | | | +--:(by-reference) | | | | +--rw stream-filter-name | | | | stream-filter-ref | | | +--:(within-subscription) | | | +--rw (filter-spec)? | | | +--:(stream-subtree-filter) | | | | +--rw stream-subtree-filter? | | | | {subtree}? | | | +--:(stream-xpath-filter) | | | +--rw stream-xpath-filter? | | | yang:xpath1.0 {xpath}? | | +--rw stream | | | stream-ref | | +--ro replay-start-time? Graf, et al. Expires 16 August 2026 [Page 14] Internet-Draft YANG Notifications Versioning February 2026 | | | yang:date-and-time {replay}? | | +--rw configured-replay? empty | | {configured,replay}? | +--:(yp:datastore) | +--rw yp:datastore | | identityref | +--rw (yp:selection-filter)? | +--:(yp:by-reference) | | +--rw yp:selection-filter-ref | | selection-filter-ref | +--:(yp:within-subscription) | +--rw (yp:filter-spec)? | +--:(yp:datastore-subtree-filter) | | +--rw yp:datastore-subtree-filter? | | {sn:subtree}? | +--:(yp:datastore-xpath-filter) | +--rw yp:datastore-xpath-filter? | yang:xpath1.0 {sn:xpath}? +--rw stop-time? | yang:date-and-time +--rw dscp? | inet:dscp {dscp}? +--rw weighting? uint8 | {qos}? +--rw dependency? | subscription-id {qos}? +--rw transport? | transport {configured}? +--rw encoding? | encoding +--rw purpose? string | {configured}? +--rw (notification-message-origin)? {configured}? | +--:(interface-originated) | | +--rw source-interface? | | if:interface-ref {interface-designation}? | +--:(address-originated) | +--rw source-vrf? | | -> /ni:network-instances/network-instance/name | | {supports-vrf}? | +--rw source-address? | inet:ip-address-no-zone +--ro configured-subscription-state? | enumeration {configured}? +--rw receivers | +--rw receiver* [name] | +--rw name string | +--ro sent-event-records? Graf, et al. Expires 16 August 2026 [Page 15] Internet-Draft YANG Notifications Versioning February 2026 | | yang:zero-based-counter64 | +--ro excluded-event-records? | | yang:zero-based-counter64 | +--ro state enumeration | +---x reset {configured}? | +--ro output | +--ro time yang:date-and-time +--rw (yp:update-trigger)? | +--:(yp:periodic) | | +--rw yp:periodic! | | +--rw yp:period centiseconds | | +--rw yp:anchor-time? yang:date-and-time | +--:(yp:on-change) {on-change}? | +--rw yp:on-change! | +--rw yp:dampening-period? centiseconds | +--rw yp:sync-on-start? boolean | +--rw yp:excluded-change* change-type +--rw ypr:module-version-subs* [name] +--rw ypr:name yang:yang-identifier +--rw (ypr:revision-version)? +--:(ypr:revision) | +--rw ypr:revision? rev:revision-date +--:(ypr:version) +--rw ypr:version? ysver:version rpcs: +---x establish-subscription | +---w input | | +---w (target) | | | +--:(stream) | | | | +---w (stream-filter)? | | | | | +--:(by-reference) | | | | | | +---w stream-filter-name | | | | | | stream-filter-ref | | | | | +--:(within-subscription) | | | | | +---w (filter-spec)? | | | | | +--:(stream-subtree-filter) | | | | | | +---w stream-subtree-filter? | | | | | | {subtree}? | | | | | +--:(stream-xpath-filter) | | | | | +---w stream-xpath-filter? | | | | | yang:xpath1.0 {xpath}? | | | | +---w stream | | | | | stream-ref | | | | +---w replay-start-time? | | | | yang:date-and-time {replay}? | | | +--:(yp:datastore) | | | +---w yp:datastore Graf, et al. Expires 16 August 2026 [Page 16] Internet-Draft YANG Notifications Versioning February 2026 | | | | identityref | | | +---w (yp:selection-filter)? | | | +--:(yp:by-reference) | | | | +---w yp:selection-filter-ref | | | | selection-filter-ref | | | +--:(yp:within-subscription) | | | +---w (yp:filter-spec)? | | | +--:(yp:datastore-subtree-filter) | | | | +---w yp:datastore-subtree-filter? | | | | {sn:subtree}? | | | +--:(yp:datastore-xpath-filter) | | | +---w yp:datastore-xpath-filter? | | | yang:xpath1.0 {sn:xpath}? | | +---w stop-time? | | | yang:date-and-time | | +---w dscp? | | | inet:dscp {dscp}? | | +---w weighting? | | | uint8 {qos}? | | +---w dependency? | | | subscription-id {qos}? | | +---w encoding? | | | encoding | | +---w (yp:update-trigger)? | | | +--:(yp:periodic) | | | | +---w yp:periodic! | | | | +---w yp:period centiseconds | | | | +---w yp:anchor-time? yang:date-and-time | | | +--:(yp:on-change) {on-change}? | | | +---w yp:on-change! | | | +---w yp:dampening-period? centiseconds | | | +---w yp:sync-on-start? boolean | | | +---w yp:excluded-change* change-type | | +---w ypr:module-version-subs* [name] | | +---w ypr:name yang:yang-identifier | | +---w (ypr:revision-version)? | | +--:(ypr:revision) | | | +---w ypr:revision? rev:revision-date | | +--:(ypr:version) | | +---w ypr:version? ysver:version | +--ro output | +--ro id subscription-id | +--ro replay-start-time-revision? yang:date-and-time | {replay}? +---x modify-subscription | +---w input | +---w id | | subscription-id Graf, et al. Expires 16 August 2026 [Page 17] Internet-Draft YANG Notifications Versioning February 2026 | +---w (target) | | +--:(stream) | | | +---w (stream-filter)? | | | +--:(by-reference) | | | | +---w stream-filter-name | | | | stream-filter-ref | | | +--:(within-subscription) | | | +---w (filter-spec)? | | | +--:(stream-subtree-filter) | | | | +---w stream-subtree-filter? | | | | {subtree}? | | | +--:(stream-xpath-filter) | | | +---w stream-xpath-filter? | | | yang:xpath1.0 {xpath}? | | +--:(yp:datastore) | | +---w yp:datastore | | | identityref | | +---w (yp:selection-filter)? | | +--:(yp:by-reference) | | | +---w yp:selection-filter-ref | | | selection-filter-ref | | +--:(yp:within-subscription) | | +---w (yp:filter-spec)? | | +--:(yp:datastore-subtree-filter) | | | +---w yp:datastore-subtree-filter? | | | {sn:subtree}? | | +--:(yp:datastore-xpath-filter) | | +---w yp:datastore-xpath-filter? | | yang:xpath1.0 {sn:xpath}? | +---w stop-time? | | yang:date-and-time | +---w (yp:update-trigger)? | | +--:(yp:periodic) | | | +---w yp:periodic! | | | +---w yp:period centiseconds | | | +---w yp:anchor-time? yang:date-and-time | | +--:(yp:on-change) {on-change}? | | +---w yp:on-change! | | +---w yp:dampening-period? centiseconds | +---w ypr:module-version-subs* [name] | +---w ypr:name yang:yang-identifier | +---w (ypr:revision-version)? | +--:(ypr:revision) | | +---w ypr:revision? rev:revision-date | +--:(ypr:version) | +---w ypr:version? ysver:version +---x delete-subscription | +---w input Graf, et al. Expires 16 August 2026 [Page 18] Internet-Draft YANG Notifications Versioning February 2026 | +---w id subscription-id +---x kill-subscription +---w input +---w id subscription-id notifications: +---n replay-completed {replay}? | +--ro id subscription-id +---n subscription-completed {configured}? | +--ro id subscription-id +---n subscription-modified | +--ro id | | subscription-id | +--ro (target) | | +--:(stream) | | | +--ro (stream-filter)? | | | | +--:(by-reference) | | | | | +--ro stream-filter-name | | | | | stream-filter-ref | | | | +--:(within-subscription) | | | | +--ro (filter-spec)? | | | | +--:(stream-subtree-filter) | | | | | +--ro stream-subtree-filter? | | | | | {subtree}? | | | | +--:(stream-xpath-filter) | | | | +--ro stream-xpath-filter? | | | | yang:xpath1.0 {xpath}? | | | +--ro stream | | | | stream-ref | | | +--ro replay-start-time? | | | yang:date-and-time {replay}? | | +--:(yp:datastore) | | +--ro yp:datastore | | | identityref | | +--ro (yp:selection-filter)? | | +--:(yp:by-reference) | | | +--ro yp:selection-filter-ref | | | selection-filter-ref | | +--:(yp:within-subscription) | | +--ro (yp:filter-spec)? | | +--:(yp:datastore-subtree-filter) | | | +--ro yp:datastore-subtree-filter? | | | {sn:subtree}? | | +--:(yp:datastore-xpath-filter) | | +--ro yp:datastore-xpath-filter? | | yang:xpath1.0 {sn:xpath}? | +--ro stop-time? | | yang:date-and-time Graf, et al. Expires 16 August 2026 [Page 19] Internet-Draft YANG Notifications Versioning February 2026 | +--ro dscp? | | inet:dscp {dscp}? | +--ro weighting? uint8 | | {qos}? | +--ro dependency? | | subscription-id {qos}? | +--ro transport? | | transport {configured}? | +--ro encoding? | | encoding | +--ro purpose? string | | {configured}? | +--ro (yp:update-trigger)? | | +--:(yp:periodic) | | | +--ro yp:periodic! | | | +--ro yp:period centiseconds | | | +--ro yp:anchor-time? yang:date-and-time | | +--:(yp:on-change) {on-change}? | | +--ro yp:on-change! | | +--ro yp:dampening-period? centiseconds | | +--ro yp:sync-on-start? boolean | | +--ro yp:excluded-change* change-type | +--ro ypr:module-version* [name] | | +--ro ypr:name yang:yang-identifier | | +--ro ypr:revision rev:revision-date | | +--ro ypr:version? ysver:version | +--ro ypr:yang-library-content-id? | -> /yanglib:yang-library/content-id +---n subscription-resumed | +--ro id subscription-id +---n subscription-started {configured}? | +--ro id | | subscription-id | +--ro (target) | | +--:(stream) | | | +--ro (stream-filter)? | | | | +--:(by-reference) | | | | | +--ro stream-filter-name | | | | | stream-filter-ref | | | | +--:(within-subscription) | | | | +--ro (filter-spec)? | | | | +--:(stream-subtree-filter) | | | | | +--ro stream-subtree-filter? | | | | | {subtree}? | | | | +--:(stream-xpath-filter) | | | | +--ro stream-xpath-filter? | | | | yang:xpath1.0 {xpath}? | | | +--ro stream Graf, et al. Expires 16 August 2026 [Page 20] Internet-Draft YANG Notifications Versioning February 2026 | | | | stream-ref | | | +--ro replay-start-time? | | | | yang:date-and-time {replay}? | | | +--ro replay-previous-event-time? | | | yang:date-and-time {replay}? | | +--:(yp:datastore) | | +--ro yp:datastore | | | identityref | | +--ro (yp:selection-filter)? | | +--:(yp:by-reference) | | | +--ro yp:selection-filter-ref | | | selection-filter-ref | | +--:(yp:within-subscription) | | +--ro (yp:filter-spec)? | | +--:(yp:datastore-subtree-filter) | | | +--ro yp:datastore-subtree-filter? | | | {sn:subtree}? | | +--:(yp:datastore-xpath-filter) | | +--ro yp:datastore-xpath-filter? | | yang:xpath1.0 {sn:xpath}? | +--ro stop-time? | | yang:date-and-time | +--ro dscp? | | inet:dscp {dscp}? | +--ro weighting? uint8 | | {qos}? | +--ro dependency? | | subscription-id {qos}? | +--ro transport? | | transport {configured}? | +--ro encoding? | | encoding | +--ro purpose? string | | {configured}? | +--ro (yp:update-trigger)? | | +--:(yp:periodic) | | | +--ro yp:periodic! | | | +--ro yp:period centiseconds | | | +--ro yp:anchor-time? yang:date-and-time | | +--:(yp:on-change) {on-change}? | | +--ro yp:on-change! | | +--ro yp:dampening-period? centiseconds | | +--ro yp:sync-on-start? boolean | | +--ro yp:excluded-change* change-type | +--ro ypr:module-version* [name] | | +--ro ypr:name yang:yang-identifier | | +--ro ypr:revision rev:revision-date | | +--ro ypr:version? ysver:version Graf, et al. Expires 16 August 2026 [Page 21] Internet-Draft YANG Notifications Versioning February 2026 | +--ro ypr:yang-library-content-id? | -> /yanglib:yang-library/content-id +---n subscription-suspended | +--ro id subscription-id | +--ro reason identityref +---n subscription-terminated +--ro id subscription-id +--ro reason identityref 5.2. YANG Module The YANG module has two leaves augmenting the model of Subscription to YANG Notifications [RFC8639]. file "ietf-yang-push-revision@2025-12-07.yang" module ietf-yang-push-revision { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-yang-push-revision"; prefix ypr; import ietf-subscribed-notifications { prefix sn; reference "RFC 8639: Subscription to YANG Notifications"; } import ietf-yang-revisions { prefix rev; reference "RFC YYYY: draft-ietf-netmod-yang-module-versioning-13, Updated YANG Module Revision Handling"; } import ietf-yang-types { prefix yang; rev:recommended-min-date "2013-07-15"; reference "RFC 6991: Common YANG Data Types."; } import ietf-yang-semver { prefix ysver; reference "RFC ZZZZ: draft-ietf-netmod-yang-semver-23, YANG Semantic Versioning"; } import ietf-yang-library { prefix yanglib; reference "RFC 8525: YANG Library"; } Graf, et al. Expires 16 August 2026 [Page 22] Internet-Draft YANG Notifications Versioning February 2026 import ietf-system-capabilities { prefix sysc; reference "RFC 9196: YANG Modules Describing Capabilities for Systems and Datastore Update Notifications"; } import ietf-notification-capabilities { prefix notc; reference "RFC 9196: YANG Modules Describing Capabilities for Systems and Datastore Update Notifications"; } organization "IETF NETCONF (Network Configuration) Working Group"; contact "WG Web: WG List: Authors: Thomas Graf Benoit Claise Alex Huang Feng "; description "Defines YANG-Push event notification header with the revision and the version. Adds the support of the revision and version selection in the YANG-Push subscription RPCs. Copyright (c) 2025 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Revised BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). All revisions of IETF and IANA published modules can be found at the YANG Parameters registry (https://www.iana.org/assignments/yang-parameters). This version of this YANG module is part of RFC XXXX; see the RFC itself for full legal notices. The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL Graf, et al. Expires 16 August 2026 [Page 23] Internet-Draft YANG Notifications Versioning February 2026 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."; revision 2025-12-07 { description "First revision"; reference "RFC XXXX: Support of Versioning in YANG Notifications Subscription"; } // Identities identity revision-unsupported { base sn:establish-subscription-error; base sn:modify-subscription-error; description "Revision not supported. This failure can be due to subscribing to a specific revision not supported by the publisher."; } identity version-unsupported { base sn:establish-subscription-error; base sn:modify-subscription-error; description "Specific version not supported. This failure can be due to subscribing to a specific version not supported by the publisher."; } identity incompatible-revision-and-version { base sn:establish-subscription-error; base sn:modify-subscription-error; description "The combination of revision and version are incompatible. This failure happens when the revision and the version are both specified in the RPC and the YANG module supported by the publisher does not support one of them."; } grouping yang-push-module-version-subs { description "This grouping combines the module name, the revision and version leaves. This grouping is to be used for configuration and the leaves are not mandatory."; leaf name { Graf, et al. Expires 16 August 2026 [Page 24] Internet-Draft YANG Notifications Versioning February 2026 type yang:yang-identifier; description "This references the YANG module name."; } choice revision-version { description "Specifies the revision or version of the YANG module sent in the subscription."; case revision { leaf revision { type rev:revision-date; description "This references the YANG module revision to be sent in the subscription."; } } case version { leaf version { type ysver:version; description "This references the YANG module semantic version to be sent in the subscription."; } } } } grouping yang-push-module-version-notif { description "This grouping combines the module name, the revision and version leaves. This grouping is to be used for read-only cases such as the content of YANG-Push Notifications. The name and revision are mandatory and MUST be present in the data."; leaf name { type yang:yang-identifier; config false; mandatory true; description "This references the YANG module name."; } leaf revision { type rev:revision-date; config false; mandatory true; description "This references the YANG module revision of the sent notification message."; Graf, et al. Expires 16 August 2026 [Page 25] Internet-Draft YANG Notifications Versioning February 2026 } leaf version { type ysver:version; description "This references the YANG module semantic version of the sent notification message."; } } grouping yang-push-module-version-notif-list { description "This grouping defines a list of yang-push-module-version-notif grouping."; list module-version { key "name"; config false; description "List of yang-push-module-version grouping. The revision is not configurable."; uses ypr:yang-push-module-version-notif; } leaf yang-library-content-id { type leafref { path "/yanglib:yang-library/yanglib:content-id"; } config false; description "Contains the YANG library content identifier RFC 8525 information."; } } grouping yang-push-module-version-subs-list { description "This grouping defines a list of yang-push-module-version-subs grouping."; list module-version-subs { key "name"; description "List of yang-push-module-version-subs grouping. The revision is configurable."; uses ypr:yang-push-module-version-subs; } } // Subscription parameters augment "/sn:establish-subscription/sn:input" { description Graf, et al. Expires 16 August 2026 [Page 26] Internet-Draft YANG Notifications Versioning February 2026 "Augment the establish-subscription RPC from the ietf-subscribed-notifications YANG module with the yang-push-module-version-subs-list grouping."; uses ypr:yang-push-module-version-subs-list; } augment "/sn:modify-subscription/sn:input" { description "Augment the modify-subscription RPC from the ietf-subscribed-notifications YANG module with the yang-push-module-version-subs-list grouping."; uses ypr:yang-push-module-version-subs-list; } // Subscription notifications augment "/sn:subscription-started" { description "Augment the subscription-started notification from the ietf-subscribed-notifications YANG module with the yang-push-module-version-notif-list grouping."; uses ypr:yang-push-module-version-notif-list; } augment "/sn:subscription-modified" { description "Augment the subscription-modified notification from the ietf-subscribed-notifications YANG module with the yang-push-module-version-notif-list grouping."; uses ypr:yang-push-module-version-notif-list; } // Subscription container augment "/sn:subscriptions/sn:subscription" { description "Augment the subscriptions RPC container from the ietf-subscribed-notifications YANG module with the yang-push-module-version-subs-list grouping."; uses ypr:yang-push-module-version-subs-list; } // Subscription capabilities augment "/sysc:system-capabilities/notc:subscription-capabilities" { description "Add system level capabilities"; leaf yang-push-module-revision-supported { type boolean; default true; description "Specifies whether the publisher supports exporting revision and version in YANG-Push subscription state change Graf, et al. Expires 16 August 2026 [Page 27] Internet-Draft YANG Notifications Versioning February 2026 notifications. If set to true, publisher supports. If set to false, publisher does not support."; reference "RFC XXXX: Support of Versioning in YANG Notifications Subscription"; } } } 6. IANA Considerations 6.1. IETF XML Registry This document registers the following URIs in the "IETF XML Registry" [RFC3688]: URI: urn:ietf:params:xml:ns:yang:ietf-yang-push-revision Registrant Contact: The IESG. XML: N/A; the requested URI is an XML namespace. 6.2. YANG Module Name This document registers the following YANG modules in the 'YANG Module Names' registry [RFC6020]: name: ietf-yang-push-revision namespace: urn:ietf:params:xml:ns:yang:ietf-yang-push-revision prefix: ypr reference: RFC-to-be 7. Operational Considerations The solution described in this document allows Subscription policies to be constrained to a particular module revisions/versions that are used by the Publisher before a Subscription is initiated. The augmentations to the Subscription state change Notifications also gives the Receiver additional context and confidence of the current schema associated with a Subscription. Graf, et al. Expires 16 August 2026 [Page 28] Internet-Draft YANG Notifications Versioning February 2026 Section 2.5.1 of [RFC8639] describes the Subscription state machine for Configured YANG-Push Subscriptions. It states that 'subscription-modified' condition is triggered when the Subscription policy is being changed. Since this document proposes YANG version and revision extensions in Subscription configuration and state change notifications, it is expected that changes in YANG version and revision of a Subscription during Subscription lifecycle accounts for changes in Subscription policy and therefore MUST trigger 'subscription-modified' Subscription state change Notifications. Note, that not all modules used or referenced under a Subscription path are included in the Subscription state change Notification, and hence, it is possible that the schema associated with a Subscription MAY change without any corresponding change to the advertise module revisions or versions. Therefore, the YANG Library content-id that is also included in the Subscription state change Notifications allows the Receiver to detect if there were changes to the device schema. This includes changes not related to the Subscription path as well. Take Figure 6 as example. The Subscription path is '/ietf- interfaces:interfaces' and the listed YANG module name is 'ietf- interfaces' with revision '2018-02-20' and version '2.0.0'. The 'ietf-interfaces' YANG module defined in Section 5 of [RFC8343] and imports 'ietf-yang-types' YANG module. If 'ietf-interfaces' YANG module version or revision would change during the Subscription lifecycle, a YANG-Push Receiver would recognize the change since the revision or version in the module-version and the YANG library content-id has changed. However, if 'ietf-yang-types' YANG module version or revision would change, a YANG-Push Receiver would only be able to recognize the change using the YANG library content-id. A YANG package [I-D.ietf-netmod-yang-packages], specifies a versioned organizational structure used to manage a set of YANG modules that collectively defines a package schema. For example, a YANG package could contain a set of YANG modules required to implement a L3VPN service on a network node. It offers therefore a complementary information to the solution in this draft by describing how one specific YANG module revision is part of a set of YANG modules. 8. Implementation Status Note to the RFC-Editor: Please remove this section before publishing. 8.1. Huawei VRP Huawei implemented in Notification the 'module', 'revision' and 'version' extension as described in Section 3 for a YANG-Push Publisher on UDP-based Transport for Configured Subscriptions [I-D.ietf-netconf-udp-notif] in their VRP platform. Graf, et al. Expires 16 August 2026 [Page 29] Internet-Draft YANG Notifications Versioning February 2026 8.2. 6WIND VSR 6WIND implemented in Notification 'module', 'revision' and 'library- content-id' extension as described in Section 3 for a YANG-Push Publisher on UDP-based Transport for Configured Subscriptions [I-D.ietf-netconf-udp-notif] in their VSR platform. 8.3. Cisco IOS XR Cisco implemented in Notification 'module', 'revision' and 'library- content-id' extension as described in Section 3 and 'module' and 'revision' in Subscription as described in Section 2 for a YANG-Push Publisher on UDP-based Transport for Configured Subscriptions [I-D.ietf-netconf-udp-notif] in their IOS XR platform. 9. Security Considerations This section uses the template described in Section 3.7 of [I-D.ietf-netmod-rfc8407bis]. The "ietf-yang-push-revision" 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 YANG-based management protocols (1) have to use a secure transport layer (e.g., SSH [RFC6242], TLS [RFC8446], and QUIC [RFC9000]) and (2) have to use mutual authentication. The Network Configuration Access Control Model (NACM) [RFC8341] provides the means to restrict access for particular NETCONF or RESTCONF users to a preconfigured 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: * /sn:establish-subscription/sn:input/ypr:module-version-subs * /sn:modify-subscription/sn:input/ypr:module-version-subs * /sn:subscriptions/sn:subscription/ypr:module-version-subs Graf, et al. Expires 16 August 2026 [Page 30] Internet-Draft YANG Notifications Versioning February 2026 The entries in the list above allow in a YANG-Push Subscription to define the revision or version of a YANG module name. Access control MUST be set so that only someone with proper access permissions has the ability to access and modify this resource. 10. Acknowledgements The authors would like to thank Qiufang Ma, Robert Wilton, Jian Ping Zhang, Robert Wills, Reshad Rahman, Camilo Cardona Holger Keller and Gabriele Galimberti for their review and valuable comments. 11. References 11.1. Normative References [I-D.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, . [I-D.ietf-netmod-yang-module-versioning] Wilton, R., Rahman, R., Lengyel, B., Clarke, J., and J. Sterne, "Updated YANG Module Revision Handling", Work in Progress, Internet-Draft, draft-ietf-netmod-yang-module- versioning-15, 18 October 2025, . [I-D.ietf-netmod-yang-semver] Clarke, J., Wilton, R., Rahman, R., Lengyel, B., Sterne, J., and B. Claise, "YANG Semantic Versioning", Work in Progress, Internet-Draft, draft-ietf-netmod-yang-semver- 24, 29 September 2025, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, . Graf, et al. Expires 16 August 2026 [Page 31] Internet-Draft YANG Notifications Versioning February 2026 [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, . [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, . [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011, . [RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, July 2013, . [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, . [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, March 2018, . [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, . [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . [RFC8525] Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K., and R. Wilton, "YANG Library", RFC 8525, DOI 10.17487/RFC8525, March 2019, . Graf, et al. Expires 16 August 2026 [Page 32] Internet-Draft YANG Notifications Versioning February 2026 [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, . [RFC8641] Clemm, A. and E. Voit, "Subscription to YANG Notifications for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641, September 2019, . [RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, May 2021, . [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, . 11.2. Informative References [I-D.ietf-netconf-https-notif] Jethanandani, M. and K. Watsen, "An HTTPS-based Transport for YANG Notifications", Work in Progress, Internet-Draft, draft-ietf-netconf-https-notif-15, 1 February 2024, . [I-D.ietf-netconf-udp-notif] Feng, A. H., Francois, P., Zhou, T., Graf, T., and P. Lucente, "UDP-based Transport for Configured Subscriptions", Work in Progress, Internet-Draft, draft- ietf-netconf-udp-notif-25, 28 January 2026, . [I-D.ietf-netmod-yang-packages] Wilton, R., Rahman, R., Clarke, J., and J. Sterne, "YANG Packages", Work in Progress, Internet-Draft, draft-ietf- netmod-yang-packages-06, 7 July 2025, . [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, December 2017, . Graf, et al. Expires 16 August 2026 [Page 33] Internet-Draft YANG Notifications Versioning February 2026 [RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, . [RFC8343] Bjorklund, M., "A YANG Data Model for Interface Management", RFC 8343, DOI 10.17487/RFC8343, March 2018, . [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, . [W3C.REC-xml-20081126] Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth Edition)", World Wide Web Consortium Recommendation REC- xml-20081126, November 2008, . Authors' Addresses Thomas Graf Swisscom Binzring 17 CH-8045 Zurich Switzerland Email: thomas.graf@swisscom.com Benoit Claise Huawei Email: benoit@everything-ops.net Alex Huang-Feng INSA-Lyon Lyon France Email: alex.huang-feng@insa-lyon.fr Graf, et al. Expires 16 August 2026 [Page 34]