draft-ietf-netconf-udp-notif-05.xml

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<?rfc toc="yes"?>
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<?rfc tocdepth="3"?>
<?rfc tocindent="yes"?>
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<rfc category="std" docName="draft-ietf-netconf-udp-notif-05"
     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="Alex Huang Feng" initials="A." surname="Huang Feng">
      <organization>INSA-Lyon</organization>

      <address>
        <postal>
          <street/>

          <city>Lyon</city>

          <region/>

          <code/>

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

        <phone/>

        <facsimile/>

        <email>alex.huang-feng@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="3" month="March" year="2022"/>

    <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 to
      provide a lightweight approach to enable higher frequency and less
      performance impact on publisher and receiver processes 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_options"/>
      describes the use of options in the notification message header. <xref
      target="sec_applicability"/> covers the applicability of the proposed
      mechanism. <xref target="sec_dtls_udp_notif"/> describes a mechanism to
      secure the protocol in open networks.</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. This
        document defines a UDP based transport. <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
            are listed in <xref target="sec_ups_format"/>. <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|  MT   |  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 media type specified in the MT field.
            When S is unset, MT represents the standard media types as defined
            in this document. When S is set, MT represents a private space to
            be freely used for non standard encodings.</t>

            <t>MT is a 4 bit identifier to indicate the media 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: Reserved;</t>

                <t>1: application/yang-data+json <xref target="RFC8040"/></t>

                <t>2: application/yang-data+xml <xref target="RFC8040"/></t>

                <t>3: application/yang-data+cbor <xref
                target="I-D.ietf-core-yang-cbor"/></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 publisher 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 <xref target="sec_options"/>.</t>
          </list></t>

        <t/>
      </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>Private encodings can be supported through the use of the S bit of
        the header. When the S bit is set, the value of the MT field is left
        to be defined and agreed upon by the users of the private encoding. An
        option is defined in <xref target="sec_enc_opt"/> for more verbose
        encoding descriptions than what can be described with the MT
        field.</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_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>

      <t>When more than one option are used in the UDP-notif header, options
      MUST be ordered by the Type value.</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 publishers 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 TBD1.</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>

        <t>When a message has multiple options and is segmented using the
        described mechanism, all the options MUST be present on the first
        segment ordered by the options Type. The rest of segmented messages
        MAY include all the options ordered by options type.</t>
      </section>

      <section anchor="sec_enc_opt" title="Private Encoding Option">
        <t>The space to describe private encodings in the MT field of the
        UDP-Notif header being limited, an option is provided to describe
        custom encodings. The fields of this option are as follows.</t>

        <figure anchor="fig_enc_option" title="Private Encoding 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 enc. descr.  
 +---------------+---------------+--------------------------------

 ]]></artwork>
        </figure>

        <t><list style="symbols">
            <t>Type: Generic option field which indicates a Private Encoding
            Option. The Type value is to be assigned TBD2.</t>

            <t>Length: Generic option field which indicates the length of this
            option. It is a variable value.</t>

            <t>Enc. Descr: The description of the private encoding used for
            this message. The values to be used for such private encodings is
            left to be defined by the users of private encodings.</t>
          </list></t>

        <t>This option SHOULD only be used when the S bit of the header is
        set, as providing a private encoding description for standard
        encodings is meaningless.</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
      and security 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="sec_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 anchor="sec_security_considerations"
               title="Security Considerations">
        <t><xref target="RFC8085"/> states that "UDP applications that need to
        protect their communications againts eavesdropping, tampering, or
        message forgery SHOULD employ end-to-end security services provided by
        other IETF protocols". As mentioned above, the proposed mechanism is
        designed to be used in controlled environments and thus, a security
        layer is unrequired. Nevertheless, a DTLS layer SHOULD be implemented
        in open or unsecured networks. A DTLS layered implementation is
        presented in <xref target="sec_dtls_udp_notif"/>.</t>

        <!-- <t>As stated in the Applicability analysis in <xref
        target="sec_applicability"/>, this protocol is to be used in controlled
        environments, so that network operators might not require to secure the transport
        mechanism described in this document. An approach to secure this protocol
        is out of the scope of this document. </t> -->
      </section>
    </section>

    <section anchor="sec_dtls_udp_notif" title="Secured layer for UDP-notif">
      <t>In open or unsecured networks, UDP-notif messages SHOULD be secured
      or encrypted. In this section, a mechanism using DTLS 1.3 to secure
      UDP-notif protocol is presented. The following sections defines the
      requirements for the implementation of the secured layer of DTLS for
      UDP-notif. No DTLS 1.3 extensions are defined nor needed.</t>

      <t>The DTLS 1.3 protocol <xref target="I-D.draft-ietf-tls-dtls13"/> is
      designed to meet the requirements of applications that need to secure
      datagram transport.</t>

      <t>DTLS can be used as a secure transport to counter all the primary
      threats to UDP-notif:</t>

      <t><list style="symbols">
          <t>Confidentiality to counter disclosure of the message
          contents.</t>

          <t>Integrity checking to counter modifications to a message on a
          hop-by-hop basis.</t>

          <t>Server or mutual authentication to counter masquerade.</t>
        </list></t>

      <t>In addition, DTLS also provides:</t>

      <t><list style="symbols">
          <t>A cookie exchange mechanism during handshake to counter Denial of
          Service attacks.</t>

          <t>A sequence number in the header to counter replay attacks.</t>
        </list></t>

      <t>Even though this security layer is unrequired, DTLS 1.3 SHOULD be
      implemented on unsecured networks to achieve privacy.</t>

      <section anchor="sec_dtl_transport" title="Transport">
        <t>As shown in <xref target="fig_dtls_layers"/>, the DTLS is layered
        next to the UDP transport providing reusable security and
        authentication functions over UDP. No DTLS extension is required to
        enable UDP-notif messages over DTLS.</t>

        <t><figure anchor="fig_dtls_layers"
            title="Protocol Stack for DTLS secured UDP-notif">
            <artwork align="center"><![CDATA[
+-----------------------------+
|      UDP-notif Message      |
+-----------------------------+
|            DTLS             |
+-----------------------------+
|            UDP              |
+-----------------------------+
|            IP               |
+-----------------------------+
          ]]></artwork>
          </figure></t>

        <t>The application implementer will map a unique combination of the
        remote address, remote port number, local address, and local port
        number to a session.</t>

        <t>Each UDP-notif message is delivered by the DTLS record protocol,
        which assigns a sequence number to each DTLS record. Although the DTLS
        implementer may adopt a queue mechanism to resolve reordering, it may
        not assure that all the messages are delivered in order when mapping
        on the UDP transport.</t>

        <t>Since UDP is an unreliable transport, with DTLS, an originator or a
        relay may not realize that a collector has gone down or lost its DTLS
        connection state, so messages may be lost.</t>

        <t>The DTLS record has its own sequence number, encryption and
        decryption will be done by the DTLS layer, so that the UDP-notif
        Message layer is not impacted by the use of DTLS.</t>
      </section>

      <section anchor="sec_port_assignment" title="Port Assignment">
        <t>When this security layer is used, the Publisher MUST always be a
        DTLS client, and the Receiver MUST always be a DTLS server. The
        Receivers MUST support accepting UDP-notif Messages on the specified
        UDP port, but MAY be configurable to listen on a different port. The
        Publisher MUST support sending UDP-notif messages to the specified UDP
        port, but MAY be configurable to send messages to a different port.
        The Publisher MAY use any source UDP port for transmitting
        messages.</t>
      </section>

      <section anchor="sec_session_lifecycle" title="Session lifecycle">
        <section title="DTLS Session Initiation">
          <t>The Publisher initiates a DTLS connection by sending a DTLS
          ClientHello to the Receiver. Implementations MAY support the denial
          of service countermeasures defined by DTLS 1.3. When these
          countermeasures are used, the Receiver responds with a DTLS
          HelloRetryRequest containing a stateless cookie. The Publisher MUST
          send a new DTLS ClientHello message containing the received cookie,
          which initiates the DTLS handshake.</t>

          <t>When DTLS is implemented, the Publisher MUST NOT send any
          UDP-notif messages before the DTLS handshake has successfully
          completed.</t>

          <t>Implementations of this security layer MUST support DTLS 1.3
          <xref target="I-D.draft-ietf-tls-dtls13"/> and MUST support the
          mandatory to implement cipher suite TLS_AES_128_GCM_SHA256 and
          SHOULD implement TLS_AES_256_GCM_SHA384 and
          TLS_CHACHA20_POLY1305_SHA256 cipher suites, as specified in TLS 1.3
          <xref target="RFC8446"/>. If additional cipher suites are supported,
          then implementations MUST NOT negotiate a cipher suite that employs
          NULL integrity or authentication algorithms.</t>

          <t>Where privacy is REQUIRED, then implementations must either
          negotiate a cipher suite that employs a non-NULL encryption
          algorithm or otherwise achieve privacy by other means, such as a
          physically secured network.</t>
        </section>

        <section title="Publish Data">
          <t>When DTLS is used, all UDP-notif messages MUST be published as
          DTLS "application_data". It is possible that multiple UDP-notif
          messages are contained in one DTLS record, or that a publication
          message is transferred in multiple DTLS records. The application
          data is defined with the following ABNF <xref target="RFC5234"/>
          expression:</t>

          <t>APPLICATION-DATA = 1*UDP-NOTIF-FRAME</t>

          <t>UDP-NOTIF-FRAME = MSG-LEN SP UDP-NOTIF-MSG</t>

          <t>MSG-LEN = NONZERO-DIGIT *DIGIT</t>

          <t>SP = %d32</t>

          <t>NONZERO-DIGIT = %d49-57</t>

          <t>DIGIT = %d48 / NONZERO-DIGIT</t>

          <t>UDP-NOTIF-MSG is defined in <xref
          target="sec_ups_transport"/>.</t>

          <t>The Publisher SHOULD attempt to avoid IP fragmentation by using
          the Segmentation Option in the UDP-notif message.</t>
        </section>

        <section title="Session termination">
          <t>A Publisher MUST close the associated DTLS connection if the
          connection is not expected to deliver any UDP-notif Messages later.
          It MUST send a DTLS close_notify alert before closing the
          connection. A Publisher (DTLS client) MAY choose to not wait for the
          Receiver's close_notify alert and simply close the DTLS connection.
          Once the Receiver gets a close_notify from the Publisher, it MUST
          reply with a close_notify.</t>

          <t>When no data is received from a DTLS connection for a long time,
          the Receiver MAY close the connection. Implementations SHOULD set
          the timeout value to 10 minutes but application specific profiles
          MAY recommend shorter or longer values. The Receiver (DTLS server)
          MUST attempt to initiate an exchange of close_notify alerts with the
          Publisher before closing the connection. Receivers that are
          unprepared to receive any more data MAY close the connection after
          sending the close_notify alert.</t>

          <t>Although closure alerts are a component of TLS and so of DTLS,
          they, like all alerts, are not retransmitted by DTLS and so may be
          lost over an unreliable network.</t>
        </section>
      </section>
    </section>

    <section title="A YANG Data Model for Management of UDP-Notif">
      <t>The YANG model defined in <xref target="sec_yang_model"/> has two
      leaves 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-segmentation?  boolean
       +--rw max-segmentation-size?  uint32]]></artwork>
        </figure></t>
    </section>

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

      <t><figure>
          <artwork><![CDATA[
<CODE BEGINS> file "ietf-udp-notif@2020-10-18.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 2021-10-18 {
    description
    "Slight change to the name of two parameters.";
    reference
    "RFC XXXX: UDP-based Transport for Configured Subscriptions";
  }
 
 /*
  * FEATURES
  */
  feature encode-cbor {
    description
      "This feature indicates that CBOR encoding of notification
       messages is supported.";
  }

 /*
  * IDENTITIES
  */  
  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 XXX.";
    reference
      "RFC XXX: draft-ietf-core-yang-cbor-18, CBOR Encoding of 
        Data Modeled with YANG";
  }

  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;
    description
      "Port number of target UDP-Notif receiver, if not specified,
      the system should use default port number.";
    }

    leaf enable-segmentation {
      type boolean;
      default false;
      description
        "The switch for the segmentation feature. When disabled, the
        publisher will not allow fragment for a very large data";
    }

    leaf max-segmentation-size {
    when "../enable-segmentation = 'true'";
    type uint32;
    description "UDP-Notif provides a configurable 
      max-segmentation-size to control the size of each message.";
    }
  }

  augment "/sn:subscriptions/sn:subscription/sn:receivers/sn:receiver" {
    when "derived-from(../../../transport, 'un:udp-notif')";
    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 document is creating 2 registries called "UDP-notif media types"
      and "UDP-notif option types" under the new heading "UDP-notif protocol".
      The registration procedure is made using the Standards Action process
      defined in <xref target="RFC8126"/>.</t>

      <t>The first requested registry is the following:</t>

      <t><figure>
          <artwork align="left"><![CDATA[
  Registry Name: UDP-notif media types
  Registry Category: UDP-notif protocol.
  Registration Procedure: Standard Action as defined in RFC8126
  Maximum value: 15]]></artwork>
        </figure></t>

      <t>These are the initial registrations for "UDP-notif media types":</t>

      <t><figure>
          <artwork align="left"><![CDATA[
  Value: 0
  Description: Reserved
  Reference: this document]]></artwork>
        </figure></t>

      <t><figure>
          <artwork align="left"><![CDATA[
  Value: 1
  Description: media type application/yang-data+json
  Reference: <xref target="RFC8040"/>]]></artwork>
        </figure></t>

      <t><figure>
          <artwork align="left"><![CDATA[
  Value: 2
  Description: media type application/yang-data+xml
  Reference: <xref target="RFC8040"/>]]></artwork>
        </figure></t>

      <t><figure>
          <artwork align="left"><![CDATA[
  Value: 3
  Description: media type application/yang-data+cbor
  Reference: <xref target="I-D.ietf-core-yang-cbor"/>]]></artwork>
        </figure></t>

      <t>The second requested registry is the following:</t>

      <t><figure>
          <artwork align="left"><![CDATA[
  Registry Name: UDP-notif option types
  Registry Category: UDP-notif protocol.
  Registration Procedure: Standard Action as defined in RFC8126
  Maximum value: 255]]></artwork>
        </figure></t>

      <t>These are the initial registrations for "UDP-notif options
      types":</t>

      <t><figure>
          <artwork align="left"><![CDATA[
  Value: 0
  Description: Reserved
  Reference: this document]]></artwork>
        </figure></t>

      <t><figure>
          <artwork align="left"><![CDATA[
  Value: TBD1 (suggested value: 1)
  Description: Segmentation Option
  Reference: this document]]></artwork>
        </figure></t>

      <t><figure>
          <artwork align="left"><![CDATA[
  Value: TBD2 (suggested value: 2)
  Description: Private Encoding Option
  Reference: this document]]></artwork>
        </figure></t>

      <t>IANA is also 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="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, Yunan Gu and Marco Tollini for their
      constructive suggestions for improving this document.</t>
    </section>
  </middle>

  <back>
    <references title="Normative References">
      <!-- <?rfc include='reference.RFC.2119'?> -->
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml"?>
      <!-- <?rfc include='reference.RFC.3688'?> -->
      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3688.xml'?>
      <!-- <?rfc include='reference.RFC.5234'?> -->
      <?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5234.xml'?>
      <!-- <?rfc include='reference.RFC.7950'?> -->
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.7950.xml"?>
      <!-- <?rfc include='reference.RFC.8085'?> -->
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.8085.xml"?>
      <!-- <?rfc include='reference.RFC.8126'?> -->
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.8126.xml"?>
      <!-- <?rfc include='reference.RFC.8446'?> -->
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.8446.xml"?>
      <!-- <?rfc include='reference.RFC.8639'?> -->
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.8639.xml"?>
      <!-- <?rfc include='reference.RFC.8640'?> -->
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.8640.xml"?>
      <!-- <?rfc include='reference.RFC.8650'?> -->
      <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.8650.xml"?>

    </references>

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

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

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

      <!-- <?rfc include='reference.I-D.ietf-core-yang-cbor'?> -->
      <?rfc include="http://xml.resource.org/public/rfc/bibxml-ids/reference.I-D.ietf-core-yang-cbor.xml"?>

      <reference anchor="I-D.draft-ietf-tls-dtls13" target="">
        <front>
          <title>The Datagram Transport Layer Security (DTLS) Protocol Version
          1.3</title>

          <author fullname="Eric Rescorla" initials="E." surname="Rescorla">
            <organization>RTFM, Inc.</organization>
          </author>

          <author fullname="Hannes Tschofenig" initials="H."
                  surname="Tschofenig">
            <organization>Arm Limited</organization>
          </author>

          <author fullname="Nagendra Modadugu" initials="N."
                  surname="Modadugu">
            <organization>Google, Inc.</organization>
          </author>

          <date month="July" year="2021"/>
        </front>

        <seriesInfo name="Internet-Draft" value="draft-ietf-tls-dtls13-43"/>
      </reference>

      <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="May" year="2021"/>
        </front>

        <seriesInfo name="Internet-Draft"
                    value="draft-ietf-netconf-distributed-notif-02"/>
      </reference>
    </references>
  </back>
</rfc>