YANG Data Model for DHCPv6 Configuration
draft-ietf-dhc-dhcpv6-yang-21

Document Type Active Internet-Draft (dhc WG)
Author Ian Farrer 
Last updated 2021-06-14
Replaces draft-cui-dhc-dhcpv6-yang
Stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
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Stream WG state WG Document (wg milestone: Jul 2021 - WGLC draft-ietf-dhc-... )
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Send notices to Timothy Winters <tim@qacafe.com>
DHC Working Group                                         I. Farrer, Ed.
Internet-Draft                                       Deutsche Telekom AG
Intended status: Standards Track                            14 June 2021
Expires: 16 December 2021

                YANG Data Model for DHCPv6 Configuration
                     draft-ietf-dhc-dhcpv6-yang-21

Abstract

   This document describes YANG data modules for the configuration and
   management of DHCPv6 (Dynamic Host Configuration Protocol for IPv6)
   servers, relays, and clients.

Requirements Language

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

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 16 December 2021.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.

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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Extensibility of the DHCPv6 Server YANG Module  . . . . .   4
       1.2.1.  DHCPv6 Option Definitions . . . . . . . . . . . . . .   4
     1.3.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   6
   2.  DHCPv6 Tree Diagrams  . . . . . . . . . . . . . . . . . . . .   6
     2.1.  DHCPv6 Server Tree Diagram  . . . . . . . . . . . . . . .   6
     2.2.  DHCPv6 Relay Tree Diagram . . . . . . . . . . . . . . . .  13
     2.3.  DHCPv6 Client Tree Diagram  . . . . . . . . . . . . . . .  16
   3.  DHCPv6 YANG Modules . . . . . . . . . . . . . . . . . . . . .  19
     3.1.  DHCPv6 Server YANG Module . . . . . . . . . . . . . . . .  19
     3.2.  DHCPv6 Relay YANG Module  . . . . . . . . . . . . . . . .  39
     3.3.  DHCPv6 Client YANG Module . . . . . . . . . . . . . . . .  48
     3.4.  DHCPv6 Common YANG Module . . . . . . . . . . . . . . . .  63
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  71
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  73
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  74
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  74
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  74
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  74
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  77
   Appendix A.  Data Tree Examples . . . . . . . . . . . . . . . . .  77
     A.1.  DHCPv6 Server Configuration Example . . . . . . . . . . .  77
     A.2.  DHCPv6 Relay Configuration Example  . . . . . . . . . . .  81
     A.3.  DHCPv6 Client Configuration Examples  . . . . . . . . . .  82
   Appendix B.  Example of Augmenting Additional DHCPv6 Option
           Definitions . . . . . . . . . . . . . . . . . . . . . . .  85
   Appendix C.  Example Vendor Specific Server Configuration
           Module  . . . . . . . . . . . . . . . . . . . . . . . . .  88
   Appendix D.  Example definition of class-selector
           configuration . . . . . . . . . . . . . . . . . . . . . .  95
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . 102

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1.  Introduction

   DHCPv6 [RFC8415] is widely used for supplying configuration and other
   relevant parameters to clients in IPv6 networks.  This document
   defines YANG [RFC7950] modules for the configuration and management
   of DHCPv6 'element' (servers, relays, and clients) using the Network
   Configuration Protocol (NETCONF [RFC6241]) or RESTCONF [RFC8040]
   protocols.

   Separate modules are defined for each element.  Additionally, a
   'common' module contains typedefs and groupings used by all of the
   element modules.  Appendix A provides XML examples for each of the
   element modules and shows their interaction.

   The relay and client modules provide configuration which is
   applicable device's interfaces.  This is done by importing the ietf-
   interfaces module [RFC8343] and using interface-refs to the relevant
   interface(s).

   It is worth noting that as DHCPv6 is itself a client configuration
   protocol, it is not the intention of this document to provide a
   replacement for the allocation of DHCPv6 assigned addressing and
   parameters by using NETCONF/YANG.  The DHCPv6 client module is
   intended for the configuration and monitoring of the DHCPv6 client
   function and does not replace DHCPv6 address and parameter
   configuration.

   The YANG modules in this document adopt the Network Management
   Datastore Architecture (NMDA) [RFC8342].

1.1.  Scope

   [RFC8415] describes the current version of the DHCPv6 base protocol
   specification.  A large number of additional specifications have also
   been published, extending DHCPv6 element functionality and adding new
   options.  The YANG modules contained in this document do not attempt
   to capture all of these extensions and additions, rather to model the
   DHCPv6 functions and options covered in [RFC8415].  A focus has also
   been given on the extensibility of the modules so that they are easy
   to augment to add additional functionality as required by a
   particular implementation or deployment scenario.

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1.2.  Extensibility of the DHCPv6 Server YANG Module

   The modules in this document only attempt to model DHCPv6-specific
   behavior and do not cover the configuration and management of
   functionality relevant for specific server implementations.  The
   level of variance between implementations is too great to attempt to
   standardize them in a way that is useful without being restrictive.

   However, it is recognized that implementation-specific configuration
   and management is also an essential part of DHCP deployment and
   operations.  To resolve this, Appendix C contains an example YANG
   module for the configuration of implementation-specific functions,
   illustrating how this functionality can be augmented into the main
   'ietf-dhcpv6-server.yang' module.

   In DHCPv6, the concept of 'class selection' for messages received by
   the server is common.  This is the identification and classification
   of messages based on a number of parameters so that the correct
   provisioning information can be supplied.  For example, allocating a
   prefix from the correct pool, or supplying a set of options relevant
   for a specific vendor's client implementation.  During the
   development of this document, implementations were researched and the
   findings were that while this function is common to all, the method
   for configuring and implementing this function differs greatly.
   Therefore, configuration of the class selection function has been
   omitted from the DHCPv6 server module to allow implementors to define
   their own suitable YANG modules.  Appendix D provides an example of
   this, to demonstrate how this is can be integrated with the main
   'ietf-dhcpv6-server.yang' module.

1.2.1.  DHCPv6 Option Definitions

   A large number of DHCPv6 options have been created in addition to
   those defined in [RFC8415].  As implementations differ widely as to
   which DHCPv6 options they support, the following approach has been
   taken to defining options: Only the DHCPv6 options defined in
   [RFC8415] are included in this document.

   Of these, only the options that require operator configuration are
   modelled.  For example, OPTION_IA_NA (3) is created by the DHCP
   server when requested by the client.  The contents of the fields in
   the option are based on a number of input configuration parameters
   which the server will apply when it receives the request (e.g., the
   T1/T2 timers that are relevant for the pool of addresses).  As a
   result, there are no fields that are directly configurable for the
   option, so it is not modelled.

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   The following table shows the DHCPv6 options that are modeled, the
   element(s) they are sent by, and the relevant YANG module name:

   +---------------------+------+-----+------+-------------------------+
   | Name                |Server|Relay|Client| Module Name             |
   +=====================+======+=====+======+=========================+
   |OPTION_ORO (6) Option|      |     |  X   | ietf-dhcpv6-client.yang |
   | Request Option      |      |     |      |                         |
   +---------------------+------+-----+------+-------------------------+
   |OPTION_PREFERENCE (7)|  X   |     |      | ietf-dhcpv6-server.yang |
   | Preference Option   |      |     |      |                         |
   +---------------------+------+-----+------+-------------------------+
   | OPTION_AUTH (11)    |  X   |  X  |      | ietf-dhcpv6-common.yang |
   |Authentication Option|      |     |      |                         |
   +---------------------+------+-----+------+-------------------------+
   | OPTION_UNICAST (12) |  X   |     |      | ietf-dhcpv6-server.yang |
   |Server Unicast Option|      |     |      |                         |
   +---------------------+------+-----+------+-------------------------+
   | OPTION_STATUS_CODE  |  X   |  X  |  X   | ietf-dhcpv6-common.yang |
   | (13) Status Code    |      |     |      |                         |
   | Option              |      |     |      |                         |
   +---------------------+------+-----+------+-------------------------+
   | OPTION_RAPID_COMMIT |  X   |     |  X   | ietf-dhcpv6-common.yang |
   | (14) Rapid Commit   |      |     |      |                         |
   | Option              |      |     |      |                         |
   +---------------------+------+-----+------+-------------------------+
   | OPTION_USER_CLASS   |      |     |  X   | ietf-dhcpv6-client.yang |
   | (15) User Class     |      |     |      |                         |
   | Option              |      |     |      |                         |
   +---------------------+------+-----+------+-------------------------+
   | OPTION_VENDOR_CLASS |      |     |  X   | ietf-dhcpv6-client.yang |
   | (16) Vendor Class   |      |     |      |                         |
   | Option              |      |     |      |                         |
   +---------------------+------+-----+------+-------------------------+
   | OPTION_VENDOR_OPTS  |  X   |     |  X   | ietf-dhcpv6-common.yang |
   |(17) Vendor-specific |      |     |      |                         |
   | Information Option  |      |     |      |                         |
   +---------------------+------+-----+------+-------------------------+
   | OPTION_INTERFACE_ID |      |  X  |      | ietf-dhcpv6-relay.yang  |
   | (18) Interface-Id   |      |     |      |                         |
   | Option              |      |     |      |                         |
   +---------------------+------+-----+------+-------------------------+
   | OPTION_RECONF_MSG   |  X   |     |      | ietf-dhcpv6-server.yang |
   | (19) Reconfigure    |      |     |      |                         |
   | Message Option      |      |     |      |                         |
   +---------------------+------+-----+------+-------------------------+
   |OPTION_RECONF_ACCEPT |  X   |     |  X   | ietf-dhcpv6-client.yang |
   | (20) Reconfigure    |      |     |      |                         |

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   | Accept Option       |      |     |      |                         |
   +---------------------+------+-----+------+-------------------------+
   | OPTION_INFORMATION  |  X   |     |      | ietf-dhcpv6-server.yang |
   | _REFRESH_TIME (32)  |      |     |      |                         |
   | Information Refresh |      |     |      |                         |
   | Time Option         |      |     |      |                         |
   +---------------------+------+-----+------+-------------------------+
   | OPTION_SOL_MAX_RT   |  X   |     |      | ietf-dhcpv6-server.yang |
   | (82) sol max rt     |      |     |      |                         |
   | Option              |      |     |      |                         |
   +---------------------+------+-----+------+-------------------------+
   | OPTION_INF_MAX_RT   |  X   |     |      | ietf-dhcpv6-server.yang |
   | (83) inf max rt     |      |     |      |                         |
   | Option              |      |     |      |                         |
   +---------------------+------+-----+------+-------------------------+

                      Table 1: Modeled DHCPv6 Options

   Further options definitions can be added using additional YANG
   modules via augmentation of the relevant element modules from this
   document.  Appendix B contains an example module showing how the
   DHCPv6 option definitions can be extended in this manner.  Some
   guidance on how to write YANG modules for additional DHCPv6 options
   is also provided.

1.3.  Terminology

   The reader should be familiar with the YANG data modeling language
   defined in [RFC7950].

   The YANG modules in this document adopt the Network Management
   Datastore Architecture (NMDA) [RFC8342].  The meanings of the symbols
   used in tree diagrams are defined in [RFC8340].

   The reader should be familiar with DHCPv6 relevant terminology as
   defined in [RFC8415] and other relevant documents.

2.  DHCPv6 Tree Diagrams

2.1.  DHCPv6 Server Tree Diagram

   The tree diagram in Figure 1 provides an overview of the DHCPv6
   server module.  The tree also includes the common functions module
   Section 3.4.

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     module: ietf-dhcpv6-server
       +--rw dhcpv6-server
          +--rw enabled?          boolean
          +--rw server-duid?      dhc6:duid
          +--rw vendor-config
          +--rw option-sets
          |  +--rw option-set* [option-set-id]
          |     +--rw option-set-id                          uint32
          |     +--rw description?                           string
          |     +--rw preference-option
          |     |  +--rw pref-value?   uint8
          |     +--rw auth-option
          |     |  +--rw protocol?           uint8
          |     |  +--rw algorithm?          uint8
          |     |  +--rw rdm?                uint8
          |     |  +--rw replay-detection?   uint64
          |     |  +--rw auth-information?   string
          |     +--rw server-unicast-option
          |     |  +--rw server-address?   inet:ipv6-address
          |     +--rw status-code-option
          |     |  +--rw status-code?      uint16
          |     |  +--rw status-message?   string
          |     +--rw rapid-commit-option!
          |     +--rw vendor-specific-information-options
          |     |  +--rw vendor-specific-information-option*
          |     |          [enterprise-number]
          |     |     +--rw enterprise-number     uint32
          |     |     +--rw vendor-option-data* [sub-option-code]
          |     |        +--rw sub-option-code    uint16
          |     |        +--rw sub-option-data?   string
          |     +--rw reconfigure-message-option
          |     |  +--rw msg-type?   uint8
          |     +--rw reconfigure-accept-option!
          |     +--rw info-refresh-time-option
          |     |  +--rw info-refresh-time?   dhc6:timer-seconds32
          |     +--rw sol-max-rt-option
          |     |  +--rw sol-max-rt-value?   dhc6:timer-seconds32
          |     +--rw inf-max-rt-option
          |        +--rw inf-max-rt-value?   dhc6:timer-seconds32
          +--rw class-selector
          +--rw network-ranges
             +--rw option-set-id*               leafref
             +--rw valid-lifetime?              dhc6:timer-seconds32
             +--rw renew-time?                  dhc6:timer-seconds32
             +--rw rebind-time?                 dhc6:timer-seconds32
             +--rw preferred-lifetime?          dhc6:timer-seconds32
             +--rw rapid-commit?                boolean
             +--rw network-range* [id]

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             |  +--rw id                    uint32
             |  +--rw description?          string
             |  +--rw network-prefix        inet:ipv6-prefix
             |  +--rw option-set-id*        leafref
             |  +--rw valid-lifetime?       dhc6:timer-seconds32
             |  +--rw renew-time?           dhc6:timer-seconds32
             |  +--rw rebind-time?          dhc6:timer-seconds32
             |  +--rw preferred-lifetime?   dhc6:timer-seconds32
             |  +--rw rapid-commit?         boolean
             |  +--rw address-pools
             |  |  +--rw address-pool* [pool-id]
             |  |     +--rw pool-id                    uint32
             |  |     +--rw pool-prefix
             |  |     |       inet:ipv6-prefix
             |  |     +--rw start-address
             |  |     |       inet:ipv6-address-no-zone
             |  |     +--rw end-address
             |  |     |       inet:ipv6-address-no-zone
             |  |     +--rw max-address-utilization?   dhc6:threshold
             |  |     +--rw option-set-id*             leafref
             |  |     +--rw valid-lifetime?
             |  |     |       dhc6:timer-seconds32
             |  |     +--rw renew-time?
             |  |     |       dhc6:timer-seconds32
             |  |     +--rw rebind-time?
             |  |     |       dhc6:timer-seconds32
             |  |     +--rw preferred-lifetime?
             |  |     |       dhc6:timer-seconds32
             |  |     +--rw rapid-commit?              boolean
             |  |     +--rw host-reservations
             |  |     |  +--rw host-reservation* [reserved-addr]
             |  |     |     +--rw client-duid?          dhc6:duid
             |  |     |     +--rw reserved-addr
             |  |     |     |       inet:ipv6-address
             |  |     |     +--rw option-set-id*        leafref
             |  |     |     +--rw valid-lifetime?
             |  |     |     |       dhc6:timer-seconds32
             |  |     |     +--rw renew-time?
             |  |     |     |       dhc6:timer-seconds32
             |  |     |     +--rw rebind-time?
             |  |     |     |       dhc6:timer-seconds32
             |  |     |     +--rw preferred-lifetime?
             |  |     |     |       dhc6:timer-seconds32
             |  |     |     +--rw rapid-commit?         boolean
             |  |     +--ro active-leases
             |  |        +--ro total-count        uint64
             |  |        +--ro allocated-count    uint64
             |  |        +--ro active-lease* [leased-address]

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             |  |           +--ro leased-address
             |  |           |       inet:ipv6-address
             |  |           +--ro client-duid?          dhc6:duid
             |  |           +--ro ia-id                 uint32
             |  |           +--ro allocation-time?
             |  |           |       yang:date-and-time
             |  |           +--ro last-renew-rebind?
             |  |           |       yang:date-and-time
             |  |           +--ro preferred-lifetime?
             |  |           |       dhc6:timer-seconds32
             |  |           +--ro valid-lifetime?
             |  |           |       dhc6:timer-seconds32
             |  |           +--ro lease-t1?
             |  |           |       dhc6:timer-seconds32
             |  |           +--ro lease-t2?
             |  |                   dhc6:timer-seconds32
             |  +--rw prefix-pools {prefix-delegation}?
             |     +--rw prefix-pool* [pool-id]
             |        +--rw pool-id                     uint32
             |        +--rw pool-prefix
             |        |       inet:ipv6-prefix
             |        +--rw client-prefix-length        uint8
             |        +--rw max-pd-space-utilization?   dhc6:threshold
             |        +--rw option-set-id*              leafref
             |        +--rw valid-lifetime?
             |        |       dhc6:timer-seconds32
             |        +--rw renew-time?
             |        |       dhc6:timer-seconds32
             |        +--rw rebind-time?
             |        |       dhc6:timer-seconds32
             |        +--rw preferred-lifetime?
             |        |       dhc6:timer-seconds32
             |        +--rw rapid-commit?               boolean
             |        +--rw host-reservations
             |        |  +--rw prefix-reservation* [reserved-prefix]
             |        |  |  +--rw client-duid?           dhc6:duid
             |        |  |  +--rw reserved-prefix
             |        |  |  |       inet:ipv6-prefix
             |        |  |  +--rw reserved-prefix-len?   uint8
             |        |  +--rw option-set-id*        leafref
             |        |  +--rw valid-lifetime?
             |        |  |       dhc6:timer-seconds32
             |        |  +--rw renew-time?
             |        |  |       dhc6:timer-seconds32
             |        |  +--rw rebind-time?
             |        |  |       dhc6:timer-seconds32
             |        |  +--rw preferred-lifetime?
             |        |  |       dhc6:timer-seconds32

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             |        |  +--rw rapid-commit?         boolean
             |        +--ro active-leases
             |           +--ro total-count        uint64
             |           +--ro allocated-count    uint64
             |           +--ro active-lease* [leased-prefix]
             |              +--ro leased-prefix
             |              |       inet:ipv6-prefix
             |              +--ro client-duid?          dhc6:duid
             |              +--ro ia-id                 uint32
             |              +--ro allocation-time?
             |              |       yang:date-and-time
             |              +--ro last-renew-rebind?
             |              |       yang:date-and-time
             |              +--ro preferred-lifetime?
             |              |       dhc6:timer-seconds32
             |              +--ro valid-lifetime?
             |              |       dhc6:timer-seconds32
             |              +--ro lease-t1?
             |              |       dhc6:timer-seconds32
             |              +--ro lease-t2?
             |                      dhc6:timer-seconds32
             +--ro solicit-count?               uint32
             +--ro advertise-count?             uint32
             +--ro request-count?               uint32
             +--ro confirm-count?               uint32
             +--ro renew-count?                 uint32
             +--ro rebind-count?                uint32
             +--ro reply-count?                 uint32
             +--ro release-count?               uint32
             +--ro decline-count?               uint32
             +--ro reconfigure-count?           uint32
             +--ro information-request-count?   uint32

       rpcs:
         +---x delete-address-lease
         |  +---w input
         |  |  +---w lease-address-to-delete    leafref
         |  +--ro output
         |     +--ro return-message?   string
         +---x delete-prefix-lease {prefix-delegation}?
            +---w input
            |  +---w lease-prefix-to-delete    leafref
            +--ro output
               +--ro return-message?   string

       notifications:
         +---n address-pool-utilization-threshold-exceeded
         |  +--ro pool-id                    leafref

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         |  +--ro total-pool-addresses       uint64
         |  +--ro max-allocated-addresses    uint64
         |  +--ro allocated-address-count    uint64
         +---n prefix-pool-utilization-threshold-exceeded
         |       {prefix-delegation}?
         |  +--ro pool-id                     leafref
         |  +--ro total-pool-prefixes         uint64
         |  +--ro max-allocated-prefixes      uint64
         |  +--ro allocated-prefixes-count    uint64
         +---n invalid-client-detected
         |  +--ro message-type?   enumeration
         |  +--ro duid?           dhc6:duid
         |  +--ro description?    string
         +---n decline-received
         |  +--ro duid?                 dhc6:duid
         |  +--ro declined-resources* []
         |     +--ro (resource-type)?
         |        +--:(declined-address)
         |        |  +--ro address?   inet:ipv6-address
         |        +--:(declined-prefix)
         |           +--ro prefix?    inet:ipv6-prefix
         +---n non-success-code-sent
            +--ro status-code    uint16
            +--ro duid?          dhc6:duid

               Figure 1: DHCPv6 Server Data Module Structure

   Descriptions of important nodes:

   *  enabled: Enables/disables the function of the DHCPv6 server.

   *  dhcpv6-server: This container holds the server's DHCPv6 specific
      configuration.

   *  server-duid: Each server must have a DUID (DHCP Unique Identifier)
      to identify itself to clients.  A DUID consists of a two-octet
      type field and an arbitrary length (of no more than 128-octets)
      content field.  Currently there are four defined types of DUIDs in
      [RFC8415] and [RFC6355].  The DUID may be configured using the
      format for one of these types, or using the 'unstructured' format.
      The DUID type definitions are imported from the 'ietf-
      dhcpv6-common.yang' module.  [IANA-HARDWARE-TYPES] and [IANA-PEN]
      are referenced for the relevant DUID types.

   *  vendor-config: This container is provided as a location for
      additional implementation-specific YANG nodes for the
      configuration of the device to be augmented.  See Appendix C for
      an example of such a module.

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   *  option-sets: The server can be configured with multiple option-
      sets.  These are groups of DHCPv6 options with common parameters
      which will be supplied to clients on request.  The 'option-set-id'
      field is used to reference an option-set elsewhere in the server's
      configuration.

   *  option-set: Holds configuration parameters for DHCPv6 options.
      The initial set of applicable option definitions are defined here
      and additional options that are also relevant to the relay and/or
      client are imported from the 'ietf-dhcpv6-common' module.  Where
      needed, other DHCPv6 option modules can be augmented as they are
      defined.

   *  class-selector: This is provided as a location for additional
      implementation specific YANG nodes for vendor specific class
      selector nodes to be augmented.  See Appendix D for an example of
      this.

   *  network-ranges: A hierarchical model is used for the allocation of
      addresses and prefixes.  At the top level, 'network-ranges' holds
      global configuration parameters.  Under this, a list of 'network-
      ranges' can be defined.  Inside 'network-rages', 'address-pools'
      (for IA_NA and IA_TA allocations), and 'prefix-pools' (for IA_PD
      allocation) are defined.  Finally within the pools, specific host-
      reservations are held.

   *  prefix-pools: Defines pools to be used for prefix delegation to
      clients.  As prefix delegation is not supported by all DHCPv6
      server implementations, it is enabled by a feature statement.

   Information about notifications:

   *  address/prefix-pool-utilization-threshold-exceeded: Raised when
      the number of leased addresses or prefixes exceeds the configured
      usage threshold.

   *  invalid-client-detected: Raised when the server detects an invalid
      client.  A description of the error and message type that has
      generated the notification can be included.

   *  decline-received: Raised when a DHCPv6 Decline message is received
      from a client.

   *  non-success-code-sent: Raised when a status message is raised for
      an error.

   Information about RPCs

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   *  delete-address-lease: Allows the deletion of a lease for an
      individual IPv6 address from the server's lease database.

   *  delete-prefix-lease: Allows the deletion of a lease for an
      individual IPv6 prefix from the server's lease database.

2.2.  DHCPv6 Relay Tree Diagram

   The tree diagram in Figure 2 provides an overview of the DHCPv6 relay
   module.  The tree also includes the common functions module
   Section 3.4.

       module: ietf-dhcpv6-relay
         +--rw dhcpv6-relay
            +--rw enabled?                                boolean
            +--rw relay-if* [if-name]
            |  +--rw if-name
            |  |       if:interface-ref
            |  +--rw enabled?                              boolean
            |  +--rw destination-address*
            |  |       inet:ipv6-address
            |  +--rw link-address?
            |  |       inet:ipv6-address
            |  +--rw relay-options
            |  |  +--rw auth-option
            |  |  |  +--rw protocol?           uint8
            |  |  |  +--rw algorithm?          uint8
            |  |  |  +--rw rdm?                uint8
            |  |  |  +--rw replay-detection?   uint64
            |  |  |  +--rw auth-information?   string
            |  |  +--rw status-code-option
            |  |  |  +--rw status-code?      uint16
            |  |  |  +--rw status-message?   string
            |  |  +--rw interface-id-option
            |  |     +--rw interface-id?   string
            |  +--ro solicit-received-count?               uint32
            |  +--ro advertise-sent-count?                 uint32
            |  +--ro request-received-count?               uint32
            |  +--ro confirm-received-count?               uint32
            |  +--ro renew-received-count?                 uint32
            |  +--ro rebind-received-count?                uint32
            |  +--ro reply-sent-count?                     uint32
            |  +--ro release-received-count?               uint32
            |  +--ro decline-received-count?               uint32
            |  +--ro reconfigure-sent-count?               uint32
            |  +--ro information-request-received-count?   uint32
            |  +--ro unknown-message-received-count?       uint32
            |  +--ro unknown-message-sent-count?           uint32

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            |  +--ro discarded-message-count?              uint32
            |  +--rw prefix-delegation! {prefix-delegation}?
            |     +--ro pd-leases* [ia-pd-prefix]
            |        +--ro ia-pd-prefix           inet:ipv6-prefix
            |        +--ro last-renew?            yang:date-and-time
            |        +--ro client-peer-address?   inet:ipv6-address
            |        +--ro client-duid?           dhc6:duid
            |        +--ro server-duid?           dhc6:duid
            +--ro relay-forward-sent-count?               uint32
            +--ro relay-forward-received-count?           uint32
            +--ro relay-reply-received-count?             uint32
            +--ro relay-forward-unknown-sent-count?       uint32
            +--ro relay-forward-unknown-received-count?   uint32
            +--ro discarded-message-count?                uint32

         rpcs:
           +---x clear-prefix-entry {prefix-delegation}?
           |  +---w input
           |  |  +---w lease-prefix    leafref
           |  +--ro output
           |     +--ro return-message?   string
           +---x clear-client-prefixes {prefix-delegation}?
           |  +---w input
           |  |  +---w client-duid    dhc6:duid
           |  +--ro output
           |     +--ro return-message?   string
           +---x clear-interface-prefixes {prefix-delegation}?
              +---w input
              |  +---w interface
              |          -> ../../dhcpv6-relay/relay-if/if-name
              +--ro output
                 +--ro return-message?   string

         notifications:
           +---n relay-event
              +--ro topology-change
                 +--ro relay-if-name?
                 |       -> /dhcpv6-relay/relay-if/if-name
                 +--ro last-ipv6-addr?   inet:ipv6-address

                Figure 2: DHCPv6 Relay Data Module Structure

   Descriptions of important nodes:

   *  enabled: Globally enables/disables all DHCPv6 relay functions.

   *  dhcpv6-relay: This container holds the relay's DHCPv6-specific
      configuration.

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   *  relay-if: As a relay may have multiple client-facing interfaces,
      they are configured in a list.  The if-name leaf is the key and is
      an interface-ref to the applicable interface defined by the 'ietf-
      interfaces' YANG module.

   *  enabled: Enables/disables all DHCPv6 relay function for the
      specific interface.

   *  destination-addresses: Defines a list of IPv6 addresses that
      client messages will be relayed to.  May include unicast or
      multicast addresses.

   *  link-address: Configures the value that the relay will put into
      the link-address field of Relay-Forward messages.

   *  prefix-delegation: As prefix delegation is not supported by all
      DHCPv6 relay implementations, it is enabled by this feature
      statement where required.

   *  pd-leases: Contains read-only nodes for holding information about
      active delegated prefix leases.

   *  relay-options: Holds configuration parameters for DHCPv6 options
      which can be sent by the relay.  The initial set of applicable
      option definitions are defined here and additional options that
      are also relevant to the server and/or client are imported from
      the 'ietf-dhcpv6-common' module.  Where needed, other DHCPv6
      option modules can be augmented as they are defined.

   Information about notifications:

   *  topology-changed: Raised when the topology of the relay agent is
      changed, e.g., a client facing interface is reconfigured.

   Information about RPCs

   *  clear-prefix-lease: Allows the removal of a delegated lease entry
      from the relay.

   *  clear-client-prefixes: Allows the removal of all of the delegated
      lease entries for a single client (referenced by client DUID) from
      the relay.

   *  clear-interface-prefixes: Allows the removal of all of the
      delegated lease entries from an interface on the relay.

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2.3.  DHCPv6 Client Tree Diagram

   The tree diagram in Figure 3 provides an overview of the DHCPv6
   client module.  The tree also includes the common functions module
   defined in Section 3.4.

      module: ietf-dhcpv6-client
        +--rw dhcpv6-client
           +--rw enabled?     boolean
           +--rw client-if* [if-name]
              +--rw if-name                      if:interface-ref
              +--rw enabled?                     boolean
              +--rw duid?                        dhc6:duid
              +--rw client-configured-options
              |  +--rw option-request-option
              |  |  +--rw oro-option*   uint16
              |  +--rw status-code-option
              |  |  +--rw status-code?      uint16
              |  |  +--rw status-message?   string
              |  +--rw rapid-commit-option!
              |  +--rw user-class-option!
              |  |  +--rw user-class-data-instance*
              |  |          [user-class-data-id]
              |  |     +--rw user-class-data-id    uint8
              |  |     +--rw user-class-data?      string
              |  +--rw vendor-class-option
              |  |  +--rw vendor-class-option-instances*
              |  |          [enterprise-number]
              |  |     +--rw enterprise-number            uint32
              |  |     +--rw vendor-class-data-element*
              |  |             [vendor-class-data-id]
              |  |        +--rw vendor-class-data-id    uint8
              |  |        +--rw vendor-class-data?      string
              |  +--rw vendor-specific-information-options
              |  |  +--rw vendor-specific-information-option*
              |  |          [enterprise-number]
              |  |     +--rw enterprise-number     uint32
              |  |     +--rw vendor-option-data* [sub-option-code]
              |  |        +--rw sub-option-code    uint16
              |  |        +--rw sub-option-data?   string
              |  +--rw reconfigure-accept-option!
              +--rw ia-na* [ia-id]
              |  +--rw ia-id            uint32
              |  +--rw ia-na-options
              |  +--ro lease-state
              |     +--ro ia-na-address?        inet:ipv6-address
              |     +--ro preferred-lifetime?   dhc6:timer-seconds32
              |     +--ro valid-lifetime?       dhc6:timer-seconds32

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              |     +--ro lease-t1?             dhc6:timer-seconds32
              |     +--ro lease-t2?             dhc6:timer-seconds32
              |     +--ro allocation-time?      yang:date-and-time
              |     +--ro last-renew-rebind?    yang:date-and-time
              |     +--ro server-duid?          dhc6:duid
              +--rw ia-ta* [ia-id]
              |  +--rw ia-id            uint32
              |  +--rw ia-ta-options
              |  +--ro lease-state
              |     +--ro ia-ta-address?        inet:ipv6-address
              |     +--ro preferred-lifetime?   dhc6:timer-seconds32
              |     +--ro valid-lifetime?       dhc6:timer-seconds32
              |     +--ro allocation-time?      yang:date-and-time
              |     +--ro last-renew-rebind?    yang:date-and-time
              |     +--ro server-duid?          dhc6:duid
              +--rw ia-pd* [ia-id] {prefix-delegation}?
              |  +--rw ia-id            uint32
              |  +--rw ia-pd-options
              |  +--ro lease-state
              |     +--ro ia-pd-prefix?         inet:ipv6-prefix
              |     +--ro preferred-lifetime?   dhc6:timer-seconds32
              |     +--ro valid-lifetime?       dhc6:timer-seconds32
              |     +--ro lease-t1?             dhc6:timer-seconds32
              |     +--ro lease-t2?             dhc6:timer-seconds32
              |     +--ro allocation-time?      yang:date-and-time
              |     +--ro last-renew-rebind?    yang:date-and-time
              |     +--ro server-duid?          dhc6:duid
              +--ro solicit-count?               uint32
              +--ro advertise-count?             uint32
              +--ro request-count?               uint32
              +--ro confirm-count?               uint32
              +--ro renew-count?                 uint32
              +--ro rebind-count?                uint32
              +--ro reply-count?                 uint32
              +--ro release-count?               uint32
              +--ro decline-count?               uint32
              +--ro reconfigure-count?           uint32
              +--ro information-request-count?   uint32

        notifications:
          +---n invalid-ia-address-detected
          |  +--ro ia-id                 uint32
          |  +--ro ia-na-t1-timer?       uint32
          |  +--ro ia-na-t2-timer?       uint32
          |  +--ro invalid-address?      inet:ipv6-address
          |  +--ro preferred-lifetime?   uint32
          |  +--ro valid-lifetime?       uint32
          |  +--ro ia-options?           binary

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          |  +--ro description?          string
          +---n transmission-failed
          |  +--ro failure-type    enumeration
          |  +--ro description?    string
          +---n unsuccessful-status-code
          |  +--ro status-code    uint16
          |  +--ro server-duid    dhc6:duid
          +---n server-duid-changed
             +--ro new-server-duid         dhc6:duid
             +--ro previous-server-duid    dhc6:duid
             +--ro lease-ia-na?
             |       -> /dhcpv6-client/client-if/ia-na/ia-id
             +--ro lease-ia-ta?
             |       -> /dhcpv6-client/client-if/ia-ta/ia-id
             +--ro lease-ia-pd?
                     -> /dhcpv6-client/client-if/ia-pd/ia-id
                     {prefix-delegation}?

               Figure 3: DHCPv6 Client Data Module Structure

   Descriptions of important nodes:

   *  enabled: Globally enables/disables all DHCPv6 client functions.

   *  dhcpv6-client: This container holds the client's DHCPv6 specific
      configuration.

   *  client-if: As a client may have multiple interfaces requesting
      configuration over DHCP, they are configured in a list.  The if-
      name leaf is the key and is an interface-ref to the applicable
      interface defined by the 'ietf-interfaces' YANG module.

   *  enabled: Enables/disables all DHCPv6 client function for the
      specific interface.

   *  client-duid: Each client must have a DUID (DHCP Unique Identifier)
      to identify itself to servers and relays.  A DUID consists of a
      two-octet type field and an arbitrary length (1-128 octets)
      content field.  Currently there are four defined types of DUIDs in
      [RFC8415] and [RFC6355].  The DUID may be configured using the
      format for one of these types, or using the 'unstructured' format.
      The DUID type definitions are imported from the 'ietf-
      dhcpv6-common.yang' module.  [IANA-HARDWARE-TYPES] and [IANA-PEN]
      are referenced for the relevant DUID types.

   *  client-configured-options: Holds configuration parameters for
      DHCPv6 options which can be sent by the client.  The initial set
      of applicable option definitions are defined here and additional

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      options that are also relevant to the relay and/or server are
      imported from the 'ietf-dhcpv6-common' module.  Where needed,
      other DHCPv6 option modules can be augmented as they are defined.

   *  ia-na, ia-ta, ia-pd: Contains configuration nodes relevant for
      requesting one or more of each of the lease types.  Read-only
      nodes related to the active leases for each type are also located
      here.  As prefix delegation is not supported by all DHCPv6 client
      implementations, it is enabled with a feature statement.

   Information about notifications:

   *  invalid-ia-detected: Raised when the identity association of the
      client can be proved to be invalid.  Possible conditions include:
      duplicated address, illegal address, etc.

   *  retransmission-failed: Raised when the retransmission mechanism
      defined in [RFC8415] has failed.

3.  DHCPv6 YANG Modules

3.1.  DHCPv6 Server YANG Module

   This module imports typedefs from [RFC6991], [RFC8343].

   <CODE BEGINS> file "ietf-dhcpv6-server@2021-06-14.yang"

   module ietf-dhcpv6-server {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-dhcpv6-server";
     prefix "dhc6-srv";

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

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

     import ietf-dhcpv6-common {
       prefix dhc6;
       reference
         "RFC XXXX: To be updated on publication";

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     }

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

     organization
       "IETF DHC (Dynamic Host Configuration) Working Group";

     contact
       "WG Web:   <http://datatracker.ietf.org/wg/dhc/>
        WG List:  <mailto:dhcwg@ietf.org>
        Author:   Yong Cui <yong@csnet1.cs.tsinghua.edu.cn>
        Author:   Linhui Sun <lh.sunlinh@gmail.com>
        Editor:   Ian Farrer <ian.farrer@telekom.de>
        Author:   Sladjana Zeichlin <sladjana.zechlin@telekom.de>
        Author:   Zihao He <hezihao9512@gmail.com>
        Author:   Michal Nowikowski <godfryd@isc.org>";

     description
       "This YANG module defines components for the configuration
       and management of DHCPv6 servers.

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

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

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

     revision 2021-06-14 {
       description
         "Initial Revision.";
       reference
         "XXXX: YANG Data Model for DHCPv6 Configuration";
     }

     /*
      * Features
      */

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     feature prefix-delegation {
       description
         "Denotes that the server implements DHCPv6 prefix
         delegation.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 6.3";
     }

     /*
      * Groupings
      */

     grouping resource-config {
       description
       "Nodes that are reused at multiple levels in the DHCPv6
       server's addressing hierarchy.";
       leaf-list option-set-id {
         type leafref {
           path "/dhcpv6-server/option-sets/option-set/option-set-id";
         }
         description
           "The ID field of relevant set of DHCPv6 options (option-set)
           to be provisioned to clients using the network-range.";
       }
       leaf valid-lifetime {
         type dhc6:timer-seconds32;
         description
           "Valid lifetime for the Identity Association (IA).";
         reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 6";
       }
       leaf renew-time {
         type dhc6:timer-seconds32;
         description
           "Renew (T1) time.";
         reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 4.2";
       }
       leaf rebind-time {
         type dhc6:timer-seconds32;
         description
           "Rebind (T2) time.";
         reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 4.2";
       }
       leaf preferred-lifetime {
         type dhc6:timer-seconds32;
         description

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           "Preferred lifetime for the Identity Association (IA).";
         reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 6";
       }
       leaf rapid-commit {
         type boolean;
         description
           "When set to 'true', Specifies that the pool supports
           client-server exchanges involving two messages.";
         reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 5.1";
       }
     }

     grouping lease-information {
       description
         "Binding information for each client that has been allocated
         an IPv6 address or prefix.";
       leaf client-duid {
         type dhc6:duid;
         description
           "Client DUID.";
         reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 11";
       }
       leaf ia-id {
         type uint32;
         mandatory true;
         description
           "Client's IAID";
         reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 12";
       }
       leaf allocation-time {
         type yang:date-and-time;
         description
           "Time and date that the lease was made.";
         reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 18";
       }
       leaf last-renew-rebind {
         type yang:date-and-time;
         description
           "Time of the last successful renew or rebind.";
         reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 18";
       }
       leaf preferred-lifetime {

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         type dhc6:timer-seconds32;
         description
           "The preferred lifetime expressed in seconds.";
         reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 6";
       }
       leaf valid-lifetime {
         type dhc6:timer-seconds32;
         description
           "The valid lifetime for the lease expressed in seconds.";
         reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 6";
       }
       leaf lease-t1 {
         type dhc6:timer-seconds32;
         description
           "The time interval after which the client should contact
           the server from which the addresses in the IA_NA were
           obtained to extend the lifetimes of the addresses assigned
           to the IA_PD.";
         reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 4.2";
       }
       leaf lease-t2 {
         type dhc6:timer-seconds32;
         description
           "The time interval after which the client should contact
           any available server to extend the lifetimes of the
           addresses assigned to the IA_PD.";
         reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 4.2";
       }
     }

     grouping message-stats {
       description
         "Counters for DHCPv6 messages.";
       leaf solicit-count {
         type uint32;
         config "false";
         description
           "Number of Solicit (1) messages received.";
       }
       leaf advertise-count {
         type uint32;
         config "false";
         description
           "Number of Advertise (2) messages sent.";

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       }
       leaf request-count {
         type uint32;
         config "false";
         description
           "Number of Request (3) messages received.";
       }
       leaf confirm-count {
         type uint32;
         config "false";
         description
           "Number of Confirm (4) messages received.";
       }
       leaf renew-count {
         type uint32;
         config "false";
         description
           "Number of Renew (5) messages received.";
       }
       leaf rebind-count {
         type uint32;
         config "false";
         description
           "Number of Rebind (6) messages received.";
       }
       leaf reply-count {
         type uint32;
         config "false";
         description
           "Number of Reply (7) messages sent.";
       }
       leaf release-count {
         type uint32;
         config "false";
         description
           "Number of Release (8) messages received.";
       }
       leaf decline-count {
         type uint32;
         config "false";
         description
           "Number of Decline (9) messages received.";
       }
       leaf reconfigure-count {
         type uint32;
         config "false";
         description
           "Number of Reconfigure (10) messages sent.";

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       }
       leaf information-request-count {
         type uint32;
         config "false";
         description
           "Number of Information-request (11) messages
           received.";
       }
     }

     grouping preference-option-group {
       description
         "OPTION_PREFERENCE (7) Preference Option.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 21.8";
      container preference-option {
        description
          "OPTION_PREFERENCE (7) Preference Option
          container.";
        leaf pref-value {
           type uint8;
           description
             "The preference value for the server in this
             message. A 1-octet unsigned integer.";
         }
       }
     }

     grouping server-unicast-option-group {
       description
         "OPTION_UNICAST (12) Server Unicast Option.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 21.12";
       container server-unicast-option {
         description
           "OPTION_UNICAST (12) Server Unicast Option container.";
         leaf server-address {
           type inet:ipv6-address;
           description
             "The 128-bit address to which the client should send
             messages delivered using unicast.";
         }
       }
     }

     grouping reconfigure-message-option-group {
       description
         "OPTION_RECONF_MSG (19) Reconfigure Message Option.";

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       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 21.19";
       container reconfigure-message-option {
         description
           "OPTION_RECONF_MSG (19) Reconfigure Message Option.";
         leaf msg-type {
           type uint8;
           description
             "5 for Renew message, 6 for Rebind message, 11 for
             Information-request message.";
         }
       }
     }

     grouping info-refresh-time-option-group {
       description
         "OPTION_INFORMATION_REFRESH_TIME (32) Information Refresh
         Time Option.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 21.23";
       container info-refresh-time-option {
         description
           "OPTION_INFORMATION_REFRESH_TIME (32)
           Information Refresh Time option container.";
         leaf info-refresh-time {
           type dhc6:timer-seconds32;
           description
             "Time duration relative to the current time, expressed
             in units of seconds.";
         }
       }
     }

     grouping sol-max-rt-option-group {
       description
         "OPTION_SOL_MAX_RT (82) SOL_MAX_RT Option (Max Solicit timeout
           value).";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 21.24";
       container sol-max-rt-option {
         description
           "OPTION_SOL_MAX_RT (82) SOL_MAX_RT option container.";
         leaf sol-max-rt-value {
           type dhc6:timer-seconds32;
           description
             "sol max rt value";
         }
       }

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     }

     grouping inf-max-rt-option-group {
       description
         "OPTION_INF_MAX_RT (83) INF_MAX_RT Option (Max
           Information-request timeout value).";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 21.25";
       container inf-max-rt-option {
         description
           "OPTION_INF_MAX_RT (83) inf max rt option
           container.";
         leaf inf-max-rt-value {
           type dhc6:timer-seconds32;
           description
             "inf max rt value";
         }
       }
     }

     /*
      * Data Nodes
      */

     container dhcpv6-server {
       description
         "Configuration nodes for the DHCPv6 server.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 18.3";
       leaf enabled {
         type boolean;
         description
           "Enables the DHCP server function.";
       }
       leaf server-duid {
         type dhc6:duid;
         description
           "DUID of the server.";
         reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 11";
       }
       container vendor-config {
         description
           "This container provides a location for
           augmenting vendor or implementation specific
           configuration nodes.";
       }
       container option-sets {

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         description
           "A server may allow different option sets
           to be configured for clients matching specific parameters
           such as topological location or client type. The
           'option-set' list is a set of options and their
           contents that will be returned to clients.";
         reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 21";
         list option-set {
           key option-set-id;
           description
             "YANG definitions for DHCPv6 options are
             contained in separate YANG modules and augmented to this
             container as required.";
           leaf option-set-id {
             type uint32;
             description
               "Option set identifier.";
           }
           leaf description {
             type string;
             description
               "An optional field for storing additional information
               relevant to the option set.";
           }
           uses preference-option-group;
           uses dhc6:auth-option-group;
           uses server-unicast-option-group;
           uses dhc6:status-code-option-group;
           uses dhc6:rapid-commit-option-group;
           uses dhc6:vendor-specific-information-option-group;
           uses reconfigure-message-option-group;
           uses dhc6:reconfigure-accept-option-group;
           uses info-refresh-time-option-group;
           uses sol-max-rt-option-group;
           uses inf-max-rt-option-group;
         }
       }

       container class-selector {
         description
           "DHCPv6 servers use a 'class-selector' function in order
           to identify and classify incoming client messages
           so that they can be given the correct configuration.
           The mechanisms used for implementing this function vary
           greatly between different implementations such it is not
           possible to include in this module. This container provides
           a location for server implementors to augment their own

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           class-selector YANG.";
       }

       container network-ranges {
         description
           "This model is based on an address and parameter
           allocation hierarchy.  The top level is 'global' - which
           is defined as the container for all network-ranges. Under
           this are the individual network-ranges.";
         uses resource-config;
         list network-range {
           key id;
           description
             "Network-ranges are identified by the 'id' key.";
           leaf id {
             type uint32;
             mandatory true;
             description
               "Unique identifier for the network range.";
           }
           leaf description {
             type string;
             description
               "Description for the network range.";
           }
           leaf network-prefix {
             type inet:ipv6-prefix;
             mandatory true;
             description
               "Network prefix.";
           }
           uses resource-config;
           container address-pools {
             description
               "Configuration for the DHCPv6 server's
               address pools.";
             list address-pool {
               key pool-id;
               description
                 "List of address pools for allocation to clients,
                 distinguished by 'pool-id'.";
               leaf pool-id {
                 type uint32;
                 mandatory true;
                 description
                   "Unique identifier for the pool.";
               }
               leaf pool-prefix {

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                 type inet:ipv6-prefix;
                 mandatory true;
                 description
                   "IPv6 prefix for the pool.";
               }
               leaf start-address {
                 type inet:ipv6-address-no-zone;
                 mandatory true;
                 description
                   "Starting IPv6 address for the pool.";
               }
               leaf end-address {
                 type inet:ipv6-address-no-zone;
                 mandatory true;
                 description
                   "Ending IPv6 address for the pool.";
               }
               leaf max-address-utilization {
                 type dhc6:threshold;
                 description
                   "Maximum amount of the addresses in the
                   pool which can be simultaneously allocated,
                   calculated as a percentage of the available
                   addresses (end-address minus start-address plus
                   one).";
               }
               uses resource-config;
               container host-reservations {
                 description
                   "Configuration for host reservations from the
                   address pool.";
                 list host-reservation {
                   key reserved-addr;
                   description
                     "List of host reservations.";
                   leaf client-duid {
                     type dhc6:duid;
                     description
                       "Client DUID for the reservation.";
                   }
                   leaf reserved-addr {
                     type inet:ipv6-address;
                     description
                       "Reserved IPv6 address.";
                   }
                   uses resource-config;
                 }
               }

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               container active-leases {
                 config false;
                 description
                   "Holds state related to active client
                   leases.";
                 leaf total-count {
                   type uint64;
                   mandatory true;
                   description
                     "The total number of addresses in the
                     pool.";
                 }
                 leaf allocated-count {
                   type uint64;
                   mandatory true;
                   description
                     "The number of addresses or prefixes
                     in the pool that are currently allocated.";
                 }
                 list active-lease {
                   key leased-address;
                   description
                     "List of active address leases.";
                   leaf leased-address {
                     type inet:ipv6-address;
                     description
                       "Active address lease entry.";
                   }
                   uses lease-information;
                 }
               }
             }
           }
           container prefix-pools {
             if-feature prefix-delegation;
             description
               "Configuration for the DHCPv6 server's prefix pools.";
             list prefix-pool {
               key pool-id;
               description
                 "List of prefix pools for allocation to
                 clients, distinguished by 'pool-id'.";
               leaf pool-id {
                 type uint32;
                 mandatory true;
                 description
                   "Unique identifier for the pool.";
               }

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               leaf pool-prefix {
                 type inet:ipv6-prefix;
                 mandatory true;
                 description
                   "IPv6 prefix for the pool.";
               }
               leaf client-prefix-length {
                 type uint8 {
                   range "1 .. 128";
                 }
                 mandatory true;
                 description
                   "Length of the prefixes that will be delegated
                   to clients.";
               }
               leaf max-pd-space-utilization {
                 type dhc6:threshold;
                 description
                   "Maximum amount of the prefixes in the
                   pool which can be simultaneously allocated,
                   calculated as a percentage of the available
                   prefixes, rounded up.";
               }
               uses resource-config;
               container host-reservations {
                 description
                   "Configuration for host reservations from the
                   prefix pool.";
                 list prefix-reservation {
                   key reserved-prefix;
                   description
                     "Reserved prefix reservation.";
                   leaf client-duid {
                     type dhc6:duid;
                     description
                       "Client DUID for the reservation.";
                   }
                   leaf reserved-prefix {
                     type inet:ipv6-prefix;
                     description
                       "Reserved IPv6 prefix";
                   }
                   leaf reserved-prefix-len {
                     type uint8;
                     description
                       "Reserved IPv6 prefix length.";
                   }
                 }

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                 uses resource-config;
               }
               container active-leases {
                 config false;
                 description
                   "Holds state related to active client prefix
                   leases.";
                 leaf total-count {
                   type uint64;
                   mandatory true;
                   description
                     "The total number of prefixes in the pool.";
                 }
                 leaf allocated-count {
                   type uint64;
                   mandatory true;
                   description
                    "The number of prefixes in the pool that are
                    currently allocated.";
                 }
                 list active-lease {
                   key leased-prefix;
                   description
                     "List of active prefix leases.";
                   leaf leased-prefix {
                     type inet:ipv6-prefix;
                     description
                       "Active leased prefix entry.";
                   }
                   uses lease-information;
                 }
               }
             }
           }
         }
         uses message-stats;
       }
     }

     /*
      * Notifications
      */

     notification address-pool-utilization-threshold-exceeded {
       description
         "Notification sent when the address pool
         utilization exceeds the threshold configured in
         max-address-utilization.";

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       leaf pool-id {
         type leafref {
           path "/dhcpv6-server/network-ranges/network-range/" +
             "address-pools/address-pool/pool-id";
         }
         mandatory true;
         description
           "Leafref to the address pool that the notification
           is being generated for.";
       }
       leaf total-pool-addresses {
         type uint64;
         mandatory true;
         description
           "Total number of addresses in the pool
           (end-address minus start-address plus one).";
       }
       leaf max-allocated-addresses {
         type uint64;
         mandatory true;
         description
           "Maximum number of addresses that can be simultaneously
           allocated from the pool. This value may be less than
           count of total addresses. Calculated as the
           max-address-utilization (percentage) of the
           total-pool-addresses, rounded up.";
       }
       leaf allocated-address-count {
         type uint64;
         mandatory true;
         description
           "Number of addresses allocated from the pool.";
       }
     }

     notification prefix-pool-utilization-threshold-exceeded {
       if-feature prefix-delegation;
       description
         "Notification sent when the prefix pool utilization
         exceeds the threshold configured in
         max-pd-space-utilization.";
       leaf pool-id {
         type leafref {
           path "/dhcpv6-server/network-ranges/network-range/" +
             "prefix-pools/prefix-pool/pool-id";
         }
         mandatory true;
         description

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           "Unique identifier for the pool.";
       }
       leaf total-pool-prefixes {
         type uint64;
         mandatory true;
         description
           "Total number of prefixes in the pool.";
       }
       leaf max-allocated-prefixes {
         type uint64;
         mandatory true;
         description
           "Maximum number of prefixes that can be simultaneously
           allocated from the pool. This value may be less than
           count of total prefixes. Calculated as the
           max-prefix-utilization (percentage) of the
           total-pool-prefixes, rounded up.";
       }
       leaf allocated-prefixes-count {
         type uint64;
         mandatory true;
         description
           "Number of prefixes allocated from the pool.";
       }
     }

     notification invalid-client-detected {
       description
         "Notification sent when the server detects an
         invalid client.";
       leaf message-type {
         type enumeration {
           enum solicit {
             description
               "Solicit (1) message.";
           }
           enum request {
             description
               "Request (3) message.";
           }
           enum confirm {
             description
               "Confirm (4) message.";
           }
           enum renew {
             description
               "Renew (5) message.";
           }

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           enum rebind {
             description
               "Rebind (6) message.";
           }
           enum release {
             description
               "Release (8) message.";
           }
           enum decline {
             description
               "Decline (9) message.";
           }
           enum info-request {
             description
               "Information request (11) message.";
           }
         }
         description
           "The message type received by the server that has caused
           the error.";
       }
       leaf duid {
         type dhc6:duid;
         description
           "Client DUID.";
       }
       leaf description {
         type string;
         description
           "Description of the event (e.g., and error code or log
           message).";
       }
     }

     notification decline-received {
       description
         "Notification sent when the server has received a
         Decline (9) message from a client.";
       leaf duid {
         type dhc6:duid;
         description
           "Client DUID.";
       }
       list declined-resources {
         description
           "List of declined addresses and/or prefixes.";
         choice resource-type {
           description

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             "Type of resource that has been declined.";
           case declined-address {
             leaf address {
               type inet:ipv6-address;
               description
                 "Address that has been declined.";
             }
           }
           case declined-prefix {
             leaf prefix {
               type inet:ipv6-prefix;
               description
                 "Prefix that has been declined.";
             }
           }
         }
       }
     }

     notification non-success-code-sent {
       description
         "Notification sent when the server responded
         to a client with non-success status code.";
       leaf status-code {
         type uint16;
         mandatory true;
         description
           "Status code returned to the client.";
       }
       leaf duid {
         type dhc6:duid;
         description
           "Client DUID.";
       }
     }

     /*
      * RPCs
      */

     rpc delete-address-lease {
       nacm:default-deny-all;
       description
         "Deletes a client's active address lease from the
         server's lease database. Note this will not cause the address
         to be revoked from the client, and the lease may be refreshed
         or renewed by the client.";
       input {

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         leaf lease-address-to-delete {
           type leafref {
             path "../../dhcpv6-server/network-ranges/network-range" +
               "/address-pools/address-pool/active-leases" +
               "/active-lease/leased-address";
           }
           mandatory true;
           description
             "IPv6 address of an active lease that will be
             deleted from the server.";
         }
       }
       output {
         leaf return-message {
           type string;
           description
             "Response message from the server.";
         }
       }
     }
     rpc delete-prefix-lease {
       nacm:default-deny-all;
       if-feature prefix-delegation;
       description
         "Deletes a client's active prefix lease from the
         server's lease database. Note, this will not cause the prefix
         to be revoked from the client, and the lease may be refreshed
         or renewed by the client.";
       input {
         leaf lease-prefix-to-delete {
           type leafref {
             path "../../dhcpv6-server/network-ranges/network-range" +
               "/prefix-pools/prefix-pool/active-leases/active-lease" +
               "/leased-prefix";
           }
           mandatory true;
           description
             "IPv6 prefix of an active lease that will be deleted
             from the server.";
         }
       }
       output {
         leaf return-message {
           type string;
           description
             "Response message from the server.";
         }
       }

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     }
   }
   <CODE ENDS>

3.2.  DHCPv6 Relay YANG Module

   This module imports typedefs from [RFC6991], [RFC8343].

   <CODE BEGINS> file "ietf-dhcpv6-relay@2021-06-14.yang"

   module ietf-dhcpv6-relay {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-dhcpv6-relay";
     prefix "dhc6-rly";

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

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

     import ietf-dhcpv6-common {
       prefix dhc6;
       reference
         "RFC XXXX: To be updated on publication";
     }

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

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

     organization
       "IETF DHC (Dynamic Host Configuration) Working Group";

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     contact
       "WG Web:   <http://datatracker.ietf.org/wg/dhc/>
        WG List:  <mailto:dhcwg@ietf.org>
        Author:   Yong Cui <yong@csnet1.cs.tsinghua.edu.cn>
        Author:   Linhui Sun <lh.sunlinh@gmail.com>
        Editor:   Ian Farrer <ian.farrer@telekom.de>
        Author:   Sladjana Zeichlin <sladjana.zechlin@telekom.de>
        Author:   Zihao He <hezihao9512@gmail.com>
        Author:   Michal Nowikowski <godfryd@isc.org>";

     description
       "This YANG module defines components necessary for the
       configuration and management of DHCPv6 relays.

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

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

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

     revision 2021-06-14 {
       description
         "Initial Revision.";
       reference
         "XXXX: YANG Data Model for DHCPv6 Configuration";
     }

     /*
      * Features
      */

     feature prefix-delegation {
       description
         "Enable if the relay functions as a delegating router for
         DHCPv6 prefix delegation.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 6.3";
     }

     /*
      * Groupings

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      */

     grouping pd-lease-state {
       description
         "State data for the relay.";
       list pd-leases {
         key ia-pd-prefix;
         config false;
         description
           "Information about an active IA_PD prefix
           delegation.";
        leaf ia-pd-prefix {
           type inet:ipv6-prefix;
           description
             "Prefix that is delegated.";
         }
         leaf last-renew {
           type yang:date-and-time;
           description
             "Time of the last successful refresh or renew of the
             delegated prefix.";
         }
         leaf client-peer-address {
           type inet:ipv6-address;
           description
             "Peer-address of the leasing client.";
         }
         leaf client-duid {
           type dhc6:duid;
           description
             "DUID of the leasing client.";
         }
         leaf server-duid {
           type dhc6:duid;
           description
             "DUID of the delegating server.";
         }
       }
     }

     grouping message-statistics {
       description
         "Contains counters for the different DHCPv6
         message types.";
       leaf solicit-received-count {
         type uint32;
         config "false";
         description

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           "Number of Solicit (1) messages received.";
       }
       leaf advertise-sent-count {
         type uint32;
         config "false";
         description
           "Number of Advertise (2) messages sent.";
       }
       leaf request-received-count {
         type uint32;
         config "false";
         description
           "Number of Request (3) messages received.";
       }
       leaf confirm-received-count {
         type uint32;
         config "false";
         description
           "Number of Confirm (4) messages received.";
       }
       leaf renew-received-count {
         type uint32;
         config "false";
         description
           "Number of Renew (5) messages received.";
       }
       leaf rebind-received-count {
         type uint32;
         config "false";
         description
           "Number of Rebind (6) messages received.";
       }
       leaf reply-sent-count {
         type uint32;
         config "false";
         description
           "Number of Reply (7) messages received.";
       }
       leaf release-received-count {
         type uint32;
         config "false";
         description
           "Number of Release (8) messages sent.";
       }
       leaf decline-received-count {
         type uint32;
         config "false";
         description

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           "Number of Decline (9) messages sent.";
       }
       leaf reconfigure-sent-count {
         type uint32;
         config "false";
         description
           "Number of Reconfigure (10) messages sent.";
       }
       leaf information-request-received-count {
         type uint32;
         config "false";
         description
           "Number of Information-request (11) messages
           received.";
       }
       leaf unknown-message-received-count {
         type uint32;
         config "false";
         description
           "Number of messages of unknown type that have
           been received.";
       }
       leaf unknown-message-sent-count {
         type uint32;
         config "false";
         description
           "Number of messages of unknown type that have
           been sent.";
       }
       leaf discarded-message-count {
         type uint32;
         config "false";
         description
           "Number of messages that have been discarded
           for any reason.";
       }
     }

     grouping global-statistics {
       description
         "Global statistics for the device.";
       leaf relay-forward-sent-count {
         type uint32;
         config "false";
         description
           "Number of Relay-forward (12) messages sent.";
       }
       leaf relay-forward-received-count {

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         type uint32;
         config "false";
         description
           "Number of Relay-forward (12) messages received.";
       }
       leaf relay-reply-received-count {
         type uint32;
         config "false";
         description
           "Number of Relay-reply (13) messages received.";
       }
       leaf relay-forward-unknown-sent-count {
         type uint32;
         config "false";
         description
           "Number of Relay-forward (12) messages containing
           a message of unknown type sent.";
       }
       leaf relay-forward-unknown-received-count {
         type uint32;
         config "false";
         description
           "Number of Relay-forward (12) messages containing
           a message of unknown type received.";
       }
       leaf discarded-message-count {
         type uint32;
         config "false";
         description
           "Number of messages that have been discarded
           for any reason.";
       }
     }

     grouping interface-id-option-group {
       description
         "OPTION_INTERFACE_ID (18) Interface-Id Option.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 21.18";
       container interface-id-option {
        description
          "OPTION_INTERFACE_ID (18) Interface-Id Option
          container.";
        leaf interface-id {
           type string;
           description
             "An opaque value of arbitrary length generated by the
             relay agent to identify one of the relay agent's

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             interfaces.";
         }
       }
     }

     /*
      * Data Nodes
      */

     container dhcpv6-relay {
       description
         "This container contains the configuration data nodes
         for the relay.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
           IPv6 (DHCPv6), Section 19";
      leaf enabled {
         type boolean;
         description
           "Globally enables the DHCP relay function.";
       }
       list relay-if {
         key if-name;
         description
           "List of interfaces configured for DHCPv6
           relaying.";
         leaf if-name {
           type if:interface-ref;
           description
             "interface-ref to the relay interface.";
         }
         leaf enabled {
           type boolean;
           description
             "Enables the DHCP relay function for this
             interface.";
         }
         leaf-list destination-address {
           type inet:ipv6-address;
           description
             "Each DHCPv6 relay agent may be configured with a list
             of destination addresses for relayed messages.
             The list may include unicast addresses, multicast
             addresses or other valid addresses.";
         }
         leaf link-address {
           type inet:ipv6-address;
           description
             "An address that may be used by the server to identify

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             the link on which the client is located.";
         }
         container relay-options {
           description
             "Definitions for DHCPv6 options that can be sent
             by the relay are augmented to this location from other
             YANG modules as required.";
           uses dhc6:auth-option-group;
           uses dhc6:status-code-option-group;
           uses interface-id-option-group;
         }
         uses message-statistics;
         container prefix-delegation {
           if-feature prefix-delegation;
           presence "Enables prefix delegation for this interface.";
           description
             "Controls and holds state information for prefix
             delegation.";
           uses pd-lease-state;
         }
       }
       uses global-statistics;
     }

     /*
      * Notifications
      */

     notification relay-event {
       description
         "DHCPv6 relay event notifications.";
       container topology-change {
         description
           "Raised if the entry for an interface with DHCPv6
           related configuration or state is removed from
           if:interface-refs.";
         leaf relay-if-name {
           type leafref {
             path "/dhcpv6-relay/relay-if/if-name";
           }
           description
             "Name of the interface that has been removed.";
         }
         leaf last-ipv6-addr {
           type inet:ipv6-address;
           description
             "Last IPv6 address configured on the interface.";
         }

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       }
     }

     /*
      * RPCs
      */

     rpc clear-prefix-entry {
       nacm:default-deny-all;
       if-feature prefix-delegation;
       description
         "Clears an entry for an active delegated prefix
         from the relay.";
       reference "RFC8987: DHCPv6 Prefix Delegating Relay Requirements,
         Section 4.4";
       input {
         leaf lease-prefix {
           type leafref {
             path "/dhcpv6-relay/relay-if/prefix-delegation" +
             "/pd-leases/ia-pd-prefix";
           }
           mandatory true;
           description
             "IPv6 prefix of an active lease entry that will
             be deleted from the relay.";
         }
       }
       output {
         leaf return-message {
           type string;
           description
             "Response message from the relay.";
         }
       }
     }
     rpc clear-client-prefixes {
       nacm:default-deny-all;
       if-feature prefix-delegation;
       description
         "Clears all active prefix entries for a single client.";
       reference "RFC8987: DHCPv6 Prefix Delegating Relay Requirements,
         Section 4.4";
      input {
         leaf client-duid {
           type dhc6:duid;
           mandatory true;
           description
             "DUID of the client.";

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         }
       }
       output {
         leaf return-message {
           type string;
           description
             "Response message from the relay.";
         }
       }
     }
     rpc clear-interface-prefixes {
       nacm:default-deny-all;
       if-feature prefix-delegation;
       description
         "Clears all delegated prefix bindings from an
         interface on the relay.";
       reference "RFC8987: DHCPv6 Prefix Delegating Relay Requirements,
         Section 4.4";
       input {
         leaf interface {
           type leafref {
             path "../../dhcpv6-relay/relay-if/if-name";
           }
           mandatory true;
           description
             "Reference to the relay interface that will have all
             active prefix delegation bindings deleted.";
         }
       }
       output {
         leaf return-message {
           type string;
           description
             "Response message from the relay.";
         }
       }
     }
   }
   <CODE ENDS>

3.3.  DHCPv6 Client YANG Module

   This module imports typedefs from [RFC6991], [RFC8343].

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   <CODE BEGINS> file "ietf-dhcpv6-client@2021-06-14.yang"

   module ietf-dhcpv6-client {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-dhcpv6-client";
     prefix "dhc6-clnt";

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

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

     import ietf-dhcpv6-common {
       prefix dhc6;
       reference
         "RFC XXXX: To be updated on publication";
     }

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

     organization
       "IETF DHC (Dynamic Host Configuration) Working Group";

     contact
       "WG Web:   <http://datatracker.ietf.org/wg/dhc/>
        WG List:  <mailto:dhcwg@ietf.org>
        Author:   Yong Cui <yong@csnet1.cs.tsinghua.edu.cn>
        Author:   Linhui Sun <lh.sunlinh@gmail.com>
        Editor:   Ian Farrer <ian.farrer@telekom.de>
        Author:   Sladjana Zeichlin <sladjana.zechlin@telekom.de>
        Author:   Zihao He <hezihao9512@gmail.com>
        Author:   Michal Nowikowski <godfryd@isc.org>";

     description
       "This YANG module defines components necessary for the
       configuration and management of DHCPv6 clients.

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

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

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

     revision 2021-06-14 {
       description
         "Initial Revision.";
       reference
         "XXXX: YANG Data Model for DHCPv6 Configuration";
     }

     /*
      * Features
      */

     feature prefix-delegation {
       description
         "Denotes that the client implements DHCPv6 prefix
         delegation.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 6.3";
     }

     /*
      * Groupings
      */

     grouping message-statistics {
       description
         "Counters for DHCPv6 messages.";
       leaf solicit-count {
         type uint32;

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         config "false";
         description
           "Number of Solicit (1) messages sent.";
       }
       leaf advertise-count {
         type uint32;
         config "false";
         description
           "Number of Advertise (2) messages received.";
       }
       leaf request-count {
         type uint32;
         config "false";
         description
           "Number of Request (3) messages sent.";
       }
       leaf confirm-count {
         type uint32;
         config "false";
         description
           "Number of Confirm (4) messages sent.";
       }
       leaf renew-count {
         type uint32;
         config "false";
         description
           "Number of Renew (5) messages sent.";
       }
       leaf rebind-count {
         type uint32;
         config "false";
         description
           "Number of Rebind (6) messages sent.";
       }
       leaf reply-count {
         type uint32;
         config "false";
         description
           "Number of Reply (7) messages received.";
       }
       leaf release-count {
         type uint32;
         config "false";
         description
           "Number of Release (8) messages sent.";
       }
       leaf decline-count {
         type uint32;

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         config "false";
         description
           "Number of Decline (9) messages sent.";
       }
       leaf reconfigure-count {
         type uint32;
         config "false";
         description
           "Number of Reconfigure (10) messages received.";
       }
       leaf information-request-count {
         type uint32;
         config "false";
         description
           "Number of Information-request (11) messages
           sent.";
       }
     }

     grouping option-request-option-group {
       description
         "OPTION_ORO (6) Option Request Option. A client MUST include
         an Option Request option in a Solicit, Request, Renew,
         Rebind, or Information-request message to inform the server
         about options the client wants the server to send to the
         client.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 21.7";
       container option-request-option {
         description
           "OPTION_ORO (6) Option Request Option container.";
         leaf-list oro-option {
           type uint16;
          description
            "List of options that the client is requesting,
            identified by option code";
         }
       }
     }

     grouping user-class-option-group {
       description
         "OPTION_USER_CLASS (15) User Class Option";
       reference "RFC 8415: Dynamic Host Configuration Protocol
         for IPv6 (DHCPv6), Section 21.15";
       container user-class-option {
         presence "Configures the option";
         description

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           "OPTION_USER_CLASS (15) User Class Option
           container.";
         list user-class-data-instance {
           key user-class-data-id;
           min-elements 1;
           description
             "The user classes of which the client
             is a member.";
           leaf user-class-data-id {
             type uint8;
             description
               "User class data ID";
           }
           leaf user-class-data {
             type string;
             description
               "Opaque field representing a User Class
               of which the client is a member.";
           }
         }
       }
     }

     grouping vendor-class-option-group {
       description
         "OPTION_VENDOR_CLASS (16) Vendor Class Option";
       reference "RFC 8415: Dynamic Host Configuration Protocol
         for IPv6 (DHCPv6), Section 21.16";
       container vendor-class-option {
         description
           "OPTION_VENDOR_CLASS (16) Vendor Class Option
           container.";
         list vendor-class-option-instances {
           key enterprise-number;
           description
             "The vendor class option allows for multiple
             instances in a single message. Each list entry defines
             the contents of an instance of the option.";
           leaf enterprise-number {
             type uint32;
             description
               "The vendor's registered Enterprise Number as
               maintained by IANA.";
           }
           list vendor-class-data-element {
             key vendor-class-data-id;
             description
               "The vendor classes of which the client is a member.";

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             leaf vendor-class-data-id {
               type uint8;
               description
                 "Vendor class data ID";
             }
             leaf vendor-class-data {
               type string;
               description
                 "Opaque field representing a vendor class of which
                 the client is a member.";
             }
           }
         }
       }
     }

     /*
      * Data Nodes
      */

     container dhcpv6-client {
       description
         "DHCPv6 client configuration and state.";
       leaf enabled {
         type boolean;
         default true;
         description
           "Globally enables the DHCP client function.";
       }
       list client-if {
         key if-name;
         description
           "The list of interfaces for which the client will
           be requesting DHCPv6 configuration.";
         leaf if-name {
           type if:interface-ref;
           mandatory true;
           description
             "Reference to the interface entry that the requested
             configuration is relevant to.";
         }
         leaf enabled {
           type boolean;
           default true;
           description
             "Enables the DHCP client function for this interface.";
         }
         leaf duid {

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           type dhc6:duid;
           description
             "Client DUID.";
           reference "RFC 8415: Dynamic Host Configuration Protocol for
             IPv6 (DHCPv6), Section 11";
         }
         container client-configured-options {
           description
             "Definitions for DHCPv6 options that can be be sent by
             the client. Additional option definitions can be
             augmented to this location from other YANG modules as
             required.";
           uses option-request-option-group;
           uses dhc6:status-code-option-group;
           uses dhc6:rapid-commit-option-group;
           uses user-class-option-group;
           uses vendor-class-option-group;
           uses dhc6:vendor-specific-information-option-group;
           uses dhc6:reconfigure-accept-option-group;
         }
         list ia-na {
           key ia-id;
           description
             "Configuration relevant for an IA_NA (Identity Association
              for Non-temporary Addresses).";
           reference "RFC 8415: Dynamic Host Configuration Protocol
             for IPv6 (DHCPv6), Section 13.1";
           leaf ia-id {
             type uint32;
             description
               "A unique identifier for this IA_NA.";
             reference "RFC 8415: Dynamic Host Configuration Protocol
               for IPv6 (DHCPv6), Section 12";
           }
           container ia-na-options {
             description
               "An augmentation point for additional options
               that the client may send in the IA_NA-options field
               of OPTION_IA_NA.";
           }
           container lease-state {
             config "false";
             description
               "Information about the active IA_NA lease.";
             leaf ia-na-address {
               type inet:ipv6-address;
               description
                 "Address that is currently leased.";

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             }
             leaf preferred-lifetime {
               type dhc6:timer-seconds32;
               description
                 "The preferred lifetime for the leased address
                 expressed in seconds.";
             }
             leaf valid-lifetime {
               type dhc6:timer-seconds32;
               description
                 "The valid lifetime for the leased address expressed
                 in seconds.";
             }
             leaf lease-t1 {
               type dhc6:timer-seconds32;
               description
                 "The time interval after which the client should
                 contact the server from which the addresses in the
                 IA_NA were obtained to extend the lifetimes of the
                 addresses assigned to the IA_NA.";
             }
             leaf lease-t2 {
               type dhc6:timer-seconds32;
               description
                 "The time interval after which the client should
                 contact any available server to extend the lifetimes
                 of the addresses assigned to the IA_NA.";
             }
             leaf allocation-time {
               type yang:date-and-time;
               description
                 "Time and date that the address was first leased.";
             }
             leaf last-renew-rebind {
               type yang:date-and-time;
               description
                 "Time of the last successful renew or rebind of the
                 leased address.";
             }
             leaf server-duid {
               type dhc6:duid;
               description
                 "DUID of the leasing server.";
             }
           }
         }
         list ia-ta {
           key ia-id;

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           description
             "Configuration relevant for an IA_TA (Identity Association
             for Temporary Addresses).";
           reference "RFC 8415: Dynamic Host Configuration Protocol for
             IPv6 (DHCPv6), Section 13.2";
             leaf ia-id {
               type uint32;
               description
                 "The unique identifier for this IA_TA.";
               reference "RFC 8415: Dynamic Host Configuration Protocol
                 for IPv6 (DHCPv6), Section 12";
             }
           container ia-ta-options {
             description
               "An augmentation point for additional options
               that the client may send in the IA_TA-options field
               of OPTION_IA_TA.";
           }
           container lease-state {
             config "false";
             description
               "Information about an active IA_TA lease.";
             leaf ia-ta-address {
               type inet:ipv6-address;
               description
                 "Address that is currently leased.";
             }
             leaf preferred-lifetime {
               type dhc6:timer-seconds32;
               description
                 "The preferred lifetime for the leased address
                 expressed in seconds.";
             }
             leaf valid-lifetime {
               type dhc6:timer-seconds32;
               description
                 "The valid lifetime for the leased address expressed
                 in seconds.";
             }
             leaf allocation-time {
               type yang:date-and-time;
               description
                 "Time and date that the address was first leased.";
             }
             leaf last-renew-rebind {
               type yang:date-and-time;
               description
                 "Time of the last successful renew or rebind of the

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                 address.";
             }
             leaf server-duid {
               type dhc6:duid;
               description
                 "DUID of the leasing server.";
             }
           }
         }
         list ia-pd {
           if-feature prefix-delegation;
           key ia-id;
           description
             "Configuration relevant for an IA_PD (Identity Association
             for Prefix Delegation).";
           reference "RFC 8415: Dynamic Host Configuration Protocol for
             IPv6 (DHCPv6), Section 13.3";
           leaf ia-id {
             type uint32;
             description
               "The unique identifier for this IA_PD.";
             reference "RFC 8415: Dynamic Host Configuration Protocol
               for IPv6 (DHCPv6), Section 12";
           }
           container ia-pd-options {
             description
               "An augmentation point for additional options that the
               client will send in the IA_PD-options field of
               OPTION_IA_TA.";
           }
           container lease-state {
             config "false";
             description
               "Information about an active IA_PD delegated prefix.";
             leaf ia-pd-prefix {
               type inet:ipv6-prefix;
               description
                 "Delegated prefix that is currently leased.";
             }
             leaf preferred-lifetime {
               type dhc6:timer-seconds32;
               description
                 "The preferred lifetime for the leased prefix expressed

                 in units of seconds.";
             }
             leaf valid-lifetime {
               type dhc6:timer-seconds32;

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               description
                 "The valid lifetime for the leased prefix expressed
                 in units of seconds.";
             }
             leaf lease-t1 {
               type dhc6:timer-seconds32;
               description
                 "The time interval after which the client should
                 contact the server from which the addresses in the
                 IA_NA were obtained to extend the lifetimes of the
                 addresses assigned to the IA_PD.";
             }
             leaf lease-t2 {
               type dhc6:timer-seconds32;
               description
                 "The time interval after which the client should
                 contact any available server to extend the lifetimes
                 of the addresses assigned to the IA_PD.";
             }
             leaf allocation-time {
               type yang:date-and-time;
               description
                 "Time and date that the prefix was first leased.";
             }
             leaf last-renew-rebind {
               type yang:date-and-time;
               description
                 "Time of the last successful renew or rebind of the
                 delegated prefix.";
             }
             leaf server-duid {
               type dhc6:duid;
               description
                 "DUID of the delegating server.";
             }
           }
         }
         uses message-statistics;
       }
     }

     /*
      * Notifications
      */

     notification invalid-ia-address-detected {
       description
         "Notification sent when an address received

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         in an identity association option is determined invalid.
         Possible conditions include a duplicate or otherwise illegal
         address.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 18.2.10.1";
       leaf ia-id {
         type uint32;
         mandatory true;
         description
           "IA-ID";
       }
       leaf ia-na-t1-timer {
         type uint32;
         description
           "The value of the T1 time field for non-temporary address
           allocations (OPTION_IA_NA).";
       }
       leaf ia-na-t2-timer {
         type uint32;
         description
           "The value of the preferred-lifetime field for non-temporary
           address allocations (OPTION_IA_NA).";
       }
       leaf invalid-address {
         type inet:ipv6-address;
         description
           "The IP address which has been detected to be invalid.";
       }
       leaf preferred-lifetime {
         type uint32;
         description
           "The value of the preferred-lifetime field in
           OPTION_IAADDR.";
       }
       leaf valid-lifetime {
         type uint32;
         description
           "The value of the valid-lifetime field in OPTION_IAADDR.";
       }
       leaf ia-options {
        type binary;
        description
          "A copy of the contents of the IAaddr-options field.";
       }
       leaf description {
         type string;
         description
           "Description of the invalid Identity Association (IA)

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           detection error.";
       }
     }

     notification transmission-failed {
       description
         "Notification sent when the transmission or retransmission
         of a message fails.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 7.6";
       leaf failure-type {
         type enumeration {
           enum "solicit-timeout" {
             description
               "Max Solicit timeout value (SOL_MAX_RT) exceeded.";
           }
           enum "request-timeout" {
             description
               "Max Request timeout value (REQ_MAX_RT) exceeded.";
           }
           enum "request-retries-exceeded" {
             description
               "Max Request retry attempts (REC_MAX_RC) exceeded.";
           }
           enum "confirm-duration-exceeded" {
             description
               "Max Confirm duration (CNF_MAX_RD) exceeded.";
           }
           enum "renew-timeout" {
             description
               "Max Renew timeout value (REN_MAX_RT) exceeded.";
           }
           enum "rebind-timeout" {
             description
               "Max Rebind timeout value (REB_MAX_RT)
               exceeded.";
           }
           enum "info-request-timeout" {
             description
               "Max Information-request timeout value (INF_MAX_RT)
               exceeded.";
           }
           enum "release-retries-exceeded" {
             description
               "Max Release retry attempts (REL_MAX_RC) exceeded.";
           }
           enum "decline-retries-exceeded" {
             description

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               "Max Decline retry attempts (DEC_MAX_RT) exceeded.";
           }
         }
         mandatory true;
         description
           "Description of the failure.";
       }
       leaf description {
         type string;
         description
           "Information related to the failure, such as number of
           retries and timer values.";
       }
     }

     notification unsuccessful-status-code {
       description
         "Notification sent when the client receives a message that
         includes an unsuccessful Status Code option.";
         reference "RFC 8415: Dynamic Host Configuration Protocol for
             IPv6 (DHCPv6), Section 21.13";
       leaf status-code {
         type uint16;
         mandatory true;
         description
           "Unsuccessful status code received by a client.";
       }
       leaf server-duid {
         type dhc6:duid;
         mandatory true;
         description
           "DUID of the server sending the unsuccessful
           error code.";
       }
     }

     notification server-duid-changed {
       description
         "Notification sent when the client receives a lease
         from a server with different DUID to the one currently stored
         by the client, e.g., in response to a Rebind message.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 18.2.5";
       leaf new-server-duid {
         type dhc6:duid;
         mandatory true;
         description
           "DUID of the new server.";

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       }
       leaf previous-server-duid {
         type dhc6:duid;
         mandatory true;
         description
           "DUID of the previous server.";
       }
       leaf lease-ia-na {
         type leafref {
           path "/dhcpv6-client/client-if/ia-na/ia-id";
         }
         description
           "Reference to the IA_NA lease.";
       }
       leaf lease-ia-ta {
         type leafref {
           path "/dhcpv6-client/client-if/ia-ta/ia-id";
         }
         description
           "Reference to the IA_TA lease.";
       }
       leaf lease-ia-pd {
         if-feature prefix-delegation;
         type leafref {
           path "/dhcpv6-client/client-if/ia-pd/ia-id";
         }
         description
           "Reference to the IA_PD lease.";
       }
     }
   }
   <CODE ENDS>

3.4.  DHCPv6 Common YANG Module

   This module imports typedefs from [RFC6991].

   <CODE BEGINS> file "ietf-dhcpv6-common@2021-06-14.yang"

   module ietf-dhcpv6-common {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-dhcpv6-common";
     prefix "dhc6";

     organization
       "IETF DHC (Dynamic Host Configuration) Working Group";

     contact

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       "WG Web:   <http://datatracker.ietf.org/wg/dhc/>
        WG List:  <mailto:dhcwg@ietf.org>
        Author:   Yong Cui <yong@csnet1.cs.tsinghua.edu.cn>
        Author:   Linhui Sun <lh.sunlinh@gmail.com>
        Editor:   Ian Farrer <ian.farrer@telekom.de>
        Author:   Sladjana Zeichlin <sladjana.zechlin@telekom.de>
        Author:   Zihao He <hezihao9512@gmail.com>
        Author:   Michal Nowikowski <godfryd@isc.org>";

     description
       "This YANG module defines common components used for the
       configuration and management of DHCPv6.

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

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

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

     revision 2021-06-14 {
       description
         "Initial Revision.";
       reference
         "XXXX: YANG Data Model for DHCPv6 Configuration";
     }

     typedef threshold {
       type uint8 {
         range 1..100;
       }
       description
         "Threshold value in percent.";
     }

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     typedef timer-seconds32 {
       type uint32;
       units "seconds";
       description
         "Timer value type, in seconds (32-bit range).";
     }

     typedef duid-base {
       type string {
         pattern '([0-9a-fA-F]{2}){3,130}';
       }
       description
         "Each DHCP server and client has a DUID (DHCP Unique
         Identifier). The DUID consists of a two-octet
         type field and an arbitrary length (1-128 octets) content
         field. The duid-base type is used by other duid types with
         additional pattern constraints.

         Currently, there are four defined types of DUIDs
         in RFC 8415 and RFC 6355 - DUID-LLT, DUID-EN, DUID-LL
         and DUID-UUID.  DUID-unstructured represents DUIDs which
         do not follow any of the defined formats.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 11
         RFC 6355: Definition of the UUID-Based DHCPv6 Unique
         Identifier (DUID-UUID), Section 4";
     }

     typedef duid-llt {
       type duid-base {
         pattern '0001'
           + '[0-9a-fA-F]{12,}';
       }
       description
         "DUID type 1, based on Link-Layer Address Plus Time
         (DUID-LLT). Constructed with a 2-octet hardware type assigned
         by IANA,  4-octet containing the time the DUID is generated
         (represented in seconds since midnight (UTC), January 1, 2000,
         modulo 2^32), and a link-layer address. The address is encoded
         without separator characters. For example:

         +------+------+----------+--------------+
         | 0001 | 0006 | 28490058 | 00005E005300 |
         +------+------+----------+--------------+

         This example includes the 2-octet DUID type of 1 (0x01), the
         hardware type is 0x06 (IEEE Hardware Types) the creation
         time is 0x028490058 (constructed as described above). Finally,

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         the link-layer address is 0x5E005300 (EUI-48 address
         00-00-5E-00-53-00)";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 11.2
         IANA 'Hardware Types' registry.
           <https://www.iana.org/assignments/arp-parameters>";
     }

     typedef duid-en {
       type duid-base {
         pattern '0002'
           + '[0-9a-fA-F]{4,}';
       }
       description
         "DUID type 2, assigned by vendor based on Enterprise
         Number (DUID-EN). This DUID consists of the 4-octet vendor's
         registered Private Enterprise Number as maintained by IANA
         followed by a unique identifier assigned by the vendor. For
         example:

         +------+----------+------------------+
         | 0002 | 00000009 | 0CC084D303000912 |
         +------+----------+------------------+

         This example includes the 2-octet DUID type of 2 (0x02),
         4-octets for the Enterprise Number (0x09), followed by
         8-octets of identifier data (0x0CC084D303000912).";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 11.3
         IANA 'Private Enterprise Numbers' registry.
           <https://www.iana.org/assignments/enterprise-numbers>";
     }

     typedef duid-ll {
       type duid-base {
         pattern '0003'
           + '([0-9a-fA-F]){4,}';
       }
       description
         "DUID type 3, based on Link-Layer Address (DUID-LL).
         Constructed with a 2-octet hardware type assigned
         by IANA, and a link-layer address. The address is encoded
         without separator characters. For example:

         +------+------+--------------+
         | 0003 | 0006 | 00005E005300 |
         +------+------+--------------+

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         This example includes the 2-octet DUID type of 3 (0x03), the
         hardware type is 0x06 (IEEE Hardware Types), and the link-layer

         address is 0x5E005300 (EUI-48 address 00-00-5E-00-53-00)";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 11.4
         IANA 'Hardware Types' registry.
           <https://www.iana.org/assignments/arp-parameters>";
     }

     typedef duid-uuid {
       type duid-base {
         pattern '0004'
           + '[0-9a-fA-F]{32}';
       }
       description
         "DUID type 4, based on Universally Unique Identifier
         (DUID-UUID).  This type of DUID consists of 16 octets
         containing a 128-bit UUID. For example:

         +------+----------------------------------+
         | 0004 | 9f03b182705747e38a1e422910078642 |
         +------+----------------------------------+

         This example includes the 2-octet DUID type of 4 (0x04), and
         the UUID 9f03b182-7057-47e3-8a1e-422910078642.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 11.5
         RFC 6355: Definition of the UUID-Based DHCPv6 Unique Identifier

         (DUID-UUID)";
     }

     typedef duid-unstructured {
       type duid-base {
         pattern '[0-9a-fA-F]{3}'
           + '[05-9a-fA-F]'
           + '([0-9a-fA-F])*';
       }
       description
         "Used for DUIDs following any other formats than DUID
         types 1-4. For example:

         +----------------------------------+
         | 7b6a164d325946539dc540fb539bc430 |
         +----------------------------------+

         Here, an arbitrary 16-octet value is used. The only constraint

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         placed on this is that the first 2-octects are not 0x01-0x04
         to avoid collision with the other defined DUID types
         (duid-llt, duid-en, duid-ll, or duid-uuid).";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 11";
     }

     typedef duid {
       type union {
         type duid-llt;
         type duid-en;
         type duid-ll;
         type duid-uuid;
         type duid-unstructured;
       }
       description
         "Represents the DUID and is neutral to the DUID's construction
         format.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 11";
     }

     /*
      * Groupings
      */

     grouping auth-option-group {
       description
       "OPTION_AUTH (11) Authentication Option.";
       reference "RFC 8415: Dynamic Host Configuration Protocol
         for IPv6 (DHCPv6), Section 21.11
         IANA 'Dynamic Host Configuration Protocol (DHCP) Authentication

         Option Name Spaces' registry.
         <https://www.iana.org/assignments/auth-namespaces>";
       container auth-option {
         description
           "OPTION_AUTH (11) Authentication Option container.";
         leaf protocol {
           type uint8;
           description
             "The authentication protocol used by this Authentication
             option.";
         }
         leaf algorithm {
           type uint8;
           description
             "The algorithm used in the authentication protocol.";

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         }
         leaf rdm {
           type uint8;
           description
             "The Replay Detection Method (RDM) used in this
             Authentication option.";
         }
         leaf replay-detection {
           type uint64;
           description
             "The replay detection information for the RDM.";
         }
         leaf auth-information {
           type string;
           description
             "The authentication information, as specified by the
             protocol and algorithm used in this Authentication
             option.";
         }
       }
     }

     grouping status-code-option-group {
       description
         "OPTION_STATUS_CODE (13) Status Code Option.";
       reference "RFC 8415: Dynamic Host Configuration Protocol
         for IPv6 (DHCPv6), Section 21.13";
       container status-code-option {
         description
           "OPTION_STATUS_CODE (13) Status Code Option container.";
         leaf status-code {
           type uint16;
           description
             "The numeric code for the status encoded in this option.
             See the Status Codes registry at
             <https://www.iana.org/assignments/dhcpv6-parameters>
             for the current list of status codes.";
         }
         leaf status-message {
           type string;
           description
             "A UTF-8 encoded text string suitable for display to an
             end user. It MUST NOT be null-terminated.";
         }
       }
     }

     grouping rapid-commit-option-group {

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       description
         "OPTION_RAPID_COMMIT (14) Rapid Commit Option.";
       reference "RFC 8415: Dynamic Host Configuration Protocol for
         IPv6 (DHCPv6), Section 21.14";
       container rapid-commit-option {
         presence "Enable sending of this option";
         description
           "OPTION_RAPID_COMMIT (14) Rapid Commit Option container.";
       }
     }

     grouping vendor-specific-information-option-group {
       description
         "OPTION_VENDOR_OPTS (17) Vendor-specific Information
         Option.";
       reference "RFC 8415: Dynamic Host Configuration Protocol
         for IPv6 (DHCPv6), Section 21.17";
       container vendor-specific-information-options {
         description
           "OPTION_VENDOR_OPTS (17) Vendor-specific Information
           Option container.";
         list vendor-specific-information-option {
           key enterprise-number;
           description
             "The vendor-specific information option allows for
             multiple instances in a single message. Each list entry
             defines the contents of an instance of the option.";
           leaf enterprise-number {
             type uint32;
             description
               "The vendor's registered Enterprise Number, as
               maintained by IANA.";
             reference "IANA 'Private Enterprise Numbers' registry.
               <https://www.iana.org/assignments/enterprise-numbers>";
           }
           list vendor-option-data {
             key sub-option-code;
             description
               "Vendor options, interpreted by vendor-specific
               client/server functions.";
             leaf sub-option-code {
               type uint16;
               description
                 "The code for the sub-option.";
             }
             leaf sub-option-data {
               type string {
                 pattern '([0-9a-fA-F]{2}){0,}';

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               }
               description
                 "The data area for the sub-option.";
             }
           }
         }
       }
     }

     grouping reconfigure-accept-option-group {
       description
         "OPTION_RECONF_ACCEPT (20) Reconfigure Accept Option.
         A client uses the Reconfigure Accept option to announce to
         the server whether the client is willing to accept Reconfigure
         messages, and a server uses this option to tell the client
         whether or not to accept Reconfigure messages.  In the absence
         of this option, the default behavior is that the client is
         unwilling to accept Reconfigure messages.  The presence node
         is used to enable the option.";
       reference "RFC 8415: Dynamic Host Configuration Protocol
         for IPv6 (DHCPv6), Section 21.20";
       container reconfigure-accept-option {
         presence "Enable sending of this option";
         description
           "OPTION_RECONF_ACCEPT (20)  Reconfigure Accept Option
           container.";
       }
     }
   }
   <CODE ENDS>

4.  Security Considerations

   The YANG modules defined in this document are designed to be accessed
   via network management protocols such as NETCONF [RFC6241] or
   RESTCONF [RFC8040].  The lowest NETCONF layer is the secure transport
   layer, and the mandatory-to-implement secure transport is Secure
   Shell (SSH) [RFC6242].  The lowest RESTCONF layer is HTTPS, and the
   mandatory-to-implement secure transport is TLS [RFC8446].

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

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   All data nodes defined in the YANG modules which can be created,
   modified, and deleted (i.e., config true, which is the default) are
   considered sensitive.  Write operations (e.g., edit-config) to these
   data nodes without proper protection can have a negative effect on
   network operations.

   As the RPCs for deleting/clearing active address and prefix entries
   in the server and relay modules are particularly sensitive, these use
   'nacm:default-deny-all'.

   An attacker who is able to access the DHCPv6 server can undertake
   various attacks, such as:

   *  Denial of service attacks, based on re-configuring messages to a
      rogue DHCPv6 server.

   *  Various attacks based on re-configuring the contents of DHCPv6
      options.  For example, changing the address of a the DNS server
      supplied in a DHCP option to point to a rogue server.

   An attacker who is able to access the DHCPv6 relay can undertake
   various attacks, such as:

   *  Re-configuring the relay's destination address to send messages to
      a rogue DHCPv6 server.

   *  Deleting information about a client's delegated prefix, causing a
      denial of service attack as traffic will no longer be routed to
      the client.

   Some of the readable data nodes in this YANG module may be considered
   sensitive or vulnerable in some network environments.  Therefore, it
   is important to control read access (e.g., only permitting get, get-
   config, or notifications) to these data nodes.  These subtrees and
   data nodes can be misused to track the activity of a host:

   *  Information the server holds about clients with active leases:
      (dhc6-srv/network-ranges/network-range/address-pools/ address-
      pool/active-leases)

   *  Information the relay holds about clients with active leases:
      (dhc6-rly/relay-if/prefix-delegation/)

   Security considerations related to DHCPv6 are discussed in [RFC8415].

   Security considerations given in [RFC7950] are also applicable here.

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5.  IANA Considerations

   This document requests IANA to register the following URIs in the
   "IETF XML Registry" [RFC3688]:

   URI:  urn:ietf:params:xml:ns:yang:ietf-dhcpv6-server
   Registrant Contact:  The IESG.
   XML:  N/A; the requested URI is an XML namespace.

   URI:  urn:ietf:params:xml:ns:yang:ietf-dhcpv6-relay
   Registrant Contact:  The IESG.
   XML:  N/A; the requested URI is an XML namespace.

   URI:  urn:ietf:params:xml:ns:yang:ietf-dhcpv6-client
   Registrant Contact:  The IESG.
   XML:  N/A; the requested URI is an XML namespace.

   URI:  urn:ietf:params:xml:ns:yang:ietf-dhcpv6-common
   Registrant Contact:  The IESG.
   XML:  N/A; the requested URI is an XML namespace.

   This document registers the following YANG modules in the "YANG
   Module Names" registry [RFC6020].

   name:           ietf-dhcpv6-server
   namespace:      urn:ietf:params:xml:ns:yang:ietf-dhcpv6-server
   prefix:         dhc6-srv
   reference:      RFC XXXX YANG Data Model for DHCPv6 Configuration

   name:           ietf-dhcpv6-relay
   namespace:      urn:ietf:params:xml:ns:yang:ietf-dhcpv6-relay
   prefix:         dhc6-rly
   reference:      RFC XXXX YANG Data Model for DHCPv6 Configuration

   name:           ietf-dhcpv6-client
   namespace:      urn:ietf:params:xml:ns:yang:ietf-dhcpv6-client
   prefix:         dhc6-clnt
   reference:      RFC XXXX YANG Data Model for DHCPv6 Configuration

   name:           ietf-dhcpv6-common
   namespace:      urn:ietf:params:xml:ns:yang:ietf-dhcpv6-common
   prefix:         dhc6
   reference:      RFC XXXX YANG Data Model for DHCPv6 Configuration

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6.  Acknowledgments

   The authors would like to thank Qi Sun, Lishan Li, Hao Wang, Tomek
   Mrugalski, Marcin Siodelski, Bernie Volz, Ted Lemon, Bing Liu, Tom
   Petch, and Acee Lindem for their valuable comments and contributions
   to this work.

7.  Contributors

   The following individuals are co-authors of this document:

           Yong Cui
           Tsinghua University
           Beijing, 100084
           P.R. China
           Email: cuiyong@tsinghua.edu.cn

           Linhui Sun
           Tsinghua University
           Beijing, 100084
           P.R. China
           Email: lh.sunlinh@gmail.com

           Sladjana Zechlin
           Deutsche Telekom AG
           CTO-IPT, Landgrabenweg 151
           53227, Bonn
           Germany
           Email: sladjana.zechlin@telekom.de

           Zihao He
           Tsinghua University
           Beijing, 100084
           P.R. China
           Email: hezihao9512@gmail.com

           Michal Nowikowski
           Internet Systems Consortium
           Gdansk
           Poland
           Email: godfryd@isc.org

8.  References

8.1.  Normative References

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

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC6355]  Narten, T. and J. Johnson, "Definition of the UUID-Based
              DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355,
              DOI 10.17487/RFC6355, August 2011,
              <https://www.rfc-editor.org/info/rfc6355>.

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

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

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

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

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

   [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>.

   [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>.

   [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>.

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   [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>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8415]  Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
              Richardson, M., Jiang, S., Lemon, T., and T. Winters,
              "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
              RFC 8415, DOI 10.17487/RFC8415, November 2018,
              <https://www.rfc-editor.org/info/rfc8415>.

   [RFC8987]  Farrer, I., Kottapalli, N., Hunek, M., and R. Patterson,
              "DHCPv6 Prefix Delegating Relay Requirements", RFC 8987,
              DOI 10.17487/RFC8987, February 2021,
              <https://www.rfc-editor.org/info/rfc8987>.

   [IANA-HARDWARE-TYPES]
              Internet Assigned Numbers Authority, "Hardware Types",
              <https://www.iana.org/assignments/arp-parameters>.

   [IANA-PEN] Internet Assigned Numbers Authority, "Private Enterprise
              Numbers",
              <https://www.iana.org/assignments/enterprise-numbers>.

   [IANA-AUTH]
              Internet Assigned Numbers Authority, "Dynamic Host
              Configuration Protocol (DHCP) Authentication Option Name
              Spaces",
              <https://www.iana.org/assignments/auth-namespaces>.

   [IANA-STATUS]
              Internet Assigned Numbers Authority, "Dynamic Host
              Configuration Protocol for IPv6 (DHCPv6) Status Codes",
              <https://www.iana.org/assignments/dhcpv6-parameters>.

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8.2.  Informative References

   [RFC3319]  Schulzrinne, H. and B. Volz, "Dynamic Host Configuration
              Protocol (DHCPv6) Options for Session Initiation Protocol
              (SIP) Servers", RFC 3319, DOI 10.17487/RFC3319, July 2003,
              <https://www.rfc-editor.org/info/rfc3319>.

Appendix A.  Data Tree Examples

   This section contains XML examples of data trees for the different
   DHCPv6 elements.

A.1.  DHCPv6 Server Configuration Example

   The following example shows a basic configuration for a server.  The
   configuration defines:

   *  Enabling the DHCP server function

   *  The server's DUID

   *  An option set (id=1) with configuration for the Solicit Max Retry
      Timeout (SOL_MAX_RT (82)) option.

   *  A single network range (2001:db8::/32)

   *  A single address pool, with start and end addresses, relevant
      lease timers and an option-set-id of "1" referencing the option
      set configured above.

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      <dhcpv6-server
          xmlns="urn:ietf:params:xml:ns:yang:ietf-dhcpv6-server">
        <enabled>true</enabled>
        <server-duid>000200090CC084D303000912</server-duid>
        <vendor-config/>
        <option-sets>
          <option-set>
            <option-set-id>1</option-set-id>
            <description>Example DHCP option set</description>
            <sol-max-rt-option>
              <sol-max-rt-value>3600</sol-max-rt-value>
            </sol-max-rt-option>
          </option-set>
        </option-sets>
        <class-selector/>
        <network-ranges>
          <valid-lifetime>54000</valid-lifetime>
          <renew-time>7200</renew-time>
          <rebind-time>32400</rebind-time>
          <preferred-lifetime>43200</preferred-lifetime>
          <network-range>
            <id>1</id>
            <description>example-network-range</description>
            <network-prefix>2001:db8::/32</network-prefix>
            <option-set-id>1</option-set-id>
            <address-pools>
              <address-pool>
                <pool-id>1</pool-id>
                <pool-prefix>2001:db8:1:1::/64</pool-prefix>
                <start-address>2001:db8:1:1::1000</start-address>
                <end-address>2001:db8:1:1::2000</end-address>
                <max-address-utilization>50</max-address-utilization>
                <option-set-id>1</option-set-id>
              </address-pool>
            </address-pools>
          </network-range>
        </network-ranges>
      </dhcpv6-server>

              Figure 4: Basic Server Configuration Example XML

   The following example shows a static host reservation within an
   address pool.  The host's lease timers are configured to be longer
   than hosts from the pool with dynamically assigned addresses.

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         <address-pools>
           <address-pool>
             <pool-id>1</pool-id>
             <pool-prefix>2001:db8:1:1::/64</pool-prefix>
             <start-address>2001:db8:1:1::1000</start-address>
             <end-address>2001:db8:1:1::2000</end-address>
             <max-address-utilization>50</max-address-utilization>
             <option-set-id>1</option-set-id>
             <host-reservations>
               <host-reservation>
                 <reserved-addr>2001:db8:1:1::1001</reserved-addr>
                 <client-duid>00052001db81</client-duid>
                 <option-set-id>1</option-set-id>
                 <valid-lifetime>604800</valid-lifetime>
                 <renew-time>86400</renew-time>
                 <rebind-time>172800</rebind-time>
                 <preferred-lifetime>345600</preferred-lifetime>
               </host-reservation>
             </host-reservations>
           </address-pool>
         </address-pools>

            Figure 5: Host Reservation Configuration Example XML

   The following example shows configuration for a network range and
   pool to be used for delegating prefixes to clients.  In this example,
   each client will receive a /56 prefix.

   The 'max-pd-space-utiliation' is set to 80 so that a 'prefix-pool-
   utilization-threshold-exceeded' notification will be raised if the
   number of prefix allocations exceeds this.

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      <network-ranges>
        <network-range>
          <id>1</id>
          <description>prefix-pool-example</description>
          <network-prefix>2001:db8::/32</network-prefix>
          <prefix-pools>
            <valid-lifetime>54000</valid-lifetime>
            <renew-time>7200</renew-time>
            <rebind-time>32400</rebind-time>
            <preferred-lifetime>43200</preferred-lifetime>
            <prefix-pool>
              <pool-id>0</pool-id>
              <option-set-id>1</option-set-id>
              <pool-prefix>2001:db8:1::/48</pool-prefix>
              <client-prefix-length>56</client-prefix-length>
              <max-pd-space-utilization>80</max-pd-space-utilization>
            </prefix-pool>
          </prefix-pools>
        </network-range>
      </network-ranges>

           Figure 6: Prefix Delegation Configuration Example XML

   The next example shows the configuration of a set of options that may
   be returned to clients, depending on the contents of a received DHCP
   request message.  The option set ID is '1', which will referenced by
   other places in the configuration (e.g., address pool configuration)
   as the available options for clients that request them.

   The example contains 2 instances of the Vendor Specific Information
   Option (OPTION_VENDOR_OPTS (17)) to show how options which allow for
   multiple instances are configured.

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          <option-sets>
            <option-set>
              <option-set-id>1</option-set-id>
              <description>Example DHCP option set</description>
              <vendor-specific-information-options>
                <vendor-specific-information-option>
                  <enterprise-number>9</enterprise-number>
                  <vendor-option-data>
                    <sub-option-code>01</sub-option-code>
                    <sub-option-data>1234abcd</sub-option-data>
                  </vendor-option-data>
                  <vendor-option-data>
                    <sub-option-code>02</sub-option-code>
                    <sub-option-data>abcd1234</sub-option-data>
                  </vendor-option-data>
                </vendor-specific-information-option>
                <vendor-specific-information-option>
                  <enterprise-number>10</enterprise-number>
                  <vendor-option-data>
                    <sub-option-code>01</sub-option-code>
                    <sub-option-data>4321dcba</sub-option-data>
                  </vendor-option-data>
                  <vendor-option-data>
                    <sub-option-code>02</sub-option-code>
                    <sub-option-data>dcba4321</sub-option-data>
                  </vendor-option-data>
                </vendor-specific-information-option>
              </vendor-specific-information-options>
              <sol-max-rt-option>
                <sol-max-rt-value>3600</sol-max-rt-value>
              </sol-max-rt-option>
            </option-set>
          </option-sets>

               Figure 7: Option Set Configuration Example XML

A.2.  DHCPv6 Relay Configuration Example

   The following example shows a basic configuration for a single DHCP
   relay interface and its interaction with the ietf-interfaces module.
   The configuration defines:

   *  Enabling the DHCP relay function globally and for the relevant
      interface.

   *  Referencing the interface that the relay configuration is relevant
      for via an inteface-ref to the ietf-interfaces module.

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   *  Defining two destination addresses that incoming DHCP messages
      will be relayed to.

   *  Configures the link-address value that will be sent in the relay-
      forward message.

   *  Configuring a value for the Interface ID Option
      (OPTION_INTERFACE_ID (18)), which will be included in the relay
      forward message.

   <interfaces xmlns="urn:ietf:params:xml:ns:yang:ietf-interfaces"
     xmlns:ianaift="urn:ietf:params:xml:ns:yang:iana-if-type">
     <interface>
       <name>eth0</name>
       <type>ianaift:ethernetCsmacd</type>
       <description>DHCPv6 Relay Interface</description>
       <enabled>true</enabled>
     </interface>
   </interfaces>
   <dhcpv6-relay xmlns="urn:ietf:params:xml:ns:yang:ietf-dhcpv6-relay">
     <enabled>true</enabled>
     <relay-if>
       <if-name>eth0</if-name>
       <enabled>true</enabled>
       <destination-address>2001:db8:2::1</destination-address>
       <destination-address>2001:db8:2::2</destination-address>
       <link-address>2001:db8:3::1</link-address>
       <relay-options>
         <interface-id-option>
           <interface-id>EXAMPLE-INTERFACE-ID</interface-id>
         </interface-id-option>
       </relay-options>
     </relay-if>
   </dhcpv6-relay>

              Figure 8: Basic Relay Configuration Example XML

A.3.  DHCPv6 Client Configuration Examples

   The following example shows a basic configuration for a DHCP client
   and its interaction with the ietf-interfaces module.  The
   configuration defines:

   *  Enabling the DHCP relay function globally and for the relevant
      interface.

   *  References the interface that the client configuration is relevant
      for via an inteface-ref to the ietf-interfaces module.

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   *  Sets the client's DUID.

   *  Configures a list of option codes that will be requested by the
      client in its Option Request Option (OPTION_ORO (5)).

   *  Configures a single instance of the Vendor-specific Information
      Option (OPTION_VENDOR_OPTS (17)) with a single sub-option data
      item.

   *  Requests a non-temporary IPv6 address (IA_NA) with an identity
      association interface identifier of 1.

   *  Requests an IPv6 delegated prefix address (IA_PD) with an identity
      association interface identifier of 2.

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   <interfaces xmlns="urn:ietf:params:xml:ns:yang:ietf-interfaces"
     xmlns:ianaift="urn:ietf:params:xml:ns:yang:iana-if-type">
     <interface>
       <name>eth0</name>
       <type>ianaift:ethernetCsmacd</type>
       <description>DHCPv6 Relay Interface</description>
       <enabled>true</enabled>
     </interface>
   </interfaces>
   <dhcpv6-client xmlns="urn:ietf:params:xml:ns:yang:ietf-dhcpv6-client"
   >
     <enabled>true</enabled>
     <client-if>
       <if-name>eth0</if-name>
       <enabled>true</enabled>
       <duid>000200090CC084D303000913</duid>
       <client-configured-options>
         <option-request-option>
           <oro-option>17</oro-option>
           <oro-option>23</oro-option>
           <oro-option>24</oro-option>
           <oro-option>82</oro-option>
         </option-request-option>
         <vendor-specific-information-options>
           <vendor-specific-information-option>
             <enterprise-number>9</enterprise-number>
             <vendor-option-data>
               <sub-option-code>1</sub-option-code>
               <sub-option-data>abcd1234</sub-option-data>
             </vendor-option-data>
           </vendor-specific-information-option>
         </vendor-specific-information-options>
       </client-configured-options>
       <ia-na>
         <ia-id>1</ia-id>
       </ia-na>
       <ia-pd>
         <ia-id>2</ia-id>
       </ia-pd>
     </client-if>
   </dhcpv6-client>

              Figure 9: Basic Server Configuration Example XML

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Appendix B.  Example of Augmenting Additional DHCPv6 Option Definitions

   The following section provides a example of how the DHCPv6 option
   definitions can be extended to include additional options.  It is
   expected that additional specification documents will be published
   for this in the future.

   The example defines YANG models for OPTION_SIP_SERVER_D (21) and
   OPTION_SIP_SERVER_D (22) defined in [RFC3319].  The module is
   constructed as follows:

   *  The module is named using a meaningful, shortened version of the
      document name in which the DHCP option format is specified.

   *  A separate grouping is used to define each option.

   *  The name of the option is taken from the registered IANA name for
      the option, with an '-option' suffix added.

   *  The description field is taken from the relevant option code name
      and number.

   *  The reference section is the number and name of the RFC in which
      the DHCPv6 option is defined.

   *  The remaining fields match the fields in the DHCP option.  They
      are in the same order as defined in the DHCP option.  Where-ever
      possible, the format that is defined for the DHCP field should be
      matched by the relevant YANG type.

   *  Fields which can have multiple entries or instances are defined
      using list or leaf-list nodes.

   Below the groupings for option definitions, augment statements are
   used to add the option definitions for use in the relevant DHCP
   element's module (server, relay and/or client).

     module example-dhcpv6-opt-sip-serv {
       yang-version 1.1;
       namespace "https://example.com/ns/" +
         "example-dhcpv6-opt-sip-serv";
       prefix "sip-srv";

       import ietf-inet-types {
         prefix inet;
       }

       import ietf-dhcpv6-server {

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         prefix dhc6-srv;
       }

       organization
         "IETF DHC (Dynamic Host Configuration) Working Group";

       contact
         "WG Web:   <http://datatracker.ietf.org/wg/dhc/>
          WG List:  <mailto:dhcwg@ietf.org>
          Author:   Yong Cui <yong@csnet1.cs.tsinghua.edu.cn>
          Author:   Linhui Sun <lh.sunlinh@gmail.com>
          Editor:   Ian Farrer <ian.farrer@telekom.de>
          Author:   Sladjana Zeichlin <sladjana.zechlin@telekom.de>
          Author:   Zihao He <hezihao9512@gmail.com>
          Author:   Michal Nowikowski <godfryd@isc.org>";

       description
         "This YANG module contains DHCPv6 options defined in RFC 8415
         that can be used by DHCPv6 servers.

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

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

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

       revision 2021-06-14 {
         description
           "Initial Revision.";
         reference
           "XXXX: YANG Data Model for DHCPv6 Configuration";
       }

       /*
        * Groupings
        */

       grouping sip-server-domain-name-list-option-group {
         description
           "OPTION_SIP_SERVER_D (21) SIP Servers Domain-Name List";
         reference "RFC 3319: Dynamic Host Configuration Protocol

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           (DHCPv6) Options for Session Initiation Protocol (SIP)
           Servers";
         container sip-server-domain-name-list-option {
          description
            "OPTION_SIP_SERVER_D (21) SIP Servers Domain Name List
            container.";
          list sip-server {
             key sip-serv-id;
             description
               "SIP server information.";
             leaf sip-serv-id {
               type uint8;
               description
                 "SIP server list identifier identifier.";
             }
             leaf sip-serv-domain-name {
               type inet:domain-name;
               description
                 "SIP server domain name.";
             }
           }
         }
       }

       grouping sip-server-address-list-option-group {
         description
           "OPTION_SIP_SERVER_A (22) SIP Servers IPv6 Address List";
         reference "RFC 3319: Dynamic Host Configuration Protocol
           (DHCPv6) Options for Session Initiation Protocol (SIP)
           Servers";
         container sip-server-address-list-option {
           description
             "OPTION_SIP_SERVER_A (22) SIP Servers IPv6 Address List
             container.";
          list sip-server {
             key sip-serv-id;
             description
               "SIP server information.";
             leaf sip-serv-id {
               type uint8;
               description
                 "SIP server list entry identifier.";
             }
             leaf sip-serv-addr {
               type inet:ipv6-address;
               description
                 "SIP server IPv6 address.";
             }

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           }
         }
       }

       /*
        * Augmentations
        */

       augment "/dhc6-srv:dhcpv6-server/dhc6-srv:option-sets/" +
         "dhc6-srv:option-set" {
         description
           "Augment the option definition groupings to the server
           module.";
         uses sip-server-domain-name-list-option-group;
         uses sip-server-address-list-option-group;
       }
     }

   The correct location to augment the new option definition(s) will
   vary according to the specific rules defined for the use of that
   specific option.  For example, for options which will be augmented
   into the ietf-dhcpv6-server module, in many cases, these will be
   augmented to:

   '/dhc6-srv:dhc6-srv/dhc6-srv:option-sets/dhc6-srv:option-set'

   So that they can be defined within option sets.  However, there are
   some options which are only applicable for specific deployment
   scenarios and in these cases it may be more logical to augment the
   option group to a location relevant for the option.

   One example for this could be OPTION_PD_EXCLUDE (67).  This option is
   only relevant in combination with a delegated prefix which contains a
   specific prefix.  In this case, the following location for the
   augmentation may be more suitable:

   '/dhc6-srv:dhc6-srv/dhc6-srv:network-ranges/dhc6-srv:network-range/
   dhc6-srv:prefix-pools/dhc6-srv:prefix-pool"

Appendix C.  Example Vendor Specific Server Configuration Module

   This section shows how to extend the server YANG module defined in
   this document with vendor specific configuration nodes, e.g.,
   configuring access to a lease storage database.

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   The example module defines additional server attributes such as name
   and description.  Storage for leases is configured using a lease-
   storage container.  It allows storing leases in one of three options:
   memory (memfile), MySQL and PosgreSQL.  For each case, the necessary
   configuration parameters are provided.

   At the end there is an augment statement which adds the vendor
   specific configuration defined in "dhcpv6-server-config:config" under
   the "/dhcpv6-server:config/dhcpv6-server:vendor-config" mount point.

   module example-dhcpv6-server-conf {
     yang-version 1.1;
     namespace "https://example.com/ns/" +
       "example-dhcpv6-server-conf";
     prefix "dhc6-srv-conf";

     import ietf-inet-types {
       prefix inet;
     }

     import ietf-interfaces {
       prefix if;
     }

     import ietf-dhcpv6-server {
       prefix dhc6-srv;
     }

     organization
       "IETF DHC (Dynamic Host Configuration) Working Group";

     contact
       "WG Web:   <http://datatracker.ietf.org/wg/dhc/>
        WG List:  <mailto:dhcwg@ietf.org>
        Author:   Yong Cui <yong@csnet1.cs.tsinghua.edu.cn>
        Author:   Linhui Sun <lh.sunlinh@gmail.com>
        Editor:   Ian Farrer <ian.farrer@telekom.de>
        Author:   Sladjana Zeichlin <sladjana.zechlin@telekom.de>
        Author:   Zihao He <hezihao9512@gmail.com>
        Author:   Michal Nowikowski <godfryd@isc.org>";

     description
       "This YANG module defines components for the configuration and
       management of vendor/implementation specific DHCPv6 server
       functionality. As this functionality varies greatly between
       different implementations, the module is provided as an example
       only.

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

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

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

     revision 2021-06-14 {
       description
         "Initial Revision.";
       reference
         "XXXX: YANG Data Model for DHCPv6 Configuration";
     }

     /*
      * Groupings
      */

     grouping config {
       description
         "Parameters necessary for the configuration of a DHCPv6
         server";
       container serv-attributes {
         description
           "Contains basic attributes necessary for running a DHCPv6
           server.";
         leaf name {
           type string;
           description
             "Name of the DHCPv6 server.";
         }
         leaf description {
           type string;
           description
             "Description of the DHCPv6 server.";
         }
         leaf ipv6-listen-port {
           type uint16;
           default 547;
           description
             "UDP port that the server will listen on.";
         }

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         choice listening-interfaces {
           default all-interfaces;
           description
             "Configures which interface or addresses the server will
             listen for incoming messages on.";
           case all-interfaces {
             container all-interfaces {
             presence true;
             description
               "Configures the server to listen for incoming messages
               on all IPv6 addresses (unicast and multicast) on all of
               its network interfaces.";
             }
           }
           case interface-list {
             leaf-list interfaces {
               type if:interface-ref;
               description
                 "List of interfaces on which the server will listen for

                 incoming messages. Messages addressed to any
                 valid IPv6 address (unicast and multicast) will be
                 received.";
             }
           }
           case address-list {
             leaf-list address-list {
               type inet:ipv6-address;
               description
                 "List of IPv6 address(es) on which the server will
                 listen for incoming DHCPv6 messages.";
             }
           }
         }
         leaf-list interfaces-config {
           type if:interface-ref;
           default "if:interfaces/if:interface/if:name";
           description
             "A leaf list of interfaces on which the server should
             listen.";
         }
         container lease-storage {
           description
             "Configures how the server will stores leases.";
           choice storage-type {
             description
               "The type storage that will be used for lease
               information.";

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             case memfile {
               description
                 "Configuration for storing leases information in a
                 Comma-Separated Value (CSV) file.";
               leaf memfile-name {
                 type string;
                 description
                   "Specifies the absolute location of the lease file.
                   The format of the string follow the semantics of
                   the relevant operating system.";
               }
               leaf memfile-lfc-interval {
                 type uint64;
                 description
                   "Specifies the interval in seconds, at which the
                   server will perform a lease file cleanup (LFC).";
               }
             }
             case mysql {
               leaf mysql-name {
                 type string;
                 description
                   "Name of the database.";
               }
               choice mysql-host {
                 description
                   "Define host or address for MySQL server.";
                 case mysql-server-hostname {
                   leaf mysql-hostname {
                     type inet:domain-name;
                     default "localhost";
                     description
                       "If the database is located on a different
                       system to the DHCPv6 server, the domain name can
                       be specified.";
                   }
                 }
                 case mysql-server-address {
                   leaf mysql-address {
                     type inet:ip-address;
                     default "::";
                     description
                       "Configure the location of the database using
                       an IP (v6 or v6) literal address";
                   }
                 }
               }
               leaf mysql-username {

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                 type string;
                 description
                   "User name of the account under which the server
                   will access the database.";
               }
               leaf mysql-password {
                 type string;
                 description
                   "Password of the account under which the server
                   will access the database.";
               }
               leaf mysql-port {
                 type inet:port-number;
                 default 5432;
                 description
                   "If the database is located on a different system,
                   the port number may be specified.";
               }
               leaf mysql-lfc-interval {
                 type uint64;
                 description
                   "Specifies the interval in seconds, at which the
                   server will perform a lease file cleanup (LFC).";
               }
               leaf mysql-connect-timeout {
                 type uint64;
                 description
                   "Defines the timeout interval for connecting to the
                   database. A longer interval can be specified if the
                   database is remote.";
               }
             }
             case postgresql {
               choice postgresql-host {
                 description
                   "Define host or address for postgresql server.";
                 case postgresql-server-hostname {
                   leaf postgresql-hostname {
                     type inet:domain-name;
                     default "localhost";
                     description
                       "If the database is located on a different system

                       to the DHCPv6 server, the domain name can be
                       specified.";
                   }
                 }
                 case postgresql-server-address {

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                   leaf postgresql-address {
                     type inet:ip-address;
                     default "::";
                     description
                       "Configure the location of the database using
                       an IP (v6 or v6) literal address";
                   }
                 }
               }
               leaf postgresql-username {
                 type string;
                 description
                   "User name of the account under which the server
                   will access the database";
               }
               leaf postgresql-password {
                 type string;
                 description
                   "Password of the account under which the server
                   will access the database";
               }
               leaf postgresql-port {
                 type inet:port-number;
                 default 5432;
                 description
                   "If the database is located on a different system,
                   the port number may be specified";
               }
               leaf postgresql-lfc-interval {
                 type uint64;
                 description
                   "Specifies the interval in seconds, at which the
                   server will perform a lease file cleanup (LFC)";
               }
               leaf postgresql-connect-timeout {
                 type uint64;
                 description
                   "Defines the timeout interval for connecting to the
                   database. A longer interval can be specified if the
                   database is remote.";
               }
             }
           }
         }
       }
     }

     /*

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      * Augmentations
      */

     augment "/dhc6-srv:dhcpv6-server/dhc6-srv:vendor-config" {
       description
         "Augment the server specific YANG to the ietf-dhcpv6-server
         module.";
       uses config;
     }
   }

Appendix D.  Example definition of class-selector configuration

   The module "ietf-example-dhcpv6-class-selector" provides an example
   of how vendor-specific class selection configuration can be modelled
   and integrated with the "ietf-dhcpv6-server" module defined in this
   document.

   The example module defines "client-class-names" with associated
   matching rules.  A client can be classified based on "client-id",
   "interface-id" (ingress interface of the client's messages), packet's
   source or destination address, relay link address, relay link
   interface-id and more.  Actually, there are endless methods for
   classifying clients.  So this standard does not try to provide full
   specification for class selection, it only shows an example how it
   could be defined.

   At the end of the example augment statements are used to add the
   defined class selector rules into the overall DHCPv6 addressing
   hierarchy.  This is done in two main parts:

   *  The augmented class-selector configuration in the main DHCPv6
      Server configuration.

   *  client-class leafrefs augmented to "network-range", "address-pool"
      and "pd-pool", pointing to the "client-class-name" that is
      required.

   The mechanism is as follows: class is associated to client based on
   rules and then client is allowed to get address(es)/prefix(es) from
   given network-range/pool if the class name matches.

   module example-dhcpv6-class-select {
     yang-version 1.1;
     namespace "https://example.com/ns/" +
       "example-dhcpv6-class-select";
     prefix "dhc6-class-sel";

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     import ietf-inet-types {
       prefix inet;
     }

     import ietf-interfaces {
       prefix if;
     }

     import ietf-dhcpv6-common {
       prefix dhc6;
     }

     import ietf-dhcpv6-server {
       prefix dhc6-srv;
     }

     organization
       "IETF DHC (Dynamic Host Configuration) Working Group";

     contact
       "WG Web:   <http://datatracker.ietf.org/wg/dhc/>
        WG List:  <mailto:dhcwg@ietf.org>
        Author:   Yong Cui <yong@csnet1.cs.tsinghua.edu.cn>
        Author:   Linhui Sun <lh.sunlinh@gmail.com>
        Editor:   Ian Farrer <ian.farrer@telekom.de>
        Author:   Sladjana Zeichlin <sladjana.zechlin@telekom.de>
        Author:   Zihao He <hezihao9512@gmail.com>
        Author:   Michal Nowikowski <godfryd@isc.org>";

     description
       "This YANG module defines components for the definition and
       configuration of the client class selector function for a
       DHCPv6 server.  As this functionality varies greatly between
       different implementations, the module provided as an example
       only.

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

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

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

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     revision 2021-06-14 {
       description
         "Initial Revision.";
       reference
         "XXXX: YANG Data Model for DHCPv6 Configuration";
     }

     /*
      * Groupings
      */

     grouping client-class-id {
       description
         "Definitions of client message classification for
         authorization and assignment purposes.";
       leaf client-class-name {
         type string;
         description
           "Unique Identifier for client class identification list
           entries.";
       }
       choice id-type {
         mandatory true;
         description
           "Definitions for different client identifier types.";
         case client-id-id {
           leaf client-id {
             type string;
             mandatory true;
             description
               "String literal client identifier.";
           }
           description
             "Client class selection based on a string literal client
             identifier.";
         }
         case received-interface-id {
           description
             "Client class selection based on the incoming interface
             of the DHCPv6 message.";
           leaf received-interface {
             type if:interface-ref;
             description
               "Reference to the interface entry for the incoming
               DHCPv6 message.";
           }
         }
         case packet-source-address-id {

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           description
             "Client class selection based on the source address of
             the DHCPv6 message.";
           leaf packet-source-address {
             type inet:ipv6-address;
             mandatory true;
             description
               "Source address of the DHCPv6 message.";
           }
         }
         case packet-destination-address-id {
           description
             "Client class selection based on the destination address
             of the DHCPv6 message.";
           leaf packet-destination-address {
             type inet:ipv6-address;
             mandatory true;
             description
               "Destination address of the DHCPv6 message.";
           }
         }
         case relay-link-address-id {
           description
             "Client class selection based on the prefix of the
             link-address field in the relay agent message header.";
           leaf relay-link-address {
             type inet:ipv6-prefix;
             mandatory true;
             description
               "Prefix of the link-address field in the relay agent
               message header.";
           }
         }
         case relay-peer-address-id {
           description
             "Client class selection based on the value of the
             peer-address field in the relay agent message header.";
           leaf relay-peer-address {
             type inet:ipv6-prefix;
             mandatory true;
             description
               "Prefix of the peer-address field in the relay agent
               message header.";
           }
         }
         case relay-interface-id {
           description
             "Client class selection based on the incoming

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             interface-id option.";
           leaf relay-interface {
             type string;
             description
               "Reference to the interface entry for the incoming
               DHCPv6 message.";
           }
         }
         case user-class-option-id {
           description
             "Client class selection based on the value of the
             OPTION_USER_CLASS(15) and its user-class-data field.";
           leaf user-class-data {
             type string;
             mandatory true;
             description
               "Value of the enterprise-number field.";
           }
         }
         case vendor-class-present-id {
           description
             "Client class selection based on the presence of
             OPTION_VENDOR_CLASS(16) in the received message.";
           leaf vendor-class-present {
             type boolean;
             mandatory true;
             description
               "Presence of OPTION_VENDOR_CLASS(16) in the received
               message.";
           }
         }
         case vendor-class-option-enterprise-number-id {
           description
             "Client class selection based on the value of the
             enterprise-number field in OPTION_VENDOR_CLASS(16).";
           leaf vendor-class-option-enterprise-number {
             type uint32;
             mandatory true;
             description
               "Value of the enterprise-number field.";
           }
         }
         case vendor-class-option-data-id {
           description
             "Client class selection based on the value of a data
             field within a vendor-class-data entry for a matching
             enterprise-number field in OPTION_VENDOR_CLASS(16).";
           container vendor-class-option-data {

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             description
               "Vendor class option data container.";
             leaf vendor-class-option-enterprise-number {
               type uint32;
               mandatory true;
               description
                 "Value of the enterprise-number field for matching
                 the data contents.";
             }
             leaf vendor-class-data {
               type string;
               mandatory true;
               description
                 "Vendor class data to match.";
             }
           }
         }
         case remote-id {
           description
             "Client class selection based on the value of Remote-ID.";
           container remote-id {
             description
               "Remote-id client class selector container.";
             leaf vendor-class-option-enterprise-number {
               type uint32;
               mandatory true;
               description
                 "Value of the enterprise-number field for matching the
                 data contents.";
             }
             leaf remote-id {
               type string;
               mandatory true;
               description
                 "Remote-ID data to match.";
             }
           }
         }
         case client-duid-id {
           description
             "Client class selection based on the value of the
             received client DUID.";
           leaf duid {
             type dhc6:duid;
             description
               "Client DUID.";
           }
         }

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       }
     }

     /*
      * Augmentations
      */

     augment "/dhc6-srv:dhcpv6-server/dhc6-srv:class-selector" {
       description
         "Augment class selector functions to the DHCPv6 server
         module.";
       container client-classes {
         description
           "Client classes to augment.";
         list class {
           key client-class-name;
           description
             "List of the client class identifiers applicable to
             clients served by this address pool";
           uses client-class-id;
         }
       }
     }

     augment "/dhc6-srv:dhcpv6-server/" +
       "dhc6-srv:network-ranges/dhc6-srv:network-range" {
       description
         "Augment class selector functions to the DHCPv6 server
         network-ranges.";
       leaf-list client-class {
         type leafref {
           path "/dhc6-srv:dhcpv6-server/dhc6-srv:" +
             "class-selector/client-classes/class/client-class-name";
         }
         description
           "Leafrefs to client classes.";
       }
     }

     augment "/dhc6-srv:dhcpv6-server/dhc6-srv:" +
       "network-ranges/dhc6-srv:network-range/dhc6-srv:" +
       "address-pools/dhc6-srv:address-pool" {
       description
         "Augment class selector functions to the DHCPv6 server
         address-pools.";
       leaf-list client-class {
         type leafref {
           path "/dhc6-srv:dhcpv6-server/dhc6-srv:" +

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             "class-selector/client-classes/class/client-class-name";
         }
         description
           "Leafrefs to client classes.";
       }
     }

     augment "/dhc6-srv:dhcpv6-server/dhc6-srv:" +
       "network-ranges/dhc6-srv:network-range/dhc6-srv:" +
       "prefix-pools/dhc6-srv:prefix-pool" {
       description
         "Augment class selector functions to the DHCPv6
         server prefix-pools.";
       leaf-list client-class {
         type leafref {
           path "/dhc6-srv:dhcpv6-server/dhc6-srv:" +
             "class-selector/client-classes/class/client-class-name";
         }
         description
           "Leafrefs to client classes.";
       }
     }
   }

Author's Address

   Ian Farrer (editor)
   Deutsche Telekom AG
   TAI, Landgrabenweg 151
   53227 Bonn
   Germany

   Email: ian.farrer@telekom.de

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