draft-ietf-netconf-udp-notif-02.xml

<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes"?>
<?rfc tocompact="yes"?>
<?rfc tocdepth="3"?>
<?rfc tocindent="yes"?>
<?rfc symrefs="yes"?>
<?rfc sortrefs="yes"?>
<?rfc comments="yes"?>
<?rfc inline="yes"?>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<rfc category="std" docName="draft-ietf-netconf-udp-notif-02"
     ipr="trust200902">
  <front>
    <title abbrev="unyte-udp-notif">UDP-based Transport for Configured
    Subscriptions</title>

    <author fullname="Guangying Zheng" initials="G." surname="Zheng">
      <organization>Huawei</organization>

      <address>
        <postal>
          <street>101 Yu-Hua-Tai Software Road</street>

          <city>Nanjing</city>

          <code/>

          <region>Jiangsu</region>

          <country>China</country>
        </postal>

        <phone/>

        <facsimile/>

        <email>zhengguangying@huawei.com</email>
      </address>
    </author>

    <author fullname="Tianran Zhou" initials="T." surname="Zhou">
      <organization>Huawei</organization>

      <address>
        <postal>
          <street>156 Beiqing Rd., Haidian District</street>

          <city>Beijing</city>

          <region/>

          <code/>

          <country>China</country>
        </postal>

        <phone/>

        <facsimile/>

        <email>zhoutianran@huawei.com</email>

        <uri/>
      </address>
    </author>

    <author fullname="Thomas Graf" initials="T." surname="Graf">
      <organization>Swisscom</organization>

      <address>
        <postal>
          <street>Binzring 17</street>

          <city>Zuerich 8045</city>

          <region/>

          <code/>

          <country>Switzerland</country>
        </postal>

        <phone/>

        <facsimile/>

        <email>thomas.graf@swisscom.com</email>

        <uri/>
      </address>
    </author>

    <author fullname="Pierre Francois" initials="P." surname="Francois">
      <organization>INSA-Lyon</organization>

      <address>
        <postal>
          <street/>

          <city>Lyon</city>

          <region/>

          <code/>

          <country>France</country>
        </postal>

        <phone/>

        <facsimile/>

        <email>pierre.francois@insa-lyon.fr</email>

        <uri/>
      </address>
    </author>

    <author fullname="Paolo Lucente" initials="P." surname="Lucente">
      <organization>NTT</organization>

      <address>
        <postal>
          <street>Siriusdreef 70-72</street>

          <city>Hoofddorp, WT 2132</city>

          <region/>

          <code/>

          <country>NL</country>
        </postal>

        <phone/>

        <facsimile/>

        <email>paolo@ntt.net</email>

        <uri/>
      </address>
    </author>

    <date day="6" month="May" year="2021"/>

    <workgroup>NETCONF</workgroup>

    <abstract>
      <t>This document describes an UDP-based notification mechanism to
      collect data from networking devices. A shim header is proposed to
      facilitate the data streaming directly from the publishing process on
      network processor of line cards to receivers. The objective is a
      lightweight approach to enable higher frequency and less performance
      impact on publisher and receiver process compared to already established
      notification mechanisms.</t>
    </abstract>

    <note title="Requirements Language">
      <t>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 <xref
      target="RFC2119">RFC 2119</xref>.</t>
    </note>
  </front>

  <middle>
    <section title="Introduction">
      <t><xref target="RFC8639">Sub-Notif</xref> defines a mechanism that lets
      a receiver subscribe to the publication of YANG-defined data maintained
      in a <xref target="RFC7950">YANG</xref> datastore. The mechanism
      separates the management and control of subscriptions from the transport
      used to deliver the data. Three transport mechanisms, namely <xref
      target="RFC8640">NETCONF transport</xref>, <xref
      target="RFC8650">RESTCONF transport</xref>, and <xref
      target="I-D.ietf-netconf-https-notif">HTTPS transport</xref> have been
      defined so far for such notification messages.</t>

      <t>While powerful in their features and general in their architecture,
      the currently available transport mechanisms need to be complemented to
      support data publications at high velocity from devices that feature a
      distributed architecture. The currently available transports are based
      on TCP and lack the efficiency needed to continuously send notifications
      at high velocity.</t>

      <t>This document specifies a transport option for Sub-Notif that
      leverages UDP. Specifically, it facilitates the distributed data
      collection mechanism described in <xref
      target="I-D.ietf-netconf-distributed-notif"/>. In the case of publishing
      from multiple network processors on multiple line cards, centralized
      designs require data to be internally forwarded from those network
      processors to the push server, presumably on a route processor, which
      then combines the individual data items into a single consolidated
      stream. The centralized data collection mechanism can result in a
      performance bottleneck, especially when large amounts of data are
      involved.</t>

      <t>What is needed is a mechanism that allows for directly publishing
      from multiple network processors on line cards, without passing them
      through an additional processing stage for internal consolidation. The
      proposed UDP-based transport allows for such a distributed data
      publishing approach.</t>

      <t><list style="symbols">
          <t>Firstly, a UDP approach reduces the burden of maintaining a large
          amount of active TCP connections at the receiver, notably in cases
          where it collects data from network processors on line cards from a
          large amount of networking devices.</t>

          <t>Secondly, as no connection state needs to be maintained, UDP
          encapsulation can be easily implemented by the hardware of the
          publication streamer, which will further improve performance.</t>

          <t>Ultimately, such advantages allow for a larger data analysis
          feature set, as more voluminous, finer grained data sets can be
          streamed to the receiver.</t>
        </list></t>

      <t>The transport described in this document can be used for transmitting
      notification messages over both IPv4 and IPv6.</t>

      <t>This document describes the notification mechanism. It is intended to
      be used in conjunction with <xref target="RFC8639"/>, extended by <xref
      target="I-D.ietf-netconf-distributed-notif"/>.</t>

      <t><xref target="sec_transport"/> describes the control of the proposed
      transport mechanism. <xref target="sec_ups_transport"/> details the
      notification mechanism and message format. <xref
      target="sec_congestion_control"/> discusses congestion control. <xref
      target="sec_applicability"/> covers the applicability of the proposed
      mechanism.</t>
    </section>

    <section anchor="sec_transport"
             title="Configured Subscription to UDP-Notif">
      <t>This section describes how the proposed mechanism can be controlled
      using subscription channels based on NETCONF or RESTCONF.</t>

      <t>Following the usual approach of Sub-Notif, configured subscriptions
      contain the location information of all the receivers, including the IP
      address and the port number, so that the publisher can actively send
      UDP-Notif messages to the corresponding receivers.</t>

      <t>Note that receivers MAY NOT be already up and running when the
      configuration of the subscription takes effect on the monitored device.
      The first message MUST be a separate subscription-started notification
      to indicate the Receiver that the stream has started flowing. Then, the
      notifications can be sent immediately without delay. All the
      subscription state notifications, as defined in <xref
      target="RFC8639"/>, MUST be encapsulated in separate notification
      messages.</t>
    </section>

    <section anchor="sec_ups_transport" title="UDP-Based Transport">
      <t>In this section, we specify the UDP-Notif Transport behavior. <xref
      target="sec_design"/> describes the general design of the solution.
      <xref target="sec_ups_format"/> specifies the UDP-Notif message format.
      <xref target="sec_options"/> describes a generic optional sub TLV
      format. <xref target="sec_fragmentation"/> uses such options to provide
      a segmentation solution for large UDP-Notif message payloads. <xref
      target="sec_encoding"/> describes the encoding of the message
      payload.</t>

      <section anchor="sec_design" title="Design Overview">
        <t>As specified in Sub-Notif, the telemetry data is encapsulated in
        the NETCONF/RESTCONF notification message, which is then encapsulated
        and carried using transport protocols such as TLS or HTTP2. <xref
        target="fig_ups_message"/> illustrates the structure of an UDP-Notif
        message.</t>

        <t><list style="symbols">
            <t>The Message Header contains information that facilitate the
            message transmission before deserializing the notification
            message.</t>

            <t>Notification Message is the encoded content that the
            publication stream transports. The common encoding methods
            include, <xref target="RFC7049">CBOR</xref>, JSON, and XML. <xref
            target="I-D.ietf-netconf-notification-messages"/> describes the
            structure of the Notification Message for single notifications and
            bundled notifications.</t>
          </list></t>

        <t><figure anchor="fig_ups_message" title="UDP-Notif Message Overview">
            <artwork align="center"><![CDATA[
+-------+  +--------------+  +--------------+
|  UDP  |  |   Message    |  | Notification |
|       |  |   Header     |  | Message      |
+-------+  +--------------+  +--------------+
]]></artwork>
          </figure></t>

        <t/>
      </section>

      <section anchor="sec_ups_format"
               title="Format of the UDP-Notif Message Header">
        <t>The UDP-Notif Message Header contains information that facilitate
        the message transmission before deserializing the notification
        message. The data format is shown in <xref
        target="fig_ups_header"/>.</t>

        <figure anchor="fig_ups_header"
                title="UDP-Notif Message Header Format">
          <artwork align="center"><![CDATA[
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-----+-+-------+---------------+-------------------------------+
 | Ver |S|  ET   |  Header Len   |      Message Length           |
 +-----+-+-------+---------------+-------------------------------+
 |                    Observation-Domain-ID                      |
 +---------------------------------------------------------------+
 |                         Message-ID                            |
 +---------------------------------------------------------------+
 ~                          Options                              ~
 +---------------------------------------------------------------+

]]></artwork>
        </figure>

        <t/>

        <t>The Message Header contains the following field:</t>

        <t><list style="symbols">
            <t>Ver represents the PDU (Protocol Data Unit) encoding version.
            The initial version value is 0.</t>

            <t>S represents the space of encoding type specified in the ET
            field. When S is unset, ET represents the standard encoding types
            as defined in this document. When S is set, ET represents a
            private space to be freely used for nonstandard encodings.</t>

            <t>ET is a 4 bit identifier to indicate the encoding type used for
            the Notification Message. 16 types of encoding can be expressed.
            When the S bit is unset, the following values apply:<list
                style="symbols">
                <t>0: CBOR;</t>

                <t>1: JSON;</t>

                <t>2: XML;</t>

                <t>others are reserved.</t>
              </list></t>

            <t>Header Len is the length of the message header in octets,
            including both the fixed header and the options.</t>

            <t>Message Length is the total length of the message within one
            UDP datagram, measured in octets, including the message
            header.</t>

            <t>Observation-Domain-ID is a 32-bit identifier of the Observation
            Domain that led to the production of the notification message, as
            defined in <xref
            target="I-D.ietf-netconf-notification-messages"/>. This allows
            disambiguation of an information source, such as the
            identification of different line cards sending the notification
            messages. The source IP address of the UDP datagrams SHOULD NOT be
            interpreted as the identifier for the host that originated the
            UDP-Notif message. Indeed, the streamer sending the UDP-Notif
            message could be a relay for the actual source of data carried
            within UDP-Notif messages.</t>

            <t>The Message ID is generated continuously by the sender of
            UDP-Notif messages. Different subscribers share the same Message
            ID sequence.</t>

            <t>Options is a variable-length field in the TLV format. When the
            Header Length is larger than 12 octets, which is the length of the
            fixed header, Options TLVs follow directly after the fixed message
            header (i.e., Message ID). The details of the options are
            described in the following section.</t>
          </list></t>

        <t/>
      </section>

      <section anchor="sec_options" title="Options">
        <t>All the options are defined with the following format, illustrated
        in <xref target="fig_ups_message_options"/>.</t>

        <t><figure anchor="fig_ups_message_options"
            title="Generic Option Format">
            <artwork align="center"><![CDATA[
  0                   1                   2                   3        
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +---------------+---------------+--------------------------------
 |     Type      |    Length     |    Variable-length data     
 +---------------+---------------+--------------------------------]]></artwork>
          </figure></t>

        <t><list style="symbols">
            <t>Type: 1 octet describing the option type;</t>

            <t>Length: 1 octet representing the total number of octets in the
            TLV, including the Type and Length fields;</t>

            <t>Variable-length data: 0 or more octets of TLV Value.</t>
          </list></t>

        <section anchor="sec_fragmentation" title="Segmentation Option">
          <t>The UDP payload length is limited to 65535. Application level
          headers will make the actual payload shorter. Even though binary
          encodings such as CBOR may not require more space than what is left,
          more voluminous encodings such as JSON and XML may suffer from this
          size limitation. Although IPv4 and IPv6 senders can fragment
          outgoing packets exceeding their Maximum Transmission Unit(MTU),
          fragmented IP packets may not be desired for operational and
          performance reasons.</t>

          <t>Consequently, implementations of the mechanism SHOULD provide a
          configurable max-segment-size option to control the maximum size of
          a payload.</t>

          <figure anchor="fig_frag_option" title="Segmentation Option Format">
            <artwork align="center"><![CDATA[
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +---------------+---------------+-----------------------------+-+
 |     Type      |     Length    |        Segment Number       |L|
 +---------------+---------------+-----------------------------+-+
 ]]></artwork>
          </figure>

          <t>The Segmentation Option is to be included when the message
          content is segmented into multiple pieces. Different segments of one
          message share the same Message ID. An illustration is provided in
          <xref target="fig_frag_option"/>. The fields of this TLV are:</t>

          <t><list style="symbols">
              <t>Type: Generic option field which indicates a Segmentation
              Option. The Type value is to be assigned.</t>

              <t>Length: Generic option field which indicates the length of
              this option. It is a fixed value of 4 octets for the
              Segmentation Option.</t>

              <t>Segment Number: 15-bit value indicating the sequence number
              of the current segment. The first segment of a segmented message
              has a Segment Number value of 0.</t>

              <t>L: is a flag to indicate whether the current segment is the
              last one of the message. When 0 is set, the current segment is
              not the last one. When 1 is set, the current segment is the last
              one, meaning that the total number of segments used to transport
              this message is the value of the current Segment Number + 1.</t>
            </list></t>

          <t>An implementation of this specification MUST NOT rely on IP
          fragmentation by default to carry large messages. An implementation
          of this specification MUST either restrict the size of individual
          messages carried over this protocol, or support the segmentation
          option.</t>
        </section>
      </section>

      <section anchor="sec_encoding" title="Data Encoding">
        <t>UDP-Notif message data can be encoded in CBOR, XML or JSON format.
        It is conceivable that additional encodings may be supported in the
        future. This can be accomplished by augmenting the subscription data
        model with additional identity statements used to refer to requested
        encodings.</t>

        <t>Implementation MAY support multiple encoding methods per
        subscription. When bundled notifications are supported between the
        publisher and the receiver, only subscribed notifications with the
        same encoding can be bundled in a given message.</t>
      </section>
    </section>

    <section anchor="sec_applicability" title="Applicability">
      <t>In this section, we provide an applicability statement for the
      proposed mechanism, following the recommendations of <xref
      target="RFC8085"/>.</t>

      <t>The proposed mechanism falls in the category of UDP applications
      "designed for use within the network of a single network operator or on
      networks of an adjacent set of cooperating network operators, to be
      deployed in controlled environments". Implementations of the proposed
      mechanism should thus follow the recommendations in place for such
      specific applications. In the following, we discuss recommendations on
      congestion control, message size guidelines, reliability
      considerations.</t>

      <section anchor="sec_congestion_control" title="Congestion Control">
        <t>The proposed application falls into the category of applications
        performing transfer of large amounts of data. It is expected that the
        operator using the solution configures QoS on its related flows. As
        per <xref target="RFC8085"/>, such applications MAY choose not to
        implement any form of congestion control, but follow the following
        principles.</t>

        <t>It is NOT RECOMMENDED to use the proposed mechanism over
        congestion-sensitive network paths. The only environments where
        UDP-Notif is expected to be used are managed networks. The deployments
        require that the network path has been explicitly provisioned to
        handle the traffic through traffic engineering mechanisms, such as
        rate limiting or capacity reservations.</t>

        <t>Implementation of the proposal SHOULD NOT push unlimited amounts of
        traffic by default, and SHOULD require the users to explicitly
        configure such a mode of operation.</t>

        <t>Burst mitigation through packet pacing is RECOMMENDED. Disabling
        burst mitigation SHOULD require the users to explicitly configure such
        a mode of operation.</t>

        <t>Applications SHOULD monitor packet losses and provide means to the
        user for retrieving information on such losses. The UDP-Notif Message
        ID can be used to deduce congestion based on packet loss detection.
        Hence the receiver can notify the device to use a lower streaming
        rate. The interaction to control the streaming rate on the device is
        out of the scope of this document.</t>

        <!-- <t>Congestion control mechanisms that respond to congestion by reducing
      traffic rates and establish a degree of fairness between flows that
      share the same path are vital to the stable operation of the Internet
      <xref target="RFC2914"/>. While efficient, UDP has no built-in
      congestion control mechanism. Because streaming telemetry can generate
      unlimited amounts of data, transferring this data over UDP may be considered
      problematic. -->
      </section>

      <section anchor="sec_message_size" title="Message Size">
        <t><xref target="RFC8085"/> recommends not to rely on IP fragmentation
        for messages whose size result in IP packets exceeding the MTU along
        the path. The segmentation option of the current specification permits
        segmentation of the UDP Notif message content without relying on IP
        fragmentation. Implementation of the current specification SHOULD
        allow for the configuration of the MTU.</t>
      </section>

      <section anchor="Reliability" title="Reliability">
        <t>The target application for UDP-Notif is the collection of
        data-plane information. The lack of reliability of the data streaming
        mechanism is thus considered acceptable as the mechanism is to be used
        in controlled environments, mitigating the risk of information loss,
        while allowing for publication of very large amounts of data.
        Moreover, in this context, sporadic events when incomplete data
        collection is provided is not critical for the proper management of
        the network, as information collected for the devices through the
        means of the proposed mechanism is to be often refreshed.</t>

        <t>A receiver implementation for this protocol SHOULD deal with
        potential loss of packets carrying a part of segmented payload, by
        discarding packets that were received, but cannot be re-assembled as a
        complete message within a given amount of time. This time SHOULD be
        configurable.</t>
      </section>
    </section>

    <section title="A YANG Data Model for Management of UDP-Notif">
      <t>The YANG model defined in Section 9 has two leaf's augmented into one
      place of <xref target="RFC8639">Sub-Notif</xref>, plus one identity.</t>

      <t><figure>
          <artwork><![CDATA[
    module: ietf-udp-subscribed-notifications
     augment /sn:subscriptions/sn:subscription/sn:receivers/sn:receiver:
       +--rw address   inet:ip-address
       +--rw port      inet:port-number
       +--rw enable-fragment?  boolean
       +--rw max-fragment-size?  uint32]]></artwork>
        </figure></t>
    </section>

    <section title="YANG Module">
      <t/>

      <t><figure>
          <artwork><![CDATA[
<CODE BEGINS> file "ietf-udp-notif@2020-04-27.yang"
module ietf-udp-notif {
  yang-version 1.1;
  namespace 
    "urn:ietf:params:xml:ns:yang:ietf-udp-notif";
  prefix un;
  import ietf-subscribed-notifications {
    prefix sn;
    reference
      "RFC 8639: Subscription to YANG Notifications";
  }
  import ietf-inet-types {
    prefix inet;
    reference
      "RFC 6991: Common YANG Data Types";
  }

  organization "IETF NETCONF (Network Configuration) Working Group";
  contact
    "WG Web:   <http:/tools.ietf.org/wg/netconf/>
     WG List:  <mailto:netconf@ietf.org>

     Authors:  Guangying Zheng
               <mailto:zhengguangying@huawei.com>
               Tianran Zhou
               <mailto:zhoutianran@huawei.com>
               Thomas Graf
               <mailto:thomas.graf@swisscom.com>
               Pierre Francois
               <mailto:pierre.francois@insa-lyon.fr>
               Paolo Lucente
               <mailto:paolo@ntt.net>";

  description
    "Defines UDP-Notif as a supported transport for subscribed
    event notifications.

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

    Redistribution and use in source and binary forms, with or without
    modification, is permitted pursuant to, and subject to the license
    terms contained in, the Simplified BSD License set forth in Section
    4.c of the IETF Trust's Legal Provisions Relating to IETF Documents
    (https://trustee.ietf.org/license-info).

    This version of this YANG module is part of RFC XXXX; see the RFC

    itself for full legal notices.";

  revision 2020-04-27 {
    description
      "Initial version";
    reference
      "RFC XXXX: UDP-based Notifications for Streaming Telemetry";
  }

  identity udp-notif {
    base sn:transport;
    description
      "UDP-Notif is used as transport for notification messages 
and state change notifications.";
  }

  identity encode-cbor {
    base sn:encoding;
    description
      "Encode data using CBOR as described in RFC 7049.";
    reference
      "RFC 7049: Concise Binary Object Representation";
  }
  
  grouping target-receiver {
    description
      "Provides a reusable description of a UDP-Notif target receiver.";
    leaf address {
      type inet:ip-address;
      mandatory true;
      description
        "IP address of target UDP-Notif receiver, which can be an 
        IPv4 address or an IPV6 address.";
    }
    leaf port {
      type inet:port-number;
      mandatory true;
      description
        "Port number of target UDP-Notif receiver, if not specified, 
        the system should use default port number.";    
    }
    
    leaf enable-fragment {
      type boolean;
      default false;
      description
        "The switch for the fragment feature. When disabled, the
         publisher will not allow fragment for a very large data";
    }
    
    leaf max-fragment-size {
      when "../enable-fragment = true";
      type uint32;
      description "UDP-Notif provides a configurable max-fragment-size
      to control the size of each message.";      
    }
  }

  augment "/sn:subscriptions/sn:subscription/sn:receivers/sn:receiver" {
    description
      "This augmentation allows UDP-Notif specific parameters to be
       exposed for a subscription.";
    uses target-receiver;
  }
}
<CODE ENDS>]]></artwork>
        </figure></t>
    </section>

    <section anchor="IANA" title="IANA Considerations">
      <t>This RFC requests that IANA assigns one UDP port number in the
      "Registered Port Numbers" range with the service name "udp-notif". This
      port will be the default port for the UDP-based notification Streaming
      Telemetry (UDP-Notif) for NETCONF and RESTCONF. Below is the
      registration template following the rules of <xref
      target="RFC6335"/>.</t>

      <t>Service Name: udp-notif</t>

      <t>Transport Protocol(s): UDP</t>

      <t>Assignee: IESG &lt;iesg@ietf.org&gt;</t>

      <t>Contact: IETF Chair &lt;chair@ietf.org&gt;</t>

      <t>Description: UDP-based Publication Streaming Telemetry</t>

      <t>Reference: RFC XXXX</t>

      <t>Port Number: PORT-X</t>

      <t/>

      <t>IANA is requested to assign a new URI from the <xref
      target="RFC3688">IETF XML Registry</xref>. The following URI is
      suggested:</t>

      <t><figure>
          <artwork align="left"><![CDATA[
URI: urn:ietf:params:xml:ns:yang:ietf-udp-notif
Registrant Contact: The IESG.
XML: N/A; the requested URI is an XML namespace.]]></artwork>
        </figure></t>

      <t>This document also requests a new YANG module name in the <xref
      target="RFC7950">YANG Module Names registry</xref> with the following
      suggestion:</t>

      <t><figure>
          <artwork align="left"><![CDATA[
name: ietf-udp-notif
namespace: urn:ietf:params:xml:ns:yang:ietf-udp-notif
prefix: un
reference: RFC XXXX]]></artwork>
        </figure></t>
    </section>

    <section anchor="Security" title="Security Considerations">
      <t>TBD</t>
    </section>

    <section anchor="Acknowledgements" title="Acknowledgements">
      <t>The authors of this documents would like to thank Alexander Clemm,
      Eric Voit, Huiyang Yang, Kent Watsen, Mahesh Jethanandani, Stephane
      Frenot, Timothy Carey, Tim Jenkins, and Yunan Gu for their constructive
      suggestions for improving this document.</t>
    </section>
  </middle>

  <back>
    <references title="Normative References">
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml"?>

      <!--      <?rfc include="reference.RFC.2119"?>-->

      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.8639.xml'?>

      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.2914.xml'?>

      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.7950.xml"?>

      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.8650.xml'?>

      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.6335.xml'?>

      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.6241.xml"?>

      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.8040.xml"?>

      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.8085.xml"?>

      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.7049.xml"?>

      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.6347.xml'?>

      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4347.xml'?>

      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5246.xml'?>

      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5234.xml'?>

      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3688.xml'?>

      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.8640.xml'?>
    </references>

    <references title="Informative References">
      <?rfc include='http://xml.resource.org/public/rfc/bibxml-ids/reference.I-D.ietf-netconf-https-notif.xml'?>

      <?rfc include="http://xml.resource.org/public/rfc/bibxml-ids/reference.I-D.ietf-netconf-notification-messages.xml"?>

      <reference anchor="I-D.ietf-netconf-distributed-notif" target="">
        <front>
          <title>Subscription to Distributed Notifications</title>

          <author fullname="Tianran Zhou" initials="T." surname="Zhou">
            <organization>Huawei</organization>
          </author>

          <author fullname="Guangying Zheng" initials="G." surname="Zheng">
            <organization>Huawei</organization>
          </author>

          <author fullname="Eric Voit" initials="E." surname="Voit">
            <organization>Cisco Systems</organization>
          </author>

          <author fullname="Thomas Graf" initials="T." surname="Graf">
            <organization>Swisscom</organization>
          </author>

          <author fullname="Pierre Francois" initials="P." surname="Francois">
            <organization>INSA-Lyon</organization>
          </author>

          <date month="June" year="2020"/>
        </front>

        <seriesInfo name="Internet-Draft"
                    value="draft-ietf-netconf-distributed-notif-01"/>
      </reference>
    </references>
  </back>
</rfc>