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NETCONF                                                          E. Voit
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                                A. Clemm
Expires: May 3, 2018                                              Huawei
                                                      A. Gonzalez Prieto
                                                                  VMWare
                                                       E. Nilsen-Nygaard
                                                             A. Tripathy
                                                           Cisco Systems
                                                        October 30, 2017


                  Custom Subscription to Event Streams
             draft-ietf-netconf-subscribed-notifications-07

Abstract

   This document defines capabilities and operations for the customized
   establishment of subscriptions upon a publisher's event streams.
   Also defined are delivery mechanisms for instances of the resulting
   notification messages.  Effectively this allows a subscriber to
   request and receive a continuous, custom feed of publisher generated
   information.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 3, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents



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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.3.  Solution Overview . . . . . . . . . . . . . . . . . . . .   5
     1.4.  Relationship to RFC-5277  . . . . . . . . . . . . . . . .   6
   2.  Solution  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.1.  Event Streams . . . . . . . . . . . . . . . . . . . . . .   6
     2.2.  Event Stream Filters  . . . . . . . . . . . . . . . . . .   7
     2.3.  Subscription State Model at the Publisher . . . . . . . .   7
   3.  Data Model Trees  . . . . . . . . . . . . . . . . . . . . . .   9
   4.  Dynamic Subscriptions . . . . . . . . . . . . . . . . . . . .  14
     4.1.  Establishing a Subscription . . . . . . . . . . . . . . .  14
     4.2.  Modifying a Subscription  . . . . . . . . . . . . . . . .  16
     4.3.  Deleting a Subscription . . . . . . . . . . . . . . . . .  16
     4.4.  Killing a Subscription  . . . . . . . . . . . . . . . . .  16
   5.  Configured Subscriptions  . . . . . . . . . . . . . . . . . .  17
     5.1.  Creating a Configured Subscription  . . . . . . . . . . .  17
     5.2.  Modifying a Configured Subscription . . . . . . . . . . .  18
     5.3.  Deleting a Configured Subscription  . . . . . . . . . . .  18
   6.  Deleting a Configured Subscription  . . . . . . . . . . . . .  19
   7.  Asynchronous Subscribed Event Delivery  . . . . . . . . . . .  19
   8.  Subscription State Notifications  . . . . . . . . . . . . . .  20
     8.1.  subscription-started  . . . . . . . . . . . . . . . . . .  20
     8.2.  subscription-modified . . . . . . . . . . . . . . . . . .  21
     8.3.  subscription-terminated . . . . . . . . . . . . . . . . .  21
     8.4.  subscription-suspended  . . . . . . . . . . . . . . . . .  21
     8.5.  subscription-resumed  . . . . . . . . . . . . . . . . . .  21
     8.6.  subscription-completed  . . . . . . . . . . . . . . . . .  22
     8.7.  replay-completed  . . . . . . . . . . . . . . . . . . . .  22
   9.  Administrative Functions  . . . . . . . . . . . . . . . . . .  22
     9.1.  Subscription Monitoring . . . . . . . . . . . . . . . . .  22
     9.2.  Advertisement . . . . . . . . . . . . . . . . . . . . . .  23
     9.3.  Event Stream Discovery  . . . . . . . . . . . . . . . . .  23
   10. Data Model  . . . . . . . . . . . . . . . . . . . . . . . . .  23
   11. Considerations  . . . . . . . . . . . . . . . . . . . . . . .  46
     11.1.  Implementation Considerations  . . . . . . . . . . . . .  46
     11.2.  Security Considerations  . . . . . . . . . . . . . . . .  46
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  47



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   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  48
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  48
     13.2.  Informative References . . . . . . . . . . . . . . . . .  48
   Appendix A.  Changes between revisions  . . . . . . . . . . . . .  49
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  52

1.  Introduction

   This document defines capabilities and operations for the customized
   establishment of subscriptions upon system generated event streams.
   Effectively this enables a "Subscribe then Publish" capability where
   the customized information needs of each target receiver are
   understood by the publisher before subscribed event records are
   marshalled and pushed.  The receiver then gets a continuous, custom
   feed of publisher generated information.

   While the functionality defined in this document is transport-
   agnostic, protocols like NETCONF [RFC6241] or RESTCONF [RFC8040] can
   be used to configure or dynamically signal subscriptions, and there
   are bindings defined for subscribed event record delivery for NETCONF
   within [I-D.draft-ietf-netconf-netconf-event-notifications], and for
   HTTP2 or HTTP1.1 within [I-D.draft-ietf-netconf-restconf-notif].

1.1.  Motivation

   There are various [RFC5277] limitations, many of which have been
   exposed in [RFC7923] which needed to be solved.  Key capabilities
   supported by this document include:

   o  multiple subscriptions on a single transport session

   o  support for dynamic and statically configured subscriptions

   o  modification of an existing subscription

   o  operational counters and instrumentation

   o  negotiation of subscription parameters (through the use of hints
      returned as part of declined subscription requests)

   o  state change notifications (e.g., publisher driven suspension,
      parameter modification)

   o  independence from transport protocol







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1.2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   Configured subscription: A subscription installed via a configuration
   interface which persists across reboots.

   Dynamic subscription: A subscription agreed between subscriber and
   publisher created via RPC subscription state signaling messages.

   Event: An occurrence of something that may be of interest. (e.g., a
   configuration change, a fault, a change in status, crossing a
   threshold, or an external input to the system.)

   Event record: A set of information detailing an event.

   NACM: NETCONF Access Control Model.

   Notification message: A set of transport encapsulated information
   intended for a receiver indicating that one or more event(s) have
   occurred.  A notification message may include event records.

   Publisher: An entity responsible for streaming notification messages
   per the terms of a Subscription.

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

   Stream (also referred to as "event stream"): A continuous ordered set
   of events aggregated under some context.

   Stream filter: Evaluation criteria which may be applied against a
   event records within a stream.  Event records pass the filter when
   specified criteria are met.

   Subscribed event records: Event records which have met the terms of
   the subscription.  This include terms (such as security checks)
   enforced by the publisher.

   Subscriber: An entity able to request and negotiate a contract for
   the generation and push of event records from a publisher.

   Subscription: A contract with a publisher, stipulating which
   information one or more receivers wish to have pushed from the
   publisher without the need for further solicitation.



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1.3.  Solution Overview

   This document describes a transport agnostic mechanism for
   subscribing to and receiving content from a stream instantiated
   within a publisher.  This mechanism is through the use of a
   subscription.

   Two types of subscriptions are supported:

   1.  Dynamic subscriptions, where a subscriber initiates a
       subscription negotiation with a publisher via RPC.  If the
       publisher wants to serve this request, it accepts it, and then
       starts pushing notification messages.  If the publisher does not
       wish to serve it as requested, then an error response is
       returned.  This response MAY include hints at subscription
       parameters which would have been accepted.

   2.  Configured subscriptions, which allow the management of
       subscriptions via a configuration interface so that a publisher
       can send notification messages to configured receiver(s).
       Support for this capability is optional.

   Additional characteristics differentiating configured from dynamic
   subscriptions include:

   o  The lifetime of a dynamic subscription is bounded by the transport
      session used to establish it.  For connection-oriented stateful
      transport like NETCONF, the loss of the transport session will
      result in the immediate termination of associated dynamic
      subscriptions.  For connectionless or stateless transports like
      HTTP, it is the lack of receipt acknowledgement of a sequential
      set of notification messages and/or keep-alives which will
      terminate dynamic subscriptions.  The lifetime of a configured
      subscription is driven by relevant configuration being present on
      the running configuration.  This implies configured subscriptions
      persist across reboots, and persist even when transport is
      unavailable.

   o  Configured subscriptions can be modified by any configuration
      client with write permission on the configuration of the
      subscription.  Dynamic subscriptions can only be modified via an
      RPC request made upon the original subscribing transport session.

   Note that there is no mixing-and-matching of dynamic and configured
   subscriptions.  Specifically, a configured subscription cannot be
   modified or deleted using RPC.  Similarly, a subscription established
   via RPC cannot be modified through configuration operations (if
   needed, an operator may use a kill RPC however).



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   The publisher MAY decide to terminate a dynamic subscription at any
   time.  Similarly, it MAY decide to temporarily suspend the sending of
   notification messages for either configured or dynamic subscriptions.
   Such termination or suspension MAY be driven by the publisher running
   out of resources to serve the subscription, or by internal errors on
   the publisher.

1.4.  Relationship to RFC-5277

   This document is intended to provide a superset of the subscription
   capabilities initially defined within [RFC5277].  Especially when
   extending an existing [RFC5277] implementation, it is important to
   understand what has been reused and what has been replaced.  Key
   realtionships between these two documents include:

   o  the data model in this document replaces the data model in
      [RFC5277].

   o  the RPC operations in this draft replaces the symetrical
      operations of [RFC5277], section 4.

   o  the one way operation of [RFC5277] is still used.  However this
      operation will no longer be required with the availability of
      [I.D.draft-ietf-netconf-notification-messages].

   o  the definition and contents of the NETCONF stream are identical
      between this document and [RFC5277].

   o  a publisher MAY implement both the data model and RPCs defined in
      [RFC5277] and this new document concurrently, in order to support
      old clients.  However the use of both alternatives on a single
      transport session is prohibited.

2.  Solution

2.1.  Event Streams

   An event stream is a named entity on a publisher which exposes a
   continuously updating set of events.  Each event stream is available
   for subscription.  It is out of the scope of this document to
   identify a) how streams are defined, b) how events are defined/
   generated, and c) how events are assigned to streams.

   There is only one reserved event stream within this document:
   NETCONF.  The NETCONF event stream contains all NETCONF XML event
   record information supported by the publisher, except for where it
   has been explicitly indicated that this the event record MUST be




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   excluded from the NETCONF stream.  Beyond NETCONF, implementations
   are free to add additional event streams.

   As events are raised by a system, they may be assigned to one or more
   streams.  The event record is distributed to receivers where: (1) a
   subscription includes the identified stream, and (2) subscription
   filtering does not exclude the event record from that receiver.

   If access control permissions are in use to secure publisher content,
   then for notification messages to be sent to a receiver, that
   receiver MUST be allowed access to all the event records on the
   stream.  If subscriber permissions change during the lifecycle of a
   subscription, then the subscription MUST be continued or terminated
   accordingly.

2.2.  Event Stream Filters

   This document defines an extensible filtering mechanism.  Two
   optional stream filtering syntaxes supported are [XPATH] and subtree
   [RFC6241].  The subsets of these filtering syntaxes supported are
   left to each implementation.  A subset of information is never
   stripped from within the event record.

   If no stream filter is provided, all event records on a stream are to
   be sent.

2.3.  Subscription State Model at the Publisher

   Below is the state machine of a subscription for the publisher for a
   dynamic subscription.  It is important to note that such a
   subscription doesn't exist at the publisher until it is accepted and
   made active.  The mere request by a subscriber to establish a
   subscription is insufficient for that asserted subscription to be
   externally visible via this state machine.

















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                       .-------.
                       | start |
                       '-------'
                           |
                        establish
                           |
                           |   .----------modify------------.
                           v   v                            '
                     .-----------.                    .-----------.
          .--------. |           |-----suspend------->|           |
        modify      '|  active   |                    | suspended |
          '--------->|           |<----resume---------|           |
                     '-----------'                    '-----------'
                           |                                |
                      delete/kill                      delete/kill
                           |                                |
                           v                                |
                       .-------.                            |
                       |  end  |<---------------------------'
                       '-------'

                   Figure 1: Dynamic subscription states

   Of interest in this state machine are the following:

   o  Successful establish or modify RPCs put the subscription into an
      active state.

   o  Failed modify RPCs will leave the subscription in its previous
      state, with no visible change to any streaming updates.

   o  A delete or kill RPC will end the subscription.

   o  Suspend and resume state changes are driven by internal process
      and prioritization.  There are no external controls over suspend
      and resume.

   As shown below, a very similar state machine exists for configured
   subscriptions.  Creation, modification, and deletion is via
   configuration operations rather than via RPC.  When a subscription is
   first created, the operational status of each receiver is initially
   set to connecting.  Individual are receivers are moved to an active
   status when a subscription-started state change notification is
   successfully delivered.  Configured subscriptions remain active if
   transport connectivity is not lost and event records are not being
   dropped due to buffer overflow.  A configured subscription MUST be
   moved connecting if transport connectivity is lost.




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   A configured subscription MUST be moved to a suspended status if
   notification messages are being dropped despite the presence of
   transport connectivity.  A configured subscription MUST be returned
   to an active status from the suspended status as soon as transport
   connectivity is re-established, and a receiver acknowledges receipt
   of a "subscription-resumed".  Otherwise, it MUST be moved to
   connecting.

                     .-------.
                     | start |
                     '-------'
                         |
                      create
                         |
                         v
                   .---------------------------------------------------.
        .--------. |  Subscription                                     |
      modify      '|             .---------------------.               |
        '--------->|          .--| connecting receiver |--.            |
                   |          |  '---------------------'  |            |
                   |          V    ^                ^     V            |
                   | .---------------. -suspend-> .------------------. |
                   | |active receiver|            |suspended receiver| |
                   | '---------------' <--resume- '------------------' |
                   '---------------------------------------------------'
                         |
                       delete
                         |
                         v
                     .-------.
                     |  end  |
                     '-------'

           Figure 2: Configured subscription and receiver states

   The interaction model described within this section is mirrored in
   the RPCs and Notifications later in the document.  It should be noted
   that these RPCs and Notifications have been designed to be extensible
   and allow subscriptions into targets other than event streams.
   [I-D.ietf-netconf-yang-push] provides an example of such an
   extension.

3.  Data Model Trees

module: ietf-subscribed-notifications
    +--ro streams
    |  +--ro stream* [name]
    |     +--ro name                        stream



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    |     +--ro description                 string
    |     +--ro replay-support?             empty {replay}?
    |     +--ro replay-log-creation-time?   yang:date-and-time {replay}?
    |     +--ro replay-log-aged-time?       yang:date-and-time {replay}?
    +--rw filters
    |  +--rw stream-filter* [identifier]
    |     +--rw identifier        filter-id
    |     +--rw (filter-spec)?
    |        +--:(subtree-filter)
    |        |  +--rw subtree-filter?               {subtree}?
    |        +--:(xpath-filter)
    |           +--rw xpath-filter?     yang:xpath1.0 {xpath}?
    +--rw subscription-config {configured}?
    |  +--rw subscription* [identifier]
    |     +--rw identifier           subscription-id
    |     +--rw encoding             encoding
    |     +--rw (target)
    |     |  +--:(stream)
    |     |     +--rw (stream-filter)?
    |     |     |  +--:(by-reference)
    |     |     |  |  +--rw stream-filter-ref    stream-filter-ref
    |     |     |  +--:(within-subscription)
    |     |     |     +--rw (filter-spec)?
    |     |     |        +--:(subtree-filter)
    |     |     |        |  +--rw subtree-filter?             {subtree}?
    |     |     |        +--:(xpath-filter)
    |     |     |           +--rw xpath-filter?   yang:xpath1.0 {xpath}?
    |     |     +--rw stream               stream
    |     |     +--rw replay-start-time?   yang:date-and-time {replay}?
    |     +--rw stop-time?                 yang:date-and-time
    |     +--rw receivers
    |     |  +--rw receiver* [address port]
    |     |     +--rw address     inet:host
    |     |     +--rw port        inet:port-number
    |     |     +--rw protocol    transport
    |     |     +--rw status?     enumeration
    |     +--rw (notification-message-origin)?
    |        +--:(interface-originated)
    |        |  +--rw source-interface?    if:interface-ref
    |        +--:(address-originated)
    |           +--rw source-vrf?          string
    |           +--rw source-address?      inet:ip-address-no-zone
    +--ro subscriptions
       +--ro subscription* [identifier]
          +--ro identifier                 subscription-id
          +--ro configured-subscription?   empty {configured}?
          +--ro encoding                   encoding
          +--ro (target)



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          |  +--:(stream)
          |     +--ro (stream-filter)?
          |     |  +--:(by-reference)
          |     |  |  +--ro stream-filter-ref          stream-filter-ref
          |     |  +--:(within-subscription)
          |     |     +--ro (filter-spec)?
          |     |        +--:(subtree-filter)
          |     |        |  +--ro subtree-filter?             {subtree}?
          |     |        +--:(xpath-filter)
          |     |           +--ro xpath-filter?   yang:xpath1.0 {xpath}?
          |     +--ro stream                     stream
          |     +--ro replay-start-time?   yang:date-and-time {replay}?
          +--ro stop-time?                 yang:date-and-time
          +--ro (notification-message-origin)?
          |  +--:(interface-originated)
          |  |  +--ro source-interface?          if:interface-ref
          |  +--:(address-originated)
          |     +--ro source-vrf?                string
          |     +--ro source-address?            inet:ip-address-no-zone
          +--ro receivers
             +--ro receiver* [address port]
                +--ro address                   inet:host
                +--ro port                      inet:port-number
                +--ro protocol                  transport
                +--ro pushed-notifications?     yang:counter64
                +--ro excluded-notifications?   yang:counter64
                +--ro status                    enumeration

  rpcs:
    +---x establish-subscription
    |  +---w input
    |  |  +---w encoding?             encoding
    |  |  +---w (target)
    |  |  |  +--:(stream)
    |  |  |     +---w (stream-filter)?
    |  |  |     |  +--:(by-reference)
    |  |  |     |  |  +---w stream-filter-ref    stream-filter-ref
    |  |  |     |  +--:(within-subscription)
    |  |  |     |     +---w (filter-spec)?
    |  |  |     |        +--:(subtree-filter)
    |  |  |     |        |  +---w subtree-filter?             {subtree}?
    |  |  |     |        +--:(xpath-filter)
    |  |  |     |           +---w xpath-filter?   yang:xpath1.0 {xpath}?
    |  |  |     +---w stream               stream
    |  |  |     +---w replay-start-time?   yang:date-and-time {replay}?
    |  |  +---w stop-time?           yang:date-and-time
    |  +--ro output
    |     +--ro subscription-result       subscription-result



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    |     +--ro (result)?
    |        +--:(no-success)
    |        |  +--ro filter-failure?           string
    |        |  +--ro replay-start-time-hint?   yang:date-and-time
    |        +--:(success)
    |           +--ro identifier                subscription-id
    +---x modify-subscription
    |  +---w input
    |  |  +---w identifier?          subscription-id
    |  |  +---w (target)
    |  |  |  +--:(stream)
    |  |  |     +---w (stream-filter)?
    |  |  |        +--:(by-reference)
    |  |  |        |  +---w stream-filter-ref    stream-filter-ref
    |  |  |        +--:(within-subscription)
    |  |  |           +---w (filter-spec)?
    |  |  |              +--:(subtree-filter)
    |  |  |              |  +---w subtree-filter?             {subtree}?
    |  |  |              +--:(xpath-filter)
    |  |  |                 +---w xpath-filter?   yang:xpath1.0 {xpath}?
    |  |  +---w stop-time?           yang:date-and-time
    |  +--ro output
    |     +--ro subscription-result    subscription-result
    |     +--ro (result)?
    |        +--:(no-success)
    |           +--ro filter-failure?        string
    +---x delete-subscription
    |  +---w input
    |  |  +---w identifier    subscription-id
    |  +--ro output
    |     +--ro subscription-result    subscription-result
    +---x kill-subscription
       +---w input
       |  +---w identifier    subscription-id
       +--ro output
          +--ro subscription-result    subscription-result

  notifications:
    +---n replay-completed {replay}?
    |  +--ro identifier    subscription-id
    +---n subscription-completed
    |  +--ro identifier    subscription-id
    +---n subscription-started {configured}?
    |  +--ro identifier           subscription-id
    |  +--ro encoding             encoding
    |  +--ro (target)
    |  |  +--:(stream)
    |  |     +--ro (stream-filter)?



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    |  |     |  +--:(by-reference)
    |  |     |  |  +--ro stream-filter-ref    stream-filter-ref
    |  |     |  +--:(within-subscription)
    |  |     |     +--ro (filter-spec)?
    |  |     |        +--:(subtree-filter)
    |  |     |        |  +--ro subtree-filter?                {subtree}?
    |  |     |        +--:(xpath-filter)
    |  |     |           +--ro xpath-filter?      yang:xpath1.0 {xpath}?
    |  |     +--ro stream               stream
    |  |     +--ro replay-start-time?   yang:date-and-time {replay}?
    |  +--ro stop-time?           yang:date-and-time
    +---n subscription-resumed
    |  +--ro identifier    subscription-id
    +---n subscription-modified {configured}?
    |  +--ro identifier           subscription-id
    |  +--ro encoding             encoding
    |  +--ro (target)
    |  |  +--:(stream)
    |  |     +--ro (stream-filter)?
    |  |     |  +--:(by-reference)
    |  |     |  |  +--ro stream-filter-ref    stream-filter-ref
    |  |     |  +--:(within-subscription)
    |  |     |     +--ro (filter-spec)?
    |  |     |        +--:(subtree-filter)
    |  |     |        |  +--ro subtree-filter?                {subtree}?
    |  |     |        +--:(xpath-filter)
    |  |     |           +--ro xpath-filter?      yang:xpath1.0 {xpath}?
    |  |     +--ro stream               stream
    |  |     +--ro replay-start-time?   yang:date-and-time {replay}?
    |  +--ro stop-time?           yang:date-and-time
    +---n subscription-terminated
    |  +--ro identifier        subscription-id
    |  +--ro error-id          subscription-errors
    |  +--ro filter-failure?   string
    +---n subscription-suspended
       +--ro identifier        subscription-id
       +--ro error-id          subscription-errors
       +--ro filter-failure?   string

   The top-level decompositions of data model are as follows:

   o  "Streams" contains a list of event streams that are supported by
      the publisher and against which subscription is allowed.

   o  "Filters" contains a configurable list of filters that can be
      applied to a subscription.  This allows users to reference an
      existing filter definition as an alternative to defining a filter
      inline for each subscription.



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   o  "Subscription-config" contains the configuration of configured
      subscriptions.  The parameters of each configured subscription are
      a superset of the parameters of a dynamic subscription and use the
      same groupings.  In addition, the configured subscriptions MUST
      also specify intended receivers and MAY specify the push source
      from which to send the stream of notification messages.

   o  "Subscriptions" contains a list of all subscriptions on a
      publisher, both configured and dynamic.  It can be used to
      retrieve information about the subscriptions which a publisher is
      serving.

   The data model also contains a number of YANG Notifications that
   allow a publisher to signal information about a subscription.
   Finally, the data model contains a number of RPC definitions that are
   used to manage dynamic subscriptions.

4.  Dynamic Subscriptions

   Dynamic subscriptions are managed via RPC, and are made against
   targets located within the publisher.  These RPCs have been designed
   extensibly so that they may be augmented for targets beyond event
   streams.

4.1.  Establishing a Subscription

   The "establish-subscription" operation allows a subscriber to request
   the creation of a subscription via RPC.  Multiple establish
   subscription RPC requests can be made within the same transport
   session.

   The input parameters of the operation are:

   o  A stream name which identifies the continuous feed of events
      against which the subscription is applied.

   o  A filter which may reduce the set of event records pushed.

   o  The desired encoding for the notification message.

   o  An optional stop time for the subscription.

   o  An optional start time which indicates that this subscription is
      requesting a replay of previously generated information from the
      event stream.

   If the publisher cannot satisfy the "establish-subscription" request,
   it sends a negative "subscription-result" element.  If the subscriber



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   has no authorization to establish the subscription, the
   "subscription-result" indicates an authorization error.  Optionally,
   the "subscription-result" MAY include one or more hints on
   alternative input parameters and value which would have resulted in
   an accepted subscription.

   Subscription requests MUST fail if a filter with invalid syntax is
   provided or if a non-existent stream is referenced.

4.1.1.  Replay Subscription

   Replay provides the ability to establish an subscription which is
   also capable of passing along recently generated event records.  In
   other words, as the subscription initializes itself, it sends any
   previously generated content from within target event stream which
   meet the filter and timeframe criteria.  These historical event
   records would then be followed by event records generated after the
   subscription has been established.  All event records will be
   delivered in the order generated.  Replay is only viable for dynamic
   subscriptions.  Replay is an optional feature.  Replay is dependent
   on an event stream supporting some form of logging, although it puts
   no restrictions on the size or form of the log, or where it resides
   within the device.

   The inclusion of a replay-start-time within an "establish-
   subscription" RPC indicates a replay request.  If the "replay-start-
   time" contains a value that is earlier than content stored within the
   publisher's replay buffer, then the subscription MUST be rejected,
   and the leaf "replay-start-time-hint" MUST be set in the reply.

   An end time MAY be specified using the optional stop-time parameter,
   which only in the case of replay MAY also be earlier than the current
   time.  If no stop-time is present, notification messages will
   continue to be sent until the subscription is terminated.  The
   publisher MUST NOT accept a replay-start-time for a future time.

   If the replay-start-time is later than any information stored in the
   replay buffer, then the publisher MUST send a "replay-completed"
   notification immediately after the "subscription-started"
   notification.

   Not all streams will support replay.  Those that do MUST include they
   do via the "replay-support" object.  In addition, a event stream that
   does support replay is not expected to have an unlimited supply of
   saved notifications available to accommodate any given replay
   request.  Subscribers MAY do a get on "replay-log-creation-time" and
   "replay-log-aged-time" to assess the availability of replay.  The
   actual size of the replay log at any given time is a publisher



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   specific matter.  Control parameters for this aspect of the feature
   are outside the scope of this document.

4.2.  Modifying a Subscription

   The "modify-subscription" operation permits changing the terms of an
   existing dynamic subscription previously established on that
   transport session.  Subscriptions created by configuration operations
   cannot be modified via this RPC.  Dynamic subscriptions can be
   modified one or multiple times.  If the publisher accepts the
   requested modifications, it replies that this change has been made,
   then immediately starts sending event records based on the new terms.
   If the publisher rejects the request, the subscription remains as
   prior to the request.  That is, the request has no impact whatsoever.
   The contents of a such a rejected modification MAY include one or
   more hints on alternative input parameters and value which would have
   resulted in a successfully modified subscription.

   Dynamic subscriptions established via RPC can only be modified via
   RPC using the same transport session used to establish that
   subscription.

4.3.  Deleting a Subscription

   The "delete-subscription" operation permits canceling an existing
   subscription previously established on that transport session.  If
   the publisher accepts the request, and the publisher has indicated
   this successful reply has been sent, the publisher MUST NOT send any
   more notification messages for this subscription.  If the publisher
   rejects the request, all subscriptions remain as prior to the
   request.  That is, the request has no impact whatsoever.

   Subscriptions established via RPC can only be deleted via RPC using
   the same transport session used for subscription establishment.
   Configured subscriptions cannot be deleted using RPCs.

4.4.  Killing a Subscription

   The "kill-subscription" operation permits an operator to end a
   dynamic subscription which is not associated the transport session
   used for the RPC.  This operation MUST be secured so that only
   connections with sufficiently privileged access rights are able to
   invoke this RPC.  A publisher MUST terminate any dynamic subscription
   identified by RPC request.  An operator may find subscription
   identifiers which may be used with "kill-subscription" by searching
   for the ip address of a receiver within the yang tree.





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   Configured subscriptions cannot be killed using this RPC.  Instead,
   configured subscriptions are deleted as part of regular configuration
   operations.  Publishers MUST reject any RPC attempt to kill a
   configured subscription.

5.  Configured Subscriptions

   A configured subscription is a subscription installed via a
   configuration interface.  Such a subscription MAY push notification
   messages to more than one receiver.  The publisher does not provide
   information about receivers are provided no information about other
   receivers.  Supporting configured subscriptions is optional and
   advertised using the "configured" feature.

   Configured subscriptions persist across reboots, and persist even
   when transport is unavailable.

   Configured subscriptions can be modified by any configuration client
   with write permissions for the configuration of the subscription.
   Subscriptions can be modified or terminated via the configuration
   interface at any point of their lifetime.

   In addition to subscription parameters that apply to dynamic
   subscriptions, the following additional parameters apply to
   configured subscriptions:

   o  One or more receiver IP addresses (and corresponding ports)
      intended as the destination for notification messages for each
      subscription.  In addition, the transport for each destination MAY
      be defined.

   o  Optional parameters to identify an egress interface, a host IP
      address, a VRF, or an IP address plus VRF out of which
      notification messages should be pushed from the publisher.  Where
      any of this info is not explicitly included, or where just the VRF
      is provided, notification messages MUST egress the publisher's
      default interface towards that receiver.

5.1.  Creating a Configured Subscription

   Configured subscriptions are established using configuration
   operations against the top-level subtree subscription-config.  There
   are two key differences between RPCs and configuration operations for
   subscription creation.  Firstly, configuration operations install a
   subscription without question, while RPCs are designed to the support
   negotiation and rejection of requests.  Secondly, while RPCs mandate
   that the subscriber establishing the subscription is the only
   receiver of the notification messages, configuration operations



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   permit specifying receivers independent of any tracked subscriber.
   Because there is no explicit association with an existing transport
   session, configuration operations require additional parameters
   beyond those of dynamic subscriptions to indicate receivers, and
   possibly whether the notification messages need to come from a
   specific egress interface on the publisher.

   After a subscription is successfully created, the publisher
   immediately sends a subscription-started state change notification to
   each receiver.  It is quite possible that upon configuration, reboot,
   or even steady-state operations, a transport session may not be
   currently available to the receiver.  In this case, when there is
   something to transport for an active subscription, transport specific
   call-home operations will be used to establish the connection.  When
   transport connectivity is available, as successful receipt of the
   subscription start change notification by a particular receiver
   indicated, notification messages may then be pushed.

   To see an example at subscription creation using configuration
   operations over NETCONF, see Appendix A of
   [I-D.draft-ietf-netconf-netconf-event-notifications].

   Note that is possible to configure replay on a configured
   subscription.  This is to allows a configured subscription to exist
   on a system so that event records generated during boot can be
   buffered and pushed as soon as the transport session is established.

5.2.  Modifying a Configured Subscription

   Configured subscriptions can be modified using configuration
   operations against the top-level subtree subscription-config.

   Immediately after a subscription is successfully modified, the
   publisher sends to the existing receivers a state change notification
   stating the subscription has been modified (i.e., subscription-
   modified).

   If the modification involved adding and/or removing receivers, those
   modified receivers are sent state change notifications, indicating
   they have been added (i.e, subscription-started to a specific
   receiver) or removed (i.e., subscription-terminated to a specific
   receiver.)

5.3.  Deleting a Configured Subscription

   Subscriptions can be deleted using configuration operations against
   the top-level subtree subscription-config.  For example, in RESTCONF:




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   DELETE /subscription-config/subscription=1922 HTTP/1.1
   Host: example.com

   HTTP/1.1 204 No Content
   Date: Sun, 24 Jul 2016 11:23:40 GMT
   Server: example-server

               Figure 3: Deleting a configured subscription

   Immediately after a subscription is successfully deleted, the
   publisher sends to all receivers of that subscription a state change
   notification stating the subscription has been terminated (i.e.,
   subscription-terminated).

6.  Deleting a Configured Subscription

   Configured subscriptions can be deleted using configuration
   operations against the top-level subtree subscription-config.

   Immediately after a subscription is successfully deleted, the
   publisher sends to the existing receivers a state change notification
   stating the subscription has been terminated (i.e., subscription-
   terminated).

7.  Asynchronous Subscribed Event Delivery

   Once a subscription has been set up, the publisher streams subscribed
   event records via notification messages per the terms of the
   subscription.  For dynamic subscriptions set up via RPC operations,
   notification messages are sent over the session used to establish the
   subscription.  For configured subscriptions, notification messages
   are sent over the specified connections.

   A notification message is sent to a receiver when something of
   interest occurs which is able to traverse all specified filtering and
   access control criteria.

   This notification message MUST be encoded as one-way notification
   element of [RFC5277], Section 4.  The following example within
   [RFC7950] section 7.16.3 is an example of a compliant message:











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      <notification
             xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
          <eventTime>2007-09-01T10:00:00Z</eventTime>
          <link-failure xmlns="http://acme.example.com/system">
              <if-name>so-1/2/3.0</if-name>
              <if-admin-status>up</if-admin-status>
              <if-oper-status>down</if-oper-status>
          </link-failure>
      </notification>

                 Figure 4: subscribed notification message

   This [RFC5277] section 4 one-way operation has the drawback of not
   including useful header information such as a subscription
   identifier.  When using this mechanism, it is left up to
   implementations or augmentations to this document to determine which
   event records belong to which subscription.

   These drawbacks, along with other useful common headers and the
   ability to bundle multiple event records together is being explored
   within [I.D.draft-ietf-netconf-notification-messages].  When the
   notification-messages is supported, this document will be updated to
   indicate support.

8.  Subscription State Notifications

   In addition to subscribed event records, a publisher will send
   subscription state notifications to indicate to receivers that an
   event related to the subscription management has occurred.

   Subscription state notifications are unlike other notifications which
   might be found in the event stream.  They cannot be filtered out, and
   they are delivered only to directly impacted receiver(s) of a
   subscription.  The definition of subscription state notifications is
   distinct from other notification messages by making use of a YANG
   extension tagging them as subscription state notification.

   Subscription state notifications include indications that a replay of
   event records has been completed, that a subscription is done because
   an end time has been reached, and that a subscription has started,
   been modified, been terminated, or been suspended.  They are
   described in the following subsections.

8.1.  subscription-started

   This indicates that a configured subscription has started and data
   updates are beginning to be sent.  This state change notification
   includes the parameters of the subscription, except for the



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   receiver(s) addressing information and origin information indicating
   where notification messages will egress the publisher.  Note that for
   RPC-based subscriptions, no "subscription-started" notifications are
   sent.

8.2.  subscription-modified

   This indicates that a configured subscription has been modified
   successfully.  This state change notification includes the parameters
   of the subscription, except for the receiver(s) addressing
   information and origin information indicating where notification
   messages will egress the publisher.  Note that for RPC-based
   subscriptions, no "subscription-modified" state change notifications
   are sent.

8.3.  subscription-terminated

   This indicates that a subscription has been terminated by the
   publisher.  The state change notification includes the reason for the
   termination.  The publisher MAY decide to terminate a subscription
   when it is running out of resources for serving it, an internal error
   occurs, etc.  Publisher-driven terminations are notified to all
   receivers.  Northbound systems MAY also terminate configured
   subscriptions using configuration operations.

   Subscribers can terminate via RPC subscriptions established via a
   delete-subscription RPC.  In such cases, no subscription-terminated
   state change notifications are sent.  However if a kill-subscription
   RPC is sent, or some other event other than reaching the
   subscription's stop time results in the end of a subscription, then
   there MUST be this state change notification that the subscription
   has been ended.

8.4.  subscription-suspended

   This indicates that a publisher has suspended a subscription.  The
   state change notification includes the reason for the suspension.  A
   possible reason is the lack of resources to serve it.  No further
   subscribed event records will be sent until the subscription resumes.
   Suspensions are notified to the subscriber (in the case of dynamic
   subscriptions) and all receivers (in the case of configured
   subscriptions).

8.5.  subscription-resumed

   This indicates that a previously suspended subscription has been
   resumed.  Subscribed event records generated after the generation of
   this state change notification will be sent.  These state change



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   notifications go to the subscriber (in the case of dynamic
   subscriptions) and all receivers (in the case of configured
   subscriptions).

8.6.  subscription-completed

   This indicates that a subscription, which includes a stop time, has
   successfully finished passing event records upon the reaching of that
   stop time.

8.7.  replay-completed

   This indicates that all of the event records prior to the current
   time have been sent.  This includes new event records generated since
   the start of the subscription.  This notification MUST NOT be sent
   for any other reason.

   If subscription contains no stop time, or has a stop time which has
   not been reached, then after the replay-completed notification has
   been sent event records will be sent in sequence as they arise
   naturally within the system.

9.  Administrative Functions

9.1.  Subscription Monitoring

   Container "subscriptions" in the YANG module below contains the state
   of all known subscriptions.  This includes subscriptions that were
   established (and have not yet been deleted) using RPCs, as well as
   subscriptions that have been configured as part of configuration.
   Using the "get" operation with NETCONF, or subscribing to this
   information via [I-D.ietf-netconf-yang-push] allows the status of
   subscriptions to be monitored.

   Each subscription is represented as a list element.  The associated
   information includes an identifier for the subscription, receiver
   counter information, the status of the subscription, as well as the
   various subscription parameters that are in effect.  The subscription
   status indicates the subscription's state with each receiver (e.g.,
   is currently active or suspended).  Leaf "configured-subscription"
   indicates whether the subscription came into being via configuration
   or via RPC.

   Subscriptions that were established by RPC are removed from the list
   once they expire (reaching stop-time) or when they are terminated.
   Subscriptions that were established by configuration need to be
   deleted from the configuration by a configuration editing operation
   even if the stop time has been passed.



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9.2.  Advertisement

   Publishers supporting this document MUST indicate support the yang
   model "ietf-subscribed-notifications" within the YANG library of the
   publisher.  In addition support for optional features: encode-xml,
   encode-json, configured, and replay MUST also be indicated if
   supported.

   If a publisher supports this specification but not subscriptions via
   [RFC5277], the publisher MUST NOT advertise
   "urn:ietf:params:netconf:capability:notification:1.0".  Even without
   this advertisement however, the publisher MUST support the one-way
   notification element of [RFC5277] Section 4.

9.3.  Event Stream Discovery

   A publisher maintains a list of available event streams as
   operational data.  This list contains both standardized and vendor-
   specific event streams.  A client can retrieve this list like any
   other YANG-defined data.

10.  Data Model

<CODE BEGINS> file "ietf-subscribed-notifications.yang"
module ietf-subscribed-notifications {
  yang-version 1.1;
  namespace
    "urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications";

  prefix sn;

  import ietf-yang-types {
    prefix yang;
  }
  import ietf-inet-types {
    prefix inet;
  }
  import ietf-interfaces {
    prefix if;
  }

  organization "IETF";
  contact
    "WG Web:   <http:/tools.ietf.org/wg/netconf/>
     WG List:  <mailto:netconf@ietf.org>

     Editor:   Alexander Clemm
               <mailto:ludwig@clemm.org>



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     Editor:   Eric Voit
               <mailto:evoit@cisco.com>

     Editor:   Alberto Gonzalez Prieto
               <mailto:agonzalezpri@vmware.com>

     Editor:   Einar Nilsen-Nygaard
               <mailto:einarnn@cisco.com>

     Editor:   Ambika Prasad Tripathy
               <mailto:ambtripa@cisco.com>";

  description
    "Contains a YANG specification for subscribing to event records
    and receiving matching content within notification messages.";

  revision 2017-10-27 {
    description
      "Initial version";
    reference
      "draft-ietf-netconf-subscribed-notifications-06";
  }

  /*
   * FEATURES
   */

  feature encode-json {
    description
      "This feature indicates that JSON encoding of notification
       messages is supported.";
  }

  feature encode-xml {
    description
      "This feature indicates that XML encoding of notification
       messages is supported.";
  }

  feature configured {
    description
      "This feature indicates that configuration of subscription is
      supported.";
  }

  feature replay {
    description
      "This feature indicates that historical event record replay is



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      supported.  With replay, it is possible for past event records to
      be streamed in chronological order.";
  }

  feature xpath {
    description
      "This feature indicates support for xpath filtering.";
    reference "http://www.w3.org/TR/1999/REC-xpath-19991116";
  }

  feature subtree {
    description
      "This feature indicates support for YANG subtree filtering.";
    reference "RFC 6241, Section 6.";
  }

  /*
   * EXTENSIONS
   */

  extension subscription-state-notif {
    description
      "This statement applies only to notifications. It indicates that
       the notification is a subscription state notification. Therefore
       it does not participate in a regular event stream and does not
       need to be specifically subscribed to in order to be received.
       This statement can only occur as a substatement to the YANG
       'notification' statement.";
  }

  /*
   * IDENTITIES
   */

  /* Identities for subscription results */
  identity subscription-result {
    description
      "Base identity for RPC responses and State Change Notifications
      providing information on the creation, modification, deletion of
       subscriptions.";
  }

  identity ok {
    base subscription-result;
    description
      "OK - RPC was successful and was performed as requested.";
  }




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  identity error {
    base subscription-result;
    description
      "Problem with subscription.  Base identity for error return
      codes for RPCs and State Change Notifications.";
  }

  /* Identities for subscription errors */

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

  identity stream-unavailable {
    base error;
    description
     "Stream does not exist or is not available to the receiver.";
  }

  identity encoding-unavailable {
    base error;
    description
     "Encoding not supported";
  }

  identity replay-unsupported {
    base error;
    description
     "Replay cannot be performed for this subscription. The publisher
     does not provide the requested historic information via replay.";
  }

  identity history-unavailable {
    base error;
    description
     "Replay request too far into the past. The publisher does store
      historic information for all parts of requested subscription, but
      not back to the requested timestamp.";
  }

  identity filter-unavailable {
    base error;
    description
     "Referenced filter does not exist";



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  }

  identity filter-type-unsupported {
    base error;
    description
     "Publisher does not support filters constructed using this
     filtering technology syntax.";
  }

  identity filter-unsupported {
    base error;
    description
     "Failure can be from a syntax error, or a syntax too complex to be
     processed by the platform. The supplemental info should include
     the invalid part of the filter.";
  }

  identity namespace-unavailable {
    base error;
    description
     "Referenced namespace doesn't exist or is unavailable
      to the receiver.";
  }

  identity no-such-subscription {
    base error;
    description
     "Referenced subscription doesn't exist. This may be as a result of
      a non-existent subscription ID, an ID which belongs to another
      subscriber, or an ID for acceptable subscription which has been
      statically configured.";
  }

  identity insufficient-resources {
    base error;
    description
      "The publisher has insufficient resources to support the
       subscription as requested by an RPC.";
  }

  identity unsupportable-volume {
    base error;
    description
      "The publisher cannot support the volume of information intended
      to be sent for an existing subscription.";
  }

  identity error-no-such-option {



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    base error;
    description
      "A requested parameter setting is not supported.";
  }

  /* Identities for encodings */
  identity encodings {
    description
      "Base identity to represent data encodings";
  }

  identity encode-xml {
    base encodings;
    if-feature "encode-xml";
    description
      "Encode data using XML";
  }

  identity encode-json {
    base encodings;
    if-feature "encode-json";
    description
      "Encode data using JSON";
  }

  /* Identities for transports */
  identity transport {
    description
      "An identity that represents a the underlying mechanism for
      passing notification messages.";
  }

  identity netconf {
    base transport;
    description
      "Netconf is used a transport for notification messages and state
       change notifications.";
    reference "draft-ietf-netconf-netconf-event-notifications";
  }

  identity http2 {
    base transport;
    description
      "HTTP2 is used a transport for notification messages and state
       change notifications.";
    reference "draft-ietf-netconf-restconf-notif-03, Sections 3.1.1" +
      "3.1.3";
  }



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  identity http1.1 {
    base transport;
    description
      "HTTP1.1 is used a transport for notification messages and state
       change notifications.";
    reference "draft-ietf-netconf-restconf-notif-03, Section 3.1.2";
  }
  /*
   * TYPEDEFs
   */

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

  typedef filter-id {
    type string;
    description
      "A type to identify filters which can be associated with a
       subscription.";
  }

  typedef subscription-result {
    type identityref {
      base subscription-result;
    }
    description
      "The result of a subscription operation";
  }

  typedef subscription-errors {
    type identityref {
      base error;
    }
    description
      "The reason for the failure of an RPC request or the sending
       of a subscription suspension or termination state change
       notification";
  }

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



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  }

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

  typedef stream {
    type string;
    description
      "Specifies a system-provided datastream.";
  }

  typedef stream-filter-ref {
    type leafref {
      path "/sn:filters/sn:stream-filter/sn:identifier";
    }
    description
      "This type is used to reference a stream filter.";
  }

  /*
   * GROUPINGS
   */

  grouping stream-filter-elements {
    description
      "This grouping defines the base for filters applied to event
       streams.";
    choice filter-spec {
      description
        "The content filter specification for this request.";
      anydata subtree-filter {
        if-feature "subtree";
        description
          "Event stream evaluation criteria encoded in a syntax of a
           supported type of an RFC 6241, Section 6 filter.  The subtree
           filter is applied to the representation of individual,
           delineated event records as contained within the event
           stream.  For example, if the notification message contains an
           instance of a notification defined in YANG, then the top-
           level element is the name of the YANG notification.  If the
           stream filter matches an event record from the stream, the
           event record should be included in a notification message



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           to the receiver(s).";
      }
      leaf xpath-filter {
        if-feature "xpath";
        type yang:xpath1.0;
        description
          "Event stream evaluation criteria encoded in a syntax of xpath
           1.0 and applied against an event stream. The result of
           applying XPath expression is converted to a boolean value
           using the standard XPath 1.0 rules.  If the boolean value is
           'true', the stream filter matches an event record within the
           stream, and the notification message should be sent to the
           receiver(s).";
      }
    }
  }

  grouping subscription-policy-modifiable {
    description
      "This grouping describes all objects which may be changed
      in a subscription via an RPC.";
    choice target {
      mandatory true;
      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.  This choice
        exists so that additional filter types can be added via
        augmentation.";
      case stream {
        choice stream-filter {
          description
            "An event stream filter can be applied to a subscription.
            That filter will come either referenced from a global list,
            or be provided within the subscription itself.";
          case by-reference {
            description
              "Apply a filter that has been configured separately.";
            leaf stream-filter-ref {
              type stream-filter-ref;
              mandatory true;
              description
                "References an existing stream-filter which is to
                be applied to stream for the subscription.";
            }
          }
          case within-subscription {
            description



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              "Local definition allows a filter to have the same
              lifecycle as the subscription.";
            uses stream-filter-elements;
          }
        }
      }
    }
    leaf stop-time {
      type yang:date-and-time;
      description
        "Identifies a time after which notification messages for a
        subscription should not be sent.  If stop-time is not present,
        the notification messages will continue until the subscription
        is terminated.  If replay-start-time exists, stop-time must be
        for a subsequent time. If replay-start-time doesn't exist,
        stop-time must be for a future time.";
    }
  }

  grouping subscription-policy {
    description
      "This grouping describes information concerning a subscription.";
    leaf encoding {
      type encoding;
      mandatory true;
      description
        "The type of encoding for the subscribed data.";
    }
    uses subscription-policy-modifiable {
      augment target/stream {
        description
          "Adds additional objects which must be set just by RPC.";
        leaf stream {
          type stream;
          mandatory true;
          description
            "Indicates a stream of event records against which to apply
            a stream filter.";
        }
        leaf replay-start-time {
          if-feature "replay";
          type yang:date-and-time;
          description
            "Used to trigger the replay feature and indicate that the
            replay should start at the time specified.  If
            replay-start-time is not present, this is not a replay
            subscription and event record push should start immediately.
            It is never valid to specify start times that are later than



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            or equal to the current time.";
        }
      }
    }
  }

  grouping notification-origin-info {
    description
      "Defines the sender source from which notification messages for a
       configured subscription are sent.";
    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 the push source is out of an interface on the
           Publisher established via static configuration.";
        leaf source-interface {
          type if:interface-ref;
          description
            "References the interface for notification messages.";
        }
      }
      case address-originated {
        description
          "When the push source is out of an IP address on the
           Publisher established via static configuration.";
        leaf source-vrf {
          type string;
          description
            "Network instance name for the VRF.  This could also have
            been a leafref to draft-ietf-rtgwg-ni-model, but that model
            is not complete, and might not be implemented on a box.";
        }
        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.";
        }
      }
    }
  }

  grouping receiver-info {
    description



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      "Defines where and how to get notification messages for a
      configured subscriptions to one or more targeted recipient.  This
      includes specifying the destination addressing as well as a
      transport protocol acceptable to the receiver.";
    container receivers {
      description
        "Set of receivers in a subscription.";
      list receiver {
        key "address port";
        min-elements 1;
        description
          "A single host or multipoint address intended as a target
           for the notification messages of a subscription.";
        leaf address {
          type inet:host;
          description
            "Specifies the address for the traffic to reach a remote
            host. One of the following must be specified: an ipv4
            address, an ipv6 address, or a host name.";
        }
        leaf port {
          type inet:port-number;
          description
            "This leaf specifies the port number to use for messages
             destined for a receiver.";
        }
        leaf protocol {
          type transport;
          mandatory true;
          description
            "This leaf specifies the transport protocol used
             to deliver messages destined for the receiver.  Each
             protocol may use the address and port information
             differently as applicable.";
        }
      }
    }
  }

  grouping error-identifier {
    description
      "A code passed back within an RPC response to describe why the RFC
       has failed, or within a state change notification to describe why
       the change has occurred.";
    leaf error-id {
      type subscription-errors;
      mandatory true;
      description



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        "Identifies the subscription error condition.";
    }
  }

  grouping hints {
    description
      "Objects passed back within an RPC response to describe why the
       RFC has failed, or within a state change notification to
       describe why the change has occurred.";
    leaf filter-failure {
      type string;
      description
        "Information describing where and/or why a provided filter was
        unsupportable for a subscription.";
    }
  }

  grouping subscription-response-with-hints {
    description
      "Defines the output for the establish-subscription and
       modify-subscription RPCs.";
    leaf subscription-result {
      type subscription-result;
      mandatory true;
      description
        "Indicates whether subscription is operational, or if a problem
         was encountered.";
    }
    choice result {
      description
        "Depending on the subscription result, different data is
         returned.";
      case no-success {
        description
          "This case applies when a subscription request was not
           successful and no subscription was created (or modified) as a
           result.  In this case, information MAY be returned that
           indicates suggested parameter settings that would have a
           high likelihood of succeeding in a subsequent establish-
           subscription or modify-subscription request.";
        uses hints;
      }
    }
  }

  /*
   * RPCs
   */



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  rpc establish-subscription {
    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. In case an error (as indicated by
       subscription-result) is returned, the subscription is not
       created.  In that case, the RPC reply MAY include suggested
       parameter settings that would have a higher likelihood of
       succeeding in a subsequent establish-subscription request.";
    input {
      uses subscription-policy {
        refine "encoding" {
          mandatory false;
          description
            "The type of encoding for the subscribed data. If not
            included as part of the RPC, the encoding MUST be set by the
            publisher to be the encoding used by this RPC.";
        }
      }
    }
    output {
      uses subscription-response-with-hints  {
        augment "result" {
          description
            "Allows information to be passed back as part of a
             successful subscription establishment.";
          case success {
            description
              "This case is used when the subscription request was
               successful.";
            leaf identifier {
              type subscription-id;
              mandatory true;
              description
                "Identifier used for this subscription.";
            }
          }
        }
        augment "result/no-success" {
          description
            "Contains establish RPC specific objects which can be
             returned as hints for future attempts.";
          leaf replay-start-time-hint {
            type yang:date-and-time;
            description
              "If a replay has been requested, but the requested replay



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              time cannot be honored, this may provide a hint at an
              alternate time which may be supportable.";
          }
        }
      }
    }
  }

  rpc modify-subscription {
    description
      "This RPC allows a subscriber to modify a subscription that was
       previously created using establish-subscription.  If successful,
       the changed subscription remains in effect for the duration of
       the subscriber's association with the publisher, or until the
       subscription is again modified or terminated.  In case an error
       is returned (as indicated by subscription-result), the
       subscription is not modified and the original subscription
       parameters remain in effect.  In that case, the rpc error
       response MAY include suggested parameter hints that would have
       a high likelihood of succeeding in a subsequent
       modify-subscription request.";
    input {
      leaf identifier {
        type subscription-id;
        description
          "Identifier to use for this subscription.";
      }
      uses subscription-policy-modifiable;
    }
    output {
      uses subscription-response-with-hints;
    }
  }

  rpc delete-subscription {
    description
      "This RPC allows a subscriber to delete a subscription that
       was previously created from by that same subscriber using the
       establish-subscription RPC.";
    input {
      leaf identifier {
        type subscription-id;
        mandatory true;
        description
          "Identifier of the subscription that is to be deleted.
           Only subscriptions that were created using
           establish-subscription can be deleted via this RPC.";
      }



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    }
    output {
      leaf subscription-result {
        type subscription-result;
        mandatory true;
        description
          "Indicates whether subscription has been deleted, or if a
          problem was encountered.";
      }
    }
  }

  rpc kill-subscription {
    description
      "This RPC allows an operator to delete a dynamic subscription
      without restrictions on the originating subscriber or underlying
      transport session.";
    input {
      leaf identifier {
        type subscription-id;
        mandatory true;
        description
          "Identifier of the subscription that is to be deleted. Only
            subscriptions that were created using establish-subscription
           can be deleted via this RPC.";
      }
    }
    output {
      leaf subscription-result {
        type subscription-result;
        mandatory true;
        description
          "Indicates whether subscription has been killed, or if a
           problem was encountered.";
      }
    }
  }

  /*
   * NOTIFICATIONS
   */

  notification replay-completed {
    sn:subscription-state-notif;
    if-feature "replay";
    description
      "This notification is sent to indicate that all of the replay
        notifications have been sent. It must not be sent for any other



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       reason.";
    leaf identifier {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
  }

  notification subscription-completed {
    sn:subscription-state-notif;
    description
      "This notification is sent to indicate that a subscription has
       finished passing event records.";
    leaf identifier {
      type subscription-id;
      mandatory true;
      description
        "This references the gracefully completed subscription.";
    }
  }

  notification subscription-started {
    sn:subscription-state-notif;
    if-feature "configured";
    description
      "This notification indicates that a subscription has started and
        notifications are beginning to be sent. This notification shall
       only be sent to receivers of a subscription; it does not
       constitute a general-purpose notification.";
    leaf identifier {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
    uses subscription-policy {
      refine "target/stream/replay-start-time" {
         description
           "Indicates the time that a replay using for the streaming of
           buffered event records.  This will be populated with the most
           recent of the following: replay-log-creation-time,
           replay-log-aged-time, replay-start-time, or the most recent
           publisher boot time.";
      }
    }
  }




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  notification subscription-resumed {
    sn:subscription-state-notif;
    description
      "This notification indicates that a subscription that had
       previously been suspended has resumed. Notifications will once
       again be sent.";
    leaf identifier {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
  }

  notification subscription-modified {
    sn:subscription-state-notif;
    if-feature "configured";
    description
      "This notification indicates that a subscription has been
       modified.  Notification messages sent from this point on will
       conform to the modified terms of the subscription.  For
       completeness, this state change notification includes both
       modified and    non-modified aspects of a subscription.";
    leaf identifier {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
    uses subscription-policy;
  }

  notification subscription-terminated {
    sn:subscription-state-notif;
    description
      "This notification indicates that a subscription has been
       terminated.";
    leaf identifier {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
    uses error-identifier;
    uses hints;
  }

  notification subscription-suspended {



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    sn:subscription-state-notif;
    description
      "This notification indicates that a suspension of the
       subscription by the publisher has occurred.  No further
       notifications will be sent until the subscription resumes.
       This notification shall only be sent to receivers of a
       subscription; it does not constitute a general-purpose
       notification.";
    leaf identifier {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
    uses error-identifier;
    uses hints;
  }

  /*
   * DATA NODES
   */

  container streams {
    config false;
    description
      "This container contains information on the built-in streams
      provided by the publisher.";
    list stream {
      key "name";
      description
        "Identifies the built-in streams that are supported by the
         publisher.";
      leaf name {
        type stream;
        description
          "A handle for a sequential set of event records, each of which
           is characterized by its own domain and semantics.";
      }
      leaf description {
        type string;
        mandatory true;
        description
          "A description of the event stream, including such information
           as the type of event records that are available within this
           stream.";
      }
      leaf replay-support {
        if-feature "replay";



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        type empty;
        description
          "Indicates that event record replay is available on this
          stream.";
      }
      leaf replay-log-creation-time {
        if-feature "replay";
        type yang:date-and-time;
        description
          "The timestamp of the creation of the log used to support the
          replay function on this stream. Note that this might be
          earlier then the earliest available information contained in
          the log. This object is updated if the log resets for some
          reason. This object MUST be present if replay is supported.";
      }
      leaf replay-log-aged-time {
        if-feature "replay";
        type yang:date-and-time;
        description
          "The timestamp of the last event record aged out of the log.
          This object MUST be present if replay is supported and any
          event record have been aged out of the log.";
      }
    }
  }

  container filters {
    description
      "This container contains a list of configurable filters
       that can be applied to subscriptions.  This facilitates
       the reuse of complex filters once defined.";
    list stream-filter {
      key "identifier";
      description
        "A list of pre-positioned filters that can be applied to
        subscriptions.";
      leaf identifier {
        type filter-id;
        description
          "An identifier to differentiate between filters.";
      }
      uses stream-filter-elements;
    }
  }

  container subscription-config {
    if-feature "configured";
    description



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      "Contains the list of subscriptions that are configured,
       as opposed to established via RPC or other means.";
    list subscription {
      key "identifier";
      description
        "The identity and specific parameters of a subscription.";
      leaf identifier {
        type subscription-id;
        description
          "Identifier to use for this subscription.";
      }
      uses subscription-policy;
      uses receiver-info {
        augment receivers/receiver {
          description
            "include operational data for receivers.";
          leaf status {
            type enumeration {
              enum connecting {
                value 5;
                description
                  "A subscription has been configured, and a
                  subscription-started state change notification should
                  be sent as quickly as possible.";
              }
              enum suspended {
                value 3;
              description
                "The status is suspended, meaning that the publisher is
                currently will not provide notification messages for
                the subscription until some status change.";
              }
            }
            default "connecting";
            description
              "Allows state initialization of a particular receiver.";
          }
        }
      }
      uses notification-origin-info;
    }
  }
  container subscriptions {
    config false;
    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



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       that have been setup via RPC primitives as well as subscriptions
       that have been established via configuration.";
    list subscription {
      key "identifier";
      description
        "The identity and specific parameterst of a subscription.
         Subscriptions within this list can be created using a control
         channel or RPC, or be established through configuration.";
      leaf identifier {
        type subscription-id;
        description
          "Identifier of a subscription; unique within a publisher";
      }
      leaf configured-subscription {
       if-feature "configured";
       type empty;
       description
         "The presence of this leaf indicates that the subscription
          originated from configuration, not through a control channel
          or RPC.";
      }
      uses subscription-policy;
      uses notification-origin-info {
        if-feature "configured";
      }
      uses receiver-info {
        augment receivers/receiver {
          description
            "include operational data for receivers.";
          leaf pushed-notifications {
            type yang:counter64;
            description
              "Operational data which provides the number of update
               notification messages pushed to a receiver.";
            }
          leaf excluded-notifications {
            type yang:counter64;
            description
              "Operational data which provides the number of event
               records from a stream explicitly removed via filtering so
               that they are not sent to a receiver.";
            }
          leaf status {
            type enumeration {
              enum active {
                value 1;
                description
                  "Connection is active and healthy.";



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              }
              enum concluded {
                value 2;
                description
                  "A subscription is inactive as it has hit a stop time,
                  but not yet been removed.";
              }
              enum suspended {
                value 3;
                description
                  "The status is suspended, meaning that the publisher
                  is currently unable to provide notification messages
                  for the subscription.";
              }
              enum in-error {
                value 4;
                description
                  "The status is in error or degraded, meaning that a
                  subscription is unsupportable with its current
                  parameters.";
              }
              enum connecting {
                value 5;
                description
                  "A subscription has been configured, but a
                  subscription-started state change notification has not
                  yet been succesfully received.";
              }
            }
            mandatory true;
            description
              "Specifies the status of a subscription from the
              perspective of a particular receiver.  With this info it
              is possible to determine whether a subscriber is currently
              generating notification messages intended for that
              receiver.";
          }
        }
      }
    }
  }
}
<CODE ENDS>








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11.  Considerations

11.1.  Implementation Considerations

   For a deployment including both configured and dynamic subscriptions,
   split subscription identifiers into static and dynamic halves.  That
   way it is unlikely there will be collisions if the configured
   subscriptions attempt to set a subscription-id which might have
   already been dynamically allocated.  The lower half SHOULD be used
   for subscriptions which will have subscription identifiers provided
   from outside the publisher, and upper half for subscription
   identifiers assigned by the publisher.

   No state change notification or nor subscribed event records within
   notification messages may be sent before the transport layer,
   including any requried capabilities exchange, has been established.

   An implementation may choose to transition between active and
   suspended subscription states more frequently than required by this
   specification.  However if a subscription is unable to marshal all
   intended updates into a transmittable message in multiple successive
   intervals, the subscription SHOULD be suspended with the reason
   "unsupportable-volume".

   For configured subscriptions, operations are against the set of
   receivers using the subscription identifier as a handle for that set.
   But for streaming up dates, state change notifications are local to a
   receiver.  In this specification it is the case that receivers get no
   information from the publisher about the existence of other
   receivers.  But if an operator wants to let the receivers correlate
   results, it is useful to use the subscription identifier handle
   across the receivers to allow that correlation.

11.2.  Security Considerations

   For dynamic subscriptions the publisher MUST authenticate and
   authorize all RPC requests.

   Subscriptions could overload a publisher's CPU.  For this reason, the
   publisher MUST have the ability to decline a dynamic subscription
   request, and provide the appropriate RPC error response to a
   subscriber should the proposed subscription overly deplete the
   publisher's resources.

   A publisher needs to be able to suspend an existing dynamic or
   configured subscription based on capacity constraints.  When this
   occurs, the subscription status MUST be updated accordingly and the
   receivers notified with subscription state notifications.



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   If a malicious or buggy subscriber sends an unexpectedly large number
   of RPCs, the result might be an excessive use of system resources.
   In such a situation, subscription interactions MAY be terminated by
   terminating the transport session.

   For both configured and dynamic subscriptions the publisher MUST
   authenticate and authorize a receiver via some transport level
   mechanism before sending any updates.

   A secure transport is highly recommended and the publisher MUST
   ensure that the user has sufficient authorization to perform the
   function they are requesting against the specific subset of content
   involved.

   A publisher MUST NOT include any content in a notification message
   for which the user has not been authorized.

   With configured subscriptions, one or more publishers could be used
   to overwhelm a receiver.  No notification messages SHOULD be sent to
   any receiver which doesn't even support subscriptions.  Subscribers
   that do not want notification messages need only terminate or refuse
   any transport sessions from the publisher.

   The NETCONF Authorization Control Model [RFC6536bis] SHOULD be used
   to control and restrict authorization of subscription configuration.
   This control models permits specifying per-user permissions to
   receive event records from specific streams.

   Where NACM is available, the NACM "very-secure" tag MUST be placed on
   the "kill-subscription" RPC so that only administrators have access
   to use this.

   One subscription id can be used for two or more receivers of the same
   configured subscription.  But due to the possibility of different
   access control permissions per receiver, it SHOULD NOT be assumed
   that each receiver is getting identical updates.

12.  Acknowledgments

   For their valuable comments, discussions, and feedback, we wish to
   acknowledge Andy Bierman, Tim Jenkins, Martin Bjorklund, Kent Watsen,
   Balazs Lengyel, Robert Wilton, Sharon Chisholm, Hector Trevino, Susan
   Hares, Michael Scharf, and Guangying Zheng.








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13.  References

13.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC6536bis]
              Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", draft-ietf-
              netconf-rfc6536bis-01 (work in progress), September 2017.

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

   [XPATH]    Clark, J. and S. DeRose, "XML Path Language (XPath)
              Version 1.0", November 1999,
              <http://www.w3.org/TR/1999/REC-xpath-19991116>.

13.2.  Informative References

   [I-D.draft-ietf-netconf-netconf-event-notifications]
              Clemm, Alexander., Voit, Eric., Gonzalez Prieto, Alberto.,
              Nilsen-Nygaard, E., Tripathy, A., Chisholm, S., and H.
              Trevino, "NETCONF support for event notifications",
              October 2016, <https://datatracker.ietf.org/doc/
              draft-ietf-netconf-netconf-event-notifications/>.

   [I-D.draft-ietf-netconf-restconf-notif]
              Voit, Eric., Clemm, Alexander., Tripathy, A., Nilsen-
              Nygaard, E., and Alberto. Gonzalez Prieto, "Restconf and
              HTTP transport for event notifications", August 2016,
              <https://datatracker.ietf.org/doc/
              draft-ietf-netconf-restconf-notif/>.

   [I-D.ietf-netconf-yang-push]
              Clemm, Alexander., Voit, Eric., Gonzalez Prieto, Alberto.,
              Tripathy, A., Nilsen-Nygaard, E., Bierman, A., and B.
              Lengyel, "YANG Datastore Subscription", October 2017,
              <https://datatracker.ietf.org/doc/
              draft-ietf-netconf-yang-push/>.







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   [I.D.draft-ietf-netconf-notification-messages]
              Voit, Eric., Clemm, Alexander., Bierman, A., and T.
              Jenkins, "YANG Notification Headers and Bundles",
              September 2017, <https://datatracker.ietf.org/doc/
              draft-ietf-netconf-notification-messages>.

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

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

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

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

Appendix A.  Changes between revisions

   (To be removed by RFC editor prior to publication)

   v06 - v07

   o  Clarification on state machine for configured susbcriptions.

   v05 - v06

   o  Made changes proposed by Martin, Kent, and others on the list.
      Most significant of these are Stream returned to string (with the
      SYSLOG identity removed), intro section on 5277 relationship, an
      identity set moved to an enumeration, clean up of definitions/
      terminology, state machine proposed for configured subscriptions
      with a clean-up of susbcription state options.

   o  JSON and XML become features.  Also Xpath and subtree filtering
      become features

   o  Terminology updates with event records, and refinement of filters
      to just stream filters.





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   o  Encoding refined in establish-subscription so it takes the RPC's
      encoding as the default.

   o  Namespaces in examples fixed.

   v04 - v05

   o  Returned to the explicit filter subtyping of v00

   o  stream object changed to 'name' from 'stream'

   o  Cleaned up examples

   o  Clarified that JSON support needs notification-messages draft.

   v03 - v04

   o  Moved back to the use of RFC5277 one-way notifications and
      encodings.

   v03 - v04

   o  Replay updated

   v02 - v03

   o  RPCs and Notification support is identified by the Notification
      2.0 capability.

   o  Updates to filtering identities and text

   o  New error type for unsupportable volume of updates

   o  Text tweaks.

   v01 - v02

   o  Subscription status moved under receiver.

   v00 - v01

   o  Security considerations updated

   o  Intro rewrite, as well as scattered text changes

   o  Added Appendix A, to help match this to related drafts in progress





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   o  Updated filtering definitions, and filter types in yang file, and
      moved to identities for filter types

   o  Added Syslog as a stream

   o  HTTP2 moved in from YANG-Push as a transport option

   o  Replay made an optional feature for events.  Won't apply to
      datastores

   o  Enabled notification timestamp to have different formats.

   o  Two error codes added.

   v01 5277bis - v00 subscribed notifications

   o  Kill subscription RPC added.

   o  Renamed from 5277bis to Subscribed Notifications.

   o  Changed the notification capabilities version from 1.1 to 2.0.

   o  Extracted create-subscription and other elements of RFC5277.

   o  Error conditions added, and made specific in return codes.

   o  Simplified yang model structure for removal of 'basic' grouping.

   o  Added a grouping for items which cannot be statically configured.

   o  Operational counters per receiver.

   o  Subscription-id and filter-id renamed to identifier

   o  Section for replay added.  Replay now cannot be configured.

   o  Control plane notification renamed to subscription state
      notification

   o  Source address: Source-vrf changed to string, default address
      option added

   o  In yang model: 'info' changed to 'policy'

   o  Scattered text clarifications

   v00 - v01 of 5277bis




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   o  YANG Model changes.  New groupings for subscription info to allow
      restriction of what is changeable via RPC.  Removed notifications
      for adding and removing receivers of configured subscriptions.

   o  Expanded/renamed definitions from event server to publisher, and
      client to subscriber as applicable.  Updated the definitions to
      include and expand on RFC 5277.

   o  Removal of redundancy with other drafts

   o  Many other clean-ups of wording and terminology

Authors' Addresses

   Eric Voit
   Cisco Systems

   Email: evoit@cisco.com


   Alexander Clemm
   Huawei

   Email: ludwig@clemm.org


   Alberto Gonzalez Prieto
   VMWare

   Email: agonzalezpri@vmware.com


   Einar Nilsen-Nygaard
   Cisco Systems

   Email: einarnn@cisco.com


   Ambika Prasad Tripathy
   Cisco Systems

   Email: ambtripa@cisco.com









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