Custom Subscription to Event Notifications
draft-ietf-netconf-subscribed-notifications-03

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Document Type Active Internet-Draft (netconf WG)
Last updated 2017-07-02
Replaces draft-ietf-netconf-rfc5277bis
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NETCONF                                                          E. Voit
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                                A. Clemm
Expires: January 3, 2018                                          Huawei
                                                      A. Gonzalez Prieto
                                                                  VMWare
                                                       E. Nilsen-Nygaard
                                                             A. Tripathy
                                                           Cisco Systems
                                                            July 2, 2017

               Custom Subscription to Event Notifications
             draft-ietf-netconf-subscribed-notifications-03

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
   events.  Effectively this allows a subscriber to request and receive
   a continuous, custom influx 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 http://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 January 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
   (http://trustee.ietf.org/license-info) in effect on the date of

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   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
   2.  Solution  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.1.  Event Streams . . . . . . . . . . . . . . . . . . . . . .   6
     2.2.  Filters . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.3.  Subscription State Model at the Publisher . . . . . . . .   7
   3.  Data Model Trees  . . . . . . . . . . . . . . . . . . . . . .   8
   4.  Dynamic Subscriptions . . . . . . . . . . . . . . . . . . . .  12
     4.1.  Establishing a Subscription . . . . . . . . . . . . . . .  12
     4.2.  Modifying a Subscription  . . . . . . . . . . . . . . . .  13
     4.3.  Deleting a Subscription . . . . . . . . . . . . . . . . .  13
     4.4.  Killing a Subscription  . . . . . . . . . . . . . . . . .  14
   5.  Configured Subscriptions  . . . . . . . . . . . . . . . . . .  14
     5.1.  Establishing a Configured Subscription  . . . . . . . . .  15
     5.2.  Modifying a Configured Subscription . . . . . . . . . . .  17
     5.3.  Deleting a Configured Subscription  . . . . . . . . . . .  17
   6.  Event (Data Plane) Notifications  . . . . . . . . . . . . . .  18
   7.  Subscription State Notifications  . . . . . . . . . . . . . .  19
     7.1.  subscription-started  . . . . . . . . . . . . . . . . . .  19
     7.2.  subscription-modified . . . . . . . . . . . . . . . . . .  20
     7.3.  subscription-terminated . . . . . . . . . . . . . . . . .  20
     7.4.  subscription-suspended  . . . . . . . . . . . . . . . . .  20
     7.5.  subscription-resumed  . . . . . . . . . . . . . . . . . .  20
     7.6.  notification-complete . . . . . . . . . . . . . . . . . .  20
     7.7.  replay-complete . . . . . . . . . . . . . . . . . . . . .  21
   8.  Administrative Functions  . . . . . . . . . . . . . . . . . .  21
     8.1.  Subscription Monitoring . . . . . . . . . . . . . . . . .  21
     8.2.  Capability Advertisement  . . . . . . . . . . . . . . . .  21
     8.3.  Event Stream Discovery  . . . . . . . . . . . . . . . . .  22
   9.  Data Model  . . . . . . . . . . . . . . . . . . . . . . . . .  22
   10. Considerations  . . . . . . . . . . . . . . . . . . . . . . .  44
     10.1.  Implementation Considerations  . . . . . . . . . . . . .  44
     10.2.  Security Considerations  . . . . . . . . . . . . . . . .  44
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  45
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  45
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  45
     12.2.  Informative References . . . . . . . . . . . . . . . . .  46

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   Appendix A.  Relationships to other drafts  . . . . . . . . . . .  47
     A.1.  ietf-netconf-netconf-event-notif  . . . . . . . . . . . .  47
     A.2.  ietf-netconf-restconf-notif . . . . . . . . . . . . . . .  47
     A.3.  ietf-netconf-yang-push  . . . . . . . . . . . . . . . . .  48
     A.4.  voit-notifications2 . . . . . . . . . . . . . . . . . . .  48
   Appendix B.  Issues that are currently being worked and resolved   48
   Appendix C.  Changes between revisions  . . . . . . . . . . . . .  48
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  50

1.  Introduction

   This document defines capabilities and operations for the customized
   establishment of subscriptions upon system generated event streams.
   Also defined are asynchronous delivery mechanisms, where the
   resulting event instances are placed within notification messages and
   sent to targeted receivers.  Effectively this enables a "Subscribe
   then Publish" capability where the customized information needs of
   each target receiver are understood by the publisher before events
   are marshalled and pushed.  The receiver then gets a continuous,
   custom influx of publisher generated events.

   While the functionality defined in this document is transport-
   agnostic, subscription control plane operations bindings exist for
   both NETCONF [RFC6241] and RESTCONF [RFC8040].  In addition, bindings
   for the pushed event instances have been defined for protocols such
   as NETCONF and HTTP2 [RFC7540].  For specifics on these bindings see
   [I-D.ietf-netconf-event-notif]) and
   [I-D.ietf-netconf-restconf-notif].

   The capabilities and operations defined in this document with
   implemented in conjunction with [I-D.ietf-netconf-event-notif] are
   intended to obsolete [RFC5277].

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

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   o  promise theory based interaction model

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

   o  independence from transport protocol

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 notification: A set of information intended for a Receiver
   indicating that one or more Event(s) have occurred.  Details of the
   Event(s) may be included within the Notification.

   Filter: Evaluation and/or selection criteria, which may be applied
   against a targeted set of objects or events in a subscription.
   Information traverses the filter only if specified filter criteria
   are met.

   NACM: NETCONF Access Control Model.

   Publisher: An entity responsible for streaming event notifications
   per the terms of a Subscription.

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

   Stream (also referred to as "event stream"): A continuous ordered set
   of events grouped under an explicit criteria.

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

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   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.

1.3.  Solution Overview

   This document describes a transport protocol-agnostic mechanism for
   subscribing to and receiving event notifications from an event
   publisher.  This mechanism is through the use 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 event notifications.  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 allows the management of
       subscriptions via a configuration interface so that a publisher
       can send event notifications 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 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 relevent 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

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   modified or deleted using RPC.  Similarly, a subscription established
   via RPC cannot be modified through configuration operations.

   The publisher may decide to terminate a dynamic subscription at any
   time.  Similarly, it may decide to temporarily suspend the sending of
   event notifications 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.

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 are two standardized event streams within this document:
   NETCONF and SYSLOG.  The NETCONF event stream contains all NETCONF
   XML event information supported by the publisher, except for where it
   has been explicitly indicated that this the event must be excluded
   from the NETCONF stream.  The SYSLOG event stream mirrors the
   discrete set entries which are concurrently being placed into a
   device's local Syslog.  Beyond these two, additional streams can be
   added via model augmentation.

   As events are raised by a system, they may be assigned to one or more
   streams.  The event is distributed to receivers where: (1) a
   subscription includes the identified stream, and (2) subscription
   filtering allows the event to traverse.

   If access control permissions are in use to secure publisher content,
   then for notifications to be sent to a receiver, that receiver must
   be allowed access to all the events on the stream.  If permissions
   change during the lifecycle of the of a subscription, then events
   must be sent or restricted accordingly.  This can be be done by re-
   establishing a subscription with the updated permissions, or by
   seamlessly updating the permissions of an existing subscription.

2.2.  Filters

   A publisher implementation MUST support the ability to perform
   filtering of notification records.  Two filtering syntaxes supported
   are [XPATH] and subtree [RFC6241].  Events which evaluate to "true",
   or return a non-null selection as a result of the evaluation by the

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   filter must traverse the filter in their entirety.  A subset of
   information is never stripped from within the event.

2.3.  Subscription State Model at the Publisher

   Below is the state machine of a subscription for the publisher for a
   dyanmic 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.

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

                Figure 1: Subscription states at publisher

   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.

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   An equivalent state machine exists for configured subscriptions.
   However the transition between states is via configuration operations
   rather than via RPC.

3.  Data Model Trees

module: ietf-subscribed-notifications
    +--ro streams
    |  +--ro stream*   stream
    +--rw filters
    |  +--rw filter* [identifier]
    |     +--rw identifier           filter-id
    |     +--rw (filter-type)?
    |        +--:(event-filter)
    |           +--rw event-filter-type    event-filter-type
    |           +--rw event-filter
    +--rw subscription-config {configured-subscriptions}?
    |  +--rw subscription* [identifier]
    |     +--rw identifier           subscription-id
    |     +--rw encoding?            encoding
    |     +--rw (target)
    |     |  +--:(event-stream)
    |     |     +--rw stream               stream
    |     +--rw (applied-filter)
    |     |  +--:(by-reference)
    |     |  |  +--rw filter-ref           filter-ref
    |     |  +--:(within-subscription)
    |     |     +--rw (filter-type)?
    |     |        +--:(event-filter)
    |     |           +--rw event-filter-type    event-filter-type
    |     |           +--rw event-filter
    |     +--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-protocol
    |     +--rw (notification-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-subscriptions}?

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          +--ro encoding?                  encoding
          +--ro (target)
          |  +--:(event-stream)
          |     +--ro stream                     stream
          |     +--ro replay-start-time?    yang:date-and-time {replay}?
          +--ro (applied-filter)
          |  +--:(by-reference)
          |  |  +--ro filter-ref                 filter-ref
          |  +--:(within-subscription)
          |     +--ro (filter-type)?
          |        +--:(event-filter)
          |           +--ro event-filter-type          event-filter-type
          |           +--ro event-filter
          +--ro stop-time?                 yang:date-and-time
          +--ro (notification-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-protocol
                +--ro pushed-notifications?     yang:counter64
                +--ro excluded-notifications?   yang:counter64
                +--ro status                    subscription-status

  rpcs:
    +---x establish-subscription
    |  +---w input
    |  |  +---w encoding?            encoding
    |  |  +---w (target)
    |  |  |  +--:(event-stream)
    |  |  |     +---w stream               stream
    |  |  |     +---w replay-start-time?   yang:date-and-time {replay}?
    |  |  +---w (applied-filter)
    |  |  |  +--:(by-reference)
    |  |  |  |  +---w filter-ref           filter-ref
    |  |  |  +--:(within-subscription)
    |  |  |     +---w (filter-type)?
    |  |  |        +--:(event-filter)
    |  |  |           +---w event-filter-type    event-filter-type
    |  |  |           +---w event-filter
    |  |  +---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 (applied-filter)
    |  |  |  +--:(by-reference)
    |  |  |  |  +---w filter-ref           filter-ref
    |  |  |  +--:(within-subscription)
    |  |  |     +---w (filter-type)?
    |  |  |        +--:(event-filter)
    |  |  |           +---w event-filter-type    event-filter-type
    |  |  |           +---w event-filter
    |  |  +---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-complete
    |  +--ro identifier    subscription-id
    +---n notification-complete
    |  +--ro identifier    subscription-id
    +---n subscription-started
    |  +--ro identifier           subscription-id
    |  +--ro encoding?            encoding
    |  +--ro (target)
    |  |  +--:(event-stream)
    |  |     +--ro stream               stream
    |  |     +--ro replay-start-time?   yang:date-and-time {replay}?
    |  +--ro (applied-filter)
    |  |  +--:(by-reference)

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    |  |  |  +--ro filter-ref           filter-ref
    |  |  +--:(within-subscription)
    |  |     +--ro (filter-type)?
    |  |        +--:(event-filter)
    |  |           +--ro event-filter-type    event-filter-type
    |  |           +--ro event-filter
    |  +--ro stop-time?           yang:date-and-time
    +---n subscription-resumed
    |  +--ro identifier    subscription-id
    +---n subscription-modified
    |  +--ro identifier           subscription-id
    |  +--ro encoding?            encoding
    |  +--ro (target)
    |  |  +--:(event-stream)
    |  |     +--ro stream               stream
    |  |     +--ro replay-start-time?   yang:date-and-time {replay}?
    |  +--ro (applied-filter)
    |  |  +--:(by-reference)
    |  |  |  +--ro filter-ref           filter-ref
    |  |  +--:(within-subscription)
    |  |     +--ro (filter-type)?
    |  |        +--:(event-filter)
    |  |           +--ro event-filter-type    event-filter-type
    |  |           +--ro event-filter
    |  +--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.

   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

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      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 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.

4.1.  Establishing a Subscription

   The <establish-subscription> operation allows a subscriber to request
   the creation of a subscription via RPC.

   The input parameters of the operation are:

   o  A stream which identifies the domain of events against which the
      subscription is applied.

   o  A filter which may reduce the set of events pushed.

   o  The desired encoding for the returned events.  By default, updates
      are encoded using XML.  Other encodings may be supported, such as
      JSON.

   o  An optional stop time for the subscription.

   o  An optional start time which indicates that this subscription is
      requesting a replay push of events previously generated.

   If the publisher cannot satisfy the <establish-subscription> request,
   it sends a negative <subscription-result> element.  If the subscriber
   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 the name of a non-existent stream is provided.

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4.1.1.  Replay Subscription

   Only viable for dynamic subscriptions made on event streams, if the
   replay feature is supported, a subscription may request that
   previously generated events be sent.  These would then be followed by
   events generated after the subscription is established.

   The presence of a start time is the indicator that there is requested
   replay for this subscription.  The start time must be earlier than
   the current time.  If the start time points earlier than the
   maintained history of Publisher's event buffer, then the subscription
   must be rejected.  In this case the error response to the <establish-
   subscription> request should include a start time supportable by the
   Publisher.

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 immediately starts sending events based
   on the new terms, completely ignoring the previous ones.  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, it immediately stops sending
   events for the 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.  Instead,
   configured subscriptions are deleted as part of regular configuration

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   operations.  Publishers MUST reject any RPC attempt to delete
   configured subscriptions.

4.4.  Killing a Subscription

   The <kill-subscription> operation permits an operator to end any
   dynamic subscription.  The publisher must accept the request for any
   dynamic subscription, and immediately stop sending events.

   Configured subscriptions cannot be kill 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.

   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.

   Supporting configured subscriptions is optional and advertised using
   the "configured-subscriptions" feature.

   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 push updates for each
      subscription.  In addition, the transport protocol for each
      destination may be defined.

   o  Optional parameters to identify an egress interface or IP address
      / VRF where a subscription updates should be pushed from the
      publisher.  Where these are not explicitly included, push updates
      should egress the publisher's default interface having
      reachability to a receiver.

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5.1.  Establishing a Configured Subscription

   Configured subscriptions are established using configuration
   operations against the top-level subtree subscription-config.  There
   are two key differences between RPC and <edit-config> RPC operations
   for subscription establishment.  Firstly, <edit-config> operations
   install a subscription without question, while RPCs may support
   negotiation and rejection of requests.  Secondly, while RPCs mandate
   that the subscriber establishing the subscription is the only
   receiver of the notifications, <edit-config> operations permit
   specifying receivers independent of any tracked subscriber.  Because
   there is no explicit association with an existing transport session,
   <edit-config> operations require additional parameters beyond those
   of dynamic subscriptions to indicate the receivers of the
   notifications and possibly the source of the notifications such as a
   specific egress interface.

   Immediately after a subscription is successfully established, the
   publisher sends to identified receivers a control-plane notification
   stating the subscription has been established (subscription-started).

   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 protocol specific call-home
   operations will be used to establish the connection.

   As an example at subscription establishment using <edit-config> over
   NETCONF, a client may send:

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   <rpc message-id="101"
          xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"
          xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0">
       <edit-config>
           <target>
               <running/>
           </target>
           <subscription-config
               xmlns="urn:ietf:params:xml:ns:netconf:notification:2.0">
               <subscription>
                   <subscription-id>
                       1922
                   </subscription-id>
                   <stream>
                       foo
                   </stream>
                   <receiver>
                       <address>
                           1.2.3.4
                       </address>
                       <port>
                           1234
                       </port>
                   </receiver>
               </subscription>
           </subscription-config>
       </edit-config>
   </rpc>

          Figure 2: Configured subscription creation via NETCONF

   if the request is accepted, the publisher would reply:

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

       Figure 3: Successful NETCONF configured subscription response

   if the request is not accepted because the publisher cannot serve it,
   the publisher may reply:

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   <rpc-reply xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
       <rpc-error>
           <error-type>application</error-type>
           <error-tag>resource-denied</error-tag>
           <error-severity>error</error-severity>
           <error-message xml:lang="en">
               Temporarily the publisher cannot serve this
               subscription due to the current workload.
           </error-message>
       </rpc-error>
   </rpc-reply>

     Figure 4: A NETCONF response for a failed configured subscription
                                 creation

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 control-plane
   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 control-plane 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:

   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 5: Deleting a configured subscription

   Immediately after a subscription is successfully deleted, the
   publisher sends to all receivers of that subscription a control-plane

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   notification stating the subscription has been terminated
   (subscription-terminated).

6.  Event (Data Plane) Notifications

   Once a subscription has been set up, the publisher streams
   (asynchronously) notifications per the terms of the subscription.  We
   refer to these as event notifications.  For dynamic subscriptions set
   up via RPC operations, event notifications are sent over the session
   used to establish the subscription.  For configured subscriptions,
   event notifications are sent over the specified connections.

   An event notification is sent to a receiver when something of
   interest occurs which is able to traverse all specified filtering and
   access control criteria.  At a minimum this event notification must
   include:

   o  a subscription-id element of type uint32 which corresponds to the
      responsible subscription in the Publisher.

   o  a timestamp indicating when event was identified and recorded by
      the event source.  This timestamp must support the indication of
      time zone.  The default timestamp is the eventTime element of type
      dateTime and compliant to [RFC3339].  Additional timestamp
      elements and formats are outside the scope of this document.

   o  the event notification content tagged and provided by a source in
      the publisher.

   Additional header and event bundling capabilities not defined in this
   document may transparently be included within the event notification.

   The following is an example of a compliant event notification.  This
   example extending the example within [RFC7950] section 7.16.3 to
   include the mandatory information described above:

   <notification
          xmlns=" urn:ietf:params:xml:ns:netconf:notification:1.0">
           <eventTime>2007-09-01T10:00:00Z</eventTime>
       <subscription-id>500</subscription-id>
       <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 6: Data plane notification

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   While this extended [RFC7950] section 7.16 notification provides a
   valid method of encapsulating subscribed notifications, other
   transport encapsulation methods are also viable.  Improvements may be
   achieved in some implementations in the following ways:

   o  transport efficiency may be gained by allowing the encapsulation
      and bundled push of multiple events within the same event
      notification.

   o  identifiers to designate the current and previous event
      notification can be used to discover duplicated and dropped
      notifications

   o  additional header types can be used to pass relevant metadata.

   o  a signature or hash can be included to verify the efficacy of the
      Publisher

   This is being explored in NETMOD Notifications 2.0
   [I-D.voit-notifications2].

7.  Subscription State Notifications

   In addition to data plane notifications, a publisher may 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 in
   that they are not general-purpose notifications.  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 notifications by making use of a
   YANG extension tagging them as subscription state notification.

   Subscription state notifications include indications that a replay of
   events 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.

7.1.  subscription-started

   This notification indicates that a configured subscription has
   started and data updates are beginning to be sent.  This notification
   includes the parameters of the subscription, except for the
   receiver(s) addressing information and push-source information.  Note
   that for RPC-based subscriptions, no such notifications are sent.

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7.2.  subscription-modified

   This notification indicates that a configured subscription has been
   modified successfully.  This notification includes the parameters of
   the subscription, except for the receiver(s) addressing information
   and push-source information.  Note that for RPC-based subscriptions,
   no such notifications are sent.

7.3.  subscription-terminated

   This notification indicates that a subscription has been terminated
   by the publisher.  The 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.  The management plane can 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
   notifications are sent.  However if a kill-subscription RPC is sent,
   or some other event results in the end of a susbcription, then there
   must be a notification that the subscription has been ended.

7.4.  subscription-suspended

   This notification indicates that a publisher has suspended a
   subscription.  The notification includes the reason for the
   suspension.  A possible reason is the lack of resources to serve it.
   No further data plane notifications 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).

7.5.  subscription-resumed

   This notification indicates that a previously suspended subscription
   has been resumed.  Data plane notifications generated in the future
   will be sent after the subscription terms.  These notifications go to
   the subscriber (in the case of dynamic subscriptions) and all
   receivers (in the case of configured subscriptions).

7.6.  notification-complete

   This notification is sent to indicate that a subscription, which
   includes a stop time, has finished passing events.

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7.7.  replay-complete

   This notification indicates that all of the events prior to the
   current time have been sent.  This includes new events 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-complete notification has
   been sent events will be sent in sequence as they arise naturally
   within the system.

8.  Administrative Functions

8.1.  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, recevier
   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.

8.2.  Capability Advertisement

   Capabilities are advertised in messages sent by each peer during
   session establishment [RFC6241].  Publishers supporting the RPCs and
   Notifications in this document must advertise the capability
   "urn:ietf:params:netconf:capability:notification:2.0".

   If a subscriber only supports [RFC5277] and not this specification,
   then they will recognize the capability

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   "urn:ietf:params:netconf:capability:notification:1.0" and ignore the
   capability defined in this document.

8.3.  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, for example using the <get> operation when
   using NETCONF.

9.  Data Model

<CODE BEGINS> file "ietf-subscribed-notifications.yang"
module ietf-subscribed-notifications {
  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>

     WG Chair: Mahesh Jethanandani
               <mailto:mjethanandani@gmail.com>

     WG Chair: Mehmet Ersue
               <mailto:mehmet.ersue@nokia.com>

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

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

     Editor:   Alberto Gonzalez Prieto

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               <mailto:agonzalezpri@vmware.com>

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

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

  description
    "This module contains conceptual YANG specification for
     subscribing to events an receiving event notifications.";

  revision 2017-05-31 {
    description
      "Filtering and stream structures updated, replay a feature.";
    reference
      "draft-ietf-netconf-subscribed-notifications-03";
  }

  /*
   * FEATURES
   */

  feature json {
    description
      "This feature indicates that JSON encoding of notifications
       is supported.";
  }

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

  feature replay {
    description
      "This feature indicates that historical event replay is
      supported.  With replay, it is possible for past events to be
      will be streamed in chronological order.";
  }

  /*
   * EXTENSIONS
   */

  extension subscription-state-notif {

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    description
      "This statement applies only to notifications. It indicates that
       the notification is a subscription state notification (aka OAM
       notification). Therefore it does not participate in a regular
       event stream and does not need to be specifically subscribed
       in order to receive notifications.";
  }

  /*
   * IDENTITIES
   */

  /* Identities for streams */
  identity stream {
    description
      "Base identity to represent a generic stream of event
       notifications exposed for subscription by a system.";
  }
  identity NETCONF {
    base stream;
    description
      "Default NETCONF event stream, containing events based on
      notifications defined as YANG modules that are supported by the
      system.  As a historical reference, this contains the same set
      of events in a default RFC-5277 NETCONF stream.";
  }
  identity SYSLOG {
    base stream;
    description
      "A stream of events mirroring the discrete set entries
      concurrently being placed into a device's local Syslog.";
  }
  identity custom-stream {
    base stream;
    description
      "A supported stream not defined via an identity in this model";
  }

  /* Identities for event filters */

  identity event-filter {
    description
      "Evaluation criteria used as a pass/fail test against events.
      If a filter element is specified to look for data of a particular
      value, and the data item is not present within a particular event
      for its value to be checked against, the event will be filtered
      out.  For example, if one were to check for 'severity=critical' in
      an event where this object does not exist, then the event would

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      not traverse.";
  }
  identity subtree-event-filter {
    base event-filter;
    description
      "An RFC-6241 based filter which attempts to select nodes within an
      event.  After evaluation, the return of a non-empty node set means
      that the filter is successully traversed.";
    reference "RFC-6241, #5.1";
  }
  identity xpath-event-filter {
    base event-filter;
    description
      "A filter applied to an event which follows the syntax specified
      in yang:xpath1.0. Success is indicated by either a positive
      boolean result, or a non-null node selection.";
    reference "XPATH: http://www.w3.org/TR/1999/REC-xpath-19991116";
  }

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

  /* Identities for subscription stream status */
  identity subscription-status {
    description
      "Base identity for the status of subscriptions and datastreams.";
  }
  identity active {
    base subscription-status;
    description
      "Status is active and healthy.";
  }

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  identity inactive {
    base subscription-status;
    description
      "Status is inactive, for example after the stop time, but not
      yet deleted from the configuration.";
  }
  identity suspended {
    base subscription-status;
    description
      "The status is suspended, meaning that the publisher is currently
       unable to provide the negotiated updates for the subscription.";
  }
  identity in-error {
    base subscription-status;
    description
      "The status is in error or degraded, meaning that stream and/or
      subscription is currently unable to provide the negotiated
      notifications.";
  }

  /* Identities for subscription errors */

  identity internal-error {
    base error;
    description
      "Error within publisher prohibits operation.";
  }
  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

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     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";
  }
  identity filter-type-unsupported {
    base error;
    description
     "Cannot parse syntax within the filter.";
  }
  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 error-insufficient-resources {
    base error;
    description
      "The server has insufficient resources to support the
       subscription as requested by an RPC.";
  }
  identity unsupportable-volume {
    base error;

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    description
      "The publisher cannot support the volume of information intended
      to be sent for an existing subscription.";
  }
  identity error-no-such-option {
    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;
    description
      "Encode data using XML";
  }
  identity encode-json {
    base encodings;
    description
      "Encode data using JSON";
  }

  /* Identities for transports */
  identity transport {
    description
      "An identity that represents a transport protocol for event
       notifications";
  }
  identity netconf {
    base transport;
    description
      "Netconf notifications as a transport.";
  }
  identity http2 {
    base transport;
    description
      "HTTP2 notifications as a transport";
  }

  /*
   * TYPEDEFs
   */

  typedef subscription-id {

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    type uint32;
    description
      "A type for subscription identifiers.";
  }

  typedef filter-id {
    type uint32;
    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 notification";
  }

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

  typedef event-filter-type {
    type identityref {
      base event-filter;
    }
    description
      "Specifies a known type of event filter.";
  }

  typedef subscription-status {
    type identityref {
      base subscription-status;

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    }
    description
      "Specifies the status of a subscription.";
  }

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

  typedef notification-origin {
    type enumeration {
      enum "interface-originated" {
        description
          "Notifications will be sent from a specific interface on a
           publisher";
      }
      enum "address-originated" {
        description
          "Notifications will be sent from a specific address on a
           publisher";
      }
    }
    description
      "Specifies from where notifications will be sourced when
       being sent by the publisher.";
  }

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

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

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  /*
   * GROUPINGS
   */

  grouping base-filter {
    description
      "This grouping defines the base for filters for notification
       events.";
    choice filter-type {
      description
        "A filter needs to be a single filter of a given type.  Mixing
        and matching of multiple filters does not occur at the level of
        this grouping.";
      case event-filter {
        leaf event-filter-type {
          type event-filter-type;
          mandatory true;
          description
            "A filter needs to be a known and understood syntax if it is
            to be interpretable by a device.";
        }
        anyxml event-filter {
          mandatory true;
          description
            "Event stream evaluation criteria encoded in a syntax of a
            supported type of filter.  If the filter is applied
            against an event stream and there is a non-empty or
            positive result, the event is passed along.";
        }
      }
    }
  }

  grouping subscription-policy-non-modifiable {
    description
      "This grouping describes the information in a subscription which
      should not change during the life of the subscription.";
    leaf encoding {
      type encoding;
      default "encode-xml";
      description
        "The type of encoding for the subscribed data. Default is XML";
    }
    choice target {
      mandatory true;
      description
        "A filter must be applied against some source of information.
        This identifies the target for the filter.";

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      case event-stream {
        leaf stream {
          type stream;
          mandatory true;
          description
            "Indicates a stream of events against which to apply
            a filter.";
        }
      }
    }
  }

  grouping subscription-policy-modifiable {
    description
      "This grouping describes all objects which may be changed
      in a subscription via an RPC.";
    choice applied-filter {
      mandatory true;
      description
        "A filter must be applied to a subscription.  And that filter
        will come either referenced from a global list, or be provided
        within the subscription itself.";
      case by-reference {
        description
          "Incorporate a filter that has been configured separately.";
        leaf filter-ref {
          type filter-ref;
          mandatory true;
          description
            "References an existing filter which is to be applied to
             the subscription.";
        }
      }
      case within-subscription {
        uses base-filter;
        description
          "Local definition allows a filter to have the same lifecycle
          as the subscription.";
      }
    }
    leaf stop-time {
      type yang:date-and-time;
      description
        "Identifies a time after which notification events should not
        be sent.  If stop-time is not present, the notifications will
        continue until the subscription is terminated.  If
        replay-start-time exists, stop-time must for a subsequent time.
        If replay-start-time doesn't exist, stop-time must for a future

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        time.";
    }
  }

  grouping subscription-policy {
    description
      "This grouping describes information concerning a subscription.";
    uses subscription-policy-non-modifiable {
      augment target/event-stream {
        description
          "Adds additional objects which must be set just by RPC.";
        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 pushes should start immediately.  It
            is never valid to specify start times that are later than
            or equal to the current time.";
        }
      }
    }
    uses subscription-policy-modifiable;
  }

  grouping notification-origin-info {
    description
      "Defines the sender source from which notifications for a
       configured subscription are sent.";
    choice notification-origin {
      description
        "Identifies the egress interface on the Publisher from which
         notifications will or are being 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 notifications.";
        }
      }
      case address-originated {
        description
          "When the push source is out of an IP address on the

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           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;
          mandatory true;
          description
            "The source address for the notifications.";
        }
      }
    }
  }

  grouping receiver-info {
    description
      "Defines where and how to get notifications 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 notifications for a subscription.";
        leaf address {
          type inet:host;
          mandatory true;
          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;
          mandatory true;
          description
            "This leaf specifies the port number to use for messages
             destined for a receiver.";
        }

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        leaf protocol {
          type transport-protocol;
          default "netconf";
          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
        "Identifies the subscription error condition.";
    }
  }

  grouping error-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

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         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 error-hints;
      }
    }
  }

  /*
   * RPCs
   */

  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 output MAY include suggested
       parameter settings that would have a high likelihood of
       succeeding in a subsequent establish-subscription request.";
    input {
      uses subscription-policy;
    }
    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 {

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              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
                 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;
    }
  }

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  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.";
      }
    }
    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.";

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      }
    }
  }

  /*
   * NOTIFICATIONS
   */

  notification replay-complete {
    sn:subscription-state-notif;
    description
      "This notification is sent to indicate that all of the replay
        notifications have been sent. It must not be sent for any other
       reason.";
    leaf identifier {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
  }

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

  notification subscription-started {
    sn:subscription-state-notif;
    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.";
    }

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    uses subscription-policy;
  }

  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;
    description
      "This notification indicates that a subscription has been
       modified.  Notifications sent from this point on will conform to
       the modified terms of the subscription.  For completeness, this
       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 error-hints;
  }

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  notification subscription-suspended {
    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 error-hints;
  }

  /*
   * DATA NODES
   */

  container streams {
    config false;
    description
      "This container contains a leaf list of built-in
       streams that are provided by the system.";
    leaf-list stream {
      type stream;
      description
        "Identifies the built-in streams that are supported by the
         system.  Built-in streams are associated with their own
         identities, each of which carries a special semantics.
         In case configurable custom streams are supported,
         as indicated by the custom-stream identity, the configuration
         of those custom streams is provided separately.";
    }
  }

  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 filter {
      key "identifier";
      description

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        "A list of configurable filters that can be applied to
         subscriptions.";
      leaf identifier {
        type filter-id;
        description
          "An identifier to differentiate between filters.";
      }
      uses base-filter;
    }
  }
  container subscription-config {
    if-feature "configured-subscriptions";
    description
      "Contains the list of subscriptions that are configured,
       as opposed to established via RPC or other means.";
    list subscription {
      key "identifier";
      description
        "Content of a subscription.";
      leaf identifier {
        type subscription-id;
        description
          "Identifier to use for this subscription.";
      }
      uses subscription-policy-non-modifiable;
      uses subscription-policy-modifiable;
      uses receiver-info {
        if-feature "configured-subscriptions";
      }
      uses notification-origin-info {
        if-feature "configured-subscriptions";
      }
    }
  }
  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
       that have been setup via RPC primitives as well as subscriptions
       that have been established via configuration.";
    list subscription {
      key "identifier";
      config false;
      description
        "Content of a subscription. Subscriptions can be created using
         a control channel or RPC, or be established through

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         configuration.";
      leaf identifier {
        type subscription-id;
        description
          "Identifier of this subscription.";
      }
      leaf configured-subscription {
       if-feature "configured-subscriptions";
       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-subscriptions";
      }
      uses receiver-info {
        refine receivers/receiver {
          min-elements "1";
        }
        augment receivers/receiver {
          description
            "include operational data for receivers.";
          leaf pushed-notifications {
            type yang:counter64;
            description
              "Operational data which provides the number of update
               notifications pushed to a receiver.";
            }
          leaf excluded-notifications {
            type yang:counter64;
            description
              "Operational data which provides the number of non-
               datastore update notifications explicitly removed via
               filtering so that they are not sent to a receiver.";
            }
          leaf status {
            type subscription-status;
            mandatory true;
            description
              "The status of the subscription.";
          }
        }
      }
    }
  }

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}
<CODE ENDS>

10.  Considerations

10.1.  Implementation Considerations

   For a deployment including both configured and dynamic subscriptions,
   split subscription identifiers into static and dynamic halves.  That
   way there should not 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 configured
   subscriptions and upper half for dynamic.

   The <notification> elements are never sent before the transport
   layer, including capabilities exchange, has been established.

   It is left to an implementation to determine when to transition
   between active and suspended subscription states.  However if a
   subscription is unable to marshal all intended updates into a
   transmitable message in multiple successive intervals, the
   subscription should be suspended with the reason "unsupportable-
   volume".

10.2.  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
   occur, the subscription status must be updated accordingly and the
   receivers notified with subscription state notifications.

   If a malicious or buggy subscriber sends an unexpectedly large number
   of RPCs, this may use up 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.

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   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 for which
   the user has not been authorized.

   With configured subscriptions, one or more publishers could be used
   to overwhelm a receiver.  No push updates should be sent to any
   receiver which doesn't even support subscriptions.  Subscribers that
   do not want pushed data 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 events from specific streams.

   Where NACM is available, the NACM "very-secure" tag should be placed
   on the <kill-subscription> RPC so that only administrators can
   access.

   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.

11.  Acknowledgments

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

12.  References

12.1.  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,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <http://www.rfc-editor.org/info/rfc3339>.

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

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <http://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>.

12.2.  Informative References

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

   [I-D.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, "Subscribing to YANG datastore push updates",
              June 2017, <https://datatracker.ietf.org/doc/draft-ietf-
              netconf-yang-push/>.

   [I-D.voit-notifications2]
              Voit, Eric., Clemm, Alexander., Bierman, A., and T.
              Jenkins, "YANG Notification Headers and Bundles", July
              2017, <https://datatracker.ietf.org/doc/draft-voit-
              netconf-notification-messages>.

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

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   [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,
              <http://www.rfc-editor.org/info/rfc6241>.

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

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

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

Appendix A.  Relationships to other drafts

   There are other related drafts which are progressing in the NETCONF
   WG.  This section details the relationship of this draft to those
   others.

A.1.  ietf-netconf-netconf-event-notif

   The [I-D.ietf-netconf-event-notif] draft augments this subscribed-
   notifications specification by defining NETCONF transport specifics.
   Included are:

   o  bindings for RPC communications and Event Notifications over
      NETCONF.

   o  encoded examples

A.2.  ietf-netconf-restconf-notif

   The [I-D.ietf-netconf-restconf-notif] draft augments this subscribed-
   notifications specification by defining transport specific guidance
   where some form of HTTP is used underneath.  Included are:

   o  bindings for RPC communications over RESTCONF

   o  bindings for Event Notifications over HTTP2 and HTTP1.1

   o  encoded examples

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   o  end-to-end deployment guidance for Call Home and TLS Heartbeat

A.3.  ietf-netconf-yang-push

   The draft [I-D.ietf-netconf-yang-push] builds upon this subscribed-
   notifications specification in order to allow a Publisher to stream
   YANG datastore objects.  In this case, the application of either an
   on-change or periodic triggers upon a YANG Datastore replace the
   system generated events within this document.

   If you wish to subscribe to a YANG datastore rather than a existing
   event stream on a publisher, please refer to this specification.

A.4.  voit-notifications2

   The draft [I-D.voit-notifications2] is not required to implement this
   subscribed-notifications specification.  Instead it defines data
   plane notification elements which improve the delivered experience.
   The following capabilities are specified:

   o  Defines common encapsulation headers objects to support
      functionality such as event severity, message signing, message
      loss discovery, message de-duplication, originating process
      identification.

   o  Defines how to bundle multiple event records into a single
      notification message.

   These are the enhanced capabilies alluded to in the Event (Data
   Plane) Notification seciton above.  This draft is not yet adopted by
   the NETCONF WG.

Appendix B.  Issues that are currently being worked and resolved

   (To be removed by RFC editor prior to publication)

   Issue #6: Data plane notifications and layered headers

   How to allow for seamless integration with non-standard encodings and
   transports (like GPB/GRPC).  Specify requirements encoding and
   transport must meet, provide examples.

Appendix C.  Changes between revisions

   (To be removed by RFC editor prior to publication)

   v02 - v03

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   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

   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.

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   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

   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

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   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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