Subscribing to YANG datastore push updates
draft-ietf-netconf-yang-push-10

NETCONF                                                         A. Clemm
Internet-Draft                                                    Huawei
Intended status: Standards Track                                 E. Voit
Expires: April 5, 2018                                     Cisco Systems
                                                      A. Gonzalez Prieto
                                                                  VMware
                                                             A. Tripathy
                                                       E. Nilsen-Nygaard
                                                           Cisco Systems
                                                              A. Bierman
                                                               YumaWorks
                                                              B. Lengyel
                                                                Ericsson
                                                         October 2, 2017


               Subscribing to YANG datastore push updates
                    draft-ietf-netconf-yang-push-10

Abstract

   Providing rapid visibility into changes made on YANG configuration
   and operational objects enables new capabilities such as remote
   mirroring of configuration and operational state.  Via the mechanism
   described in this document, subscriber applications may request a
   continuous, customized stream of updates from a YANG datastore.

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
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

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

   This Internet-Draft will expire on April 5, 2018.








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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Definitions and Acronyms  . . . . . . . . . . . . . . . . . .   4
   3.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Event Subscription Model  . . . . . . . . . . . . . . . .   5
     3.2.  Negotiation of Subscription Policies  . . . . . . . . . .   6
     3.3.  On-Change Considerations  . . . . . . . . . . . . . . . .   6
     3.4.  Promise-Theory Considerations . . . . . . . . . . . . . .   7
     3.5.  Data Encodings  . . . . . . . . . . . . . . . . . . . . .   8
     3.6.  Datastore Selection Filters . . . . . . . . . . . . . . .   8
     3.7.  Streaming Updates . . . . . . . . . . . . . . . . . . . .  10
     3.8.  Subscription Management . . . . . . . . . . . . . . . . .  13
     3.9.  Receiver Authorization  . . . . . . . . . . . . . . . . .  14
     3.10. On-change Notifiable YANG objects . . . . . . . . . . . .  16
     3.11. Other Considerations  . . . . . . . . . . . . . . . . . .  17
   4.  A YANG data model for management of datastore push
       subscriptions . . . . . . . . . . . . . . . . . . . . . . . .  18
     4.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .  18
     4.2.  Subscription configuration  . . . . . . . . . . . . . . .  25
     4.3.  YANG Notifications  . . . . . . . . . . . . . . . . . . .  27



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     4.4.  YANG RPCs . . . . . . . . . . . . . . . . . . . . . . . .  28
   5.  YANG module . . . . . . . . . . . . . . . . . . . . . . . . .  33
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  48
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  48
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  49
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  49
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  49
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  50
   Appendix A.  Changes between revisions  . . . . . . . . . . . . .  50
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  53

1.  Introduction

   Traditional approaches to remote visibility have been built on
   polling.  With polling, data is periodically requested and retrieved
   by a client from a server to stay up-to-date.  However, there are
   issues associated with polling-based management:

   o  Polling incurs significant latency.  This latency prohibits many
      application types.

   o  Polling cycles may be missed, requests may be delayed or get lost,
      often when the network is under stress and the need for the data
      is the greatest.

   o  Polling requests may undergo slight fluctuations, resulting in
      intervals of different lengths.  The resulting data is difficult
      to calibrate and compare.

   o  For applications that monitor for changes, many remote polling
      cycles place ultimately fruitless load on the network, devices,
      and applications.

   A more effective alternative to polling is for an application to
   receive automatic and continuous updates from a targeted subset of a
   datastore.  Accordingly, there is a need for a service that allows
   applications to subscribe to updates from a YANG datastore and that
   enables the publisher to push and in effect stream those updates.
   The requirements for such a service have been documented in
   [RFC7923].

   This document defines a corresponding solution that is built on top
   of "Custom Subscription to Event Notifications" [subscribe].
   Supplementing that work are YANG data model augmentations, extended
   RPCs, and new datastore specific update notifications.  Transport
   options for [subscribe] will work seamlessly with this solution.





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2.  Definitions and Acronyms

   The terms below supplement those defined in [subscribe].

   Data node: An instance of management information in a YANG datastore.

   Data node update: A data item containing the current value/property
   of a Data node at the time the data node update was created.

   Datastore: A conceptual store of instantiated management information,
   with individual data items represented by data nodes which are
   arranged in hierarchical manner.

   Data subtree: An instantiated data node and the data nodes that are
   hierarchically contained within it.

   Notification message: A transport encapsulated update record(s) and/
   or event notification(s) intended to be sent to a receiver.

   Update notification message: A notification message that contains an
   update record.

   Update record: A representation data node update(s) resulting from
   the application of a filter for a subscription.  An update record
   will include the value/property of one or more data nodes at a point
   in time.  It may contain the update type for each data node (e.g.,
   add, change, delete).  Also included may be metadata/headers such as
   a subscription-id.

   Update trigger: A mechanism that determines when an update record
   needs to be generated.

   YANG-Push: The subscription and push mechanism for YANG datastores
   that is specified in this document.

3.  Solution Overview

   This document specifies a solution for a push update subscription
   service.  This solution supports the dynamic as well as configured
   subscriptions to information updates from YANG datastores.
   Subscriptions specify when update notification messages should be
   sent and what data to include in update records.  YANG objects are
   subsequently pushed from the publisher to the receiver per the terms
   of the subscription.







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3.1.  Event Subscription Model

   YANG-push subscriptions are defined using a data model that is itself
   defined in YANG.  This model enhances the event subscription model
   defined in [subscribe] with capabilities that allow subscribers to
   subscribe to data node updates, specifically to specify the triggers
   defining when to generate update records as well as what to include
   in an update record.  Key enhancements include:

   o  Specification of selection filters which identify targeted YANG
      data nodes and/or subtrees within a datastore for which updates
      are to be pushed.

   o  An encoding (using anydata) for the contents of periodic and on-
      change push updates.

   o  Specification of update policies contain conditions which trigger
      the generation and pushing of new update records.  There are two
      types of triggers for subscriptions: periodic and on-change.

      *  For periodic subscriptions, the trigger is specified by two
         parameters that define when updates are to be pushed.  These
         parameters are the period interval with which to report
         updates, and an anchor time which can be used to calculate at
         which point in time updates need to be assembled and sent.

      *  For on-change subscriptions, a trigger occurs whenever a change
         in the subscribed information is detected.  Included are
         additional parameters such as:

         +  Dampening period: In an on-change subscription, the first
            change that is detected results in an update to be sent
            immediately.  However, sending successive updates whenever
            further changes are detected might result in quick
            exhaustion of resources in case of very rapid changes.  In
            order to protect against that, a dampening period is used to
            specify the interval which must pass before successive
            update records for the same subscription are generated.  The
            dampening period collectively applies to the set of all data
            nodes of a single subscription.  This means that when there
            is a change to a subscribed object, an update record
            containing that object is created either immediately when no
            dampening period is already in effect, or at the end of a
            dampening period.

         +  Change type: This parameter can be used to reduce the types
            of datastore changes for which updates are sent (e.g., you




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            might only send when an object is created or deleted, but
            not when an object value changes).

         +  No Synch on start: defines whether or not a complete push-
            update of all subscribed data will be sent at the beginning
            of a subscription.  Such early synchronization establishes
            the frame of reference for subsequent updates.

3.2.  Negotiation of Subscription Policies

   A dynamic subscription request SHOULD be declined if a publisher's
   assessment is that it may be unable to provide update records meeting
   the terms of the request.  In this case, a subscriber may quickly
   follow up with a new subscription request using different parameters.

   Random guessing at different parameters by a subscriber is to be
   discouraged.  Therefore, in order to minimize the number of
   subscription iterations between subscriber and publisher, dynamic
   subscriptions SHOULD support a simple negotiation between subscribers
   and publishers for subscription parameters.  This negotiation is in
   the form of a no-success response to a failed establish or modify
   subscription request.  The no-success message SHOULD include in the
   returned error response information that, when considered, increases
   the likelihood of success for subsequent requests.  However, there
   are no guarantees that subsequent requests for this subscriber will
   be accepted.

   [subscribe] contains several negotiable subscription parameters.
   Additional yang-push negotiation information defined in this
   specification includes hints at acceptable time intervals, size
   estimates for the number or objects which would be returned from a
   filter, and the location of an error in a provided filter.

3.3.  On-Change Considerations

   On-change subscriptions allow subscribers to subscribe to updates
   whenever changes to targeted objects occur.  As such, on-change
   subscriptions are particularly effective for data that changes
   infrequently, yet for which applications need to be quickly notified
   whenever a change does occur with minimal delay.

   On-change subscriptions tend to be more difficult to implement than
   periodic subscriptions.  Accordingly, on-change subscriptions may not
   be supported by all implementations or for every object.

   Whether or not to accept or reject on-change subscription requests
   when the scope of the subscription contains objects for which on-
   change is not supported is up to the publisher implementation.  A



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   publisher MAY accept an on-change subscription even when the scope of
   the subscription contains objects for which on-change is not
   supported.  In that case, updates are sent only for those objects
   within the scope that do support on-change updates whereas other
   objects are excluded from update records, whether or not their values
   actually change.  In order for a subscriber to determine whether
   objects support on-change subscriptions, objects are marked
   accordingly on a publisher.  Accordingly, when subscribing, it is the
   responsibility of the subscriber to ensure it is aware of which
   objects support on-change and which do not.  For more on how objects
   are so marked, see Section 3.10.

   Alternatively, a publisher MAY decide to simply reject an on-change
   subscription in case the scope of the subscription contains objects
   for which on-change is not supported.  In case of a configured
   subscription, the subscription MAY be suspended.

   To avoid flooding receivers with repeated updates for subscriptions
   containing fast-changing objects, or objects with oscillating values,
   an on-change subscription allows for the definition of a dampening
   period.  Once an update record for a given object is generated, no
   other updates for this particular subscription will be created until
   the end of the dampening period.  Values sent at the end of the
   dampening period are the current values of all changed objects which
   are current at the time the dampening period expires.  Changed
   objects include those which were deleted or newly created during that
   dampening period.  If an object has returned to its original value
   (or even has been created and then deleted) during the dampening-
   period, the last change will still be sent.  This will indicate churn
   is occurring on that object.

   In cases where a subscriber wants to have separate dampening periods
   for different objects, multiple subscriptions with different objects
   in a selection filter can be created.

   On-change subscriptions can be refined to let users subscribe only to
   certain types of changes.  For example, a subscriber might only want
   object creations and deletions, but not modifications of object
   values.

3.4.  Promise-Theory Considerations

   A subscription to updates from a YANG datastore is intended to
   obviate the need for polling.  However, in order to do so, it is
   critical that subscribers can rely on the subscription and have
   confidence that they will indeed receive the subscribed updates
   without having to worry updates being silently dropped.  In other
   words, a subscription constitutes a promise on the side of the



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   publisher to provide the receivers with updates per the terms of the
   subscription.

   Now, there are many reasons why a publisher may at some point no
   longer be able to fulfill the terms of the subscription, even if the
   subscription had been entered into with good faith.  For example, the
   volume of data objects may be larger than anticipated, the interval
   may prove too short to send full updates in rapid succession, or an
   internal problem may prevent objects from being collected.  If for
   some reason the publisher of a subscription is not able to keep its
   promise, receivers MUST be notified immediately and reliably.  The
   publisher MAY also suspend the subscription.

   A publisher SHOULD reject a request for a subscription if it is
   unlikely that the publisher will be able fulfill the terms of that
   subscription request.  In such cases, it is preferable to have a
   subscriber request a less resource intensive subscription than to
   deal with frequently degraded behavior.

3.5.  Data Encodings

   A publisher MUST support XML encoding and MAY support other encodings
   such as JSON encoding.

3.5.1.  Periodic Subscriptions

   In a periodic subscription, the data included as part of an update
   corresponds to data that could have been simply retrieved using a get
   operation and is encoded in the same way.  XML encoding rules for
   data nodes are defined in [RFC7950].  JSON encoding rules are defined
   in [RFC7951].

3.5.2.  On-Change Subscriptions

   In an on-change subscription, updates need to indicate not only
   values of changed data nodes but also the types of changes that
   occurred since the last update.  Therefore encoding rules for data in
   on-change updates will follow YANG-patch operation as specified in
   [RFC8072].  The YANG-patch will describe what needs to be applied to
   the earlier state reported by the preceding update, to result in the
   now-current state.  Note that contrary to [RFC8072], objects
   encapsulated are not restricted to configuration objects only.

3.6.  Datastore Selection Filters

   Subscription policy specifies both the selection filters and the
   datastores against which these selection filters will be applied.




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   The result is the push of information necessary to remotely maintain
   an extract of the publisher's datastore.

   Only a single selection filter can be applied to a subscription at a
   time.  The following selection filter types are included in the yang-
   push data model, and may be applied against a datastore:

   o  subtree: A subtree selection filter identifies one or more
      subtrees.  When specified, updates will only come from the data
      nodes of selected YANG subtree(s).  The syntax and semantics
      correspond to that specified for [RFC6241] section 6.

   o  xpath: An xpath selection filter is an XPath expression which may
      be meaningfully applied to a datastore.  It is the results of this
      expression which will be pushed.

   These filters are intended to be used as selectors that define which
   objects are within the scope of a subscription.  Filters are not
   intended to be used to filter objects based on a non-key property.
   Supporting non-key property filtering so would have a number of
   implications that would result in significant complexity.  While it
   is possible to define extensions in the future that will support
   selection filtering based on values, this is not supported in this
   version of yang-push and a publisher MAY reject a subscription
   request that contains a filter for object values.

   Xpath itself provides powerful filtering constructs, and care must be
   used in filter definition.  As an example, consider an xpath filter
   with a boolean result; such a result will not provide an easily
   interpretable subset of a datastore.  Beyond the boolean example, it
   is quite possible to define an xpath filter where results are easy
   for an application to mis-interpret.  Consider an xpath filter which
   only passes a datastore object when an interface is up.  It is up to
   the receiver to understand implications of the presence or absence of
   objects in each update.

   It is not expected that implementations will support comprehensive
   filter syntax and boundless complexity.  It will be up to
   implementations to describe what is viable, but the goal is to
   provide equivalent capabilities to what is available with a GET.
   Implementations MUST reject dynamic subscriptions or suspend
   configured subscriptions if they include filters which are
   unsupportable on a platform.








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3.7.  Streaming Updates

   Contrary to traditional data retrieval requests, datastore
   subscription enables an unbounded series of update records to be
   streamed over time.  Two generic notifications for update records
   have been defined for this: "push-update" and "push-change-update".

   A push-update notification defines a complete, filtered update of the
   datastore per the terms of a subscription.  This type of notification
   is used for continuous updates of periodic subscriptions.  A push-
   update notification can also be used for the on-change subscriptions
   in two cases.  First it will be used as the initial push-update if
   there is a need to synchronize the receiver at the start of a new
   subscription.  It also MAY be sent if the publisher later chooses to
   resynch an on-change subscription.  The push-update record contains a
   data snippet that contains an instantiated subtree with the
   subscribed contents.  The content of the update record is equivalent
   to the contents that would be obtained had the same data been
   explicitly retrieved using e.g., a NETCONF "get" operation, with the
   same filters applied.

   A push-change-update notification is the most common type of update
   for on-change subscriptions.  The update record in this case contains
   a data snippet that indicates the set of changes that data nodes have
   undergone since the last notification of YANG objects.  In other
   words, this indicates which data nodes have been created, deleted, or
   have had changes to their values.  In cases where multiple changes
   have occurred and the object has not been deleted, the object's most
   current value is reported.  (In other words, for each object, only
   one change is reported, not its entire history.  Doing so would
   defeat the purpose of the dampening period.)

   These new push-update or push-change-update are encoded and placed
   within notification messages, and ultimately queued for egress over
   the specified transport.

   The following is an example of an XML encoded notification message
   over NETCONF transport as per [netconf-notif].













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        <notification
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
           <eventTime>2015-03-09T19:14:56Z</eventTime>
           <push-update
               xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
             <subscription-id>1011</subscription-id>
             <time-of-update>2015-03-09T19:14:55.233Z</time-of-update>
             <datastore-contents>
                <foo>
                   <bar>some_string</bar>
                </foo>
             </datastore-contents>
           </push-update>
        </notification>

                          Figure 1: Push example

   The following is an example of an on-change notification.  It
   contains an update for subscription 89, including a new value for a
   leaf called beta, which is a child of a top-level container called
   alpha:

        <notification
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
           <eventTime>2015-03-09T19:14:56Z</eventTime>
           <push-change-update xmlns=
               "urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
             <subscription-id>89</subscription-id>
             <time-of-update>2015-03-09T19:14:55.233Z</time-of-update>
             <datastore-changes>
               <alpha xmlns="http://example.com/sample-data/1.0" >
                 <beta>1500</beta>
               </alpha>
             </datastore-changes>
           </push-change-update>
        </notification>

                   Figure 2: Push example for on change

   The equivalent update when requesting json encoding:











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        <notification
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
           <eventTime>2015-03-09T19:14:56Z</eventTime>
           <push-change-update xmlns=
               "urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
             <subscription-id>89</subscription-id>
             <time-of-update>2015-03-09T19:14:55.233Z</time-of-update>
             <datastore-changes>
               {
                "ietf-yang-patch:yang-patch": {
                "patch-id": [
                  null
                ],
                "edit": [
                  {
                      "edit-id": "edit1",
                      "operation": "merge",
                      "target": "/alpha/beta",
                      "value": {
                          "beta": 1500
                      }
                  }
                ]
               }
             }
             </datastore-changes>
           </push-change-update>
        </notification>

              Figure 3: Push example for on change with JSON

   When the beta leaf is deleted, the publisher may send



















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        <notification
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
           <eventTime>2015-03-09T19:14:56Z</eventTime>
           <push-change-update xmlns=
               "urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
             <subscription-id>89</subscription-id>
             <time-of-update>2015-03-09T19:14:55.233Z</time-of-update>
             <datastore-changes-xml>
               <alpha xmlns="http://example.com/sample-data/1.0" >
                 <beta urn:ietf:params:xml:ns:netconf:base:1.0:
                     operation="delete"/>
               </alpha>
             </datastore-changes-xml>
           </push-change-update>
        </notification>

              Figure 4: 2nd push example for on change update

3.8.  Subscription Management

   The RPCs defined within [subscribe] have been enhanced to support
   YANG datastore subscription negotiation.  Included in these
   enhancements are error codes which can indicate why a datastore
   subscription attempt has failed.

   A datastore subscription can be rejected for multiple reasons.  This
   includes a too large subtree request, or the inability of the
   publisher push update records as frequently as requested.  In such
   cases, no subscription is established.  Instead, the subscription-
   result with the failure reason is returned as part of the RPC
   response.  As part of this response, a set of alternative
   subscription parameters MAY be returned that would likely have
   resulted in acceptance of the subscription request.  The subscriber
   may consider these as part of future subscription attempts.

   For instance, for the following request:















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   <netconf:rpc message-id="101"
      xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
      <establish-subscription
            xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
         <datastore>
               <source>operational</source>
               <subtree-filter netconf:type="xpath"
               xmlns:ex="http://example.com/sample-data/1.0"
               select="/ex:foo"/>
             </datastore>
         <period>500</period>
         <encoding>encode-xml</encoding>
      </establish-subscription>
   </netconf:rpc>

                 Figure 5: Establish-Subscription example

   the publisher might return:

   <rpc-reply message-id="101"
        xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <subscription-result
        xmlns="http://urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
        error-insufficient-resources
      </subscription-result>
      <period>2000</period>
   </rpc-reply>

                     Figure 6: Error response example

   As can be seen above the rejected subscription does not result in the
   generation of an rpc-reply with an rpc-error element.  YANG-push
   specific errors and negotiation hints part are returned as part of
   normal RPC operations.

3.9.  Receiver Authorization

   A receiver of subscription data MUST only be sent updates for which
   they have proper authorization.  A publisher MUST ensure that no non-
   authorized data is included in push updates.  To do so, it needs to
   apply all corresponding checks applicable at the time of a specific
   pushed update and if necessary silently remove any non-authorized
   data from subtrees.  This enables YANG data pushed based on
   subscriptions to be authorized equivalently to a regular data
   retrieval (get) operation.

   A publisher MAY allow subscriptions which select non-existent or
   access-protected data.  Such a capability permits a receiver the



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   ability to monitor the entire lifecyle of the data.  In this case,
   all push-updates must be sent empty, and no push-change-updates will
   be sent until the data becomes visible for a receiver.

   A publisher MAY alternatively choose not to allow subscriptions which
   select non-existent or access-protected data.  Such a capability
   enables the publisher to avoid having to perform filtering of
   authorized content on each update.  Relevant scenarios here include:

   o  the rejecting of a subscription request to access-protected
      objects,

   o  the suspension of a subscription where new access-controlled
      objects are selected mid-subscription for which the receiver does
      not have the necessary authorization, or

   o  the authorization privileges of a receiver change over the course
      of the subscription.

   In all these cases, the error identity "data-unavailable" SHOULD be
   returned.  This reduces the possibility of access permission leakage.

   The contextual authorization model for data in YANG datastores is the
   NETCONF Access Control Model [RFC6536bis], Section 3.2.4.  A
   clarification to this is that each of the individual nodes in a
   resulting update record MUST also have applied access control to
   resulting pushed messages.  This includes validating that read access
   is ok for any nodes newly selected since the last update record for
   each receiver.

                          +-------------+      +-------------------+
     push-update / -->    |  data node  |  yes |                   |
     push-change-update   |   access    | ---> | add data node     |
                          |  allowed?   |      | to update message |
                          +-------------+      +-------------------+

                 Figure 7: Access control for push updates

   If read access into previously accessible nodes has been lost due to
   a receiver permissions change, this SHOULD be reported as node
   'delete' operations for on-change subscriptions.  If not capable of
   handling such receiver permission changes with such a 'delete',
   publisher implementations MUST force dynamic subscription re-
   establishment or configured subscription re-initialization so that
   appropriate filtering is installed.






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3.10.  On-change Notifiable YANG objects

   In some cases, a publisher supporting on-change notifications may not
   be able to push updates for some object types on-change.  Reasons for
   this might be that the value of the data node changes frequently
   (e.g., [RFC7223]'s in-octets counter), that small object changes are
   frequent and meaningless (e.g., a temperature gauge changing 0.1
   degrees), or that the implementation is not capable of on-change
   notification for a particular object.

   Support for on-change notification is usually specific to the
   individual YANG model and/or implementation so it is possible to
   define in design time.  System integrators need this information
   (without reading any data from a live node).

   The default assumption is that no data nodes support on-change
   notification.  Schema nodes and subtrees that support on-change
   notifications MUST be marked by accordingly with the YANG extension
   "notifiable-on-change".  This extension is defined in the data model
   below.

   When an on-change subscription is established, data-nodes are
   automatically excluded unless they are marked with notifiable-on-
   change as true.  This also means that authorization checks SHALL NOT
   be performed on them.  A subscriber can identify which nodes may be
   included in on-change updates by retrieving the data nodes in the
   subscription's scope and checking for which notifiable-on-change is
   marked as true.

   In theory, adding notifiable-on-change markings can be done within
   corresponding YANG models.  But a more extensible way to avoid having
   to modify existing module definitions is to add notifiable-on-change
   markings within separate module deviations.  This means that when a
   YANG model designer wants to add a notifiable-on-change marking to
   nodes of an existing module without modifying the module definitions,
   a new module is introduced that contains deviation statements which
   add "notifiable-on-change" statements as applicable.

    deviation /sys:system/sys:system-time {
      deviate add {
         yp:notifiable-on-change false;
      }
    }

                        Figure 8: Deviation Example






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3.11.  Other Considerations

3.11.1.  Robustness and reliability

   Particularly in the case of on-change push updates, it is important
   that push updates do not get lost or, in case the loss of an update
   is unavoidable, that the receiver is notified accordingly.

   Update messages for a single subscription MAY NOT be resequenced.

   It is conceivable that under certain circumstances, a publisher will
   recognize that it is unable to include within an update record the
   full set of objects desired per the terms of a subscription.  In this
   case, the publisher MUST take one or more of the following actions.

   o  A publisher MUST set the updates-not-sent flag on any update
      record which is known to be missing information.

   o  It MAY choose to suspend a subscription as per [subscribe].

   o  When resuming an on-change subscription, the publisher SHOULD
      generate a complete patch from the previous update record.  If
      this is not possible and the synch-on-start option is configured,
      then the full datastore contents MAY be sent via a push-update
      instead (effectively replacing the previous contents).  If neither
      of these are possible, then an updates-not-sent flag MUST be
      included on the next push-change-update.

   Note: It is perfectly acceptable to have a series of push-change-
   updates (and even push updates) serially queued at the transport
   layer awaiting transmission.  It is not required to merge pending
   update messages.  I.e., the dampening period applies to update record
   creation, not transmission.

3.11.2.  Publisher capacity

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

   Whether or not a subscription can be supported will be determined by
   a combination of several factors such as the subscription trigger
   (on-change or periodic), the period in which to report changes (1
   second periods will consume more resources than 1 hour periods), the
   amount of data in the subtree that is being subscribed to, and the
   number and combination of other subscriptions that are concurrently
   being serviced.





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4.  A YANG data model for management of datastore push subscriptions

4.1.  Overview

   The YANG data model for datastore push subscriptions is depicted in
   the following figure.  Following YANG tree convention in the
   depiction, brackets enclose list keys, "rw" means configuration, "ro"
   operational state data, "?" designates optional nodes, "*" designates
   nodes that can have multiple instances.  Parentheses with a name in
   the middle enclose choice and case nodes.  New YANG objects defined
   here (i.e., beyond those from [subscribe]) are identified with "yp".

module: ietf-subscribed-notifications
    +--ro streams
    |  +--ro stream* [name]
    |     +--ro name                        stream
    |     +--ro description                 string
    |     +--ro replay-support?             empty {replay}?
    |     +--ro replay-log-creation-time?   yang:date-and-time {replay}?
    |     +--ro replay-log-aged-time?       yang:date-and-time {replay}?
    +--rw filters
    |  +--rw event-filter* [identifier]
    |  |  +--rw identifier        filter-id
    |  |  +--rw (filter-spec)?
    |  |     +--:(subtree-filter)
    |  |     |  +--rw subtree-filter?
    |  |     +--:(xpath-filter)
    |  |        +--rw xpath-filter?     yang:xpath1.0
    |  +--rw yp:selection-filter* [identifier]
    |     +--rw yp:identifier        sn:filter-id
    |     +--rw (yp:filter-spec)?
    |        +--:(yp:subtree-filter)
    |        |  +--rw yp:subtree-filter?
    |        +--:(yp:xpath-filter)
    |           +--rw yp:xpath-filter?     yang:xpath1.0
    +--rw subscription-config {configured-subscriptions}?
    |  +--rw subscription* [identifier]
    |     +--rw identifier                 subscription-id
    |     +--rw encoding?                  encoding
    |     +--rw (target)
    |     |  +--:(stream)
    |     |  |  +--rw (event-filter)?
    |     |  |  |  +--:(by-reference)
    |     |  |  |  |  +--rw event-filter-ref           event-filter-ref
    |     |  |  |  +--:(within-subscription)
    |     |  |  |     +--rw (filter-spec)?
    |     |  |  |        +--:(subtree-filter)
    |     |  |  |        |  +--rw subtree-filter?



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    |     |  |  |        +--:(xpath-filter)
    |     |  |  |           +--rw xpath-filter?            yang:xpath1.0
    |     |  |  +--rw stream                     stream
    |     |  |  +--rw replay-start-time?    yang:date-and-time {replay}?
    |     |  +--:(yp:datastore)
    |     |     +--rw yp:source                  identityref
    |     |     +--rw (yp:selected-content)?
    |     |        +--:(yp:by-reference)
    |     |        |  +--rw yp:selection-filter-ref selection-filter-ref
    |     |        +--:(yp:within-subscription)
    |     |           +--rw (yp:filter-spec)?
    |     |              +--:(yp:subtree-filter)
    |     |              |  +--rw yp:subtree-filter?
    |     |              +--:(yp:xpath-filter)
    |     |                 +--rw yp:xpath-filter?         yang:xpath1.0
    |     +--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
    |     +--rw (yp:update-trigger)?
    |     |  +--:(yp:periodic)
    |     |  |  +--rw yp:period                  yang:timeticks
    |     |  |  +--rw yp:anchor-time?            yang:date-and-time
    |     |  +--:(yp:on-change) {on-change}?
    |     |     +--rw yp:dampening-period        yang:timeticks
    |     |     +--rw yp:no-synch-on-start?      empty
    |     |     +--rw yp:excluded-change*        change-type
    |     +--rw yp:dscp?                   inet:dscp
    |     +--rw yp:weighting?              uint8
    |     +--rw yp:dependency?             sn:subscription-id
    +--ro subscriptions
       +--ro subscription* [identifier]
          +--ro identifier                 subscription-id
          +--ro configured-subscription?
          |                            empty {configured-subscriptions}?
          +--ro encoding?                  encoding
          +--ro (target)
          |  +--:(stream)
          |  |  +--ro (event-filter)?
          |  |  |  +--:(by-reference)



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          |  |  |  |  +--ro event-filter-ref           event-filter-ref
          |  |  |  +--:(within-subscription)
          |  |  |     +--ro (filter-spec)?
          |  |  |        +--:(subtree-filter)
          |  |  |        |  +--ro subtree-filter?
          |  |  |        +--:(xpath-filter)
          |  |  |           +--ro xpath-filter?            yang:xpath1.0
          |  |  +--ro stream                     stream
          |  |  +--ro replay-start-time?    yang:date-and-time {replay}?
          |  +--:(yp:datastore)
          |     +--ro yp:source                  identityref
          |     +--ro (yp:selected-content)?
          |        +--:(yp:by-reference)
          |        |  +--ro yp:selection-filter-ref selection-filter-ref
          |        +--:(yp:within-subscription)
          |           +--ro (yp:filter-spec)?
          |              +--:(yp:subtree-filter)
          |              |  +--ro yp:subtree-filter?
          |              +--:(yp:xpath-filter)
          |                 +--ro yp:xpath-filter?         yang:xpath1.0
          +--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
          +--ro (yp:update-trigger)?
          |  +--:(yp:periodic)
          |  |  +--ro yp:period                  yang:timeticks
          |  |  +--ro yp:anchor-time?            yang:date-and-time
          |  +--:(yp:on-change) {on-change}?
          |     +--ro yp:dampening-period        yang:timeticks
          |     +--ro yp:no-synch-on-start?      empty
          |     +--ro yp:excluded-change*        change-type
          +--ro yp:dscp?                   inet:dscp
          +--ro yp:weighting?              uint8
          +--ro yp:dependency?             sn:subscription-id

  rpcs:



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    +---x establish-subscription
    |  +---w input
    |  |  +---w encoding?                  encoding
    |  |  +---w (target)
    |  |  |  +--:(stream)
    |  |  |  |  +---w (event-filter)?
    |  |  |  |  |  +--:(by-reference)
    |  |  |  |  |  |  +---w event-filter-ref           event-filter-ref
    |  |  |  |  |  +--:(within-subscription)
    |  |  |  |  |     +---w (filter-spec)?
    |  |  |  |  |        +--:(subtree-filter)
    |  |  |  |  |        |  +---w subtree-filter?
    |  |  |  |  |        +--:(xpath-filter)
    |  |  |  |  |           +---w xpath-filter?            yang:xpath1.0
    |  |  |  |  +---w stream                     stream
    |  |  |  |  +---w replay-start-time?    yang:date-and-time {replay}?
    |  |  |  +--:(yp:datastore)
    |  |  |     +---w yp:source                  identityref
    |  |  |     +---w (yp:selected-content)?
    |  |  |        +--:(yp:by-reference)
    |  |  |        |  +---w yp:selection-filter-ref selection-filter-ref
    |  |  |        +--:(yp:within-subscription)
    |  |  |           +---w (yp:filter-spec)?
    |  |  |              +--:(yp:subtree-filter)
    |  |  |              |  +---w yp:subtree-filter?
    |  |  |              +--:(yp:xpath-filter)
    |  |  |                 +---w yp:xpath-filter?         yang:xpath1.0
    |  |  +---w stop-time?                 yang:date-and-time
    |  |  +---w (yp:update-trigger)?
    |  |  |  +--:(yp:periodic)
    |  |  |  |  +---w yp:period                  yang:timeticks
    |  |  |  |  +---w yp:anchor-time?            yang:date-and-time
    |  |  |  +--:(yp:on-change) {on-change}?
    |  |  |     +---w yp:dampening-period        yang:timeticks
    |  |  |     +---w yp:no-synch-on-start?      empty
    |  |  |     +---w yp:excluded-change*        change-type
    |  |  +---w yp:dscp?                   inet:dscp
    |  |  +---w yp:weighting?              uint8
    |  |  +---w yp:dependency?             sn:subscription-id
    |  +--ro output
    |     +--ro subscription-result         subscription-result
    |     +--ro (result)?
    |        +--:(no-success)
    |        |  +--ro filter-failure?             string
    |        |  +--ro replay-start-time-hint?     yang:date-and-time
    |        |  +--ro yp:period-hint?             yang:timeticks
    |        |  +--ro yp:error-path?              string
    |        |  +--ro yp:object-count-estimate?   uint32



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    |        |  +--ro yp:object-count-limit?      uint32
    |        |  +--ro yp:kilobytes-estimate?      uint32
    |        |  +--ro yp:kilobytes-limit?         uint32
    |        +--:(success)
    |           +--ro identifier                  subscription-id
    +---x modify-subscription
    |  +---w input
    |  |  +---w identifier?                subscription-id
    |  |  +---w (target)
    |  |  |  +--:(stream)
    |  |  |  |  +---w (event-filter)?
    |  |  |  |     +--:(by-reference)
    |  |  |  |     |  +---w event-filter-ref           event-filter-ref
    |  |  |  |     +--:(within-subscription)
    |  |  |  |        +---w (filter-spec)?
    |  |  |  |           +--:(subtree-filter)
    |  |  |  |           |  +---w subtree-filter?
    |  |  |  |           +--:(xpath-filter)
    |  |  |  |              +---w xpath-filter?            yang:xpath1.0
    |  |  |  +--:(yp:datastore)
    |  |  |     +---w (yp:selected-content)?
    |  |  |        +--:(yp:by-reference)
    |  |  |        |  +---w yp:selection-filter-ref selection-filter-ref
    |  |  |        +--:(yp:within-subscription)
    |  |  |           +---w (yp:filter-spec)?
    |  |  |              +--:(yp:subtree-filter)
    |  |  |              |  +---w yp:subtree-filter?
    |  |  |              +--:(yp:xpath-filter)
    |  |  |                 +---w yp:xpath-filter?         yang:xpath1.0
    |  |  +---w stop-time?                 yang:date-and-time
    |  |  +---w (yp:update-trigger)?
    |  |     +--:(yp:periodic)
    |  |     |  +---w yp:period                  yang:timeticks
    |  |     |  +---w yp:anchor-time?            yang:date-and-time
    |  |     +--:(yp:on-change) {on-change}?
    |  |        +---w yp:dampening-period        yang:timeticks
    |  +--ro output
    |     +--ro subscription-result         subscription-result
    |     +--ro (result)?
    |        +--:(no-success)
    |           +--ro filter-failure?             string
    |           +--ro yp:period-hint?             yang:timeticks
    |           +--ro yp:error-path?              string
    |           +--ro yp:object-count-estimate?   uint32
    |           +--ro yp:object-count-limit?      uint32
    |           +--ro yp:kilobytes-estimate?      uint32
    |           +--ro yp:kilobytes-limit?         uint32
    +---x delete-subscription



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    |  +---w input
    |  |  +---w identifier    subscription-id
    |  +--ro output
    |     +--ro subscription-result    subscription-result
    +---x kill-subscription
       +---w input
       |  +---w identifier    subscription-id
       +--ro output
          +--ro subscription-result    subscription-result

  notifications:
    +---n replay-completed
    |  +--ro identifier    subscription-id
    +---n subscription-completed
    |  +--ro identifier    subscription-id
    +---n subscription-started
    |  +--ro identifier                 subscription-id
    |  +--ro encoding?                  encoding
    |  +--ro (target)
    |  |  +--:(stream)
    |  |  |  +--ro (event-filter)?
    |  |  |  |  +--:(by-reference)
    |  |  |  |  |  +--ro event-filter-ref           event-filter-ref
    |  |  |  |  +--:(within-subscription)
    |  |  |  |     +--ro (filter-spec)?
    |  |  |  |        +--:(subtree-filter)
    |  |  |  |        |  +--ro subtree-filter?
    |  |  |  |        +--:(xpath-filter)
    |  |  |  |           +--ro xpath-filter?              yang:xpath1.0
    |  |  |  +--ro stream                     stream
    |  |  |  +--ro replay-start-time?       yang:date-and-time {replay}?
    |  |  +--:(yp:datastore)
    |  |     +--ro yp:source                  identityref
    |  |     +--ro (yp:selected-content)?
    |  |        +--:(yp:by-reference)
    |  |        |  +--ro yp:selection-filter-ref    selection-filter-ref
    |  |        +--:(yp:within-subscription)
    |  |           +--ro (yp:filter-spec)?
    |  |              +--:(yp:subtree-filter)
    |  |              |  +--ro yp:subtree-filter?
    |  |              +--:(yp:xpath-filter)
    |  |                 +--ro yp:xpath-filter?           yang:xpath1.0
    |  +--ro stop-time?                 yang:date-and-time
    |  +--ro (yp:update-trigger)?
    |  |  +--:(yp:periodic)
    |  |  |  +--ro yp:period                  yang:timeticks
    |  |  |  +--ro yp:anchor-time?            yang:date-and-time
    |  |  +--:(yp:on-change) {on-change}?



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    |  |     +--ro yp:dampening-period        yang:timeticks
    |  |     +--ro yp:no-synch-on-start?      empty
    |  |     +--ro yp:excluded-change*        change-type
    |  +--ro yp:dscp?                   inet:dscp
    |  +--ro yp:weighting?              uint8
    |  +--ro yp:dependency?             sn:subscription-id
    +---n subscription-resumed
    |  +--ro identifier    subscription-id
    +---n subscription-modified
    |  +--ro identifier                 subscription-id
    |  +--ro encoding?                  encoding
    |  +--ro (target)
    |  |  +--:(stream)
    |  |  |  +--ro (event-filter)?
    |  |  |  |  +--:(by-reference)
    |  |  |  |  |  +--ro event-filter-ref           event-filter-ref
    |  |  |  |  +--:(within-subscription)
    |  |  |  |     +--ro (filter-spec)?
    |  |  |  |        +--:(subtree-filter)
    |  |  |  |        |  +--ro subtree-filter?
    |  |  |  |        +--:(xpath-filter)
    |  |  |  |           +--ro xpath-filter?              yang:xpath1.0
    |  |  |  +--ro stream                     stream
    |  |  |  +--ro replay-start-time?       yang:date-and-time {replay}?
    |  |  +--:(yp:datastore)
    |  |     +--ro yp:source                  identityref
    |  |     +--ro (yp:selected-content)?
    |  |        +--:(yp:by-reference)
    |  |        |  +--ro yp:selection-filter-ref    selection-filter-ref
    |  |        +--:(yp:within-subscription)
    |  |           +--ro (yp:filter-spec)?
    |  |              +--:(yp:subtree-filter)
    |  |              |  +--ro yp:subtree-filter?
    |  |              +--:(yp:xpath-filter)
    |  |                 +--ro yp:xpath-filter?           yang:xpath1.0
    |  +--ro stop-time?                 yang:date-and-time
    |  +--ro (yp:update-trigger)?
    |  |  +--:(yp:periodic)
    |  |  |  +--ro yp:period                  yang:timeticks
    |  |  |  +--ro yp:anchor-time?            yang:date-and-time
    |  |  +--:(yp:on-change) {on-change}?
    |  |     +--ro yp:dampening-period        yang:timeticks
    |  |     +--ro yp:no-synch-on-start?      empty
    |  |     +--ro yp:excluded-change*        change-type
    |  +--ro yp:dscp?                   inet:dscp
    |  +--ro yp:weighting?              uint8
    |  +--ro yp:dependency?             sn:subscription-id
    +---n subscription-terminated



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    |  +--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

module: ietf-yang-push

  rpcs:
    +---x resynch-subscription {on-change}?
       +---w input
       |  +---w identifier    sn:subscription-id
       +--ro output
          +--ro subscription-result    sn:subscription-result

  notifications:
    +---n push-update
    |  +--ro subscription-id?      sn:subscription-id
    |  +--ro time-of-update?       yang:date-and-time
    |  +--ro updates-not-sent?     empty
    |  +--ro datastore-contents?
    +---n push-change-update {on-change}?
       +--ro subscription-id?     sn:subscription-id
       +--ro time-of-update?      yang:date-and-time
       +--ro updates-not-sent?    empty
       +--ro datastore-changes?



                         Figure 9: Model structure

   Selected components of the model are summarized below.

4.2.  Subscription configuration

   Both configured and dynamic subscriptions are represented within the
   list subscription.  But only configured subscriptions are listed
   within list subscription-config.  In both lists, each subscription
   has own list elements.  New and enhanced parameters extending the
   basic subscription data model in [subscribe] include:

   o  The targeted datastore from which the selection is being made.
      The potential datastores include those from [revised-datastores].
      A platform may also choose to support a custom datastore.





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   o  A selection filter identifying yang nodes of interest within a
      datastore.  Filter contents are specified via a reference to an
      existing filter, or via an in-line definition for only that
      subscription.  Referenced filters allows an implementation to
      avoid evaluating filter acceptability during a dynamic
      subscription request.  The case statement differentiates the
      options.

   o  For periodic subscriptions, triggered updates will occur at the
      boundaries of a specified time interval.  These boundaries many be
      calculated from the periodic parameters:

      *  a "period" which defines duration between period push updates.

      *  an "anchor-time"; update intervals always fall on the points in
         time that are a multiple of a period from an anchor time.  If
         anchor time is not provided, then the anchor time MUST be set
         with the creation time of the initial update record.

   o  For on-change subscriptions, assuming the dampening period has
      completed, triggering occurs whenever a change in the subscribed
      information is detected.  On-change subscriptions have more
      complex semantics that is guided by its own set of parameters:

      *  a "dampening-period" specifies the interval that must pass
         before a successive update for the subscription is sent.  If no
         dampening period is in effect, the update is sent immediately.
         If a subsequent change is detected, another update is only sent
         once the dampening period has passed for this subscription.

      *  an "excluded-change" flag which allows restriction of the types
         of changes for which updates should be sent (e.g., only add to
         an update record on object creation).

      *  a "no-synch-on-start" flag which specifies whether a complete
         update with all the subscribed data is to be sent at the
         beginning of a subscription.

   o  Optional QoS parameters to indicate the treatment of a
      subscription relative to other traffic between publisher and
      receiver.  These include:

      *  A "dscp" QoS marking which MUST be stamped on notification
         messages to differentiate network QoS behavior.

      *  A "weighting" so that bandwidth proportional to this weighting
         can be allocated to this subscription relative to other
         subscriptions destined for that receiver.



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      *  a "dependency" upon another subscription.  Notification
         messages MUST NOT be sent prior to other notification messages
         containing update record(s) for the referenced subscription.

   o  A subscription's weighting MUST work identically to stream
      dependency weighting as described within RFC 7540, section 5.3.2.

   o  A subscription's dependency MUST work identically to stream
      dependency as described within RFC 7540, sections 5.3.1, 5.3.3,
      and 5.3.4.  If a dependency is attempted via an RPC, but the
      referenced subscription does not exist, the dependency will be
      removed.

4.3.  YANG Notifications

4.3.1.  State Change Notifications

   Subscription state notifications and mechanism are reused from
   [subscribe].  Some have been augmented to include the YANG datastore
   specific objects.

4.3.2.  Notifications for Subscribed Content

   Along with the subscribed content, there are other objects which
   might be part of a push-update or push-change-update

   A subscription-id MUST be transported along with the subscribed
   contents.  An [RFC5277]  Section 4 one-way notification MAY be used
   for encoding updates.  Where it is, the relevant subscription-id MUST
   be encoded as the first element within each push-update or push-
   change-update.  This allows a receiver to differentiate which
   subscription resulted in a particular push.

   A "time-of-update" which represents the time an update record
   snapshot was generated.  A receiver MAY assume that a publisher's
   objects have these pushed values at this point in time.

   An "updates-not-sent" flag is set, which indicates that the update
   record is incomplete.  If the application detects an informational
   discontinuity in either notification, the notification MUST include a
   flag "updates-not-sent".  This flag which indicates that not all
   changes which have occurred since the last update are actually
   included with this update.  In other words, the publisher has failed
   to fulfill its full subscription obligations.  (For example a
   datastore missed a window in providing objects to a publisher
   process.)  To facilitate re-synchronization of on-change
   subscriptions, a publisher MAY subsequently send a push-update
   containing a full selection snapshot of subscribed data.



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4.4.  YANG RPCs

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

4.4.1.  Establish-subscription RPC

   The subscriber sends an establish-subscription RPC with the
   parameters in section 3.1.  An example might look like:

   <netconf:rpc message-id="101"
      xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
      <establish-subscription
            xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
         <datastore>
               <source>operational</source>
               <selection-filter netconf:type="xpath"
               xmlns:ex="http://example.com/sample-data/1.0"
               select="/ex:foo"/>
             </datastore>
         <period>500</period>
         <encoding>encode-xml</encoding>
      </establish-subscription>
   </netconf:rpc>

                   Figure 10: Establish-subscription RPC

   The publisher MUST respond explicitly positively (i.e., subscription
   accepted) or negatively (i.e., subscription rejected) to the request.
   Positive responses include the subscription-id of the accepted
   subscription.  In that case a publisher MAY respond:

   <rpc-reply message-id="101"
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
       <subscription-result
            xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
          ok
       </subscription-result>
       <subscription-id
            xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
          52
       </subscription-id>
   </rpc-reply>

          Figure 11: Establish-subscription positive RPC response

   A subscription can be rejected for multiple reasons, including the
   lack of authorization to establish a subscription, the lack of read



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   authorization on the requested data node, or the inability of the
   publisher to provide a stream with the requested semantics.

   When the requester is not authorized to read the requested data node,
   the returned information indicates the node is unavailable.  For
   instance, if the above request was unauthorized to read node "ex:foo"
   the publisher may return:

   <rpc-reply message-id="101"
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
       <subscription-result
             xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
          subtree-unavailable
       </subscription-result>
       <filter-failure
             xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
          /ex:foo
       </filter-failure>
   </rpc-reply>

         Figure 12: Establish-subscription access denied response

   If a request is rejected because the publisher is not able to serve
   it, the publisher SHOULD include in the returned error what
   subscription parameters would have been accepted for the request.
   However, there are no guarantee that subsequent requests using this
   info will in fact be accepted.

   For example, for the following request:

   <netconf:rpc message-id="101"
      xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
      <establish-subscription
            xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
         <datastore>
               <source>running</source>
           <selection-filter netconf:type="xpath"
               xmlns:ex="http://example.com/sample-data/1.0"
               select="/ex:foo"/>
             </datastore>
         <dampening-period>10</dampening-period>
         <encoding>encode-xml</encoding>
      </establish-subscription>
   </netconf:rpc>

            Figure 13: Establish-subscription request example 2





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   a publisher that cannot serve on-change updates but periodic updates
   might return the following:

   <rpc-reply message-id="101"
         xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
       <subscription-result
             xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
          period-unsupported
       </subscription-result>
       <period-hint>100</period-hint>
   </rpc-reply>

        Figure 14: Establish-subscription error response example 2

4.4.2.  Modify-subscription RPC

   The subscriber MAY invoke the modify-subscription RPC for a
   subscription it previously established.  The subscriber will include
   newly desired values in the modify-subscription RPC.  Parameters not
   included MUST remain unmodified.  Below is an example where a
   subscriber attempts to modify the period of a subscription.

   <netconf:rpc message-id="102"
      xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
      <modify-subscription
           xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
         <datastore>
           <selection-filter netconf:type="xpath"
               xmlns:ex="http://example.com/sample-data/1.0"
               select="/ex:bar"/>
             </datastore>
         <subscription-id>
            1011
         </subscription-id>
         <period>250</period>
      </modify-subscription>
   </netconf:rpc>

                  Figure 15: Modify subscription request

   The publisher MUST respond explicitly positively or negatively to the
   request.  A response to a successful modification might look like:









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   <rpc-reply message-id="102"
      xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <subscription-result
            xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
         ok
      </subscription-result>
   </rpc-reply>

                  Figure 16: Modify subscription response

   If the subscription modification is rejected, the publisher MUST send
   a response like it does for an establish-subscription and maintain
   the subscription as it was before the modification request.
   Responses MAY include hints.  A subscription MAY be modified multiple
   times.

   A configured subscription cannot be modified using modify-
   subscription RPC.  Instead, the configuration needs to be edited as
   needed.

4.4.3.  Delete-subscription RPC

   To stop receiving updates from a subscription and effectively delete
   a subscription that had previously been established using an
   establish-subscription RPC, a subscriber can send a delete-
   subscription RPC, which takes as only input the subscription-id.

   Configured subscriptions cannot be deleted via RPC, but have to be
   removed from the configuration.  This RPC is identical to the RPC
   from [subscribe].

4.4.4.  Resynch-subscription RPC

   This RPC is only applicable only for on-change subscriptions
   previously been established using an establish-subscription RPC.  On
   receipt, a publisher must either reply 'ok' and quickly follow with a
   push-update, or send an appropriate error such as on-change-synch-
   unsupported.  For example:













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

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

                           Resynch subscription

4.4.5.  YANG Module Synchronization

   To make subscription requests, the subscriber needs to know the YANG
   module library available on the publisher.  The YANG 1.0 module
   library information is sent by a NETCONF server in the NETCONF
   'hello' message.  For YANG 1.1 modules and all modules used with the
   RESTCONF [RFC8040] protocol, this information is provided by the YANG
   Library module (ietf-yang-library.yang from [RFC7895].  This YANG
   library information is important for the receiver to reproduce the
   set of object definitions used within the publisher.

   The YANG library includes a module list with the name, revision,
   enabled features, and applied deviations for each YANG module
   implemented by the publisher.  The receiver is expected to know the
   YANG library information before starting a subscription.  The
   "/modules-state/module-set-id" leaf in the "ietf-yang-library" module
   can be used to cache the YANG library information.

   The set of modules, revisions, features, and deviations can change at
   run-time (if supported by the publisher implementation).  In this
   case, the receiver needs to be informed of module changes before data
   nodes from changed modules can be processed correctly.  The YANG
   library provides a simple "yang-library-change" notification that
   informs the subscriber that the library has changed.  The receiver
   then needs to re-read the entire YANG library data for the replicated
   publisher in order to detect the specific YANG library changes.  The
   "ietf-netconf-notifications" module defined in [RFC6470] contains a
   "netconf-capability-change" notification that can identify specific



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   module changes.  For example, the module URI capability of a newly
   loaded module will be listed in the "added-capability" leaf-list, and
   the module URI capability of an removed module will be listed in the
   "deleted-capability" leaf-list.

5.  YANG module

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

  import ietf-inet-types {
    prefix inet;
  }
  import ietf-yang-types {
    prefix yang;
  }
  import ietf-subscribed-notifications {
    prefix sn;
  }
  import ietf-datastores {
    prefix ds;
  }

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

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

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

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

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

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

     Editor:   Andy Bierman
               <mailto:andy@yumaworks.com>



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     Editor:   Balazs Lengyel
               <mailto:balazs.lengyel@ericsson.com>";

  description
    "This module contains conceptual YANG specifications
     for YANG push.";

  revision 2017-10-02 {
    description
      "Initial revision.";
    reference
      "YANG Datastore Push, draft-ietf-netconf-yang-push-09";
  }

 /*
  * EXTENSIONS
  */

  extension notifiable-on-change {
    argument "value";
    description
      "Indicates whether changes to the data node are reportable in
      on-change subscriptions.

      The statement MUST only be a substatement of the leaf, leaf-list,
      container, list, anyxml, anydata  statements. Zero or One
      notifiable-on-change statement is allowed per parent statement.
      NO substatements are allowed.

      The argument is a boolean value indicating whether on-change
      notifications are supported. If notifiable-on-change is not
      specified, the default is the same as the parent data node's
      value. For top level data nodes the default value is false.";
  }

 /*
  * FEATURES
  */

  feature on-change {
    description
      "This feature indicates that on-change triggered subscriptions
       are supported.";
  }

 /*
  * IDENTITIES
  */



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  /* Error type identities for datastore subscription  */
  identity period-unsupported {
    base sn:error;
    description
      "Requested time period is too short. This can be for both
       periodic and on-change dampening.";
  }

  identity qos-unsupported {
    base sn:error;
    description
      "Subscription QoS parameters not supported on this platform.";
  }

  identity dscp-unavailable {
    base sn:error;
    description
      "Requested DSCP marking not allocatable.";
  }

  identity on-change-unsupported {
    base sn:error;
    description
      "On-change not supported.";
  }

  identity on-change-synch-unsupported {
    base sn:error;
    description
      "On-change synch-on-start and resynchonization not supported.";
  }

  identity reference-mismatch {
    base sn:error;
    description
      "Mismatch in filter key and referenced yang subtree.";
  }

  identity data-unavailable {
    base sn:error;
    description
      "Referenced yang node or subtree doesn't exist, or read
       access is not permitted.";
  }

  identity datatree-size {
    base sn:error;
    description



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      "Resulting periodic or on-change push updates may exceed a size
      limit during normal conditions.";
  }

  identity synchronization-datatree-size {
    base sn:error;
    description
      "The resulting Synch-on-start or resynchronization would push a
      datatree which exceeds size limit for a one-time update.";
  }

  /* Datastore identities */

  identity custom-datastore {
    base ds:datastore;
    description
      "A datastore with boundaries not defined within
       draft-ietf-netmod-revised-datastores";
  }


  /*
   * TYPE DEFINITIONS
   */

  typedef change-type {
    type enumeration {
      enum "create" {
        description
          "Create a new data resource if it does not already exist.  If
          it already exists, replace.";
      }
      enum "delete" {
        description
          "Delete a data resource if it already exists. If it does not
          exists, take no action.";
      }
      enum "insert" {
        description
          "Insert a new user-ordered data resource";
      }
      enum "merge" {
        description
          "merge the edit value with the target data resource; create
          if it does not already exist";
      }
      enum "move" {
        description



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          "Reorder the target data resource";
      }
      enum "replace" {
        description
          "Replace the target data resource with the edit value";
      }
      enum "remove" {
        description
          "Remove a data resource if it already exists ";
      }
    }
    description
      "Specifies different types of datastore changes.";
    reference
      "RFC 8072 section 2.5, with a delta that it is ok to receive
      ability create on an existing node, or receive a delete on a
      missing node.";
  }

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

  /*
   * GROUP DEFINITIONS
   */

  grouping datastore-criteria {
    description
      "A grouping to define criteria for which selected objects from
       a targeted datastore should be included in push updates.";
    leaf source {
       type identityref {
         base ds:datastore;
       }
       mandatory true;
       description
         "Datastore from which to retrieve data.";
    }
    uses selection-filter-objects;
  }

  grouping selection-filter-types {
    description



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      "This grouping defines a selector for objects from a
       datastore.";
    choice filter-spec {
      description
        "The content filter specification for this request.";
      anydata subtree-filter {
        description
          "This parameter identifies the portions of the
           target datastore to retrieve.";
        reference "RFC 6241, Section 6.";
      }
      leaf xpath-filter {
        type yang:xpath1.0;
        description
          "This parameter contains an XPath expression identifying the
          portions of the target datastore to retrieve.";
        reference "http://www.w3.org/TR/1999/REC-xpath-19991116";
      }
    }
  }

  grouping selection-filter-objects {
    description
      "This grouping defines a selector for objects from a
       datastore.";
    choice selected-content {
      description
        "The source of the selection filter applied to the subscription.
        This 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 selection-filter-ref {
          type selection-filter-ref;
          mandatory true;
          description
            "References an existing selection filter which is to be
             applied to the subscription.";
        }
      }
      case within-subscription {
        description
          "Local definition allows a filter to have the same lifecycle
          as the subscription.";
        uses selection-filter-types;

      }



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    }
  }

  grouping update-policy-modifiable {
    description
      "This grouping describes the datastore specific subscription
       conditions that can be changed during the lifetime of the
       subscription.";
    choice update-trigger {
      description
        "Defines necessary conditions for sending an event to
         the subscriber.";
      case periodic {
        description
          "The agent is requested to notify periodically the current
           values of the datastore as defined by the selection filter.";
        leaf period {
          type yang:timeticks;
          mandatory true;
          description
            "Duration of time which should occur between periodic
             push updates.  Where the anchor-time is
             available, the push will include the objects and their
             values which exist at an exact multiple of timeticks
             aligning to this start-time anchor.";
        }
        leaf anchor-time {
          type yang:date-and-time;
          description
            "Designates a timestamp before or after which a series of
             periodic push updates are determined. The next update will
             take place at a whole multiple interval from the anchor
             time.  For example, for an anchor time is set for the top
             of a particular minute and a period interval of a minute,
             updates will be sent at the top of every minute this
             subscription is active.";
        }
      }
      case on-change {
        if-feature "on-change";
        description
          "The agent is requested to notify changes in values in the
           datastore subset as defined by a selection filter.";
        leaf dampening-period {
          type yang:timeticks;
          mandatory true;
          description
            "The shortest time duration which is allowed between the



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            creation of independent yang object update messages.
            Effectively this is the amount of time that needs to have
            passed since the last update.  Zero indicates no delay.";
        }
      }
    }
  }

  grouping update-policy {
    description
      "This grouping describes the datastore specific subscription
       conditions of a subscription.";
    uses update-policy-modifiable {
      augment "update-trigger/on-change" {
        description
          "Includes objects not modifiable once subscription is
           established.";
        leaf no-synch-on-start {
          type empty;
          description
            "This leaf acts as a flag that determines behavior at the
             start of the subscription.  When present, synchronization
             of state at the beginning of the subscription is outside
             the scope of the subscription. Only updates about changes
             that are observed from the start time, i.e. only push-
             change-update notifications are sent. When absent (default
             behavior), in order to facilitate a receiver's
             synchronization, a full update is sent when the
             subscription starts using a push-update notification, just
             like in the case of a periodic subscription.  After that,
             push-change-update notifications only are sent unless the
             Publisher chooses to resynch the subscription again.";
        }
        leaf-list excluded-change {
          type change-type;
          description
            "Use to restrict which changes trigger an update.
             For example, if modify is excluded, only creation and
             deletion of objects is reported.";
        }
      }
    }
  }

  grouping update-qos {
    description
      "This grouping describes Quality of Service information
       concerning a subscription.  This information is passed to lower



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       layers for transport prioritization and treatment";
    leaf dscp {
      type inet:dscp;
      default "0";
      description
        "The push update's IP packet transport priority. This is made
         visible across network hops to receiver. The transport
         priority is shared for all receivers of a given subscription.";
    }
    leaf weighting {
      type uint8 {
         range "0 .. 255";
      }
      description
        "Relative weighting for a subscription. Allows an underlying
         transport layer perform informed load balance allocations
         between various subscriptions";
      reference
        "RFC-7540, section 5.3.2";
    }
    leaf dependency {
      type sn:subscription-id;
      description
        "Provides the Subscription ID of a parent subscription which
         has absolute priority should that parent have push updates
         ready to egress the publisher. In other words, there should be
         no streaming of objects from the current subscription if
         the parent has something ready to push.";
      reference
        "RFC-7540, section 5.3.1";
    }
  }

  grouping update-error-hints {
    description
      "Allow return additional negotiation hints that apply
       specifically to push updates.";
    leaf period-hint {
      type yang:timeticks;
      description
        "Returned when the requested time period is too short. This
         hint can assert an viable period for both periodic push
         cadence and on-change dampening.";
    }
    leaf error-path {
      type string;
      description
        "Reference to a YANG path which is associated with the error



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         being returned.";
    }
    leaf object-count-estimate {
      type uint32;
      description
        "If there are too many objects which could potentially be
         returned by the selection filter, this identifies the estimate
         of the number of objects which the filter would potentially
         pass.";
    }
    leaf object-count-limit {
      type uint32;
      description
        "If there are too many objects which could be returned by the
         selection filter, this identifies the upper limit of the
         publisher's ability to service for this subscription.";
    }
    leaf kilobytes-estimate {
      type uint32;
      description
        "If the returned information could be beyond the capacity of
         the publisher, this would identify the data size which could
         result from this selection filter.";
    }
    leaf kilobytes-limit {
      type uint32;
      description
        "If the returned information would be beyond the capacity of
         the publisher, this identifies the upper limit of the
         publisher's ability to service for this subscription.";
    }
  }

  /*
   * RPCs
   */

   rpc resynch-subscription {
    if-feature "on-change";
    description
      "This RPC allows a subscriber of an active on-change
       subscription to request a full push of objects in there current
       state. A successful result would be the set of YANG objects
       equivalent to a Get using the existing selection criteria. This
       request may only come from the same subscriber using the
       establish-subscription RPC.";
    input {
      leaf identifier {



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        type sn:subscription-id;
        mandatory true;
        description
          "Identifier of the subscription that is to be resynched.";
      }
    }
    output {
      leaf subscription-result {
        type sn:subscription-result;
        mandatory true;
        description
          "Indicates whether the request for the subscription resynch
          has been accepted, or why it has been denied.";
      }
    }
  }

  /*
   * DATA NODES
   */

  augment "/sn:establish-subscription/sn:input" {
    description
      "This augmentation adds additional subscription parameters that
      apply specifically to datastore updates to RPC input.";
    uses update-policy;
    uses update-qos;
  }
  augment "/sn:establish-subscription/sn:input/sn:target" {
    description
      "This augmentation adds the datastore as a valid parameter object
      for the subscription to RPC input.  This provides a target for
      the filter.";
    case datastore {
       uses datastore-criteria;
    }
  }
  augment "/sn:establish-subscription/sn:output/"+
    "sn:result/sn:no-success" {
    description
      "This augmentation adds datastore specific error info
      and hints to RPC output.";
    uses update-error-hints;
  }
  augment "/sn:modify-subscription/sn:input" {
    description
      "This augmentation adds additional subscription parameters
       specific to datastore updates.";



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    uses update-policy-modifiable;
  }
  augment "/sn:modify-subscription/sn:input/sn:target" {
    description
      "This augmentation adds the datastore as a valid parameter object
      for the subscription to RPC input.  This provides a target for
      the filter.";
    case datastore {
       uses selection-filter-objects;
    }
  }
  augment "/sn:modify-subscription/sn:output/"+
    "sn:result/sn:no-success" {
    description
      "This augmentation adds push datastore error info and hints to
      RPC output.";
    uses update-error-hints;
  }

  notification push-update {
    description
      "This notification contains a push update, containing data
       subscribed to via a subscription. This notification is sent for
       periodic updates, for a periodic subscription.  It can also be
       used for synchronization updates of an on-change subscription.
       This notification shall only be sent to receivers of a
       subscription; it does not constitute a general-purpose
       notification.";
    leaf subscription-id {
      type sn:subscription-id;
      description
        "This references the subscription which drove the notification
         to be sent.";
    }
    leaf time-of-update {
      type yang:date-and-time;
      description
        "This leaf identifies the generation time of the datastore
         selection within a push-update.";
    }
    leaf updates-not-sent {
      type empty;
      description
        "This is a flag which indicates that not all data nodes
         subscribed to are included with this update. In other words,
         the publisher has failed to fulfill its full subscription
         obligations. The result is intermittent loss of
         synchronization of data at the receiver.";



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    }
    anydata datastore-contents {
      description
        "This contains the updated data.  It constitutes a snapshot
         at the time-of-update of the set of data that has been
         subscribed to.  The format and syntax of the data
         corresponds to the format and syntax of data that would be
         returned in a corresponding get operation with the same
         selection filter parameters applied.";
    }
  }

  notification push-change-update {
    if-feature "on-change";
    description
      "This notification contains an on-change push update. This
       notification shall only be sent to the receivers of a
       subscription; it does not constitute a general-purpose
       notification.";
    leaf subscription-id {
      type sn:subscription-id;
      description
        "This references the subscription which drove the notification
         to be sent.";
    }
    leaf time-of-update {
      type yang:date-and-time;
      description
        "This leaf identifies the generation time of the datastore
         changes extract.  If a dampening-period was in effect before
         the notification was generated, this may not be the time any of
         the datastore-changes were actually made.";
    }
    leaf updates-not-sent {
      type empty;
      description
        "This is a flag which indicates that not all changes which
         have occurred since the last update are included with this
         update.  In other words, the publisher has failed to
         fulfill its full subscription obligations, for example in
         cases where it was not able to keep up with a change burst.";
    }
    anydata datastore-changes {
      description
        "This contains an incremental set of datastore changes needed
         to update a remote datastore starting at the time of the
         previous update, per the terms of the subscription.  Changes
         are encoded analogous to the syntax of a corresponding yang-



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         patch operation, i.e. a yang-patch operation applied to the
         YANG datastore implied by the previous update to result in the
         current state.";
      reference
        "RFC 8072 section 2.5, with a delta that it is ok to receive
         ability create on an existing node, or receive a delete on a
         missing node.";
    }
  }

  augment "/sn:subscription-started" {
    description
      "This augmentation adds many yang datastore specific objects to
       the notification that a subscription has started.";
    uses update-policy;
    uses update-qos;
  }
  augment "/sn:subscription-started/sn:target" {
    description
      "This augmentation allows the datastore to be included as part
       of the notification that a subscription has started.";
    case datastore {
       uses datastore-criteria;
    }
  }
  augment "/sn:filters" {
    description
      "This augmentation allows the datastore to be included as part
       of the selection filtering criteria for a subscription.";
    list selection-filter {
      key "identifier";
      description
        "A list of pre-positioned filters that can be applied
         to datastore subscriptions.";
      leaf identifier {
        type sn:filter-id;
        description
          "An identifier to differentiate between selection filters.";
      }
      uses selection-filter-types;
    }
  }
  augment "/sn:subscription-modified" {
    description
      "This augmentation adds many yang datastore specific objects to
       the notification that a subscription has been modified.";
    uses update-policy;
    uses update-qos;



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  }
  augment "/sn:subscription-modified/sn:target" {
    description
      "This augmentation allows the datastore to be included as part
      of the notification that a subscription has been modified.";
    case datastore {
       uses datastore-criteria;
    }
  }
  augment "/sn:subscription-config/sn:subscription" {
    description
      "This augmentation adds many yang datastore specific objects
      which can be configured as opposed to established via RPC.";
    uses update-policy;
    uses update-qos;
  }
  augment "/sn:subscription-config/sn:subscription/sn:target" {
    description
      "This augmentation adds the datastore to the selection filtering
      criteria for a subscription.";
    case datastore {
       uses datastore-criteria;
    }
  }
  augment "/sn:subscriptions/sn:subscription" {
    yp:notifiable-on-change true;
    description
      "This augmentation adds many datastore specific objects to a
       subscription.";
    uses update-policy;
    uses update-qos;
  }
  augment "/sn:subscriptions/sn:subscription/sn:target" {
    description
      "This augmentation allows the datastore to be included as part
      of the selection filtering criteria for a subscription.";
    case datastore {
       uses datastore-criteria;
    }
  }

/* YANG Parser Pyang crashing on syntax below, due to fixed bug
         https://github.com/mbj4668/pyang/issues/300

  deviation "/sn:subscriptions/sn:subscription/sn:receivers/"
             + "sn:receiver/sn:pushed-notifications" {
    deviate add {
      yp:notifiable-on-change false;



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    }
  }
  deviation "/sn:subscriptions/sn:subscription/sn:receivers/"
             + "sn:receiver/sn:excluded-notifications" {
    deviate add {
      yp:notifiable-on-change false;
    }
  }
YANG Parser Pyang crashing on syntax above */
}


<CODE ENDS>


6.  IANA Considerations

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

   URI: urn:ietf:params:xml:ns:yang:ietf-yang-push
   Registrant Contact: The IESG.
   XML: N/A; the requested URI is an XML namespace.

   This document registers the following YANG module in the "YANG Module
   Names" registry [RFC6020]:

   Name: ietf-yang-push
   Namespace: urn:ietf:params:xml:ns:yang:ietf-yang-push
   Prefix: yp
   Reference: draft-ietf-netconf-yang-push-08.txt (RFC form)

7.  Security Considerations

   All security considerations from [subscribe] are relevant for
   datastores.  In addition there are specific security considerations
   for receivers defined in Section 3.9

   If the access control permissions on subscribed YANG nodes change
   during the lifecycle of a subscription, a publisher MUST either
   transparently conform to the new access control permissions, or must
   terminate or restart the subscriptions so that new access control
   permissions are re-established.

   The NETCONF Authorization Control Model SHOULD be used to restrict
   the delivery of YANG nodes for which the receiver has no access.





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8.  Acknowledgments

   For their valuable comments, discussions, and feedback, we wish to
   acknowledge Tim Jenkins, Kent Watsen, Susan Hares, Yang Geng, Peipei
   Guo, Michael Scharf, Sharon Chisholm, and Guangying Zheng.

9.  References

9.1.  Normative References

   [revised-datastores]
              Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore
              Architecture", draft-ietf-netmod-revised-datastores-04
              (work in progress), August 2017.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [RFC6470]  Bierman, A., "Network Configuration Protocol (NETCONF)
              Base Notifications", RFC 6470, DOI 10.17487/RFC6470,
              February 2012, <https://www.rfc-editor.org/info/rfc6470>.

   [RFC6536bis]
              Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", draft-ietf-
              netconf-rfc6536bis-05 (work in progress), September 2017.

   [RFC7895]  Bierman, A., Bjorklund, M., and K. Watsen, "YANG Module
              Library", RFC 7895, DOI 10.17487/RFC7895, June 2016,
              <https://www.rfc-editor.org/info/rfc7895>.

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

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,
              <https://www.rfc-editor.org/info/rfc7951>.






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   [RFC8072]  Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch
              Media Type", RFC 8072, DOI 10.17487/RFC8072, February
              2017, <https://www.rfc-editor.org/info/rfc8072>.

   [subscribe]
              Voit, E., Clemm, A., Gonzalez Prieto, A., Tripathy, A.,
              and E. Nilsen-Nygaard, "Custom Subscription to Event
              Notifications", draft-ietf-netconf-subscribed-
              notifications-04 (work in progress), September 2017.

9.2.  Informative References

   [netconf-notif]
              Gonzalez Prieto, A., Clemm, A., Voit, E., Nilsen-Nygaard,
              E., and A. Tripathy, "NETCONF Support for Event
              Notifications", September 2017.

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

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

   [RFC7223]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 7223, DOI 10.17487/RFC7223, May 2014,
              <https://www.rfc-editor.org/info/rfc7223>.

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

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

Appendix A.  Changes between revisions

   (To be removed by RFC editor prior to publication)

   v09 - v10

   o  Returned to the explicit filter subtyping of v00-v05

   o  identityref to ds:datastore made explicit



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   o  Returned ability to modify a selection filter via RPC.

   v08 - v09

   o  Minor tweaks cleaning up text, removing appendicies, and making
      reference to revised-datastores.

   o  Subscription-id optional in push updates, except when encoded in
      RFC5277, Section 4 one-way notification.

   o  Finished adding the text descibing the resynch subscription RPC.

   o  Removed relationships to other drafts and future technology
      appendicies as this work is being explored elsewhere.

   o  Deferred the multi-line card issue to new drafts

   o  Simplified the NACM interactions.

   v07 - v08

   o  Updated YANG models with minor tweaks to accommodate changes of
      ietf-subscribed-notifications.

   v06 - v07

   o  Clarifying text tweaks.

   o  Clarification that filters act as selectors for subscribed data
      nodes; support for value filters not included but possible as a
      future extension

   o  Filters don't have to be matched to existing YANG objects

   v05 - v06

   o  Security considerations updated.

   o  Base YANG model in [subscribe] updated as part of move to
      identities, YANG augmentations in this doc matched up

   o  Terms refined and text updates throughout

   o  Appendix talking about relationship to other drafts added.

   o  Datastore replaces stream

   o  Definitions of filters improved



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   v04 to v05

   o  Referenced based subscription document changed to Subscribed
      Notifications from 5277bis.

   o  Getting operational data from filters

   o  Extension notifiable-on-change added

   o  New appendix on potential futures.  Moved text into there from
      several drafts.

   o  Subscription configuration section now just includes changed
      parameters from Subscribed Notifications

   o  Subscription monitoring moved into Subscribed Notifications

   o  New error and hint mechanisms included in text and in the yang
      model.

   o  Updated examples based on the error definitions

   o  Groupings updated for consistency

   o  Text updates throughout

   v03 to v04

   o  Updates-not-sent flag added

   o  Not notifiable extension added

   o  Dampening period is for whole subscription, not single objects

   o  Moved start/stop into rfc5277bis

   o  Client and Server changed to subscriber, publisher, and receiver

   o  Anchor time for periodic

   o  Message format for synchronization (i.e. synch-on-start)

   o  Material moved into 5277bis

   o  QoS parameters supported, by not allowed to be modified by RPC

   o  Text updates throughout




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Authors' Addresses

   Alexander Clemm
   Huawei

   Email: ludwig@clemm.org


   Eric Voit
   Cisco Systems

   Email: evoit@cisco.com


   Alberto Gonzalez Prieto
   VMware

   Email: agonzalezpri@vmware.com


   Ambika Prasad Tripathy
   Cisco Systems

   Email: ambtripa@cisco.com


   Einar Nilsen-Nygaard
   Cisco Systems

   Email: einarnn@cisco.com


   Andy Bierman
   YumaWorks

   Email: andy@yumaworks.com


   Balazs Lengyel
   Ericsson

   Email: balazs.lengyel@ericsson.com









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