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

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

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

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

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

1. Introduction

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

1.1. Motivation

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

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

1.2. Terminology

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

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

Dynamic subscription: A subscription agreed between subscriber and publisher via create, establish, modify, and delete RPC control plane signaling messages.

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

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

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

Publisher: An entity responsible for streaming Event Notifications per the terms of a Subscriptions

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

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

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

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

1.3. Solution Overview

This document describes mechanisms for subscribing and receiving event notifications from an event server publisher. This document builds on top of the capabilities defined in [RFC5277], extending them, and generalizing them to be protocol-agnostic.

Some enhancements over RFC 5277 include the ability to have multiple subscriptions on a single transport session, to terminate a single subscriptions without terminating the transport session, and to modify existing subscriptions.

These enhancements do not affect existing RFC 5277 subscribers that do not support these particular subscription requirements.

Note that there is no mixing-and-matching of dynamic and configured subscriptions. Specifically, a configured subscription cannot be modified or deleted using RPC. Similarly, a subscription created via RPC cannot be modified through configuration operations.

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

2. Solution

2.1. Event Streams

An event stream is a set of events available for subscription from a publisher. It is out of the scope of this document to identify a) how streams are defined, b) how events are defined/generated, and c) how events are assigned to streams.

That said, some event streams will be standardized whereas others may be vendor specific. One standardized event stream is the "NETCONF" notification event stream. The NETCONF event stream contains all NETCONF XML event notifications supported by the publisher, except for those belonging only to streams that explicitly indicate that they must be excluded from the NETCONF stream, such as notifications that serve OAM and signaling purposes.

The following is a high-level description of the flow of a notification. Note that it does not mandate and/or preclude an implementation. As events are raised, they are assigned to streams. An event may be assigned to multiple streams. The event is distributed to subscribers and receivers based on the current subscriptions and access control. Access control is needed because if any receiver of that subscription does not have permission to receive an event, then it never makes it into a notification, and processing of the event is completed for that subscription.

2.2. Event Stream Discovery

A publisher maintains a list of available event streams as operational data. This list contains both standardized and vendor-specific event streams. A client can retrieve this list like any other YANG-defined data, for example using the <get> operation when using NETCONF.

2.3. Filters

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

2.4. Subscription State Model at the Publisher

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

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

Figure 1: Subscription states at publisher

Of interest in this state machine are the following:

Successful <establish-subscription> or <modify-subscription> requests put the subscription into an active state.
Failed <modify-subscription> requests will leave the subscription in its previous state, with no visible change to any streaming updates.
A <delete-subscription> request will delete the entire subscription.

3. Data Model Trees for Event Notifications

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

               
module: ietf-event-notifications
    +--ro streams
    |  +--ro stream*   stream
    +--rw filters
    |  +--rw filter* [filter-id]
    |     +--rw filter-id    filter-id
    |     +--rw (filter-type)?
    |        +--:(rfc5277)
    |           +--rw filter?
    +--rw subscription-config {configured-subscriptions}?
    |  +--rw subscription* [subscription-id]
    |     +--rw subscription-id     subscription-id
    |     +--rw stream?             stream
    |     +--rw encoding?           encoding
    |     +--rw (filter-type)?
    |     |  +--:(rfc5277)
    |     |  |  +--rw filter?
    |     |  +--:(by-reference)
    |     |     +--rw filter-ref?         filter-ref
    |     +--rw startTime?          yang:date-and-time
    |     +--rw stopTime?           yang:date-and-time
    |     +--rw receivers
    |     |  +--rw receiver* [address]
    |     |     +--rw address     inet:host
    |     |     +--rw port        inet:port-number
    |     |     +--rw protocol?   transport-protocol
    |     +--rw (push-source)?
    |        +--:(interface-originated)
    |        |  +--rw source-interface?   if:interface-ref
    |        +--:(address-originated)
    |           +--rw source-vrf?         uint32
    |           +--rw source-address      inet:ip-address-no-zone
    +--ro subscriptions
       +--ro subscription* [subscription-id]
          +--ro subscription-id            subscription-id
          +--ro configured-subscription?   
          |                 empty {configured-subscriptions}?
          +--ro subscription-status?       subscription-status
          +--ro stream?                    stream
          +--ro encoding?                  encoding
          +--ro (filter-type)?
          |  +--:(rfc5277)
          |  |  +--ro filter?
          |  +--:(by-reference)
          |     +--ro filter-ref?                filter-ref
          +--ro startTime?                 yang:date-and-time
          +--ro stopTime?                  yang:date-and-time
          +--ro receivers
          |  +--ro receiver* [address]
          |     +--ro address     inet:host
          |     +--ro port        inet:port-number
          |     +--ro protocol?   transport-protocol
          +--ro (push-source)?
             +--:(interface-originated)
             |  +--ro source-interface?          if:interface-ref
             +--:(address-originated)
                +--ro source-vrf?         uint32
                +--ro source-address      inet:ip-address-no-zone

  rpcs:
    +---x establish-subscription
    |  +---w input
    |  |  +---w stream?       stream
    |  |  +---w encoding?     encoding
    |  |  +---w (filter-type)?
    |  |  |  +--:(rfc5277)
    |  |  |  |  +---w filter?
    |  |  |  +--:(by-reference)
    |  |  |     +---w filter-ref?   filter-ref
    |  |  +---w startTime?    yang:date-and-time
    |  |  +---w stopTime?     yang:date-and-time
    |  +--ro output
    |     +--ro subscription-result    subscription-result
    |     +--ro (result)?
    |        +--:(success)
    |        |  +--ro subscription-id        subscription-id
    |        +--:(no-success)
    |           +--ro stream?                stream
    |           +--ro encoding?              encoding
    |           +--ro (filter-type)?
    |           |  +--:(rfc5277)
    |           |  |  +--ro filter?
    |           |  +--:(by-reference)
    |           |     +--ro filter-ref?            filter-ref
    |           +--ro startTime?             yang:date-and-time
    |           +--ro stopTime?              yang:date-and-time
    +---x create-subscription
    |  +---w input
    |     +---w stream?      stream
    |     +---w encoding?    encoding
    |     +---w (filter-type)?
    |     |  +--:(rfc5277)
    |     |     +---w filter?
    |     +---w startTime?   yang:date-and-time
    |     +---w stopTime?    yang:date-and-time
    +---x modify-subscription
    |  +---w input
    |  |  +---w subscription-id?   subscription-id
    |  |  +---w (filter-type)?
    |  |  |  +--:(rfc5277)
    |  |  |  |  +---w filter?
    |  |  |  +--:(by-reference)
    |  |  |     +---w filter-ref?        filter-ref
    |  |  +---w startTime?         yang:date-and-time
    |  |  +---w stopTime?          yang:date-and-time
    |  +--ro output
    |     +--ro subscription-result    subscription-result
    |     +--ro (result)?
    |        +--:(success)
    |        |  +--ro subscription-id        subscription-id
    |        +--:(no-success)
    |           +--ro stream?                stream
    |           +--ro encoding?              encoding
    |           +--ro (filter-type)?
    |           |  +--:(rfc5277)
    |           |  |  +--ro filter?
    |           |  +--:(by-reference)
    |           |     +--ro filter-ref?            filter-ref
    |           +--ro startTime?             yang:date-and-time
    |           +--ro stopTime?              yang:date-and-time
    +---x delete-subscription
       +---w input
       |  +---w subscription-id    subscription-id
       +--ro output
          +--ro subscription-result    subscription-result

  notifications:
    +---n replay-complete
    |  +--ro subscription-id    subscription-id
    +---n notification-complete
    |  +--ro subscription-id    subscription-id
    +---n subscription-started
    |  +--ro subscription-id    subscription-id
    |  +--ro stream?            stream
    |  +--ro encoding?          encoding
    |  +--ro (filter-type)?
    |  |  +--:(rfc5277)
    |  |  |  +--ro filter?
    |  |  +--:(by-reference)
    |  |     +--ro filter-ref?        filter-ref
    |  +--ro startTime?         yang:date-and-time
    |  +--ro stopTime?          yang:date-and-time
    +---n subscription-suspended
    |  +--ro subscription-id    subscription-id
    |  +--ro reason?            subscription-susp-reason
    +---n subscription-resumed
    |  +--ro subscription-id    subscription-id
    +---n subscription-modified
    |  +--ro subscription-id    subscription-id
    |  +--ro stream?            stream
    |  +--ro encoding?          encoding
    |  +--ro (filter-type)?
    |  |  +--:(rfc5277)
    |  |  |  +--ro filter?
    |  |  +--:(by-reference)
    |  |     +--ro filter-ref?        filter-ref
    |  +--ro startTime?         yang:date-and-time
    |  +--ro stopTime?          yang:date-and-time
    +---n subscription-terminated
       +--ro subscription-id    subscription-id
       +--ro reason?            subscription-term-reason

The data model is structured as follows:

"Streams" contains a list of event streams that are supported by the publisher and that can be subscribed to.
"Filters" contains a configurable list of filters that can be applied to a subscription. This allows users to reference an existing filter definition as an alternative to defining a filter inline for each subscription.
"Subscription-config" contains the configuration of configured subscriptions. The parameters of each configured subscription are a superset of the parameters of a dynamic subscription and use the same groupings. In addition, the configured subscriptions must also specify intended receivers and may specify the push source from which to send the stream of notification messages.
"Subscriptions" contains a list of all subscriptions on a publisher, both configured and dynamic. It can be used to retrieve information about the subscriptions which an publisher is serving.

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

4. Dynamic Subscriptions

Dynamic subscriptions are managed via RPC.

4.1. Establishing a Subscription

This operation includes and extends the "create-subscription" operation defined in RFC 5277. It allows a subscriber to request the creation of a subscription both via RPC and configuration operations. When invoking the RPC, establish-subscription permits negotiating the subscription terms, changing them dynamically.

The input parameters of the operation are those of create subscription plus:

filter-ref: filters that have been previously (and separately) configured can be referenced by a subscription. This mechanism enables the reuse of filters.
encoding: by default, updates are encoded using XML. Other encodings may be supported, such as JSON.

If the publisher cannot satisfy the request, it sends a negative <subscription-result> element.

If the subscriber has no authorization to establish the subscription, the <subscription-result> indicates an authorization error. If the 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 when it was processed. However, they is no guarantee that subsequent requests with those parameters for this subscriber or others will be accepted. For instance, consider a subscription from [I-D.ietf-netconf-yang-push], which augments the establish-subscription with some additional parameters, including "period".

Subscription requests will fail if a filter with invalid syntax is provided or if the name of a non-existent stream is provided.

4.2. Modifying a Subscription

This operation permits modifying the terms of a dynamic subscription previously established. Subscriptions created by configuration cannot be modified. Dynamic subscriptions can be modified one or multiple times. If the publisher accepts the request, it immediately starts sending events based on the new terms, completely ignoring the previous ones. If the publisher rejects the request, the subscription remains as prior to the request. That is, the request has no impact whatsoever. The contents of negative responses to modify-subscription requests are the subset of the establish subscription request parameters which are allowed to be dynamically modified.

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

Configured subscriptions cannot be modified (or deleted) using RPCs. Instead, configured subscriptions are modified (or deleted) as part of regular configuration operations. Publishers MUST reject any attempts to modify (or delete) configured subscriptions via RPC.

4.3. Deleting a Subscription

This operation permits canceling a subscription previously established. If the publisher accepts the request, it immediately stops sending events for the subscription. If the publisher rejects the request, all subscriptions remain as prior to the request. That is, the request has no impact whatsoever.

Subscriptions created via RPC can only be deleted via RPC using the same transport session used for subscription establishment. Configured subscriptions cannot be deleted using RPCs. Instead, configured subscriptions are deleted as part of regular configuration operations. Publishers MUST reject any RPC attempt to delete configured subscriptions.

The only parameter to delete-subscription is the identifier of the subscription to delete.

If the publisher can satisfy the request, it sends an OK element.

If the publisher cannot satisfy the request, it sends an error-rpc element.

5. Configured Subscriptions

A configured subscription is a subscription installed via a configuration interface.

Configured subscriptions persist across reboots, and persist even when transport is unavailable. This also means configured subscriptions do not support negotiation.

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

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

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

One or more receiver IP addresses (and corresponding ports) intended as the destination for push updates for each subscription. In addition, the transport protocol for each destination may be defined.
Optional parameters to identify an egress interface or IP address / VRF where a subscription updates should be pushed from the publisher.

5.1. Establishing a Configured Subscription

Configured subscriptions are established using configuration operations against the top-level subtree subscription-config. There are two key differences between RPC and configuration operations for subscription establishment. Firstly, configuration operations do not support negotiation while RPCs do. Secondly, while RPCs mandate that the subscriber establishing the subscription is the only receiver of the notifications, configuration operations permit specifying receivers independent of any tracked subscriber. Immediately after a subscription is successfully established, the publisher sends to its receivers a control-plane notification stating the subscription has been established (subscription-started).

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

For example at subscription establishment, a client may send:

<rpc message-id="101" 
       xmlns="urn:ietf:params:xml:ns:netconf:base:1.0" 
       xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0">
    <edit-config>
        <target>
            <running/>
        </target>
        <subscription-config 
            xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
            <subscription>
                <subscription-id>
                    1922
                </subscription-id>
                <stream>
                    foo
                </stream>
                <receiver>
                    <address>
                        1.2.3.4
                    </address>
                    <port>
                        1234
                    </port>
                </receiver>
            </subscription>
        </subscription-config>
    </edit-config>
</rpc>

Figure 2: Establish configured subscription

if the request is accepted, the publisher would reply:

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

Figure 3: Response to a successful configured subscription establishment

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

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

Figure 4: Response to a failed configured subscription establishment

5.2. Modifying a Configured Subscription

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

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

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

5.3. Deleting a Configured Subscription

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

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

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

Figure 5: Deleting a configured subscription

Immediately after a subscription is successfully deleted, the publisher sends to all receivers a control-plane notification stating the subscription has been terminated (subscription-terminated).

6. Event (Data Plane) Notifications

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

An event notification is sent to the receiver(s) when an event of interest (i.e., meeting the specified filtering criteria) has occurred. An event notification is a complete and well-formed XML document. Note that <notification> is not a Remote Procedure Call (RPC) method but rather the top-level element identifying the one-way message as a notification. Note that event notifications never trigger responses.

The event notification always includes an <eventTime> element. It is the time the event was generated by the event source. This parameter is of type dateTime and compliant to [RFC3339]. Implementations must support time zones.

The event notifications must also include the subscription-id if the establish-subscription was used in its establishment, or if it was configured via an operational interface.

The event notification also contains notification-specific tagged content, if any.

The following is an example of an event notification from [RFC7950]:

notification link-failure {
  description "A link failure has been detected";
    leaf if-name {
      type leafref {
        path "/interface/name";
      }
    }
    leaf if-admin-status {
      type admin-status;
    }
    leaf if-oper-status {
      type oper-status;
    }
}

Figure 6: Definition of a data plane notification

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

Figure 7: Data plane notification

The equivalent using json encoding would be

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

Figure 8: Data plane notification using JSON encoding

7. Control Plane Notifications

In addition to data plane notifications, a publisher may send control plane notifications to indicate to receivers that an event related to the subscription management has occurred.

Control plane notifications are unlike other notifications in that they are not general-purpose notifications. They cannot be filtered out, and they are delivered only to the receiver of a subscription. The definition of control plane notifications is distinct from other notifications by making use of a YANG extension tagging them as control plane notification.

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

7.1. replayComplete

This notification is originally defined in [RFC5277]. It is sent to indicate that all of the replay notifications have been sent. This notification must not be sent for any other reason.

In the case of a subscription without a stop time or a stop time which has not been reached, after the <replayComplete> notification has been sent, it can be expected that any notifications generated since the start of the subscription creation will be sent, followed by notifications in sequence as they arise naturally within the system.

7.2. notificationComplete

This notification is originally defined in [RFC5277]. It is sent to indicate that a subscription, which includes a stop time, has finished passing events.

7.3. subscription-started

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

7.4. subscription-modified

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

7.5. subscription-terminated

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

Subscribers can terminate via RPC subscriptions established via RPC. In such cases, no subscription-terminated notifications are sent.

7.6. subscription-suspended

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

7.7. subscription-resumed

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

8. Data Model for Event Notifications

<CODE BEGINS> file "ietf-event-notifications@2016-10-27.yang"
module ietf-event-notifications {
  namespace 
    "urn:ietf:params:xml:ns:yang:ietf-event-notifications";

  prefix notif-bis;

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

  organization "IETF";
  contact
    "WG Web:   &lt;http://tools.ietf.org/wg/netconf/&gt;
     WG List:  &lt;mailto:netconf@ietf.org&gt;
     
     WG Chair: Mahesh Jethanandani
               &lt;mailto:mjethanandani@gmail.com&gt;
     
     WG Chair: Mehmet Ersue
               &lt;mailto:mehmet.ersue@nokia.com&gt;

     Editor:   Alexander Clemm
               &lt;mailto:alex@sympotech.com&gt;

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

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

     Editor:   Einar Nilsen-Nygaard
               &lt;mailto:einarnn@cisco.com&gt;

     Editor:   Ambika Prasad Tripathy
               &lt;mailto:ambtripa@cisco.com&gt;
     
     Editor:   Sharon Chisholm
               &lt;mailto:schishol@ciena.com&gt;

     Editor:   Hector Trevino               
               &lt;mailto:htrevino@cisco.com";

  description
    "This module contains conceptual YANG specifications
     for NETCONF Event Notifications.";
  
  revision 2016-10-27 {
    description
      "Tweaks to remove two notifications,
	  RPC for create subscription refined with stream default,
	  new grouping to eliminate some dymanically modifiable 
	  parameters in modifiy subscription RPC";
    reference 
      "draft-ietf-netconf-rfc5277bis-01";
  }
  
  
  /*
   * FEATURES
   */
  
  feature json {
    description
      "This feature indicates that JSON encoding of notifications
       is supported.";
  }

  feature configured-subscriptions {
    description
      "This feature indicates that management plane configuration 
       of subscription is supported.";
  }
  
  /* 
   * EXTENSIONS
   */
   
  extension control-plane-notif {
    description
      "This statement applies only to notifications.
       It indicates that the notification is a control-plane
       notification (aka OAM notification). Therefore it does 
       not participate in a regular event stream and does not 
       need to be specifically subscribed to."; 
  }
  
  /*
   * IDENTITIES
   */

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

  identity NETCONF {
    base stream;
    description
      "Default NETCONF event stream, containing events based on 
       notifications defined as YANG modules that are supported 
       by the system.";  
  }

  /* Identities for subscription results */
  identity subscription-result {
    description
      "Base identity for RPC responses to requests surrounding
       management (e.g. creation, modification, deletion) of 
       subscriptions.";
  }

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

  identity error {
    base subscription-result;
    description
      "RPC was not successful.
       Base identity for error return codes.";
  }

  identity error-no-such-subscription {
    base error;
    description
      "A subscription with the requested subscription ID
       does not exist.";
  }

  identity error-no-such-option {
    base error;
    description
      "A requested parameter setting is not supported.";
  }

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

  identity error-configured-subscription {
    base error;
    description
      "Cannot apply RPC to a configured subscription, i.e. 
       to a subscription that was not established via RPC.";
  }

  identity error-other {
    base error;
    description
      "An unspecified error has occurred (catch all).";
  }

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

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

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

  identity suspended {
    base subscription-stream-status;
    description
      "The status is suspended, meaning that the publisher
       is currently unable to provide the negotiated updates
       for the subscription.";
  }

  identity in-error {
    base subscription-stream-status;
    description
      "The status is in error or degraded, meaning that
       stream and/or subscription is currently unable to provide
       the negotiated notifications.";
  }

  /* Identities for subscription errors */
  identity subscription-errors {
    description
      "Base identity for subscription error status.
       This identity is not to be confused with error return 
       codes for RPCs";
  }

  identity internal-error {
    base subscription-errors;
    description
      "Subscription failures caused by server internal error.";
  }

  identity no-resources {
    base subscription-errors;
    description
      "Lack of resources, e.g. CPU, memory, bandwidth";
  }

  identity subscription-deleted {
    base subscription-errors;
    description
      "The subscription was terminated because the subscription
       was deleted.";
  }

  identity other {
    base subscription-errors;
    description
      "Fallback reason - any other reason";
  }

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

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

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

  /* Identities for transports */
  identity transport {
    description
      "An identity that represents a transport protocol for  
       event notifications";
  }

  identity netconf {
    base transport;
    description
      "Netconf notifications as a transport.";
  }

  /*
   * TYPEDEFs
   */

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

  typedef filter-id {
    type uint32;
    description
      "A type to identify filters which can be associated with a 
       subscription.";
  }

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

  typedef subscription-term-reason {
    type identityref {
      base subscription-errors;
    }
    description
      "Reason for a publisher to terminate a subscription.";
  }

  typedef subscription-susp-reason {
    type identityref {
      base subscription-errors;
    }
    description
      "Reason for a publisher to suspend a subscription.";
  }

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

  typedef subscription-status {
    type identityref {
      base subscription-stream-status;
    }
    description
      "Specifies the status of a subscription or datastream.";
  }
  
  typedef transport-protocol {
    type identityref {
      base transport;
    }
    description
      "Specifies transport protocol used to send notifications to a
       receiver.";
  }

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

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

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

  /*
   * GROUPINGS
   */

  grouping base-filter {
    description
      "This grouping defines the base for filters for 
       notification events.
       It includes the filter defined in 5277 and
       it enables extending filtering to other 
       types of filters";
    choice filter-type {
      description
        "A filter needs to be a single filter of a given type.
         Mixing and matching of multiple filters does not occur
         at the level of this grouping.";
      case rfc5277 {
        anyxml filter {
          description
            "Filter per RFC 5277. Notification filter.
            If a filter element is specified to look for data of a 
            particular value, and the data item is not present 
            within a particular event notification for its value to 
            be checked against, the notification will be filtered 
            out. For example, if one were to check for
            'severity=critical' in a configuration event 
            notification where this field was not supported, then 
            the notification would be filtered out. For subtree 
            filtering, a non-empty node set means that the filter 
            matches.  For XPath filtering, the mechanisms defined 
            in [XPATH] should be used to convert the returned 
            value to boolean.";
        }
      }
    }
  }

  grouping subscription-info-basic-non-modifiable {
    description
      "This grouping describes the information in a basic 
       subscription request.";
    leaf stream {
      type stream; 
      description
        "Indicates which stream of events is of interest.  
         If not present, events in the default NETCONF stream 
         will be sent.";
    }
	leaf encoding {
      type encoding;
      default "encode-xml";
      description
        "The type of encoding for the subscribed data.
         Default is XML";
    }
  }
  
  grouping subscription-info-basic-modifiable {
    description
      "This grouping describes some objects which may be changed
	  in a subscription via an RPC.";
    uses base-filter;
    leaf startTime {
      type yang:date-and-time;
      description
        "Used to trigger the replay feature
         and indicate that the replay should start at the time
         specified.  If <startTime> is not present, this is not a 
         replay subscription.  It is not valid to specify start 
         times that are later than the current time.  If the 
         <startTime> specified is earlier than the log can support, 
         the replay will begin with the earliest available 
         notification.  This parameter is of type dateTime and 
         compliant to [RFC3339].  Implementations must
         support time zones.";
    }
    leaf stopTime {
      type yang:date-and-time;
      must "current()  > ../startTime" {
        description 
          "stopTime must be used with and be later than <startTime>";
      }
      description
        "Used with the optional replay feature to indicate the 
         newest notifications of interest.  If <stopTime> is 
         not present, the notifications will continue until the 
         subscription is terminated.  Must be used with and be 
         later than <startTime>.  Values of <stopTime> in the 
         future are valid.  This parameter is of type dateTime and
         compliant to [RFC3339].  Implementations must support time
         zones.";
    }
  }

  grouping subscription-info-all-modifiable {
    description
      "This grouping describes all rpc modifiable objects in a
       subscription.";
    uses subscription-info-basic-modifiable {
      augment "filter-type" {
        description
          "Post-5277 subscriptions allow references to existing 
           filters";
        case by-reference {
          description
            "Incorporate a filter that has been configured
             separately.";
          leaf filter-ref {
            type filter-ref;
            description
              "References filter which is associated with the
               subscription.";
          }
        }
      }
    }
  }
  
  grouping subscription-info {
    description
      "This grouping describes information concerning a
       subscription.";
	uses subscription-info-basic-non-modifiable;
	uses subscription-info-all-modifiable;
  }
  
  grouping push-source-info {
    description
      "Defines the sender source from which notifications 
       for a configured subscription are sent.";
    choice push-source {
      description
        "Identifies the egress interface on the Publisher from
         which notifications will or are being sent.";
      case interface-originated {
        description
          "When the push source is out of an interface on the 
           Publisher established via static configuration.";
        leaf source-interface {
          type if:interface-ref;
          description
            "References the interface for notifications.";
        }
      }
      case address-originated {
        description
          "When the push source is out of an IP address on the 
           Publisher established via static configuration.";
        leaf source-vrf {
          type uint32 {
            range "16..1048574";
          }
          description
            "Label of the vrf.";
        }
        leaf source-address {
          type inet:ip-address-no-zone;
          mandatory true;
          description
            "The source address for the notifications.";
        }
      }
    }
  }

  grouping receiver-info {
    description
      "Defines where and how to deliver notifications for a 
       configured subscription.  This includes
       specifying the receiver, as well as defining  
       any network and transport aspects when sending of 
       notifications occurs outside of Netconf.";
    container receivers {
      description
        "Set of receivers in a subscription.";
      list receiver {
        key "address";
        min-elements 1;
        description
          "A single host or multipoint address intended as a target
           for the notifications for a subscription.";
        leaf address {
          type inet:host;
          mandatory true;
          description
            "Specifies the address for the traffic to reach a
             remote host. One of the following must be
             specified: an ipv4 address, an ipv6 address,
             or a host name.";
        }
        leaf port {
          type inet:port-number;
          mandatory true;
          description
            "This leaf specifies the port number to use for 
             messages destined for a receiver.";
        }
        leaf protocol {
          type transport-protocol;
          default "netconf";
          description
            "This leaf specifies the transport protocol used
             to deliver messages destined for the receiver.";
        }
      }
    }
  }

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

  /*
   * RPCs
   */
   
  rpc establish-subscription {
    description
      "This RPC allows a subscriber to create 
       (and possibly negotiate) a subscription on its own behalf.  
       If successful, the subscription
       remains in effect for the duration of the subscriber's
       association with the publisher, or until the subscription
       is terminated by virtue of a delete-subscription request.
       In case an error (as indicated by subscription-result)
       is returned, the subscription is 
       not created.  In that case, the RPC output   
       MAY include suggested parameter settings
       that would have a high likelihood of succeeding in a 
       subsequent establish-subscription request.";
    input {
      uses subscription-info;
    }
    output {
      uses subscription-response;
    }
  }
  
  rpc create-subscription {
    description
      "This operation initiates an event notification subscription 
       that will send asynchronous event notifications to the 
       initiator of the command until the association terminates.
       It is not possible to modify or delete a subscription 
       that was created using this operation.  It is included for 
       reasons of backward compatibility with RFC 5277 
       implementations.";
    input {
      uses subscription-info-basic-non-modifiable{
	    refine "stream" {
		   default "NETCONF";
		}
	  }
	  uses subscription-info-basic-modifiable;
	}
  }
  
  rpc modify-subscription {
    description
      "This RPC allows a subscriber to modify a subscription
       that was previously created using establish-subscription.
       If successful, the subscription
       remains in effect for the duration of the subscriber's
       association with the publisher, or until the subscription
       is terminated by virtue of a delete-subscription request.
       In case an error is returned (as indicated by 
       subscription-result), the subscription is 
       not modified and the original subscription parameters 
       remain in effect.  In that case, the rpc error response 
       MAY include suggested parameter settings
       that would have a high likelihood of succeeding in a 
       subsequent modify-subscription request.";
    input {
      leaf subscription-id {
        type subscription-id;
        description
          "Identifier to use for this subscription.";
      }
      uses subscription-info-all-modifiable;
    }
    output {
      uses subscription-response;
    }
  }
  
  rpc delete-subscription {
    description
      "This RPC allows a subscriber to delete a subscription that
       was previously created using establish-subscription.";
    input {
      leaf subscription-id {
        type subscription-id;
        mandatory true;
        description
          "Identifier of the subscription that is to be deleted.
           Only subscriptions that were created using
           establish-subscription can be deleted via this RPC.";
      }
    }
    output {
      leaf subscription-result {
        type subscription-result;
        mandatory true;
        description
          "Indicates whether subscription is operational, 
           or if a problem was encountered.";
      }
    }
  }
  
  
  /*
   * NOTIFICATIONS
   */

  notification replay-complete {
    notif-bis:control-plane-notif;
    description
      "This notification is sent to indicate that all of the 
       replay notifications have been sent. It must not be 
       sent for any other reason.";
    leaf subscription-id {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
  }
  
  notification notification-complete {
    notif-bis:control-plane-notif;
    description
      "This notification is sent to indicate that a 
       subscription, which includes a stop time, has
       finished passing events.";
    leaf subscription-id {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
  }

  notification subscription-started {
    notif-bis:control-plane-notif;
    description
      "This notification indicates that a subscription has
       started and notifications are beginning to be sent.
       This notification shall only be sent to receivers
       of a subscription; it does not constitute a general-purpose
       notification.";
    leaf subscription-id {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
    uses subscription-info;
  }
  
  notification subscription-suspended {
    notif-bis:control-plane-notif;
    description
      "This notification indicates that a suspension of the
       subscription by the publisher has occurred.  No further
       notifications will be sent until subscription
       resumes.
       This notification shall only be sent to receivers
       of a subscription; it does not constitute a general-purpose
       notification.";
    leaf subscription-id {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
    leaf reason {
      type subscription-susp-reason;
      description
        "Provides a reason for why the subscription was
         suspended.";
    }
  }

  notification subscription-resumed {
    notif-bis:control-plane-notif;
    description
      "This notification indicates that a subscription that had
       previously been suspended has resumed. Notifications
       will once again be sent.";
    leaf subscription-id {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
  }
  
  notification subscription-modified {
    notif-bis:control-plane-notif;
    description
      "This notification indicates that a subscription has
       been modified.  Notifications sent from this point
       on will conform to the modified terms of the
       subscription.";
    leaf subscription-id {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
    uses subscription-info;
  }
  
  notification subscription-terminated {
    notif-bis:control-plane-notif;
    description
      "This notification indicates that a subscription has been
       terminated.";
    leaf subscription-id {
      type subscription-id;
      mandatory true;
      description
        "This references the affected subscription.";
    }
    leaf reason {
      type subscription-term-reason;
      description
        "Provides a reason for why the subscription was
         terminated.";
    }
  }

               
  /*
   * DATA NODES
   */

  container streams {
    config false;
    description
      "This container contains a leaf list of built-in
       streams that are provided by the system.";
    leaf-list stream {
      type stream;
      description
        "Identifies the built-in streams that are supported by the
         system.  Built-in streams are associated with their own 
         identities, each of which carries a special semantics.
         In case configurable custom streams are supported, 
         as indicated by the custom-stream identity, the  
         configuration of those custom streams is provided 
		 separately.";
    }
  }
  container filters {
    description
      "This container contains a list of configurable filters
       that can be applied to subscriptions.  This facilitates
       the reuse of complex filters once defined.";
    list filter {
      key "filter-id";
      description
        "A list of configurable filters that can be applied to
         subscriptions.";
      leaf filter-id {
        type filter-id;
        description
          "An identifier to differentiate between filters.";
      }
      uses base-filter;
    }
  }
  container subscription-config {
    if-feature "configured-subscriptions";
    description
      "Contains the list of subscriptions that are configured,
       as opposed to established via RPC or other means.";
    list subscription {
      key "subscription-id";
      description
        "Content of a subscription.";
      leaf subscription-id {
        type subscription-id;
        description
          "Identifier to use for this subscription.";
      }
      uses subscription-info;
      uses receiver-info {
        if-feature "configured-subscriptions";
      }
      uses push-source-info {
        if-feature "configured-subscriptions";
      }
    }
  }
  container subscriptions {
    config false;
    description
      "Contains the list of currently active subscriptions,
       i.e. subscriptions that are currently in effect,
       used for subscription management and monitoring purposes.
       This includes subscriptions that have been setup via RPC
       primitives, e.g. create-subscription, establish-
       subscription, and modify-subscription, as well as 
       subscriptions that have been established via 
	   configuration.";
    list subscription {
      key "subscription-id";
      config false;
      description
        "Content of a subscription.
         Subscriptions can be created using a control channel
         or RPC, or be established through configuration.";
      leaf subscription-id {
        type subscription-id;
        description
          "Identifier of this subscription.";
      }

      leaf configured-subscription {
       if-feature "configured-subscriptions";
       type empty;
       description
         "The presence of this leaf indicates that the
          subscription originated from configuration, not 
          through a control channel or RPC.";
      }
      
      leaf subscription-status {
        type subscription-status;
        description
          "The status of the subscription.";
      }
      uses subscription-info;
      uses receiver-info {
        if-feature "configured-subscriptions";
      }
      uses push-source-info {
        if-feature "configured-subscriptions";
      }
    }
  }
}
<CODE ENDS>

9. Backwards Compatibility

Capabilities are advertised in messages sent by each peer during session establishment [RFC6241]. Publishers supporting the features in this document must advertise both capabilities "urn:ietf:params:netconf:capability:notification:1.0" and "urn:ietf:params:netconf:capability:notification:1.1".

An example of a hello message by a publisher during session establishment would be:

<hello xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
    <capabilities>
        <capability>
            urn:ietf:params:xml:ns:netconf:base:1.0
        </capability>
        <capability>
            urn:ietf:params:netconf:capability:startup:1.0
        </capability>
        <capability>
            urn:ietf:params:netconf:capability:notification:1.0
        </capability>
        <capability>
            urn:ietf:params:netconf:capability:notification:1.1
        </capability>
    </capabilities>
    <session-id>4</session-id>
</hello>

Figure 9: Hello message

Subscribers that only support [RFC5277] recognize capability "urn:ietf:params:netconf:capability:notification:1.0" and ignore capability "urn:ietf:params:netconf:capability:notification:1.1". This allows them interacting with the publisher as per [RFC5277]. Subscribers that support the features in this document recognize both capabilities. This allows them interacting with the publisher as per this document.

Note that to support backwards compatibility, the yang models in this document include two types of naming conventions. That used in [RFC5277], e.g., replayComplete; and that commonly used in yang models, e.g., subscription-started.

10. Security Considerations

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

A secure transport is highly recommended and the publisher must ensure that the user has sufficient authorization to perform the function they are requesting against the specific subset of content involved. When a <get> is received that refers to the content defined in this memo, clients should only be able to view the content for which they have sufficient privileges. <create-subscription> and <establish-subscription> operations can be considered like deferred <get>, and the content that different users can access may vary. This different access is reflected in the <notificationt> to which different users are able to subscribe.

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

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

A subscription could be configured on another receiver's behalf, with the goal of flooding that receiver with updates. One or more publishers could be used to overwhelm a receiver, which doesn't even support subscriptions. Subscribers that do not want pushed data need only terminate or refuse any transport sessions from the publisher. In addition, the NETCONF Authorization Control Model [RFC6536] SHOULD be used to control and restrict authorization of subscription configuration. This control models permits specifying per-user permissions to receive specific event notification types. The permissions are specified as a set of access control rules.

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

11. Acknowledgments

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

12. References

12.1. Normative References

[RFC2119]	Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC3339]	Klyne, G. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002.
[RFC5277]	Chisholm, S. and H. Trevino, "NETCONF Event Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008.
[RFC6241]	Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011.
[RFC6536]	Bierman, A. and M. Bjorklund, "Network Configuration Protocol (NETCONF) Access Control Model", RFC 6536, DOI 10.17487/RFC6536, March 2012.
[RFC7950]	Bjorklund, M., "The YANG 1.1 Data Modeling Language", RFC 7950, August 2016.

12.2. Informative References

[I-D.ietf-netconf-netconf-event-notif]	Gonzalez Prieto, Alberto., Clemm, Alexander., Voit, Eric., Nilsen-Nygaard, E., Tripathy, A., Chisholm, S. and H. Trevino, "NETCONF support for event notifications", August 2016.
[I-D.ietf-netconf-restconf]	Bierman, A., Bjorklund, M. and K. Watsen, "RESTCONF Protocol", I-D draft-ietf-netconf-restconf-17, September 2016.
[I-D.ietf-netconf-restconf-notif]	Voit, Eric., Clemm, Alexander., Tripathy, A., Nilsen-Nygaard, E. and Alberto. Gonzalez Prieto, "Restconf and HTTP transport for event notifications", August 2016.
[I-D.ietf-netconf-yang-push]	Clemm, Alexander., Gonzalez Prieto, Alberto., Voit, Eric., Tripathy, A. and E. Nilsen-Nygaard, "Subscribing to YANG datastore push updates", June 2016.

Appendix A. Issues that are currently being worked and resolved

(To be removed by RFC editor prior to publication)

A.1. Unresolved and yet-to-be addressed issues

EN1 - Definition of basic set of Stream types. What streams are provided and what do they contain (includes default 5277 stream).

EN2 - Clarify interplay between filter definitions and different streams. Includes information in subtrees of event payloads.

EN3 - Mechanisms for diagnostics, e.g. deal with dropped updates, monitoring when they occur, etc

A.2. Agreement in principal

EN4 - How to allow for seamless integration with non-standard encodings and transports (like GPB/GRPC). Specify requirements encoding and transport must meet, provide examples.

EN7 - Detecting loss of a sequential update notification, and mechanisms to resend. Implications to transports must be thought through.

EN6 - Stream discovery. Allow to discover additional stream properties.

EN12 - Test-only option for a subscription is desired. But it still needs to be defined.

EN14 - Ensure that Configured Subscriptions are fully defined in YANG model.

A.3. Resolved Issues

EN5 - This draft obsoletes 5277, as opposed to being in parallel with it

EN8 - No mandatory transport

EN15 - Term for Dynamic and Static Subscriptions (move to "Configured")

EN9 - Multiple receivers per Configured Subscription is ok.

EN13 - RFC6241 Subtree-filter definition in 5277bis cannot apply to elements of an event. Must explicitly define how 6241 doesn't apply filtering within a 5277bis event.

EN10 - Replay support will be provided for selected stream types (modify vs. delete)

EN11 - Required layering security requirements/considerations will be added into the YANG model for Configured Subscriptions. It will be up to the transport to meet these requirements.

Appendix B. Changes between revisions