NETCONF                                                         G. Zheng
Internet-Draft                                                   T. Zhou
Intended status: Standards Track                                  Huawei
Expires: 4 September 2022                                        T. Graf
                                                                Swisscom
                                                             P. Francois
                                                           A. Huang Feng
                                                               INSA-Lyon
                                                              P. Lucente
                                                                     NTT
                                                            3 March 2022


            UDP-based Transport for Configured Subscriptions
                    draft-ietf-netconf-udp-notif-05

Abstract

   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.

Requirements Language

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

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 4 September 2022.



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Copyright Notice

   Copyright (c) 2022 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 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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Configured Subscription to UDP-Notif  . . . . . . . . . . . .   4
   3.  UDP-Based Transport . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Design Overview . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Format of the UDP-Notif Message Header  . . . . . . . . .   5
     3.3.  Data Encoding . . . . . . . . . . . . . . . . . . . . . .   7
   4.  Options . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Segmentation Option . . . . . . . . . . . . . . . . . . .   8
     4.2.  Private Encoding Option . . . . . . . . . . . . . . . . .   9
   5.  Applicability . . . . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  Congestion Control  . . . . . . . . . . . . . . . . . . .  10
     5.2.  Message Size  . . . . . . . . . . . . . . . . . . . . . .  10
     5.3.  Reliability . . . . . . . . . . . . . . . . . . . . . . .  11
     5.4.  Security Considerations . . . . . . . . . . . . . . . . .  11
   6.  Secured layer for UDP-notif . . . . . . . . . . . . . . . . .  11
     6.1.  Transport . . . . . . . . . . . . . . . . . . . . . . . .  12
     6.2.  Port Assignment . . . . . . . . . . . . . . . . . . . . .  13
     6.3.  Session lifecycle . . . . . . . . . . . . . . . . . . . .  13
       6.3.1.  DTLS Session Initiation . . . . . . . . . . . . . . .  13
       6.3.2.  Publish Data  . . . . . . . . . . . . . . . . . . . .  13
       6.3.3.  Session termination . . . . . . . . . . . . . . . . .  14
   7.  A YANG Data Model for Management of UDP-Notif . . . . . . . .  14
   8.  YANG Module . . . . . . . . . . . . . . . . . . . . . . . . .  15
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     11.2.  Informative References . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21






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1.  Introduction

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

   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.

   This document specifies a transport option for Sub-Notif that
   leverages UDP.  Specifically, it facilitates the distributed data
   collection mechanism described in
   [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.

   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.

   *  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.

   *  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.

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



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

   This document describes the notification mechanism.  It is intended
   to be used in conjunction with [RFC8639], extended by
   [I-D.ietf-netconf-distributed-notif].

   Section 2 describes the control of the proposed transport mechanism.
   Section 3 details the notification mechanism and message format.
   Section 4 describes the use of options in the notification message
   header.  Section 5 covers the applicability of the proposed
   mechanism.  Section 6 describes a mechanism to secure the protocol in
   open networks.

2.  Configured Subscription to UDP-Notif

   This section describes how the proposed mechanism can be controlled
   using subscription channels based on NETCONF or RESTCONF.

   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.

   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
   [RFC8639], MUST be encapsulated in separate notification messages.

3.  UDP-Based Transport

   In this section, we specify the UDP-Notif Transport behavior.
   Section 3.1 describes the general design of the solution.
   Section 3.2 specifies the UDP-Notif message format.  Section 4
   describes a generic optional sub TLV format.  Section 4.1 uses such
   options to provide a segmentation solution for large UDP-Notif
   message payloads.  Section 3.3 describes the encoding of the message
   payload.










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3.1.  Design Overview

   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.  Figure 1 illustrates the
   structure of an UDP-Notif message.

   *  The Message Header contains information that facilitate the
      message transmission before deserializing the notification
      message.

   *  Notification Message is the encoded content that the publication
      stream transports.  The common encoding methods are listed in
      Section 3.2.  [I-D.ietf-netconf-notification-messages] describes
      the structure of the Notification Message for single notifications
      and bundled notifications.

               +-------+  +--------------+  +--------------+
               |  UDP  |  |   Message    |  | Notification |
               |       |  |   Header     |  | Message      |
               +-------+  +--------------+  +--------------+

                    Figure 1: UDP-Notif Message Overview


3.2.  Format of the UDP-Notif Message Header

   The UDP-Notif Message Header contains information that facilitate the
   message transmission before deserializing the notification message.
   The data format is shown in Figure 2.

      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                              ~
     +---------------------------------------------------------------+

                 Figure 2: UDP-Notif Message Header Format


   The Message Header contains the following field:



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   *  Ver represents the PDU (Protocol Data Unit) encoding version.  The
      initial version value is 0.

   *  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.

   *  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:

      -  0: Reserved;

      -  1: application/yang-data+json [RFC8040]

      -  2: application/yang-data+xml [RFC8040]

      -  3: application/yang-data+cbor [I-D.ietf-core-yang-cbor]

   *  Header Len is the length of the message header in octets,
      including both the fixed header and the options.

   *  Message Length is the total length of the message within one UDP
      datagram, measured in octets, including the message header.

   *  Observation-Domain-ID is a 32-bit identifier of the Observation
      Domain that led to the production of the notification message, as
      defined in [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.

   *  The Message ID is generated continuously by the publisher of UDP-
      Notif messages.  Different subscribers share the same Message ID
      sequence.

   *  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 Section 4.





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3.3.  Data Encoding

   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.

   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 Section 4.2 for more verbose encoding
   descriptions than what can be described with the MT field.

   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.

4.  Options

   All the options are defined with the following format, illustrated in
   Figure 3.

      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
     +---------------+---------------+--------------------------------

                      Figure 3: Generic Option Format

   *  Type: 1 octet describing the option type;

   *  Length: 1 octet representing the total number of octets in the
      TLV, including the Type and Length fields;

   *  Variable-length data: 0 or more octets of TLV Value.

   When more than one option are used in the UDP-notif header, options
   MUST be ordered by the Type value.










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4.1.  Segmentation Option

   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.

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

      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|
     +---------------+---------------+-----------------------------+-+

                    Figure 4: Segmentation Option Format

   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 Figure 4.
   The fields of this TLV are:

   *  Type: Generic option field which indicates a Segmentation Option.
      The Type value is to be assigned TBD1.

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

   *  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.

   *  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.







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   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.

   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.

4.2.  Private Encoding Option

   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.

      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.
     +---------------+---------------+--------------------------------


                  Figure 5: Private Encoding Option Format

   *  Type: Generic option field which indicates a Private Encoding
      Option.  The Type value is to be assigned TBD2.

   *  Length: Generic option field which indicates the length of this
      option.  It is a variable value.

   *  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.

   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.

5.  Applicability

   In this section, we provide an applicability statement for the
   proposed mechanism, following the recommendations of [RFC8085].

   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



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   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.

5.1.  Congestion Control

   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 [RFC8085], such applications MAY choose not to implement any
   form of congestion control, but follow the following principles.

   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.

   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.

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

   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.

5.2.  Message Size

   [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.







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5.3.  Reliability

   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.

   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.

5.4.  Security Considerations

   [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
   Section 6.

6.  Secured layer for UDP-notif

   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.

   The DTLS 1.3 protocol [I-D.draft-ietf-tls-dtls13] is designed to meet
   the requirements of applications that need to secure datagram
   transport.

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

   *  Confidentiality to counter disclosure of the message contents.

   *  Integrity checking to counter modifications to a message on a hop-
      by-hop basis.



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   *  Server or mutual authentication to counter masquerade.

   In addition, DTLS also provides:

   *  A cookie exchange mechanism during handshake to counter Denial of
      Service attacks.

   *  A sequence number in the header to counter replay attacks.

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

6.1.  Transport

   As shown in Figure 6, 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.

                      +-----------------------------+
                      |      UDP-notif Message      |
                      +-----------------------------+
                      |            DTLS             |
                      +-----------------------------+
                      |            UDP              |
                      +-----------------------------+
                      |            IP               |
                      +-----------------------------+

            Figure 6: Protocol Stack for DTLS secured UDP-notif

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

   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.

   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.

   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.




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6.2.  Port Assignment

   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.

6.3.  Session lifecycle

6.3.1.  DTLS Session Initiation

   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.

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

   Implementations of this security layer MUST support DTLS 1.3
   [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 [RFC8446].  If additional cipher
   suites are supported, then implementations MUST NOT negotiate a
   cipher suite that employs NULL integrity or authentication
   algorithms.

   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.

6.3.2.  Publish Data

   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 [RFC5234] expression:

   APPLICATION-DATA = 1*UDP-NOTIF-FRAME



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   UDP-NOTIF-FRAME = MSG-LEN SP UDP-NOTIF-MSG

   MSG-LEN = NONZERO-DIGIT *DIGIT

   SP = %d32

   NONZERO-DIGIT = %d49-57

   DIGIT = %d48 / NONZERO-DIGIT

   UDP-NOTIF-MSG is defined in Section 3.

   The Publisher SHOULD attempt to avoid IP fragmentation by using the
   Segmentation Option in the UDP-notif message.

6.3.3.  Session termination

   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.

   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.

   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.

7.  A YANG Data Model for Management of UDP-Notif

   The YANG model defined in Section 8 has two leaves augmented into one
   place of Sub-Notif [RFC8639], plus one identity.









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    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

8.  YANG Module


   <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



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       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



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         "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>







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9.  IANA Considerations

   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 [RFC8126].

   The first requested registry is the following:

     Registry Name: UDP-notif media types
     Registry Category: UDP-notif protocol.
     Registration Procedure: Standard Action as defined in RFC8126
     Maximum value: 15

   These are the initial registrations for "UDP-notif media types":

     Value: 0
     Description: Reserved
     Reference: this document

     Value: 1
     Description: media type application/yang-data+json
     Reference: <xref target="RFC8040"/>

     Value: 2
     Description: media type application/yang-data+xml
     Reference: <xref target="RFC8040"/>

     Value: 3
     Description: media type application/yang-data+cbor
     Reference: <xref target="I-D.ietf-core-yang-cbor"/>

   The second requested registry is the following:

     Registry Name: UDP-notif option types
     Registry Category: UDP-notif protocol.
     Registration Procedure: Standard Action as defined in RFC8126
     Maximum value: 255

   These are the initial registrations for "UDP-notif options types":

     Value: 0
     Description: Reserved
     Reference: this document

     Value: TBD1 (suggested value: 1)
     Description: Segmentation Option
     Reference: this document



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     Value: TBD2 (suggested value: 2)
     Description: Private Encoding Option
     Reference: this document

   IANA is also requested to assign a new URI from the IETF XML Registry
   [RFC3688].  The following URI is suggested:

   URI: urn:ietf:params:xml:ns:yang:ietf-udp-notif
   Registrant Contact: The IESG.
   XML: N/A; the requested URI is an XML namespace.

   This document also requests a new YANG module name in the YANG Module
   Names registry [RFC7950] with the following suggestion:

   name: ietf-udp-notif
   namespace: urn:ietf:params:xml:ns:yang:ietf-udp-notif
   prefix: un
   reference: RFC XXXX

10.  Acknowledgements

   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.

11.  References

11.1.  Normative References

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

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.




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   [RFC8085]  Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
              Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
              March 2017, <https://www.rfc-editor.org/info/rfc8085>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8639]  Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
              E., and A. Tripathy, "Subscription to YANG Notifications",
              RFC 8639, DOI 10.17487/RFC8639, September 2019,
              <https://www.rfc-editor.org/info/rfc8639>.

   [RFC8640]  Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
              E., and A. Tripathy, "Dynamic Subscription to YANG Events
              and Datastores over NETCONF", RFC 8640,
              DOI 10.17487/RFC8640, September 2019,
              <https://www.rfc-editor.org/info/rfc8640>.

   [RFC8650]  Voit, E., Rahman, R., Nilsen-Nygaard, E., Clemm, A., and
              A. Bierman, "Dynamic Subscription to YANG Events and
              Datastores over RESTCONF", RFC 8650, DOI 10.17487/RFC8650,
              November 2019, <https://www.rfc-editor.org/info/rfc8650>.

11.2.  Informative References

   [I-D.draft-ietf-tls-dtls13]
              Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", Work in Progress, Internet-Draft, draft-ietf-tls-
              dtls13-43, July 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-tls-
              dtls13-43>.

   [I-D.ietf-core-yang-cbor]
              Veillette, M., Petrov, I., Pelov, A., Bormann, C., and M.
              Richardson, "CBOR Encoding of Data Modeled with YANG",
              Work in Progress, Internet-Draft, draft-ietf-core-yang-
              cbor-18, 19 December 2021,
              <https://www.ietf.org/archive/id/draft-ietf-core-yang-
              cbor-18.txt>.





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   [I-D.ietf-netconf-distributed-notif]
              Zhou, T., Zheng, G., Voit, E., Graf, T., and P. Francois,
              "Subscription to Distributed Notifications", Work in
              Progress, Internet-Draft, draft-ietf-netconf-distributed-
              notif-02, May 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
              distributed-notif-02>.

   [I-D.ietf-netconf-https-notif]
              Jethanandani, M. and K. Watsen, "An HTTPS-based Transport
              for YANG Notifications", Work in Progress, Internet-Draft,
              draft-ietf-netconf-https-notif-09, 24 October 2021,
              <https://www.ietf.org/archive/id/draft-ietf-netconf-https-
              notif-09.txt>.

   [I-D.ietf-netconf-notification-messages]
              Voit, E., Jenkins, T., Birkholz, H., Bierman, A., and A.
              Clemm, "Notification Message Headers and Bundles", Work in
              Progress, Internet-Draft, draft-ietf-netconf-notification-
              messages-08, 17 November 2019,
              <https://www.ietf.org/archive/id/draft-ietf-netconf-
              notification-messages-08.txt>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

Authors' Addresses

   Guangying Zheng
   Huawei
   101 Yu-Hua-Tai Software Road
   Nanjing
   Jiangsu,
   China
   Email: zhengguangying@huawei.com


   Tianran Zhou
   Huawei
   156 Beiqing Rd., Haidian District
   Beijing
   China
   Email: zhoutianran@huawei.com







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   Thomas Graf
   Swisscom
   Binzring 17
   CH- Zuerich 8045
   Switzerland
   Email: thomas.graf@swisscom.com


   Pierre Francois
   INSA-Lyon
   Lyon
   France
   Email: pierre.francois@insa-lyon.fr


   Alex Huang Feng
   INSA-Lyon
   Lyon
   France
   Email: alex.huang-feng@insa-lyon.fr


   Paolo Lucente
   NTT
   Siriusdreef 70-72
   Hoofddorp, WT 2132
   Netherlands
   Email: paolo@ntt.net























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