Network Working Group                                              N. Wu
Internet-Draft                                                    Huawei
Intended status: Standards Track                            A. Kumar S N
Expires: May 1, September 6, 2018                                  RtBrick Inc.
                                                                 Y. Zhao
                                                                Ericsson
                                                                D. Dhody
                                                                  Huawei
                                                                A. Sinha
                                                                  Huawei
                                                        October 28, 2017
                                                            RtBrick Inc.
                                                           March 5, 2018

                       A YANG Data Model for NTP
                   draft-ietf-ntp-yang-data-model-01
                   draft-ietf-ntp-yang-data-model-02

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 May 1, September 6, 2018.

Copyright Notice

   Copyright (c) 2017 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Operational State . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.3.  Tree Diagrams . . . . . . . . . . . . . . . . . . . . . .   3
   2.  NTP data model  . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Relationship with NTPv4-MIB . . . . . . . . . . . . . . . . .   6
   4.  Relationship with RFC7317 . RFC 7317  . . . . . . . . . . . . . . . . .   7
   5.  NTP YANG Module . . . . . . . . . . . . . . . . . . . . . . .   8
   6.  Usage Example . . . . . . . . . . . . . . . . . . . . . . . .  27  28
     6.1.  Unicast association . . . . . . . . . . . . . . . . . . .  27  28
     6.2.  Refclock master . . . . . . . . . . . . . . . . . . . . .  29
     6.3.  Authentication configuration  . . . . . . . . . . . . . .  30
     6.4.  Access configuration  . . . . . . . . . . . . . . . . . .  31  32
     6.5.  Multicast configuration . . . . . . . . . . . . . . . . .  32
     6.6.  Manycast configuration  . . . . . . . . . . . . . . . . .  35  36
     6.7.  Clock state . . . . . . . . . . . . . . . . . . . . . . .  38  39
     6.8.  Get all association . . . . . . . . . . . . . . . . . . .  38  39
     6.9.  Global statistic  . . . . . . . . . . . . . . . . . . . .  40  41
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  40  41
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  41  42
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  41  43
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  41  43
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  41  43
     10.2.  Informative References . . . . . . . . . . . . . . . . .  42  44
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  42  44

1.  Introduction

   This document defines a YANG [RFC6020] data model for Network Time
   Protocol [RFC5905] implementations.

   The data model convers configuration of system parameters of NTP,
   such as access rules, authentication and VRF VPN Routing and Forwarding
   (VRF) binding, and also associations of NTP in different modes and
   parameters of per-
   interface. per-interface.  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 [I-D.ietf-netmod-revised-datastores].  NTP current state
   and statistics are also maintained in the operational state.
   Additionally, the operational state also include the associations
   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 [I-D.ietf-netmod-yang-tree-diagrams].

2.  NTP data model

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

   module: ietf-ntp
       +--rw ntp!
          +--rw port?                    uint16 {ntp-port}?
          +--rw refclock-master!
          |  +--rw master-stratum?   ntp-stratum
          +--rw authentication
          |  +--rw auth-enabled?          boolean
          |  +--rw trusted-keys* [key-id]
          |  |  +--rw key-id    -> /ntp/authentication/authentication-keys/key-id    leafref
          |  +--rw authentication-keys* [key-id]
          |     +--rw key-id       uint32
          |     +--rw algorithm?   identityref
          |     +--rw password?    ianach:crypt-hash
          +--rw access-rules
          |  +--rw access-rule* [access-mode]
          |     +--rw access-mode    access-modes
          |     +--rw acl?           -> /acl:access-lists/acl/acl-name /acl:access-lists/acl/name
          +--ro clock-state
          |  +--ro system-status
          |     +--ro clock-state                  ntp-clock-status
          |     +--ro clock-stratum                ntp-stratum
          |     +--ro clock-refid                  union
          |     +--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              uint8
          |     +--ro clock-offset?                decimal64
          |     +--ro root-delay?                  decimal64
          |     +--ro root-dispersion?             decimal64
          |     +--ro reference-time?              yang:date-and-time
          |     +--ro sync-state                   ntp-sync-state
          +--rw unicast* unicast-configuration* [address type]
          |  +--rw address           inet:host
          |  +--rw type              unicast-configuration-type
          |  +--rw authentication
          |  |  +--rw (authentication-type)?
          |  |     +--:(symmetric-key)
          |  |        +--rw key-id?   -> /ntp/authentication/authentication-keys/key-id   leafref
          |  +--rw prefer?           boolean
          |  +--rw burst?            boolean
          |  +--rw iburst?           boolean
          |  +--rw source?           if:interface-ref
          |  +--rw minpoll?          ntp-minpoll
          |  +--rw maxpoll?          ntp-maxpoll
          |  +--rw port?             uint16 {ntp-port}?
          |  +--rw version?          ntp-version
          +--ro associations* [address local-mode isConfigured]
          |  +--ro address           inet:host
          |  +--ro local-mode        association-modes
          |  +--ro isConfigured      boolean
          |  +--ro stratum?          ntp-stratum
          |  +--ro refid?            union
          |  +--ro authentication?
          |  |       -> /ntp/authentication/authentication-keys/key-id
          |  +--ro prefer?           boolean
          |  +--ro peer-interface?   if:interface-ref
          |  +--ro minpoll?          ntp-minpoll
          |  +--ro maxpoll?          ntp-maxpoll
          |  +--ro port?             uint16 {ntp-port}?
          |  +--ro version?          ntp-version
          |  +--ro reach?            uint8
          |  +--ro unreach?          uint8
          |  +--ro poll?             uint8
          |  +--ro now?              uint32
          |  +--ro offset?           decimal64
          |  +--ro delay?            decimal64
          |  +--ro dispersion?       decimal64
          |  +--ro originate-time?   yang:date-and-time
          |  +--ro receive-time?     yang:date-and-time
          |  +--ro transmit-time?    yang:date-and-time
          |  +--ro input-time?       yang:date-and-time
          |  +--ro ntp-statistics
          |     +--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!
          |     |  +--rw ttl?              uint8
          |     |  +--rw authentication
          |     |  |  +--rw (authentication-type)?
          |     |  |     +--:(symmetric-key)
          |     |  |        +--rw key-id?   -> /ntp/authentication/authentication-keys/key-id   leafref
          |     |  +--rw minpoll?          ntp-minpoll
          |     |  +--rw maxpoll?          ntp-maxpoll
          |     |  +--rw port?             uint16 {ntp-port}?
          |     |  +--rw version?          ntp-version
          |     +--rw broadcast-client!
          |     +--rw multicast-server* [address]
          |     |  +--rw address
          |     |  |       rt-types:ip-multicast-group-address
          |     |  +--rw ttl?              uint8
          |     |  +--rw authentication
          |     |  |  +--rw (authentication-type)?
          |     |  |     +--:(symmetric-key)
          |     |  |        +--rw key-id?   -> /ntp/authentication/authentication-keys/key-id   leafref
          |     |  +--rw minpoll?          ntp-minpoll
          |     |  +--rw maxpoll?          ntp-maxpoll
          |     |  +--rw port?             uint16 {ntp-port}?
          |     |  +--rw version?          ntp-version
          |     +--rw multicast-client* [address]
          |     |  +--rw address    rt-types:ip-multicast-group-address
          |     +--rw manycast-server* [address]
          |     |  +--rw address    rt-types:ip-multicast-group-address
          |     +--rw manycast-client* [address]
          |        +--rw address
          |        |       rt-types:ip-multicast-group-address
          |        +--rw authentication
          |        |  +--rw (authentication-type)?
          |        |     +--:(symmetric-key)
          |        |        +--rw key-id?   -> /ntp/authentication/authentication-keys/key-id   leafref
          |        +--rw ttl?              uint8
          |        +--rw minclock?         uint8
          |        +--rw maxclock?         uint8
          |        +--rw beacon?           uint8
          |        +--rw minpoll?          ntp-minpoll
          |        +--rw maxpoll?          ntp-maxpoll
          |        +--rw port?             uint16 {ntp-port}?
          |        +--rw version?          ntp-version
          +--ro ntp-statistics
             +--ro packet-sent?        yang:counter32
             +--ro packet-sent-fail?   yang:counter32
             +--ro packet-received?    yang:counter32
             +--ro packet-dropped?     yang:counter32

   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, unicast configurations,
   interfaces, system status and associations.

3.  Relationship with NTPv4-MIB

   If the device implements the NTPv4-MIB [RFC5907], data nodes in
   container ntp and ntp-state 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 data nodes in /ntp/ |    NTPv4-MIB objects     |
          +--------------------------+--------------------------+
          |       ntp-enabled        | ntpEntStatusCurrentMode  |
          +--------------------------+--------------------------+

      +--------------------------------------+---------------------+
      | YANG data nodes in /ntp/associations |  NTPv4-MIB objects  |
      +--------------------------------------+---------------------+
      |               address                | ntpAssocAddressType |
      |                                      |   ntpAssocAddress   |
      +--------------------------------------+---------------------+

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

   YANG NTP State Data Nodes and Related NTPv4-MIB Objects

4.  Relationship with RFC7317 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 supports interface related per-interface configurations which is not
   supported in /system/ntp
      +---------------------------+--------------------------------+
    +-------------------------------+--------------------------------+
    |    YANG data nodes in /ntp/   | YANG data nodes in /system/ntp |
      +---------------------------+--------------------------------+
    +-------------------------------+--------------------------------+
    |          ntp-enabled          |            enabled             |
    |          unicast     unicast-configuration     |             server             |
    |                               |          server/name           |
    |      unicast/address unicast-configuration/address |  server/transport/udp/address  |
    |        unicast/port   unicast-configuration/port  |   server/transport/udp/port    |
    |        unicast/type   unicast-configuration/type  |    server/association-type     |
    |       unicast/iburst  unicast-configuration/iburst |         server/iburst          |
    |       unicast/prefer  unicast-configuration/prefer |         server/prefer          |
      +---------------------------+--------------------------------+
    +-------------------------------+--------------------------------+

      YANG NTP Configuration Data Nodes and counterparts in RFC7317 RFC 7317
                                  Objects

5.  NTP YANG Module

      <CODE BEGINS> file "ietf-ntp@2017-10-28.yang" "ietf-ntp@2018-03-05.yang"
    module ietf-ntp {

      namespace "urn:ietf:params:xml:ns:yang:ietf-ntp";

      prefix "ntp";

      import ietf-yang-types {
        prefix "yang";
      }

      import ietf-inet-types {
        prefix "inet";
      }

      import ietf-interfaces {
        prefix "if";
      }

      import iana-crypt-hash {
        prefix ianach; "ianach";
      }

      import ietf-key-chain {
        prefix "key-chain";
      }

      import ietf-access-control-list {
        prefix "acl";
      }
      import ietf-routing-types {
        prefix "rt-types";
      }

      organization
        "IETF NTP (Network Time Protocol) Working Group";

      contact
        "WG Web:  <http://tools.ietf.org/wg/ntp/>
         WG List:  <mailto: ntpwg@lists.ntp.org
      WG Chair: Karen O'Donoghue
                <mailto: odonoghue@isoc.org>
         Editor:   Eric Wu
                   <mailto:eric.wu@huawei.com>
         Editor:   Anil Kumar S N
                   <mailto:anil.ietf@gmail.com>
         Editor:   Yi Zhao
                   <mailto:yi.z.zhao@ericsson.com>
         Editor:   Dhruv Dhody
                   <mailto:dhruv.ietf@gmail.com>
         Editor:   Ankit Kumar Sinha
                   <mailto:ankit.ietf@gmail.com>";
      description
        "This YANG module defines essential components for the
         management of a routing subsystem.

         Copyright (c) 2017 2018 IETF Trust and the persons identified
         as authors of the code. All rights reserved.

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

         This version of this YANG module is part of RFC XXXX;
         see the RFC itself for full legal notices.";

      revision 2017-10-28 2018-03-05 {
        description
          "Updated revision.";
        reference
          "RFC XXXX: A YANG Data Model for NTP Management";
      }

      /* Typedef Definitions */

      typedef ntp-stratum {
        type uint8 {
          range "1..16";
        }
        description
          "The level of each server in the hierarchy is defined by
          a stratum number. Primary servers are assigned stratum
          one; secondary servers at each lower level are assigned
          stratum numbers one greater than the preceding level";
      }

      typedef ntp-version {
        type uint8 {
          range "1..4";
        }
        default "3";
        description
          "The current NTP version supported by corresponding
          association.";
      }

      typedef ntp-minpoll {
        type uint8 {
          range "4..17";
        }
        default "6";
        description
          "The minimum poll exponent for this NTP association.";
      }

      typedef ntp-maxpoll {
        type uint8 {
          range "4..17";
        }
        default "10";
        description
          "The maximul poll exponent for this NTP association.";
      }

      typedef access-modes {
        type enumeration {
          enum peer {
            value "0";
            description
              "Sets the fully access authority. Both time
              request and control query can be performed
              on the local NTP service, and the local clock
              can be synchronized to the remote server.";
          }
          enum server {
            value "1";
            description
              "Enables the server access and query.
              Both time requests and control query can be
              performed on the local NTP service, but the
              local clock cannot be synchronized to the
              remote server.";
          }
          enum synchronization {
            value "2";
            description
              "Enables the server to access.
              Only time request can be performed on the
              local NTP service.";
          }
          enum query {
            value "3";
            description
              "Sets the maximum access limitation.
              Control query can be performed only on the
              local NTP service.";
          }
        }
        description
          "This defines NTP acess modes.";
      }

      typedef unicast-configuration-type {
        type enumeration {
          enum server {
            value "0";
            description
              "Use client association mode. This device
              will not provide synchronization to the
              configured NTP server.";
          }
          enum peer {
            value "1";
            description
              "Use symmetric active association mode.
              This device may provide synchronization
              to the configured NTP server.";
          }
        }
        description
          "This defines NTP unicast mode of operation.";
      }
      typedef association-modes {
        type enumeration {
          enum client {
            value "0";
            description
              "Use client association mode(mode 3).
              This device will not provide synchronization
              to the configured NTP server.";
          }
          enum active {
            value "1";
            description
              "Use symmetric active association mode(mode 1).
              This device may synchronize with its NTP peer,
              or provide synchronization to configured NTP peer.";
          }
          enum passive {
            value "2";
            description
              "Use symmetric passive association mode(mode 2).
              This device has learnt this asso dynamically.
              This device may synchronize with its NTP peer.";
          }
          enum broadcast {
            value "3";
            description
              "Use broadcast mode(mode 5).
              This mode defines that its eigther working
              as broadcast-server or multicast-server.";
          }
          enum broadcast-client {
            value "4";
            description
              "This mode defines that its eigther working
              as broadcast-client or multicast-client.";
          }
        }
        description
          "This defines NTP association modes.";
      }

      typedef ntp-clock-status {
        type enumeration {
          enum synchronized {
            value "0";
            description
              "Indicates that the local clock has been
              synchronized with an NTP server or
              the reference clock.";
          }
          enum unsynchronized {
            value "1";
            description
              "Indicates that the local clock has not been
              synchronized with any NTP server.";
          }
        }
        description
          "This defines NTP clock status.";
      }

      typedef ntp-sync-state {
        type enumeration {
          enum clock-not-set {
            value "0";
            description
              "Indicates the clock is not updated.";
          }
          enum freq-set-by-cfg {
            value "1";
            description
              "Indicates the clock frequency is set by
              NTP configuration.";
          }
          enum clock-set {
            value "2";
            description
              "Indicates the clock is set.";
          }
          enum freq-not-determined {
            value "3";
            description
              "Indicates the clock is set but the frequency
              is not determined.";
          }
          enum clock-synchronized {
            value "4";
            description
              "Indicates that the clock is synchronized";
          }
          enum spike {
            value "5";
            description
              "Indicates a time difference of more than 128
              milliseconds is detected between NTP server
              and client clock. The clock change will take
              effect in XXX seconds.";
          }
        }
        description
          "This defines NTP clock sync states.";
      }

     /* feature */
     feature ntp-port {
       description
         "Indicates that the device supports the configuration of
          the port for NTP.

          This is a 'feature', since many implementations do not
          support any port other than the default port.";
     }

      /* Groupings */
      grouping authentication-key {
        description
          "To define an authentication key for a Network Time
          Protocol (NTP) time source.";
        leaf key-id {
          type uint32 {
            range "1..max";
          }
          description
            "Authentication key identifier.";
        }
        leaf algorithm {
          type identityref {
            base key-chain:crypto-algorithm;
          }
          description
            "Authentication algorithm.";
        }
        leaf password {
          type ianach:crypt-hash;
          description "Clear or encrypted mode for password text.";
        }
      }

      grouping authentication-type-param {
        description
            "Authentication type.";
        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.";
            }
          }
        }
      }

      grouping statistics {
        description
          "NTP packet statistic.";
        leaf packet-sent {
          type yang:counter32;
          description
            "Indicates the total number of packets sent.";
        }
        leaf packet-sent-fail {
          type yang:counter32;
          description
            "Indicates the number of times packet
            sending failed.";
        }
        leaf packet-received {
          type yang:counter32;
          description
            "Indicates the total number of packets received.";
        }
        leaf packet-dropped {
          type yang:counter32;
          description
            "Indicates the number of packets dropped.";
        }
      }

      grouping comman-attributes {
        description
          "NTP common attributes for configuration.";
        leaf minpoll {
          type ntp-minpoll;
          description
            "The minimum poll interval used in this association.";
        }
        leaf maxpoll {
          type ntp-maxpoll;
          description
            "The maximul poll interval used in this association.";
        }
        leaf port {
          if-feature ntp-port;
          type uint16 {
            range "123 | 1025..max";
          }
          default "123";
          description
            "Specify the port used to send NTP packets.";
        }
        leaf version {
          type ntp-version;
          description
            "NTP version.";
        }
      }

      grouping association-ref {
        description
          "Reference to NTP association node";
        leaf associations-address {
            type leafref {
                path "/ntp:ntp/ntp:associations/ntp:address";
            }
            description
              "Indicates the association address
              which result in clock synchronization.";
        }
        leaf associations-local-mode {
            type leafref {
                path "/ntp:ntp/ntp:associations/ntp:local-mode";
            }
            description
              "Indicates the association local-mode
              which result in clock synchronization.";
        }
        leaf associations-isConfigured {
            type leafref {
                path "/ntp:ntp/ntp:associations/ntp:isConfigured"; "/ntp:ntp/ntp:associations/"
                     + "ntp:isConfigured";
            }
            description
              "Indicates the association was configured or
              dynamic which result in clock synchronization.";

        }
      }

      /* Configuration data nodes */
      container ntp {
        presence
          "NTP is enable";
        description
          "Configuration parameters for NTP.";
        leaf port {
          if-feature ntp-port;
          type uint16 {
            range "123 | 1025..max";
          }
          default "123";
          description
            "Specify the port used to send NTP packets.";
        }
        container refclock-master {
          presence
             "NTP master clock is enable";
          description
             "Configures the 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 {
         description
            "Configuration of authentication.";
            leaf auth-enabled {
              type boolean;
              default false;
              description
                "Controls whether NTP authentication is enabled
                or disabled on this device.";
            }
            list trusted-keys {
              key "key-id";
              description
                "List of keys trusted by NTP.";
              leaf key-id {
                type leafref {
                  path "/ntp:ntp/ntp:authentication/"
                      + "ntp:authentication-keys/ntp:key-id";
                }
                description
                "The key trusted by NTP.";
              }
            }
            list authentication-keys {
              key "key-id";
              uses authentication-key;
              description
                "List of authentication key.";
            }
       }

       container access-rules {
         description
           "Configuration of access rules.";
            list access-rule {
              key "access-mode";
              description
                "List of access rules.";
              leaf access-mode {
                type access-modes;
                description
                  "NTP access mode.";
               }
              leaf acl {
                type leafref {
                 path "/acl:access-lists/acl:acl/acl:acl-name"; "/acl:access-lists/acl:acl/acl:name";
                }
                description
                  "NTP ACL.";
               }
             }
       }

       container clock-state {
         config "false";
         description
           "Operational state of the NTP.";

         container system-status {
           description
              "System status of NTP.";
           leaf clock-state {
             type ntp-clock-status;
             mandatory true;
             description "Indicates the state of system clock.";

           }
           leaf clock-stratum {
               type ntp-stratum;
               mandatory true;
               description
                 "Indicates the stratum of the reference clock.";
           }
           leaf clock-refid {
               type union {
                   type inet:ipv4-address;
                   type binary {
                       length "4";
                   }
                   type string {
                       length "4";
                   }
               }
               mandatory true;
               description
                 "IPv4 address or first 32 bits of the MD5 hash of
                 the IPv6 address or reference clock of the peer to
                 which clock is synchronized.";
           }

           uses association-ref {
             description
               "Reference to Association node";
           }
           leaf nominal-freq {
               type decimal64 {
                   fraction-digits 4;
               }
               mandatory true;
               description
                 "Indicates the nominal frequency of the
                 local clock, in Hz.";
           }
           leaf actual-freq {
               type decimal64 {
                   fraction-digits 4;
               }
               mandatory true;
               description
                 "Indicates the actual frequency of the
                 local clock, in Hz.";
           }
           leaf clock-precision {
               type uint8;
               mandatory true;
               description
                 "Precision of the clock of this system
                 in Hz.(prec=2^(-n))";
           }
           leaf clock-offset {
               type decimal64 {
                   fraction-digits 4;
               }
               description
                 "Offset of clock to synchronized peer,
                 in milliseconds.";
           }
           leaf root-delay {
               type decimal64 {
                   fraction-digits 2;
               }
               description
                 "Total delay along path to root clock,
                 in milliseconds.";
           }
           leaf root-dispersion {
               type decimal64 {
                   fraction-digits 2;
               }
               description
                 "Indicates the dispersion between the local clock
                 and the master reference clock, in milliseconds.";
           }
           leaf reference-time {
               type yang:date-and-time;
               description
                 "Indicates reference timestamp.";
           }
           leaf sync-state {
             type ntp-sync-state;
             mandatory true;
             description
               "Indicates the synchronization status of
               the local clock.";
           }
         }
       }
     list unicast unicast-configuration {
       key "address type";
       description
         "list of unicast configuration."; unicast-configuration.";
       leaf address {
         type inet:host;
         description
           "The address of this association.";
       }
       leaf type {
         type unicast-configuration-type;
         description
           "Type for this NTP configuration";
       }
       container authentication{
         description
           "Authentication type.";
         uses authentication-type-param;
       }
       leaf prefer {
         type boolean;
         default "false";
         description
           "Whether this association is preferred.";
       }
       leaf burst {
         type boolean;
         default "false";
         description
           "Sends a series of packets instead of a single packet
           within each synchronization interval to achieve faster
           synchronization.";
       }
       leaf iburst {
         type boolean;
         default "false";
         description
           "Sends a series of packets instead of a single packet
           within the initial synchronization interval to achieve
           faster initial synchronization.";
       }
       leaf source {
         type if:interface-ref;
         description
           "The interface whose ip address this association used
           as source address.";
       }
       uses comman-attributes {
         description
           "Common attribute like port, version, min and max
           poll.";
       }
     }
     list associations {
       key "address local-mode isConfigured";
       config "false";
       description
         "list of NTP association.";
       leaf address {
         type inet:host;
         description
           "The address of this association.";
       }
       leaf local-mode {
         type association-modes;
         description
           "Local mode for this NTP association.";
       }
       leaf isConfigured {
         type boolean;
         description
           "Whether this association is configured or
            dynamically learnt.";
       }
       leaf stratum {
         type ntp-stratum;
         description
           "Indicates the stratum of the reference clock.";
       }
       leaf refid {
         type union {
           type inet:ipv4-address;
           type binary {
             length "4";
           }
           type string {
             length "4";
           }
         }
         description
           "Reference clock type or address for the peer.";
       }
       leaf 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
           "Whether this association is preferred.";
       }
       leaf peer-interface {
         type if:interface-ref;
         description
           "The interface which is used for communication.";
       }
       uses comman-attributes {
         description
           "Common attribute like port, version, min and
            max poll.";
       }
       leaf reach {
         type uint8;
         description
            "Indicates the reachability of the configured
            server or peer.";
       }
       leaf unreach {
         type uint8;
         description
           "Indicates the unreachability of the configured
           server or peer.";
       }
       leaf poll {
         type uint8;
         description
           "Indicates the polling interval for current,
           in seconds.";
       }
       leaf now {
         type uint32;
         description
           "Indicates the time since the NTP packet was
           not received or last synchronized, in seconds.";
       }
       leaf offset {
         type decimal64 {
           fraction-digits 4;
         }
         description
           "Indicates the offset between the local clock
           and the superior reference clock.";
       }
       leaf delay {
         type decimal64 {
           fraction-digits 2;
         }
         description
           "Indicates the delay between the local clock
           and the superior reference clock.";
       }
       leaf dispersion {
         type decimal64 {
           fraction-digits 2;
         }
         description
           "Indicates the dispersion between the local
           clock and the superior reference clock.";
       }
       leaf originate-time {
         type yang:date-and-time;
         description
           "Indicates packet originate timestamp(T1).";
       }
       leaf receive-time {
         type yang:date-and-time;
         description
           "Indicates packet receive timestamp(T2).";
       }
       leaf transmit-time {
         type yang:date-and-time;
         description
           "Indicates packet transmit timestamp(T3).";
       }
       leaf input-time {
         type yang:date-and-time;
         description
           "Indicates packet input timestamp(T4).";
       }
       container ntp-statistics {
         description
           "Per Peer packet send and receive statistic.";
         uses statistics {
             description
               "NTP send and receive packet statistic.";
         }
       }
     }

     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 {
           presence
             "NTP broadcast-server is configured";
           description
             "Configuration of broadcast server.";
           leaf ttl {
             type uint8;
             description
               "Specifies the time to live (TTL) of a
               broadcast packet.";
           }
           container authentication{
             description
               "Authentication type.";
               uses authentication-type-param;
           }
           uses comman-attributes {
             description
               "Common attribute like port, version, min and
                max poll.";
           }
         }

         container broadcast-client {
           presence
             "NTP broadcast-client is configured";
           description
             "Configuration of broadcast-client.";
         }

         list 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) of a
               multicast packet.";
           }
           container authentication{
             description
               "Authentication type.";
               uses authentication-type-param;
           }
           uses comman-attributes {
             description
               "Common attribute like port, version, min and
                max poll.";
           }
         }
         list multicast-client {
           key "address";
           description
             "Configuration of multicast-client.";
           leaf address {
             type rt-types:ip-multicast-group-address;
             description
               "The IP address of the multicast group to
                join.";
           }
         }
         list 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 .";
           }
         }
         list 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{
             description
               "Authentication type.";
               uses authentication-type-param;
           }
           leaf ttl {
             type uint8;
             description
               "Specifies the maximum time to live (TTL) for
               the expanding ring search.";
           }
           leaf minclock {
             type uint8;
             description
               "The minimum manycast survivors in this
               association.";
           }
           leaf maxclock {
             type uint8;
             description
               "The maximum manycast candidates in this
               association.";
           }
           leaf beacon {
             type uint8;
             description
               "The maximum interval between beacons in this
               association.";
           }
           uses comman-attributes {
             description
               "Common attribute like port, version, min and
                max poll.";
           }
         }
        }
       }
    /* Operational state data */
     container ntp-statistics {
       config "false";
       description
         "Total NTP packet statistic.";
       uses statistics {
           description
             "NTP send and receive packet statistic.";
       }

     }
    }
   }
   <CODE ENDS>

6.  Usage Example

6.1.  Unicast association

   Below is the example on how to configure a preferred unicast server
   present at 1.1.1.1 running at port 1025 with authentication-key 10
   and version 4

     <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>
           <unicast-configuration>
             <address>1.1.1.1</address>
             <type>server</type>
             <prefer>true</prefer>
             <version>4</version>
             <port>1025</port>
             <authentication>
               <symmetric-key>
                 <key-id>10</key-id>
               </symmetric-key>
             </authentication>
                  </unicast>
           </unicast-configuration>
         </ntp>
       </config>
     </edit-config>

   Below is the example on how to get unicast configuration

   <get>
     <filter type="subtree">
     <sys:ntp xmlns:sys="urn:ietf:params:xml:ns:yang:ietf-ntp">
                  <sys:unicast>
                  </sys:unicast>
         <sys:unicast-configuration>
         </sys:unicast-configuration>
     </sys: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>
       <unicast-configuration>
         <address>1.1.1.1</address>
         <type>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>
         <port>1025</port>
         <version>4</version>
         <stratum>9</stratum>
         <refid>20.1.1.1</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> Z+05:30
         </originate-time>
         <receive-time>10-10-2017 07:33:55.258 Z+05:30</receive-time> Z+05:30
         </receive-time>
         <transmit-time>10-10-2017 07:33:55.300 Z+05:30</transmit-time> Z+05:30
         </transmit-time>
         <input-time>10-10-2017 07:33:55.305 Z+05:30</input-time> 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>
       </unicast-configuration>
     </ntp>
   </data>

6.2.  Refclock master

   Below is the example on 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>

   Below is the example on how to get reference clock configuration

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

6.3.  Authentication configuration

   Below is the example on how to enable authentication and configure
   authentication key 10 with mode as md5 and password as abcd
   <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>md5</algorithm>
             <password>abcd</password>
           </authentication-keys>
         </authentication>
       </ntp>
     </config>
   </edit-config>

   Below is the example on how to get authentication related
   configuration

   <get>
     <filter type="subtree">
       <sys:ntp xmlns:sys="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <sys:authentication>
         </sys:authentication>
       </sys: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>md5</algorithm>
           <password>abcd</password>
         </authentication-keys>
       </authentication>
     </ntp>
   </data>

6.4.  Access configuration

   Below is the example on how to configure acess type 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>
             <acl>2000</acl>
           </access-rule>
         </access-rules>
       </ntp>
     </config>
   </edit-config>

   Below is the example on how to get access related configuration

   <get>
     <filter type="subtree">
       <sys:ntp xmlns:sys="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <sys:access-rules>
         </sys:access-rules>
       </sys: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>
           <acl>2000</acl>
         </access-rule>
       </access-rules>
     </ntp>
   </data>

6.5.  Multicast configuration

   Below is the example on how to configure multicast-server with
   address as 224.1.1.1, 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>
             <multicast-server>
               <address>224.1.1.1</address>
               <authentication>
                 <symmetric-key>
                   <key-id>10</key-id>
                 </symmetric-key>
               </authentication>
               <port>1025</port>
             </multicast-server>
           </interface>
         </interfaces>
       </ntp>
     </config>
   </edit-config>

   Below is the example on how to get multicast-server related
   configuration
   <get>
     <filter type="subtree">
       <sys:ntp xmlns:sys="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <sys:interfaces>
           <sys:interface>
             <sys:multicast-server>
             </sys:multicast-server>
           </sys:interface>
         </sys:interfaces>
       </sys: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>224.1.1.1</address>
             <ttl>224.1.1.1</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>

   Below is the example on how to configure multicast-client with
   address as 224.1.1.1
   <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>224.1.1.1</address>
             </multicast-client>
           </interface>
         </interfaces>
       </ntp>
     </config>
   </edit-config>

   Below is the example on how to get multicast-client related
   configuration

   <get>
     <filter type="subtree">
       <sys:ntp xmlns:sys="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <sys:interfaces>
           <sys:interface>
             <sys:multicast-client>
             </sys:multicast-client>
           </sys:interface>
         </sys:interfaces>
       </sys: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>224.1.1.1</address>
           </multicast-client>
         </interface>
       </interfaces>
     </ntp>
   </data>

6.6.  Manycast configuration

   Below is the example on how to configure manycast-client with address
   as 224.1.1.1, 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>224.1.1.1</address>
               <authentication>
                 <symmetric-key>
                   <key-id>10</key-id>
                 </symmetric-key>
               </authentication>
               <port>1025</port>
             </manycast-client>
           </interface>
         </interfaces>
       </ntp>
     </config>
   </edit-config>

   Below is the example on how to get manycast-client related
   configuration
   <get>
     <filter type="subtree">
       <sys:ntp xmlns:sys="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <sys:interfaces>
           <sys:interface>
             <sys:manycast-client>
             </sys:manycast-client>
           </sys:interface>
         </sys:interfaces>
       </sys: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>224.1.1.1</address>
             <authentication>
               <symmetric-key>
                 <key-id>10</key-id>
               </symmetric-key>
             </authentication>
             <ttl>255</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>

   Below is the example on how to configure manycast-server with address
   as 224.1.1.1
   <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>224.1.1.1</address>
             </manycast-server>
           </interface>
         </interfaces>
       </ntp>
     </config>
   </edit-config>

   Below is the example on how to get manycast-server related
   configuration

   <get>
     <filter type="subtree">
       <sys:ntp xmlns:sys="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <sys:interfaces>
           <sys:interface>
             <sys:manycast-server>
             </sys:manycast-server>
           </sys:interface>
         </sys:interfaces>
       </sys: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>224.1.1.1</address>
           </manycast-server>
         </interface>
       </interfaces>
     </ntp>
   </data>

6.7.  Clock state

   Below is the example on how to get clock current state

   <get>
     <filter type="subtree">
       <sys:ntp xmlns:sys="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <sys:clock-state>
         </sys:clock-state>
       </sys: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>1.1.1.1</clock-refid>
                    <associations-address>1.1.1.1</associations-address>
                    <associations-local-mode>client</associations-local-mode>
                    <associations-isConfigured>yes</associations-isConfigured>
           <associations-address>1.1.1.1
           </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> Z+05:30
           </reference-time>
           <sync-state>clock-synchronized</sync-state>
         </system-status>
       </clock-state>
     </ntp>
   </data>

6.8.  Get all association

   Below is the example on how to get all association present
   <get>
     <filter type="subtree">
       <sys:ntp xmlns:sys="urn:ietf:params:xml:ns:yang:ietf-ntp">
         <sys:associations>
         </sys:associations>
       </sys: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>1.1.1.1</address>
         <stratum>9</stratum>
         <refid>20.1.1.1</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> Z+05:30
         </originate-time>
         <receive-time>10-10-2017 07:33:55.258 Z+05:30</receive-time> Z+05:30
         </receive-time>
         <transmit-time>10-10-2017 07:33:55.300 Z+05:30</transmit-time> Z+05:30
         </transmit-time>
         <input-time>10-10-2017 07:33:55.305 Z+05:30</input-time> 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>

6.9.  Global statistic

   Below is the example on how to get clock current state

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

7.  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 NETMOD WG of the IETF.

   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

8.  Security Considerations

   The YANG module defined specified in this memo document defines a schema for data
   that is designed to be accessed via
   the network management protocols such
   as NETCONF protocol [RFC6241]. [RFC6241] or RESTCONF [RFC8040].  The lowest NETCONF layer
   is the secure transport layer layer, and the mandatory-to-implement secure
   transport is SSH Secure Shell (SSH) [RFC6242].  The lowest RESTCONF layer
   is HTTPS, and the mandatory-to-implement secure transport is TLS
   [RFC5246].

   The NETCONF access control model [RFC6536] provides the means to
   restrict access for particular NETCONF or RESTCONF users to a pre-configured
   preconfigured subset of all available NETCONF or RESTCONF protocol
   operations and content.

   There are a number of data nodes defined in the this YANG module which 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>) 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.
      Car 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 inclide 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
   notification) to these data nodes.  These are the subtrees and data
   nodes and their sensitivity/vulnerability:

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

9.  Acknowledgments

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

10.  References

10.1.  Normative References

   [I-D.ietf-netmod-yang-tree-diagrams]
              Bjorklund, M. and L. Berger, "YANG Tree Diagrams", draft-
              ietf-netmod-yang-tree-diagrams-02
              ietf-netmod-yang-tree-diagrams-06 (work in progress),
              October 2017.
              February 2018.

   [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>.

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

   [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>.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536,
              DOI 10.17487/RFC6536, March 2012,
              <https://www.rfc-editor.org/info/rfc6536>.

   [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>.

10.2.  Informative References

   [I-D.ietf-netmod-revised-datastores]
              Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore
              Architecture", draft-ietf-netmod-revised-datastores-05 draft-ietf-netmod-revised-datastores-10
              (work in progress), October 2017.

   [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>. January 2018.

   [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>.

Authors' Addresses

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

   Email: eric.wu@huawei.com
   Anil Kumar S N
   RtBrick Inc.
   Bangalore, Kanataka  560037
   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

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

   Email: dhruv.ietf@gmail.com

   Ankit kumar Sinha
   Huawei
   Divyashree Techno Park, Whitefield
   RtBrick Inc.
   Bangalore, Kanataka  560066
   India

   Email: ankit.ietf@gmail.com