module ietf-ntp {

    yang-version 1.1;

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

    prefix ntp;

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


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


    }
    import ietf-interfaces {
      prefix if;
      reference
        "RFC 8343: A YANG Data Model for Interface Management";


    }
    import ietf-system {
      prefix sys;
      reference
        "RFC 7317: A YANG Data Model for System Management";


    }
    import ietf-access-control-list {
      prefix acl;
      reference
        "RFC 8519: YANG Data Model for Network Access Control
        Lists (ACLs)";


    }
    import ietf-routing-types {
      prefix rt-types;
      reference
        "RFC 8294: Common YANG Data Types for the Routing Area";


    }
    import ietf-netconf-acm {
      prefix nacm;
      reference
        "RFC 8341: Network Configuration Access Control Model";


    }

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

    contact
      "WG Web:  <https://datatracker.ietf.org/wg/ntp/>
     WG List:  <mailto: ntp@ietf.org
     Editor:   Dhruv Dhody
              <mailto:dhruv.ietf@gmail.com>
     Editor:   Ankit Kumar Sinha
              <mailto:ankit.ietf@gmail.com>";

    description
      "This document defines a YANG data model that can be used
     to configure and manage  Network Time Protocol (NTP) version 4.
     It can also be used to configure and manage version 3.
     The data model includes configuration data and state data.

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

     Copyright (c) 2022 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 Revised BSD License
     set forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (https://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC 9249; see the
     RFC itself for full legal notices.";

    revision "2022-07-05" {
      description "Initial revision";
      reference
        "RFC 9249: A YANG Data Model for NTP";

    }


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

    }

    typedef ntp-version {
      type uint8 {
        range "3..max";
      }
      default "4";
      description
        "The current NTP version supported by the corresponding
       association";
      reference
        "RFC 5905: Network Time Protocol Version 4: Protocol and
        Algorithms Specification, Section 1";

    }

    typedef refid {
      type union {
        type inet:ipv4-address;
        type uint32;
        type string {
          length "4";
        }
      }
      description
        "A code identifying the particular server or reference
       clock.  The interpretation depends upon stratum.  It
       could be an IPv4 address, the first 32 bits of the MD5 hash
       of the IPv6 address, or a string for the Reference Identifier
       and kiss codes.  Some examples:

       -- a refclock ID like '127.127.1.0' for local clock sync

       -- uni/multi/broadcast associations for IPv4 will look like
          '203.0.113.1' and '0x4321FEDC' for IPv6

       -- sync with a primary source will look like 'DCN', 'NIST',
          'ATOM'

       -- kiss codes will look like 'AUTH', 'DROP', or 'RATE'

       Note that the use of an MD5 hash for IPv6 addresses is not
       for cryptographic purposes.";
      reference
        "RFC 5905: Network Time Protocol Version 4: Protocol and
        Algorithms Specification, Section 7.3";

    }

    typedef ntp-date-and-time {
      type union {
        type yang:date-and-time;
        type uint8;
      }
      description
        "Follows the date-and-time format when valid values exist.
       Otherwise, allows for setting a special value such as
       zero.";
      reference
        "RFC 6991: Common YANG Data Types";

    }

    typedef log2seconds {
      type int8;
      description
        "An 8-bit signed integer that represents signed log2
       seconds.";
    }

    feature ntp-port {
      description
        "Support for NTP port configuration";
      reference
        "RFC 5905: Network Time Protocol Version 4: Protocol and
        Algorithms Specification, Section 7.2";

    }

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

    }

    feature deprecated {
      description
        "Support deprecated MD5-based authentication (RFC 8573),
       SHA-1, or any other deprecated authentication mechanism.
       It is enabled to support legacy compatibility when secure
       cryptographic algorithms are not available to use.
       It is also used to configure keystrings in ASCII format.";
      reference
        "RFC 1321: The MD5 Message-Digest Algorithm,
         RFC 3174: US Secure Hash Algorithm 1 (SHA1),
        SHS: Secure Hash Standard (SHS) (FIPS PUB 180-4)";

    }

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

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

    }

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

    }

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

    }

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

    }

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

    }

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

    }

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

    }

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

    }

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

    identity uc-server {
      base unicast-configuration-type;
      description
        "Use client association mode where the unicast server
       address is configured.";
    }

    identity uc-peer {
      base unicast-configuration-type;
      description
        "Use symmetric active association mode where the peer
       address is configured.";
    }

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

    }

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

    identity passive {
      base association-mode;
      description
        "Use symmetric passive association mode (mode 2).
       This device has learned this association dynamically.
       This device may synchronize with its NTP peer.";
    }

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

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

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

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

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

    }

    identity peer-access-mode {
      base access-mode;
      description
        "Permit others to synchronize their time with this NTP
       or vice versa.
       NTP control queries are also accepted.  This enables
       full access authority.";
    }

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

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

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

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

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

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

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

    }

    identity clock-never-set {
      base ntp-sync-state;
      description
        "Indicates the clock was never set.";
    }

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

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

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

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

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

    identity md5 {
      base crypto-algorithm;
      description
        "The MD5 algorithm.  Note that RFC 8573
       deprecates the use of MD5-based authentication.";
      reference
        "RFC 1321: The MD5 Message-Digest Algorithm";

    }

    identity sha-1 {
      base crypto-algorithm;
      description "The SHA-1 algorithm";
      reference
        "RFC 3174: US Secure Hash Algorithm 1 (SHA1)";

    }

    identity hmac-sha-1 {
      base crypto-algorithm;
      description
        "HMAC-SHA-1 authentication algorithm";
      reference
        "SHS: Secure Hash Standard (SHS) (FIPS PUB 180-4)";

    }

    identity hmac-sha1-12 {
      base crypto-algorithm;
      description
        "The HMAC-SHA1-12 algorithm";
    }

    identity hmac-sha-256 {
      description
        "HMAC-SHA-256 authentication algorithm";
      reference
        "SHS: Secure Hash Standard (SHS) (FIPS PUB 180-4)";

    }

    identity hmac-sha-384 {
      description
        "HMAC-SHA-384 authentication algorithm";
      reference
        "SHS: Secure Hash Standard (SHS) (FIPS PUB 180-4)";

    }

    identity hmac-sha-512 {
      description
        "HMAC-SHA-512 authentication algorithm";
      reference
        "SHS: Secure Hash Standard (SHS) (FIPS PUB 180-4)";

    }

    identity aes-cmac {
      base crypto-algorithm;
      description
        "The AES-CMAC algorithm -- required by
       RFC 8573 for MAC for the NTP.";
      reference
        "RFC 4493: The AES-CMAC Algorithm,
         RFC 8573: Message Authentication Code for the Network
        Time Protocol";

    }

    grouping key {
      nacm:default-deny-all;
      description "The key";
      choice key-string-style {
        description "Key string styles";
        leaf keystring {
          if-feature deprecated;
          type string;
          description
            "Key string in ASCII format";
        }

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

    grouping authentication-key {
      description
        "To define an authentication key for an NTP
       time source.";
      reference
        "RFC 5905: Network Time Protocol Version 4: Protocol and
        Algorithms Specification, Sections 7.3 and 7.4";

      leaf keyid {
        type uint32 {
          range "1..max";
        }
        description
          "Authentication key identifier";
      }

      leaf algorithm {
        type identityref {
          base crypto-algorithm;
        }
        description
          "Authentication algorithm.  Note that RFC 8573
         deprecates the use of MD5-based authentication
         and recommends AES-CMAC.";
      }

      container key {
        description
          "The key.  Note that RFC 8573 deprecates the use
         of MD5-based authentication.";
        uses key;
      }  // container key

      leaf istrusted {
        type boolean;
        description
          "Keyid is trusted or not";
      }
    }  // grouping authentication-key

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

    grouping statistics {
      description "NTP packet statistic";
      leaf discontinuity-time {
        type ntp-date-and-time;
        description
          "The time on the most recent occasion at which any one or
         more of these NTP counters suffered a discontinuity.  If
         no such discontinuities have occurred, then this node
         contains the time the NTP association was
         (re-)initialized.";
      }

      leaf packet-sent {
        type yang:counter32;
        description
          "The total number of NTP packets delivered to the
         transport service by this NTP entity for this
         association.
         Discontinuities in the value of this counter can occur
         upon cold start, reinitialization of the NTP entity or the
         management system, and at other times.";
      }

      leaf packet-sent-fail {
        type yang:counter32;
        description
          "The number of times NTP packet sending failed.";
      }

      leaf packet-received {
        type yang:counter32;
        description
          "The total number of NTP packets delivered to the
         NTP entity from this association.
         Discontinuities in the value of this counter can occur
         upon cold start, reinitialization of the NTP entity or the
         management system, and at other times.";
      }

      leaf packet-dropped {
        type yang:counter32;
        description
          "The total number of NTP packets that were delivered
         to this NTP entity from this association and that this
         entity was not able to process due to an NTP error.
         Discontinuities in the value of this counter can occur
         upon cold start, reinitialization of the NTP entity or the
         management system, and at other times.";
      }
    }  // grouping statistics

    grouping common-attributes {
      description
        "NTP common attributes for configuration";
      reference
        "RFC 5905: Network Time Protocol Version 4: Protocol and
        Algorithms Specification";

      leaf minpoll {
        type log2seconds;
        default "6";
        description
          "The minimum poll interval used in this association";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
          Algorithms Specification, Section 7.2";

      }

      leaf maxpoll {
        type log2seconds;
        default "10";
        description
          "The maximum poll interval used in this association";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
          Algorithms Specification, Section 7.2";

      }

      leaf port {
        if-feature ntp-port;
        type inet:port-number {
          range "123 | 1024..max";
        }
        default "123";
        description
          "Specify the port used to send NTP packets.";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
          Algorithms Specification, Section 7.2";

      }

      leaf version {
        type ntp-version;
        description "NTP version";
      }
    }  // grouping common-attributes

    grouping association-ref {
      description
        "Reference to NTP association mode";
      leaf associations-address {
        type leafref {
          path
            "/ntp:ntp/ntp:associations/ntp:association"
              + "/ntp:address";
        }
        description
          "Indicates the association's address
         that results in clock synchronization.";
      }

      leaf associations-local-mode {
        type leafref {
          path
            "/ntp:ntp/ntp:associations/ntp:association"
              + "/ntp:local-mode";
        }
        description
          "Indicates the association's local-mode
         that results in clock synchronization.";
      }

      leaf associations-isconfigured {
        type leafref {
          path
            "/ntp:ntp/ntp:associations/ntp:association/"
              + "ntp:isconfigured";
        }
        description
          "Indicates if the association (that resulted in the
         clock synchronization) is explicitly configured.";
      }
    }  // grouping association-ref

    container ntp {
      when
        'false() = boolean(/sys:system/sys:ntp)' {
        description
          "Applicable when the system /sys/ntp/ is not used.";
      }
      presence
        "NTP is enabled and system should attempt to
              synchronize the system clock with an NTP server
              from the 'ntp/associations' list.";
      description
        "Configuration parameters for NTP";
      leaf port {
        if-feature ntp-port;
        type inet:port-number {
          range "123 | 1024..max";
        }
        default "123";
        description
          "Specify the port used to send and receive NTP packets.";
        reference
          "RFC 5905: Network Time Protocol Version 4: Protocol and
          Algorithms Specification, Section 7.2";

      }

      container refclock-master {
        presence
          "NTP master clock is enabled.";
        description
          "Configures the local clock of this device as NTP server.";
        leaf master-stratum {
          type ntp-stratum;
          default "16";
          description
            "Stratum level from which NTP clients get their time
           synchronized.";
        }
      }  // container refclock-master

      container authentication {
        if-feature authentication;
        description
          "Configuration of authentication";
        leaf auth-enabled {
          type boolean;
          default "false";
          description
            "Controls whether NTP authentication is enabled
           or disabled on this device.";
        }

        list authentication-keys {
          key "keyid";
          description
            "List of authentication keys";
          uses authentication-key;
        }  // list authentication-keys
      }  // container authentication

      container access-rules {
        if-feature access-rules;
        description
          "Configuration to control access to NTP service
         by using the NTP access-group feature.
         The access-mode identifies how the ACL is
         applied with NTP.";
        list access-rule {
          key "access-mode";
          description "List of access rules";
          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol and
            Algorithms Specification, Section 9.2";

          leaf access-mode {
            type identityref {
              base access-mode;
            }
            description
              "The NTP access-mode.  Some of the possible values
             include peer, server, synchronization, query,
             etc.";
          }

          leaf acl {
            type leafref {
              path "/acl:acls/acl:acl/acl:name";
            }
            description
              "Control access configuration to be used.";
          }
        }  // list access-rule
      }  // container access-rules

      container clock-state {
        config false;
        description
          "Clock operational state of the NTP";
        container system-status {
          description "System status of NTP";
          leaf clock-state {
            type identityref {
              base clock-state;
            }
            mandatory true;
            description
              "The state of the system clock.  Some of the possible
             values include synchronized and unsynchronized.";
          }

          leaf clock-stratum {
            type ntp-stratum;
            mandatory true;
            description
              "The NTP entity's own stratum value.  Should be one
             greater than the preceding level.
             16 if unsynchronized.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Section 3";

          }

          leaf clock-refid {
            type refid;
            mandatory true;
            description
              "A code identifying the particular server or reference
             clock.  The interpretation depends upon stratum.  It
             could be an IPv4 address, the first 32 bits of the MD5
             hash of the IPv6 address, or a string for the Reference
             Identifier and kiss codes.  Some examples:

             -- a refclock ID like '127.127.1.0' for local clock sync

             -- uni/multi/broadcast associations for IPv4 will look
                like '203.0.113.1' and '0x4321FEDC' for IPv6

             -- sync with primary source will look like 'DCN',
                'NIST', 'ATOM'

             -- kiss codes will look like 'AUTH', 'DROP', 'RATE'

             Note that the use of MD5 hash for IPv6 address is not
             for cryptographic purposes.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Section 7.3";

          }

          uses association-ref {
            description
              "Reference to association";
          }

          leaf nominal-freq {
            type decimal64 {
              fraction-digits 4;
            }
            units "Hz";
            mandatory true;
            description
              "The nominal frequency of the local clock.  An ideal
             frequency with zero uncertainty.";
          }

          leaf actual-freq {
            type decimal64 {
              fraction-digits 4;
            }
            units "Hz";
            mandatory true;
            description
              "The actual frequency of the local clock";
          }

          leaf clock-precision {
            type log2seconds;
            mandatory true;
            description
              "Clock precision of this system in signed integer format,
             in log 2 seconds -  (prec=2^(-n)).  A value of 5 would
             mean 2^-5 = 0.03125 seconds = 31.25 ms.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Section 7.3";

          }

          leaf clock-offset {
            type decimal64 {
              fraction-digits 3;
            }
            units "milliseconds";
            description
              "The signed time offset to the current selected reference
             time source, e.g., '0.032ms' or '1.232ms'.  The negative
             value indicates that the local clock is behind the
             current selected reference time source.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Section 9.1";

          }

          leaf root-delay {
            type decimal64 {
              fraction-digits 3;
            }
            units "milliseconds";
            description
              "Total delay along the path to the root clock";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Sections 4 and 7.3";

          }

          leaf root-dispersion {
            type decimal64 {
              fraction-digits 3;
            }
            units "milliseconds";
            description
              "The dispersion to the local clock
             and the root clock, e.g., '6.927ms'.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Sections 4, 7.3, and 10";

          }

          leaf reference-time {
            type ntp-date-and-time;
            description
              "The reference timestamp.  Time when the system clock was
             last set or corrected.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Section 7.3";

          }

          leaf sync-state {
            type identityref {
              base ntp-sync-state;
            }
            mandatory true;
            description
              "The synchronization status of the local clock.  Referred
             to as 'Clock state definitions' in RFC 5905.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Appendix A.1.1";

          }
        }  // container system-status
      }  // container clock-state

      list unicast-configuration {
        if-feature unicast-configuration;
        key "address type";
        description
          "List of NTP unicast-configurations";
        leaf address {
          type inet:ip-address;
          description
            "Address of this association";
        }

        leaf type {
          type identityref {
            base unicast-configuration-type;
          }
          description
            "The unicast configuration type, for example,
           unicast-server";
        }

        container authentication {
          if-feature authentication;
          description
            "Authentication used for this association";
          uses authentication;
        }  // container authentication

        leaf prefer {
          type boolean;
          default "false";
          description
            "Whether or not this association is preferred";
        }

        leaf burst {
          type boolean;
          default "false";
          description
            "If set, a series of packets are sent instead of a single
           packet within each synchronization interval to achieve
           faster synchronization.";
          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol
            and Algorithms Specification, Section 13.1";

        }

        leaf iburst {
          type boolean;
          default "false";
          description
            "If set, a series of packets are sent instead of a single
           packet within the initial synchronization interval to
           achieve faster initial synchronization.";
          reference
            "RFC 5905: Network Time Protocol Version 4: Protocol
            and Algorithms Specification, Section 13.1";

        }

        leaf source {
          type if:interface-ref;
          description
            "The interface whose IP address is used by this association
           as the source address.";
        }

        uses common-attributes {
          description
            "Common attributes like port, version, and min and max
           poll.";
        }
      }  // list unicast-configuration

      container associations {
        description "Association parameters";
        list association {
          key "address local-mode isconfigured";
          config false;
          description
            "List of NTP associations.  Here address, local-mode,
           and isconfigured are required to uniquely identify
           a particular association.  Let's take the following
           examples:

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

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

           Thus, all three leaves are needed as key to uniquely
           identify the association.";
          leaf address {
            type inet:ip-address;
            description
              "The remote address of this association.  Represents the
             IP address of a unicast/multicast/broadcast address.";
          }

          leaf local-mode {
            type identityref {
              base association-mode;
            }
            description
              "Local-mode of this NTP association";
          }

          leaf isconfigured {
            type boolean;
            description
              "Indicates if this association is configured (true) or
             dynamically learned (false).";
          }

          leaf stratum {
            type ntp-stratum;
            description
              "The association stratum value";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Section 3";

          }

          leaf refid {
            type refid;
            description
              "A code identifying the particular server or reference
             clock.  The interpretation depends upon stratum.  It
             could be an IPv4 address or first 32 bits of the MD5
             hash of the IPv6 address or a string for the Reference
             Identifier and kiss codes.  Some examples:

             -- a refclock ID like '127.127.1.0' for local clock sync

             -- uni/multi/broadcast associations for IPv4 will look
                like '203.0.113.1' and '0x4321FEDC' for IPv6

             -- sync with primary source will look like 'DCN',
                'NIST', or 'ATOM'

             -- kiss codes will look like 'AUTH', 'DROP', or 'RATE'

             Note that the use of an MD5 hash for IPv6 address is
             not for cryptographic purposes.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Section 7.3";

          }

          leaf authentication {
            if-feature authentication;
            type leafref {
              path "/ntp:ntp/ntp:authentication/ntp:authentication-keys/ntp:keyid";
            }
            description
              "Authentication key used for this association";
          }

          leaf prefer {
            type boolean;
            default "false";
            description
              "Indicates if this association is preferred";
          }

          leaf peer-interface {
            type if:interface-ref;
            description
              "The interface that is used for communication";
          }

          uses common-attributes {
            description
              "Common attributes like port, version, and min and
             max poll";
          }

          leaf reach {
            type uint8;
            description
              "An 8-bit shift register that tracks packet
             generation and receipt.  It is used to determine
             whether the server is reachable and the data are
             fresh.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Sections 9.2 and 13";

          }

          leaf unreach {
            type uint8;
            units "seconds";
            description
              "A count of how long in second the server has been
             unreachable, i.e., the reach value has been zero.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Sections 9.2 and 13";

          }

          leaf poll {
            type log2seconds;
            description
              "The polling interval for current association in signed
             log2 seconds.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Section 7.3";

          }

          leaf now {
            type uint32;
            units "seconds";
            description
              "The time since the last NTP packet was
             received or last synchronized.";
          }

          leaf offset {
            type decimal64 {
              fraction-digits 3;
            }
            units "milliseconds";
            description
              "The signed offset between the local clock
             and the peer clock, e.g., '0.032ms' or '1.232ms'.  The
             negative value indicates that the local clock is behind
             the peer.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Section 8";

          }

          leaf delay {
            type decimal64 {
              fraction-digits 3;
            }
            units "milliseconds";
            description
              "The network delay between the local clock
             and the peer clock";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Section 8";

          }

          leaf dispersion {
            type decimal64 {
              fraction-digits 3;
            }
            units "milliseconds";
            description
              "The root dispersion between the local clock
             and the peer clock.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Section 10";

          }

          leaf originate-time {
            type ntp-date-and-time;
            description
              "This is the local time, in timestamp format,
             when the latest NTP packet was sent to the peer
             (called T1).";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol and
              Algorithms Specification, Section 8";

          }

          leaf receive-time {
            type ntp-date-and-time;
            description
              "This is the local time, in timestamp format,
             when the latest NTP packet arrived at the peer
             (called T2).  If the peer becomes unreachable,
             the value is set to zero.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol
              and Algorithms Specification, Section 8";

          }

          leaf transmit-time {
            type ntp-date-and-time;
            description
              "This is the local time, in timestamp format,
             at which the NTP packet departed the peer
             (called T3).  If the peer becomes unreachable,
             the value is set to zero.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol
              and Algorithms Specification, Section 8";

          }

          leaf input-time {
            type ntp-date-and-time;
            description
              "This is the local time, in timestamp format,
             when the latest NTP message from the peer arrived
             (called T4).  If the peer becomes unreachable,
             value is set to zero.";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol
              and Algorithms Specification, Section 8";

          }

          container ntp-statistics {
            description
              "Per peer packet send and receive statistics";
            uses statistics {
              description
                "NTP send and receive packet statistics";
            }
          }  // container ntp-statistics
        }  // list association
      }  // container associations

      container interfaces {
        description
          "Configuration parameters for NTP interfaces";
        list interface {
          key "name";
          description "List of interfaces";
          leaf name {
            type if:interface-ref;
            description "The interface name";
          }

          container broadcast-server {
            if-feature broadcast-server;
            presence
              "NTP broadcast-server is configured on this
                    interface.";
            description
              "Configuration of broadcast server";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol
              and Algorithms Specification, Section 3.1";

            leaf ttl {
              type uint8;
              description
                "Specifies the time to live (TTL) for a
               broadcast packet";
              reference
                "RFC 5905: Network Time Protocol Version 4: Protocol
                and Algorithms Specification, Section 3.1";

            }

            container authentication {
              if-feature authentication;
              description
                "Authentication used on this interface";
              uses authentication;
            }  // container authentication

            uses common-attributes {
              description
                "Common attributes such as port, version, and min and
               max poll";
            }
          }  // container broadcast-server

          container broadcast-client {
            if-feature broadcast-client;
            presence
              "NTP broadcast-client is configured on this
                    interface.";
            description
              "Configuration of broadcast client";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol
              and Algorithms Specification, Section 3.1";

          }  // container broadcast-client

          list multicast-server {
            if-feature multicast-server;
            key "address";
            description
              "Configuration of multicast server";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol
              and Algorithms Specification, Section 3.1";

            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 TTL for a  multicast packet";
              reference
                "RFC 5905: Network Time Protocol Version 4: Protocol
                and Algorithms Specification, Section 3.1";

            }

            container authentication {
              if-feature authentication;
              description
                "Authentication used on this interface";
              uses authentication;
            }  // container authentication

            uses common-attributes {
              description
                "Common attributes such as port, version, and min and
               max poll";
            }
          }  // list multicast-server

          list multicast-client {
            if-feature multicast-client;
            key "address";
            description
              "Configuration of a multicast client";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol
              and Algorithms Specification, Section 3.1";

            leaf address {
              type rt-types:ip-multicast-group-address;
              description
                "The IP address of the multicast group to
               join";
            }
          }  // list multicast-client

          list manycast-server {
            if-feature manycast-server;
            key "address";
            description
              "Configuration of a manycast server";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol
              and Algorithms Specification, Section 3.1";

            leaf address {
              type rt-types:ip-multicast-group-address;
              description
                "The multicast group IP address to receive
               manycast client messages.";
            }
          }  // list manycast-server

          list manycast-client {
            if-feature manycast-client;
            key "address";
            description
              "Configuration of manycast-client";
            reference
              "RFC 5905: Network Time Protocol Version 4: Protocol
              and Algorithms Specification, Section 3.1";

            leaf address {
              type rt-types:ip-multicast-group-address;
              description
                "The group IP address that the manycast client
               broadcasts the request message to";
            }

            container authentication {
              if-feature authentication;
              description
                "Authentication used on this interface";
              uses authentication;
            }  // container authentication

            leaf ttl {
              type uint8;
              description
                "Specifies the maximum TTL for the expanding
               ring search";
              reference
                "RFC 5905: Network Time Protocol Version 4: Protocol
                and Algorithms Specification, Section 3.1";

            }

            leaf minclock {
              type uint8;
              description
                "The minimum manycast survivors in this
               association";
              reference
                "RFC 5905: Network Time Protocol Version 4: Protocol
                and Algorithms Specification, Section 13.2";

            }

            leaf maxclock {
              type uint8;
              description
                "The maximum manycast candidates in this
               association";
              reference
                "RFC 5905: Network Time Protocol Version 4: Protocol
                and Algorithms Specification, Section 13.2";

            }

            leaf beacon {
              type log2seconds;
              description
                "The beacon is the upper limit of the poll interval.
               When the TTL reaches its limit without finding the
               minimum number of manycast servers, the poll interval
               increases until reaching the beacon value, when it
               starts over from the beginning.";
              reference
                "RFC 5905: Network Time Protocol Version 4: Protocol
                and Algorithms Specification, Section 13.2";

            }

            uses common-attributes {
              description
                "Common attributes like port, version, and min and
               max poll";
            }
          }  // list manycast-client
        }  // list interface
      }  // container interfaces

      container ntp-statistics {
        config false;
        description
          "Total NTP packet statistics";
        uses statistics {
          description
            "NTP send and receive packet statistics";
        }
      }  // container ntp-statistics
    }  // container ntp

    rpc statistics-reset {
      description
        "Reset statistics collected.";
      input {
        choice association-or-all {
          description
            "Resets statistics for a particular association or
           all.";
          case association {
            description
              "This resets all the statistics collected for
             the association.";
            uses association-ref;
          }  // case association

          case all {
            description
              "This resets all the statistics collected.";
          }  // case all
        }  // choice association-or-all
      }
    }  // rpc statistics-reset
  }  // module ietf-ntp