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Versions: 00 draft-ietf-netconf-netconf-event-notifications

NETCONF                                               A. Gonzalez Prieto
Internet-Draft                                                  A. Clemm
Intended status: Standards Track                                 E. Voit
Expires: December 17, 2016                             E. Nilsen-Nygaard
                                                             A. Tripathy
                                                           Cisco Systems
                                                             S. Chisholm
                                                                   Ciena
                                                              H. Trevino
                                                           Cisco Systems
                                                           June 15, 2016


                NETCONF Support for Event Notifications
             draft-gonzalez-netconf-event-notifications-00

Abstract

   This document defines the support of [event-notifications] by the
   Network Configuration protocol (NETCONF). [event-notifications]
   describes capabilities and operations for providing asynchronous
   message notification delivery.  This document discussed how to
   provide them on top of NETCONF.  The capabilities and operations
   defined between this document and [event-notifications] are intended
   to obsolete RFC 5277.

Status of This Memo

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

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

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

   This Internet-Draft will expire on December 17, 2016.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Solution Overview . . . . . . . . . . . . . . . . . . . .   5
   2.  Solution  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Event Streams . . . . . . . . . . . . . . . . . . . . . .   5
     2.2.  Event Stream Discovery  . . . . . . . . . . . . . . . . .   6
     2.3.  Default Event Stream  . . . . . . . . . . . . . . . . . .   8
     2.4.  Creating a Subscription . . . . . . . . . . . . . . . . .   8
     2.5.  Establishing a Subscription . . . . . . . . . . . . . . .  11
     2.6.  Modifying a Subscription  . . . . . . . . . . . . . . . .  15
     2.7.  Deleting a Subscription . . . . . . . . . . . . . . . . .  20
     2.8.  Configured Subscriptions  . . . . . . . . . . . . . . . .  23
     2.9.  Event (Data Plane) Notifications  . . . . . . . . . . . .  31
     2.10. Control Plane Notifications . . . . . . . . . . . . . . .  33
   3.  Backwards Compatibility . . . . . . . . . . . . . . . . . . .  43
     3.1.  Capabilities  . . . . . . . . . . . . . . . . . . . . . .  43
     3.2.  Stream Discovery  . . . . . . . . . . . . . . . . . . . .  44
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  44
   5.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  45
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  45
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  45
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  46
   Appendix A.  Issues being worked and resolved . . . . . . . . . .  46
     A.1.  Unresolved Issues . . . . . . . . . . . . . . . . . . . .  46
     A.2.  Agreement in principal  . . . . . . . . . . . . . . . . .  46
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  47

1.  Introduction

   [RFC6241] can be conceptually partitioned into four layers:









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         Layer                         Example
       +-------------+     +-------------------------------------------+
       |   Content   |     |     Configuration data                    |
       +-------------+     +-------------------------------------------+
             |                           |
       +-------------+     +-------------------------------------------+
       | Operations  |     |<get-config>, <edit-config>, <notification>|
       +-------------+     +-------------------------------------------+
             |                           |                       |
       +-------------+     +-----------------------------+       |
       |     RPC     |     |    <rpc>, <rpc-reply>       |       |
       +-------------+     +-----------------------------+       |
             |                           |                       |
       +-------------+     +-------------------------------------------+
       |  Transport  |     |          BEEP, SSH, SSL, console          |
       |  Protocol   |     |                                           |
       +-------------+     +-------------------------------------------+

                   Figure 1: NETCONF layer architecture

   This document defines mechanisms that provide an asynchronous message
   notification delivery service for the NETCONF protocol [RFC6241]
   based on [event-notifications].  This is an optional capability built
   on top of the base NETCONF definition.

   [event-notifications] and this document enhance the capabilities of
   RFC 5277 while maintaining backwards capability with existing
   implementations.  It is intended that a final version of this
   document might obsolete [RFC5277].

   The enhancements over [RFC5277] include the ability to terminate
   subscriptions without terminating the client session, to modify
   existing subscriptions, and to have multiple subscriptions on a
   NETCONF session.

   These enhancements do not affect [RFC5277] clients that do not
   support these particular subscription requirements.

   [event-notifications] covers the following functionality:

   o  Ability to subscribe to event notifications using two mechanisms:
      dynamic and configuration subscriptions.

   o  Ability to subscribe to event notifications using two mechanisms:
      dynamic and configuration subscriptions.

   o  Ability to negotiate acceptable subscription parameters.




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

   o  Ability to support multiple encodings for the notification.

   o  Mechanism to communicate the notifications.

   o  Ability to replay locally logged notifications.

   To support this functionality, NETCONF agents must implement the
   operations, configuration and operational state defined in
   [event-notifications].  In addition, they need to:

   o  support multiple subscriptions over a single NETCONF session.

   o  support a revised definition of the default NETCONF stream

   o  be backwards compatible with RFC 5277 implementations.

1.1.  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].

1.1.1.  Event Notifications

   The following terms are defined in [event-notifications]:

   o  Event

   o  Event notification

   o  Stream (also referred to as "event stream")

   o  Subscriber

   o  Receiver

   o  Subscription

   o  Filter

   o  Dynamic subscription

   o  Configured subscription





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1.1.2.  NETCONF

   The following terms are defined in [RFC6241] :

   o  Operation

   o  RPC: remote procedure call

1.1.3.  NETCONF Access Control

   The following terms are defined in [RFC6536] :

   o  NACM: NETCONF Access Control Model

1.2.  Solution Overview

   [event-notifications] defines mechanisms that provide an asynchronous
   message notification delivery service.  This document discusses its
   realization on top of the NETCONF protocol [RFC6241].

   The functionality to support is defined in [event-notifications].  It
   is formalized in a set of yang models.  The mapping of yang
   constructs into NETCONF is described in [RFC6020].

   Supporting [event-notifications] requires enhancements and
   modifications in NETCONF.  The key enhacement is suporting multiple
   subscriptions on a NETCONF session.  A key modification is the
   definition of the NETCONF stream

   These enhancements do not affect [RFC5277] clients that do not
   support [event-notifications].

2.  Solution

   In this section, we describe and exemplify how [event-notifications]
   must be supported over NETCONF.

2.1.  Event Streams

   In the context of NETCONF, an event stream is a set of events
   available for subscription from a NETCONF server.  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.

   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.



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   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 NETCONF client can retrieve the list of available event streams
   from a NETCONF server using the <get> operation.  The reply contains
   the elements defined in the YANG model under the container
   "/streams", which includes the stream identifier.

   The following example ilustrates the retrieval of the list of
   available event streams using the <get> operation.

   <rpc message-id="101"
          xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <get>
       <filter type="subtree">
         <streams
          xmlns="urn:ietf:params:xml:ns:yang:ietf-event-notifications"/>
         </filter>
     </get>
   </rpc>

                           Figure 2: Get streams

   The NETCONF server returns a list of event streams available for
   subscription.  In this example, the list contains the NETCONF, SNMP,
   and syslog-critical streams.

   <rpc-reply message-id="101"
           xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <data>
       <streams
           xmlns="urn:ietf:params:xml:ns:yang:ietf-event-notifications">
         <stream>NETCONF</stream>
         <stream>SNMP</stream>
         <stream>syslog-critical</stream>
         <stream>NETCONF</stream>
         </streams>
     </data>
   </rpc-reply>

                      Figure 3: Get streams response




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2.2.1.  Backwards Compatibility

   In order to maintain backwards compatibility, clients that only
   support [RFC5277] can retrieve the list of available event streams
   executing a <get> operation against the container "/netconf/streams".

   The following example ilustrates this mechanism.

   <rpc message-id="101"
          xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <get>
       <filter type="subtree">
         <netconf
               xmlns="urn:ietf:params:xml:ns:netmod:notification">
           <streams/>
         </netconf>
       </filter>
     </get>
   </rpc>

              Figure 4: Get streams (backwards compatibility)

   The NETCONF server returns a list of event streams available for
   subscription.  In this example, the list contains the NETCONF, SNMP,
   and syslog-critical streams.

   <rpc-reply message-id="101"
           xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <data>
       <netconf
               xmlns="urn:ietf:params:xml:ns:netmod:notification">
         <streams>
           <stream>
             <name>
               NETCONF
             </name>
             <description>
               default NETCONF event stream
             </description>
             <replaySupport>
               true
             </replaySupport>
             <replayLogCreationTime>
               2016-02-05T00:00:00Z
             </replayLogCreationTime>
           </stream>
           <stream>
             <name>



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               SNMP
             </name>
             <description>
               SNMP notifications
             </description>
             <replaySupport>
               false
             </replaySupport>
           </stream>
           <stream>
             <name>
               syslog-critical
             </name>
             <description>
               Critical and higher severity
             </description>
             <replaySupport>
               true
             </replaySupport>
             <replayLogCreationTime>
               2007-07-01T00:00:00Z
             </replayLogCreationTime>
           </stream>
         </streams>
       </netconf>
     </data>
   </rpc-reply>

         Figure 5: Get streams response (backwards compatibility)

2.3.  Default Event Stream

   A NETCONF server implementation supporting the notification
   capability MUST support the "NETCONF" notification event stream.
   This stream contains all NETCONF XML event notifications supported by
   the NETCONF server, except for those belonging only to streams that
   explicitly indicate that they must be excluded from the NETCONF
   stream.  The exact string "NETCONF" is used during the advertisement
   of stream support during the <get> operation on <streams> and during
   the <create-subscription> and <establish-subscription> operations.

2.4.  Creating a Subscription

   The following illustrates the creation of a simple subscription.







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2.4.1.  Usage Example

   The following demonstrates dynamically creating a subscription.  This
   operation is fully defined in [RFC5277]

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

                       Figure 6: Create subscription

2.4.2.  Positive Response

   If the NETCONF server can satisfy the request, the server sends an
   <ok> element.

   <netconf:rpc netconf:message-id="102"
          xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
     <create-subscription
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
       <filter netconf:type="xpath"
                   xmlns:ex="http://example.com/event/1.0"
                select="/ex:event[ex:eventClass='fault' and
                         (ex:severity='minor' or ex:severity='major'
                          or ex:severity='critical')]"/>
     </create-subscription>
   </netconf:rpc>

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

                 Figure 7: Successful create subscription

2.4.3.  Negative Response

   If the request cannot be completed for any reason, an <rpc-error>
   element is included within the <rpc-reply>.  Subscription requests
   can fail for several reasons including if a filter with invalid
   syntax is provided or if the name of a non-existent stream is
   provided.

   If a stopTime is specified in a request without having specified a
   startTime, the following error is returned:



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   Tag: missing-element
   Error-type: protocol
   Severity: error
   Error-info: <bad-element>: startTime
   Description: An expected element is missing.

             Figure 8: Create subscription missing an element

   If the optional replay feature is requested but the NETCONF server
   does not support it, the following error is returned:

   Tag: operation-failed
   Error-type: protocol
   Severity: error
   Error-info: none
   Description: Request could not be completed because the
                requested operation failed for some reason
                not covered by any other error condition.

              Figure 9: Create subscription pperation failed

   If a stopTime is requested that is earlier than the specified
   startTime, the following error is returned:

   Tag: bad-element
   Error-type: protocol
   Severity: error
   Error-info: <bad-element>: stopTime
   Description: An element value is not correct;
                e.g., wrong type, out of range, pattern mismatch.

             Figure 10: Create subscription incorrect stopTime

   If a startTime is requested that is later than the current time, the
   following error is returned:

   Tag: bad-element
   Error-type: protocol
   Severity: error
   Error-info: <bad-element>: startTime
   Description: An element value is not correct;
                e.g., wrong type, out of range, pattern mismatch.

            Figure 11: Create subscription incorrect startTime







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2.5.  Establishing a Subscription

2.5.1.  Usage Example

   The following illustrates the establishment of a simple subscription.

   <netconf:rpc message-id="101"
          xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
     <establish-subscription
             xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
     </establish-subscription>
   </netconf:rpc>

                     Figure 12: Establish subscription

2.5.2.  Positive Response

   If the NETCONF server can satisfy the request, the server sends a
   positive <subscription-result> element, and the subscription-id of
   the accepted subscription.

   <netconf:rpc netconf:message-id="102"
          xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
     <establish-subscription
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       <filter netconf:type="xpath"
                   xmlns:ex="http://example.com/event/1.0"
                select="/ex:event[ex:eventClass='fault' and
                         (ex:severity='minor' or ex:severity='major'
                          or ex:severity='critical')]"/>
     </establish-subscription>
   </netconf:rpc>

   <rpc-reply message-id="102"
          xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <subscription-result
             xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       ok
     </subscription-result>
     <subscription-id
             xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       52
     </subscription-id>
   </rpc-reply>

               Figure 13: Successful establish subscription





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2.5.3.  Negative Response

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

   If the client has no authorization to establish the subscription, the
   <subscription-result> indicates an authorization error.  For
   instance:

   <netconf:rpc netconf:message-id="103"
          xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
     <establish-subscription
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       <stream>foo</stream>
     </establish-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:netconf:notification:1.1">
       error-data-not-authorized
     </subscription-result>
   </rpc-reply>

              Figure 14: Unsuccessful establish subscription

   If the request is rejected because the server is not able to serve
   it, the server SHOULD include in the returned error what subscription
   parameters would have been accepted for the request when it was
   processed.  However, they are no guarantee that subsequent requests
   with those parameters for this client or others will be accepted.
   For instance, consider a subscription from [netconf-yang-push], which
   augments the establish-subscription with some additional parameters,
   including "period".  If the client requests a period the NETCONF
   server cannot serve, the exchange may be:















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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:netconf:notification:1.1">
       <stream>push-update</stream>
       <filter netconf:type="xpath"
               xmlns:ex="http://example.com/sample-data/1.0"
               select="/ex:foo"/>
       <period xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
         500
       </period>
       <encoding>encode-xml</encoding>
     </establish-subscription>
   </netconf:rpc>


   <rpc-reply message-id="101"
         xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <subscription-result
           xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       error-insufficient-resources
     </subscription-result>
     <period
           xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
       2000
     </period>
   </rpc-reply>

             Figure 15: Subscription establishment negotiation

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

2.5.4.  Multiple Subscriptions over a Single NETCONF Session

   Note that [event-notifications] requires supporting multiple
   subscriptions over a single NETCONF session.  In contrast, [RFC5277]
   mandated server to return an error when a create-subscription was
   sent while a subscription was active on that session.

2.5.5.  Message Flow Examples










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   +------------+                 +-----------+
   |   Client   |                 |   Server  |
   +------------+                 +-----------+
         |                              |
         |    Capability Exchange       |
         |<---------------------------->|
         |                              |
         |                              |
         |    Establish Subscription    |
         |----------------------------->|
         | RPC Reply: OK, subs-id = 22  |
         |<-----------------------------|
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |                              |
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |                              |
         |                              |


          Figure 16: Message flow for subscription establishment

























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   +------------+                 +-----------+
   |   Client   |                 |   Server  |
   +------------+                 +-----------+
         |                              |
         |    Capability Exchange       |
         |<---------------------------->|
         |                              |
         |                              |
         |    Establish Subscription    |
         |----------------------------->|
         | RPC Reply: OK, subs-id = 22  |
         |<-----------------------------|
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |                              |
         |                              |
         |    Establish Subscription    |
         |----------------------------->|
         | RPC Reply: OK, subs-id = 23  |
         |<-----------------------------|
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |                              |
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |  Notification (subs-id 23)   |
         |<-----------------------------|
         |                              |
         |                              |


   Figure 17: Message Flow for multiple subscription establishments over
                             a single session

2.6.  Modifying a Subscription

2.6.1.  Usage Example

   The following demonstrates modifying a subscription.  Consider a
   subscription from [netconf-yang-push], which augments the establish-
   subscription with some additional parameters, including "period".  A
   subscription may be established as follows.






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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:netconf:notification:1.1">
       <stream>push-update</stream>
       <filter netconf:type="xpath"
               xmlns:ex="http://example.com/sample-data/1.0"
               select="/ex:foo"/>
       <period xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
         500
       </period>
       <encoding>encode-xml</encoding>
     </establish-subscription>
   </netconf:rpc>

   <rpc-reply message-id="101"
          xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <subscription-result
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       ok
     </subscription-result>
     <subscription-id
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       1922
     </subscription-id>
   </rpc-reply>

             Figure 18: Establish subscription to be modified

   The subscription may be modified with:





















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   <netconf:rpc message-id="102"
          xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
     <modify-subscription
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       <subscription-id>1922</subscription-id>
       <period>1000</period>
     </modify-subscription >
   </netconf:rpc>

   <rpc-reply message-id="102"
          xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <subscription-result
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       ok
     </subscription-result>
     <subscription-id
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       1922
     </subscription-id>
   </rpc-reply>

                      Figure 19: Modify subscription

2.6.2.  Positive Response

   If the NETCONF server can satisfy the request, the server sends a
   positive <subscription-result> element.  This response is like that
   to an establish-subscription request. but without the subscription-
   id, which would be redundant.






















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   <netconf:rpc message-id="102"
          xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
     <modify-subscription
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       <subscription-id>1922</subscription-id>
       <period
                 xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
         1000
       </period>
     </modify-subscription >
   </netconf:rpc>

   <rpc-reply message-id="102"
          xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <subscription-result
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       ok
     </subscription-result>
   </rpc-reply>

                 Figure 20: Successful modify subscription

2.6.3.  Negative Response

   If the NETCONF server cannot satisfy the request, the server sends a
   negative <subscription-result> element.  Its contents and semantics
   are identical to those to an establish-subscription request.  For
   instance:























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   <netconf:rpc message-id="102"
          xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
     <modify-subscription
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       <subscription-id>1922</subscription-id>
       <period xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push:1.0">
         100
       </period>
     </modify-subscription>
   </netconf:rpc>

   <rpc-reply message-id="102"
          xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <subscription-result
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       error-insufficient-resources
     </subscription-result>
     <period>500</period>
   </rpc-reply>

                Figure 21: Unsuccessful modify subscription

2.6.4.  Message Flow Example




























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   +------------+                 +-----------+
   |   Client   |                 |   Server  |
   +------------+                 +-----------+
         |                              |
         |    Capability Exchange       |
         |<---------------------------->|
         |                              |
         |                              |
         |    Establish Subscription    |
         |----------------------------->|
         | RPC Reply: OK, subs-id = 22  |
         |<-----------------------------|
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |                              |
         |                              |
         |                              |
         |                              |
         |     Modify Subscription      |
         |----------------------------->|
         |                              |
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |                              |
         |                              |


           Figure 22: Message flow for subscription modification

2.7.  Deleting a Subscription

2.7.1.  Usage Example

   The following demonstrates deleting a subscription.

   <netconf:rpc message-id="101"
          xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
     <delete-subscription
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       <subscription-id>1922</subscription-id>
     </delete-subscription>
   </netconf:rpc>

                      Figure 23: Delete subscription



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2.7.2.  Positive Response

   If the NETCONF server can satisfy the request, the server sends an OK
   element.  For example:

   <netconf:rpc message-id="103"
          xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
     <delete-subscription
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       <subscription-id>1922</subscription-id>
     </delete-subscription>
   </netconf:rpc>

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

                 Figure 24: Successful delete subscription

2.7.3.  Negative Response

   If the NETCONF server cannot satisfy the request, the server sends an
   error-rpc element.  For example:



























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   <netconf:rpc message-id="103"
          xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
     <delete-subscription
              xmlns="urn:ietf:params:xml:ns:netconf:notification:1.1">
       <subscription-id>2017</subscription-id>
     </delete-subscription>
   </netconf:rpc>

   <rpc-reply message-id="101"
          xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <rpc-error>
       <error-type>application</error-type>
       <error-tag>invalid-value</error-tag>
       <error-severity>error</error-severity>
       <error-path
              xmlns:t="urn:ietf:params:xml:ns:netconf:notification:1.1">
         /t:subscription-id
       </error-path>
       <error-message xml:lang="en">
         Subscription-id 2017 does not exist
       </error-message>
     </rpc-error>
   </rpc-reply>

                Figure 25: Unsuccessful delete subscription

2.7.4.  Message Flow Example
























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   +------------+                 +-----------+
   |   Client   |                 |   Server  |
   +------------+                 +-----------+
         |                              |
         |    Capability Exchange       |
         |<---------------------------->|
         |                              |
         |                              |
         |    Establish Subscription    |
         |----------------------------->|
         | RPC Reply: OK, subs-id = 22  |
         |<-----------------------------|
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |                              |
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |                              |
         |                              |
         |     Delete Subscription      |
         |----------------------------->|
         |                              |
         |                              |
         |                              |
         |                              |


             Figure 26: Message flow for subscription deletion

2.8.  Configured Subscriptions

   A configured subscription is a subscription installed via a
   configuration interface, and do not support negotiation.

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

   In this section, we present examples of how to manage configuration
   subscriptions using a NETCONF client.







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2.8.1.  Establishing a Configured Subscription

   Subscriptions are established using configuration operations against
   the top-level subtree subscription-config.

   For example at subscription establishment, a NETCONF 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 27: Establish static subscription

   if the request is accepted, the server would reply:

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

   Figure 28: Response to a successful static subscription establishment





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   if the request is not accepted because the server cannot serve it,
   the server 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 server cannot serve this
           subscription due to the current workload.
       </error-message>
     </rpc-error>
   </rpc-reply>

     Figure 29: Response to a failed static subscription establishment

2.8.1.1.  Message Flow Example

































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 +----------+                 +-----------+     +---------+  +---------+
 |  Client  |                 |   Server  |     | Rcver A |  | Rcver B |
 +----------+                 +-----------+     +---------+  +---------+
       |                            |                |            |
       |    Capability Exchange     |                |            |
       |<-------------------------->|                |            |
       |                            |                |            |
       |                            |                |            |
       |        Edit-config         |                |            |
       |--------------------------->|                |            |
       |       RPC Reply: OK        |                |            |
       |<---------------------------|                |            |
       |                            |  Subscription  |            |
       |                            |  Started       |            |
       |                            |  (subs-id 22)  |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |                            |  Notification  |            |
       |                            |  (subs-id 22)  |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |
       |                            |  Notification  |            |
       |                            |  (subs-id 22)  |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |                            |  Notification  |            |
       |                            |  (subs-id 22)  |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |



    Figure 30: Message flow for subscription establishment (configured
                               subscription)

2.8.2.  Modifying a Configured Subscription

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




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   For example, the subscription established in the previous section
   could be modified as follows, choosing a different receiver:

   <rpc message-id="102"
          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>
               1.2.3.5
             </address>
             <port>
               1234
             </port>
           </receiver>
         </subscription>
       </subscription-config>
     </edit-config>
   </rpc>

                 Figure 31: Modify configured subscription

   if the request is accepted, the server would reply:

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

        Figure 32: Response to a successful configured subscription
                               modification








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2.8.2.1.  Message Flow Example


















































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 +----------+                 +-----------+     +---------+  +---------+
 |  Client  |                 |   Server  |     | Rcver A |  | Rcver B |
 +----------+                 +-----------+     +---------+  +---------+
       |                            |                |            |
       |    Capability Exchange     |                |            |
       |<-------------------------->|                |            |
       |                            |                |            |
       |                            |                |            |
       |        Edit-config         |                |            |
       |--------------------------->|                |            |
       |       RPC Reply: OK        |                |            |
       |<---------------------------|                |            |
       |                            |  Subscription  |            |
       |                            |  Started       |            |
       |                            |  (subs-id 22)  |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |                            |  Notification  |            |
       |                            |  (subs-id 22)  |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |
       |        Edit-config         |                |            |
       |--------------------------->|                |            |
       |       RPC Reply: OK        |                |            |
       |<---------------------------|                |            |
       |                            |                |            |
       |                            |                |            |
       |                            |  Subscription  |            |
       |                            |  Modified      |            |
       |                            |  (subs-id 22)  |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |                            |  Notification  |            |
       |                            |  (subs-id 22)  |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |



     Figure 33: Message flow for subscription modification (configured
                               subscription)




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2.8.3.  Deleting a Configured Subscription

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

   <rpc message-id="103"
          xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <edit-config>
       <target>
         <running/>
       </target>
       <subscription-config
           xmlns:xc="urn:ietf:params:xml:ns:netconf:notification:1.1">
         <subscription xc:operation="delete">
           <subscription-id>
             1922
           </subscription-id>
         </subscription>
       </subscription-config>
     </edit-config>
   </rpc>

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


               Figure 34: Deleting a configured subscription

2.8.3.1.  Message Flow Example


 +----------+                 +-----------+     +---------+  +---------+
 |  Client  |                 |   Server  |     | Rcver A |  | Rcver B |
 +----------+                 +-----------+     +---------+  +---------+
       |                            |                |            |
       |    Capability Exchange     |                |            |
       |<-------------------------->|                |            |
       |                            |                |            |
       |                            |                |            |
       |        Edit-config         |                |            |
       |--------------------------->|                |            |
       |       RPC Reply: OK        |                |            |
       |<---------------------------|                |            |
       |                            |  Subscription  |            |
       |                            |  Started       |            |
       |                            |  (subs-id 22)  |            |



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       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |                            |  Notification  |            |
       |                            |  (subs-id 22)  |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |
       |                            |  Notification  |            |
       |                            |  (subs-id 22)  |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |        Edit-config         |                |            |
       |--------------------------->|                |            |
       |       RPC Reply: OK        |                |            |
       |<---------------------------|                |            |
       |                            |                |            |
       |                            |                |            |
       |                            |  Subscription  |            |
       |                            |  Terminated    |            |
       |                            |  (subs-id 22)  |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |


       Figure 35: Message flow for subscription deletion (configured
                               subscription)

2.9.  Event (Data Plane) Notifications

   Once a subscription has been set up, the NETCONF server sends
   (asynchronously) the event notifications from the subscribed stream.
   We refer to these as data plane notifications.  For dynamic
   subscriptions set up via RPC operations, event notifications are sent
   over the NETCONF session used to create or establish the
   subscription.  For static subscriptions, event notifications are sent
   over the specified connections.





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   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 notification also contains notification-specific tagged
   content, if any.  With the exception of <eventTime>, the content of
   the notification is beyond the scope of this document.

   For the encodings other than XML, notifications include an additional
   XML element so that the notification is a well-formed XML.  The
   element is <notification-contents-{encoding}>, E.g., <notification-
   contents-json>.  That element contains the notification contents in
   the desired encoding

   The following is an example of an event notification from [RFC6020]:

   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 36: Definition of a data plane notification










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

                    Figure 37: 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 38: Data plane notification using JSON encoding

2.10.  Control Plane Notifications

   In addition to data plane notifications, a server may send control
   plane notifications (defined in [event-notifications]) to indicate to
   receivers that an event related to the subscription management has
   occurred.  Control plane notifications cannot be filtered out.  Next
   we exemplify them using both XML, and JSON encondings for the data:

2.10.1.  replayComplete

  <notification
         xmlns=" urn:ietf:params:xml:ns:netconf:notification:1.0">
    <eventTime>2007-09-01T10:00:00Z</eventTime>
    <replayComplete xmlns="urn:ietf:params:xml:ns:netmod:notification"/>
  </notification>

           Figure 39: replayComplete control plane notification




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   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>
          {
             "netmod-notif:replayComplete": { }
           }
     </notification-contents-json>
   </notification>

   Figure 40: replayComplete control plane notification (JSON encoding)

2.10.1.1.  Message Flow Example




































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   +------------+                 +-----------+
   |   Client   |                 |   Server  |
   +------------+                 +-----------+
         |                              |
         |    Capability Exchange       |
         |<---------------------------->|
         |                              |
         |                              |
         |    Establish Subscription    |
         |----------------------------->|
         | RPC Reply: OK, subs-id = 22  |
         |<-----------------------------|
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |                              |
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         | Replay Complete (subs-id 22) |
         |<-----------------------------|
         |                              |
         |                              |
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |                              |
         |                              |
         |                              |


                  Figure 41: replayComplete notification

2.10.2.  notificationComplete

   <notification
       xmlns=" urn:ietf:params:xml:ns:netconf:notification:1.0">
     <eventTime>2007-09-01T10:00:00Z</eventTime>
     <notificationComplete
       xmlns="urn:ietf:params:xml:ns:netmod:notification"/>
   </notification>

        Figure 42: notificationComplete control plane notification





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2.10.2.1.  Message Flow Example


















































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   +------------+                 +-----------+
   |   Client   |                 |   Server  |
   +------------+                 +-----------+
         |                              |
         |    Capability Exchange       |
         |<---------------------------->|
         |                              |
         |                              |
         |    Establish Subscription    |
         |----------------------------->|
         | RPC Reply: OK, subs-id = 22  |
         |<-----------------------------|
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |                              |
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         | Replay Complete (subs-id 22) |
         |<-----------------------------|
         |                              |
         |                              |
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |                              |
         |  Notification (subs-id 22)   |
         |<-----------------------------|
         |                              |
         |                              |
         |                              |
         |    Notification Complete     |
         |        (subs-id 22)          |
         |<-----------------------------|
         |                              |
         |                              |
         |                              |
         |            RPC               |
         |----------------------------->|
         |          RPC Reply           |
         |<-----------------------------|
         |                              |
         |                              |


               Figure 43: notificationComplete notification




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2.10.3.  subscription-started

  <notification
      xmlns=" urn:ietf:params:xml:ns:netconf:notification:1.0">
    <eventTime>2007-09-01T10:00:00Z</eventTime>
    <subscription-started
          xmlns="urn:ietf:params:xml:ns:yang:ietf-event-notifications"/>
      <subscription-id>52</subscription-id>
      <filter netconf:type="xpath"
                 xmlns:ex="http://example.com/event/1.0"
                 select="/ex:event[ex:eventClass='fault' and
                        (ex:severity='minor' or ex:severity='major'
                         or ex:severity='critical')]"/>
    </subscription-started/>
  </notification>

        Figure 44: subscription-started control 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>
          {
             "notif-bis:subscription-started": {
                 "subscription-id" : 52
                 ((Open Item: express filter in json))
             }
           }
     </notification-contents-json>
   </notification>

     Figure 45: subscription-started control plane notification (JSON
                                 encoding)

2.10.4.  subscription-modified














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  <notification
      xmlns=" urn:ietf:params:xml:ns:netconf:notification:1.0">
    <eventTime>2007-09-01T10:00:00Z</eventTime>
    <subscription-modified
          xmlns="urn:ietf:params:xml:ns:yang:ietf-event-notifications"/>
      <subscription-id>52</subscription-id>
      <filter netconf:type="xpath"
                 xmlns:ex="http://example.com/event/1.0"
                 select="/ex:event[ex:eventClass='fault']"/>
    </subscription-modified/>
  </notification>

        Figure 46: subscription-modified control plane notification

2.10.5.  subscription-terminated

  <notification
      xmlns=" urn:ietf:params:xml:ns:netconf:notification:1.0">
    <eventTime>2007-09-01T10:00:00Z</eventTime>
    <subscription-terminated
          xmlns="urn:ietf:params:xml:ns:yang:ietf-event-notifications"/>
      <subscription-id>52</subscription-id>
      <reason>subscription-deleted</reason>
    </subscription-terminated/>
  </notification>

       Figure 47: subscription-terminated control plane notification

2.10.6.  subscription-suspended

  <notification
      xmlns=" urn:ietf:params:xml:ns:netconf:notification:1.0">
    <eventTime>2007-09-01T10:00:00Z</eventTime>
    <subscription-suspended
          xmlns="urn:ietf:params:xml:ns:yang:ietf-event-notifications"/>
      <subscription-id>52</subscription-id>
      <reason>internal-error</reason>
    </subscription-suspended/>
  </notification>

       Figure 48: subscription-suspended control plane notification

2.10.7.  subscription-resumed








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  <notification
      xmlns=" urn:ietf:params:xml:ns:netconf:notification:1.0">
    <eventTime>2007-09-01T10:00:00Z</eventTime>
    <subscription-resumed
          xmlns="urn:ietf:params:xml:ns:yang:ietf-event-notifications"/>
      <subscription-id>52</subscription-id>
      <reason>internal-error</reason>
    </subscription-resumed/>
  </notification>

        Figure 49: subscription-resumed control plane notification

2.10.7.1.  Message Flow Examples






































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   +------------+                 +-----------+
   |   Client   |                 |   Server  |
   +------------+                 +-----------+
         |                              |
         |    Capability Exchange       |
         |<---------------------------->|
         |                              |
         |                              |
         |    Establish Subscription    |
         |----------------------------->|
         | RPC Reply: OK, subs-id = 22  |
         |<-----------------------------|
         |                              |
         |        Notification          |
         |<-----------------------------|
         |                              |
         |                              |
         |        Notification          |
         |<-----------------------------|
         |        Notification          |
         |<-----------------------------|
         |                              |
         |                              |
         |   Subscription Suspended     |
         |<-----------------------------|
         |                              |
         |                              |
         |                              |
         |    Subscription Resumed      |
         |<-----------------------------|
         |                              |
         |                              |
         |                              |
         |                              |
         |        Notification          |
         |<-----------------------------|
         |                              |
         |                              |


        Figure 50: subscription-suspended and Resumed Notifications


 +----------+                 +-----------+     +---------+  +---------+
 |  Client  |                 |   Server  |     | Rcver A |  | Rcver B |
 +----------+                 +-----------+     +---------+  +---------+
       |                            |                |            |
       |    Capability Exchange     |                |            |



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       |<-------------------------->|                |            |
       |                            |                |            |
       |                            |                |            |
       |        Edit-config         |                |            |
       |--------------------------->|                |            |
       |       RPC Reply: OK        |                |            |
       |<---------------------------|                |            |
       |                            |  Subscription  |            |
       |                            |  Started       |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |                            |  Notification  |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |
       |                            |  Subscription  |            |
       |                            |  Suspended     |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |
       |                            |  Subscription  |            |
       |                            |  Resumed       |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |
       |                            |  Notification  |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |                            |  Notification  |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |
       |                            |                |            |





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        Figure 51: subscription-suspended and subscription-resumed
                 notifications (configured subscriptions)

3.  Backwards Compatibility

3.1.  Capabilities

   Capabilities are advertised in messages sent by each peer during
   session establishment [RFC6241].  Servers 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 server 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 52: Hello message

   Clients 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 server as per [RFC5277].
   Clients that support the features in this document recognize both
   capabilities.  This allows them interacting with the server as per
   this document.








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3.2.  Stream Discovery

   In order to maintain backwards compatibility, clients that only
   support [RFC5277] can retrieve the list of available event streams
   executing a <get> operation against the container "/netconf/streams".

4.  Security Considerations

   The security considerations from the base NETCONF document [RFC6241]
   also apply to the notification capability.

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

   A secure transport must be used and the server must ensure that the
   user has sufficient authorization to perform the function they are
   requesting against the specific subset of NETCONF 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-subscriptiont> and <establish-
   subscriptiont> 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> that different users are
   able to subscribe to.

   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 NETCONF server
   MUST NOT include any content in a notification that the user is not
   authorized to view.

   If a malicious or buggy NETCONF client 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 client uses <establish-
   subscription>, the server 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.  Clients 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
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   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 [netconf-yang-push] each of the elements in its data
   plane notifications must also go through access control.

5.  Acknowledgments

   We wish to acknowledge the helpful contributions, comments, and
   suggestions that were received from: Andy Bierman, Yan Gang, Peipei
   Guo, Susan Hares, Tim Jenkins, Balazs Lengyel, Kent Watsen, and
   Guangying Zheng.

6.  References

6.1.  Normative References

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

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

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

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

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

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






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6.2.  Informative References

   [event-notifications]
              Gonzalez Prieto, A., Clemm, A., Voit, Eric., Nilsen-
              Nygaard, E., Tripathy, A., Chisholm, S., and H. Trevino,
              "Subscribing to YANG-Defined Event Notifications", June
              2016, <https://datatracker.ietf.org/doc/draft-gonzalez-
              netconf-5277bis/>.

   [netconf-yang-push]
              Clemm, A., Gonzalez Prieto, A., Voit, Eric., Tripathy, A.,
              and E. Nilsen-Nygaard, "Subscribing to YANG datastore push
              updates", February 2016,
              <https://datatracker.ietf.org/doc/draft-ietf-netconf-yang-
              push/>.

Appendix A.  Issues being worked and resolved

   (To be removed by RFC editor prior to publication)

A.1.  Unresolved Issues

   NT1 - Support multiple create-subscriptions over a single NETCONF
   session? or only multiple establish-subscription?  Recommend only
   establish-subscription anytime there may be more than one
   subscription, otherwise variations of supported RFCs and error states
   proliferate.

   NT2 - Configured subscription need to be refined in
   [event-notifications] and then adjust this document based on it.

   NT3 - Express filter in JSON should be documented.

A.2.  Agreement in principal

   NT1 - When a list of requirements for secure transport is provided
   via a Configured Subscription, this list must be met via Netconf
   transport.  Specifics still are needed for draft on the "how".

   NT2 - Along with rfc5277bis, this draft to obsolete 5277

   NT3 - Stream discovery.  Adopted mechanism in 5277-bis and include
   backwards comptability support.








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Authors' Addresses

   Alberto Gonzalez Prieto
   Cisco Systems

   Email: albertgo@cisco.com


   Alexander Clemm
   Cisco Systems

   Email: alex@cisco.com


   Eric Voit
   Cisco Systems

   Email: evoit@cisco.com


   Einar Nilsen-Nygaard
   Cisco Systems

   Email: einarnn@cisco.com


   Ambika Prasad Tripathy
   Cisco Systems

   Email: ambtripa@cisco.com


   Sharon Chisholm
   Ciena

   Email: schishol@ciena.com


   Hector Trevino
   Cisco Systems

   Email: htrevino@cisco.com









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