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

NETCONF                                                         G. Zheng
Internet-Draft                                                   T. Zhou
Intended status: Standards Track                                  Huawei
Expires: November 7, 2021                                        T. Graf
                                                                Swisscom
                                                             P. Francois
                                                               INSA-Lyon
                                                              P. Lucente
                                                                     NTT
                                                             May 6, 2021


            UDP-based Transport for Configured Subscriptions
                    draft-ietf-netconf-udp-notif-02

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 a
   lightweight approach to enable higher frequency and less performance
   impact on publisher and receiver process 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 November 7, 2021.




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Copyright Notice

   Copyright (c) 2021 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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Configured Subscription to UDP-Notif  . . . . . . . . . . . .   4
   3.  UDP-Based Transport . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Design Overview . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Format of the UDP-Notif Message Header  . . . . . . . . .   5
     3.3.  Options . . . . . . . . . . . . . . . . . . . . . . . . .   6
       3.3.1.  Segmentation Option . . . . . . . . . . . . . . . . .   7
     3.4.  Data Encoding . . . . . . . . . . . . . . . . . . . . . .   8
   4.  Applicability . . . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Congestion Control  . . . . . . . . . . . . . . . . . . .   8
     4.2.  Message Size  . . . . . . . . . . . . . . . . . . . . . .   9
     4.3.  Reliability . . . . . . . . . . . . . . . . . . . . . . .   9
   5.  A YANG Data Model for Management of UDP-Notif . . . . . . . .   9
   6.  YANG Module . . . . . . . . . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     10.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

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




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   [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.

   o  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.

   o  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.

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

   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].




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   Section 2 describes the control of the proposed transport mechanism.
   Section 3 details the notification mechanism and message format.
   Section 4.1 discusses congestion control.  Section 4 covers the
   applicability of the proposed mechanism.

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 3.3
   describes a generic optional sub TLV format.  Section 3.3.1 uses such
   options to provide a segmentation solution for large UDP-Notif
   message payloads.  Section 3.4 describes the encoding of the message
   payload.

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

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

   o  Notification Message is the encoded content that the publication
      stream transports.  The common encoding methods include, CBOR
      [RFC7049], JSON, and XML.
      [I-D.ietf-netconf-notification-messages] describes the structure



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      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|  ET   |  Header Len   |      Message Length           |
     +-----+-+-------+---------------+-------------------------------+
     |                    Observation-Domain-ID                      |
     +---------------------------------------------------------------+
     |                         Message-ID                            |
     +---------------------------------------------------------------+
     ~                          Options                              ~
     +---------------------------------------------------------------+


                 Figure 2: UDP-Notif Message Header Format

   The Message Header contains the following field:

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

   o  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.

   o  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:

      *  0: CBOR;

      *  1: JSON;



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      *  2: XML;

      *  others are reserved.

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

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

   o  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.

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

   o  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.

3.3.  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

   o  Type: 1 octet describing the option type;

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



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

3.3.1.  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 senders 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:

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

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

   o  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.

   o  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.

3.4.  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.

   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.  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
   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.

4.1.  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.




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   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.

4.2.  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.

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

   The YANG model defined in Section 9 has two leaf's 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-fragment?  boolean
       +--rw max-fragment-size?  uint32

6.  YANG Module

<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.



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    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.";



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    }

    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>

7.  IANA Considerations

   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 [RFC6335].

   Service Name: udp-notif

   Transport Protocol(s): UDP

   Assignee: IESG <iesg@ietf.org>

   Contact: IETF Chair <chair@ietf.org>

   Description: UDP-based Publication Streaming Telemetry

   Reference: RFC XXXX

   Port Number: PORT-X



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   IANA is 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

8.  Security Considerations

   TBD

9.  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, and Yunan Gu for their
   constructive suggestions for improving this document.

10.  References

10.1.  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>.

   [RFC2914]  Floyd, S., "Congestion Control Principles", BCP 41,
              RFC 2914, DOI 10.17487/RFC2914, September 2000,
              <https://www.rfc-editor.org/info/rfc2914>.

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

   [RFC4347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security", RFC 4347, DOI 10.17487/RFC4347, April 2006,
              <https://www.rfc-editor.org/info/rfc4347>.





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   [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>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

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

   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry", BCP 165,
              RFC 6335, DOI 10.17487/RFC6335, August 2011,
              <https://www.rfc-editor.org/info/rfc6335>.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <https://www.rfc-editor.org/info/rfc6347>.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <https://www.rfc-editor.org/info/rfc7049>.

   [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>.

   [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>.

   [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>.

   [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>.





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   [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>.

10.2.  Informative References

   [I-D.ietf-netconf-distributed-notif]
              Zhou, T., Zheng, G., Voit, E., Graf, T., and P. Francois,
              "Subscription to Distributed Notifications", draft-ietf-
              netconf-distributed-notif-01 (work in progress), June
              2020.

   [I-D.ietf-netconf-https-notif]
              Jethanandani, M. and K. Watsen, "An HTTPS-based Transport
              for YANG Notifications", draft-ietf-netconf-https-notif-08
              (work in progress), February 2021.

   [I-D.ietf-netconf-notification-messages]
              Voit, E., Jenkins, T., Birkholz, H., Bierman, A., and A.
              Clemm, "Notification Message Headers and Bundles", draft-
              ietf-netconf-notification-messages-08 (work in progress),
              November 2019.

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
   Zuerich 8045
   Switzerland

   Email: thomas.graf@swisscom.com


   Pierre Francois
   INSA-Lyon
   Lyon
   France

   Email: pierre.francois@insa-lyon.fr


   Paolo Lucente
   NTT
   Siriusdreef 70-72
   Hoofddorp, WT 2132
   NL

   Email: paolo@ntt.net



























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