A YANG Data Model for NTP
draft-ietf-ntp-yang-data-model-14

Versions: (draft-wu-ntp-ntp-cfg)  00 01 02 03 04         Standards Track
          05 06 07 08 09 10 11 12 13 14                                 
NTP Working Group                                                  N. Wu
Internet-Draft                                             D. Dhody, Ed.
Intended status: Standards Track                                  Huawei
Expires: August 26, 2021                                   A. Sinha, Ed.
                                                            A. Kumar S N
                                                            RtBrick Inc.
                                                                 Y. Zhao
                                                                Ericsson
                                                       February 22, 2021


                       A YANG Data Model for NTP
                   draft-ietf-ntp-yang-data-model-14

Abstract

   This document defines a YANG data model for Network Time Protocol
   (NTP) implementations.  The data model includes configuration data
   and state data.

Requirements Language

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

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 August 26, 2021.







Wu, et al.               Expires August 26, 2021                [Page 1]


Internet-Draft                YANG for NTP                 February 2021


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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Operational State . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.3.  Tree Diagrams . . . . . . . . . . . . . . . . . . . . . .   3
     1.4.  Prefixes in Data Node Names . . . . . . . . . . . . . . .   3
     1.5.  References in the Model . . . . . . . . . . . . . . . . .   4
   2.  NTP data model  . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Relationship with NTPv4-MIB . . . . . . . . . . . . . . . . .   6
   4.  Relationship with RFC 7317  . . . . . . . . . . . . . . . . .   7
   5.  Access Rules  . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Key Management  . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  NTP Version . . . . . . . . . . . . . . . . . . . . . . . . .   8
   8.  NTP YANG Module . . . . . . . . . . . . . . . . . . . . . . .   8
   9.  Usage Example . . . . . . . . . . . . . . . . . . . . . . . .  38
     9.1.  Unicast association . . . . . . . . . . . . . . . . . . .  38
     9.2.  Refclock master . . . . . . . . . . . . . . . . . . . . .  40
     9.3.  Authentication configuration  . . . . . . . . . . . . . .  41
     9.4.  Access configuration  . . . . . . . . . . . . . . . . . .  42
     9.5.  Multicast configuration . . . . . . . . . . . . . . . . .  43
     9.6.  Manycast configuration  . . . . . . . . . . . . . . . . .  47
     9.7.  Clock state . . . . . . . . . . . . . . . . . . . . . . .  50
     9.8.  Get all association . . . . . . . . . . . . . . . . . . .  50
     9.9.  Global statistic  . . . . . . . . . . . . . . . . . . . .  52
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  52
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  53
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  54
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  54
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  54
     13.2.  Informative References . . . . . . . . . . . . . . . . .  56
   Appendix A.  Full YANG Tree . . . . . . . . . . . . . . . . . . .  57
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  60



Wu, et al.               Expires August 26, 2021                [Page 2]


Internet-Draft                YANG for NTP                 February 2021


1.  Introduction

   This document defines a YANG [RFC7950] data model for Network Time
   Protocol [RFC5905] implementations.

   The data model covers configuration of system parameters of NTP, such
   as access rules, authentication and VPN Routing and Forwarding (VRF)
   binding, and also associations of NTP in different modes and per-
   interface parameters.  It also provides information about running
   state of NTP implementations.

1.1.  Operational State

   NTP Operational State is included in the same tree as NTP
   configuration, consistent with Network Management Datastore
   Architecture (NMDA) [RFC8342].  NTP current state and statistics are
   also maintained in the operational state.  The operational state also
   includes the NTP association state.

1.2.  Terminology

   The terminology used in this document is aligned to [RFC5905].

1.3.  Tree Diagrams

   A simplified graphical representation of the data model is used in
   this document.  This document uses the graphical representation of
   data models defined in [RFC8340].

1.4.  Prefixes in Data Node Names

   In this document, names of data nodes and other data model objects
   are often used without a prefix, as long as it is clear from the
   context in which YANG module each name is defined.  Otherwise, names
   are prefixed using the standard prefix associated with the
   corresponding YANG module, as shown in Table 1.















Wu, et al.               Expires August 26, 2021                [Page 3]


Internet-Draft                YANG for NTP                 February 2021


            +----------+--------------------------+-----------+
            | Prefix   | YANG module              | Reference |
            +----------+--------------------------+-----------+
            | yang     | ietf-yang-types          | [RFC6991] |
            | inet     | ietf-inet-types          | [RFC6991] |
            | if       | ietf-interfaces          | [RFC8343] |
            | sys      | ietf-system              | [RFC7317] |
            | acl      | ietf-access-control-list | [RFC8519] |
            | rt-types | ietf-routing-types       | [RFC8294] |
            | nacm     | ietf-netconf-acm         | [RFC8341] |
            +----------+--------------------------+-----------+

             Table 1: Prefixes and corresponding YANG modules

1.5.  References in the Model

   Following documents are referenced in the model defined in this
   document -

   +-------------------------------------------------------+-----------+
   | Title                                                 | Reference |
   +-------------------------------------------------------+-----------+
   | Network Time Protocol Version 4: Protocol and         | [RFC5905] |
   | Algorithms Specification                              |           |
   | Common YANG Data Types                                | [RFC6991] |
   | A YANG Data Model for System Management               | [RFC7317] |
   | YANG Data Model for Key Chains                        | [RFC8177] |
   | Common YANG Data Types for the Routing Area           | [RFC8294] |
   | Network Configuration Access Control Model            | [RFC8341] |
   | A YANG Data Model for Interface Management            | [RFC8343] |
   | YANG Data Model for Network Access Control Lists      | [RFC8519] |
   | (ACLs)                                                |           |
   | Message Authentication Code for the Network Time      | [RFC8573] |
   | Protocol                                              |           |
   | The AES-CMAC Algorithm                                | [RFC4493] |
   | The MD5 Message-Digest Algorithm                      | [RFC1321] |
   | US Secure Hash Algorithm 1 (SHA1)                     | [RFC3174] |
   +-------------------------------------------------------+-----------+

                  Table 2: References in the YANG modules

2.  NTP data model

   This document defines the YANG module "ietf-ntp", which has the
   following condensed structure:

   module: ietf-ntp
     +--rw ntp!



Wu, et al.               Expires August 26, 2021                [Page 4]


Internet-Draft                YANG for NTP                 February 2021


        +--rw port?                    inet:port-number {ntp-port}?
        +--rw refclock-master!
        |  +--rw master-stratum?   ntp-stratum
        +--rw authentication {authentication}?
        |  +--rw auth-enabled?          boolean
        |  +--rw authentication-keys* [key-id]
        |     +--rw key-id       uint32
        |     |  ...
        +--rw access-rules {access-rules}?
        |  +--rw access-rule* [access-mode]
        |     +--rw access-mode    identityref
        |     +--rw acl?           -> /acl:acls/acl/name
        +--ro clock-state
        |  +--ro system-status
        |     +--ro clock-state                  identityref
        |     +--ro clock-stratum                ntp-stratum
        |     +--ro clock-refid                  refid
        |     |  ...
        +--rw unicast-configuration* [address type]
        |       {unicast-configuration}?
        |  +--rw address           inet:ip-address
        |  +--rw type              identityref
        |  |  ...
        +--ro associations* [address local-mode isconfigured]
        |  +--ro address           inet:ip-address
        |  +--ro local-mode        identityref
        |  +--ro isconfigured      boolean
        |  |  ...
        |  +--ro ntp-statistics
        |        ...
        |  +--rw interface* [name]
        |     +--rw name                if:interface-ref
        |     +--rw broadcast-server! {broadcast-server}?
        |     |  ...
        |     +--rw broadcast-client! {broadcast-client}?
        |     +--rw multicast-server* [address] {multicast-server}?
        |     |  +--rw address
        |     |  |       rt-types:ip-multicast-group-address
        |     |  |  ...
        |     +--rw multicast-client* [address] {multicast-client}?
        |     |  +--rw address    rt-types:ip-multicast-group-address
        |     +--rw manycast-server* [address] {manycast-server}?
        |     |  +--rw address    rt-types:ip-multicast-group-address
        |     +--rw manycast-client* [address] {manycast-client}?
        |        +--rw address
        |        |       rt-types:ip-multicast-group-address
        |        |  ...
        +--ro ntp-statistics



Wu, et al.               Expires August 26, 2021                [Page 5]


Internet-Draft                YANG for NTP                 February 2021


           +--...

   The full data model tree for the YANG module "ietf-ntp" is in
   Appendix A.

   This data model defines one top-level container which includes both
   the NTP configuration and the NTP running state including access
   rules, authentication, associations, unicast configurations,
   interfaces, system status and associations.

3.  Relationship with NTPv4-MIB

   If the device implements the NTPv4-MIB [RFC5907], data nodes from
   YANG module can be mapped to table entries in NTPv4-MIB.

   The following tables list the YANG data nodes with corresponding
   objects in the NTPv4-MIB.

   YANG NTP Configuration Data Nodes and Related NTPv4-MIB Objects

   +---------------------------------+---------------------------------+
   |  YANG data nodes in /ntp/clock- |        NTPv4-MIB objects        |
   |       state/system-status       |                                 |
   +---------------------------------+---------------------------------+
   |           clock-state           |     ntpEntStatusCurrentMode     |
   |          clock-stratum          |       ntpEntStatusStratum       |
   |           clock-refid           |  ntpEntStatusActiveRefSourceId  |
   |                                 | ntpEntStatusActiveRefSourceName |
   |         clock-precision         |       ntpEntTimePrecision       |
   |           clock-offset          |     ntpEntStatusActiveOffset    |
   |         root-dispersion         |      ntpEntStatusDispersion     |
   +---------------------------------+---------------------------------+

   +---------------------------------------+---------------------------+
   | YANG data nodes in /ntp/associations/ |     NTPv4-MIB objects     |
   +---------------------------------------+---------------------------+
   |                address                |    ntpAssocAddressType    |
   |                                       |      ntpAssocAddress      |
   |                stratum                |      ntpAssocStratum      |
   |                 refid                 |       ntpAssocRefId       |
   |                 offset                |       ntpAssocOffset      |
   |                 delay                 |    ntpAssocStatusDelay    |
   |               dispersion              |  ntpAssocStatusDispersion |
   |       ntp-statistics/packet-sent      |    ntpAssocStatOutPkts    |
   |     ntp-statistics/packet-received    |     ntpAssocStatInPkts    |
   |     ntp-statistics/packet-dropped     | ntpAssocStatProtocolError |
   +---------------------------------------+---------------------------+




Wu, et al.               Expires August 26, 2021                [Page 6]


Internet-Draft                YANG for NTP                 February 2021


   YANG NTP State Data Nodes and Related NTPv4-MIB Objects

4.  Relationship with RFC 7317

   This section describes the relationship with NTP definition in
   Section 3.2 System Time Management of [RFC7317] .  YANG data nodes in
   /ntp/ also support per-interface configuration which is not supported
   in /system/ntp.  If the yang model defined in this document is
   implemented, then /system/ntp SHOULD NOT be used and MUST be ignored.

    +-------------------------------+--------------------------------+
    |    YANG data nodes in /ntp/   | YANG data nodes in /system/ntp |
    +-------------------------------+--------------------------------+
    |              ntp!             |            enabled             |
    |     unicast-configuration     |             server             |
    |                               |          server/name           |
    | unicast-configuration/address |  server/transport/udp/address  |
    |   unicast-configuration/port  |   server/transport/udp/port    |
    |   unicast-configuration/type  |    server/association-type     |
    |  unicast-configuration/iburst |         server/iburst          |
    |  unicast-configuration/prefer |         server/prefer          |
    +-------------------------------+--------------------------------+

      YANG NTP Configuration Data Nodes and counterparts in RFC 7317
                                  Objects

5.  Access Rules

   An Access Control List (ACL) is one of the basic elements used to
   configure device-forwarding behavior.  An ACL is a user-ordered set
   of rules that is used to filter traffic on a networking device.

   As per [RFC1305] and [RFC5905], NTP could include an access-control
   feature that prevents unauthorized access and controls which peers
   are allowed to update the local clock.  Further it is useful to
   differentiate between the various kinds of access and attach a
   different acl-rule to each.  For this, the YANG module allows such
   configuration via /ntp/access-rules.  The access-rule itself is
   configured via [RFC8519].

   Following access modes are supported -

   o  Peer: Permit others to synchronize their time with the NTP entity
      or it can synchornize its time with others.  NTP control queries
      are also accepted.






Wu, et al.               Expires August 26, 2021                [Page 7]


Internet-Draft                YANG for NTP                 February 2021


   o  Server: Permit others to synchronize their time with the NTP
      entity, but vice versa is not supported.  NTP control queries are
      accepted.

   o  Server-only: Permit others to synchronize their time with NTP
      entity, but vice versa is not supported.  NTP control queries are
      not accepted.

   o  Query-only: Only control queries are accepted.

   Query-only is the most restricted where as the peer is the full
   access authority.  The ability to give different ACL rules for
   different access modes allows for a greater control by the operator.

6.  Key Management

   As per [RFC1305] and [RFC5905], when authentication is enabled, NTP
   employs a crypto-checksum, computed by the sender and checked by the
   receiver, together with a set of predistributed algorithms, and
   cryptographic keys indexed by a key identifier included in the NTP
   message.  This key-id is a 32-bit unsigned integer that MUST be
   configured on the NTP peers before the authentication could be used.
   For this reason, this YANG module allows such configuration via
   /ntp/authentication/authentication-keys/. Further at the time of
   configuration of NTP association (for example unicast-server), the
   key-id is specified.

7.  NTP Version

   This YANG model allow a version to be configured for the NTP
   association i.e. an operator can control the use of NTPv3 [RFC1305]
   or NTPv4 [RFC5905] for each association it forms.  This allows
   backward compatibility with a legacy system.

8.  NTP YANG Module

<CODE BEGINS> file "ietf-ntp@2021-02-22.yang"
module ietf-ntp {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-ntp";
  prefix ntp;

  import ietf-yang-types {
    prefix yang;
    reference
      "RFC 6991: Common YANG Data Types";
  }
  import ietf-inet-types {



Wu, et al.               Expires August 26, 2021                [Page 8]


Internet-Draft                YANG for NTP                 February 2021


    prefix inet;
    reference
      "RFC 6991: Common YANG Data Types";
  }
  import ietf-interfaces {
    prefix if;
    reference
      "RFC 8343: A YANG Data Model for Interface Management";
  }
  import ietf-system {
    prefix sys;
    reference
      "RFC 7317: A YANG Data Model for System Management";
  }
  import ietf-access-control-list {
    prefix acl;
    reference
      "RFC 8519: YANG Data Model for Network Access Control
       Lists (ACLs)";
  }
  import ietf-routing-types {
    prefix rt-types;
    reference
      "RFC 8294: Common YANG Data Types for the Routing Area";
  }
  import ietf-netconf-acm {
    prefix nacm;
    reference
      "RFC 8341: Network Configuration Protocol (NETCONF) Access
       Control Model";
  }

  organization
    "IETF NTP (Network Time Protocol) Working Group";
  contact
    "WG Web:  <http://tools.ietf.org/wg/ntp/>
     WG List:  <mailto: ntp@ietf.org
     Editor:   Dhruv Dhody
              <mailto:dhruv.ietf@gmail.com>
     Editor:   Ankit Kumar Sinha
              <mailto:ankit.ietf@gmail.com>";
  description
    "This document defines a YANG data model for Network Time Protocol
     (NTP) implementations. The data model includes configuration data
     and state data.

     Copyright (c) 2021 IETF Trust and the persons identified
     as authors of the code. All rights reserved.



Wu, et al.               Expires August 26, 2021                [Page 9]


Internet-Draft                YANG for NTP                 February 2021


     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.

     The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
     NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED',
     'MAY', and 'OPTIONAL' in this document are to be interpreted as
     described in BCP 14 (RFC 2119) (RFC 8174) when, and only when,
     they appear in all capitals, as shown here.";

  revision 2021-02-22 {
    description
      "Initial revision.";
    reference
      "RFC XXXX: A YANG Data Model for NTP.";
  }

  /* Note: The RFC Editor will replace XXXX with the number assigned
  to this document once it becomes an RFC.*/
  /* Typedef Definitions */

  typedef ntp-stratum {
    type uint8 {
      range "1..16";
    }
    description
      "The level of each server in the hierarchy is defined by
       a stratum. Primary servers are assigned with stratum
       one; secondary servers at each lower level are assigned with
       one stratum greater than the preceding level";
    reference
      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Section 3";
  }

  typedef ntp-version {
    type uint8;
    default "4";
    description
      "The current NTP version supported by corresponding
       association.";
    reference



Wu, et al.               Expires August 26, 2021               [Page 10]


Internet-Draft                YANG for NTP                 February 2021


      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Section 1";
  }

  typedef refid {
    type union {
      type inet:ipv4-address;
      type uint32;
      type string {
        length "4";
      }
    }
    description
      "A code identifying the particular server or reference
       clock.  The interpretation depends upon stratum. It
       could be an IPv4 address or first 32 bits of the MD5 hash of
       the IPv6 address or a string for the Reference Identifier
       and KISS codes. Some examples:
       -- a refclock ID like '127.127.1.0' for local clock sync
       -- uni/multi/broadcast associations for IPv4 will look like
       '203.0.113.1' and '0x4321FEDC' for IPv6
       -- sync with primary source will look like 'DCN', 'NIST',
       'ATOM'
       -- KISS codes will look like 'AUTH', 'DROP', 'RATE'
       Note that the use of MD5 hash for IPv6 address is not for
       cryptographic purposes ";
    reference
      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Section 7.3";
  }

  typedef ntp-date-and-time {
    type union {
      type yang:date-and-time;
      type uint8;
    }
    description
      "Follows the normal date-and-time format when valid value
       exist, otherwise allows for setting special value such as
       zero.";
  }

  /* features */

  feature ntp-port {
    description
      "Support for NTP port configuration";
    reference



Wu, et al.               Expires August 26, 2021               [Page 11]


Internet-Draft                YANG for NTP                 February 2021


      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Section 7.2";
  }

  feature authentication {
    description
      "Support for NTP symmetric key authentication";
    reference
      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Section 7.3";
  }

  feature deprecated {
    description
      "Support deprecated MD5-based authentication (RFC 8573) or
       SHA-1 or any other deprecated authentication.
       It is enabled to support legacy compatibility when secure
       cryptographic algorithm is not availaible to use.";
    reference
      "RFC 1321: The MD5 Message-Digest Algorithm
       RFC 3174: US Secure Hash Algorithm 1 (SHA1)";
  }

  feature hex-key-string {
    description
      "Support hexadecimal key string.";
  }

  feature access-rules {
    description
      "Support for NTP access control";
    reference
      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Section 9.2";
  }

  feature unicast-configuration {
    description
      "Support for NTP client/server or active/passive
       in unicast";
    reference
      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Section 3";
  }

  feature broadcast-server {
    description
      "Support for broadcast server";



Wu, et al.               Expires August 26, 2021               [Page 12]


Internet-Draft                YANG for NTP                 February 2021


    reference
      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Section 3";
  }

  feature broadcast-client {
    description
      "Support for broadcast client";
    reference
      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Section 3";
  }

  feature multicast-server {
    description
      "Support for multicast server";
    reference
      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Section 3.1";
  }

  feature multicast-client {
    description
      "Support for multicast client";
    reference
      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Section 3.1";
  }

  feature manycast-server {
    description
      "Support for manycast server";
    reference
      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Section 3.1";
  }

  feature manycast-client {
    description
      "Support for manycast client";
    reference
      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Section 3.1";
  }

  /* Identity */
  /* unicast-configurations types */




Wu, et al.               Expires August 26, 2021               [Page 13]


Internet-Draft                YANG for NTP                 February 2021


  identity unicast-configuration-type {
    if-feature "unicast-configuration";
    description
      "This defines NTP unicast mode of operation as used
       for unicast-configurations.";
  }

  identity uc-server {
    if-feature "unicast-configuration";
    base unicast-configuration-type;
    description
      "Use client association mode. This device
       will not provide synchronization to the
       configured NTP server.";
  }

  identity uc-peer {
    if-feature "unicast-configuration";
    base unicast-configuration-type;
    description
      "Use symmetric active association mode.
       This device may provide synchronization
       to the configured NTP server.";
  }

  /* association-modes */

  identity association-mode {
    description
      "The NTP association modes.";
    reference
      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Section 3";
  }

  identity active {
    base association-mode;
    description
      "Use symmetric active association mode (mode 1).
       This device may synchronize with its NTP peer,
       or provide synchronization to configured NTP peer.";
  }

  identity passive {
    base association-mode;
    description
      "Use symmetric passive association mode (mode 2).
       This device has learned this association dynamically.



Wu, et al.               Expires August 26, 2021               [Page 14]


Internet-Draft                YANG for NTP                 February 2021


       This device may synchronize with its NTP peer.";
  }

  identity client {
    base association-mode;
    description
      "Use client association mode (mode 3).
       This device will not provide synchronization
       to the configured NTP server.";
  }

  identity server {
    base association-mode;
    description
      "Use server association mode (mode 4).
       This device will provide synchronization to
       NTP clients.";
  }

  identity broadcast-server {
    base association-mode;
    description
      "Use broadcast server mode (mode 5).
       This mode defines that its either working
       as broadcast-server or multicast-server.";
  }

  identity broadcast-client {
    base association-mode;
    description
      "This mode defines that its either working
       as broadcast-client (mode 6) or multicast-client.";
  }

  /* access-mode */

  identity access-mode {
    if-feature "access-rules";
    description
      "This defines NTP access modes. These identifies
       how the ACL is applied with NTP.";
    reference
      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Section 9.2";
  }

  identity peer-access-mode {
    if-feature "access-rules";



Wu, et al.               Expires August 26, 2021               [Page 15]


Internet-Draft                YANG for NTP                 February 2021


    base access-mode;
    description
      "Permit others to synchronize their time with this NTP
       entity or it can synchornize its time with others.
       NTP control queries are also accepted. This enables
       full access authority.";
  }

  identity server-access-mode {
    if-feature "access-rules";
    base access-mode;
    description
      "Permit others to synchronize their time with this NTP
       entity, but vice versa is not supported. NTP control
       queries are accepted.";
  }

  identity server-only-access-mode {
    if-feature "access-rules";
    base access-mode;
    description
      "Permit others to synchronize their time with this NTP
       entity, but vice versa is not supported. NTP control
       queries are not accepted.";
  }

  identity query-only-access-mode {
    if-feature "access-rules";
    base access-mode;
    description
      "Only control queries are accepted.";
  }

  /* clock-state */

  identity clock-state {
    description
      "This defines NTP clock status at a high level.";
  }

  identity synchronized {
    base clock-state;
    description
      "Indicates that the local clock has been synchronized with
       an NTP server or the reference clock.";
  }

  identity unsynchronized {



Wu, et al.               Expires August 26, 2021               [Page 16]


Internet-Draft                YANG for NTP                 February 2021


    base clock-state;
    description
      "Indicates that the local clock has not been synchronized
       with any NTP server.";
  }

  /* ntp-sync-state */

  identity ntp-sync-state {
    description
      "This defines NTP clock sync state at a more granular
       level. Referred as 'Clock state definitions' in RFC 5905";
    reference
      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Appendix A.1.1";
  }

  identity clock-not-set {
    base ntp-sync-state;
    description
      "Indicates the clock is not updated.";
  }

  identity freq-set-by-cfg {
    base ntp-sync-state;
    description
      "Indicates the clock frequency is set by
       NTP configuration or file.";
  }

  identity spike {
    base ntp-sync-state;
    description
      "Indicates a spike is detected.";
  }

  identity freq {
    base ntp-sync-state;
    description
      "Indicates the frequency mode.";
  }

  identity clock-synchronized {
    base ntp-sync-state;
    description
      "Indicates that the clock is synchronized";
  }




Wu, et al.               Expires August 26, 2021               [Page 17]


Internet-Draft                YANG for NTP                 February 2021


  /* crypto-algorithm */

  identity crypto-algorithm {
    description
      "Base identity of cryptographic algorithm options.";
  }

  identity hmac-sha-1-12 {
    base crypto-algorithm;
    description
      "The HMAC-SHA1-12 algorithm.";
  }

  identity md5 {
    if-feature "deprecated";
    base crypto-algorithm;
    description
      "The MD5 algorithm. Note that RFC 8573
       deprecates the use of MD5-based authentication.";
  }

  identity sha-1 {
    if-feature "deprecated";
    base crypto-algorithm;
    description
      "The SHA-1 algorithm.";
  }

  identity hmac-sha-1 {
    base crypto-algorithm;
    description
      "HMAC-SHA-1 authentication algorithm.";
  }

  identity hmac-sha-256 {
    description
      "HMAC-SHA-256 authentication algorithm.";
  }

  identity hmac-sha-384 {
    description
      "HMAC-SHA-384 authentication algorithm.";
  }

  identity hmac-sha-512 {
    description
      "HMAC-SHA-512 authentication algorithm.";
  }



Wu, et al.               Expires August 26, 2021               [Page 18]


Internet-Draft                YANG for NTP                 February 2021


  identity aes-cmac {
    base crypto-algorithm;
    description
      "The AES-CMAC algorithm - required by
       RFC 8573 for MAC for the NTP";
    reference
      "RFC 4493: The AES-CMAC Algorithm";
  }

  /* Groupings */

  grouping key {
    description
      "The key.";
    nacm:default-deny-all;
    choice key-string-style {
      description
        "Key string styles";
      case keystring {
        leaf keystring {
          type string;
          description
            "Key string in ASCII format.";
        }
      }
      case hexadecimal {
        if-feature "hex-key-string";
        leaf hexadecimal-string {
          type yang:hex-string;
          description
            "Key in hexadecimal string format.  When compared
             to ASCII, specification in hexadecimal affords
             greater key entropy with the same number of
             internal key-string octets.  Additionally, it
             discourages usage of well-known words or
             numbers.";
        }
      }
    }
  }

  grouping authentication-key {
    description
      "To define an authentication key for a Network Time
       Protocol (NTP) time source.";
    nacm:default-deny-all;
    leaf key-id {
      type uint32 {



Wu, et al.               Expires August 26, 2021               [Page 19]


Internet-Draft                YANG for NTP                 February 2021


        range "1..max";
      }
      description
        "Authentication key identifier.";
    }
    leaf algorithm {
      type identityref {
        base crypto-algorithm;
      }
      description
        "Authentication algorithm. Note that RFC 8573
         deprecates the use of MD5-based authentication
         and recommends AES-CMAC.";
    }
    container key {
      uses key;
      description
        "The key. Note that RFC 8573 deprecates the use
         of MD5-based authentication.";
    }
    leaf istrusted {
      type boolean;
      description
        "Key-id is trusted or not";
    }
    reference
      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification, Section 7.3";
  }

  grouping authentication {
    description
      "Authentication.";
    choice authentication-type {
      description
        "Type of authentication.";
      case symmetric-key {
        leaf key-id {
          type leafref {
            path "/ntp:ntp/ntp:authentication/"
               + "ntp:authentication-keys/ntp:key-id";
          }
          description
            "Authentication key id referenced in this
             association.";
        }
      }
    }



Wu, et al.               Expires August 26, 2021               [Page 20]


Internet-Draft                YANG for NTP                 February 2021


  }

  grouping statistics {
    description
      "NTP packet statistic.";
    leaf discontinuity-time {
      type ntp-date-and-time;
      description
        "The time on the most recent occasion at which any one or
         more of this NTP counters suffered a discontinuity. If
         no such discontinuities have occurred, then this node
         contains the time the NTP association was
         (re-)initialized.";
    }
    leaf packet-sent {
      type yang:counter32;
      description
        "The total number of NTP packets delivered to the
         transport service by this NTP entity for this
         association.
         Discontinuities in the value of this counter can occur
         upon cold start or reinitialization of the NTP entity, the
         management system and at other times.";
    }
    leaf packet-sent-fail {
      type yang:counter32;
      description
        "The number of times NTP packets sending failed.";
    }
    leaf packet-received {
      type yang:counter32;
      description
        "The total number of NTP packets delivered to the
         NTP entity from this association.
         Discontinuities in the value of this counter can occur
         upon cold start or reinitialization of the NTP entity, the
         management system and at other times.";
    }
    leaf packet-dropped {
      type yang:counter32;
      description
        "The total number of NTP packets that were delivered
         to this NTP entity from this association and this entity
         was not able to process due to an NTP protocol error.
         Discontinuities in the value of this counter can occur
         upon cold start or reinitialization of the NTP entity, the
         management system and at other times.";
    }



Wu, et al.               Expires August 26, 2021               [Page 21]


Internet-Draft                YANG for NTP                 February 2021


  }

  grouping common-attributes {
    description
      "NTP common attributes for configuration.";
    leaf minpoll {
      type int8;
      default "6";
      description
        "The minimum poll interval used in this association.";
      reference
        "RFC 5905: Network Time Protocol Version 4: Protocol and
         Algorithms Specification, Section 7.2";
    }
    leaf maxpoll {
      type int8;
      default "10";
      description
        "The maximum poll interval used in this association.";
      reference
        "RFC 5905: Network Time Protocol Version 4: Protocol and
         Algorithms Specification, Section 7.2";
    }
    leaf port {
      if-feature "ntp-port";
      type inet:port-number {
        range "123 | 1025..max";
      }
      default "123";
      description
        "Specify the port used to send NTP packets.";
      reference
        "RFC 5905: Network Time Protocol Version 4: Protocol and
         Algorithms Specification, Section 7.2";
    }
    leaf version {
      type ntp-version;
      description
        "NTP version.";
    }
    reference
      "RFC 5905: Network Time Protocol Version 4: Protocol and
       Algorithms Specification";
  }

  grouping association-ref {
    description
      "Reference to NTP association mode";



Wu, et al.               Expires August 26, 2021               [Page 22]


Internet-Draft                YANG for NTP                 February 2021


    leaf associations-address {
      type leafref {
        path "/ntp:ntp/ntp:associations/ntp:address";
      }
      description
        "Indicates the association's address
         which result in clock synchronization.";
    }
    leaf associations-local-mode {
      type leafref {
        path "/ntp:ntp/ntp:associations/ntp:local-mode";
      }
      description
        "Indicates the association's local-mode
         which result in clock synchronization.";
    }
    leaf associations-isconfigured {
      type leafref {
        path "/ntp:ntp/ntp:associations/"
           + "ntp:isconfigured";
      }
      description
        "The association was configured or dynamic
         which result in clock synchronization.";
    }
  }

  /* Configuration data nodes */

  container ntp {
    when 'false() = boolean(/sys:system/sys:ntp)' {
      description
        "Applicable when the system /sys/ntp/ is not used.";
    }
    presence "NTP is enabled and system should attempt to
              synchronize the system clock with an NTP server
              from the 'ntp/associations' list.";
    description
      "Configuration parameters for NTP.";
    leaf port {
      if-feature "ntp-port";
      type inet:port-number {
        range "123 | 1025..max";
      }
      default "123";
      description
        "Specify the port used to send and receive NTP packets.";
      reference



Wu, et al.               Expires August 26, 2021               [Page 23]


Internet-Draft                YANG for NTP                 February 2021


        "RFC 5905: Network Time Protocol Version 4: Protocol and
         Algorithms Specification, Section 7.2";
    }
    container refclock-master {
      presence "NTP master clock is enabled.";
      description
        "Configures the local clock of this device as NTP server.";
      leaf master-stratum {
        type ntp-stratum;
        default "16";
        description
          "Stratum level from which NTP clients get their time
           synchronized.";
      }
    }
    container authentication {
      if-feature "authentication";
      description
        "Configuration of authentication.";
      leaf auth-enabled {
        type boolean;
        default "false";
        description
          "Controls whether NTP authentication is enabled
           or disabled on this device.";
      }
      list authentication-keys {
        key "key-id";
        uses authentication-key;
        description
          "List of authentication keys.";
      }
    }
    container access-rules {
      if-feature "access-rules";
      description
        "Configuration to control access to NTP service
         by using NTP access-group feature.
         The access-mode identifies how the acl is
         applied with NTP.";
      list access-rule {
        key "access-mode";
        description
          "List of access rules.";
        leaf access-mode {
          type identityref {
            base access-mode;
          }



Wu, et al.               Expires August 26, 2021               [Page 24]


Internet-Draft                YANG for NTP                 February 2021


          description
            "NTP access mode. The definition of each possible value:
             peer: Both time request and control query can be
             performed.
             server: Enables the server access and query.
             synchronization: Enables the server access only.
             query: Enables control query only.";
        }
        leaf acl {
          type leafref {
            path "/acl:acls/acl:acl/acl:name";
          }
          description
            "Control access configuration to be used.";
        }
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
           Algorithms Specification, Section 9.2";
      }
    }
    container clock-state {
      config false;
      description
        "Clock operational state of the NTP.";
      container system-status {
        description
          "System status of NTP.";
        leaf clock-state {
          type identityref {
            base clock-state;
          }
          mandatory true;
          description
            "The state of system clock. The definition of each
             possible value is:
             synchronized: Indicates local clock is synchronized.
             unsynchronized: Indicates local clock is not
             synchronized.";
        }
        leaf clock-stratum {
          type ntp-stratum;
          mandatory true;
          description
            "The NTP entity's own stratum value. Should be one greater
             than preceeding level. 16 if unsyncronized.";
          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol and
             Algorithms Specification, Section 3";



Wu, et al.               Expires August 26, 2021               [Page 25]


Internet-Draft                YANG for NTP                 February 2021


        }
        leaf clock-refid {
          type refid;
          mandatory true;
          description
            "A code identifying the particular server or reference
             clock.  The interpretation depends upon stratum. It
             could be an IPv4 address or first 32 bits of the MD5 hash
             of the IPv6 address or a string for the Reference
             Identifier and KISS codes. Some examples:
             -- a refclock ID like '127.127.1.0' for local clock sync
             -- uni/multi/broadcast associations for IPv4 will look like
             '203.0.113.1' and '0x4321FEDC' for IPv6
             -- sync with primary source will look like 'DCN', 'NIST',
             'ATOM'
             -- KISS codes will look like 'AUTH', 'DROP', 'RATE'
             Note that the use of MD5 hash for IPv6 address is not for
             cryptographic purposes ";
          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol and
             Algorithms Specification, Section 7.3";
        }
        uses association-ref {
          description
            "Reference to Association.";
        }
        leaf nominal-freq {
          type decimal64 {
            fraction-digits 4;
          }
          units "Hz";
          mandatory true;
          description
            "The nominal frequency of the local clock. An ideal
             frequency with zero uncertainty.";
        }
        leaf actual-freq {
          type decimal64 {
            fraction-digits 4;
          }
          units "Hz";
          mandatory true;
          description
            "The actual frequency of the local clock.";
        }
        leaf clock-precision {
          type int8;
          units "Hz";



Wu, et al.               Expires August 26, 2021               [Page 26]


Internet-Draft                YANG for NTP                 February 2021


          mandatory true;
          description
            "Clock precision of this system in integer format
             (prec=2^(-n)). A value of 5 would mean 2^-5 = 31.25 ms.";
          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol and
             Algorithms Specification, Section 7.3";
        }
        leaf clock-offset {
          type decimal64 {
            fraction-digits 3;
          }
          units "milliseconds";
          description
            "The time offset to the current selected reference time
             source e.g., '0.032ms' or '1.232ms'.";
          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol and
             Algorithms Specification, Section 9.1";
        }
        leaf root-delay {
          type decimal64 {
            fraction-digits 3;
          }
          units "milliseconds";
          description
            "Total delay along the path to root clock.";
          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol and
             Algorithms Specification, Section 4 and 7.3";
        }
        leaf root-dispersion {
          type decimal64 {
            fraction-digits 3;
          }
          units "milliseconds";
          description
            "The dispersion between the local clock
             and the root clock, e.g., '6.927ms'.";
          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol and
             Algorithms Specification, Section 4 and 7.3";
        }
        leaf reference-time {
          type ntp-date-and-time;
          description
            "The reference timestamp. Time when the system clock was
             last set or corrected";



Wu, et al.               Expires August 26, 2021               [Page 27]


Internet-Draft                YANG for NTP                 February 2021


          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol and
             Algorithms Specification, Section 7.3";
        }
        leaf sync-state {
          type identityref {
            base ntp-sync-state;
          }
          mandatory true;
          description
            "The synchronization status of the local clock. Referred to
             as 'Clock state definitions' in RFC 5905";
          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol and
             Algorithms Specification, Appendix A.1.1";
        }
      }
    }
    list unicast-configuration {
      if-feature "unicast-configuration";
      key "address type";
      description
        "List of NTP unicast-configurations.";
      leaf address {
        type inet:ip-address;
        description
          "Address of this association.";
      }
      leaf type {
        type identityref {
          base unicast-configuration-type;
        }
        description
          "Use client association mode.  This device
           will not provide synchronization to the
           configured NTP server.";
      }
      container authentication {
        if-feature "authentication";
        description
          "Authentication used for this association.";
        uses authentication;
      }
      leaf prefer {
        type boolean;
        default "false";
        description
          "Whether this association is preferred or not.";



Wu, et al.               Expires August 26, 2021               [Page 28]


Internet-Draft                YANG for NTP                 February 2021


      }
      leaf burst {
        type boolean;
        default "false";
        description
          "If set, a series of packets are sent instead of a single
           packet within each synchronization interval to achieve
           faster synchronization.";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
           Algorithms Specification, Section 13.1";
      }
      leaf iburst {
        type boolean;
        default "false";
        description
          "If set, a series of packets are sent instead of a single
           packet within the initial synchronization interval to
           achieve faster initial synchronization.";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
           Algorithms Specification, Section 13.1";
      }
      leaf source {
        type if:interface-ref;
        description
          "The interface whose IP address is used by this association
           as the source address.";
      }
      uses common-attributes {
        description
          "Common attributes like port, version, min and max
           poll.";
      }
    }
    list associations {
      key "address local-mode isconfigured";
      config false;
      description
        "List of NTP associations. Here address, local-mode
         and isconfigured are required to uniquely identify
         a particular association. Lets take following examples -

         1) If RT1 acting as broadcast server,
         and RT2 acting as broadcast client, then RT2
         will form dynamic association with address as RT1,
         local-mode as client and isconfigured as false.




Wu, et al.               Expires August 26, 2021               [Page 29]


Internet-Draft                YANG for NTP                 February 2021


         2) When RT2 is configured
         with unicast-server RT1, then RT2 will form
         association with address as RT1, local-mode as client
         and isconfigured as true.

         Thus all 3 leaves are needed as key to unique identify
         the association.";
      leaf address {
        type inet:ip-address;
        description
          "The address of this association. Represents the IP
           address of a unicast/multicast/broadcast address.";
      }
      leaf local-mode {
        type identityref {
          base association-mode;
        }
        description
          "Local mode of this NTP association.";
      }
      leaf isconfigured {
        type boolean;
        description
          "Indicates if this association is configured or
           dynamically learned.";
      }
      leaf stratum {
        type ntp-stratum;
        description
          "The association stratum value.";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
           Algorithms Specification, Section 3";
      }
      leaf refid {
        type refid;
        description
          "A code identifying the particular server or reference
           clock.  The interpretation depends upon stratum. It
           could be an IPv4 address or first 32 bits of the MD5 hash of
           the IPv6 address or a string for the Reference Identifier
           and KISS codes. Some examples:
           -- a refclock ID like '127.127.1.0' for local clock sync
           -- uni/multi/broadcast associations for IPv4 will look like
           '203.0.113.1' and '0x4321FEDC' for IPv6
           -- sync with primary source will look like 'DCN', 'NIST',
           'ATOM'
           -- KISS codes will look like 'AUTH', 'DROP', 'RATE'



Wu, et al.               Expires August 26, 2021               [Page 30]


Internet-Draft                YANG for NTP                 February 2021


           Note that the use of MD5 hash for IPv6 address is not for
           cryptographic purposes";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
           Algorithms Specification, Section 7.3";
      }
      leaf authentication {
        if-feature "authentication";
        type leafref {
          path "/ntp:ntp/ntp:authentication/"
             + "ntp:authentication-keys/ntp:key-id";
        }
        description
          "Authentication Key used for this association.";
      }
      leaf prefer {
        type boolean;
        default "false";
        description
          "Indicates if this association is preferred.";
      }
      leaf peer-interface {
        type if:interface-ref;
        description
          "The interface which is used for communication.";
      }
      uses common-attributes {
        description
          "Common attributes like port, version, min and
           max poll.";
      }
      leaf reach {
        type uint8;
        description
          "The reachability of the configured
           server or peer.";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
           Algorithms Specification, Section 9.2 and 13";
      }
      leaf unreach {
        type uint8;
        description
          "The unreachability of the configured
           server or peer.";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
           Algorithms Specification, Section 9.2 and 13";



Wu, et al.               Expires August 26, 2021               [Page 31]


Internet-Draft                YANG for NTP                 February 2021


      }
      leaf poll {
        type int8;
        units "seconds";
        description
          "The polling interval for current association";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
           Algorithms Specification, Section 7.3";
      }
      leaf now {
        type uint32;
        units "seconds";
        description
          "The time since the last NTP packet was
           received or last synchronized.";
      }
      leaf offset {
        type decimal64 {
          fraction-digits 3;
        }
        units "milliseconds";
        description
          "The offset between the local clock
           and the peer clock, e.g., '0.032ms' or '1.232ms'";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
           Algorithms Specification, Section 8";
      }
      leaf delay {
        type decimal64 {
          fraction-digits 3;
        }
        units "milliseconds";
        description
          "The network delay between the local clock
           and the peer clock.";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
           Algorithms Specification, Section 8";
      }
      leaf dispersion {
        type decimal64 {
          fraction-digits 3;
        }
        units "milliseconds";
        description
          "The root dispersion between the local clock



Wu, et al.               Expires August 26, 2021               [Page 32]


Internet-Draft                YANG for NTP                 February 2021


           and the peer clock.";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
           Algorithms Specification, Section 10";
      }
      leaf originate-time {
        type ntp-date-and-time;
        description
          "This is the local time, in timestamp format,
           when latest NTP packet was sent to peer (called T1).";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
           Algorithms Specification, Section 8";
      }
      leaf receive-time {
        type ntp-date-and-time;
        description
          "This is the local time, in timestamp format,
           when latest NTP packet arrived at peer (called T2).
           If the peer becomes unreachable the value is set to zero.";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
           Algorithms Specification, Section 8";
      }
      leaf transmit-time {
        type ntp-date-and-time;
        description
          "This is the local time, in timestamp format,
           at which the NTP packet departed the peer (called T3).
           If the peer becomes unreachable the value is set to zero.";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
           Algorithms Specification, Section 8";
      }
      leaf input-time {
        type ntp-date-and-time;
        description
          "This is the local time, in timestamp format,
           when the latest NTP message from the peer arrived (called
           T4). If the peer becomes unreachable the value is set to
           zero.";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
           Algorithms Specification, Section 8";
      }
      container ntp-statistics {
        description
          "Per Peer packet send and receive statistics.";



Wu, et al.               Expires August 26, 2021               [Page 33]


Internet-Draft                YANG for NTP                 February 2021


        uses statistics {
          description
            "NTP send and receive packet statistics.";
        }
      }
    }
    container interfaces {
      description
        "Configuration parameters for NTP interfaces.";
      list interface {
        key "name";
        description
          "List of interfaces.";
        leaf name {
          type if:interface-ref;
          description
            "The interface name.";
        }
        container broadcast-server {
          if-feature "broadcast-server";
          presence "NTP broadcast-server is configured";
          description
            "Configuration of broadcast server.";
          leaf ttl {
            type uint8;
            description
              "Specifies the time to live (TTL) for a
               broadcast packet.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
               Algorithms Specification, Section 3.1";
          }
          container authentication {
            if-feature "authentication";
            description
              "Authentication used for this association.";
            uses authentication;
          }
          uses common-attributes {
            description
              "Common attributes such as port, version, min and
               max poll.";
          }
          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol and
             Algorithms Specification, Section 3.1";
        }
        container broadcast-client {



Wu, et al.               Expires August 26, 2021               [Page 34]


Internet-Draft                YANG for NTP                 February 2021


          if-feature "broadcast-client";
          presence "NTP broadcast-client is configured.";
          description
            "Configuration of broadcast-client.";
          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol and
             Algorithms Specification, Section 3.1";
        }
        list multicast-server {
          if-feature "multicast-server";
          key "address";
          description
            "Configuration of multicast server.";
          leaf address {
            type rt-types:ip-multicast-group-address;
            description
              "The IP address to send NTP multicast packets.";
          }
          leaf ttl {
            type uint8;
            description
              "Specifies the time to live (TTL) for a
               multicast packet.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
               Algorithms Specification, Section 3.1";
          }
          container authentication {
            if-feature "authentication";
            description
              "Authentication used for this association.";
            uses authentication;
          }
          uses common-attributes {
            description
              "Common attributes such as port, version, min and
               max poll.";
          }
          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol and
             Algorithms Specification, Section 3.1";
        }
        list multicast-client {
          if-feature "multicast-client";
          key "address";
          description
            "Configuration of multicast-client.";
          leaf address {



Wu, et al.               Expires August 26, 2021               [Page 35]


Internet-Draft                YANG for NTP                 February 2021


            type rt-types:ip-multicast-group-address;
            description
              "The IP address of the multicast group to
               join.";
          }
          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol and
             Algorithms Specification, Section 3.1";
        }
        list manycast-server {
          if-feature "manycast-server";
          key "address";
          description
            "Configuration of manycast server.";
          leaf address {
            type rt-types:ip-multicast-group-address;
            description
              "The multicast group IP address to receive
               manycast client messages.";
          }
          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol and
             Algorithms Specification, Section 3.1";
        }
        list manycast-client {
          if-feature "manycast-client";
          key "address";
          description
            "Configuration of manycast-client.";
          leaf address {
            type rt-types:ip-multicast-group-address;
            description
              "The group IP address that the manycast client
               broadcasts the request message to.";
          }
          container authentication {
            if-feature "authentication";
            description
              "Authentication used for this association.";
            uses authentication;
          }
          leaf ttl {
            type uint8;
            description
              "Specifies the maximum time to live (TTL) for
               the expanding ring search.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and



Wu, et al.               Expires August 26, 2021               [Page 36]


Internet-Draft                YANG for NTP                 February 2021


               Algorithms Specification, Section 3.1";
          }
          leaf minclock {
            type uint8;
            description
              "The minimum manycast survivors in this
               association.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
               Algorithms Specification, Section 13.2";
          }
          leaf maxclock {
            type uint8;
            description
              "The maximum manycast candidates in this
               association.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
               Algorithms Specification, Section 13.2";
          }
          leaf beacon {
            type int8;
            units "seconds";
            description
              "The beacon is the upper limit of poll interval. When the
               ttl reaches its limit without finding the minimum number
               of manycast servers, the poll interval increases until
               reaching the beacon value, when it starts over from the
               beginning.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
               Algorithms Specification, Section 13.2";
          }
          uses common-attributes {
            description
              "Common attributes like port, version, min and
               max poll.";
          }
          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol and
             Algorithms Specification, Section 3.1";
        }
      }
    }
    container ntp-statistics {
      config false;
      description
        "Total NTP packet statistics.";



Wu, et al.               Expires August 26, 2021               [Page 37]


Internet-Draft                YANG for NTP                 February 2021


      uses statistics {
        description
          "NTP send and receive packet statistics.";
      }
    }
  }
}
<CODE ENDS>

9.  Usage Example

   This section include examples for illustration purposes.

   Note: '\' line wrapping per [RFC8792].

9.1.  Unicast association

   This example describes how to configure a preferred unicast server
   present at 192.0.2.1 running at port 1025 with authentication-key 10
   and version 4 (default).

     <edit-config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
       <target>
         <running/>
       </target>
       <config>
         <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
           <unicast-configuration>
             <address>192.0.2.1</address>
             <type>uc-server</type>
             <prefer>true</prefer>
             <port>1025</port>
             <authentication>
               <symmetric-key>
                 <key-id>10</key-id>
               </symmetric-key>
             </authentication>
           </unicast-configuration>
         </ntp>
       </config>
     </edit-config>

   An example with IPv6 would used the an IPv6 address (say 2001:db8::1)
   in the "address" leaf with no change in any other data tree.







Wu, et al.               Expires August 26, 2021               [Page 38]


Internet-Draft                YANG for NTP                 February 2021


     <edit-config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
       <target>
         <running/>
       </target>
       <config>
         <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
           <unicast-configuration>
             <address>2001:db8::1</address>
             <type>uc-server</type>
             <prefer>true</prefer>
             <port>1025</port>
             <authentication>
               <symmetric-key>
                 <key-id>10</key-id>
               </symmetric-key>
             </authentication>
           </unicast-configuration>
         </ntp>
       </config>
     </edit-config>

   This example is for retrieving unicast configurations -

   <get>
     <filter type="subtree">
     <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <unicast-configuration>
         </unicast-configuration>
     </ntp>
     </filter>
   </get>

   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
       <unicast-configuration>
         <address>192.0.2.1</address>
         <type>uc-server</type>
           <authentication>
             <symmetric-key>
               <key-id>10</key-id>
             </symmetric-key>
           </authentication>
         <prefer>true</prefer>
         <burst>false</burst>
         <iburst>true</iburst>
         <source/>
         <minpoll>6</minpoll>
         <maxpoll>10</maxpoll>



Wu, et al.               Expires August 26, 2021               [Page 39]


Internet-Draft                YANG for NTP                 February 2021


         <port>1025</port>
         <stratum>9</stratum>
         <refid>203.0.113.1</refid>
         <reach>255</reach>
         <unreach>0</unreach>
         <poll>128</poll>
         <now>10</now>
         <offset>0.025</offset>
         <delay>0.5</delay>
         <dispersion>0.6</dispersion>
         <originate-time>10-10-2017 07:33:55.253 Z+05:30\
         </originate-time>
         <receive-time>10-10-2017 07:33:55.258 Z+05:30\
         </receive-time>
         <transmit-time>10-10-2017 07:33:55.300 Z+05:30\
         </transmit-time>
         <input-time>10-10-2017 07:33:55.305 Z+05:30\
         </input-time>
         <ntp-statistics>
           <packet-sent>20</packet-sent>
           <packet-sent-fail>0</packet-sent-fail>
           <packet-received>20</packet-received>
           <packet-dropped>0</packet-dropped>
         </ntp-statistics>
       </unicast-configuration>
     </ntp>
   </data>

9.2.  Refclock master

   This example describes how to configure reference clock with stratum
   8 -

   <edit-config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <target>
       <running/>
     </target>
     <config>
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <refclock-master>
           <master-stratum>8</master-stratum>
         </refclock-master>
       </ntp>
     </config>
   </edit-config>

   This example describes how to get reference clock configuration -




Wu, et al.               Expires August 26, 2021               [Page 40]


Internet-Draft                YANG for NTP                 February 2021


   <get>
     <filter type="subtree">
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <refclock-master>
         </refclock-master>
       </ntp>
     </filter>
   </get>

   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
       <refclock-master>
         <master-stratum>8</master-stratum>
       </refclock-master>
     </ntp>
   </data>

9.3.  Authentication configuration

   This example describes how to enable authentication and configure
   trusted authentication key 10 with mode as AES-CMAC and an
   hexadecimal string key -

   <edit-config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <target>
       <running/>
     </target>
     <config>
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <authentication>
           <auth-enabled>true</auth-enabled>
           <authentication-keys>
             <key-id>10</key-id>
             <algorithm>aes-cmac</algorithm>
             <key>
               <hexadecimal-string>
                 bb1d6929e95937287fa37d129b756746
               </hexadecimal-string>
             </key>
             <istrusted>true</istrusted>
           </authentication-keys>
         </authentication>
       </ntp>
     </config>
   </edit-config>

   This example describes how to get authentication related
   configuration -



Wu, et al.               Expires August 26, 2021               [Page 41]


Internet-Draft                YANG for NTP                 February 2021


   <get>
     <filter type="subtree">
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <authentication>
         </authentication>
       </ntp>
     </filter>
   </get>

   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
       <authentication>
         <auth-enabled>false</auth-enabled>
         <trusted-keys/>
         <authentication-keys>
           <key-id>10</key-id>
           <algorithm>aes-cmac</algorithm>
             <key>
               <hexadecimal-string>
                 bb1d6929e95937287fa37d129b756746
               </hexadecimal-string>
             </key>
           <istrusted>true</istrusted>
         </authentication-keys>
       </authentication>
     </ntp>
   </data>

9.4.  Access configuration

   This example describes how to configure access mode "peer" associated
   with acl 2000 -

   <edit-config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <target>
       <running/>
     </target>
     <config>
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <access-rules>
           <access-rule>
             <access-mode>peer-access-mode</access-mode>
             <acl>2000</acl>
           </access-rule>
         </access-rules>
       </ntp>
     </config>
   </edit-config>



Wu, et al.               Expires August 26, 2021               [Page 42]


Internet-Draft                YANG for NTP                 February 2021


   This example describes how to get access related configuration -

   <get>
     <filter type="subtree">
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <access-rules>
         </access-rules>
       </ntp>
     </filter>
   </get>

   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
       <access-rules>
         <access-rule>
           <access-mode>peer-access-mode</access-mode>
           <acl>2000</acl>
         </access-rule>
       </access-rules>
     </ntp>
   </data>

9.5.  Multicast configuration

   This example describes how to configure multicast-server with address
   as "224.0.1.1", port as 1025, and version as 3 and authentication
   keyid as 10 -
























Wu, et al.               Expires August 26, 2021               [Page 43]


Internet-Draft                YANG for NTP                 February 2021


   <edit-config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <target>
       <running/>
     </target>
     <config>
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <interfaces>
           <interface>
             <name>Ethernet3/0/0</name>
             <multicast-server>
               <address>224.0.1.1</address>
               <authentication>
                 <symmetric-key>
                   <key-id>10</key-id>
                 </symmetric-key>
               </authentication>
               <port>1025</port>
               <version>3</version>
             </multicast-server>
           </interface>
         </interfaces>
       </ntp>
     </config>
   </edit-config>

   This example describes how to get multicast-server related
   configuration -
























Wu, et al.               Expires August 26, 2021               [Page 44]


Internet-Draft                YANG for NTP                 February 2021


   <get>
     <filter type="subtree">
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <interfaces>
           <interface>
             <multicast-server>
             </multicast-server>
           </interface>
         </interfaces>
       </ntp>
     </filter>
   </get>

   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
       <interfaces>
         <interface>
           <name>Ethernet3/0/0</name>
           <multicast-server>
             <address>224.0.1.1</address>
             <ttl>8</ttl>
             <authentication>
               <symmetric-key>
                 <key-id>10</key-id>
               </symmetric-key>
             </authentication>
             <minpoll>6</minpoll>
             <maxpoll>10</maxpoll>
             <port>1025</port>
             <version>3</version>
           </multicast-server>
         </interface>
       </interfaces>
     </ntp>
   </data>

   This example describes how to configure multicast-client with address
   as "224.0.1.1" -













Wu, et al.               Expires August 26, 2021               [Page 45]


Internet-Draft                YANG for NTP                 February 2021


   <edit-config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <target>
       <running/>
     </target>
     <config>
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <interfaces>
           <interface>
             <name>Ethernet3/0/0</name>
             <multicast-client>
               <address>224.0.1.1</address>
             </multicast-client>
           </interface>
         </interfaces>
       </ntp>
     </config>
   </edit-config>

   This example describes how to get multicast-client related
   configuration -

   <get>
     <filter type="subtree">
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <interfaces>
           <interface>
             <multicast-client>
             </multicast-client>
           </interface>
         </interfaces>
       </ntp>
     </filter>
   </get>

   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
       <interfaces>
         <interface>
           <name>Ethernet3/0/0</name>
           <multicast-client>
             <address>224.0.1.1</address>
           </multicast-client>
         </interface>
       </interfaces>
     </ntp>
   </data>





Wu, et al.               Expires August 26, 2021               [Page 46]


Internet-Draft                YANG for NTP                 February 2021


9.6.  Manycast configuration

   This example describes how to configure manycast-client with address
   as "224.0.1.1", port as 1025 and authentication keyid as 10 -

   <edit-config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <target>
       <running/>
     </target>
     <config>
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <interfaces>
           <interface>
             <name>Ethernet3/0/0</name>
             <manycast-client>
               <address>224.0.1.1</address>
               <authentication>
                 <symmetric-key>
                   <key-id>10</key-id>
                 </symmetric-key>
               </authentication>
               <port>1025</port>
             </manycast-client>
           </interface>
         </interfaces>
       </ntp>
     </config>
   </edit-config>

   This example describes how to get manycast-client related
   configuration -




















Wu, et al.               Expires August 26, 2021               [Page 47]


Internet-Draft                YANG for NTP                 February 2021


   <get>
     <filter type="subtree">
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <interfaces>
           <interface>
             <manycast-client>
             </manycast-client>
           </interface>
         </interfaces>
       </ntp>
     </filter>
   </get>

   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
       <interfaces>
         <interface>
           <name>Ethernet3/0/0</name>
           <manycast-client>
             <address>224.0.1.1</address>
             <authentication>
               <symmetric-key>
                 <key-id>10</key-id>
               </symmetric-key>
             </authentication>
             <ttl>8</ttl>
             <minclock>3</minclock>
             <maxclock>10</maxclock>
             <beacon>6</beacon>
             <minpoll>6</minpoll>
             <maxpoll>10</maxpoll>
             <port>1025</port>
           </manycast-client>
         </interface>
       </interfaces>
     </ntp>
   </data>

   This example describes how to configure manycast-server with address
   as "224.0.1.1" -











Wu, et al.               Expires August 26, 2021               [Page 48]


Internet-Draft                YANG for NTP                 February 2021


   <edit-config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <target>
       <running/>
     </target>
     <config>
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <interfaces>
           <interface>
             <name>Ethernet3/0/0</name>
             <manycast-server>
               <address>224.0.1.1</address>
             </manycast-server>
           </interface>
         </interfaces>
       </ntp>
     </config>
   </edit-config>

   This example describes how to get manycast-server related
   configuration -

   <get>
     <filter type="subtree">
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <interfaces>
           <interface>
             <manycast-server>
             </manycast-server>
           </interface>
         </interfaces>
       </ntp>
     </filter>
   </get>

   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
       <interfaces>
         <interface>
           <name>Ethernet3/0/0</name>
           <manycast-server>
             <address>224.0.1.1</address>
           </manycast-server>
         </interface>
       </interfaces>
     </ntp>
   </data>





Wu, et al.               Expires August 26, 2021               [Page 49]


Internet-Draft                YANG for NTP                 February 2021


9.7.  Clock state

   This example describes how to get clock current state -

   <get>
     <filter type="subtree">
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <clock-state>
         </clock-state>
       </ntp>
     </filter>
   </get>

   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
       <clock-state>
         <system-status>
           <clock-state>synchronized</clock-state>
           <clock-stratum>7</clock-stratum>
           <clock-refid>192.0.2.1</clock-refid>
           <associations-address>192.0.2.1\
           </associations-address>
           <associations-local-mode>client\
           </associations-local-mode>
           <associations-isconfigured>yes\
           </associations-isconfigured>
           <nominal-freq>100.0</nominal-freq>
           <actual-freq>100.0</actual-freq>
           <clock-precision>18</clock-precision>
           <clock-offset>0.025</clock-offset>
           <root-delay>0.5</root-delay>
           <root-dispersion>0.8</root-dispersion>
           <reference-time>10-10-2017 07:33:55.258 Z+05:30\
           </reference-time>
           <sync-state>clock-synchronized</sync-state>
         </system-status>
       </clock-state>
     </ntp>
   </data>

9.8.  Get all association

   This example describes how to get all association present in the
   system -







Wu, et al.               Expires August 26, 2021               [Page 50]


Internet-Draft                YANG for NTP                 February 2021


   <get>
     <filter type="subtree">
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <associations>
         </associations>
       </ntp>
     </filter>
   </get>

   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
       <associations>
         <address>192.0.2.1</address>
         <stratum>9</stratum>
         <refid>203.0.113.1</refid>
         <local-mode>client</local-mode>
         <isconfigured>true</isconfigured>
         <authentication-key>10</authentication-key>
         <prefer>true</prefer>
         <peer-interface>Ethernet3/0/0</peer-interface>
         <minpoll>6</minpoll>
         <maxpoll>10</maxpoll>
         <port>1025</port>
         <version>4</version>
         <reach>255</reach>
         <unreach>0</unreach>
         <poll>128</poll>
         <now>10</now>
         <offset>0.025</offset>
         <delay>0.5</delay>
         <dispersion>0.6</dispersion>
         <originate-time>10-10-2017 07:33:55.253 Z+05:30\
         </originate-time>
         <receive-time>10-10-2017 07:33:55.258 Z+05:30\
         </receive-time>
         <transmit-time>10-10-2017 07:33:55.300 Z+05:30\
         </transmit-time>
         <input-time>10-10-2017 07:33:55.305 Z+05:30\
         </input-time>
         <ntp-statistics>
           <packet-sent>20</packet-sent>
           <packet-sent-fail>0</packet-sent-fail>
           <packet-received>20</packet-received>
           <packet-dropped>0</packet-dropped>
         </ntp-statistics>
       </associations>
     </ntp>
   </data>



Wu, et al.               Expires August 26, 2021               [Page 51]


Internet-Draft                YANG for NTP                 February 2021


9.9.  Global statistic

   This example describes how to get clock current state -

   <get>
     <filter type="subtree">
       <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <ntp-statistics>
         </ntp-statistics>
       </ntp>
     </filter>
   </get>

   <data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <ntp xmlns="urn:ietf:params:xml:ns:yang:ietf-ntp">
       <ntp-statistics>
         <packet-sent>30</packet-sent>
         <packet-sent-fail>5</packet-sent-fail>
         <packet-received>20</packet-received>
         <packet-dropped>2</packet-dropped>
       </ntp-statistics>
     </ntp>
   </data>

10.  IANA Considerations

   This document registers a URI in the "IETF XML Registry" [RFC3688].
   Following the format in RFC 3688, the following registration has been
   made.

   URI: urn:ietf:params:xml:ns:yang:ietf-ntp

   Registrant Contact: The IESG.

   XML: N/A; the requested URI is an XML namespace.

   This document registers a YANG module in the "YANG Module Names"
   registry [RFC6020].

   Name: ietf-ntp

   Namespace: urn:ietf:params:xml:ns:yang:ietf-ntp

   Prefix: ntp

   Reference: RFC XXXX





Wu, et al.               Expires August 26, 2021               [Page 52]


Internet-Draft                YANG for NTP                 February 2021


   Note: The RFC Editor will replace XXXX with the number assigned to
   this document once it becomes an RFC.

11.  Security Considerations

   The YANG module specified in this document defines a schema for data
   that is designed to be accessed via network management protocols such
   as NETCONF [RFC6241] or RESTCONF [RFC8040].  The lowest NETCONF layer
   is the secure transport layer, and the mandatory-to-implement secure
   transport is Secure Shell (SSH) [RFC6242].  The lowest RESTCONF layer
   is HTTPS, and the mandatory-to-implement secure transport is TLS
   [RFC8446].

   The NETCONF Access Control Model (NACM) [RFC8341] provides the means
   to restrict access for particular NETCONF or RESTCONF users to a
   preconfigured subset of all available NETCONF or RESTCONF protocol
   operations and content.

   There are a number of data nodes defined in this YANG module that are
   writable/creatable/deletable (i.e., config true, which is the
   default).  These data nodes may be considered sensitive or vulnerable
   in some network environments.  Write operations (e.g., edit-config)
   to these data nodes without proper protection can have a negative
   effect on network operations.  These are the subtrees and data nodes
   and their sensitivity/vulnerability:

      /ntp/port - This data node specify the port number to be used to
      send NTP packets.  Unexpected changes could lead to disruption
      and/or network misbehavior.

      /ntp/authentication and /ntp/access-rules - The entries in the
      list include the authentication and access control configurations.
      Care should be taken while setting these parameters.

      /ntp/unicast-configuration - The entries in the list include all
      unicast configurations (server or peer mode), and indirectly
      creates or modify the NTP associations.  Unexpected changes could
      lead to disruption and/or network misbehavior.

      /ntp/interfaces/interface - The entries in the list include all
      per-interface configurations related to broadcast, multicast and
      manycast mode, and indirectly creates or modify the NTP
      associations.  Unexpected changes could lead to disruption and/or
      network misbehavior.

   Some of the readable data nodes in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control read access (e.g., via get, get-config, or



Wu, et al.               Expires August 26, 2021               [Page 53]


Internet-Draft                YANG for NTP                 February 2021


   notification) to these data nodes.  These are the subtrees and data
   nodes and their sensitivity/vulnerability:

      /ntp/authentication/authentication-keys - The entries in the list
      includes all the NTP authentication keys.  This information is
      sensitive and can be exploited and thus unauthorized access to
      this needs to be curtailed.

      /ntp/associations - The entries in the list includes all active
      NTP associations of all modes.  Unauthorized access to this also
      needs to be curtailed.

   The leaf /ntp/authentication/authentication-keys/algorithm can be set
   to cryptographic algorithms that are no longer considered to be
   secure.  As per [RFC8573], AES-CMAC is the recommended algorithm.

12.  Acknowledgments

   The authors would like to express their thanks to Sladjana Zoric,
   Danny Mayer, Harlan Stenn, Ulrich Windl, Miroslav Lichvar, Maurice
   Angermann, Watson Ladd, and Rich Salz for their review and
   suggestions.

   Thanks to Andy Bierman for the YANG doctor review.

   Thanks to Dieter Sibold for being the document shepherd and Erik
   Kline for being the responsible AD.

   Thanks to Takeshi Takahashi for SECDIR review.  Thanks to Tim Evens
   for GENART review.

   A special thanks to Tom Petch for a very detailed YANG review and
   providing great suggestions for improvements.

13.  References

13.1.  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>.





Wu, et al.               Expires August 26, 2021               [Page 54]


Internet-Draft                YANG for NTP                 February 2021


   [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
              "Network Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
              <https://www.rfc-editor.org/info/rfc5905>.

   [RFC5907]  Gerstung, H., Elliott, C., and B. Haberman, Ed.,
              "Definitions of Managed Objects for Network Time Protocol
              Version 4 (NTPv4)", RFC 5907, DOI 10.17487/RFC5907, June
              2010, <https://www.rfc-editor.org/info/rfc5907>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [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>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
              RFC 6991, DOI 10.17487/RFC6991, July 2013,
              <https://www.rfc-editor.org/info/rfc6991>.

   [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>.

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

   [RFC8177]  Lindem, A., Ed., Qu, Y., Yeung, D., Chen, I., and J.
              Zhang, "YANG Data Model for Key Chains", RFC 8177,
              DOI 10.17487/RFC8177, June 2017,
              <https://www.rfc-editor.org/info/rfc8177>.







Wu, et al.               Expires August 26, 2021               [Page 55]


Internet-Draft                YANG for NTP                 February 2021


   [RFC8294]  Liu, X., Qu, Y., Lindem, A., Hopps, C., and L. Berger,
              "Common YANG Data Types for the Routing Area", RFC 8294,
              DOI 10.17487/RFC8294, December 2017,
              <https://www.rfc-editor.org/info/rfc8294>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [RFC8343]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
              <https://www.rfc-editor.org/info/rfc8343>.

   [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>.

   [RFC8519]  Jethanandani, M., Agarwal, S., Huang, L., and D. Blair,
              "YANG Data Model for Network Access Control Lists (ACLs)",
              RFC 8519, DOI 10.17487/RFC8519, March 2019,
              <https://www.rfc-editor.org/info/rfc8519>.

   [RFC8573]  Malhotra, A. and S. Goldberg, "Message Authentication Code
              for the Network Time Protocol", RFC 8573,
              DOI 10.17487/RFC8573, June 2019,
              <https://www.rfc-editor.org/info/rfc8573>.

13.2.  Informative References

   [RFC1305]  Mills, D., "Network Time Protocol (Version 3)
              Specification, Implementation and Analysis", RFC 1305,
              DOI 10.17487/RFC1305, March 1992,
              <https://www.rfc-editor.org/info/rfc1305>.

   [RFC1321]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              DOI 10.17487/RFC1321, April 1992,
              <https://www.rfc-editor.org/info/rfc1321>.

   [RFC3174]  Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1
              (SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001,
              <https://www.rfc-editor.org/info/rfc3174>.





Wu, et al.               Expires August 26, 2021               [Page 56]


Internet-Draft                YANG for NTP                 February 2021


   [RFC4493]  Song, JH., Poovendran, R., Lee, J., and T. Iwata, "The
              AES-CMAC Algorithm", RFC 4493, DOI 10.17487/RFC4493, June
              2006, <https://www.rfc-editor.org/info/rfc4493>.

   [RFC7317]  Bierman, A. and M. Bjorklund, "A YANG Data Model for
              System Management", RFC 7317, DOI 10.17487/RFC7317, August
              2014, <https://www.rfc-editor.org/info/rfc7317>.

   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore Architecture
              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
              <https://www.rfc-editor.org/info/rfc8342>.

   [RFC8792]  Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
              "Handling Long Lines in Content of Internet-Drafts and
              RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
              <https://www.rfc-editor.org/info/rfc8792>.

Appendix A.  Full YANG Tree

   The full tree for ietf-ntp YANG model is -

   module: ietf-ntp
     +--rw ntp!
        +--rw port?                    inet:port-number {ntp-port}?
        +--rw refclock-master!
        |  +--rw master-stratum?   ntp-stratum
        +--rw authentication {authentication}?
        |  +--rw auth-enabled?          boolean
        |  +--rw authentication-keys* [key-id]
        |     +--rw key-id       uint32
        |     +--rw algorithm?   identityref
        |     +--rw key
        |     |  +--rw (key-string-style)?
        |     |     +--:(keystring)
        |     |     |  +--rw keystring?            string
        |     |     +--:(hexadecimal) {hex-key-string}?
        |     |        +--rw hexadecimal-string?   yang:hex-string
        |     +--rw istrusted?   boolean
        +--rw access-rules {access-rules}?
        |  +--rw access-rule* [access-mode]
        |     +--rw access-mode    identityref
        |     +--rw acl?           -> /acl:acls/acl/name
        +--ro clock-state
        |  +--ro system-status
        |     +--ro clock-state                  identityref
        |     +--ro clock-stratum                ntp-stratum
        |     +--ro clock-refid                  refid



Wu, et al.               Expires August 26, 2021               [Page 57]


Internet-Draft                YANG for NTP                 February 2021


        |     +--ro associations-address?
        |     |       -> /ntp/associations/address
        |     +--ro associations-local-mode?
        |     |       -> /ntp/associations/local-mode
        |     +--ro associations-isconfigured?
        |     |       -> /ntp/associations/isconfigured
        |     +--ro nominal-freq                 decimal64
        |     +--ro actual-freq                  decimal64
        |     +--ro clock-precision              int8
        |     +--ro clock-offset?                decimal64
        |     +--ro root-delay?                  decimal64
        |     +--ro root-dispersion?             decimal64
        |     +--ro reference-time?              ntp-date-and-time
        |     +--ro sync-state                   identityref
        +--rw unicast-configuration* [address type]
        |       {unicast-configuration}?
        |  +--rw address           inet:ip-address
        |  +--rw type              identityref
        |  +--rw authentication {authentication}?
        |  |  +--rw (authentication-type)?
        |  |     +--:(symmetric-key)
        |  |        +--rw key-id?   leafref
        |  +--rw prefer?           boolean
        |  +--rw burst?            boolean
        |  +--rw iburst?           boolean
        |  +--rw source?           if:interface-ref
        |  +--rw minpoll?          int8
        |  +--rw maxpoll?          int8
        |  +--rw port?             inet:port-number {ntp-port}?
        |  +--rw version?          ntp-version
        +--ro associations* [address local-mode isconfigured]
        |  +--ro address           inet:ip-address
        |  +--ro local-mode        identityref
        |  +--ro isconfigured      boolean
        |  +--ro stratum?          ntp-stratum
        |  +--ro refid?            refid
        |  +--ro authentication?
        |  |       -> /ntp/authentication/authentication-keys/key-id
        |  |       {authentication}?
        |  +--ro prefer?           boolean
        |  +--ro peer-interface?   if:interface-ref
        |  +--ro minpoll?          int8
        |  +--ro maxpoll?          int8
        |  +--ro port?             inet:port-number {ntp-port}?
        |  +--ro version?          ntp-version
        |  +--ro reach?            uint8
        |  +--ro unreach?          uint8
        |  +--ro poll?             int8



Wu, et al.               Expires August 26, 2021               [Page 58]


Internet-Draft                YANG for NTP                 February 2021


        |  +--ro now?              uint32
        |  +--ro offset?           decimal64
        |  +--ro delay?            decimal64
        |  +--ro dispersion?       decimal64
        |  +--ro originate-time?   ntp-date-and-time
        |  +--ro receive-time?     ntp-date-and-time
        |  +--ro transmit-time?    ntp-date-and-time
        |  +--ro input-time?       ntp-date-and-time
        |  +--ro ntp-statistics
        |     +--ro discontinuity-time?   ntp-date-and-time
        |     +--ro packet-sent?          yang:counter32
        |     +--ro packet-sent-fail?     yang:counter32
        |     +--ro packet-received?      yang:counter32
        |     +--ro packet-dropped?       yang:counter32
        +--rw interfaces
        |  +--rw interface* [name]
        |     +--rw name                if:interface-ref
        |     +--rw broadcast-server! {broadcast-server}?
        |     |  +--rw ttl?              uint8
        |     |  +--rw authentication {authentication}?
        |     |  |  +--rw (authentication-type)?
        |     |  |     +--:(symmetric-key)
        |     |  |        +--rw key-id?   leafref
        |     |  +--rw minpoll?          int8
        |     |  +--rw maxpoll?          int8
        |     |  +--rw port?             inet:port-number {ntp-port}?
        |     |  +--rw version?          ntp-version
        |     +--rw broadcast-client! {broadcast-client}?
        |     +--rw multicast-server* [address] {multicast-server}?
        |     |  +--rw address
        |     |  |       rt-types:ip-multicast-group-address
        |     |  +--rw ttl?              uint8
        |     |  +--rw authentication {authentication}?
        |     |  |  +--rw (authentication-type)?
        |     |  |     +--:(symmetric-key)
        |     |  |        +--rw key-id?   leafref
        |     |  +--rw minpoll?          int8
        |     |  +--rw maxpoll?          int8
        |     |  +--rw port?             inet:port-number {ntp-port}?
        |     |  +--rw version?          ntp-version
        |     +--rw multicast-client* [address] {multicast-client}?
        |     |  +--rw address    rt-types:ip-multicast-group-address
        |     +--rw manycast-server* [address] {manycast-server}?
        |     |  +--rw address    rt-types:ip-multicast-group-address
        |     +--rw manycast-client* [address] {manycast-client}?
        |        +--rw address
        |        |       rt-types:ip-multicast-group-address
        |        +--rw authentication {authentication}?



Wu, et al.               Expires August 26, 2021               [Page 59]


Internet-Draft                YANG for NTP                 February 2021


        |        |  +--rw (authentication-type)?
        |        |     +--:(symmetric-key)
        |        |        +--rw key-id?   leafref
        |        +--rw ttl?              uint8
        |        +--rw minclock?         uint8
        |        +--rw maxclock?         uint8
        |        +--rw beacon?           int8
        |        +--rw minpoll?          int8
        |        +--rw maxpoll?          int8
        |        +--rw port?             inet:port-number {ntp-port}?
        |        +--rw version?          ntp-version
        +--ro ntp-statistics
           +--ro discontinuity-time?   ntp-date-and-time
           +--ro packet-sent?          yang:counter32
           +--ro packet-sent-fail?     yang:counter32
           +--ro packet-received?      yang:counter32
           +--ro packet-dropped?       yang:counter32


Authors' Addresses

   Nan Wu
   Huawei
   Huawei Bld., No.156 Beiqing Rd.
   Beijing  100095
   China

   Email: eric.wu@huawei.com


   Dhruv Dhody (editor)
   Huawei
   Divyashree Techno Park, Whitefield
   Bangalore, Kanataka  560066
   India

   Email: dhruv.ietf@gmail.com


   Ankit kumar Sinha (editor)
   RtBrick Inc.
   Bangalore, Kanataka
   India

   Email: ankit.ietf@gmail.com






Wu, et al.               Expires August 26, 2021               [Page 60]


Internet-Draft                YANG for NTP                 February 2021


   Anil Kumar S N
   RtBrick Inc.
   Bangalore, Kanataka
   India

   Email: anil.ietf@gmail.com


   Yi Zhao
   Ericsson
   China Digital Kingdom Bld., No.1 WangJing North Rd.
   Beijing  100102
   China

   Email: yi.z.zhao@ericsson.com




































Wu, et al.               Expires August 26, 2021               [Page 61]