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A YANG Data Model for NTP
draft-wu-ntp-ntp-cfg-00

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This is an older version of an Internet-Draft whose latest revision state is "Replaced".
Author Nan Wu
Last updated 2015-01-28
Replaced by draft-ietf-ntp-yang-data-model, RFC 9249
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draft-wu-ntp-ntp-cfg-00
Network Working Group                                              N. Wu
Internet-Draft                                              A. Kumar S N
Intended status: Standards Track                                  Huawei
Expires: August 1, 2015                                 January 28, 2015

                       A YANG Data Model for NTP
                        draft-wu-ntp-ntp-cfg-00

Abstract

   This document defines a YANG data model for Network Time Protocol
   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", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://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 1, 2015.

Copyright Notice

   Copyright (c) 2015 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
   (http://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

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   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.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Tree Diagrams . . . . . . . . . . . . . . . . . . . . . .   3
   2.  NTP data model  . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Relationship to NTPv4-MIB . . . . . . . . . . . . . . . . . .   5
   4.  NTP YANG Module . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  22
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  22
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

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 binding, and also
   associations of NTP in different modes and parameters of per-
   interface.  It also provides information about running state of NTP
   implementations.

1.1.  Terminology

   The following terms are defined in [RFC6020]:

   o  configuration data

   o  data model

   o  module

   o  state data

   The terminology for describing YANG data models is found in
   [RFC6020].

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1.2.  Tree Diagrams

   A simplified graphical representation of the data model is used in
   this document.  The meaning of the symbols in these diagrams is as
   follows:

   o  Brackets "[" and "]" enclose list keys.

   o  Abbreviations before data node names: "rw" means configuration
      data (read-write), and "ro" means state data (read-only).

   o  Symbols after data node names: "?" means an optional node, "!"
      means a presence container, and "*" denotes a list and leaf-list.

   o  Parentheses enclose choice and case nodes, and case nodes are also
      marked with a colon (":").

   o  Ellipsis ("...") stands for contents of subtrees that are not
      shown.

2.  NTP data model

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

   module: ietf-ntp
      +--rw ntp-cfg!
      |  +--rw ntp-enabled?       boolean
      |  +--rw refclock-master
      |  |  +--rw master?           boolean
      |  |  +--rw master-stratum?   ntp-stratum
      |  +--rw authentication!
      |  |  +--rw auth-enabled?          boolean
      |  |  +--rw trusted-key?           uint32
      |  |  +--rw authentication-keys* [key-id]
      |  |     +--rw key-id       uint32
      |  |     +--rw algorithm?   enumeration
      |  |     +--rw password?    union
      |  +--rw access-rules
      |  |  +--rw access-rule* [access-mode]
      |  |     +--rw access-mode    enumeration
      |  |     +--rw acl-number
      |  |        +--rw (acl-type)?
      |  |           +--:(ipv4)
      |  |           |  +--rw acl-number-ipv4?   uint16
      |  |           +--:(ipv6)
      |  |              +--rw acl-number-ipv6?   uint16
      |  +--rw associations

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      |  |  +--rw peers
      |  |  |  +--rw peer* [address vrf]
      |  |  |     +--rw version?   ntp-version
      |  |  |     +--rw address    inet:ip-address
      |  |  |     +--rw key-id?    leafref
      |  |  |     +--rw minpoll?   ntp-minpoll
      |  |  |     +--rw maxpoll?   ntp-maxpoll
      |  |  |     +--rw prefer?    boolean
      |  |  |     +--rw burst?     boolean
      |  |  |     +--rw iburst?    boolean
      |  |  |     +--rw vrf        string
      |  |  |     +--rw source?    leafref
      |  |  +--rw servers
      |  |     +--rw server* [address vrf]
      |  |        +--rw version?   ntp-version
      |  |        +--rw address    inet:ip-address
      |  |        +--rw key-id?    leafref
      |  |        +--rw minpoll?   ntp-minpoll
      |  |        +--rw maxpoll?   ntp-maxpoll
      |  |        +--rw prefer?    boolean
      |  |        +--rw burst?     boolean
      |  |        +--rw iburst?    boolean
      |  |        +--rw vrf        string
      |  |        +--rw source?    leafref
      |  +--rw ntp-interfaces
      |     +--rw ntp-interface* [ntp-ifname]
      |        +--rw ntp-ifname          leafref
      |        +--rw multicast-client
      |        |  +--rw multicast-client-address?   union
      |        +--rw multicast-server
      |        |  +--rw multicast-server-address?   inet:ip-address
      |        |  +--rw multicast-server-ttl?       uint8
      |        |  +--rw multicast-server-version?   ntp-version
      |        |  +--rw multicast-server-keyid?     leafref
      |        +--rw broadcast-client
      |        |  +--rw broadcast-client-enabled?   boolean
      |        +--rw broadcast-server
      |           +--rw broadcast-server-version?   ntp-version
      |           +--rw broadcast-server-keyid?     leafref
      +--ro ntp-state
         +--ro system-status
         |  +--ro clock-state?       enumeration
         |  +--ro clock-stratum?     ntp-stratum
         |  +--ro clock-refid?       union
         |  +--ro nominal-freq?      decimal64
         |  +--ro actual-freq?       decimal64
         |  +--ro clock-precision?   uint8
         |  +--ro clock-offset?      decimal64

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         |  +--ro root-delay?        decimal64
         |  +--ro root-dispersion?   decimal64
         |  +--ro peer-dispersion?   decimal64
         |  +--ro reference-time?    string
         |  +--ro sync-state?        enumeration
         +--ro associations-status
         |  +--ro association-status* [association-source]
         |     +--ro association-source        union
         |     +--ro association-stratum?      ntp-stratum
         |     +--ro association-refid?        union
         |     +--ro association-reach?        uint8
         |     +--ro association-poll?         uint8
         |     +--ro association-now?          uint32
         |     +--ro association-offset?       decimal64
         |     +--ro association-delay?        decimal64
         |     +--ro association-dispersion?   decimal64
         |     +--ro association-sent?         uint32
         |     +--ro association-sent-fail?    uint32
         |     +--ro association-received?     uint32
         |     +--ro association-dropped?      uint32
         +--ro ntp-statistics
            +--ro packet-sent?        uint32
            +--ro packet-sent-fail?   uint32
            +--ro packet-received?    uint32
            +--ro packet-dropped?     uint32

   This data model defines two primary containers, one for NTP
   configuration and the other is for NTP running state.  The NTP
   configuration container includes data nodes for access rules,
   authentication, associations and interfaces.  In the NTP running
   state container, there are data nodes for system status and
   associations.

3.  Relationship to NTPv4-MIB

   If the device implements the NTPv4-MIB [RFC5907], data nodes in
   container ntp-cfg 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.

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   +--------------------------------+----------------------------------+
   | YANG data nodes in /ntp-cfg/   |    NTPv4-MIB objects             |
   +--------------------------------+----------------------------------|
   | ntp-enabled                    | ntpEntStatusCurrentMode          |
   +-------------------------------------------------------------------+

   +-------------------------------------+-----------------------------+
   | YANG data nodes in                  | NTPv4-MIB objects           |
   | /ntp-cfg/associations/peers/peer    |                             |
   | /ntp-cfg/associations/servers/server|                             |
   +-------------------------------------+-----------------------------+
   | address                             | ntpAssocAddressType         |
   |                                     | ntpAssocAddress             |
   +-------------------------------------------------------------------+
    YANG NTP Configuration Data Nodes and Related NTPv4-MIB Objects

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

        YANG NTP State Data Nodes and Related NTPv4-MIB Objects

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4.  NTP YANG Module

   //<CODE BEGINS> file "ietf-ntp@2015-01-28.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 ietf-ip {
           prefix "ip";
         }

         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>";

         description
           "This YANG module defines essential components for the management
            of a routing subsystem.

            Copyright (c) 2014 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

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            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 2015-01-28 {
           description
             "Initial revision.";
           reference
             "RFC XXXX: A YANG Data Model for NTP Management";
         }

    /* Typedef Definitions */
    typedef ntp-stratum {
      type uint8;
      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 minimul poll interval for this NTP association.";
    }

    typedef ntp-maxpoll {
        type uint8 {
            range "4..17";
        }
        default "10";

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        description
            "The maximul poll interval for this NTP association.";
    }

    typedef multicast-client-v4address {
        type inet:ipv4-address;
        default "224.0.1.1";
        description
            "The IPv4 address for NTP multicast client.";
    }

    typedef multicast-client-v6address {
        type inet:ipv6-address;
        default "FF0E::0101";
        description
            "The IPv6 address for NTP multicast client.";
    }

    /* Groupings */
    grouping authentication-key {
       description
         "To define an authentication key for a NTP time source.";
       leaf key-id {
         type uint32 {
            range "1..max";
         }
         description
           "Authentication key identifier.";
       }
       leaf algorithm {
         type enumeration {
           enum md5 {
             description
               "Message Digest 5 (MD5) algorithm.";
           }
           enum hmac-sha256 {
             description
               "Secure Hash Algorithm 256 algorithm.";
           }
         }
         description
           "Authentication algorithm.";
       }
        leaf password {
            type union {
                type string {
                    length "1..255";
                }

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                type string {
                    length "20..392";
                }
            }
            description
                "Clear or encrypted mode for password text.";
        }
    }

    grouping association-param {
       description
         "To define parameters for a NTP associations.";
       leaf version {
         type ntp-version;
         description
           "NTP version.";
       }
       leaf address {
         type inet:ip-address;
         description
           "The IP address of this association.";
       }
       leaf key-id {
           type leafref {
             path "/ntp:ntp-cfg/ntp:authentication/ntp:authentication-keys/ntp:key-id";
           }
           description
             "Authentication key id referenced in this association.";
       }
       leaf minpoll {
           type ntp-minpoll;
           description
             "The minimul poll interval used in this association.";
       }
       leaf maxpoll {
           type ntp-maxpoll;
           description
             "The maximul poll interval used in this association.";
       }
       leaf prefer {
           type boolean;
           default "false";
           description
             "Whether this association is preferred.";
       }
       leaf burst {
           type boolean;
           default "false";

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           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 vrf {
           type string;
           description
             "The VRF instance this association binded to.";
       }
       leaf source {
           type leafref {
            path "/if:interfaces/if:interface/if:name";
        }
           description
             "The interface whose ip address this association used as source address.";
       }
    }

    /* Configuration data nodes */
    container ntp-cfg {
        presence
          "Enables NTP unless the 'ntp-enabled' leaf
          (which defaults to 'true') is set to 'false'";
        description
          "Configuration parameters for NTP.";
        leaf ntp-enabled {
          type boolean;
          default true;
          description
            "Controls whether NTP is enabled or disabled on this device.";
        }
        container refclock-master {
        leaf master {
          type boolean;
          default false;
          description
            "Use its own NTP master clock to synchronize with peers when true.";
          }

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        leaf master-stratum {
          type ntp-stratum;
          default "16";
          description
            "Use its own NTP master clock to synchronize with peers when true.";
          }
        }

     container authentication {
            presence
                "Enables NTP authentication when the 'auth-enabled'
                leaf is set to 'true'.";
            description
               "Configuration of authentication.";
            leaf auth-enabled {
              type boolean;
              default false;
              description
                "Controls whether NTP authentication is enabled or disabled
                 on this device.";
            }
            leaf trusted-key {
                type uint32;
              description
                "The key trusted by NTP.";

            }
             list authentication-keys {
                key "key-id";
                uses authentication-key;

             }

        }

     container access-rules {
          list access-rule {
              key "access-mode";
              leaf access-mode {
                 type enumeration {
                   enum peer {
                     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.";
                   }

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                   enum server {
                     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 {
                     description
                       "Enables the server to access.
                       Only time request can be performed
                       on the local NTP service.";
                   }
                   enum query {
                     description
                       "Sets the maximum access limitation.
                       Control query can be performed only
                       on the local NTP service.";
                   }
                 }
                 description
                   "NTP access mode.";
              }
            container acl-number {
                choice acl-type {
                   case ipv4 {
                       leaf acl-number-ipv4 {
                           type uint16;
                           description "IPv4 acl number.";
                       }
                   }
                   case ipv6 {
                       leaf acl-number-ipv6 {
                           type uint16;
                           description "IPv6 acl number.";
                       }
                   }
                }
            }
          }
        }

     container associations {
          container peers {
             description
               "Peer associations.";
             list peer {
                key "address vrf";

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                uses association-param;

             }
          }
          container servers {
             description
               "Sever associations.";
             list server {
                key "address vrf";
                uses association-param;

             }
          }
        }

     container ntp-interfaces {
            description "Configuration parameters for NTP interfaces.";
            list ntp-interface {
                key "ntp-ifname";
                leaf ntp-ifname {
                       type leafref {
                        path "/if:interfaces/if:interface/if:name";
                    }
                }
                container multicast-client {
                  leaf multicast-client-address {
                    type union {
                        type multicast-client-v4address;
                        type multicast-client-v6address;
                    }
                  description
                    "The IP address of the multicast group to join.";
                  }
                }
                container multicast-server {
                  leaf multicast-server-address {
                    type inet:ip-address;
                  description
                    "The IP address to send NTP multicast packets.";
                  }
                  leaf multicast-server-ttl {
                    type uint8;
                  description
                    "Specifies the time to live (TTL) of a multicast packet.";
                  }
                  leaf multicast-server-version {
                    type ntp-version;
                  description

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                    "Specifies the version a multicast packet.";
                  }
                  leaf multicast-server-keyid {
                    type leafref {
                      path "/ntp:ntp-cfg/ntp:authentication/ntp:authentication-keys/ntp:key-id";
                    }
                  description
                    "Specifies the authentication key id of a multicast packet.";
                  }
                }
                container broadcast-client {
                  leaf broadcast-client-enabled {
                    type boolean;
                  description
                    "Allows a device to receive NTP broadcast packets on an interface.";
                  }
                }
                container broadcast-server {
                  leaf broadcast-server-version {
                    type ntp-version;
                  description
                    "Specifies the version of a broadcast packet.";
                  }
                  leaf broadcast-server-keyid {
                    type leafref {
                      path "/ntp:ntp-cfg/ntp:authentication/ntp:authentication-keys/ntp:key-id";
                    }
                    description
                     "Specifies the authentication key id of a broadcast packet.";
                  }
                }
            }
        }

    }

    /* Operational state data */
     container ntp-state {
       config "false";
       description
         "Operational state of the NTP.";

       container system-status {
            description
               "System status of NTP.";
            leaf clock-state {
                type enumeration {

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                   enum synchronized {
                     description
                       "Indicates that the local clock has been
                       synchronized with an NTP server
                       or the reference clock.";
                   }
                   enum unsynchronized {
                     description
                       "Indicates that the local clock has not been
                        synchronized with any NTP server.";
                   }
                }
                description
                    "Indicates the state of system clock.";
            }
            leaf clock-stratum {
                type ntp-stratum;
                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";
                    }
                }
                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.";
            }
            leaf nominal-freq {
                type decimal64 {
                    fraction-digits 4;
                }
                description
                    "Indicates the nominal frequency of the local clock, in Hz.";
            }
            leaf actual-freq {
                type decimal64 {
                    fraction-digits 4;
                }
                description
                    "Indicates the actual frequency of the local clock, in Hz.";

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            }
            leaf clock-precision {
                type uint8;
                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 peer-dispersion {
                type decimal64 {
                    fraction-digits 2;
                }
                description
                    "Indicates the dispersion between the local clock
                     and the peer clock, in milliseconds.";
            }
            leaf reference-time {
                type string;
                description "Indicates reference timestamp.";
            }
            leaf sync-state {
                type enumeration {
                   enum clock-not-set {
                     description
                       "Indicates the clock is not updated.";
                   }
                   enum freq-set-by-cfg {
                     description

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                       "Indicates the clock frequency is set
                       by NTP configuration.";
                   }
                   enum clock-set {
                     description
                       "Indicates the clock is set.";
                   }
                   enum freq-not-determined {
                     description
                       "Indicates the clock is set but the frequency
                        is not determined.";
                   }
                   enum clock-synchronized {
                     description
                       "Indicates that the clock is synchronized.";
                   }
                   enum spike {
                     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
                    "Indicates the synchronization status of the local clock.";
            }
       }

        container associations-status {
            description
               "System status of NTP.";
             list association-status {
                 key "association-source";
                 leaf association-source {
                    type union {
                        type inet:ipv4-address;
                        type inet:ipv6-address;
                    }
                    description
                        "IPv4 or IPv6 address of the peer.
                        If a nondefault VRF is configured for the peer,
                        the VRF follows the address.";
                 }
                 leaf association-stratum {
                    type ntp-stratum;
                    description
                        "Indicates the stratum of the reference clock.";

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                 }
                 leaf association-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 association-reach {
                    type uint8;
                    description
                        "Indicates the reachability of the configured server or peer.";
                 }
                 leaf association-poll {
                    type uint8;
                    description
                        "Indicates the polling interval for current, in seconds.";
                 }
                 leaf association-now {
                    type uint32;
                    description
                        "Indicates the time since the NTP packet was not
                         received or last synchronized, in seconds.";
                 }
                 leaf association-offset {
                    type decimal64 {
                        fraction-digits 4;
                    }
                    description
                        "Indicates the offset between the local clock
                         and the superior reference clock.";
                 }
                 leaf association-delay {
                    type decimal64 {
                        fraction-digits 2;
                    }
                    description
                        "Indicates the delay between the local clock
                         and the superior reference clock.";
                 }
                 leaf association-dispersion {
                    type decimal64 {

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                        fraction-digits 2;
                    }
                    description
                        "Indicates the dispersion between the local clock
                         and the superior reference clock.";
                 }
                 leaf association-sent {
                     type uint32;
                     description
                        "Indicates the total number of packets
                         this association sent.";
                 }
                 leaf association-sent-fail {
                     type uint32;
                     description
                        "Indicates the number of times packet sending
                         failed by this association.";
                 }
                 leaf association-received {
                     type uint32;
                     description
                        "Indicates the total number of packets
                         this association received.";
                 }
                 leaf association-dropped {
                     type uint32;
                     description
                        "Indicates the number of packets
                         this association dropped.";
                 }
             }
        }

        container ntp-statistics {
            description
               "Packet statistics of NTP.";
            leaf packet-sent {
                type uint32;
                description
                    "Indicates the total number of packets sent.";
            }
            leaf packet-sent-fail {
                type uint32;
                description
                    "Indicates the number of times packet sending failed.";
            }
            leaf packet-received {
                type uint32;

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                description
                    "Indicates the total number of packets received.";
            }
            leaf packet-dropped {
                type uint32;
                description
                    "Indicates the number of packets dropped.";
            }
        }

     }

}

//<CODE ENDS>

5.  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

6.  Security Considerations

   The YANG module defined in this memo is designed to be accessed via
   the NETCONF protocol [RFC6241].  The lowest NETCONF layer is the
   secure transport layer and the mandatory-to-implement secure
   transport is SSH [RFC6242].  The NETCONF access control model
   [RFC6536] provides the means to restrict access for particular

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   NETCONF users to a pre-configured subset of all available NETCONF
   protocol operations and content.

   There are a number of data nodes defined in the YANG module which 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.

7.  Acknowledgments

   TBD.

8.  References

8.1.  Normative References

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

   [RFC5905]  Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
              Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, June 2010.

   [RFC5907]  Gerstung, H., Elliott, C., and B. Haberman, "Definitions
              of Managed Objects for Network Time Protocol Version 4
              (NTPv4)", RFC 5907, June 2010.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)", RFC
              6241, June 2011.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, June 2011.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536, March
              2012.

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8.2.  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

Authors' Addresses

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

   Email: eric.wu@huawei.com

   Anil Kumar S N
   Huawei
   Kundalahalli Village, Whitefield
   Bangalore, Kanataka  560037
   India

   Email: anil.sn@huawei.comA

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