YANG Datastore Telemetry (YANG Push Lite)

3.1. Background and Motivation for YANG Push Lite

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.¶

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 Lite.¶

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

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.¶

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.¶

3.4. Relationships to existing RFCs and Internet Drafts

This document, specifying YANG Push Lite, 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 Lite functionality and module structure.¶

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.¶

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.¶

• 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:¶

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

    • 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.¶

Below is a tree diagram for the "filters" container. All objects contained in this tree are described in the YANG module in Section 12.¶

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

  augment /ypl:establish-subscription/ypl:input/ypl:target
            /ypl:filter:
    +--:(by-reference)
  augment /ypl:subscription-started/ypl:target:
    +-- filter-ref?   filter-ref

6.3. Decomposing Subscription Filters

In order to address the issues described in Section 3.2, YANG Push Lite 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:¶

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.¶

7.1. 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 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.¶

{
  "ietf-yp-notification:envelope": {
    "event-time": "2024-10-10T08:00:05.22Z",
    "hostname": "example-router",
    "sequence-number": 3219,
    "contents": {
      "ietf-yp-lite:update": {
        "id": 1011,
        "snapshot-type": "periodic",
        "observation-time": "2024-10-10T08:00:05.11Z",
        "updates": [
          {
            "target-path": "ietf-interfaces:interfaces/interface",
            "data": {
              "ietf-interfaces:interfaces": {
                "ietf-interfaces: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"
                  }
                ]
              }
            }
          }
        ]
      }
    }
  }
}

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?          <anydata>
    |  +--ro complete?           empty

The normative definitions for the notifications fields are given in the YANG module in Section 12. 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, either providing the replacement data for, or that data node that is being deleted.¶

• data - the full replacement data subtree for the content at the target-path, encoded from the path-prefix.¶

• complete - if present, this flag indicates that a periodic collection (TODO, what about on-change) is complete. Setting this flag 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:¶

module: ietf-yp-lite-config
  +--rw datastore-telemetry!
     +--rw subscriptions
        +--rw subscription* [name]
           +--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 /ypl:establish-subscription/ypl:input/ypl:target
            /ypl:filter:
    +--:(by-reference)
  augment /ypl:subscription-started/ypl:target:
    +-- filter-ref?   filter-ref

The normative definitions for the update-trigger fields are given in the ietf-yp-lite YANG module in Section 12. 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.¶

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.¶

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. update records SHOULD be generated at the same subtree as equivalent periodic subscription rather than only the specific data node that is on-change notifiable. The goal is to ensure that the update message contains a consistent set of data on the subscription path.¶

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.¶

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.¶

7.7. Streaming Update Examples

TODO, Generate new JSON based example of a periodic, and delete messages. Current placeholders are the existing YANG Push Notifications.¶

Figure XXX provides an example of a notification message for a subscription tracking the operational status of a single Ethernet interface (per [RFC8343]). This notification message is encoded XML W3C.REC-xml-20081126 over the Network Configuration Protocol (NETCONF) as per [RFC8640].¶

<notification
  xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
<eventTime>2017-10-25T08:00:11.22Z</eventTime>
<push-update xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push">
  <id>1011</id>
  <datastore-contents>
    <interfaces
     xmlns="urn:ietf:params:xml:ns:yang:ietf-interfaces">
      <interface>
        <name>eth0</name>
        <oper-status>up</oper-status>
      </interface>
    </interfaces>
  </datastore-contents>
</push-update>
</notification>

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

<notification
  xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
<eventTime>2017-10-25T08:22:33.44Z</eventTime>
<push-change-update
    xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push">
  <id>89</id>
  <datastore-changes>
    <yang-patch>
      <patch-id>0</patch-id>
      <edit>
        <edit-id>edit1</edit-id>
        <operation>replace</operation>
        <target>/ietf-interfaces:interfaces</target>
        <value>
          <interfaces
              xmlns="urn:ietf:params:xml:ns:yang:ietf-interfaces">
            <interface>
              <name>eth0</name>
              <oper-status>down</oper-status>
            </interface>
          </interfaces>
        </value>
      </edit>
    </yang-patch>
  </datastore-changes>
</push-change-update>
</notification>

8.1. Receivers

Every subscription is associated with one or more receivers, which each identify 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.¶

module: ietf-yp-lite-config
  +--rw datastore-telemetry!
     +--rw receivers
        +--rw receiver* [name]
           +--rw name                      string
           +--rw encoding                  ypl: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 /ypl:establish-subscription/ypl:input/ypl:target
            /ypl:filter:
    +--:(by-reference)
  augment /ypl:subscription-started/ypl:target:
    +-- filter-ref?   filter-ref

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

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 Lite. The requirements for these transport specifications are documented in the following section:¶

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. Constrained platforms may not be able to support JSON and hence may choose to only support CBOR encoding. JSON encoding 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-yp-lite.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-yp-lite-capabilities YANG module's transport capabilities Section 14.2.¶

9.1. Common Subscription Parameters

All subscriptions require the following state to be instantiated:¶

• a name 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.¶

• 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 names 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 name that conflicts with any other subscription (configured or dynamic) MUST fail,¶

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

• TODO: We want to make the name optional to be specified for dynamic subscriptions? If not provided then the publisher could allocate using "dyn-<XXX>", where XXX is an increasing numeric subscription id?¶

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

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

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.¶

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

    +---n subscription-started
    |  +--ro id                subscription-id
    |  +--ro name              subscription-name
    |  +--ro description?      string
    |  +--ro target
    |  |  +--ro datastore?       identityref
    |  |  +--ro (filter)
    |  |     +--:(path)
    |  |     |  +--ro path       ypath
    |  |     +--:(subtree)
    |  |     |  +--ro subtree    <anydata> {ypl:subtree}?
    |  |     +--:(xpath)
    |  |        +--ro xpath      yang:xpath1.0 {ypl:xpath}?
    |  +--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

    +---n subscription-terminated
    |  +--ro name      subscription-name
    |  +--ro id        subscription-id
    |  +--ro reason    identityref

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

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

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-yp-lite-config YANG module Section 13.2 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¶

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

• one or more associated receivers for the subscription, as described in Section 8.1. The references receivers specify 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 subscriptions have the ability to send notification messages to more than one receiver. All receivers for a given subscription MUST use the same encoding.¶

• 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:¶

  • 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 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.¶

  • 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.¶

9.4. 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-yp-lite YANG module Section 12.2, and also via the capabilities module Section 14.2.¶

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.¶

• Active dynamic subscriptions cannot be modified on the fly, instead, the client is required to send a delete-subscription YANG RPC followed by a establish-subscription YANG RPC.¶

• 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.¶

• 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.¶

    +---x establish-subscription {dynamic}?
    |  +---w input
    |  |  +---w name              subscription-name
    |  |  +---w description?      string
    |  |  +---w target
    |  |  |  +---w datastore?       identityref
    |  |  |  +---w (filter)
    |  |  |     +--:(path)
    |  |  |     |  +---w path       ypath
    |  |  |     +--:(subtree)
    |  |  |     |  +---w subtree    <anydata> {ypl:subtree}?
    |  |  |     +--:(xpath)
    |  |  |        +---w xpath      yang:xpath1.0 {ypl: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 delete-subscription {dynamic}?
    |  +---w input
    |     +---w name    subscription-name

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

  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

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 Lite achieves this in several ways:¶

• the complete flag in update notification, or the equivalent update-complete notification, are used to signal when all data for a periodic collection event has been enqueued. 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 either the subscription is terminated, or in the case of a configured subscription with multiple receivers the slow receiver is disconnected from the subscription. In the case of dynamic subscriptions, the client may attempt to re-created the subscription. For configured subscriptions, the publisher should attempt to periodically recreate the subscription or reconnect the receiver.¶

  • TODO, do we want to allow for a more lossy mode where the publisher just tail drops if the buffer is full? If we do, then this looks like it should be a configurable option.¶

  • TODO, ensure that we document how to reconnect to an new 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].¶

  • TODO, sequence-numbers are unique except for the receiver-disconnected message.¶

• 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).¶

• 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.¶

Dynamic subscriptions are only present in the datastore-telemetry/subscriptions/subscription list when they are active, and are removed as soon as they are terminated. Whereas configured subscriptions are present if the list if they are configured, regardless of whether they are active.¶

TODO, should dynamic receivers be listed? Do we need to report per-receiver stats for dynamic subscriptions?¶

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

It is far preferable to decline a subscription request than to accept such a request when it cannot be met.¶

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 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.¶

11.1. Capabilities

Publishers SHOULD implement the ietf-system-capabilities YANG module, defined in [RFC9196], and the ietf-yp-lite-capabilities YANG module, defined in Section 14.2) that augments ietf-system-capabilities.¶

The ietf-yp-lite-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-yp-lite-capabilities is given below.¶

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 yplca:datastore-telemetry
     |        +--ro yplca:periodic-notifications-supported?
     |        |       notification-support
     |        +--ro (yplca:update-period)?
     |        |  +--:(yplca:minimum-update-period)
     |        |  |  +--ro yplca:minimum-update-period?        uint32
     |        |  +--:(yplca:supported-update-period)
     |        |     +--ro yplca:supported-update-period*      uint32
     |        +--ro yplca:on-change-supported?
     |                notification-support
     +--ro yplca:datastore-telemetry
        +--ro yplca:periodic-notifications-supported?
        |       notification-support
        +--ro (yplca:update-period)?
        |  +--:(yplca:minimum-update-period)
        |  |  +--ro yplca:minimum-update-period?        uint32
        |  +--:(yplca:supported-update-period)
        |     +--ro yplca:supported-update-period*      uint32
        +--ro yplca:on-change-supported?
        |       notification-support
        +--ro yplca:transport
           +--ro yplca:transport-capability* [transport-protocol]
              +--ro yplca:transport-protocol    identityref
              +--ro yplca:security-protocol?    identityref
              +--ro yplca:encoding-format*      identityref

TODO, do we need additional capabilities, as per Issue 18¶

11.2. Subscription Content Schema Identification

YANG Module Synchronization¶

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.¶

12.1. ietf-yp-lite YANG tree

This section shows the full tree output for ietf-yp-lite 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-yp-lite

  rpcs:
    +---x establish-subscription {dynamic}?
    |  +---w input
    |  |  +---w name              subscription-name
    |  |  +---w description?      string
    |  |  +---w target
    |  |  |  +---w datastore?       identityref
    |  |  |  +---w (filter)
    |  |  |     +--:(path)
    |  |  |     |  +---w path       ypath
    |  |  |     +--:(subtree)
    |  |  |     |  +---w subtree    <anydata> {ypl:subtree}?
    |  |  |     +--:(xpath)
    |  |  |        +---w xpath      yang:xpath1.0 {ypl: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 delete-subscription {dynamic}?
    |  +---w input
    |     +---w name    subscription-name
    +---x kill-subscription {dynamic}?
       +---w input
          +---w name    subscription-name

  notifications:
    +---n subscription-started
    |  +--ro id                subscription-id
    |  +--ro name              subscription-name
    |  +--ro description?      string
    |  +--ro target
    |  |  +--ro datastore?       identityref
    |  |  +--ro (filter)
    |  |     +--:(path)
    |  |     |  +--ro path       ypath
    |  |     +--:(subtree)
    |  |     |  +--ro subtree    <anydata> {ypl:subtree}?
    |  |     +--:(xpath)
    |  |        +--ro xpath      yang:xpath1.0 {ypl:xpath}?
    |  +--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
    +---n subscription-terminated
    |  +--ro name      subscription-name
    |  +--ro id        subscription-id
    |  +--ro reason    identityref
    +---n receiver-disconnected
    |  +--ro name      subscription-name
    |  +--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?          <anydata>
    |  +--ro complete?           empty
    +---n update-complete
       +--ro id    subscription-id

12.2. ietf-yp-lite 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].¶

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-yp-lite.yang#0.1.0"

module ietf-yp-lite {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-yp-lite";
  prefix ypl;

  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)";
  }

  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,
     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 Push Lite";
  }

  /*
   * FEATURES
   */

  feature dynamic {
    description
      "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
       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
      "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.";
  }

  /* Identities for encodings */

  identity configurable-encoding {
    description
      "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).";
  }

  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-name {
    type string {
      length "1..64";
      // TODO, is it reasonable to limit this to 64 characters?
    }
    description
      "A user friendly name for a subscription.";
  }

  typedef subscription-id {
    type uint32;
    description
      "A type for subscription identifiers.";
  }

  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 any
          connected receivers";
      }
      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";
  }

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

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

    leaf name {
      type subscription-name;
      mandatory true;
      description
        "The client provided name for the subscription.

         This MUST be unique across all subscriptions.  Configuring
         a subscription with a name already used by a dynamic
         subscription will replace the dynamic subscription, forcing
         it to be terminated.";
    }

    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
       'establish-subscription' request.";
    input {
      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.";
      }
    }
  }

  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.";
      }
    }
  }

  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 name {
        type subscription-name;
        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 name {
        type subscription-name;
        mandatory true;
        description
          "The name of the dynamic subscription to be deleted.";
      }
    }
  }

  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
   */

  notification subscription-started {
    //ypl:subscription-state-notification;
    description
      "This notification indicates that a configured subscription
       has started and notifications will now be sent.";
    leaf id {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
    uses subscription-common;
  }

  notification subscription-terminated {
    //ypl:subscription-state-notification;
    description
      "This notification indicates that a subscription has been
       terminated.";
    leaf name {
      type subscription-name;
      mandatory true;
      description
        "The name of the subscription that has been terminated.";
    }
    leaf id {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
    leaf reason {
      type identityref {
        base subscription-terminated-reason;
      }
      mandatory true;
      description
        "Identifies the condition that resulted in the
         termination.";
    }
  }

  notification receiver-disconnected {
    description
      "This notification indicates that a receiver has been
       disconnected from a subscription.  This notification is only
       sent to the affected receiver if the transport is still
       available, and only if the subscription remains active due
       to other active receivers.

       The receiver will not receive any further notifications
       for this subscription unless it receives a new
       'subscription-started' notification for this
       subscription.";
    leaf name {
      type subscription-name;
      mandatory true;
      description
        "The name of the subscription.";
    }
    leaf id {
      type subscription-id;
      mandatory true;
      description
        "The subscription identifier";
    }
    leaf reason {
      type identityref {
        base subscription-terminated-reason;
          // TODO, add new receiver disconnected reasons.
      }
      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
        "This references the subscription that drove the
         notification to be sent.";
    }

    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.";
        }
      }
      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.";
      }

      anydata data {
        description
          "This 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.

          For an on-change delete notification, the
          datastore-snapshot will be absent for the given target
          path.

          The snapshot is encoded relative to the path-prefix.";
      }
    }

    leaf complete {
      type empty;
      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.";
    }
  }

  // TODO - Need to signal when an initial replay has completed, or
  //        possibly when any period subscription has completed.
  // TODO - Need to think about list key entries that are no longer
  //        present.
  notification update-complete {
    //ypl:subscription-state-notification;
    //if-feature "replay";
    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
       notification MAY be used instead of sending this notification
       as a separate message, and both are semantically equivalent.";
    leaf id {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
  }
}

<CODE ENDS>

13.1. ietf-yp-lite-config YANG tree

This section shows the full tree output for ietf-yp-lite-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-yp-lite-config
  +--rw datastore-telemetry!
     +--rw filters
     |  +--rw filter* [name]
     |     +--rw name             string
     |     +--rw (filter)
     |        +--:(path)
     |        |  +--rw path       ypath
     |        +--:(subtree)
     |        |  +--rw subtree    <anydata> {ypl:subtree}?
     |        +--:(xpath)
     |           +--rw xpath      yang:xpath1.0 {ypl:xpath}?
     +--rw subscriptions
     |  +--rw subscription* [name]
     |     +--rw name
     |     |       subscription-name
     |     +--rw description?                        string
     |     +--rw target
     |     |  +--rw datastore?          identityref
     |     |  +--rw (filter)
     |     |     +--:(path)
     |     |     |  +--rw path          ypath
     |     |     +--:(subtree)
     |     |     |  +--rw subtree       <anydata> {ypl:subtree}?
     |     |     +--:(xpath)
     |     |     |  +--rw xpath         yang:xpath1.0 {ypl: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 receivers* [name]
     |     |  +--rw name
     |     |  |       -> /datastore-telemetry/receivers/receiver/name
     |     |  +--ro status?       enumeration
     |     |  +--ro statistics
     |     |     +--ro receiver-disconnected-count?
     |     |             yang:zero-based-counter64
     |     +--ro id
     |     |       ypl:subscription-id
     |     +--ro status?
     |     |       ypl:subscription-status
     |     +--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-notification-count?
     |     |  |       yang:zero-based-counter64
     |     |  +--ro terminated-notification-count?
     |     |  |       yang:zero-based-counter64
     |     |  +--ro update-notification-count?
     |     |  |       yang:zero-based-counter64
     |     |  +--ro periodic-collection-count?
     |     |  |       yang:zero-based-counter64
     |     |  +--ro excluded-event-records?
     |     |          yang:zero-based-counter64
     |     +---x reset
     +--rw receivers
        +--rw receiver* [name]
           +--rw name                      string
           +--rw encoding                  ypl: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 /ypl:establish-subscription/ypl:input/ypl:target
            /ypl:filter:
    +--:(by-reference)
       +-- filter-ref?   filter-ref
  augment /ypl:subscription-started/ypl:target:
    +-- filter-ref?   filter-ref

13.2. ietf-yp-lite-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-yp-lite-config.yang#0.1.0"

module ietf-yp-lite-config {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-yp-lite-config";
  prefix yplco;

  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-yp-lite {
    prefix ypl;
    reference
      "RFC XXXX: YANG Push Lite";
  }

  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
     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 Push Lite";
  }

  /*
   * FEATURES
   */

  feature interface-designation {
    description
      "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";
    description
    "YANG Push Lite 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;
          description
            "A unique name to identify the selection filters.";
        }
        uses ypl: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 "name";
        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 ypl:subscription-common;

        list receivers {
          key "name";
          min-elements 1;
          description
            "A host intended as a recipient for the notification
            messages of a subscription.  For configured
            subscriptions, transport-specific network parameters
            (or a leafref to those parameters) may be augmented to a
            specific receiver in this list.";
          leaf name {
            type leafref {
              path "/datastore-telemetry/receivers/receiver/name";
            }
            description
              "Identifies a unique 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.";
          }

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

            leaf receiver-disconnected-count {
              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";
            }
          }
        }

        leaf id {
          type ypl:subscription-id;
          config false;
          mandatory true;
          description
            "Publisher allocated identifier for a subscription;
              Unique in a given publisher.";
        }

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

        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;
          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-notification-count {
            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
               was applied by the publisher.";
          }

          leaf terminated-notification-count {
            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-notification-count {
            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-collection-count {
            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-event-records {
            type yang:zero-based-counter64;
            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.";
          }
        }

        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;
          description
            "An arbitrary but unique name for this receiver
            instance.";
        }

        leaf encoding {
  /*        when 'not(../transport) or derived-from(../transport,
          "ypl:configurable-encoding")';*/
          type ypl: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 ypl:dscp;

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

             This action is directly equivalent to invoking the
             'reset' action on all subscriptions that references
             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";
              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 "/ypl:establish-subscription/ypl:input/ypl:"
        + "target/ypl:filter" {

    description
      "Augment the 'establish-subscription' RPC to allow
       referencing a configured receiver.";

    case by-reference {
      description
        "Incorporates a filter that has been configured
         separately.";
      uses filter-ref {
        refine "filter-ref" {
          mandatory false;
        }
      }
    }
  }

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

    description
      "Allow a subscription-started 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>

14.1. ietf-yp-lite-capabilities YANG tree

This section shows the tree output for ietf-yp-lite-capabilities YANG module, which augments the ietf-system-capabilities YANG module [RFC9196].¶

14.2. ietf-yp-lite-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-yp-lite-capabilities.yang#0.1.0"

module ietf-yp-lite-capabilities {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-yp-lite-capabilities";
  prefix yplca;

  import ietf-system-capabilities {
    prefix sysc;
    reference
      "RFC 9196: YANG Modules Describing Capabilities for Systems
       and Datastore Update Notifications";
  }
  import ietf-yp-lite {
    prefix ypl;
    reference
      "RFC XXX: YANG Push Lite";
  }

  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 Push Lite";
  }

  /*
   * IDENTITIES
   */

  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
      "Indicates SSH.";
  }


  grouping yp-lite-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
           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 yp-lite-transport-capabilities {
    description
      "Capabilities related to transports supporting Yang Push Lite";
    container transport {
      description
        "Specifies capabilities related to YANG-Push transports.";
      list transport-capability {
        key "transport-protocol";
        description
          "Indicates a list of capabilities related to notification
                  transport.";
        leaf transport-protocol {
          type identityref {
            base ypl: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 ypl:encoding;
          }
          description
            "Indicates supported encoding formats.";
        }
      }
    }
  }

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

  augment "/sysc:system-capabilities/yplca:datastore-telemetry" {
    description
      "Adds system level Yang Push Lite transport capabilities";
    uses yp-lite-transport-capabilities;
  }

  augment "/sysc:system-capabilities/sysc:datastore-capabilities"
        + "/sysc:per-node-capabilities" {
    description
      "Add datastore and node-level capabilities";
    uses yp-lite-capabilities;
  }
}

<CODE ENDS>

module: ietf-yp-lite-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
  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

15.1. Use of YANG Push Lite with NACM

TODO, do we even need this section?¶

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.¶

15.2. 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   |
                     +-----------------+      +--------------------+

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.¶

15.3. 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-yp-lite" 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.¶

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.¶

16.1. Namespace URI registrations

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

For all registrations:¶

• Registrant Contact: The IESG.¶

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

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-03, 20 October 2025, <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-notif-envelope-03>.

[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>.

[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>.

[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>.

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-16, 19 October 2025, <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-distributed-notif-16>.

[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-23, 14 October 2025, <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-udp-notif-23>.

[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-16, 19 October 2025, <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-distributed-notif-16>.

[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-05, 6 September 2025, <https://datatracker.ietf.org/doc/html/draft-ietf-nmop-network-anomaly-architecture-05>.

[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-09, 20 October 2025, <https://datatracker.ietf.org/doc/html/draft-ietf-nmop-yang-message-broker-integration-09>.

[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>.

[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>.

[RFC8071]

Watsen, K., "NETCONF Call Home and RESTCONF Call Home", RFC 8071, DOI 10.17487/RFC8071, February 2017, <https://www.rfc-editor.org/rfc/rfc8071>.

[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>.

[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/>.

A.1. Removed Functionality

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

• 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. 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.¶

• 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.¶

A.2. Changed Functionality

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

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

• 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).¶

  • If a subscription uses multiple receivers then:¶

    • Update messages and lifecycle notifications are sent to all receivers (to preserve sequence numbers)¶

    • all receivers must be configured with the same encoding¶

  • 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.¶

• 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.¶

• On-change dampening:¶

  • Client configurable on-change dampening has been removed.¶

  • However, YANG Push Lite 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 Lite.¶

• 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 RFC 8639/RFC 8649:¶

  • 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).¶

• YANG Push Lite 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.¶

• A collection-complete notification, and associated configuration, has been defined to inform collectors when a subscription's periodic collection cycle is complete.¶

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

• All YANG Push Lite configuration is under a new datastore-telemetry presence container¶

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.¶

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.¶

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

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? **¶

{
  "ietf-yp-lite:update": {
    "id": 1011,
    "path-prefix": "/ietf-interfaces:interfaces/interface",
    "snapshot-type": "periodic",
    "observation-time": "2024-10-10T08:00:05.11Z",
    "updates": [
      {
        "target-path": "",
        "data": {
          "ietf-interfaces: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": [null]
  }
}

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.¶

• 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-yp-lite:update": {
    "id": 1011,
    "path-prefix": "/ietf-interfaces:interfaces/interface",
    "snapshot-type": "periodic",
    "observation-time": "2024-10-10T08:00:05.21Z",
    "updates": [
      {
        "target-path": "",
        "data": {
          "ietf-interfaces:interface": [
            {
              "name": "eth0",
              "statistics": {
                "in-octets": 123456,
                "out-octets": 654321
              }
            },
            {
              "name": "eth1",
              "statistics": {
                "in-octets": 789012,
                "out-octets": 210987
              }
            }
          ]
        }
      }
    ]
  }
}

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:¶

• 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.¶

<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>

C.3. Example of an on-change-delete notification using the new style update message

{
  "ietf-yp-lite:update": {
    "id": 1012,
    "snapshot-type": "on-change-delete",
    "observation-time": "2025-10-10T08:16:15.11Z",
    "updates": [
      {
        "target-path": "/ietf-interfaces:interfaces/interface[name='eth0']"
      }
    ]
  }
}

{
  "ietf-yp-lite:update": {
    "id": 1013,
    "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']"
      }
    ]
  }
}

C.4. Subscription RPC examples (from RFC 8641)

YANG-Push subscriptions are established, modified, and deleted using RPCs augmented from [RFC8639].¶

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

                  Figure 10: "establish-subscription" RPC

 <rpc-reply message-id="101"
    xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
    <id
      xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
       52
    </id>
 </rpc-reply>

         Figure 11: "establish-subscription" Positive RPC Response

  <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

 <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

  <rpc message-id="103"
        xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
    <resync-subscription
        xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push">
      <id>1011</id>
    </resync-subscription>
  </rpc>

                  Figure 15: "resync-subscription"

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.¶

2. Do we need to fold in any text from RFC 8640? and RESTCONF. I.e., there was this text in the one of the previous docs: Bindings for subscribed event record delivery for NETCONF and RESTCONF are defined in [RFC8640] and RESTCONF-Notif, respectively.¶

   • Rob: If text is needed for NETCONF and/or RESTCONF then I suspect that it would be better added to this document than to require small separate documents (as was done before).¶

3. What is the right name. Should we be calling this Yang Push 2 (YPv2) to more clearly indicate that this is intended to be a replacement for Yang Push? We need to be slightly careful in that this is only specifying implementing a subset of the functionality.¶

D.2. Issue related to Terminology/Definitions

1. Should we use the object terminology?¶

   • Holger: should try and use same terminology as existing YANG Push RFCs.¶

   • Rob: This issue can be a place holder, to go through and check/update the terminology used, and see if any of the referenced terminology isn't needed in YP Lite.¶

   • Rob: Update, possible should refine the definition of object to make it clear that it may refer to a single data node or set of data nodes.¶

D.3. Issues related to YANG Push Lite 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.¶

   • Vendors already support a simple JSON like path (e.g., using module-names rather than XML namespaces).¶

   • Open questions (for further discussion):¶

     • Do we support filtering on non-keys, e.g., this example from Thomas (but which filters on a non-key): /if:interfaces-state/if:interface[if:type='ianaift:ethernetCsmacd']/if:statistics¶

     • Do we support simple regex filtering on the keys (and if so, how would that be expressed, would it be compatible with JSON Path)¶

     • Do we need any more complex filtering (e.g., Holger's example of only getting entries from a list if they are in a particular state.), or do we always use subtree filters for that?¶

   • Authors: I provides some suggested text in Section 6.1, but I expect further discussion may be needed. (E.g., how multiple keys should be expressed)¶

2. Advertising subscription schema: https://github.com/rgwilton/draft-yp-observability/issues/11¶

D.5. Issues related to Datastore Event Streams

D.6. Issues related to Receivers, Transports, & Encodings

D.7. Issues related to Setting up & Managing Subscriptions

D.8. Issues related to Subscription Lifecycle

1. Use subscription name as the unique identifier for the subscription configuration. Subscription id identifies a subscription session. I.e., if a configured subscription is terminated and re-established then a new subscription id is allocated.¶

2. 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?¶

   • Tracked via https://github.com/rgwilton/draft-yp-observability/issues/11¶

3. 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?¶

   • Thomas: Do we need referenced filters at all? Subscriptions could be simplified if everything was done inline.¶

   • gNMI is only done inline.¶

   • Juniper also supports filters.¶

   • Thomas try to simplify as much as possible, then do we need templating?¶

4. When a subscription is terminated, should it be MUST NOT send any more notifications after the terminated message, or SHOULD NOT? For a dynamic subscription, should the RPC be synchronous and not reply until it knows that all queues have been drained?¶

   • Tracked via https://github.com/rgwilton/draft-yp-observability/issues/13¶

5. 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?¶

   • Holger, terminate & recreate.¶

   • gNMI, not specified.¶

   • Thomas: Keep this as implementation detail.¶

   • Sequence-id indicates that a client is dropping message anyway.¶

   • Receiver can already monitor and see that there is a problem anyway.¶

6. If the parameters for a subscription change in any way (e.g., the config changes for a configured subscription, or a referenced filter changes in a dynamic subscription) then do we want to say that the subscription MUST be killed and recreated. I.e., with subscription-terminated/subscription-started notifications? (Section 11)¶

   • Holger, kill/re-create.¶

   • Collector would need to no.¶

   • Ebben: Includes addition or deletion of the path.¶

   • Benoit: Which parameters are changing, this could impact. It depends. Maybe forcing it down keeps it simple. Would need further definition of what parameters would cause this to be pulled down.¶

   • Locally relevant, e.g., modifying transport parameters doesn't force a change.¶

   • Benoit: If you are not sure what you are doing you must recreate.¶

7. Should we have a YANG Action to reset a receiver or a subscription? E.g., discussed in Section 9.3.4.¶

   • There seems to be consensus that having/keeping such a YANG action is useful if a configured subscription is stuck.¶

   • Further discussion is needed to indicate where such an RPC should be in the data model, and what effect it should have:¶

     • It could be under the subscription list, which would effectively be equivalent to forcing the subscription to terminate and re-initialize across all receivers.¶

     • It could also be under the receiver list, which would effectively be equivalent to forcing all subscriptions using that receiver to terminate and re-initialize.¶

     • We also need to consider whether this would clear subscription counters or not.¶

     • We also consider whether configured subscription MAY/SHOULD share transport sessions where possible, or whether each subscription uses a separate transport session, or whether this is down to the transport session definition. This decision may impact the design of the data model, and perhaps the transport requirements text.¶

     • Rob: I've written up some text for the reset action on a subscription and under the receiver (that applies to all subscriptions that reference the receiver configuration). Unlike the existing reset action, I've removed the return parameter (timestamp of when it took effect), and I think that we should allow it to be processed asynchronously w.r.t the RPC caller. Authors, please check the latest text.¶

8. Should we support configurable subscription-level keepalives?¶

D.9. Issues related to Performance, Reliability & Subscription Monitoring

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)?¶

   • The current doc uses a mixture of both (e.g., features for supporting config vs dynamic subscriptions), capabilities for advertising other capabilities that either cannot be advertised via features, or would arguably be too fine grained.¶

2. For on-change, should a subscription be rejected (or not brought up) if there are no on-change notifiable nodes? Alternative is to offer implementation flexibility between these two approaches.¶

   • Holger: Prefer for the subscription to be rejected.¶

3. CBOR SID encoding:¶

   • In terms of conformance, we have SHOULD for CBOR, but the draft is silent on whether this means with SIDs or not.¶

   • Further discussion is required on how to manage SID files.¶

4. Check of the current approach in the draft of using a separate tree for YP Lite capabilities rather than reusing the YP capabilities (and augmentations) previously defined.¶

   • Rob: The draft currently includes a separate tree, which I think is necessary because the supported functionality is different (e.g., dampening), and a implementation may support both YANG Push and YANG Push Lite.¶

5. 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.¶

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 Lite, 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.¶

   • (James) Take out tight binding to NACM from YANG Push Lite altogether. I.e., decouple YANG Push Lite from what security mechanism is being used.¶

   • (Rob) Another choice could be to use NACM as an example rather than the only way.¶

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.¶

D.13. Issues related to the IANA

None open.¶

D.14. Issues related to the Appendixes

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.¶

D.16. Changes

1. Aligned configured and dynamic subscription data models: - Both are configured by name. - Made "purpose" field common and renamed to "description" (limited to 1k max characters, previously unrestricted), i.e., now available for dynamic subscriptions.¶