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NETCONF                                                          E. Voit
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                                A. Clemm
Expires: August 27, 2017                                          Huawei
                                                      A. Gonzalez Prieto
                                                       E. Nilsen-Nygaard
                                                             A. Tripathy
                                                           Cisco Systems
                                                       February 23, 2017


                   Subscribing to Event Notifications
             draft-ietf-netconf-subscribed-notifications-00

Abstract

   This document defines capabilities and operations for subscribing to
   content and providing asynchronous notification message delivery on
   that content.  Notification delivery can occur over a variety of
   protocols used commonly in conjunction with YANG, such as NETCONF and
   RESTCONF.  The capabilities and operations defined in this document
   when using in conjunction with draft-ietf-netconf-netconf-event-
   notifications are intended to obsolete RFC 5277.

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 August 27, 2017.

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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   (http://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
   2.  Solution  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.1.  Event Streams . . . . . . . . . . . . . . . . . . . . . .   6
     2.2.  Filters . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.3.  Subscription State Model at the Publisher . . . . . . . .   6
   3.  Data Model Trees for Event Notifications  . . . . . . . . . .   7
   4.  Dynamic Subscriptions . . . . . . . . . . . . . . . . . . . .  11
     4.1.  Establishing a Subscription . . . . . . . . . . . . . . .  11
     4.2.  Modifying a Subscription  . . . . . . . . . . . . . . . .  12
     4.3.  Deleting a Subscription . . . . . . . . . . . . . . . . .  12
     4.4.  Killing a Subscription  . . . . . . . . . . . . . . . . .  13
   5.  Configured Subscriptions  . . . . . . . . . . . . . . . . . .  13
     5.1.  Establishing a Configured Subscription  . . . . . . . . .  14
     5.2.  Modifying a Configured Subscription . . . . . . . . . . .  16
     5.3.  Deleting a Configured Subscription  . . . . . . . . . . .  16
   6.  Event (Data Plane) Notifications  . . . . . . . . . . . . . .  17
   7.  Subscription State Notifications  . . . . . . . . . . . . . .  18
     7.1.  subscription-started  . . . . . . . . . . . . . . . . . .  18
     7.2.  subscription-modified . . . . . . . . . . . . . . . . . .  18
     7.3.  subscription-terminated . . . . . . . . . . . . . . . . .  19
     7.4.  subscription-suspended  . . . . . . . . . . . . . . . . .  19
     7.5.  subscription-resumed  . . . . . . . . . . . . . . . . . .  19
     7.6.  notification-complete . . . . . . . . . . . . . . . . . .  19
     7.7.  replay-complete . . . . . . . . . . . . . . . . . . . . .  19
   8.  Administrative Functions  . . . . . . . . . . . . . . . . . .  20
     8.1.  Subscription Monitoring . . . . . . . . . . . . . . . . .  20
     8.2.  Capability Advertisement  . . . . . . . . . . . . . . . .  20
     8.3.  Event Stream Discovery  . . . . . . . . . . . . . . . . .  21
   9.  Data Model for Event Notifications  . . . . . . . . . . . . .  21
   10. Considerations  . . . . . . . . . . . . . . . . . . . . . . .  41
     10.1.  Implementation Considerations  . . . . . . . . . . . . .  41
     10.2.  Security Considerations  . . . . . . . . . . . . . . . .  41
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  42
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  42
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  42



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     12.2.  Informative References . . . . . . . . . . . . . . . . .  43
   Appendix A.  Issues that are currently being worked and resolved   43
   Appendix B.  Changes between revisions  . . . . . . . . . . . . .  44
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  45

1.  Introduction

   This document defines mechanisms that provide an asynchronous message
   notification delivery service in a protocol-agnostic manner.  This
   document defines capabilities and operations for providing
   asynchronous message notification delivery for notifications
   including those necessary to establish, monitor, and support
   subscriptions to notification delivery.

   Notification delivery can occur over a variety of protocols used
   commonly in conjunction with YANG, such as NETCONF [RFC6241] (defined
   in [I-D.ietf-netconf-netconf-event-notif]) and Restconf [RFC8040]
   (defined in [I-D.ietf-netconf-restconf-notif]).  The capabilities and
   operations defined in this document are intended to obsolete RFC
   5277, along with their mapping onto NETCONF transport.

1.1.  Motivation

   The motivation for this work is to enable the sending of transport
   agnostic asynchronous notification messages driven by a YANG
   Subscription that are consistent with the data model (content) and
   security model.  Predating this work was [RFC5277] which defined a
   limited defines a notification mechanism for for NETCONF.  However,
   there are various [RFC5277] has limitations, many of which have been
   exposed in [RFC7923].

   The scope of the work aims at meeting the operational needs of
   network subscriptions:

   o  Ability to dynamically or statically subscribe to event
      notifications available on a publisher.

   o  Ability to negotiate acceptable dynamic subscription parameters.

   o  Ability to filter the subset of notifications to be pushed with
      stream-specific semantics.

   o  Ability for the notification payload to be interpreted
      independently of the transport protocol.  (In other words, the
      encoded notification fully describes itself.)

   o  Mechanism to communicate the notifications.




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   o  Ability to replay locally logged notifications.

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

   NACM: NETCONF Access Control Model.

   OAM: Operations, Administration, Maintenance.

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

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

   RPC: Remote Procedure Call.

   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 receipt of event notifications from a publisher.

   Subscription: A contract with a publisher, stipulating which
   information receiver(s) wishes to have pushed from the publisher
   without the need for further solicitation.



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1.3.  Solution Overview

   This document describes mechanisms for subscribing and receiving
   event notifications from an event server publisher.  This document
   has similarities to the capabilities orginally defined in [RFC5277].
   This document extends the supported capabilties, and generalizes
   functionality to be protocol-agnostic.

   Some enhancements over [RFC5277] include the ability to have multiple
   subscriptions on a single transport session, to terminate a single
   subscriptions without terminating the transport session, and to
   modify existing subscriptions.

   The solution supports subscribing to event notifications using two
   mechanisms:

   1.  Dynamic subscriptions, where a subscriber initiates a
       subscription negotiation with a publisher via RPC.  If the
       publisher wants to serve this request, it will accept it, and
       then start 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 is an optional mechanism that
       enables managing subscriptions via a configuration interface so
       that a publisher can send event notifications to configured
       receiver(s).

   Some key characteristics of configured and dynamic subscriptions
   include:

   o  The lifetime of a dynamic subscription is limited by the lifetime
      of the subscriber session used to establish it.  Typically loss of
      the transport session tears down any dependent dynamic
      subscriptions.

   o  The lifetime of a configured subscription is driven by
      configuration being present on the running configuration.  This
      implies configured subscriptions persist across reboots, and
      persists even when transport is unavailable.

   o  Subscriptions can be modified or terminated at any point of their
      lifetime.  Configured subscriptions can be modified by any
      configuration client with write rights on the configuration of the
      subscription.





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   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.

   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 set of events available for subscription from a
   publisher.  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.

   That said, there is one standardized event stream, this is the
   "NETCONF" event stream.  The NETCONF event stream contains all
   NETCONF XML event information supported by the publisher, except for
   where it has been explicitly indicate that this info must be excluded
   from the NETCONF stream.

   As events are raised by a system, they may be assigned to one or more
   streams.  The event is distributed to receivers meeting all three
   critera: (1) a subscription includes the identified stream, (2)
   susbcription filtering allows the event to traverse, and (3) no
   access control rules prohibit the receiver from receiving the event.

2.2.  Filters

   a publisher implementation SHOULD support the ability to perform
   filtering of notification records per [RFC5277].  (TODO: since 5277
   is to be obsoleted, we should describe the filter here.)

2.3.  Subscription State Model at the Publisher

   Below is the state machine of a subscription for the publisher.  It
   is important to note that 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: Subscription states at publisher

   Of interest in this state machine are the following:

   o  Successful <establish-subscription> or <modify-subscription>
      requests put the subscription into an active state.

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

   o  A <delete-subscription> or <kill-subscription> will end the
      subscription.

3.  Data Model Trees for Event Notifications

   The YANG data model for event notifications is depicted in this
   section.

 module: ietf-subscribed-notifications
     +--ro streams
     |  +--ro stream*   stream
     +--rw filters
     |  +--rw filter* [identifier]
     |     +--rw identifier    filter-id
     |     +--rw (filter-type)?
     |        +--:(by-reference)



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     |        |  +--rw filter-ref?   filter-ref
     |        +--:(event-filter)
     |           +--rw filter?
     +--rw subscription-config {configured-subscriptions}?
     |  +--rw subscription* [identifier]
     |     +--rw identifier          subscription-id
     |     +--rw stream?             stream
     |     +--rw encoding?           encoding
     |     +--rw stop-time?          yang:date-and-time
     |     +--rw (filter-type)?
     |     |  +--:(by-reference)
     |     |  |  +--rw filter-ref?         filter-ref
     |     |  +--:(event-filter)
     |     |     +--rw filter?
     |     +--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}?
           +--ro stream?                    stream
           +--ro encoding?                  encoding
           +--ro replay-start-time?         yang:date-and-time
           +--ro stop-time?                 yang:date-and-time
           +--ro (filter-type)?
           |  +--:(by-reference)
           |  |  +--ro filter-ref?                filter-ref
           |  +--:(event-filter)
           |     +--ro filter?
           +--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]
           |     +--ro address                   inet:host



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           |     +--ro port                      inet:port-number
           |     +--ro protocol?                 transport-protocol
           |     +--ro pushed-notifications?     yang:counter64
           |     +--ro excluded-notifications?   yang:counter64
           +--ro subscription-status?       subscription-status

   rpcs:
     +---x establish-subscription
     |  +---w input
     |  |  +---w stream?              stream
     |  |  +---w encoding?            encoding
     |  |  +---w replay-start-time?   yang:date-and-time
     |  |  +---w stop-time?           yang:date-and-time
     |  |  +---w (filter-type)?
     |  |     +--:(by-reference)
     |  |     |  +---w filter-ref?          filter-ref
     |  |     +--:(event-filter)
     |  |        +---w filter?
     |  +--ro output
     |     +--ro subscription-result       subscription-result
     |     +--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 stop-time?    yang:date-and-time
     |  |  +---w (filter-type)?
     |  |     +--:(by-reference)
     |  |     |  +---w filter-ref?   filter-ref
     |  |     +--:(event-filter)
     |  |        +---w filter?
     |  +--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



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        +--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 stream?              stream
     |  +--ro encoding?            encoding
     |  +--ro replay-start-time?   yang:date-and-time
     |  +--ro stop-time?           yang:date-and-time
     |  +--ro (filter-type)?
     |     +--:(by-reference)
     |     |  +--ro filter-ref?          filter-ref
     |     +--:(event-filter)
     |        +--ro filter?
     +---n subscription-resumed
     |  +--ro identifier    subscription-id
     +---n subscription-modified
     |  +--ro identifier           subscription-id
     |  +--ro stream?              stream
     |  +--ro encoding?            encoding
     |  +--ro replay-start-time?   yang:date-and-time
     |  +--ro stop-time?           yang:date-and-time
     |  +--ro (filter-type)?
     |     +--:(by-reference)
     |     |  +--ro filter-ref?          filter-ref
     |     +--:(event-filter)
     |        +--ro filter?
     +---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 data model is structured as follows:

   o  "Streams" contains a list of event streams that are supported by
      the publisher and that can be subscribed to.

   o  "Filters" contains a configurable list of filters that can be
      applied to a subscription.  This allows users to reference an



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      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
      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 an 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 filter which identifies what is being subscribed to, as well as
      what should be included (or not) in the pushed results.

   o  An optional stream which may identify or reduce the domain of
      events against which the subscription is applied.

   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



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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 the name of a non-existent stream is provided.

4.1.1.  Replay Subscription

   The presence of a start time indicates that this is a replay
   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 (or
   deleted) 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.



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   Configured subscriptions cannot be deleted using RPCs.  Instead,
   configured subscriptions are deleted as part of regular configuration
   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.  If not included, push updates will go off a default
      interface for the device.






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

   Because there is no explicit association with an existing transport
   session, <edit-config> operations require additional parameters to
   indicate the receivers of the notifications and possibly the source
   of the notifications such as a specific egress interface.

   For example at subscription establishment if NETCONF transport is
   being used, 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.  The event notification must include:

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

   o  an eventTime element which provides the time the event was
      generated by the event source.  This event time parameter is of
      type dateTime and compliant to [RFC3339].  Implementations must
      support time zones.

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

   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

   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:



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   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
   notifications has been completed, that a subscription is done sending
   notifications 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.

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



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   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 dubscription
   has been resumed.  Data plane notifications generated in the future
   will be sent after the subscription terms.  Resumptions are notified
   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.

7.7.  replay-complete

   This notification indicates that all of the notifications prior to
   the current time have been sent.  This includes new notifications
   generated since the start of the subscription.  This notification
   must not be sent for any other reason.



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   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 notifications 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 subscriptions that are currently active.  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, a
   subscription status, as well as the various subscription parameters
   that are in effect.  The subscription status indicates whether the
   subscription is currently active and healthy, or if it is degraded in
   some form.  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 features
   in this document must advertise the capability
   "urn:ietf:params:netconf:capability:notification:2.0".

   The mechanism defined in this document is identified by
   "urn:ietf:params:netconf:capability:notification:2.0".  If a
   subscriber only supports [RFC5277] and not this specification, then
   they will recognize the capability
   "urn:ietf:params:netconf:capability:notification:1.0" and ignore the
   capability defined in this document.







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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 for Event Notifications

<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:   &lt;http://tools.ietf.org/wg/netconf/&gt;
     WG List:  &lt;mailto:netconf@ietf.org&gt;

     WG Chair: Mahesh Jethanandani
               &lt;mailto:mjethanandani@gmail.com&gt;

     WG Chair: Mehmet Ersue
               &lt;mailto:mehmet.ersue@nokia.com&gt;

     Editor:   Alexander Clemm
               &lt;mailto:ludwig@clemm.org&gt;

     Editor:   Eric Voit
               &lt;mailto:evoit@cisco.com&gt;

     Editor:   Alberto Gonzalez Prieto
               &lt;mailto:albertgo@cisco.com&gt;

     Editor:   Einar Nilsen-Nygaard



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               &lt;mailto:einarnn@cisco.com&gt;

     Editor:   Ambika Prasad Tripathy
               &lt;mailto:ambtripa@cisco.com&gt";


  description
    "This module contains conceptual YANG specifications for NETCONF
    Event Notifications.";

  revision 2017-02-23 {
    description
      "Tweaks to remove two notifications, RPC for create subscription
      refined with stream default, new grouping to eliminate some
      dymanically modifiable parameters in modifiy subscription RPC";
    reference
      "draft-ietf-netconf-subscribed-notifications-00";
  }


  /*
   * 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.";
  }

  /*
   * EXTENSIONS
   */

  extension subscription-state-notif {
    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.";
  }



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  /*
   * IDENTITIES
   */

   /* Identities for streams */
   identity stream {
    description
      "Base identity to represent a generic stream of event
       notifications.";
  }

  identity NETCONF {
    base stream;
    description
      "Default NETCONF event stream, containing events based on
       notifications defined as YANG modules that are supported by the
       system.  This contains the same set of events in a default
       RFC-5277 NETCONF stream";
  }

  /* Identities for subscription results */
  identity subscription-result {
    description
      "Base identity for RPC responses to requests surrounding
       management (e.g. 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
      "RPC was not successful.
       Base identity for error return codes.";
  }

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

  identity active {



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    base subscription-stream-status;
    description
      "Status is active and healthy.";
  }

  identity inactive {
    base subscription-stream-status;
    description
      "Status is inactive, for example outside the interval between
      start time and stop time.";
  }

  identity suspended {
    base subscription-stream-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-stream-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 name does not exist or is not available to the receiver.";
  }



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  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";
  }

  identity filter-unsupported {
    base error;
    description
     "Cannot parse syntax within the filter. 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



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      subscriber, or an ID for acceptable subscription which has been
      statically configured.";
  }

  /* 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.";
  }

  /*
   * TYPEDEFs
   */

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

  typedef filter-id {
    type uint32;
    description



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      "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 subscription-status {
    type identityref {
      base subscription-stream-status;
    }
    description
      "Specifies the status of a subscription or datastream.";
  }

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

  typedef notification-origin {
    type enumeration {



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      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.";
  }

  /*
   * 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 by-reference {
        description
          "Incorporate a filter that has been configured separately.";



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        leaf filter-ref {
          type filter-ref;
          description
            "References an existing filter which is to be applied to
            the potential events of the subscription.";
        }
      }
      case event-filter {
        anyxml filter {
          description
           "Filter which excludes whole event-notifications. 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 notification for its value to be checked against, the
            notification will be filtered  out. For example, if one
            were to check for 'severity=critical' in a configuration
            event notification where this field was not supported, then
            the notification would be filtered out. For subtree
            filtering, a non-empty node set means that the filter
            matches.  For XPath filtering, the mechanisms defined in
            [XPATH] should be used to convert the returned  value to
            boolean.";
        }
       }
     }
  }

  grouping subscription-policy-non-configurable {
    description
      "This grouping describes the information which can only be set
       in a dynamic subscription request via RPC.";
    leaf replay-start-time {
      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.";
    }
  }

  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 stream {



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      type stream;
      description
        "Indicates which stream of events is of interest.
         If not present, events in the default NETCONF stream
         will be sent.";
    }
    leaf encoding {
      type encoding;
      default "encode-xml";
      description
        "The type of encoding for the subscribed data.
         Default is XML";
    }
  }

  grouping subscription-policy-modifiable {
    description
      "This grouping describes all objects which may be changed
      in a subscription via an RPC.";
    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
        time.";
    }
    uses base-filter;
  }

  grouping subscription-policy {
    description
      "This grouping describes information concerning a subscription.";
    uses subscription-policy-non-modifiable;
    uses subscription-policy-non-configurable;
    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.";



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      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
           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
            in not complete, and may not be implemented on a box.";
        }
        leaf source-address {
          type inet:ip-address-no-zone;
          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 reciever.";
    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;



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          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.";
        }
        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 descibe why the RFC
       has failed, or within a state change notification to describe why
       the change has occured.";
    leaf filter-failure {
      type string;
      description
        "Information describing where and/or why a provided filter was
        unsupportable for a subscription.";



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    }
  }

  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 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 {



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      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 {
              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



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       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.";
      }
    }
    output {
      leaf subscription-result {
        type subscription-result;
        mandatory true;
        description
          "Indicates whether subscription is operational, 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;



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        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 is operational, or if a
           problem was encountered.";
      }
    }
  }

  /*
   * 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.";
    }
  }



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

  notification subscription-terminated {
    sn:subscription-state-notif;
    description



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      "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;
  }

  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



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         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
        "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



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      "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 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 {
        augment receivers/receiver {
          description
            "include operational data on configured 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.";
            }
        }
      }



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      leaf subscription-status {
        type subscription-status;
        description
          "The status of the subscription.";
      }
    }
  }
}
<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 <notification> elements are never sent before the transport
   layer, including capabilities exchange, has been established.

10.2.  Security Considerations

   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.  When a <get> is received that refers to the content
   defined in this memo, recievers should only be able to view the
   content for which they have sufficient privileges.  <establish-
   subscription> operations can be considered like deferred <get>, and
   the content that different users can access may vary.  This different
   access is reflected in the <notificationt> to which different users
   are able to subscribe.

   The contents of notifications, as well as the names of event streams,
   may contain sensitive information and care should be taken to ensure
   that they are viewed only by authorized users.  The publisher MUST
   NOT include any content in a notification that the user is not
   authorized to view.

   If a malicious or buggy subscriber sends a number of <establish-
   subscription> requests, then these subscriptions accumulate and may
   use up system resources.  In such a situation, subscriptions can be
   terminated by terminating the transport session.  The publisher can
   also suspend or terminate subscriptions with per-subscription
   granularity.



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   A subscription could be configured on another receiver's behalf, with
   the goal of flooding that receiver with updates.  One or more
   publishers could be used to overwhelm a 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.
   In addition, the NETCONF Authorization Control Model [RFC6536] SHOULD
   be used to control and restrict authorization of subscription
   configuration.  This control models permits specifying per-user
   permissions to receive specific event notification types.  The
   permissions are specified as a set of access control rules.

   Note that streams can define additional authorization requirements.
   For instance, in [I-D.ietf-netconf-yang-push], each of the elements
   in its data plane notifications must also go through access control.

   It is recommended that the NACM "very-secure" tag is placed on the
   <kill-subscription> RPC so that only administrators can access.

11.  Acknowledgments

   For their valuable comments, discussions, and feedback, we wish to
   acknowledge Andy Bierman, Tim Jenkins, Balazs Lengyel, Shaon
   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>.

   [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>.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536,
              DOI 10.17487/RFC6536, March 2012,
              <http://www.rfc-editor.org/info/rfc6536>.




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   [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>.

12.2.  Informative References

   [I-D.ietf-netconf-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., and E. Nilsen-Nygaard, "Subscribing to YANG
              datastore push updates", February 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", February
              2017, <https://datatracker.ietf.org/draft-voit-netmod-
              yang-notifications2/>.

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

   [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.  Issues that are currently being worked and resolved

   (To be removed by RFC editor prior to publication)

   Issue #9: validate that Subscription ID will only be relevant locally
   to a single receiver




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   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 B.  Changes between revisions

   (To be removed by RFC editor prior to publication)

   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 as
      this is not RFC-5277 compatible.

   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  Streams extracted if favor of more information in the filters
      section.

   o  Operational counters per receiver.

   o  Subscription-id and filter-id renamed to identifier

   o  Section for replay added.  Replay-start and stop-time updated.
      Replay now cannot be configured.

   o  Control plane notification renamed to subscription state
      notification

   o  Souce 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 changable via RPC.  Removed notifications
      for adding and removing receivers of configured subscriptions.

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

   o  Removal of redundant 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
   Cisco Systems

   Email: albertgo@cisco.com


   Einar Nilsen-Nygaard
   Cisco Systems

   Email: einarnn@cisco.com


   Ambika Prasad Tripathy
   Cisco Systems

   Email: ambtripa@cisco.com









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