Internet Engineering Task Force (IETF)                       X. Liu, Ed.
Request for Comments: 8347                                   A. Kyparlis
Category: Standards Track                                          Jabil
ISSN: 2070-1721                                                R. Parikh
                                                                  VMware
                                                               A. Lindem
                                                           Cisco Systems
                                                                M. Zhang
                                                     Huawei Technologies
                                                              March 2018

A YANG Data Model for the Virtual Router Redundancy Protocol (VRRP)

Abstract

   This document describes a data model for the Virtual Router
   Redundancy Protocol (VRRP).  Both versions 2 and 3 of VRRP are
   covered.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8347.

Copyright Notice

   Copyright (c) 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.

   1. Introduction ....................................................2
      1.1. Terminology ................................................2
      1.2. Tree Diagrams ..............................................3
      1.3. Prefixes in Data Node Names ................................3
   2. Design of the Data Model ........................................3
      2.1. Scope of the Model .........................................3
      2.2. Relationships with the Interface Model and IP Model ........4
      2.3. Protocol Configuration .....................................5
      2.4. Protocol States ............................................6
      2.5. Notifications ..............................................9
   3. Tree Structure .................................................10
   4. YANG Module ....................................................13
   5. IANA Considerations ............................................35
   6. Security Considerations ........................................36
   7. References .....................................................37
      7.1. Normative References ......................................37
      7.2. Informative References ....................................38
   Appendix A. Data Tree Example .....................................40
   Authors' Addresses ................................................45

1. Introduction

   This document introduces a YANG data model [RFC6020] [RFC7950] for
   the Virtual Router Redundancy Protocol (VRRP) [RFC3768] [RFC5798].
   VRRP provides higher resiliency by specifying an election protocol
   that dynamically assigns responsibility for a virtual router to one
   of the VRRP routers on a LAN.

   The YANG module specified in this document supports both versions 2
   and 3 of VRRP.  VRRP version 2 (defined in [RFC3768]) supports IPv4.
   VRRP version 3 (defined in [RFC5798]) supports both IPv4 and IPv6.

1.1. Terminology

   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.

   The following terms are defined in [RFC7950] and are not redefined
   here:

   o  augment

   o  data model

   o  data node

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
   defined in [RFC8340].

1.3. Prefixes in Data Node Names

2. Design of the Data Model

2.1. Scope of the Model

   The model covers VRRP version 2 [RFC3768] and VRRP version 3
   [RFC5798].  The model is designed to be implemented on a device where
   VRRP version 2 or 3 is implemented.  With the help of a proper
   management protocol, the defined model can be used to:

   o  Configure VRRP version 2 or 3.

   o  Manage the protocol operational behavior.

o Retrieve the protocol operational status.

o Receive the protocol notifications.

2.2. Relationships with the Interface Model and IP Model

   This model augments the interface data model "ietf-interfaces"
   [RFC8343] and the IP management model "ietf-ip" [RFC8344].  The
   augmentation relationships are shown as follows:

   module: ietf-interfaces
      +--rw interfaces
         +--rw interface* [name]
               ...
            +--rw ip:ipv4!
            |  +--rw ip:address* [ip]
                     ...
            |  +--rw vrrp:vrrp
            |     +--rw vrrp:vrrp-instance* [vrid]
            |        +--rw vrrp:vrid                            uint8
            |        +--rw vrrp:virtual-ipv4-addresses
                           ...
            +--rw ip:ipv6!
               +--rw ip:address* [ip]
                     ...
               +--rw vrrp:vrrp
                  +--rw vrrp:vrrp-instance* [vrid]
                     +--rw vrrp:vrid                            uint8
                     +--rw vrrp:virtual-ipv6-addresses
                           ...

   In the above figure, a tree node without a prefix is from the model
   "ietf-interfaces".  A tree node with prefix "ip:" is from the model
   "ietf-ip".  A tree node with prefix "vrrp:" is from the VRRP model
   specified in this document.

   The "vrrp" container contains a list of vrrp-instance nodes, which
   are instantiated under an interface for a specified address family
   (IPv4 or IPv6).

   Each vrrp-instance node represents a VRRP router state machine, as
   described in Section 6.4 of [RFC5798], providing the configuration
   and state information for the election process of a virtual router.
   The IP addresses on the augmented interface are the real addresses
   through which the VRRP router operates.  The IPv4 or IPv6 address or
   addresses associated with a virtual router (described in Section 1 of
   [RFC5798]) are modeled as a list of IPv4 or IPv6 addresses under the
   vrrp-instance.

2.3. Protocol Configuration

   The model structure for the protocol configuration is as shown below:

     augment /if:interfaces/if:interface/ip:ipv4:
       +--rw vrrp
          +--rw vrrp-instance* [vrid]
             +--rw vrid                            uint8
             |     ...
             +--rw track
             |  +--rw interfaces
             |  |  +--rw interface* [interface]
             |  |     +--rw interface             if:interface-ref
             |  |           ...
             |  +--rw networks
             |     +--rw network* [prefix]
             |        +--rw prefix                inet:ipv4-prefix
             |              ...
             +--rw virtual-ipv4-addresses
                +--rw virtual-ipv4-address* [ipv4-address]
                   +--rw ipv4-address    inet:ipv4-address

     augment /if:interfaces/if:interface/ip:ipv6:
       +--rw vrrp
          +--rw vrrp-instance* [vrid]
             +--rw vrid                            uint8
             |     ...
             +--rw track
             |  +--rw interfaces
             |  |  +--rw interface* [interface]
             |  |     +--rw interface             if:interface-ref
             |  |           ...
             |  +--rw networks
             |     +--rw network* [prefix]
             |        +--rw prefix                inet:ipv6-prefix
             |              ...
             +--rw virtual-ipv6-addresses
                +--rw virtual-ipv6-address* [ipv6-address]
                   +--rw ipv6-address    inet:ipv6-address

   The model allows the following protocol entities to be configured:

   o  VRRP instance (version 2 or 3), representing a VRRP router.

   o  Virtual IPv4 or IPv6 address associated with a virtual router.

   o  Tracking interface, to detect interface connectivity failures.

   o  Tracking network, to detect network connectivity failures.

2.4. Protocol States

   The model structure for the protocol states is as shown below:

   module: ietf-vrrp
       +--ro vrrp
          |     // global operational states
          +--ro virtual-routers?   uint32
          +--ro interfaces?        uint32
          +--ro statistics                 // global statistics
             +--ro discontinuity-datetime?   yang:date-and-time
             +--ro checksum-errors?          yang:counter64
             +--ro version-errors?           yang:counter64
             +--ro vrid-errors?              yang:counter64
             +--ro ip-ttl-errors?            yang:counter64

     augment /if:interfaces/if:interface/ip:ipv4:
       +--rw vrrp
          +--rw vrrp-instance* [vrid]
             +--rw vrid                            uint8
             |     ...
             +--rw track
             |  +--rw interfaces
             |  |  +--rw interface* [interface]
             |  |     +--rw interface             if:interface-ref
             |  |           ...
             |  +--rw networks
             |     +--rw network* [prefix]
             |        +--rw prefix                inet:ipv4-prefix
             |              ...

             +--rw virtual-ipv4-addresses
             |  +--rw virtual-ipv4-address* [ipv4-address]
             |     +--rw ipv4-address    inet:ipv4-address
             |
             |     // per-instance operational states
             +--ro state?                         identityref
             +--ro is-owner?                      boolean
             +--ro last-adv-source?               inet:ip-address
             +--ro up-datetime?                   yang:date-and-time
             +--ro master-down-interval?          uint32
             +--ro skew-time?                     uint32
             +--ro last-event?                    identityref
             +--ro new-master-reason?             new-master-reason-type
             +--ro statistics                // per-instance statistics
                +--ro discontinuity-datetime?    yang:date-and-time
                +--ro master-transitions?        yang:counter32
                +--ro advertisement-rcvd?        yang:counter64
                +--ro advertisement-sent?        yang:counter64
                +--ro interval-errors?           yang:counter64
                |       {validate-interval-errors}?
                +--ro priority-zero-pkts-rcvd?   yang:counter64
                +--ro priority-zero-pkts-sent?   yang:counter64
                +--ro invalid-type-pkts-rcvd?    yang:counter64
                +--ro address-list-errors?       yang:counter64
                |       {validate-address-list-errors}?
                +--ro packet-length-errors?      yang:counter64

     augment /if:interfaces/if:interface/ip:ipv6:
       +--rw vrrp
          +--rw vrrp-instance* [vrid]
             +--rw vrid                            uint8
             +     ...
             +--rw track
             |  +--rw interfaces
             |  |  +--rw interface* [interface]
             |  |     +--rw interface             if:interface-ref
             |  |           ...
             |  +--rw networks
             |     +--rw network* [prefix]
             |        +--rw prefix                inet:ipv6-prefix
             |              ...
             +--rw virtual-ipv6-addresses
             |  +--rw virtual-ipv6-address* [ipv6-address]
             |     +--rw ipv6-address    inet:ipv6-address
             |

             |     // per-instance operational states
             +--ro state?                         identityref
             +--ro is-owner?                      boolean
             +--ro last-adv-source?               inet:ip-address
             +--ro up-datetime?                   yang:date-and-time
             +--ro master-down-interval?          uint32
             +--ro skew-time?                     uint32
             +--ro last-event?                    identityref
             +--ro new-master-reason?             new-master-reason-type
             +--ro statistics                // per-instance statistics
                +--ro discontinuity-datetime?    yang:date-and-time
                +--ro master-transitions?        yang:counter32
                +--ro advertisement-rcvd?        yang:counter64
                +--ro advertisement-sent?        yang:counter64
                +--ro interval-errors?           yang:counter64
                |       {validate-interval-errors}?
                +--ro priority-zero-pkts-rcvd?   yang:counter64
                +--ro priority-zero-pkts-sent?   yang:counter64
                +--ro invalid-type-pkts-rcvd?    yang:counter64
                +--ro address-list-errors?       yang:counter64
                |       {validate-address-list-errors}?
                +--ro packet-length-errors?      yang:counter64

   This model conforms to the Network Management Datastore Architecture
   (NMDA) [RFC8342].  The operational state data is combined with the
   associated configuration data in the same hierarchy
   [YANG-Guidelines].  When protocol states are retrieved from the NMDA
   operational state datastore, the returned states cover all
   "config true" (rw) and "config false" (ro) nodes defined in the
   schema.

   The model allows the retrieval of protocol states at the following
   levels:

   o  VRRP instance (version 2 or 3), representing a VRRP router.

   o  Virtual IPv4 or IPv6 address associated with a virtual router.

   o  Tracking interface, to detect interface connectivity failures.

   o  Tracking network, to detect network connectivity failures.

   o  Global states and statistics summarizing all instances.

2.5. Notifications

   This model defines the following VRRP-specific notifications:

   notifications:
      +---n vrrp-new-master-event
      |  +--ro master-ip-address    inet:ip-address
      |  +--ro new-master-reason    new-master-reason-type
      +---n vrrp-protocol-error-event
      |  +--ro protocol-error-reason    identityref
      +---n vrrp-virtual-router-error-event
         +--ro interface                      if:interface-ref
         +--ro (ip-version)
         |  +--:(ipv4)
         |  |  +--ro ipv4
         |  |     +--ro vrid    leafref
         |  +--:(ipv6)
         |     +--ro ipv6
         |        +--ro vrid    leafref
         +--ro virtual-router-error-reason    identityref

   Each notification type is used to indicate a type of VRRP state
   change or error occurrence:

   vrrp-new-master-event
      VRRP new master event, indicating that a new master has been
      elected.

   vrrp-protocol-error-event
      VRRP protocol error event for a message that fails to reach a VRRP
      instance to be processed.

   vrrp-virtual-router-error-event
      VRRP virtual router error event for a message processed on a VRRP
      instance.

   In addition to the notifications specified above, the mechanisms
   defined in [Subscribed-Notifications] and [YANG-Push] can be used for
   other general notifications.  These mechanisms currently allow the
   user to:

   o  Subscribe notifications on a per-client basis.

   o  Specify subtree filters or XML Path Language (XPath) filters so
      that only contents of interest will be sent.

   o  Specify either periodic or on-demand notifications.

3. Tree Structure

   The VRRP YANG data model defined in this document has the following
   tree structure:

   module: ietf-vrrp
       +--ro vrrp
          +--ro virtual-routers?   uint32
          +--ro interfaces?        uint32
          +--ro statistics
             +--ro discontinuity-datetime?   yang:date-and-time
             +--ro checksum-errors?          yang:counter64
             +--ro version-errors?           yang:counter64
             +--ro vrid-errors?              yang:counter64
             +--ro ip-ttl-errors?            yang:counter64
     augment /if:interfaces/if:interface/ip:ipv4:
       +--rw vrrp
          +--rw vrrp-instance* [vrid]
             +--rw vrid                            uint8
             +--rw version                         identityref
             +--rw log-state-change?               boolean
             +--rw preempt
             |  +--rw enabled?     boolean
             |  +--rw hold-time?   uint16
             +--rw priority?                       uint8
             +--rw accept-mode?                    boolean
             +--rw (advertise-interval-choice)?
             |  +--:(v2)
             |  |  +--rw advertise-interval-sec?         uint8
             |  +--:(v3)
             |     +--rw advertise-interval-centi-sec?   uint16
             +--rw track
             |  +--rw interfaces
             |  |  +--rw interface* [interface]
             |  |     +--rw interface             if:interface-ref
             |  |     +--rw priority-decrement?   uint8
             |  +--rw networks
             |     +--rw network* [prefix]
             |        +--rw prefix                inet:ipv4-prefix
             |        +--rw priority-decrement?   uint8
             +--rw virtual-ipv4-addresses
             |  +--rw virtual-ipv4-address* [ipv4-address]
             |     +--rw ipv4-address    inet:ipv4-address
             +--ro state?                          identityref
             +--ro is-owner?                       boolean
             +--ro last-adv-source?                inet:ip-address
             +--ro up-datetime?                    yang:date-and-time
             +--ro master-down-interval?           uint32

             +--ro skew-time?                      uint32
             +--ro last-event?                     identityref
             +--ro new-master-reason?
    new-master-reason-type
             +--ro statistics
                +--ro discontinuity-datetime?    yang:date-and-time
                +--ro master-transitions?        yang:counter32
                +--ro advertisement-rcvd?        yang:counter64
                +--ro advertisement-sent?        yang:counter64
                +--ro interval-errors?           yang:counter64
                |       {validate-interval-errors}?
                +--ro priority-zero-pkts-rcvd?   yang:counter64
                +--ro priority-zero-pkts-sent?   yang:counter64
                +--ro invalid-type-pkts-rcvd?    yang:counter64
                +--ro address-list-errors?       yang:counter64
                |       {validate-address-list-errors}?
                +--ro packet-length-errors?      yang:counter64
     augment /if:interfaces/if:interface/ip:ipv6:
       +--rw vrrp
          +--rw vrrp-instance* [vrid]
             +--rw vrid                            uint8
             +--rw version                         identityref
             +--rw log-state-change?               boolean
             +--rw preempt
             |  +--rw enabled?     boolean
             |  +--rw hold-time?   uint16
             +--rw priority?                       uint8
             +--rw accept-mode?                    boolean
             +--rw advertise-interval-centi-sec?   uint16
             +--rw track
             |  +--rw interfaces
             |  |  +--rw interface* [interface]
             |  |     +--rw interface             if:interface-ref
             |  |     +--rw priority-decrement?   uint8
             |  +--rw networks
             |     +--rw network* [prefix]
             |        +--rw prefix                inet:ipv6-prefix
             |        +--rw priority-decrement?   uint8
             +--rw virtual-ipv6-addresses
             |  +--rw virtual-ipv6-address* [ipv6-address]
             |     +--rw ipv6-address    inet:ipv6-address
             +--ro state?                          identityref
             +--ro is-owner?                       boolean
             +--ro last-adv-source?                inet:ip-address
             +--ro up-datetime?                    yang:date-and-time
             +--ro master-down-interval?           uint32

             +--ro skew-time?                      uint32
             +--ro last-event?                     identityref
             +--ro new-master-reason?
    new-master-reason-type
             +--ro statistics
                +--ro discontinuity-datetime?    yang:date-and-time
                +--ro master-transitions?        yang:counter32
                +--ro advertisement-rcvd?        yang:counter64
                +--ro advertisement-sent?        yang:counter64
                +--ro interval-errors?           yang:counter64
                |       {validate-interval-errors}?
                +--ro priority-zero-pkts-rcvd?   yang:counter64
                +--ro priority-zero-pkts-sent?   yang:counter64
                +--ro invalid-type-pkts-rcvd?    yang:counter64
                +--ro address-list-errors?       yang:counter64
                |       {validate-address-list-errors}?
                +--ro packet-length-errors?      yang:counter64

     notifications:
       +---n vrrp-new-master-event
       |  +--ro master-ip-address    inet:ip-address
       |  +--ro new-master-reason    new-master-reason-type
       +---n vrrp-protocol-error-event
       |  +--ro protocol-error-reason    identityref
       +---n vrrp-virtual-router-error-event
          +--ro interface                      if:interface-ref
          +--ro (ip-version)
          |  +--:(ipv4)
          |  |  +--ro ipv4
          |  |     +--ro vrid    leafref
          |  +--:(ipv6)
          |     +--ro ipv6
          |        +--ro vrid    leafref
          +--ro virtual-router-error-reason    identityref

4. YANG Module

   This module references [RFC2787], [RFC3768], [RFC5798], and
   [RFC6527].

   <CODE BEGINS> file "ietf-vrrp@2018-03-13.yang"

   module ietf-vrrp {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-vrrp";
     prefix "vrrp";

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

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

     import ietf-interfaces {
       prefix "if";
     }

     import ietf-ip {
       prefix "ip";
     }

     organization
       "IETF Routing Area Working Group (RTGWG)";
     contact
       "WG Web:   <https://datatracker.ietf.org/wg/rtgwg/>
        WG List:  <mailto:rtgwg@ietf.org>

        Editor:   Xufeng Liu
                  <mailto:xufeng.liu.ietf@gmail.com>

        Editor:   Athanasios Kyparlis
                  <mailto:Athanasios_Kyparlis@jabil.com>
        Editor:   Ravi Parikh
                  <mailto:parikhr@vmware.com>

        Editor:   Acee Lindem
                  <mailto:acee@cisco.com>

        Editor:   Mingui Zhang
                  <mailto:zhangmingui@huawei.com>";

     description
       "This YANG module defines a model for managing Virtual Router
        Redundancy Protocol (VRRP) versions 2 and 3.

        Copyright (c) 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
        (https://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC 8347; see the
        RFC itself for full legal notices.";

     revision 2018-03-13 {
       description
         "Initial revision.";
       reference
         "RFC 8347: A YANG Data Model for the Virtual Router Redundancy
                    Protocol (VRRP)
          RFC 2787: Definitions of Managed Objects for the Virtual
                    Router Redundancy Protocol
          RFC 3768: Virtual Router Redundancy Protocol (VRRP)
          RFC 5798: Virtual Router Redundancy Protocol (VRRP)
                    Version 3 for IPv4 and IPv6
          RFC 6527: Definitions of Managed Objects for the Virtual
                    Router Redundancy Protocol Version 3 (VRRPv3)";
     }

     /*
      * Features
      */

     feature validate-interval-errors {
       description
         "This feature indicates that the system validates that the
          advertisement interval from advertisement packets received
          is the same as the interval configured for the local
          VRRP router.";
     }

     feature validate-address-list-errors {
       description
         "This feature indicates that the system validates that
          the address list from received packets matches the

          locally configured list for the VRRP router.";
     }

     /*
      * Typedefs
      */

     typedef new-master-reason-type {
       type enumeration {
         enum not-master {
           description
             "The virtual router has never transitioned to master
              state.";
         }
         enum priority {
           description
             "Priority was higher.";
         }
         enum preempted {
           description
             "The master was preempted.";
         }
         enum no-response {
           description
             "Previous master did not respond.";
         }
       }
       description
         "Indicates why the virtual router has transitioned to
          master state.";
     } // new-master-reason-type

     /*
      * Identities
      */

     /* vrrp-event-type identity and its derivatives. */
     identity vrrp-event-type {
       description
         "Indicates the type of a VRRP protocol event.";
     }
     identity vrrp-event-none {
       base vrrp-event-type;
       description
         "Indicates a non-meaningful event.";
     }
     identity vrrp-event-startup {
       base vrrp-event-type;

       description
         "Indicates that a VRRP router has initiated the protocol.";
     }
     identity vrrp-event-shutdown {
       base vrrp-event-type;
       description
         "Indicates that a VRRP router has closed down the protocol.";
     }
     identity vrrp-event-higher-priority-backup {
       base vrrp-event-type;
       description
         "Indicates that a backup router has a higher priority than
          the current master.";
     }
     identity vrrp-event-master-timeout {
       base vrrp-event-type;
       description
         "Indicates that the current master has not sent an
          advertisement within the limit of master-down-interval.";
     }
     identity vrrp-event-interface-up {
       base vrrp-event-type;
       description
         "Indicates that the VRRP-enabled interface has become
          'operational up'.";
     }
     identity vrrp-event-interface-down {
       base vrrp-event-type;
       description
         "Indicates that the VRRP-enabled interface has become
          'operational down'.";
     }
     identity vrrp-event-no-primary-ip-address {
       base vrrp-event-type;
       description
         "Indicates that the primary IP address on the VRRP-enabled
          interface has become unavailable.";
     }
     identity vrrp-event-primary-ip-address {
       base vrrp-event-type;
       description
         "Indicates that the primary IP address on the VRRP-enabled
          interface has become available.";
     }
     identity vrrp-event-no-virtual-ip-addresses {
       base vrrp-event-type;
       description
         "Indicates that there are no virtual IP addresses on the

          virtual router.";
     }
     identity vrrp-event-virtual-ip-addresses {
       base vrrp-event-type;
       description
         "Indicates that there are virtual IP addresses on the
          virtual router.";
     }
     identity vrrp-event-preempt-hold-timeout {
       base vrrp-event-type;
       description
         "Indicates that the configured preemption hold time has
          passed.";
     }
     identity vrrp-event-lower-priority-master {
       base vrrp-event-type;
       description
         "Indicates that there is a lower-priority VRRP master.";
     }
     identity vrrp-event-owner-preempt {
       base vrrp-event-type;
       description
         "Indicates that the owner has preempted another router to
          become the master.";
     }

     /* vrrp-error-global identity and its derivatives. */
     identity vrrp-error-global {
       description
         "Indicates the type of a VRRP error that occurred
          for a packet before it reaches a VRRP router.";
     }
     identity checksum-error {
       base vrrp-error-global;
       description
         "A packet has been received with an invalid VRRP checksum
          value.";
     }
     identity ip-ttl-error {
       base vrrp-error-global;
       description
         "A packet has been received with IP TTL (Time-To-Live)
          not equal to 255.";
     }
     identity version-error {
       base vrrp-error-global;
       description
         "A packet has been received with an unknown or unsupported

          version number.";
     }
     identity vrid-error {
       base vrrp-error-global;
       description
         "A packet has been received with a Virtual Router Identifier
          (VRID) that is not valid for any virtual router on this
          router.";
     }

     /* vrrp-error-virtual-router identity and its derivatives. */
     identity vrrp-error-virtual-router {
       description
         "Indicates the type of a VRRP error that occurred
          after a packet reaches a VRRP router.";
     }
     identity address-list-error {
       base vrrp-error-virtual-router;
       description
         "A packet has been received with an address list that
          does not match the locally configured address list for
          the virtual router.";
     }
     identity interval-error {
       base vrrp-error-virtual-router;
       description
         "A packet has been received with an advertisement interval
          different than the interval configured for the local
          virtual router.";
     }
     identity packet-length-error {
       base vrrp-error-virtual-router;
       description
         "A packet has been received with a packet length less
          than the length of the VRRP header.";
     }

     /* vrrp-state-type identity and its derivatives. */
     identity vrrp-state-type {
       description
         "Indicates the state of a virtual router.";
     }
     identity initialize {
       base vrrp-state-type;
       description
         "Indicates that the virtual router is waiting
          for a startup event.";
     }

     identity backup {
       base vrrp-state-type;
       description
         "Indicates that the virtual router is monitoring the
          availability of the master router.";
     }
     identity master {
       base vrrp-state-type;
       description
         "Indicates that the virtual router is forwarding
          packets for IP addresses that are associated with
          this virtual router.";
     }

     /* vrrp-version identity and its derivatives. */
     identity vrrp-version {
       description
         "The version of VRRP.";
     }
     identity vrrp-v2 {
       base vrrp-version;
       description
         "Indicates version 2 of VRRP.";
     }
     identity vrrp-v3 {
       base vrrp-version;
       description
         "Indicates version 3 of VRRP.";
     }

     /*
      * Groupings
      */

     grouping vrrp-common-attributes {
       description
         "Group of VRRP attributes common to versions 2 and 3.";

       leaf vrid {
         type uint8 {
           range "1..255";
         }
         description
           "Virtual Router ID (i.e., VRID).";
       }

       leaf version {
         type identityref {

           base vrrp:vrrp-version;
         }
         mandatory true;
         description
           "Version 2 or 3 of VRRP.";
       }

       leaf log-state-change {
         type boolean;
         default "false";
         description
           "Generates VRRP state change messages each time the
            VRRP instance changes state (from 'up' to 'down'
            or 'down' to 'up').";
       }

       container preempt {
         description
           "Enables a higher-priority VRRP backup router to preempt a
            lower-priority VRRP master.";
         leaf enabled {
           type boolean;
           default "true";
           description
             "'true' if preemption is enabled.";
         }
         leaf hold-time {
           type uint16;
           units seconds;
           default 0;
           description
             "Hold time, in seconds, for which a higher-priority VRRP
              backup router must wait before preempting a lower-priority
              VRRP master.";
         }
       }

       leaf priority {
         type uint8 {
           range "1..254";
         }
         default 100;
         description
           "Configures the VRRP election priority for the backup
            virtual router.";
       }

       leaf accept-mode {

         when "derived-from-or-self(current()/../version, 'vrrp-v3')" {
           description
             "Applicable only to version 3.";
         }
         type boolean;
         default "false";
         description
           "Controls whether a virtual router in master state will
            accept packets addressed to the address owner's IPvX address
            as its own if it is not the IPvX address owner.  The default
            is 'false'.  Deployments that rely on, for example, pinging
            the address owner's IPvX address may wish to configure
            accept-mode to 'true'.

            Note: IPv6 Neighbor Solicitations and Neighbor
            Advertisements MUST NOT be dropped when accept-mode
            is 'false'.";
       }
     } // vrrp-common-attributes

     grouping vrrp-ipv4-attributes {
       description
         "Group of VRRP attributes for IPv4.";

       uses vrrp-common-attributes;

       choice advertise-interval-choice {
         description
           "The options for the advertisement interval at which VRRPv2
            or VRRPv3 advertisements are sent from the specified
            interface.";

         case v2 {
           when "derived-from-or-self(version, 'vrrp-v2')" {
             description
               "Applicable only to version 2.";
           }
           leaf advertise-interval-sec {
             type uint8 {
               range "1..254";
             }
             units seconds;
             default 1;
             description
               "Configures the interval that VRRPv2 advertisements
                are sent from the specified interface.";
           }
         }

         case v3 {
           when "derived-from-or-self(version, 'vrrp-v3')" {
             description
               "Applicable only to version 3.";
           }
           leaf advertise-interval-centi-sec {
             type uint16 {
               range "1..4095";
             }
             units centiseconds;
             default 100;
             description
               "Configures the interval that VRRPv3 advertisements
                are sent from the specified interface.";
           }
         }
       } // advertise-interval-choice

       container track {
         description
           "Enables the specified VRRP instance to track interfaces
            or networks.";
         container interfaces {
           description
             "Enables the specified VRRPv2 or VRRPv3 instance to track
              interfaces.  Interface tracking prevents traffic loss by
              detecting the availability of interfaces.  The operational
              states of other interfaces are associated with the
              priority of a VRRP router.  When a tracked interface
              becomes unavailable (or 'operational down'), the priority
              of the VRRP router decrements.  When an unavailable
              interface becomes available again, the priority of the
              VRRP router is incremented by the same amount.";

           list interface {
             key "interface";
             description
               "Interface to track.";
             leaf interface {
               type if:interface-ref;
               must "/if:interfaces/if:interface[if:name=current()]/"
                  + "ip:ipv4" {
                 description
                   "Interface is IPv4.";
               }
               description
                 "Interface to track.";
             }

             leaf priority-decrement {
               type uint8 {
                 range "1..254";
               }
               default 10;
               description
                 "Specifies how much to decrement the priority of the
                  VRRP instance if the interface goes down.";
             }
           } // interface
         } // interfaces

         container networks {
           description
             "Enables the VRRPv2 or VRRPv3 router instance to track the
              specified networks through their IPv4 network prefixes.
              Network tracking prevents traffic loss by detecting
              network connectivity failure.  The states of
              connectivity to some networks are associated with the
              priority of a VRRP router.  When connectivity to a
              tracked network represented by its prefix is lost, the
              priority of the VRRP router decrements.  When an
              unavailable network is again reachable, the priority of
              the VRRP router is incremented by the same amount.";
           list network {
             key "prefix";
             description
               "Enables the specified VRRPv2 or VRRPv3 instance to
                track an IPv4 network by specifying the prefix of the
                IPv4 network.";

             leaf prefix {
               type inet:ipv4-prefix;
               description
                 "The IPv4 prefix of the network to track.";
             }

             leaf priority-decrement {
               type uint8 {
                 range "1..254";
               }
               default 10;
               description
                 "Specifies how much to decrement the priority of the
                  VRRP router if there is a failure in the IPv4
                  network.";
             }
           } // network

         } // networks
       } // track

       container virtual-ipv4-addresses {
         description
           "Configures the virtual IPv4 address for the
            VRRP interface.";

         list virtual-ipv4-address {
           key "ipv4-address";
           max-elements 16;
           description
             "Virtual IPv4 addresses for a single VRRP instance.  For a
              VRRP owner router, the virtual address must match one
              of the IPv4 addresses configured on the interface
              corresponding to the virtual router.";

           leaf ipv4-address {
             type inet:ipv4-address;
             description
               "An IPv4 address associated with a virtual router.";
             reference
               "RFC 5798: Virtual Router Redundancy Protocol (VRRP)
                          Version 3 for IPv4 and IPv6.  Section 1.2";
           }
         } // virtual-ipv4-address
       } // virtual-ipv4-addresses
     } // vrrp-ipv4-attributes

     grouping vrrp-ipv6-attributes {
       description
         "Group of VRRP attributes for IPv6.";

       uses vrrp-common-attributes;

       leaf advertise-interval-centi-sec {
         type uint16 {
           range "1..4095";
         }
         units centiseconds;
         default 100;
         description
           "Configures the interval that VRRPv3 advertisements
            are sent from the specified interface.";
       }

       container track {
         description

           "Enables the specified VRRP instance to track interfaces
            or networks.";
         container interfaces {
           description
             "Enables the specified VRRPv2 or VRRPv3 instance to track
              interfaces.  Interface tracking prevents traffic loss by
              detecting the availability of interfaces.  The operational
              states of other interfaces are associated with the
              priority of a VRRP router.  When a tracked interface
              becomes unavailable (or 'operational down'), the priority
              of the VRRP router decrements.  When an unavailable
              interface becomes available again, the priority of the
              VRRP router is incremented by the same amount.";
           list interface {
             key "interface";
             description
               "Interface to track.";

             leaf interface {
               type if:interface-ref;
               must "/if:interfaces/if:interface[if:name=current()]/"
                  + "ip:ipv6" {
                 description
                   "Interface is IPv6.";
               }
               description
                 "Interface to track.";
             }

             leaf priority-decrement {
               type uint8 {
                 range "1..254";
               }
               default 10;
               description
                 "Specifies how much to decrement the priority of the
                  VRRP instance if the interface goes down.";
             }
           } // interface
         } // interfaces

         container networks {
           description
             "Enables the VRRPv2 or VRRPv3 router instance to track the
              specified networks through their IPv6 network prefixes.
              Network tracking prevents traffic loss by detecting
              network connectivity failure.  The states of
              connectivity to some networks are associated with the

              priority of a VRRP router.  When connectivity to a
              tracked network represented by its prefix is lost, the
              priority of the VRRP router decrements.  When an
              unavailable network is again reachable, the priority of
              the VRRP router is incremented by the same amount.";
           list network {
             key "prefix";
             description
               "Enables the specified VRRPv2 or VRRPv3 instance to
                track an IPv6 network by specifying the prefix of the
                IPv6 network.";

             leaf prefix {
               type inet:ipv6-prefix;
               description
                 "The IPv6 prefix of the network to track.";
             }

             leaf priority-decrement {
               type uint8 {
                 range "1..254";
               }
               default 10;
               description
                 "Specifies how much to decrement the priority of the
                  VRRP router if there is a failure in the IPv6
                  network.";
             }
           } // network
         } // networks
       } // track

       container virtual-ipv6-addresses {
         description
           "Configures the virtual IPv6 address for the
            VRRP interface.";
         list virtual-ipv6-address {
           key "ipv6-address";
           max-elements 2;
           description
             "Two IPv6 addresses are allowed.  The first address must
              be a link-local address.  The second address can be a
              link-local or global address.";

           leaf ipv6-address {
             type inet:ipv6-address;
             description
               "An IPv6 address associated with a virtual router.";

             reference
               "RFC 5798: Virtual Router Redundancy Protocol (VRRP)
                          Version 3 for IPv4 and IPv6.  Section 1.3";
           }
         } // virtual-ipv6-address
       } // virtual-ipv6-addresses
     } // vrrp-ipv6-attributes

     grouping vrrp-state-attributes {
       description
         "Group of VRRP state attributes.";

       leaf state {
         type identityref {
           base vrrp:vrrp-state-type;
         }
         config false;
         description
           "Operational state.";
       }

       leaf is-owner {
         type boolean;
         config false;
         description
           "Set to 'true' if this virtual router is the owner.";
       }

       leaf last-adv-source {
         type inet:ip-address;
         config false;
         description
           "Last advertised IPv4/IPv6 source address.";
       }

       leaf up-datetime {
         type yang:date-and-time;
         config false;
         description
           "The date and time when this virtual router
            transitioned out of 'init' state.";
       }

       leaf master-down-interval {
         type uint32;
         units centiseconds;
         config false;
         description

           "Time interval for the backup virtual router to declare
            'master down'.";
       }

       leaf skew-time {
         type uint32;
         units microseconds;
         config false;
         description
           "Calculated based on the priority and advertisement
            interval configuration command parameters.  See RFC 3768.";
       }

       leaf last-event {
         type identityref {
           base vrrp:vrrp-event-type;
         }
         config false;
         description
           "Last reported event.";
       }

       leaf new-master-reason {
         type new-master-reason-type;
         config false;
         description
           "Indicates why the virtual router has transitioned to
            master state.";
       }

       container statistics {
         config false;
         description
           "VRRP statistics.";

         leaf discontinuity-datetime {
           type yang:date-and-time;
           description
             "The time on the most recent occasion at which any one or
              more of the VRRP statistics counters suffered a
              discontinuity.  If no such discontinuities have occurred
              since the last re-initialization of the local management
              subsystem, then this node contains the time that the
              local management subsystem re-initialized itself.";
         }

         leaf master-transitions {
           type yang:counter32;

           description
             "The total number of times that this virtual router's
              state has transitioned to 'master'.";
         }

         leaf advertisement-rcvd {
           type yang:counter64;
           description
             "The total number of VRRP advertisements received by
              this virtual router.";
         }

         leaf advertisement-sent {
           type yang:counter64;
           description
             "The total number of VRRP advertisements sent by
              this virtual router.";
         }

         leaf interval-errors {
           if-feature validate-interval-errors;
           type yang:counter64;
           description
             "The total number of VRRP advertisement packets received
              with an advertisement interval different than the
              interval configured for the local virtual router.";
         }

         leaf priority-zero-pkts-rcvd {
           type yang:counter64;
           description
             "The total number of VRRP packets received by the
              virtual router with a priority of 0.";
         }

         leaf priority-zero-pkts-sent {
           type yang:counter64;
           description
             "The total number of VRRP packets sent by the
              virtual router with a priority of 0.";
         }

         leaf invalid-type-pkts-rcvd {
           type yang:counter64;
           description
             "The number of VRRP packets received by the virtual
              router with an invalid value in the 'type' field.";
         }

         leaf address-list-errors {
           if-feature validate-address-list-errors;
           type yang:counter64;
           description
             "The total number of packets received with an
              address list that does not match the locally
              configured address list for the virtual router.";
         }

         leaf packet-length-errors {
           type yang:counter64;
           description
             "The total number of packets received with a packet
              length less than the length of the VRRP header.";
         }
       } // statistics
     } // vrrp-state-attributes

     grouping vrrp-global-state-attributes {
       description
         "Group of VRRP global state attributes.";

       leaf virtual-routers {
         type uint32;
         description
           "Number of configured virtual routers.";
       }

       leaf interfaces {
         type uint32;
         description
           "Number of interfaces with VRRP configured.";
       }

       container statistics {
         description
           "VRRP global statistics.";

         leaf discontinuity-datetime {
           type yang:date-and-time;
           description
             "The time on the most recent occasion at which any
              one or more of checksum-errors, version-errors,
              vrid-errors, or ip-ttl-errors suffered a
              discontinuity.

              If no such discontinuities have occurred since the last
              re-initialization of the local management subsystem,

              then this node contains the time that the local management
              subsystem re-initialized itself.";
         }

         leaf checksum-errors {
           type yang:counter64;
           description
             "The total number of VRRP packets received with an invalid
              VRRP checksum value.";
           reference
             "RFC 5798: Virtual Router Redundancy Protocol (VRRP)
                        Version 3 for IPv4 and IPv6.  Section 5.2.8";
         }

         leaf version-errors {
           type yang:counter64;
           description
             "The total number of VRRP packets received with an unknown
              or unsupported version number.";
           reference
             "RFC 5798: Virtual Router Redundancy Protocol (VRRP)
                        Version 3 for IPv4 and IPv6.  Section 5.2.1";
         }

         leaf vrid-errors {
           type yang:counter64;
           description
             "The total number of VRRP packets received with a VRID that
              is not valid for any virtual router on this router.";
           reference
             "RFC 5798: Virtual Router Redundancy Protocol (VRRP)
                        Version 3 for IPv4 and IPv6.  Section 5.2.3";
         }

         leaf ip-ttl-errors {
           type yang:counter64;
           description
             "The total number of VRRP packets received by the
              virtual router with IP TTL (IPv4) or Hop Limit (IPv6)
              not equal to 255.";
           reference
             "RFC 5798: Virtual Router Redundancy Protocol (VRRP)
                        Version 3 for IPv4 and IPv6.
                        Sections 5.1.1.3 and 5.1.2.3";
         }
       } // statistics
     } // vrrp-global-state-attributes

     /*
      * Configuration data and operational state data nodes
      */

     augment "/if:interfaces/if:interface/ip:ipv4" {
       description
         "Augments IPv4 interface.";

       container vrrp {
         description
           "Configures VRRP version 2 or 3 for IPv4.";

         list vrrp-instance {
           key "vrid";
           description
             "Defines a virtual router, identified by a VRID, within the
              IPv4 address space.";

           uses vrrp-ipv4-attributes;
           uses vrrp-state-attributes;
         }
       }
     } // augments ipv4

     augment "/if:interfaces/if:interface/ip:ipv6" {
       description
         "Augments IPv6 interface.";

       container vrrp {
         description
           "Configures VRRP version 3 for IPv6.";

         list vrrp-instance {
           must "derived-from-or-self(version, 'vrrp-v3')" {
             description
               "IPv6 is only supported by version 3.";
           }
           key "vrid";
           description
             "Defines a virtual router, identified by a VRID, within the
              IPv6 address space.";

           uses vrrp-ipv6-attributes;
           uses vrrp-state-attributes;
         }
       }
     } // augments ipv6

     container vrrp {
       config false;
       description
         "VRRP data at the global level.";

       uses vrrp-global-state-attributes;
     }

     /*
      * Notifications
      */

     notification vrrp-new-master-event {
       description
         "Notification event for the election of a new VRRP master.";
       leaf master-ip-address {
         type inet:ip-address;
         mandatory true;
         description
           "IPv4 or IPv6 address of the new master.";
       }
       leaf new-master-reason {
         type new-master-reason-type;
         mandatory true;
         description
           "Indicates why the virtual router has transitioned to
            master state.";
       }
     }

     notification vrrp-protocol-error-event {
       description
         "Notification event for a VRRP protocol error.";
       leaf protocol-error-reason {
         type identityref {
           base vrrp:vrrp-error-global;
         }
         mandatory true;
         description
           "Indicates the reason for the protocol error.";
       }
     }

     notification vrrp-virtual-router-error-event {
       description
         "Notification event for an error that happened on a
          virtual router.";
       leaf interface {

         type if:interface-ref;
         mandatory true;
         description
           "Indicates the interface on which the event has occurred.";
       }

       choice ip-version {
         mandatory true;
         description
           "The error may have happened on either an IPv4 virtual
            router or an IPv6 virtual router.  The information
            related to a specific IP version is provided by one of
            the following cases.";
         case ipv4 {
           description
             "IPv4.";
           container ipv4 {
             description
               "Error information for IPv4.";
             leaf vrid {
               type leafref {
                 path "/if:interfaces/if:interface"
                   + "[if:name = current()/../../vrrp:interface]/"
                   + "ip:ipv4/vrrp:vrrp/vrrp:vrrp-instance/vrrp:vrid";
               }
               mandatory true;
               description
                 "Indicates the virtual router on which the event has
                  occurred.";
             }
           }
         }
         case ipv6 {
           description
             "IPv6.";
           container ipv6 {
             description
               "Error information for IPv6.";
             leaf vrid {
               type leafref {
                 path "/if:interfaces/if:interface"
                   + "[if:name = current()/../../vrrp:interface]/"
                   + "ip:ipv6/vrrp:vrrp/vrrp:vrrp-instance/vrrp:vrid";
               }
               mandatory true;
               description
                 "Indicates the virtual router on which the event has
                  occurred.";

             }
           }
         }
       }

       leaf virtual-router-error-reason {
         type identityref {
           base vrrp:vrrp-error-virtual-router;
         }
         mandatory true;
         description
           "Indicates the reason for the virtual router error.";
       }
     }
   }

   <CODE ENDS>

5. IANA Considerations

   This document registers the following namespace URI in the "IETF XML
   Registry" [RFC3688]:

   --------------------------------------------------------------------
   URI: urn:ietf:params:xml:ns:yang:ietf-vrrp
   Registrant Contact: The IESG.
   XML: N/A; the requested URI is an XML namespace.
   --------------------------------------------------------------------

   This document registers the following YANG module in the "YANG Module
   Names" registry [RFC7950]:

   --------------------------------------------------------------------
   name:         ietf-vrrp
   namespace:    urn:ietf:params:xml:ns:yang:ietf-vrrp
   prefix:       vrrp
   reference:    RFC 8347
   --------------------------------------------------------------------

6. Security Considerations

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

   The NETCONF access control model [RFC8341] provides the means to
   restrict access for particular NETCONF or RESTCONF users to a
   preconfigured subset of all available NETCONF or RESTCONF protocol
   operations and content.

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

   /if:interfaces/if:interface/ip:ipv4/vrrp:vrrp/vrrp:vrrp-instance

   /if:interfaces/if:interface/ip:ipv6/vrrp:vrrp/vrrp:vrrp-instance

   Unauthorized access to any data node of these subtrees can adversely
   affect the routing subsystem of both the local device and the
   network.  This may lead to network malfunctions, delivery of packets
   to inappropriate destinations, and other problems.

   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:

   /ietf-vrrp:vrrp

   /if:interfaces/if:interface/ip:ipv4/vrrp:vrrp/vrrp:vrrp-instance

   /if:interfaces/if:interface/ip:ipv6/vrrp:vrrp/vrrp:vrrp-instance

   Unauthorized access to any data node of these subtrees can disclose
   the operational state information of VRRP on this device.

7. References

7.1. Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2787]  Jewell, B. and D. Chuang, "Definitions of Managed Objects
              for the Virtual Router Redundancy Protocol", RFC 2787,
              DOI 10.17487/RFC2787, March 2000,
              <https://www.rfc-editor.org/info/rfc2787>.

   [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>.

   [RFC5798]  Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP)
              Version 3 for IPv4 and IPv6", RFC 5798,
              DOI 10.17487/RFC5798, March 2010,
              <https://www.rfc-editor.org/info/rfc5798>.

   [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>.

   [RFC6527]  Tata, K., "Definitions of Managed Objects for Virtual
              Router Redundancy Protocol Version 3 (VRRPv3)", RFC 6527,
              DOI 10.17487/RFC6527, March 2012,
              <https://www.rfc-editor.org/info/rfc6527>.

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

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

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

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

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

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

   [RFC8344]  Bjorklund, M., "A YANG Data Model for IP Management",
              RFC 8344, DOI 10.17487/RFC8344, March 2018,
              <https://www.rfc-editor.org/info/rfc8344>.

7.2. Informative References

   [RFC3768]  Hinden, R., Ed., "Virtual Router Redundancy Protocol
              (VRRP)", RFC 3768, DOI 10.17487/RFC3768, April 2004,
              <https://www.rfc-editor.org/info/rfc3768>.

   [RFC7224]  Bjorklund, M., "IANA Interface Type YANG Module",
              RFC 7224, DOI 10.17487/RFC7224, May 2014,
              <https://www.rfc-editor.org/info/rfc7224>.

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,
              <https://www.rfc-editor.org/info/rfc7951>.

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

   [Subscribed-Notifications]
              Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
              E., and A. Tripathy, "Custom Subscription to Event
              Streams", Work in Progress, draft-ietf-netconf-subscribed-
              notifications-10, February 2018.

   [YANG-Push]
              Clemm, A., Voit, E., Gonzalez Prieto, A., Tripathy, A.,
              Nilsen-Nygaard, E., Bierman, A., and B. Lengyel, "YANG
              Datastore Subscription", Work in Progress,
              draft-ietf-netconf-yang-push-15, February 2018.

   [YANG-Guidelines]
              Bierman, A., "Guidelines for Authors and Reviewers of YANG
              Data Model Documents", Work in Progress,
              draft-ietf-netmod-rfc6087bis-20, March 2018.

Appendix A. Data Tree Example

   This section contains an example of an instance data tree in JSON
   encoding [RFC7951], containing both configuration and state data.
   (This example includes "iana-if-type", which is defined in
   [RFC7224].)

                 Virtual router IP address: fe80::1
              +-----------------+        +-----------------+
              |                 |        |                 |
              |    Router 1     |        |    Router 2     |
              |                 |        |                 |
              +--------+--------+        +--------+--------+
                       |eth1                      |eth1
                       |fe80::11                  |fe80::12
                -------+--------------------------+-------
                       |                          |
                       |fe80::51                  |fe80::52
              +--------+--------+        +--------+--------+
              |     Host 1      |        |     Host 2      |
              | Default gateway:|        | Default gateway:|
              |     fe80::1     |        |     fe80::1     |
              +-----------------+        +-----------------+

   The configuration instance data for Router 1 in the above figure
   could be as follows:

   {
     "ietf-interfaces:interfaces": {
       "interface": [
         {
           "name": "eth1",
           "description": "An interface with VRRP enabled.",
           "type": "iana-if-type:ethernetCsmacd",
           "ietf-ip:ipv6": {
             "address": [
               {
                 "ip": "2001:db8:0:1::1",
                 "prefix-length": 64
               },
               {
                 "ip": "fe80::11",
                 "prefix-length": 64
               }
             ],
             "forwarding": true,
             "ietf-vrrp:vrrp": {
               "vrrp-instance": [
                 {
                   "vrid": 1,
                   "version": "vrrp-v3",
                   "priority": 200,
                   "advertise-interval-centi-sec": 50,
                   "virtual-ipv6-addresses": {
                     "virtual-ipv6-address": [
                       "ipv6-address": "fe80::1"
                     ]
                   }
                 }
               ]
             }
           }
         }
       ]
     }
   }

   The corresponding operational state data for Router 1 could be as
   follows:

   {
     "ietf-interfaces:interfaces": {
       "interface": [
         {
           "name": "eth1",
           "description": "An interface with VRRP enabled.",
           "type": "iana-if-type:ethernetCsmacd",
           "phys-address": "00:00:5e:00:53:01",
           "oper-status": "up",
           "statistics": {
             "discontinuity-time": "2016-10-24T17:11:27+02:00"
           },
           "ietf-ip:ipv6": {
             "forwarding": true,
             "mtu": 1500,
             "address": [
               {
                 "ip": "2001:db8:0:1::1",
                 "prefix-length": 64,
                 "origin": "static",
                 "status": "preferred"
               },
               {
                 "ip": "fe80::11",
                 "prefix-length": 64,
                 "origin": "static",
                 "status": "preferred"
               }
             ]

             "ietf-vrrp:vrrp": {
               "vrrp-instance": [
                 {
                   "vrid": 1,
                   "version": "vrrp-v3",
                   "log-state-change": false,
                   "preempt": {
                     "enabled": true,
                     "hold-time": 0
                   }
                   "priority": 200,
                   "accept-mode": false,
                   "advertise-interval-centi-sec": 50,
                   "virtual-ipv6-addresses": {
                     "virtual-ipv6-address": [
                       "ipv6-address": "fe80::1"
                     ]
                   },
                   "state": "master",
                   "is-owner": false,
                   "last-adv-source": "fe80::11",
                   "up-datetime": "2016-10-24T17:11:27+02:00",
                   "master-down-interval": 161,
                   "skew-time": 11,
                   "last-event": "vrrp-event-interface-up",
                   "new-master-reason": "priority",
                   "statistics": {
                     "discontinuity-datetime":
                       "2016-10-24T17:11:27+02:00",
                     "master-transitions": 2,
                     "advertisement-rcvd": 20,
                     "advertisement-sent": 12,
                     "interval-errors": 0,
                     "priority-zero-pkts-rcvd": 0,
                     "priority-zero-pkts-sent": 0,
                     "invalid-type-pkts-rcvd": 0,
                     "address-list-errors": 0,
                     "packet-length-errors": 1
                   }
                 }
               ]
             }
           }
         }
       ]
     }
   }

   {
     "ietf-vrrp:vrrp": {
       "virtual-routers": 3,
       "interfaces": 2,
       "statistics": {
         "discontinuity-datetime": "2016-10-24T17:11:27+02:00",
         "checksum-errors": 2,
         "version-errors": 0,
         "vrid-errors": 0,
         "ip-ttl-errors": 1
       }
     }
   }

Authors' Addresses

   Xufeng Liu (editor)
   Jabil
   8281 Greensboro Drive, Suite 200
   McLean, VA  22102
   United States of America

   Email: xufeng.liu.ietf@gmail.com

   Athanasios Kyparlis
   Jabil
   8281 Greensboro Drive, Suite 200
   McLean, VA  22102
   United States of America

   Email: Athanasios_Kyparlis@jabil.com

   Ravi Parikh
   VMware
   3425 Hillview Avenue
   Palo Alto, CA  94304
   United States of America

   Email: parikhr@vmware.com

   Acee Lindem
   Cisco Systems
   301 Midenhall Way
   Cary, NC  27513
   United States of America

   Email: acee@cisco.com

   Mingui Zhang
   Huawei Technologies
   No. 156 Beiqing Rd. Haidian District
   Beijing  100095
   China

   Email: zhangmingui@huawei.com