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NETCONF                                                          E. Voit
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                                A. Clemm
Expires: April 7, 2019                                            Huawei
                                                      A. Gonzalez Prieto
                                                               Microsoft
                                                       E. Nilsen-Nygaard
                                                             A. Tripathy
                                                           Cisco Systems
                                                         October 4, 2018


                NETCONF Support for Event Notifications
           draft-ietf-netconf-netconf-event-notifications-13

Abstract

   This document provides a NETCONF binding to the dynamic subscription
   capability of both subscribed notifications and YANG push.

   RFC Editor note: please replace the four references to pre-RFC
   normative drafts with the actual assigned RFC numbers.

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 https://datatracker.ietf.org/drafts/current/.

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

   This Internet-Draft will expire on April 7, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of



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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Compatibility with RFC-5277's create-subscription . . . . . .   3
   4.  Mandatory XML, event stream and datastore support . . . . . .   3
   5.  NETCONF connectivity and the Dynamic Subscriptions  . . . . .   4
   6.  Notification Messages . . . . . . . . . . . . . . . . . . . .   4
   7.  Dynamic Subscriptions and RPC Error Responses . . . . . . . .   4
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   10. Notes to the RFC Editor . . . . . . . . . . . . . . . . . . .   6
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     11.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .   7
     A.1.  Event Stream Discovery  . . . . . . . . . . . . . . . . .   7
     A.2.  Dynamic Subscriptions . . . . . . . . . . . . . . . . . .   8
     A.3.  Subscription State Notifications  . . . . . . . . . . . .  12
     A.4.  Filter Examples . . . . . . . . . . . . . . . . . . . . .  14
   Appendix B.  Changes between revisions  . . . . . . . . . . . . .  15
     B.1.  v11 to v13  . . . . . . . . . . . . . . . . . . . . . . .  15
     B.2.  v10 to v11  . . . . . . . . . . . . . . . . . . . . . . .  16
     B.3.  v09 to v10  . . . . . . . . . . . . . . . . . . . . . . .  16
     B.4.  v08 to v09  . . . . . . . . . . . . . . . . . . . . . . .  16
     B.5.  v07 to v08  . . . . . . . . . . . . . . . . . . . . . . .  16
     B.6.  v06 to v07  . . . . . . . . . . . . . . . . . . . . . . .  16
     B.7.  v05 to v06  . . . . . . . . . . . . . . . . . . . . . . .  16
     B.8.  v03 to v04  . . . . . . . . . . . . . . . . . . . . . . .  16
     B.9.  v01 to v03  . . . . . . . . . . . . . . . . . . . . . . .  17
     B.10. v00 to v01  . . . . . . . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   This document provides a binding for events streamed over the NETCONF
   protocol [RFC6241] for dynamic subscriptions as defined in
   [I-D.draft-ietf-netconf-subscribed-notifications].  In addition, as
   [I-D.ietf-netconf-yang-push] is itself built upon
   [I-D.draft-ietf-netconf-subscribed-notifications], this document




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   enables a NETCONF client to request via a dynamic subscription and
   receive updates from a YANG datastore located on a NETCONF server.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The following terms are defined in
   [I-D.draft-ietf-netconf-subscribed-notifications]: dynamic
   subscription, event stream, notification message, publisher,
   receiver, subscriber, subscription.

3.  Compatibility with RFC-5277's create-subscription

   A publisher is allowed to concurrently support dynamic subscription
   RPCs of [I-D.draft-ietf-netconf-subscribed-notifications] at the same
   time as [RFC5277]'s "create-subscription" RPC.  However a single
   NETCONF transport session cannot support both this specification and
   a subscription established by [RFC5277]'s "create-subscription" RPC.
   To protect against any attempts to use a single NETCONF transport
   session in this way:

   o  A solution must reply with the [RFC6241] error "operation-not-
      supported" if a "create-subscription" RPC is received on a NETCONF
      session where an [I-D.draft-ietf-netconf-subscribed-notifications]
      established subscription exists.
   o  A solution must reply with the [RFC6241] error "operation-not-
      supported" if an "establish-subscription" request is been received
      on a NETCONF session where the "create-subscription" RPC has
      successfully [RFC5277] created a subscription.

   If a publisher supports this specification but not subscriptions via
   [RFC5277], the publisher MUST NOT advertise
   "urn:ietf:params:netconf:capability:notification:1.0".

4.  Mandatory XML, event stream and datastore support

   The "encode-xml" feature of
   [I-D.draft-ietf-netconf-subscribed-notifications] is mandatory to
   support.  This indicates that XML is a valid encoding for RPCs, state
   change notifications, and subscribed content.






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   A NETCONF publisher supporting event stream subscription via
   [I-D.draft-ietf-netconf-subscribed-notifications] MUST support the
   "NETCONF" event stream identified in that draft.

5.  NETCONF connectivity and the Dynamic Subscriptions

   For a dynamic subscription, if the NETCONF session involved with the
   "establish-subscription" terminates, the subscription MUST be
   terminated.

   For a dynamic subscription a "modify-subscription", "delete-
   subscription", or "resynch-subscription" RPC MUST be sent using same
   the NETCONF session upon which the referenced subscription was
   established.

6.  Notification Messages

   Notification messages transported over the NETCONF protocol MUST be
   encoded in a <notification> message as defined within [RFC5277],
   Section 4.  And per [RFC5277]'s "eventTime" object definition, the
   "eventTime" MUST be populated with the event occurrence time.

   For dynamic subscriptions, all notification messages MUST use the
   NETCONF transport session used by the "establish-subscription" RPC.

7.  Dynamic Subscriptions and RPC Error Responses

   Management of dynamic subscriptions occurs via RPCs as defined in
   [I-D.ietf-netconf-yang-push] and
   [I-D.draft-ietf-netconf-subscribed-notifications].  When an RPC error
   occurs, the NETCONF RPC reply MUST include an "rpc-error" element per
   [RFC6241] with the error information populated as follows:

   o  an "error-type" node of "application".
   o  an "error-tag" node of "operation-failed".
   o  an "error-severity" of "error" (this MAY but does not have to be
      included).
   o  an "error-app-tag" node with the value being a string that
      corresponds to an identity associated with the error, as defined
      in [I-D.draft-ietf-netconf-subscribed-notifications] section 2.4.6
      for general subscriptions, and [I-D.ietf-netconf-yang-push]
      Appendix A.1, for datastore subscriptions.  The specific identity
      to use depends on the RPC for which the error occurred.  Viable
      errors for different RPCs are as follows:







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            RPC                     use base identity
            ----------------------  ----------------------------
            establish-subscription  establish-subscription-error
            modify-subscription     modify-subscription-error
            delete-subscription     delete-subscription-error
            kill-subscription       kill-subscription-error
            resynch-subscription    resynch-subscription-error

   Each error identity will be inserted as the "error-app-tag" using
   JSON encoding following the form <modulename>:<identityname>.  An
   example of such as valid encoding would be "ietf-subscribed-
   notifications:no-such-subscription".

   o  In case of error responses to an "establish-subscription" or
      "modify-subscription" request there is the option of including an
      "error-info" node.  This node may contain XML-encoded data with
      hints for parameter settings that might lead to successful RPC
      requests in the future.  Following are the yang-data structures
      which may be returned:

      establish-subscription returns hints in yang-data structure
      ---------------------- ------------------------------------
      target: event stream   establish-subscription-stream-error-info
      target: datastore      establish-subscription-datastore-error-info

      modify-subscription    returns hints in yang-data structure
      ---------------------- ------------------------------------
      target: event stream   modify-subscription-stream-error-info
      target: datastore      modify-subscription-datastore-error-info

      The yang-data included within "error-info" SHOULD NOT include the
      optional leaf "error-reason", as such a leaf would be redundant
      with information that is already placed within the
      "error-app-tag".

      In case of an rpc error resulting from a "delete-subscription",
      "kill-subscription", or "resynch-subscription" request, no
      "error-info" needs to be included, as the "subscription-id" is
      the only RPC input parameter and no hints regarding this RPC input
      parameters need to be provided.

8.  Security Considerations

   If a malicious or buggy NETCONF subscriber sends a number of
   establish-subscription requests, then these subscriptions accumulate
   and may use up system resources.  In such a situation, subscriptions
   MAY be terminated by terminating the underlying NETCONF session.  The




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   publisher MAY also suspend or terminate a subset of the active
   subscriptions on that NETCONF session.

9.  Acknowledgments

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

10.  Notes to the RFC Editor

   This section can be removed by the RFC editor after the requests have
   been performed.

   RFC 6241 need to be updated.  RFC-6241 refers to RFC-5277 which says
   that a notification message can only be sent after a successful
   "create-subscription".  This text must be modified to also allow
   notification messages be sent after a successful "establish-
   subscription".

11.  References

11.1.  Normative References

   [I-D.draft-ietf-netconf-subscribed-notifications]
              Voit, E., Clemm, A., Gonzalez Prieto, A., Tripathy, A.,
              and E. Nilsen-Nygaard, "Customized Subscriptions to a
              Publisher's Event Streams", draft-ietf-netconf-subscribed-
              notifications-17 (work in progress), September 2018.

   [I-D.ietf-netconf-yang-push]
              Clemm, Alexander., Voit, Eric., Gonzalez Prieto, Alberto.,
              Tripathy, A., Nilsen-Nygaard, E., Bierman, A., and B.
              Lengyel, "YANG Datastore Subscription", September 2018,
              <https://datatracker.ietf.org/doc/
              draft-ietf-netconf-yang-push/>.

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

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




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

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

11.2.  Informative References

   [RFC8347]  Liu, X., Ed., Kyparlis, A., Parikh, R., Lindem, A., and M.
              Zhang, "A YANG Data Model for the Virtual Router
              Redundancy Protocol (VRRP)", RFC 8347,
              DOI 10.17487/RFC8347, March 2018,
              <https://www.rfc-editor.org/info/rfc8347>.

   [XPATH]    Clark, J. and S. DeRose, "XML Path Language (XPath)
              Version 1.0", November 1999,
              <http://www.w3.org/TR/1999/REC-xpath-19991116>.

Appendix A.  Examples

   This section is non-normative.

A.1.  Event Stream Discovery

   As defined in [I-D.draft-ietf-netconf-subscribed-notifications] an
   event stream exposes a continuous set of events available for
   subscription.  A NETCONF client can retrieve the list of available
   event streams from a NETCONF publisher using the "get" operation
   against the top-level container "/streams" defined in
   [I-D.draft-ietf-netconf-subscribed-notifications] Section 3.1.

   The following example illustrates the retrieval of the list of
   available event streams:

<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-subscribed-notifications"/>
    </filter>
  </get>
</rpc>

                       Figure 1: Get streams request



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   After such a request, the NETCONF publisher returns a list of event
   streams available, as well as additional information which might
   exist in the container.

A.2.  Dynamic Subscriptions

A.2.1.  Establishing Dynamic Subscriptions

   The following figure shows two successful "establish-subscription"
   RPC requests as per
   [I-D.draft-ietf-netconf-subscribed-notifications].  The first request
   is given a subscription "id" of 22, the second, an "id" of 23.

      +------------+                 +-----------+
      | Subscriber |                 | Publisher |
      +------------+                 +-----------+
            |                              |
            |    Capability Exchange       |
            |<---------------------------->|
            |                              |
            |                              |
            |    establish-subscription    |
            |----------------------------->|  (a)
            | RPC Reply: OK, id = 22       |
            |<-----------------------------|  (b)
            |                              |
            | notification message (for 22)|
            |<-----------------------------|
            |                              |
            |                              |
            |    establish-subscription    |
            |----------------------------->|
            | notification message (for 22)|
            |<-----------------------------|
            | RPC Reply: OK, id = 23       |
            |<-----------------------------|
            |                              |
            |                              |
            | notification message (for 22)|
            |<-----------------------------|
            | notification message (for 23)|
            |<-----------------------------|
            |                              |

          Figure 2: Multiple subscriptions over a NETCONF session

   To provide examples of the information being transported, example
   messages for interactions (a) and (b) in Figure 2 are detailed below:



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<rpc message-id="102" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <establish-subscription
      xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
    <stream>NETCONF</stream>
    <stream-xpath-filter xmlns:ds="http://example.com/events">
      /ds:foo/
    </stream-xpath-filter>
    <dscp>10</dscp>
  </establish-subscription>
</rpc>

               Figure 3: establish-subscription request (a)

   As NETCONF publisher was able to fully satisfy the request (a), the
   publisher sends the subscription "id" of the accepted subscription
   within message (b):

  <rpc-reply message-id="102"
    xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
    <id
      xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
      22
    </id>
  </rpc-reply>

               Figure 4: establish-subscription success (b)

   If the NETCONF publisher had not been able to fully satisfy the
   request, or subscriber has no authorization to establish the
   subscription, the publisher would have sent an RPC error response.
   For instance, if the "dscp" value of 10 asserted by the subscriber in
   Figure 3 proved unacceptable, the publisher may have returned:

   <rpc-reply message-id="102"
     xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <rpc-error>
      <error-type>application</error-type>
      <error-tag>operation-failed</error-tag>
      <error-severity>error</error-severity>
      <error-app-tag>
        ietf-subscribed-notifications:dscp-unavailable
      </error-app-tag>
     </rpc-error>
   </rpc-reply>

             Figure 5: an unsuccessful establish subscription





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   The subscriber can use this information in future attempts to
   establish a subscription.

A.2.2.  Modifying Dynamic Subscriptions

   An existing subscription may be modified.  The following exchange
   shows a negotiation of such a modification via several exchanges
   between a subscriber and a publisher.  This negotiation consists of a
   failed RPC modification request/response, followed by a successful
   one.

      +------------+                 +-----------+
      | Subscriber |                 | Publisher |
      +------------+                 +-----------+
            |                              |
            | notification message (for 23)|
            |<-----------------------------|
            |                              |
            | modify-subscription (id = 23)|
            |----------------------------->|  (c)
            | RPC error (with hint)        |
            |<-----------------------------|  (d)
            |                              |
            | modify-subscription (id = 23)|
            |----------------------------->|
            | RPC Reply: OK                |
            |<-----------------------------|
            |                              |
            | notification message (for 23)|
            |<-----------------------------|
            |                              |

   Figure 6: Interaction model for successful subscription modification

   If the subscription being modified in Figure 6 is a datastore
   subscription as per [I-D.ietf-netconf-yang-push], the modification
   request made in (c) may look like that shown in Figure 7.  As can be
   seen, the modifications being attempted are the application of a new
   xpath filter as well as the setting of a new periodic time interval.












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<rpc message-id="303"
  xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <modify-subscription
       xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
       xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
    <id>23</id>
    <yp:datastore-xpath-filter xmlns:ds="http://example.com/datastore">
        /ds:foo/ds:bar
    </yp:datastore-xpath-filter>
    <yp:periodic>
      <yp:period>500</yp:period>
    </yp:periodic>
  </modify-subscription>
</rpc>

              Figure 7: Subscription modification request (c)

   If the NETCONF publisher can satisfy both changes, the publisher
   sends a positive result for the RPC.  If the NETCONF publisher cannot
   satisfy either of the proposed changes, the publisher sends an RPC
   error response (d).  The following is an example RPC error response
   for (d) which includes a hint.  This hint is an alternative time
   period value which might have resulted in a successful modification:

   <rpc-reply message-id="303"
     xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <rpc-error>
       <error-type>application</error-type>
       <error-tag>operation-failed</error-tag>
       <error-severity>error</error-severity>
       <error-app-tag>
           ietf-yang-push:period-unsupported
       </error-app-tag>
       <error-info
          xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-push">
          <modify-subscription-datastore-error-info>
            <period-hint>
                3000
            </period-hint>
          </modify-subscription-datastore-error-info>
       </error-info>
     </rpc-error>
   </rpc-reply>

            Figure 8: Modify subscription failure with Hint (d)






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A.2.3.  Deleting Dynamic Subscriptions

   The following demonstrates deleting a subscription.  This
   subscription may have been to either a stream or a datastore.

  <rpc message-id="103"
    xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
    <delete-subscription
      xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
      <id>22</id>
    </delete-subscription>
  </rpc>

                       Figure 9: Delete subscription

   If the NETCONF publisher can satisfy the request, the publisher
   replies with success to the RPC request.

   If the NETCONF publisher cannot satisfy the request, the publisher
   sends an error-rpc element indicating the modification didn't work.
   Figure 10 shows a valid response for existing valid subscription
   "id", but that subscription "id" was created on a different NETCONF
   transport session:

   <rpc-reply message-id="103"
     xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <rpc-error>
       <error-type>application</error-type>
       <error-tag>operation-failed</error-tag>
       <error-severity>error</error-severity>
       <error-app-tag>
           ietf-subscribed-notifications:no-such-subscription
       </error-app-tag>
     </rpc-error>
   </rpc-reply>

                Figure 10: Unsuccessful delete subscription

A.3.  Subscription State Notifications

   A publisher will send subscription state notifications for dynamic
   subscriptions according to the definitions within
   [I-D.draft-ietf-netconf-subscribed-notifications]).








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A.3.1.  subscription-modified

   As per Section 2.7.2 of
   [I-D.draft-ietf-netconf-subscribed-notifications], a "subscription-
   modified" might be sent if over NETCONF if the definition of a
   configured filter changes.  A subscription state notification encoded
   in XML would look like:

<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-subscribed-notifications">
    <id>39</id>
    <transport xmlns:nsn=
    "urn:ietf:params:xml:ns:yang:ietf-netconf-subscribed-notifications">
      nsn:netconf
    <transport>
    <stream-xpath-filter xmlns:ex="http://example.com/events">
      /ex:foo
    </stream-xpath-filter>
    <stream>NETCONF</stream>
  </subscription-modified>
</notification>

     Figure 11: subscription-modified subscription state notification

A.3.2.  subscription-resumed, and replay-complete

   A "subscription-resumed" would look like:

  <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-subscribed-notifications">
      <id>39</id>
    </subscription-resumed>
  </notification>

            Figure 12: subscription-resumed notification in XML

   The "replay-complete" is virtually identical, with "subscription-
   resumed" simply being replaced by "replay-complete".








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A.3.3.  subscription-terminated and subscription-suspended

   A "subscription-terminated" would look like:

  <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-subscribed-notifications">
      <id>39</id>
      <reason>
         suspension-timeout
      </reason>
    </subscription-terminated>
  </notification>

    Figure 13: subscription-terminated subscription state notification

   The "subscription-suspended" is virtually identical, with
   "subscription-terminated" simply being replaced by "subscription-
   suspended".

A.4.  Filter Examples

   This section provides examples which illustrate both xpath and
   subtree methods of filtering event record contents.  The examples are
   based on the YANG notification "vrrp-protocol-error-event" as defined
   per the ietf-vrrp.yang model within [RFC8347].  Event records based
   on this specification which are generated by the publisher might
   appear as:

  <notification xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
    <eventTime>2018-09-14T08:22:33.44Z</eventTime>
    <vrrp-protocol-error-event
         xmlns="urn:ietf:params:xml:ns:yang:ietf-vrrp">
       <protocol-error-reason>checksum-error</protocol-error-reason>
    </vrrp-protocol-error-event>
  </notification>

             Figure 14: RFC 8347 (VRRP) - Example Notification

   Suppose a subscriber wanted to establish a subscription which only
   passes instances of event records where there is a "checksum-error"
   as part of a VRRP protocol event.  Also assume the publisher places
   such event records into the NETCONF stream.  To get a continuous
   series of matching event records, the subscriber might request the
   application of an XPath filter against the NETCONF stream.  An
   "establish-subscription" RPC to meet this objective might be:



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<rpc message-id="601" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <establish-subscription
      xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
    <stream>NETCONF</stream>
    <stream-xpath-filter xmlns="urn:ietf:params:xml:ns:yang:ietf-vrrp">
      /vrrp-protocol-error-event[protocol-error-reason="checksum-error"]
    </stream-xpath-filter>
  </establish-subscription>
</rpc>

       Figure 15: Establishing a subscription error reason via XPATH

   For more examples of xpath filters, see [XPATH].

   Suppose the "establish-subscription" in Figure 15 was accepted.  And
   suppose later a subscriber decided they wanted to broaden this
   subscription cover to all VRRP protocol events (i.e., not just those
   with a "checksum error").  The subscriber might attempt to modify the
   subscription in a way which replaces the XPath filter with a subtree
   filter which sends all VRRP protocol events to a subscriber.  Such a
   "modify-subscription" RPC might look like:

 <rpc message-id="602" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
   <modify-subscription
      xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
     <id>99</id>
     <stream-subtree-filter>
      <vrrp-protocol-error-event
             xmlns="urn:ietf:params:xml:ns:yang:ietf-vrrp"/>
     </stream-subtree-filter>
   </modify-subscription>
 </rpc>

                                 Figure 16

   For more examples of subtree filters, see [RFC6241], section 6.4.

Appendix B.  Changes between revisions

   (To be removed by RFC editor prior to publication)

B.1.  v11 to v13

   o  Subscription identifier renamed to id.
   o  Appendix A.4 for filter examples
   o  for v13, Tweak of example to /foo/bar





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B.2.  v10 to v11

   o  Configured removed.

B.3.  v09 to v10

   o  Tweaks to examples and text.
   o  Downshifted state names.
   o  Removed address from examples.

B.4.  v08 to v09

   o  Tweaks based on Kent's comments.
   o  Updated examples in Appendix A.  And updates to some object names
      based on changes in the subscribed-notifications draft.
   o  Added a YANG model for the NETCONF identity.

B.5.  v07 to v08

   o  Tweaks and clarification on :interleave.

B.6.  v06 to v07

   o  XML encoding and operational datastore mandatory.
   o  Error mechanisms and examples updated.

B.7.  v05 to v06

   o  Moved examples to appendices
   o  All examples rewritten based on namespace learnings
   o  Normative text consolidated in front
   o  Removed all mention of JSON
   o  Call home process detailed
   o  Note: this is a major revision attempting to cover those comments
      received from two week review.

B.8.  v03 to v04

   o  Added additional detail to "configured subscriptions"
   o  Added interleave capability
   o  Adjusted terminology to that in draft-ietf-netconf-subscribed-
      notifications
   o  Corrected namespaces in examples








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B.9.  v01 to v03

   o  Text simplifications throughout
   o  v02 had no meaningful changes

B.10.  v00 to v01

   o  Added Call Home in solution for configured subscriptions.
   o  Clarified support for multiple subscription on a single session.
      No need to support multiple create-subscription.
   o  Added mapping between terminology in yang-push and [RFC6241] (the
      one followed in this document).
   o  Editorial improvements.

Authors' Addresses

   Eric Voit
   Cisco Systems

   Email: evoit@cisco.com


   Alexander Clemm
   Huawei

   Email: ludwig@clemm.org


   Alberto Gonzalez Prieto
   Microsoft

   Email: alberto.gonzalez@microsoft.com


   Einar Nilsen-Nygaard
   Cisco Systems

   Email: einarnn@cisco.com


   Ambika Prasad Tripathy
   Cisco Systems

   Email: ambtripa@cisco.com







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