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rfc:rfc3315

Network Working Group R. Droms, Ed. Request for Comments: 3315 Cisco Category: Standards Track J. Bound

                                                       Hewlett Packard
                                                               B. Volz
                                                              Ericsson
                                                              T. Lemon
                                                               Nominum
                                                            C. Perkins
                                                 Nokia Research Center
                                                             M. Carney
                                                      Sun Microsystems
                                                             July 2003
       Dynamic Host Configuration Protocol for IPv6 (DHCPv6)

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

 The Dynamic Host Configuration Protocol for IPv6 (DHCP) enables DHCP
 servers to pass configuration parameters such as IPv6 network
 addresses to IPv6 nodes.  It offers the capability of automatic
 allocation of reusable network addresses and additional configuration
 flexibility.  This protocol is a stateful counterpart to "IPv6
 Stateless Address Autoconfiguration" (RFC 2462), and can be used
 separately or concurrently with the latter to obtain configuration
 parameters.

Droms, et al. Standards Track [Page 1] RFC 3315 DHCP for IPv6 July 2003

Table of Contents

 1.  Introduction and Overview . . . . . . . . . . . . . . . . . .   5
     1.1.   Protocols and Addressing . . . . . . . . . . . . . . .   6
     1.2.   Client-server Exchanges Involving Two Messages . . . .   6
     1.3.   Client-server Exchanges Involving Four Messages. . . .   7
 2.  Requirements. . . . . . . . . . . . . . . . . . . . . . . . .   7
 3.  Background. . . . . . . . . . . . . . . . . . . . . . . . . .   8
 4.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.   IPv6 Terminology . . . . . . . . . . . . . . . . . . .   9
     4.2.   DHCP Terminology . . . . . . . . . . . . . . . . . . .  10
 5.  DHCP Constants. . . . . . . . . . . . . . . . . . . . . . . .  12
     5.1.   Multicast Addresses. . . . . . . . . . . . . . . . . .  13
     5.2.   UDP Ports. . . . . . . . . . . . . . . . . . . . . . .  13
     5.3.   DHCP Message Types . . . . . . . . . . . . . . . . . .  13
     5.4.   Status Codes . . . . . . . . . . . . . . . . . . . . .  15
     5.5.   Transmission and Retransmission Parameters . . . . . .  16
     5.6    Representation of time values and "Infinity" as a time
            value. . . . . . . . . . . . . . . . . . . . . . . . .  16
 6.  Client/Server Message Formats . . . . . . . . . . . . . . . .  16
 7.  Relay Agent/Server Message Formats. . . . . . . . . . . . . .  17
     7.1.   Relay-forward Message. . . . . . . . . . . . . . . . .  18
     7.2.   Relay-reply Message. . . . . . . . . . . . . . . . . .  19
 8.  Representation and Use of Domain Names. . . . . . . . . . . .  19
 9.  DHCP Unique Identifier (DUID) . . . . . . . . . . . . . . . .  19
     9.1.   DUID Contents. . . . . . . . . . . . . . . . . . . . .  20
     9.2.   DUID Based on Link-layer Address Plus Time [DUID-LLT].  20
     9.3.   DUID Assigned by Vendor Based on Enterprise Number
            [DUID-EN]. . . . . . . . . . . . . . . . . . . . . . .  22
     9.4.   DUID Based on Link-layer Address [DUID-LL] . . . . . .  22
 10. Identity Association. . . . . . . . . . . . . . . . . . . . .  23
 11. Selecting Addresses for Assignment to an IA . . . . . . . . .  24
 12. Management of Temporary Addresses . . . . . . . . . . . . . .  25
 13. Transmission of Messages by a Client. . . . . . . . . . . . .  25
 14. Reliability of Client Initiated Message Exchanges . . . . . .  26
 15. Message Validation. . . . . . . . . . . . . . . . . . . . . .  27
     15.1.  Use of Transaction IDs . . . . . . . . . . . . . . . .  28
     15.2.  Solicit Message. . . . . . . . . . . . . . . . . . . .  28
     15.3.  Advertise Message. . . . . . . . . . . . . . . . . . .  28
     15.4.  Request Message. . . . . . . . . . . . . . . . . . . .  29
     15.5.  Confirm Message. . . . . . . . . . . . . . . . . . . .  29
     15.6.  Renew Message. . . . . . . . . . . . . . . . . . . . .  29
     15.7.  Rebind Message . . . . . . . . . . . . . . . . . . . .  29
     15.8.  Decline Messages . . . . . . . . . . . . . . . . . . .  30
     15.9.  Release Message. . . . . . . . . . . . . . . . . . . .  30
     15.10. Reply Message. . . . . . . . . . . . . . . . . . . . .  30
     15.11. Reconfigure Message. . . . . . . . . . . . . . . . . .  31
     15.12. Information-request Message. . . . . . . . . . . . . .  31

Droms, et al. Standards Track [Page 2] RFC 3315 DHCP for IPv6 July 2003

     15.13. Relay-forward Message. . . . . . . . . . . . . . . . .  31
     15.14. Relay-reply Message. . . . . . . . . . . . . . . . . .  31
 16. Client Source Address and Interface Selection . . . . . . . .  32
 17. DHCP Server Solicitation. . . . . . . . . . . . . . . . . . .  32
     17.1.  Client Behavior. . . . . . . . . . . . . . . . . . . .  32
            17.1.1. Creation of Solicit Messages . . . . . . . . .  32
            17.1.2. Transmission of Solicit Messages . . . . . . .  33
            17.1.3. Receipt of Advertise Messages. . . . . . . . .  35
            17.1.4. Receipt of Reply Message . . . . . . . . . . .  35
     17.2.  Server Behavior. . . . . . . . . . . . . . . . . . . .  36
            17.2.1. Receipt of Solicit Messages  . . . . . . . . .  36
            17.2.2. Creation and Transmission of Advertise Messages 36
            17.2.3. Creation and Transmission of Reply Messages. .  38
 18. DHCP Client-Initiated Configuration Exchange. . . . . . . . .  38
     18.1.  Client Behavior. . . . . . . . . . . . . . . . . . . .  39
            18.1.1. Creation and Transmission of Request Messages.  39
            18.1.2. Creation and Transmission of Confirm Messages.  40
            18.1.3. Creation and Transmission of Renew Messages. .  41
            18.1.4. Creation and Transmission of Rebind Messages .  43
            18.1.5. Creation and Transmission of Information-
                    request Messages  . . .. . . . . . . . . . . .  44
            18.1.6. Creation and Transmission of Release Messages.  44
            18.1.7. Creation and Transmission of Decline Messages.  46
            18.1.8. Receipt of Reply Messages. . . . . . . . . . .  46
     18.2.  Server Behavior. . . . . . . . . . . . . . . . . . . .  48
            18.2.1. Receipt of Request Messages. . . . . . . . . .  49
            18.2.2. Receipt of Confirm Messages. . . . . . . . . .  50
            18.2.3. Receipt of Renew Messages. . . . . . . . . . .  51
            18.2.4. Receipt of Rebind Messages . . . . . . . . . .  51
            18.2.5. Receipt of Information-request Messages. . . .  52
            18.2.6. Receipt of Release Messages. . . . . . . . . .  53
            18.2.7. Receipt of Decline Messages. . . . . . . . . .  53
            18.2.8. Transmission of Reply Messages . . . . . . . .  54
 19. DHCP Server-Initiated Configuration Exchange. . . . . . . . .  54
     19.1.  Server Behavior. . . . . . . . . . . . . . . . . . . .  55
            19.1.1. Creation and Transmission of Reconfigure
                    Messages . . . . . . . . . . . . . . . . . . .  55
            19.1.2. Time Out and Retransmission of Reconfigure
                    Messages . . . . . . . . . . . . . . . . . . .  56
     19.2.  Receipt of Renew Messages. . . . . . . . . . . . . . .  56
     19.3.  Receipt of Information-request Messages. . . . . . . .  56
     19.4.  Client Behavior. . . . . . . . . . . . . . . . . . . .  57
            19.4.1. Receipt of Reconfigure Messages. . . . . . . .  57
            19.4.2. Creation and Transmission of Renew Messages. .  58
            19.4.3. Creation and Transmission of Information-
                    request Messages . . . . . . . . . . . . . . .  58
            19.4.4. Time Out and Retransmission of Renew or
                    Information-request Messages . . . . . . . . .  58

Droms, et al. Standards Track [Page 3] RFC 3315 DHCP for IPv6 July 2003

            19.4.5. Receipt of Reply Messages. . . . . . . . . . .  58
 20. Relay Agent Behavior. . . . . . . . . . . . . . . . . . . . .  58
     20.1.  Relaying a Client Message or a Relay-forward Message .  59
            20.1.1. Relaying a Message from a Client . . . . . . .  59
            20.1.2. Relaying a Message from a Relay Agent. . . . .  59
     20.2.  Relaying a Relay-reply Message . . . . . . . . . . . .  60
     20.3.  Construction of Relay-reply Messages . . . . . . . . .  60
 21. Authentication of DHCP Messages . . . . . . . . . . . . . . .  61
     21.1.  Security of Messages Sent Between Servers and Relay
            Agents  . . . . . .  . . . . . . . . . . . . . . . . .  61
     21.2.  Summary of DHCP Authentication . . . . . . . . . . . .  63
     21.3.  Replay Detection . . . . . . . . . . . . . . . . . . .  63
     21.4.  Delayed Authentication Protocol. . . . . . . . . . . .  63
            21.4.1. Use of the Authentication Option in the Delayed
                    Authentication Protocol. . . . . . . . . . . .  64
            21.4.2. Message Validation . . . . . . . . . . . . . .  65
            21.4.3. Key Utilization  . . . . . . . . . . . . . . .  65
            21.4.4. Client Considerations for Delayed Authentication
                    Protocol . . . . . . . . . . . . . . . . . . .  66
            21.4.5. Server Considerations for Delayed Authentication
                    Protocol . . . . . . . . . . . . . . . . . . .  67
     21.5.  Reconfigure Key Authentication Protocol. . . . . . . .  68
            21.5.1. Use of the Authentication Option in the
                    Reconfigure Key Authentication Protocol. . . .  69
            21.5.2. Server considerations for Reconfigure Key
                    protocol . . . . . . . . . . . . . . . . . . .  69
            21.5.3. Client considerations for Reconfigure Key
                    protocol . . . . . . . . . . . . . . . . . . .  70
 22. DHCP Options. . . . . . . . . . . . . . . . . . . . . . . . .  70
     22.1.  Format of DHCP Options . . . . . . . . . . . . . . . .  71
     22.2.  Client Identifier Option . . . . . . . . . . . . . . .  71
     22.3.  Server Identifier Option . . . . . . . . . . . . . . .  72
     22.4.  Identity Association for Non-temporary Addresses Option 72
     22.5.  Identity Association for Temporary Addresses Option. .  75
     22.6.  IA Address Option. . . . . . . . . . . . . . . . . . .  76
     22.7.  Option Request Option. . . . . . . . . . . . . . . . .  78
     22.8.  Preference Option. . . . . . . . . . . . . . . . . . .  79
     22.9.  Elapsed Time Option. . . . . . . . . . . . . . . . . .  79
     22.10. Relay Message Option . . . . . . . . . . . . . . . . .  80
     22.11. Authentication Option. . . . . . . . . . . . . . . . .  81
     22.12. Server Unicast Option. . . . . . . . . . . . . . . . .  82
     22.13. Status Code Option . . . . . . . . . . . . . . . . . .  82
     22.14. Rapid Commit Option. . . . . . . . . . . . . . . . . .  83
     22.15. User Class Option. . . . . . . . . . . . . . . . . . .  84
     22.16. Vendor Class Option. . . . . . . . . . . . . . . . . .  85
     22.17. Vendor-specific Information Option . . . . . . . . . .  86
     22.18. Interface-Id Option. . . . . . . . . . . . . . . . . .  87
     22.19. Reconfigure Message Option . . . . . . . . . . . . . .  88

Droms, et al. Standards Track [Page 4] RFC 3315 DHCP for IPv6 July 2003

     22.20. Reconfigure Accept Option. . . . . . . . . . . . . . .  89
 23. Security Considerations . . . . . . . . . . . . . . . . . . .  89
 24. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  91
     24.1.  Multicast Addresses. . . . . . . . . . . . . . . . . .  92
     24.2.  DHCP Message Types . . . . . . . . . . . . . . . . . .  93
     24.3.  DHCP Options . . . . . . . . . . . . . . . . . . . . .  94
     24.4.  Status Codes . . . . . . . . . . . . . . . . . . . . .  95
     24.5.  DUID . . . . . . . . . . . . . . . . . . . . . . . . .  95
 25. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  95
 26. References. . . . . . . . . . . . . . . . . . . . . . . . . .  96
     26.1.  Normative References . . . . . . . . . . . . . . . . .  96
     26.2.  Informative References . . . . . . . . . . . . . . . .  97
 A. Appearance of Options in Message Types . . . . . . . . . . . .  98
 B. Appearance of Options in the Options Field of DHCP Options . .  99
 Chair's Address . . . . . . . . . . . . . . . . . . . . . . . . .  99
 Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . . . 100
 Full Copyright Statement. . . . . . . . . . . . . . . . . . . . . 101

1. Introduction and Overview

 This document describes DHCP for IPv6 (DHCP), a client/server
 protocol that provides managed configuration of devices.
 DHCP can provide a device with addresses assigned by a DHCP server
 and other configuration information, which are carried in options.
 DHCP can be extended through the definition of new options to carry
 configuration information not specified in this document.
 DHCP is the "stateful address autoconfiguration protocol" and the
 "stateful autoconfiguration protocol" referred to in "IPv6 Stateless
 Address Autoconfiguration" [17].
 The operational models and relevant configuration information for
 DHCPv4 [18][19] and DHCPv6 are sufficiently different that
 integration between the two services is not included in this
 document.  If there is sufficient interest and demand, integration
 can be specified in a document that extends DHCPv6 to carry IPv4
 addresses and configuration information.
 The remainder of this introduction summarizes DHCP, explaining the
 message exchange mechanisms and example message flows.  The message
 flows in sections 1.2 and 1.3 are intended as illustrations of DHCP
 operation rather than an exhaustive list of all possible
 client-server interactions.  Sections 17, 18, and 19 explain client
 and server operation in detail.

Droms, et al. Standards Track [Page 5] RFC 3315 DHCP for IPv6 July 2003

1.1. Protocols and Addressing

 Clients and servers exchange DHCP messages using UDP [15].  The
 client uses a link-local address or addresses determined through
 other mechanisms for transmitting and receiving DHCP messages.
 DHCP servers receive messages from clients using a reserved,
 link-scoped multicast address.  A DHCP client transmits most messages
 to this reserved multicast address, so that the client need not be
 configured with the address or addresses of DHCP servers.
 To allow a DHCP client to send a message to a DHCP server that is not
 attached to the same link, a DHCP relay agent on the client's link
 will relay messages between the client and server.  The operation of
 the relay agent is transparent to the client and the discussion of
 message exchanges in the remainder of this section will omit the
 description of message relaying by relay agents.
 Once the client has determined the address of a server, it may under
 some circumstances send messages directly to the server using
 unicast.

1.2. Client-server Exchanges Involving Two Messages

 When a DHCP client does not need to have a DHCP server assign it IP
 addresses, the client can obtain configuration information such as a
 list of available DNS servers [20] or NTP servers [21] through a
 single message and reply exchanged with a DHCP server.  To obtain
 configuration information the client first sends an
 Information-Request message to the All_DHCP_Relay_Agents_and_Servers
 multicast address.  Servers respond with a Reply message containing
 the configuration information for the client.
 This message exchange assumes that the client requires only
 configuration information and does not require the assignment of any
 IPv6 addresses.
 When a server has IPv6 addresses and other configuration information
 committed to a client, the client and server may be able to complete
 the exchange using only two messages, instead of four messages as
 described in the next section.  In this case, the client sends a
 Solicit message to the All_DHCP_Relay_Agents_and_Servers requesting
 the assignment of addresses and other configuration information.
 This message includes an indication that the client is willing to
 accept an immediate Reply message from the server.  The server that
 is willing to commit the assignment of addresses to the client

Droms, et al. Standards Track [Page 6] RFC 3315 DHCP for IPv6 July 2003

 immediately responds with a Reply message.  The configuration
 information and the addresses in the Reply message are then
 immediately available for use by the client.
 Each address assigned to the client has associated preferred and
 valid lifetimes specified by the server.  To request an extension of
 the lifetimes assigned to an address, the client sends a Renew
 message to the server.  The server sends a Reply message to the
 client with the new lifetimes, allowing the client to continue to use
 the address without interruption.

1.3. Client-server Exchanges Involving Four Messages

 To request the assignment of one or more IPv6 addresses, a client
 first locates a DHCP server and then requests the assignment of
 addresses and other configuration information from the server.  The
 client sends a Solicit message to the
 All_DHCP_Relay_Agents_and_Servers address to find available DHCP
 servers.  Any server that can meet the client's requirements responds
 with an Advertise message.  The client then chooses one of the
 servers and sends a Request message to the server asking for
 confirmed assignment of addresses and other configuration
 information.  The server responds with a Reply message that contains
 the confirmed addresses and configuration.
 As described in the previous section, the client sends a Renew
 message to the server to extend the lifetimes associated with its
 addresses, allowing the client to continue to use those addresses
 without interruption.

2. Requirements

 The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
 SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
 document, are to be interpreted as described in [1].
 This document also makes use of internal conceptual variables to
 describe protocol behavior and external variables that an
 implementation must allow system administrators to change.  The
 specific variable names, how their values change, and how their
 settings influence protocol behavior are provided to demonstrate
 protocol behavior.  An implementation is not required to have them in
 the exact form described here, so long as its external behavior is
 consistent with that described in this document.

Droms, et al. Standards Track [Page 7] RFC 3315 DHCP for IPv6 July 2003

3. Background

 The IPv6 Specification provides the base architecture and design of
 IPv6.  Related work in IPv6 that would best serve an implementor to
 study includes the IPv6 Specification [3], the IPv6 Addressing
 Architecture [5], IPv6 Stateless Address Autoconfiguration [17], IPv6
 Neighbor Discovery Processing [13], and Dynamic Updates to DNS [22].
 These specifications enable DHCP to build upon the IPv6 work to
 provide both robust stateful autoconfiguration and autoregistration
 of DNS Host Names.
 The IPv6 Addressing Architecture specification [5] defines the
 address scope that can be used in an IPv6 implementation, and the
 various configuration architecture guidelines for network designers
 of the IPv6 address space.  Two advantages of IPv6 are that support
 for multicast is required and nodes can create link-local addresses
 during initialization.  The availability of these features means that
 a client can use its link-local address and a well-known multicast
 address to discover and communicate with DHCP servers or relay agents
 on its link.
 IPv6 Stateless Address Autoconfiguration [17] specifies procedures by
 which a node may autoconfigure addresses based on router
 advertisements [13], and the use of a valid lifetime to support
 renumbering of addresses on the Internet.  In addition, the protocol
 interaction by which a node begins stateless or stateful
 autoconfiguration is specified.  DHCP is one vehicle to perform
 stateful autoconfiguration.  Compatibility with stateless address
 autoconfiguration is a design requirement of DHCP.
 IPv6 Neighbor Discovery [13] is the node discovery protocol in IPv6
 which replaces and enhances functions of ARP [14].  To understand
 IPv6 and stateless address autoconfiguration, it is strongly
 recommended that implementors understand IPv6 Neighbor Discovery.
 Dynamic Updates to DNS [22] is a specification that supports the
 dynamic update of DNS records for both IPv4 and IPv6.  DHCP can use
 the dynamic updates to DNS to integrate addresses and name space to
 not only support autoconfiguration, but also autoregistration in
 IPv6.

4. Terminology

 This sections defines terminology specific to IPv6 and DHCP used in
 this document.

Droms, et al. Standards Track [Page 8] RFC 3315 DHCP for IPv6 July 2003

4.1. IPv6 Terminology

 IPv6 terminology relevant to this specification from the IPv6
 Protocol [3], IPv6 Addressing Architecture [5], and IPv6 Stateless
 Address Autoconfiguration [17] is included below.
    address                   An IP layer identifier for an interface
                              or a set of interfaces.
    host                      Any node that is not a router.
    IP                        Internet Protocol Version 6 (IPv6).  The
                              terms IPv4 and IPv6 are used only in
                              contexts where it is necessary to avoid
                              ambiguity.
    interface                 A node's attachment to a link.
    link                      A communication facility or medium over
                              which nodes can communicate at the link
                              layer, i.e., the layer immediately
                              below IP.  Examples are Ethernet (simple
                              or bridged); Token Ring; PPP links,
                              X.25, Frame Relay, or ATM networks; and
                              Internet (or higher) layer "tunnels",
                              such as tunnels over IPv4 or IPv6
                              itself.
    link-layer identifier     A link-layer identifier for an
                              interface.  Examples include IEEE 802
                              addresses for Ethernet or Token Ring
                              network interfaces, and E.164 addresses
                              for ISDN links.
    link-local address        An IPv6 address having a link-only
                              scope, indicated by having the prefix
                              (FE80::/10), that can be used to reach
                              neighboring nodes attached to the same
                              link.  Every interface has a link-local
                              address.
    multicast address         An identifier for a set of interfaces
                              (typically belonging to different
                              nodes).  A packet sent to a multicast
                              address is delivered to all interfaces
                              identified by that address.
    neighbor                  A node attached to the same link.

Droms, et al. Standards Track [Page 9] RFC 3315 DHCP for IPv6 July 2003

    node                      A device that implements IP.
    packet                    An IP header plus payload.
    prefix                    The initial bits of an address, or a
                              set of IP addresses that share the same
                              initial bits.
    prefix length             The number of bits in a prefix.
    router                    A node that forwards IP packets not
                              explicitly addressed to itself.
    unicast address           An identifier for a single interface.
                              A packet sent to a unicast address is
                              delivered to the interface identified by
                              that address.

4.2. DHCP Terminology

 Terminology specific to DHCP can be found below.
    appropriate to the link   An address is "appropriate to the link"
                              when the address is consistent with the
                              DHCP server's knowledge of the network
                              topology, prefix assignment and address
                              assignment policies.
    binding                   A binding (or, client binding) is a
                              group of server data records containing
                              the information the server has about
                              the addresses in an IA or configuration
                              information explicitly assigned to the
                              client.  Configuration information that
                              has been returned to a client through a
                              policy - for example, the information
                              returned to all clients on the same
                              link - does not require a binding.  A
                              binding containing information about
                              an IA is indexed by the tuple <DUID,
                              IA-type, IAID> (where IA-type is the
                              type of address in the IA; for example,
                              temporary).  A binding containing
                              configuration information for a client
                              is indexed by <DUID>.

Droms, et al. Standards Track [Page 10] RFC 3315 DHCP for IPv6 July 2003

    configuration parameter   An element of the configuration
                              information set on the server and
                              delivered to the client using DHCP.
                              Such parameters may be used to carry
                              information to be used by a node to
                              configure its network subsystem and
                              enable communication on a link or
                              internetwork, for example.
    DHCP                      Dynamic Host Configuration Protocol
                              for IPv6.  The terms DHCPv4 and DHCPv6
                              are used only in contexts where it is
                              necessary to avoid ambiguity.
    DHCP client (or client)   A node that initiates requests on a link
                              to obtain configuration parameters from
                              one or more DHCP servers.
    DHCP domain               A set of links managed by DHCP and
                              operated by a single administrative
                              entity.
    DHCP realm                A name used to identify the DHCP
                              administrative domain from which a DHCP
                              authentication key was selected.
    DHCP relay agent (or relay agent) A node that acts as an
                              intermediary to deliver DHCP messages
                              between clients and servers, and is on
                              the same link as the client.
    DHCP server (or server)   A node that responds to requests from
                              clients, and may or may not be on the
                              same link as the client(s).
    DUID                      A DHCP Unique IDentifier for a DHCP
                              participant; each DHCP client and server
                              has exactly one DUID.  See section 9 for
                              details of the ways in which a DUID may
                              be constructed.
    Identity association (IA) A collection of addresses assigned to
                              a client.  Each IA has an associated
                              IAID.  A client may have more than one
                              IA assigned to it; for example, one for
                              each of its interfaces.

Droms, et al. Standards Track [Page 11] RFC 3315 DHCP for IPv6 July 2003

                              Each IA holds one type of address;
                              for example, an identity association
                              for temporary addresses (IA_TA) holds
                              temporary addresses (see "identity
                              association for temporary addresses").
                              Throughout this document, "IA" is used
                              to refer to an identity association
                              without identifying the type of
                              addresses in the IA.
    Identity association identifier (IAID) An identifier for an IA,
                              chosen by the client.  Each IA has an
                              IAID, which is chosen to be unique among
                              all IAIDs for IAs belonging to that
                              client.
    Identity association for non-temporary addresses (IA_NA) An IA
                              that carries assigned addresses that are
                              not temporary addresses (see "identity
                              association for temporary addresses")
    Identity association for temporary addresses (IA_TA) An IA that
                              carries temporary addresses (see RFC
                              3041 [12]).
    message                   A unit of data carried as the payload
                              of a UDP datagram, exchanged among DHCP
                              servers, relay agents and clients.
    Reconfigure key           A key supplied to a client by a server
                              used to provide security for Reconfigure
                              messages.
    relaying                  A DHCP relay agent relays DHCP messages
                              between DHCP participants.
    transaction ID            An opaque value used to match responses
                              with replies initiated either by a
                              client or server.

5. DHCP Constants

 This section describes various program and networking constants used
 by DHCP.

Droms, et al. Standards Track [Page 12] RFC 3315 DHCP for IPv6 July 2003

5.1. Multicast Addresses

 DHCP makes use of the following multicast addresses:
    All_DHCP_Relay_Agents_and_Servers (FF02::1:2) A link-scoped
                multicast address used by a client to communicate with
                neighboring (i.e., on-link) relay agents and servers.
                All servers and relay agents are members of this
                multicast group.
    All_DHCP_Servers (FF05::1:3) A site-scoped multicast address used
                by a relay agent to communicate with servers, either
                because the relay agent wants to send messages to
                all servers or because it does not know the unicast
                addresses of the servers.  Note that in order for
                a relay agent to use this address, it must have an
                address of sufficient scope to be reachable by the
                servers.  All servers within the site are members of
                this multicast group.

5.2. UDP Ports

 Clients listen for DHCP messages on UDP port 546.  Servers and relay
 agents listen for DHCP messages on UDP port 547.

5.3. DHCP Message Types

 DHCP defines the following message types.  More detail on these
 message types can be found in sections 6 and 7.  Message types not
 listed here are reserved for future use.  The numeric encoding for
 each message type is shown in parentheses.
    SOLICIT (1)        A client sends a Solicit message to locate
                       servers.
    ADVERTISE (2)      A server sends an Advertise message to indicate
                       that it is available for DHCP service, in
                       response to a Solicit message received from a
                       client.
    REQUEST (3)        A client sends a Request message to request
                       configuration parameters, including IP
                       addresses, from a specific server.
    CONFIRM (4)        A client sends a Confirm message to any
                       available server to determine whether the
                       addresses it was assigned are still appropriate
                       to the link to which the client is connected.

Droms, et al. Standards Track [Page 13] RFC 3315 DHCP for IPv6 July 2003

    RENEW (5)          A client sends a Renew message to the server
                       that originally provided the client's addresses
                       and configuration parameters to extend the
                       lifetimes on the addresses assigned to the
                       client and to update other configuration
                       parameters.
    REBIND (6)         A client sends a Rebind message to any
                       available server to extend the lifetimes on the
                       addresses assigned to the client and to update
                       other configuration parameters; this message is
                       sent after a client receives no response to a
                       Renew message.
    REPLY (7)          A server sends a Reply message containing
                       assigned addresses and configuration parameters
                       in response to a Solicit, Request, Renew,
                       Rebind message received from a client.  A
                       server sends a Reply message containing
                       configuration parameters in response to an
                       Information-request message.  A server sends a
                       Reply message in response to a Confirm message
                       confirming or denying that the addresses
                       assigned to the client are appropriate to the
                       link to which the client is connected.  A
                       server sends a Reply message to acknowledge
                       receipt of a Release or Decline message.
    RELEASE (8)        A client sends a Release message to the server
                       that assigned addresses to the client to
                       indicate that the client will no longer use one
                       or more of the assigned addresses.
    DECLINE (9)        A client sends a Decline message to a server to
                       indicate that the client has determined that
                       one or more addresses assigned by the server
                       are already in use on the link to which the
                       client is connected.
    RECONFIGURE (10)   A server sends a Reconfigure message to a
                       client to inform the client that the server has
                       new or updated configuration parameters, and
                       that the client is to initiate a Renew/Reply
                       or Information-request/Reply transaction with
                       the server in order to receive the updated
                       information.

Droms, et al. Standards Track [Page 14] RFC 3315 DHCP for IPv6 July 2003

    INFORMATION-REQUEST (11) A client sends an Information-request
                       message to a server to request configuration
                       parameters without the assignment of any IP
                       addresses to the client.
    RELAY-FORW (12)    A relay agent sends a Relay-forward message
                       to relay messages to servers, either directly
                       or through another relay agent.  The received
                       message, either a client message or a
                       Relay-forward message from another relay
                       agent, is encapsulated in an option in the
                       Relay-forward message.
    RELAY-REPL (13)    A server sends a Relay-reply message to a relay
                       agent containing a message that the relay
                       agent delivers to a client.  The Relay-reply
                       message may be relayed by other relay agents
                       for delivery to the destination relay agent.
                       The server encapsulates the client message as
                       an option in the Relay-reply message, which the
                       relay agent extracts and relays to the client.

5.4. Status Codes

 DHCPv6 uses status codes to communicate the success or failure of
 operations requested in messages from clients and servers, and to
 provide additional information about the specific cause of the
 failure of a message.  The specific status codes are defined in
 section 24.4.

Droms, et al. Standards Track [Page 15] RFC 3315 DHCP for IPv6 July 2003

5.5. Transmission and Retransmission Parameters

 This section presents a table of values used to describe the message
 transmission behavior of clients and servers.
 Parameter     Default  Description
 -------------------------------------
 SOL_MAX_DELAY     1 sec   Max delay of first Solicit
 SOL_TIMEOUT       1 sec   Initial Solicit timeout
 SOL_MAX_RT      120 secs  Max Solicit timeout value
 REQ_TIMEOUT       1 sec   Initial Request timeout
 REQ_MAX_RT       30 secs  Max Request timeout value
 REQ_MAX_RC       10       Max Request retry attempts
 CNF_MAX_DELAY     1 sec   Max delay of first Confirm
 CNF_TIMEOUT       1 sec   Initial Confirm timeout
 CNF_MAX_RT        4 secs  Max Confirm timeout
 CNF_MAX_RD       10 secs  Max Confirm duration
 REN_TIMEOUT      10 secs  Initial Renew timeout
 REN_MAX_RT      600 secs  Max Renew timeout value
 REB_TIMEOUT      10 secs  Initial Rebind timeout
 REB_MAX_RT      600 secs  Max Rebind timeout value
 INF_MAX_DELAY     1 sec   Max delay of first Information-request
 INF_TIMEOUT       1 sec   Initial Information-request timeout
 INF_MAX_RT      120 secs  Max Information-request timeout value
 REL_TIMEOUT       1 sec   Initial Release timeout
 REL_MAX_RC        5       MAX Release attempts
 DEC_TIMEOUT       1 sec   Initial Decline timeout
 DEC_MAX_RC        5       Max Decline attempts
 REC_TIMEOUT       2 secs  Initial Reconfigure timeout
 REC_MAX_RC        8       Max Reconfigure attempts
 HOP_COUNT_LIMIT  32       Max hop count in a Relay-forward message

5.6 Representation of time values and "Infinity" as a time value

 All time values for lifetimes, T1 and T2 are unsigned integers.  The
 value 0xffffffff is taken to mean "infinity" when used as a lifetime
 (as in RFC2461 [17]) or a value for T1 or T2.

6. Client/Server Message Formats

 All DHCP messages sent between clients and servers share an identical
 fixed format header and a variable format area for options.
 All values in the message header and in options are in network byte
 order.

Droms, et al. Standards Track [Page 16] RFC 3315 DHCP for IPv6 July 2003

 Options are stored serially in the options field, with no padding
 between the options.  Options are byte-aligned but are not aligned in
 any other way such as on 2 or 4 byte boundaries.
 The following diagram illustrates the format of DHCP messages sent
 between clients and servers:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    msg-type   |               transaction-id                  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .                            options                            .
    .                           (variable)                          .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    msg-type             Identifies the DHCP message type; the
                         available message types are listed in
                         section 5.3.
    transaction-id       The transaction ID for this message exchange.
    options              Options carried in this message; options are
                         described in section 22.

7. Relay Agent/Server Message Formats

 Relay agents exchange messages with servers to relay messages between
 clients and servers that are not connected to the same link.
 All values in the message header and in options are in network byte
 order.
 Options are stored serially in the options field, with no padding
 between the options.  Options are byte-aligned but are not aligned in
 any other way such as on 2 or 4 byte boundaries.

Droms, et al. Standards Track [Page 17] RFC 3315 DHCP for IPv6 July 2003

 There are two relay agent messages, which share the following format:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    msg-type   |   hop-count   |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
    |                                                               |
    |                         link-address                          |
    |                                                               |
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
    |                               |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
    |                                                               |
    |                         peer-address                          |
    |                                                               |
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
    |                               |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
    .                                                               .
    .            options (variable number and length)   ....        .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The following sections describe the use of the Relay Agent message
 header.

7.1. Relay-forward Message

 The following table defines the use of message fields in a Relay-
 forward message.
    msg-type       RELAY-FORW
    hop-count      Number of relay agents that have relayed this
                   message.
    link-address   A global or site-local address that will be used by
                   the server to identify the link on which the client
                   is located.
    peer-address   The address of the client or relay agent from which
                   the message to be relayed was received.
    options        MUST include a "Relay Message option" (see
                   section 22.10); MAY include other options added by
                   the relay agent.

Droms, et al. Standards Track [Page 18] RFC 3315 DHCP for IPv6 July 2003

7.2. Relay-reply Message

 The following table defines the use of message fields in a
 Relay-reply message.
    msg-type       RELAY-REPL
    hop-count      Copied from the Relay-forward message
    link-address   Copied from the Relay-forward message
    peer-address   Copied from the Relay-forward message
    options        MUST include a "Relay Message option"; see
                   section 22.10; MAY include other options

8. Representation and Use of Domain Names

 So that domain names may be encoded uniformly, a domain name or a
 list of domain names is encoded using the technique described in
 section 3.1 of RFC 1035 [10].  A domain name, or list of domain
 names, in DHCP MUST NOT be stored in compressed form, as described in
 section 4.1.4 of RFC 1035.

9. DHCP Unique Identifier (DUID)

 Each DHCP client and server has a DUID.  DHCP servers use DUIDs to
 identify clients for the selection of configuration parameters and in
 the association of IAs with clients.  DHCP clients use DUIDs to
 identify a server in messages where a server needs to be identified.
 See sections 22.2 and 22.3 for the representation of a DUID in a DHCP
 message.
 Clients and servers MUST treat DUIDs as opaque values and MUST only
 compare DUIDs for equality.  Clients and servers MUST NOT in any
 other way interpret DUIDs.  Clients and servers MUST NOT restrict
 DUIDs to the types defined in this document, as additional DUID types
 may be defined in the future.
 The DUID is carried in an option because it may be variable length
 and because it is not required in all DHCP messages.  The DUID is
 designed to be unique across all DHCP clients and servers, and stable
 for any specific client or server - that is, the DUID used by a
 client or server SHOULD NOT change over time if at all possible; for
 example, a device's DUID should not change as a result of a change in
 the device's network hardware.

Droms, et al. Standards Track [Page 19] RFC 3315 DHCP for IPv6 July 2003

 The motivation for having more than one type of DUID is that the DUID
 must be globally unique, and must also be easy to generate.  The sort
 of globally-unique identifier that is easy to generate for any given
 device can differ quite widely.  Also, some devices may not contain
 any persistent storage.  Retaining a generated DUID in such a device
 is not possible, so the DUID scheme must accommodate such devices.

9.1. DUID Contents

 A DUID consists of a two-octet type code represented in network byte
 order, followed by a variable number of octets that make up the
 actual identifier.  A DUID can be no more than 128 octets long (not
 including the type code).  The following types are currently defined:
    1        Link-layer address plus time
    2        Vendor-assigned unique ID based on Enterprise Number
    3        Link-layer address
 Formats for the variable field of the DUID for each of the above
 types are shown below.

9.2. DUID Based on Link-layer Address Plus Time [DUID-LLT]

 This type of DUID consists of a two octet type field containing the
 value 1, a two octet hardware type code, four octets containing a
 time value, followed by link-layer address of any one network
 interface that is connected to the DHCP device at the time that the
 DUID is generated.  The time value is the time that the DUID is
 generated represented in seconds since midnight (UTC), January 1,
 2000, modulo 2^32.  The hardware type MUST be a valid hardware type
 assigned by the IANA as described in RFC 826 [14].  Both the time and
 the hardware type are stored in network byte order.  The link-layer
 address is stored in canonical form, as described in RFC 2464 [2].
 The following diagram illustrates the format of a DUID-LLT:
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |               1               |    hardware type (16 bits)    |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        time (32 bits)                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  .                                                               .
  .             link-layer address (variable length)              .
  .                                                               .
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Droms, et al. Standards Track [Page 20] RFC 3315 DHCP for IPv6 July 2003

 The choice of network interface can be completely arbitrary, as long
 as that interface provides a globally unique link-layer address for
 the link type, and the same DUID-LLT SHOULD be used in configuring
 all network interfaces connected to the device, regardless of which
 interface's link-layer address was used to generate the DUID-LLT.
 Clients and servers using this type of DUID MUST store the DUID-LLT
 in stable storage, and MUST continue to use this DUID-LLT even if the
 network interface used to generate the DUID-LLT is removed.  Clients
 and servers that do not have any stable storage MUST NOT use this
 type of DUID.
 Clients and servers that use this DUID SHOULD attempt to configure
 the time prior to generating the DUID, if that is possible, and MUST
 use some sort of time source (for example, a real-time clock) in
 generating the DUID, even if that time source could not be configured
 prior to generating the DUID.  The use of a time source makes it
 unlikely that two identical DUID-LLTs will be generated if the
 network interface is removed from the client and another client then
 uses the same network interface to generate a DUID-LLT.  A collision
 between two DUID-LLTs is very unlikely even if the clocks have not
 been configured prior to generating the DUID.
 This method of DUID generation is recommended for all general purpose
 computing devices such as desktop computers and laptop computers, and
 also for devices such as printers, routers, and so on, that contain
 some form of writable non-volatile storage.
 Despite our best efforts, it is possible that this algorithm for
 generating a DUID could result in a client identifier collision.  A
 DHCP client that generates a DUID-LLT using this mechanism MUST
 provide an administrative interface that replaces the existing DUID
 with a newly-generated DUID-LLT.

Droms, et al. Standards Track [Page 21] RFC 3315 DHCP for IPv6 July 2003

9.3. DUID Assigned by Vendor Based on Enterprise Number [DUID-EN]

 This form of DUID is assigned by the vendor to the device.  It
 consists of the vendor's registered Private Enterprise Number as
 maintained by IANA [6] followed by a unique identifier assigned by
 the vendor.  The following diagram summarizes the structure of a
 DUID-EN:
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |               2               |       enterprise-number       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |   enterprise-number (contd)   |                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
  .                           identifier                          .
  .                       (variable length)                       .
  .                                                               .
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The source of the identifier is left up to the vendor defining it,
 but each identifier part of each DUID-EN MUST be unique to the device
 that is using it, and MUST be assigned to the device at the time it
 is manufactured and stored in some form of non-volatile storage.  The
 generated DUID SHOULD be recorded in non-erasable storage.  The
 enterprise-number is the vendor's registered Private Enterprise
 Number as maintained by IANA [6].  The enterprise-number is stored as
 an unsigned 32 bit number.
 An example DUID of this type might look like this:
  +---+---+---+---+---+---+---+---+
  | 0 | 2 | 0 | 0 | 0 |  9| 12|192|
  +---+---+---+---+---+---+---+---+
  |132|221| 3 | 0 | 9 | 18|
  +---+---+---+---+---+---+
 This example includes the two-octet type of 2, the Enterprise Number
 (9), followed by eight octets of identifier data
 (0x0CC084D303000912).

9.4. DUID Based on Link-layer Address [DUID-LL]

 This type of DUID consists of two octets containing the DUID type 3,
 a two octet network hardware type code, followed by the link-layer
 address of any one network interface that is permanently connected to
 the client or server device.  For example, a host that has a network
 interface implemented in a chip that is unlikely to be removed and

Droms, et al. Standards Track [Page 22] RFC 3315 DHCP for IPv6 July 2003

 used elsewhere could use a DUID-LL.  The hardware type MUST be a
 valid hardware type assigned by the IANA, as described in RFC 826
 [14].  The hardware type is stored in network byte order.  The
 link-layer address is stored in canonical form, as described in RFC
 2464 [2].  The following diagram illustrates the format of a DUID-LL:
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |               3               |    hardware type (16 bits)    |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  .                                                               .
  .             link-layer address (variable length)              .
  .                                                               .
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The choice of network interface can be completely arbitrary, as long
 as that interface provides a unique link-layer address and is
 permanently attached to the device on which the DUID-LL is being
 generated.  The same DUID-LL SHOULD be used in configuring all
 network interfaces connected to the device, regardless of which
 interface's link-layer address was used to generate the DUID.
 DUID-LL is recommended for devices that have a permanently-connected
 network interface with a link-layer address, and do not have
 nonvolatile, writable stable storage.  DUID-LL MUST NOT be used by
 DHCP clients or servers that cannot tell whether or not a network
 interface is permanently attached to the device on which the DHCP
 client is running.

10. Identity Association

 An "identity-association" (IA) is a construct through which a server
 and a client can identify, group, and manage a set of related IPv6
 addresses.  Each IA consists of an IAID and associated configuration
 information.
 A client must associate at least one distinct IA with each of its
 network interfaces for which it is to request the assignment of IPv6
 addresses from a DHCP server.  The client uses the IAs assigned to an
 interface to obtain configuration information from a server for that
 interface.  Each IA must be associated with exactly one interface.
 The IAID uniquely identifies the IA and must be chosen to be unique
 among the IAIDs on the client.  The IAID is chosen by the client.
 For any given use of an IA by the client, the IAID for that IA MUST
 be consistent across restarts of the DHCP client.  The client may
 maintain consistency either by storing the IAID in non-volatile

Droms, et al. Standards Track [Page 23] RFC 3315 DHCP for IPv6 July 2003

 storage or by using an algorithm that will consistently produce the
 same IAID as long as the configuration of the client has not changed.
 There may be no way for a client to maintain consistency of the IAIDs
 if it does not have non-volatile storage and the client's hardware
 configuration changes.
 The configuration information in an IA consists of one or more IPv6
 addresses along with the times T1 and T2 for the IA.  See section
 22.4 for the representation of an IA in a DHCP message.
 Each address in an IA has a preferred lifetime and a valid lifetime,
 as defined in RFC 2462 [17].  The lifetimes are transmitted from the
 DHCP server to the client in the IA option.  The lifetimes apply to
 the use of IPv6 addresses, as described in section 5.5.4 of RFC 2462.

11. Selecting Addresses for Assignment to an IA

 A server selects addresses to be assigned to an IA according to the
 address assignment policies determined by the server administrator
 and the specific information the server determines about the client
 from some combination of the following sources:
  1. The link to which the client is attached. The server determines

the link as follows:

  • If the server receives the message directly from the client and

the source address in the IP datagram in which the message was

       received is a link-local address, then the client is on the
       same link to which the interface over which the message was
       received is attached.
  • If the server receives the message from a forwarding relay

agent, then the client is on the same link as the one to which

       the interface, identified by the link-address field in the
       message from the relay agent, is attached.
  • If the server receives the message directly from the client and

the source address in the IP datagram in which the message was

       received is not a link-local address, then the client is on the
       link identified by the source address in the IP datagram (note
       that this situation can occur only if the server has enabled
       the use of unicast message delivery by the client and the
       client has sent a message for which unicast delivery is
       allowed).
  1. The DUID supplied by the client.
  1. Other information in options supplied by the client.

Droms, et al. Standards Track [Page 24] RFC 3315 DHCP for IPv6 July 2003

  1. Other information in options supplied by the relay agent.
 Any address assigned by a server that is based on an EUI-64
 identifier MUST include an interface identifier with the "u"
 (universal/local) and "g" (individual/group) bits of the interface
 identifier set appropriately, as indicated in section 2.5.1 of RFC
 2373 [5].
 A server MUST NOT assign an address that is otherwise reserved for
 some other purpose.  For example, a server MUST NOT assign reserved
 anycast addresses, as defined in RFC 2526, from any subnet.

12. Management of Temporary Addresses

 A client may request the assignment of temporary addresses (see RFC
 3041 [12] for the definition of temporary addresses).  DHCPv6
 handling of address assignment is no different for temporary
 addresses.  DHCPv6 says nothing about details of temporary addresses
 like lifetimes, how clients use temporary addresses, rules for
 generating successive temporary addresses, etc.
 Clients ask for temporary addresses and servers assign them.
 Temporary addresses are carried in the Identity Association for
 Temporary Addresses (IA_TA) option (see section 22.5).  Each IA_TA
 option contains at most one temporary address for each of the
 prefixes on the link to which the client is attached.
 The IAID number space for the IA_TA option IAID number space is
 separate from the IA_NA option IAID number space.
 The server MAY update the DNS for a temporary address, as described
 in section 4 of RFC 3041.

13. Transmission of Messages by a Client

 Unless otherwise specified in this document, or in a document that
 describes how IPv6 is carried over a specific type of link (for link
 types that do not support multicast), a client sends DHCP messages to
 the All_DHCP_Relay_Agents_and_Servers.
 A client uses multicast to reach all servers or an individual server.
 An individual server is indicated by specifying that server's DUID in
 a Server Identifier option (see section 22.3) in the client's message
 (all servers will receive this message but only the indicated server
 will respond).  All servers are indicated by not supplying this
 option.

Droms, et al. Standards Track [Page 25] RFC 3315 DHCP for IPv6 July 2003

 A client may send some messages directly to a server using unicast,
 as described in section 22.12.

14. Reliability of Client Initiated Message Exchanges

 DHCP clients are responsible for reliable delivery of messages in the
 client-initiated message exchanges described in sections 17 and 18.
 If a DHCP client fails to receive an expected response from a server,
 the client must retransmit its message.  This section describes the
 retransmission strategy to be used by clients in client-initiated
 message exchanges.
 Note that the procedure described in this section is slightly
 modified when used with the Solicit message.  The modified procedure
 is described in section 17.1.2.
 The client begins the message exchange by transmitting a message to
 the server.  The message exchange terminates when either the client
 successfully receives the appropriate response or responses from a
 server or servers, or when the message exchange is considered to have
 failed according to the retransmission mechanism described below.
 The client retransmission behavior is controlled and described by the
 following variables:
    RT     Retransmission timeout
    IRT    Initial retransmission time
    MRC    Maximum retransmission count
    MRT    Maximum retransmission time
    MRD    Maximum retransmission duration
    RAND   Randomization factor
 With each message transmission or retransmission, the client sets RT
 according to the rules given below.  If RT expires before the message
 exchange terminates, the client recomputes RT and retransmits the
 message.
 Each of the computations of a new RT include a randomization factor
 (RAND), which is a random number chosen with a uniform distribution
 between -0.1 and +0.1.  The randomization factor is included to
 minimize synchronization of messages transmitted by DHCP clients.

Droms, et al. Standards Track [Page 26] RFC 3315 DHCP for IPv6 July 2003

 The algorithm for choosing a random number does not need to be
 cryptographically sound.  The algorithm SHOULD produce a different
 sequence of random numbers from each invocation of the DHCP client.
 RT for the first message transmission is based on IRT:
    RT = IRT + RAND*IRT
 RT for each subsequent message transmission is based on the previous
 value of RT:
    RT = 2*RTprev + RAND*RTprev
 MRT specifies an upper bound on the value of RT (disregarding the
 randomization added by the use of RAND).  If MRT has a value of 0,
 there is no upper limit on the value of RT.  Otherwise:
    if (RT > MRT)
       RT = MRT + RAND*MRT
 MRC specifies an upper bound on the number of times a client may
 retransmit a message.  Unless MRC is zero, the message exchange fails
 once the client has transmitted the message MRC times.
 MRD specifies an upper bound on the length of time a client may
 retransmit a message.  Unless MRD is zero, the message exchange fails
 once MRD seconds have elapsed since the client first transmitted the
 message.
 If both MRC and MRD are non-zero, the message exchange fails whenever
 either of the conditions specified in the previous two paragraphs are
 met.
 If both MRC and MRD are zero, the client continues to transmit the
 message until it receives a response.

15. Message Validation

 Clients and servers SHOULD discard any messages that contain options
 that are not allowed to appear in the received message.  For example,
 an IA option is not allowed to appear in an Information-request
 message.  Clients and servers MAY choose to extract information from
 such a message if the information is of use to the recipient.
 A server MUST discard any Solicit, Confirm, Rebind or
 Information-request messages it receives with a unicast destination
 address.

Droms, et al. Standards Track [Page 27] RFC 3315 DHCP for IPv6 July 2003

 Message validation based on DHCP authentication is discussed in
 section 21.4.2.
 If a server receives a message that contains options it should not
 contain (such as an Information-request message with an IA option),
 is missing options that it should contain, or is otherwise not valid,
 it MAY send a Reply (or Advertise as appropriate) with a Server
 Identifier option, a Client Identifier option if one was included in
 the message and a Status Code option with status UnSpecFail.

15.1. Use of Transaction IDs

 The "transaction-id" field holds a value used by clients and servers
 to synchronize server responses to client messages.  A client SHOULD
 generate a random number that cannot easily be guessed or predicted
 to use as the transaction ID for each new message it sends.  Note
 that if a client generates easily predictable transaction
 identifiers, it may become more vulnerable to certain kinds of
 attacks from off-path intruders.  A client MUST leave the transaction
 ID unchanged in retransmissions of a message.

15.2. Solicit Message

 Clients MUST discard any received Solicit messages.
 Servers MUST discard any Solicit messages that do not include a
 Client Identifier option or that do include a Server Identifier
 option.

15.3. Advertise Message

 Clients MUST discard any received Advertise messages that meet any of
 the following conditions:
  1. the message does not include a Server Identifier option.
  1. the message does not include a Client Identifier option.
  1. the contents of the Client Identifier option does not match the

client's DUID.

  1. the "transaction-id" field value does not match the value the

client used in its Solicit message.

 Servers and relay agents MUST discard any received Advertise
 messages.

Droms, et al. Standards Track [Page 28] RFC 3315 DHCP for IPv6 July 2003

15.4. Request Message

 Clients MUST discard any received Request messages.
 Servers MUST discard any received Request message that meet any of
 the following conditions:
  1. the message does not include a Server Identifier option.
  1. the contents of the Server Identifier option do not match the

server's DUID.

  1. the message does not include a Client Identifier option.

15.5. Confirm Message

 Clients MUST discard any received Confirm messages.
 Servers MUST discard any received Confirm messages that do not
 include a Client Identifier option or that do include a Server
 Identifier option.

15.6. Renew Message

 Clients MUST discard any received Renew messages.
 Servers MUST discard any received Renew message that meets any of the
 following conditions:
  1. the message does not include a Server Identifier option.
  1. the contents of the Server Identifier option does not match the

server's identifier.

  1. the message does not include a Client Identifier option.

15.7. Rebind Message

 Clients MUST discard any received Rebind messages.
 Servers MUST discard any received Rebind messages that do not include
 a Client Identifier option or that do include a Server Identifier
 option.

Droms, et al. Standards Track [Page 29] RFC 3315 DHCP for IPv6 July 2003

15.8. Decline Messages

 Clients MUST discard any received Decline messages.
 Servers MUST discard any received Decline message that meets any of
 the following conditions:
  1. the message does not include a Server Identifier option.
  1. the contents of the Server Identifier option does not match the

server's identifier.

  1. the message does not include a Client Identifier option.

15.9. Release Message

 Clients MUST discard any received Release messages.
 Servers MUST discard any received Release message that meets any of
 the following conditions:
  1. the message does not include a Server Identifier option.
  1. the contents of the Server Identifier option does not match the

server's identifier.

  1. the message does not include a Client Identifier option.

15.10. Reply Message

 Clients MUST discard any received Reply message that meets any of the
 following conditions:
  1. the message does not include a Server Identifier option.
  1. the "transaction-id" field in the message does not match the value

used in the original message.

 If the client included a Client Identifier option in the original
 message, the Reply message MUST include a Client Identifier option
 and the contents of the Client Identifier option MUST match the DUID
 of the client; OR, if the client did not include a Client Identifier
 option in the original message, the Reply message MUST NOT include a
 Client Identifier option.
 Servers and relay agents MUST discard any received Reply messages.

Droms, et al. Standards Track [Page 30] RFC 3315 DHCP for IPv6 July 2003

15.11. Reconfigure Message

 Servers and relay agents MUST discard any received Reconfigure
 messages.
 Clients MUST discard any Reconfigure messages that meets any of the
 following conditions:
  1. the message was not unicast to the client.
  1. the message does not include a Server Identifier option.
  1. the message does not include a Client Identifier option that

contains the client's DUID.

  1. the message does not contain a Reconfigure Message option and the

msg-type must be a valid value.

  1. the message includes any IA options and the msg-type in the

Reconfigure Message option is INFORMATION-REQUEST.

  1. the message does not include DHCP authentication:
  • the message does not contain an authentication option.
  • the message does not pass the authentication validation

performed by the client.

15.12. Information-request Message

 Clients MUST discard any received Information-request messages.
 Servers MUST discard any received Information-request message that
 meets any of the following conditions:
  1. The message includes a Server Identifier option and the DUID in

the option does not match the server's DUID.

  1. The message includes an IA option.

15.13. Relay-forward Message

 Clients MUST discard any received Relay-forward messages.

15.14. Relay-reply Message

 Clients and servers MUST discard any received Relay-reply messages.

Droms, et al. Standards Track [Page 31] RFC 3315 DHCP for IPv6 July 2003

16. Client Source Address and Interface Selection

 When a client sends a DHCP message to the
 All_DHCP_Relay_Agents_and_Servers address, it SHOULD send the message
 through the interface for which configuration information is being
 requested.  However, the client MAY send the message through another
 interface attached to the same link, if and only if the client is
 certain the two interfaces are attached to the same link.  The client
 MUST use a link-local address assigned to the interface for which it
 is requesting configuration information as the source address in the
 header of the IP datagram.
 When a client sends a DHCP message directly to a server using unicast
 (after receiving the Server Unicast option from that server), the
 source address in the header of the IP datagram MUST be an address
 assigned to the interface for which the client is interested in
 obtaining configuration and which is suitable for use by the server
 in responding to the client.

17. DHCP Server Solicitation

 This section describes how a client locates servers that will assign
 addresses to IAs belonging to the client.
 The client is responsible for creating IAs and requesting that a
 server assign IPv6 addresses to the IA.  The client first creates an
 IA and assigns it an IAID.  The client then transmits a Solicit
 message containing an IA option describing the IA.  Servers that can
 assign addresses to the IA respond to the client with an Advertise
 message.  The client then initiates a configuration exchange as
 described in section 18.
 If the client will accept a Reply message with committed address
 assignments and other resources in response to the Solicit message,
 the client includes a Rapid Commit option (see section 22.14) in the
 Solicit message.

17.1. Client Behavior

 A client uses the Solicit message to discover DHCP servers configured
 to assign addresses or return other configuration parameters on the
 link to which the client is attached.

17.1.1. Creation of Solicit Messages

 The client sets the "msg-type" field to SOLICIT.  The client
 generates a transaction ID and inserts this value in the
 "transaction-id" field.

Droms, et al. Standards Track [Page 32] RFC 3315 DHCP for IPv6 July 2003

 The client MUST include a Client Identifier option to identify itself
 to the server.  The client includes IA options for any IAs to which
 it wants the server to assign addresses.  The client MAY include
 addresses in the IAs as a hint to the server about addresses for
 which the client has a preference.  The client MUST NOT include any
 other options in the Solicit message, except as specifically allowed
 in the definition of individual options.
 The client uses IA_NA options to request the assignment of non-
 temporary addresses and uses IA_TA options to request the assignment
 of temporary addresses.  Either IA_NA or IA_TA options, or a
 combination of both, can be included in DHCP messages.
 The client SHOULD include an Option Request option (see section 22.7)
 to indicate the options the client is interested in receiving.  The
 client MAY additionally include instances of those options that are
 identified in the Option Request option, with data values as hints to
 the server about parameter values the client would like to have
 returned.
 The client includes a Reconfigure Accept option (see section 22.20)
 if the client is willing to accept Reconfigure messages from the
 server.

17.1.2. Transmission of Solicit Messages

 The first Solicit message from the client on the interface MUST be
 delayed by a random amount of time between 0 and SOL_MAX_DELAY.  In
 the case of a Solicit message transmitted when DHCP is initiated by
 IPv6 Neighbor Discovery, the delay gives the amount of time to wait
 after IPv6 Neighbor Discovery causes the client to invoke the
 stateful address autoconfiguration protocol (see section 5.5.3 of RFC
 2462).  This random delay desynchronizes clients which start at the
 same time (for example, after a power outage).
 The client transmits the message according to section 14, using the
 following parameters:
    IRT   SOL_TIMEOUT
    MRT   SOL_MAX_RT
    MRC   0
    MRD   0

Droms, et al. Standards Track [Page 33] RFC 3315 DHCP for IPv6 July 2003

 If the client has included a Rapid Commit option in its Solicit
 message, the client terminates the waiting process as soon as a Reply
 message with a Rapid Commit option is received.
 If the client is waiting for an Advertise message, the mechanism in
 section 14 is modified as follows for use in the transmission of
 Solicit messages.  The message exchange is not terminated by the
 receipt of an Advertise before the first RT has elapsed.  Rather, the
 client collects Advertise messages until the first RT has elapsed.
 Also, the first RT MUST be selected to be strictly greater than IRT
 by choosing RAND to be strictly greater than 0.
 A client MUST collect Advertise messages for the first RT seconds,
 unless it receives an Advertise message with a preference value of
 255.  The preference value is carried in the Preference option
 (section 22.8).  Any Advertise that does not include a Preference
 option is considered to have a preference value of 0.  If the client
 receives an Advertise message that includes a Preference option with
 a preference value of 255, the client immediately begins a client-
 initiated message exchange (as described in section 18) by sending a
 Request message to the server from which the Advertise message was
 received.  If the client receives an Advertise message that does not
 include a Preference option with a preference value of 255, the
 client continues to wait until the first RT elapses.  If the first RT
 elapses and the client has received an Advertise message, the client
 SHOULD continue with a client-initiated message exchange by sending a
 Request message.
 If the client does not receive any Advertise messages before the
 first RT has elapsed, it begins the retransmission mechanism
 described in section 14.  The client terminates the retransmission
 process as soon as it receives any Advertise message, and the client
 acts on the received Advertise message without waiting for any
 additional Advertise messages.
 A DHCP client SHOULD choose MRC and MRD to be 0.  If the DHCP client
 is configured with either MRC or MRD set to a value other than 0, it
 MUST stop trying to configure the interface if the message exchange
 fails.  After the DHCP client stops trying to configure the
 interface, it SHOULD restart the reconfiguration process after some
 external event, such as user input, system restart, or when the
 client is attached to a new link.

Droms, et al. Standards Track [Page 34] RFC 3315 DHCP for IPv6 July 2003

17.1.3. Receipt of Advertise Messages

 The client MUST ignore any Advertise message that includes a Status
 Code option containing the value NoAddrsAvail, with the exception
 that the client MAY display the associated status message to the
 user.
 Upon receipt of one or more valid Advertise messages, the client
 selects one or more Advertise messages based upon the following
 criteria.
  1. Those Advertise messages with the highest server preference value

are preferred over all other Advertise messages.

  1. Within a group of Advertise messages with the same server

preference value, a client MAY select those servers whose

    Advertise messages advertise information of interest to the
    client.  For example, the client may choose a server that returned
    an advertisement with configuration options of interest to the
    client.
  1. The client MAY choose a less-preferred server if that server has a

better set of advertised parameters, such as the available

    addresses advertised in IAs.
 Once a client has selected Advertise message(s), the client will
 typically store information about each server, such as server
 preference value, addresses advertised, when the advertisement was
 received, and so on.
 If the client needs to select an alternate server in the case that a
 chosen server does not respond, the client chooses the next server
 according to the criteria given above.

17.1.4. Receipt of Reply Message

 If the client includes a Rapid Commit option in the Solicit message,
 it will expect a Reply message that includes a Rapid Commit option in
 response.  The client discards any Reply messages it receives that do
 not include a Rapid Commit option.  If the client receives a valid
 Reply message that includes a Rapid Commit option, it processes the
 message as described in section 18.1.8.  If it does not receive such
 a Reply message and does receive a valid Advertise message, the
 client processes the Advertise message as described in section
 17.1.3.

Droms, et al. Standards Track [Page 35] RFC 3315 DHCP for IPv6 July 2003

 If the client subsequently receives a valid Reply message that
 includes a Rapid Commit option, it either:
    processes the Reply message as described in section 18.1.8, and
    discards any Reply messages received in response to the Request
    message, or
    processes any Reply messages received in response to the Request
    message and discards the Reply message that includes the Rapid
    Commit option.

17.2. Server Behavior

 A server sends an Advertise message in response to valid Solicit
 messages it receives to announce the availability of the server to
 the client.

17.2.1. Receipt of Solicit Messages

 The server determines the information about the client and its
 location as described in section 11 and checks its administrative
 policy about responding to the client.  If the server is not
 permitted to respond to the client, the server discards the Solicit
 message.  For example, if the administrative policy for the server is
 that it may only respond to a client that is willing to accept a
 Reconfigure message, if the client indicates with a Reconfigure
 Accept option in the Solicit message that it will not accept a
 Reconfigure message, the servers discard the Solicit message.
 If the client has included a Rapid Commit option in the Solicit
 message and the server has been configured to respond with committed
 address assignments and other resources, the server responds to the
 Solicit with a Reply message as described in section 17.2.3.
 Otherwise, the server ignores the Rapid Commit option and processes
 the remainder of the message as if no Rapid Commit option were
 present.

17.2.2. Creation and Transmission of Advertise Messages

 The server sets the "msg-type" field to ADVERTISE and copies the
 contents of the transaction-id field from the Solicit message
 received from the client to the Advertise message.  The server
 includes its server identifier in a Server Identifier option and
 copies the Client Identifier from the Solicit message into the
 Advertise message.

Droms, et al. Standards Track [Page 36] RFC 3315 DHCP for IPv6 July 2003

 The server MAY add a Preference option to carry the preference value
 for the Advertise message.  The server implementation SHOULD allow
 the setting of a server preference value by the administrator.  The
 server preference value MUST default to zero unless otherwise
 configured by the server administrator.
 The server includes a Reconfigure Accept option if the server wants
 to require that the client accept Reconfigure messages.
 The server includes options the server will return to the client in a
 subsequent Reply message.  The information in these options may be
 used by the client in the selection of a server if the client
 receives more than one Advertise message.  If the client has included
 an Option Request option in the Solicit message, the server includes
 options in the Advertise message containing configuration parameters
 for all of the options identified in the Option Request option that
 the server has been configured to return to the client.  The server
 MAY return additional options to the client if it has been configured
 to do so.  The server must be aware of the recommendations on packet
 sizes and the use of fragmentation in section 5 of RFC 2460.
 If the Solicit message from the client included one or more IA
 options, the server MUST include IA options in the Advertise message
 containing any addresses that would be assigned to IAs contained in
 the Solicit message from the client.  If the client has included
 addresses in the IAs in the Solicit message, the server uses those
 addresses as hints about the addresses the client would like to
 receive.
 If the server will not assign any addresses to any IAs in a
 subsequent Request from the client, the server MUST send an Advertise
 message to the client that includes only a Status Code option with
 code NoAddrsAvail and a status message for the user, a Server
 Identifier option with the server's DUID, and a Client Identifier
 option with the client's DUID.
 If the Solicit message was received directly by the server, the
 server unicasts the Advertise message directly to the client using
 the address in the source address field from the IP datagram in which
 the Solicit message was received.  The Advertise message MUST be
 unicast on the link from which the Solicit message was received.
 If the Solicit message was received in a Relay-forward message, the
 server constructs a Relay-reply message with the Advertise message in
 the payload of a "relay-message" option.  If the Relay-forward
 messages included an Interface-id option, the server copies that
 option to the Relay-reply message.  The server unicasts the
 Relay-reply message directly to the relay agent using the address in

Droms, et al. Standards Track [Page 37] RFC 3315 DHCP for IPv6 July 2003

 the source address field from the IP datagram in which the Relay-
 forward message was received.

17.2.3. Creation and Transmission of Reply Messages

 The server MUST commit the assignment of any addresses or other
 configuration information message before sending a Reply message to a
 client in response to a Solicit message.
 DISCUSSION:
    When using the Solicit-Reply message exchange, the server commits
    the assignment of any addresses before sending the Reply message.
    The client can assume it has been assigned the addresses in the
    Reply message and does not need to send a Request message for
    those addresses.
    Typically, servers that are configured to use the Solicit-Reply
    message exchange will be deployed so that only one server will
    respond to a Solicit message.  If more than one server responds,
    the client will only use the addresses from one of the servers,
    while the addresses from the other servers will be committed to
    the client but not used by the client.
 The server includes a Rapid Commit option in the Reply message to
 indicate that the Reply is in response to a Solicit message.
 The server includes a Reconfigure Accept option if the server wants
 to require that the client accept Reconfigure messages.
 The server produces the Reply message as though it had received a
 Request message, as described in section 18.2.1.  The server
 transmits the Reply message as described in section 18.2.8.

18. DHCP Client-Initiated Configuration Exchange

 A client initiates a message exchange with a server or servers to
 acquire or update configuration information of interest.  The client
 may initiate the configuration exchange as part of the operating
 system configuration process, when requested to do so by the
 application layer, when required by Stateless Address
 Autoconfiguration or as required to extend the lifetime of an address
 (Renew and Rebind messages).

Droms, et al. Standards Track [Page 38] RFC 3315 DHCP for IPv6 July 2003

18.1. Client Behavior

 A client uses Request, Renew, Rebind, Release and Decline messages
 during the normal life cycle of addresses.  It uses Confirm to
 validate addresses when it may have moved to a new link.  It uses
 Information-Request messages when it needs configuration information
 but no addresses.
 If the client has a source address of sufficient scope that can be
 used by the server as a return address, and the client has received a
 Server Unicast option (section 22.12) from the server, the client
 SHOULD unicast any Request, Renew, Release and Decline messages to
 the server.
 DISCUSSION:
    Use of unicast may avoid delays due to the relaying of messages by
    relay agents, as well as avoid overhead and duplicate responses by
    servers due to the delivery of client messages to multiple
    servers.  Requiring the client to relay all DHCP messages through
    a relay agent enables the inclusion of relay agent options in all
    messages sent by the client.  The server should enable the use of
    unicast only when relay agent options will not be used.

18.1.1. Creation and Transmission of Request Messages

 The client uses a Request message to populate IAs with addresses and
 obtain other configuration information.  The client includes one or
 more IA options in the Request message.  The server then returns
 addresses and other information about the IAs to the client in IA
 options in a Reply message.
 The client generates a transaction ID and inserts this value in the
 "transaction-id" field.
 The client places the identifier of the destination server in a
 Server Identifier option.
 The client MUST include a Client Identifier option to identify itself
 to the server.  The client adds any other appropriate options,
 including one or more IA options (if the client is requesting that
 the server assign it some network addresses).
 The client MUST include an Option Request option (see section 22.7)
 to indicate the options the client is interested in receiving.  The
 client MAY include options with data values as hints to the server
 about parameter values the client would like to have returned.

Droms, et al. Standards Track [Page 39] RFC 3315 DHCP for IPv6 July 2003

 The client includes a Reconfigure Accept option (see section 22.20)
 indicating whether or not the client is willing to accept Reconfigure
 messages from the server.
 The client transmits the message according to section 14, using the
 following parameters:
    IRT   REQ_TIMEOUT
    MRT   REQ_MAX_RT
    MRC   REQ_MAX_RC
    MRD   0
 If the message exchange fails, the client takes an action based on
 the client's local policy.  Examples of actions the client might take
 include:
  1. Select another server from a list of servers known to the client;

for example, servers that responded with an Advertise message.

  1. Initiate the server discovery process described in section 17.
  1. Terminate the configuration process and report failure.

18.1.2. Creation and Transmission of Confirm Messages

 Whenever a client may have moved to a new link, the prefixes from the
 addresses assigned to the interfaces on that link may no longer be
 appropriate for the link to which the client is attached.  Examples
 of times when a client may have moved to a new link include:
 o  The client reboots.
 o  The client is physically connected to a wired connection.
 o  The client returns from sleep mode.
 o  The client using a wireless technology changes access points.
 In any situation when a client may have moved to a new link, the
 client MUST initiate a Confirm/Reply message exchange.  The client
 includes any IAs assigned to the interface that may have moved to a
 new link, along with the addresses associated with those IAs, in its

Droms, et al. Standards Track [Page 40] RFC 3315 DHCP for IPv6 July 2003

 Confirm message.  Any responding servers will indicate whether those
 addresses are appropriate for the link to which the client is
 attached with the status in the Reply message it returns to the
 client.
 The client sets the "msg-type" field to CONFIRM.  The client
 generates a transaction ID and inserts this value in the
 "transaction-id" field.
 The client MUST include a Client Identifier option to identify itself
 to the server.  The client includes IA options for all of the IAs
 assigned to the interface for which the Confirm message is being
 sent.  The IA options include all of the addresses the client
 currently has associated with those IAs.  The client SHOULD set the
 T1 and T2 fields in any IA_NA options, and the preferred-lifetime and
 valid-lifetime fields in the IA Address options to 0, as the server
 will ignore these fields.
 The first Confirm message from the client on the interface MUST be
 delayed by a random amount of time between 0 and CNF_MAX_DELAY.  The
 client transmits the message according to section 14, using the
 following parameters:
    IRT   CNF_TIMEOUT
    MRT   CNF_MAX_RT
    MRC   0
    MRD   CNF_MAX_RD
 If the client receives no responses before the message transmission
 process terminates, as described in section 14, the client SHOULD
 continue to use any IP addresses, using the last known lifetimes for
 those addresses, and SHOULD continue to use any other previously
 obtained configuration parameters.

18.1.3. Creation and Transmission of Renew Messages

 To extend the valid and preferred lifetimes for the addresses
 associated with an IA, the client sends a Renew message to the server
 from which the client obtained the addresses in the IA containing an
 IA option for the IA.  The client includes IA Address options in the
 IA option for the addresses associated with the IA.  The server
 determines new lifetimes for the addresses in the IA according to the
 administrative configuration of the server.  The server may also add

Droms, et al. Standards Track [Page 41] RFC 3315 DHCP for IPv6 July 2003

 new addresses to the IA.  The server may remove addresses from the IA
 by setting the preferred and valid lifetimes of those addresses to
 zero.
 The server controls the time at which the client contacts the server
 to extend the lifetimes on assigned addresses through the T1 and T2
 parameters assigned to an IA.
 At time T1 for an IA, the client initiates a Renew/Reply message
 exchange to extend the lifetimes on any addresses in the IA.  The
 client includes an IA option with all addresses currently assigned to
 the IA in its Renew message.
 If T1 or T2 is set to 0 by the server (for an IA_NA) or there are no
 T1 or T2 times (for an IA_TA), the client may send a Renew or Rebind
 message, respectively, at the client's discretion.
 The client sets the "msg-type" field to RENEW.  The client generates
 a transaction ID and inserts this value in the "transaction-id"
 field.
 The client places the identifier of the destination server in a
 Server Identifier option.
 The client MUST include a Client Identifier option to identify itself
 to the server.  The client adds any appropriate options, including
 one or more IA options.  The client MUST include the list of
 addresses the client currently has associated with the IAs in the
 Renew message.
 The client MUST include an Option Request option (see section 22.7)
 to indicate the options the client is interested in receiving.  The
 client MAY include options with data values as hints to the server
 about parameter values the client would like to have returned.
 The client transmits the message according to section 14, using the
 following parameters:
    IRT   REN_TIMEOUT
    MRT   REN_MAX_RT
    MRC   0
    MRD   Remaining time until T2

Droms, et al. Standards Track [Page 42] RFC 3315 DHCP for IPv6 July 2003

 The message exchange is terminated when time T2 is reached (see
 section 18.1.4), at which time the client begins a Rebind message
 exchange.

18.1.4. Creation and Transmission of Rebind Messages

 At time T2 for an IA (which will only be reached if the server to
 which the Renew message was sent at time T1 has not responded), the
 client initiates a Rebind/Reply message exchange with any available
 server.  The client includes an IA option with all addresses
 currently assigned to the IA in its Rebind message.
 The client sets the "msg-type" field to REBIND.  The client generates
 a transaction ID and inserts this value in the "transaction-id"
 field.
 The client MUST include a Client Identifier option to identify itself
 to the server.  The client adds any appropriate options, including
 one or more IA options.  The client MUST include the list of
 addresses the client currently has associated with the IAs in the
 Rebind message.
 The client MUST include an Option Request option (see section 22.7)
 to indicate the options the client is interested in receiving.  The
 client MAY include options with data values as hints to the server
 about parameter values the client would like to have returned.
 The client transmits the message according to section 14, using the
 following parameters:
    IRT   REB_TIMEOUT
    MRT   REB_MAX_RT
    MRC   0
    MRD   Remaining time until valid lifetimes of all addresses have
          expired
 The message exchange is terminated when the valid lifetimes of all
 the addresses assigned to the IA expire (see section 10), at which
 time the client has several alternative actions to choose from; for
 example:
  1. The client may choose to use a Solicit message to locate a new

DHCP server and send a Request for the expired IA to the new

    server.

Droms, et al. Standards Track [Page 43] RFC 3315 DHCP for IPv6 July 2003

  1. The client may have other addresses in other IAs, so the client

may choose to discard the expired IA and use the addresses in the

    other IAs.

18.1.5. Creation and Transmission of Information-request Messages

 The client uses an Information-request message to obtain
 configuration information without having addresses assigned to it.
 The client sets the "msg-type" field to INFORMATION-REQUEST.  The
 client generates a transaction ID and inserts this value in the
 "transaction-id" field.
 The client SHOULD include a Client Identifier option to identify
 itself to the server.  If the client does not include a Client
 Identifier option, the server will not be able to return any client-
 specific options to the client, or the server may choose not to
 respond to the message at all.  The client MUST include a Client
 Identifier option if the Information-Request message will be
 authenticated.
 The client MUST include an Option Request option (see section 22.7)
 to indicate the options the client is interested in receiving.  The
 client MAY include options with data values as hints to the server
 about parameter values the client would like to have returned.
 The first Information-request message from the client on the
 interface MUST be delayed by a random amount of time between 0 and
 INF_MAX_DELAY.  The client transmits the message according to section
 14, using the following parameters:
    IRT   INF_TIMEOUT
    MRT   INF_MAX_RT
    MRC   0
    MRD   0

18.1.6. Creation and Transmission of Release Messages

 To release one or more addresses, a client sends a Release message to
 the server.
 The client sets the "msg-type" field to RELEASE.  The client
 generates a transaction ID and places this value in the
 "transaction-id" field.

Droms, et al. Standards Track [Page 44] RFC 3315 DHCP for IPv6 July 2003

 The client places the identifier of the server that allocated the
 address(es) in a Server Identifier option.
 The client MUST include a Client Identifier option to identify itself
 to the server.  The client includes options containing the IAs for
 the addresses it is releasing in the "options" field.  The addresses
 to be released MUST be included in the IAs.  Any addresses for the
 IAs the client wishes to continue to use MUST NOT be added to the
 IAs.
 The client MUST NOT use any of the addresses it is releasing as the
 source address in the Release message or in any subsequently
 transmitted message.
 Because Release messages may be lost, the client should retransmit
 the Release if no Reply is received.  However, there are scenarios
 where the client may not wish to wait for the normal retransmission
 timeout before giving up (e.g., on power down).  Implementations
 SHOULD retransmit one or more times, but MAY choose to terminate the
 retransmission procedure early.
 The client transmits the message according to section 14, using the
 following parameters:
    IRT   REL_TIMEOUT
    MRT   0
    MRC   REL_MAX_RC
    MRD   0
 The client MUST stop using all of the addresses being released as
 soon as the client begins the Release message exchange process.  If
 addresses are released but the Reply from a DHCP server is lost, the
 client will retransmit the Release message, and the server may
 respond with a Reply indicating a status of NoBinding.  Therefore,
 the client does not treat a Reply message with a status of NoBinding
 in a Release message exchange as if it indicates an error.
 Note that if the client fails to release the addresses, each address
 assigned to the IA will be reclaimed by the server when the valid
 lifetime of that address expires.

Droms, et al. Standards Track [Page 45] RFC 3315 DHCP for IPv6 July 2003

18.1.7. Creation and Transmission of Decline Messages

 If a client detects that one or more addresses assigned to it by a
 server are already in use by another node, the client sends a Decline
 message to the server to inform it that the address is suspect.
 The client sets the "msg-type" field to DECLINE.  The client
 generates a transaction ID and places this value in the
 "transaction-id" field.
 The client places the identifier of the server that allocated the
 address(es) in a Server Identifier option.
 The client MUST include a Client Identifier option to identify itself
 to the server.  The client includes options containing the IAs for
 the addresses it is declining in the "options" field.  The addresses
 to be declined MUST be included in the IAs.  Any addresses for the
 IAs the client wishes to continue to use should not be in added to
 the IAs.
 The client MUST NOT use any of the addresses it is declining as the
 source address in the Decline message or in any subsequently
 transmitted message.
 The client transmits the message according to section 14, using the
 following parameters:
    IRT   DEC_TIMEOUT
    MRT   0
    MRC   DEC_MAX_RC
    MRD   0
 If addresses are declined but the Reply from a DHCP server is lost,
 the client will retransmit the Decline message, and the server may
 respond with a Reply indicating a status of NoBinding.  Therefore,
 the client does not treat a Reply message with a status of NoBinding
 in a Decline message exchange as if it indicates an error.

18.1.8. Receipt of Reply Messages

 Upon the receipt of a valid Reply message in response to a Solicit
 (with a Rapid Commit option), Request, Confirm, Renew, Rebind or
 Information-request message, the client extracts the configuration

Droms, et al. Standards Track [Page 46] RFC 3315 DHCP for IPv6 July 2003

 information contained in the Reply.  The client MAY choose to report
 any status code or message from the status code option in the Reply
 message.
 The client SHOULD perform duplicate address detection [17] on each of
 the addresses in any IAs it receives in the Reply message before
 using that address for traffic.  If any of the addresses are found to
 be in use on the link, the client sends a Decline message to the
 server as described in section 18.1.7.
 If the Reply was received in response to a Solicit (with a Rapid
 Commit option), Request, Renew or Rebind message, the client updates
 the information it has recorded about IAs from the IA options
 contained in the Reply message:
  1. Record T1 and T2 times.
  1. Add any new addresses in the IA option to the IA as recorded by

the client.

  1. Update lifetimes for any addresses in the IA option that the

client already has recorded in the IA.

  1. Discard any addresses from the IA, as recorded by the client, that

have a valid lifetime of 0 in the IA Address option.

  1. Leave unchanged any information about addresses the client has

recorded in the IA but that were not included in the IA from the

    server.
 Management of the specific configuration information is detailed in
 the definition of each option in section 22.
 If the client receives a Reply message with a Status Code containing
 UnspecFail, the server is indicating that it was unable to process
 the message due to an unspecified failure condition.  If the client
 retransmits the original message to the same server to retry the
 desired operation, the client MUST limit the rate at which it
 retransmits the message and limit the duration of the time during
 which it retransmits the message.
 When the client receives a Reply message with a Status Code option
 with the value UseMulticast, the client records the receipt of the
 message and sends subsequent messages to the server through the
 interface on which the message was received using multicast.  The
 client resends the original message using multicast.

Droms, et al. Standards Track [Page 47] RFC 3315 DHCP for IPv6 July 2003

 When the client receives a NotOnLink status from the server in
 response to a Confirm message, the client performs DHCP server
 solicitation, as described in section 17, and client-initiated
 configuration as described in section 18.  If the client receives any
 Reply messages that do not indicate a NotOnLink status, the client
 can use the addresses in the IA and ignore any messages that indicate
 a NotOnLink status.
 When the client receives a NotOnLink status from the server in
 response to a Request, the client can either re-issue the Request
 without specifying any addresses or restart the DHCP server discovery
 process (see section 17).
 The client examines the status code in each IA individually.  If the
 status code is NoAddrsAvail, the client has received no usable
 addresses in the IA and may choose to try obtaining addresses for the
 IA from another server.  The client uses addresses and other
 information from any IAs that do not contain a Status Code option
 with the NoAddrsAvail code.  If the client receives no addresses in
 any of the IAs, it may either try another server (perhaps restarting
 the DHCP server discovery process) or use the Information-request
 message to obtain other configuration information only.
 When the client receives a Reply message in response to a Renew or
 Rebind message, the client examines each IA independently.  For each
 IA in the original Renew or Rebind message, the client:
  1. sends a Request message if the IA contained a Status Code option

with the NoBinding status (and does not send any additional

    Renew/Rebind messages)
  1. sends a Renew/Rebind if the IA is not in the Reply message
  1. otherwise accepts the information in the IA
 When the client receives a valid Reply message in response to a
 Release message, the client considers the Release event completed,
 regardless of the Status Code option(s) returned by the server.
 When the client receives a valid Reply message in response to a
 Decline message, the client considers the Decline event completed,
 regardless of the Status Code option(s) returned by the server.

18.2. Server Behavior

 For this discussion, the Server is assumed to have been configured in
 an implementation specific manner with configuration of interest to
 clients.

Droms, et al. Standards Track [Page 48] RFC 3315 DHCP for IPv6 July 2003

 In most instances, the server will send a Reply in response to a
 client message.  This Reply message MUST always contain the Server
 Identifier option containing the server's DUID and the Client
 Identifier option from the client message if one was present.
 In most Reply messages, the server includes options containing
 configuration information for the client.  The server must be aware
 of the recommendations on packet sizes and the use of fragmentation
 in section 5 of RFC 2460.  If the client included an Option Request
 option in its message, the server includes options in the Reply
 message containing configuration parameters for all of the options
 identified in the Option Request option that the server has been
 configured to return to the client.  The server MAY return additional
 options to the client if it has been configured to do so.

18.2.1. Receipt of Request Messages

 When the server receives a Request message via unicast from a client
 to which the server has not sent a unicast option, the server
 discards the Request message and responds with a Reply message
 containing a Status Code option with the value UseMulticast, a Server
 Identifier option containing the server's DUID, the Client Identifier
 option from the client message, and no other options.
 When the server receives a valid Request message, the server creates
 the bindings for that client according to the server's policy and
 configuration information and records the IAs and other information
 requested by the client.
 The server constructs a Reply message by setting the "msg-type" field
 to REPLY, and copying the transaction ID from the Request message
 into the transaction-id field.
 The server MUST include a Server Identifier option containing the
 server's DUID and the Client Identifier option from the Request
 message in the Reply message.
 If the server finds that the prefix on one or more IP addresses in
 any IA in the message from the client is not appropriate for the link
 to which the client is connected, the server MUST return the IA to
 the client with a Status Code option with the value NotOnLink.
 If the server cannot assign any addresses to an IA in the message
 from the client, the server MUST include the IA in the Reply message
 with no addresses in the IA and a Status Code option in the IA
 containing status code NoAddrsAvail.

Droms, et al. Standards Track [Page 49] RFC 3315 DHCP for IPv6 July 2003

 For any IAs to which the server can assign addresses, the server
 includes the IA with addresses and other configuration parameters,
 and records the IA as a new client binding.
 The server includes a Reconfigure Accept option if the server wants
 to require that the client accept Reconfigure messages.
 The server includes other options containing configuration
 information to be returned to the client as described in section
 18.2.
 If the server finds that the client has included an IA in the Request
 message for which the server already has a binding that associates
 the IA with the client, the client has resent a Request message for
 which it did not receive a Reply message.  The server either resends
 a previously cached Reply message or sends a new Reply message.

18.2.2. Receipt of Confirm Messages

 When the server receives a Confirm message, the server determines
 whether the addresses in the Confirm message are appropriate for the
 link to which the client is attached.  If all of the addresses in the
 Confirm message pass this test, the server returns a status of
 Success.  If any of the addresses do not pass this test, the server
 returns a status of NotOnLink.  If the server is unable to perform
 this test (for example, the server does not have information about
 prefixes on the link to which the client is connected), or there were
 no addresses in any of the IAs sent by the client, the server MUST
 NOT send a reply to the client.
 The server ignores the T1 and T2 fields in the IA options and the
 preferred-lifetime and valid-lifetime fields in the IA Address
 options.
 The server constructs a Reply message by setting the "msg-type" field
 to REPLY, and copying the transaction ID from the Confirm message
 into the transaction-id field.
 The server MUST include a Server Identifier option containing the
 server's DUID and the Client Identifier option from the Confirm
 message in the Reply message.  The server includes a Status Code
 option indicating the status of the Confirm message.

Droms, et al. Standards Track [Page 50] RFC 3315 DHCP for IPv6 July 2003

18.2.3. Receipt of Renew Messages

 When the server receives a Renew message via unicast from a client to
 which the server has not sent a unicast option, the server discards
 the Renew message and responds with a Reply message containing a
 Status Code option with the value UseMulticast, a Server Identifier
 option containing the server's DUID, the Client Identifier option
 from the client message, and no other options.
 When the server receives a Renew message that contains an IA option
 from a client, it locates the client's binding and verifies that the
 information in the IA from the client matches the information stored
 for that client.
 If the server cannot find a client entry for the IA the server
 returns the IA containing no addresses with a Status Code option set
 to NoBinding in the Reply message.
 If the server finds that any of the addresses are not appropriate for
 the link to which the client is attached, the server returns the
 address to the client with lifetimes of 0.
 If the server finds the addresses in the IA for the client then the
 server sends back the IA to the client with new lifetimes and T1/T2
 times.  The server may choose to change the list of addresses and the
 lifetimes of addresses in IAs that are returned to the client.
 The server constructs a Reply message by setting the "msg-type" field
 to REPLY, and copying the transaction ID from the Renew message into
 the transaction-id field.
 The server MUST include a Server Identifier option containing the
 server's DUID and the Client Identifier option from the Renew message
 in the Reply message.
 The server includes other options containing configuration
 information to be returned to the client as described in section
 18.2.

18.2.4. Receipt of Rebind Messages

 When the server receives a Rebind message that contains an IA option
 from a client, it locates the client's binding and verifies that the
 information in the IA from the client matches the information stored
 for that client.

Droms, et al. Standards Track [Page 51] RFC 3315 DHCP for IPv6 July 2003

 If the server cannot find a client entry for the IA and the server
 determines that the addresses in the IA are not appropriate for the
 link to which the client's interface is attached according to the
 server's explicit configuration information, the server MAY send a
 Reply message to the client containing the client's IA, with the
 lifetimes for the addresses in the IA set to zero.  This Reply
 constitutes an explicit notification to the client that the addresses
 in the IA are no longer valid.  In this situation, if the server does
 not send a Reply message it silently discards the Rebind message.
 If the server finds that any of the addresses are no longer
 appropriate for the link to which the client is attached, the server
 returns the address to the client with lifetimes of 0.
 If the server finds the addresses in the IA for the client then the
 server SHOULD send back the IA to the client with new lifetimes and
 T1/T2 times.
 The server constructs a Reply message by setting the "msg-type" field
 to REPLY, and copying the transaction ID from the Rebind message into
 the transaction-id field.
 The server MUST include a Server Identifier option containing the
 server's DUID and the Client Identifier option from the Rebind
 message in the Reply message.
 The server includes other options containing configuration
 information to be returned to the client as described in section
 18.2.

18.2.5. Receipt of Information-request Messages

 When the server receives an Information-request message, the client
 is requesting configuration information that does not include the
 assignment of any addresses.  The server determines all configuration
 parameters appropriate to the client, based on the server
 configuration policies known to the server.
 The server constructs a Reply message by setting the "msg-type" field
 to REPLY, and copying the transaction ID from the Information-request
 message into the transaction-id field.
 The server MUST include a Server Identifier option containing the
 server's DUID in the Reply message.  If the client included a Client
 Identification option in the Information-request message, the server
 copies that option to the Reply message.

Droms, et al. Standards Track [Page 52] RFC 3315 DHCP for IPv6 July 2003

 The server includes options containing configuration information to
 be returned to the client as described in section 18.2.
 If the Information-request message received from the client did not
 include a Client Identifier option, the server SHOULD respond with a
 Reply message containing any configuration parameters that are not
 determined by the client's identity.  If the server chooses not to
 respond, the client may continue to retransmit the
 Information-request message indefinitely.

18.2.6. Receipt of Release Messages

 When the server receives a Release message via unicast from a client
 to which the server has not sent a unicast option, the server
 discards the Release message and responds with a Reply message
 containing a Status Code option with value UseMulticast, a Server
 Identifier option containing the server's DUID, the Client Identifier
 option from the client message, and no other options.
 Upon the receipt of a valid Release message, the server examines the
 IAs and the addresses in the IAs for validity.  If the IAs in the
 message are in a binding for the client, and the addresses in the IAs
 have been assigned by the server to those IAs, the server deletes the
 addresses from the IAs and makes the addresses available for
 assignment to other clients.  The server ignores addresses not
 assigned to the IA, although it may choose to log an error.
 After all the addresses have been processed, the server generates a
 Reply message and includes a Status Code option with value Success, a
 Server Identifier option with the server's DUID, and a Client
 Identifier option with the client's DUID.  For each IA in the Release
 message for which the server has no binding information, the server
 adds an IA option using the IAID from the Release message, and
 includes a Status Code option with the value NoBinding in the IA
 option.  No other options are included in the IA option.
 A server may choose to retain a record of assigned addresses and IAs
 after the lifetimes on the addresses have expired to allow the server
 to reassign the previously assigned addresses to a client.

18.2.7. Receipt of Decline Messages

 When the server receives a Decline message via unicast from a client
 to which the server has not sent a unicast option, the server
 discards the Decline message and responds with a Reply message
 containing a Status Code option with the value UseMulticast, a Server
 Identifier option containing the server's DUID, the Client Identifier
 option from the client message, and no other options.

Droms, et al. Standards Track [Page 53] RFC 3315 DHCP for IPv6 July 2003

 Upon the receipt of a valid Decline message, the server examines the
 IAs and the addresses in the IAs for validity.  If the IAs in the
 message are in a binding for the client, and the addresses in the IAs
 have been assigned by the server to those IAs, the server deletes the
 addresses from the IAs.  The server ignores addresses not assigned to
 the IA (though it may choose to log an error if it finds such an
 address).
 The client has found any addresses in the Decline messages to be
 already in use on its link.  Therefore, the server SHOULD mark the
 addresses declined by the client so that those addresses are not
 assigned to other clients, and MAY choose to make a notification that
 addresses were declined.  Local policy on the server determines when
 the addresses identified in a Decline message may be made available
 for assignment.
 After all the addresses have been processed, the server generates a
 Reply message and includes a Status Code option with the value
 Success, a Server Identifier option with the server's DUID, and a
 Client Identifier option with the client's DUID.  For each IA in the
 Decline message for which the server has no binding information, the
 server adds an IA option using the IAID from the Release message and
 includes a Status Code option with the value NoBinding in the IA
 option.  No other options are included in the IA option.

18.2.8. Transmission of Reply Messages

 If the original message was received directly by the server, the
 server unicasts the Reply message directly to the client using the
 address in the source address field from the IP datagram in which the
 original message was received.  The Reply message MUST be unicast
 through the interface on which the original message was received.
 If the original message was received in a Relay-forward message, the
 server constructs a Relay-reply message with the Reply message in the
 payload of a Relay Message option (see section 22.10).  If the
 Relay-forward messages included an Interface-id option, the server
 copies that option to the Relay-reply message.  The server unicasts
 the Relay-reply message directly to the relay agent using the address
 in the source address field from the IP datagram in which the
 Relay-forward message was received.

19. DHCP Server-Initiated Configuration Exchange

 A server initiates a configuration exchange to cause DHCP clients to
 obtain new addresses and other configuration information.  For
 example, an administrator may use a server-initiated configuration
 exchange when links in the DHCP domain are to be renumbered.  Other

Droms, et al. Standards Track [Page 54] RFC 3315 DHCP for IPv6 July 2003

 examples include changes in the location of directory servers,
 addition of new services such as printing, and availability of new
 software.

19.1. Server Behavior

 A server sends a Reconfigure message to cause a client to initiate
 immediately a Renew/Reply or Information-request/Reply message
 exchange with the server.

19.1.1. Creation and Transmission of Reconfigure Messages

 The server sets the "msg-type" field to RECONFIGURE.  The server sets
 the transaction-id field to 0.  The server includes a Server
 Identifier option containing its DUID and a Client Identifier option
 containing the client's DUID in the Reconfigure message.
 The server MAY include an Option Request option to inform the client
 of what information has been changed or new information that has been
 added.  In particular, the server specifies the IA option in the
 Option Request option if the server wants the client to obtain new
 address information.  If the server identifies the IA option in the
 Option Request option, the server MUST include an IA option that
 contains no other sub-options to identify each IA that is to be
 reconfigured on the client.
 Because of the risk of denial of service attacks against DHCP
 clients, the use of a security mechanism is mandated in Reconfigure
 messages.  The server MUST use DHCP authentication in the Reconfigure
 message.
 The server MUST include a Reconfigure Message option (defined in
 section 22.19) to select whether the client responds with a Renew
 message or an Information-Request message.
 The server MUST NOT include any other options in the Reconfigure
 except as specifically allowed in the definition of individual
 options.
 A server sends each Reconfigure message to a single DHCP client,
 using an IPv6 unicast address of sufficient scope belonging to the
 DHCP client.  If the server does not have an address to which it can
 send the Reconfigure message directly to the client, the server uses
 a Relay-reply message (as described in section 20.3) to send the
 Reconfigure message to a relay agent that will relay the message to
 the client.  The server may obtain the address of the client (and the

Droms, et al. Standards Track [Page 55] RFC 3315 DHCP for IPv6 July 2003

 appropriate relay agent, if required) through the information the
 server has about clients that have been in contact with the server,
 or through some external agent.
 To reconfigure more than one client, the server unicasts a separate
 message to each client.  The server may initiate the reconfiguration
 of multiple clients concurrently; for example, a server may send a
 Reconfigure message to additional clients while previous
 reconfiguration message exchanges are still in progress.
 The Reconfigure message causes the client to initiate a Renew/Reply
 or Information-request/Reply message exchange with the server.  The
 server interprets the receipt of a Renew or Information-request
 message (whichever was specified in the original Reconfigure message)
 from the client as satisfying the Reconfigure message request.

19.1.2. Time Out and Retransmission of Reconfigure Messages

 If the server does not receive a Renew or Information-request message
 from the client in REC_TIMEOUT milliseconds, the server retransmits
 the Reconfigure message, doubles the REC_TIMEOUT value and waits
 again.  The server continues this process until REC_MAX_RC
 unsuccessful attempts have been made, at which point the server
 SHOULD abort the reconfigure process for that client.
 Default and initial values for REC_TIMEOUT and REC_MAX_RC are
 documented in section 5.5.

19.2. Receipt of Renew Messages

 The server generates and sends a Reply message to the client as
 described in sections 18.2.3 and 18.2.8, including options for
 configuration parameters.
 The server MAY include options containing the IAs and new values for
 other configuration parameters in the Reply message, even if those
 IAs and parameters were not requested in the Renew message from the
 client.

19.3. Receipt of Information-request Messages

 The server generates and sends a Reply message to the client as
 described in sections 18.2.5 and 18.2.8, including options for
 configuration parameters.

Droms, et al. Standards Track [Page 56] RFC 3315 DHCP for IPv6 July 2003

 The server MAY include options containing new values for other
 configuration parameters in the Reply message, even if those
 parameters were not requested in the Information-request message from
 the client.

19.4. Client Behavior

 A client receives Reconfigure messages sent to the UDP port 546 on
 interfaces for which it has acquired configuration information
 through DHCP.  These messages may be sent at any time.  Since the
 results of a reconfiguration event may affect application layer
 programs, the client SHOULD log these events, and MAY notify these
 programs of the change through an implementation-specific interface.

19.4.1. Receipt of Reconfigure Messages

 Upon receipt of a valid Reconfigure message, the client responds with
 either a Renew message or an Information-request message as indicated
 by the Reconfigure Message option (as defined in section 22.19).  The
 client ignores the transaction-id field in the received Reconfigure
 message.  While the transaction is in progress, the client silently
 discards any Reconfigure messages it receives.
 DISCUSSION:
    The Reconfigure message acts as a trigger that signals the client
    to complete a successful message exchange.  Once the client has
    received a Reconfigure, the client proceeds with the message
    exchange (retransmitting the Renew or Information-request message
    if necessary); the client ignores any additional Reconfigure
    messages until the exchange is complete.  Subsequent Reconfigure
    messages cause the client to initiate a new exchange.
    How does this mechanism work in the face of duplicated or
    retransmitted Reconfigure messages?  Duplicate messages will be
    ignored because the client will begin the exchange after the
    receipt of the first Reconfigure.  Retransmitted messages will
    either trigger the exchange (if the first Reconfigure was not
    received by the client) or will be ignored.  The server can
    discontinue retransmission of Reconfigure messages to the client
    once the server receives the Renew or Information-request message
    from the client.
    It might be possible for a duplicate or retransmitted Reconfigure
    to be sufficiently delayed (and delivered out of order) to arrive
    at the client after the exchange (initiated by the original
    Reconfigure) has been completed.  In this case, the client would
    initiate a redundant exchange.  The likelihood of delayed and out

Droms, et al. Standards Track [Page 57] RFC 3315 DHCP for IPv6 July 2003

    of order delivery is small enough to be ignored.  The consequence
    of the redundant exchange is inefficiency rather than incorrect
    operation.

19.4.2. Creation and Transmission of Renew Messages

 When responding to a Reconfigure, the client creates and sends the
 Renew message in exactly the same manner as outlined in section
 18.1.3, with the exception that the client copies the Option Request
 option and any IA options from the Reconfigure message into the Renew
 message.

19.4.3. Creation and Transmission of Information-request Messages

 When responding to a Reconfigure, the client creates and sends the
 Information-request message in exactly the same manner as outlined in
 section 18.1.5, with the exception that the client includes a Server
 Identifier option with the identifier from the Reconfigure message to
 which the client is responding.

19.4.4. Time Out and Retransmission of Renew or Information-request

      Messages
 The client uses the same variables and retransmission algorithm as it
 does with Renew or Information-request messages generated as part of
 a client-initiated configuration exchange.  See sections 18.1.3 and
 18.1.5 for details.  If the client does not receive a response from
 the server by the end of the retransmission process, the client
 ignores and discards the Reconfigure message.

19.4.5. Receipt of Reply Messages

 Upon the receipt of a valid Reply message, the client processes the
 options and sets (or resets) configuration parameters appropriately.
 The client records and updates the lifetimes for any addresses
 specified in IAs in the Reply message.

20. Relay Agent Behavior

 The relay agent MAY be configured to use a list of destination
 addresses, which MAY include unicast addresses, the All_DHCP_Servers
 multicast address, or other addresses selected by the network
 administrator.  If the relay agent has not been explicitly
 configured, it MUST use the All_DHCP_Servers multicast address as the
 default.

Droms, et al. Standards Track [Page 58] RFC 3315 DHCP for IPv6 July 2003

 If the relay agent relays messages to the All_DHCP_Servers multicast
 address or other multicast addresses, it sets the Hop Limit field to
 32.

20.1. Relaying a Client Message or a Relay-forward Message

 A relay agent relays both messages from clients and Relay-forward
 messages from other relay agents.  When a relay agent receives a
 valid message to be relayed, it constructs a new Relay-forward
 message.  The relay agent copies the source address from the header
 of the IP datagram in which the message was received to the
 peer-address field of the Relay-forward message.  The relay agent
 copies the received DHCP message (excluding any IP or UDP headers)
 into a Relay Message option in the new message.  The relay agent adds
 to the Relay-forward message any other options it is configured to
 include.

20.1.1. Relaying a Message from a Client

 If the relay agent received the message to be relayed from a client,
 the relay agent places a global or site-scoped address with a prefix
 assigned to the link on which the client should be assigned an
 address in the link-address field.  This address will be used by the
 server to determine the link from which the client should be assigned
 an address and other configuration information.  The hop-count in the
 Relay-forward message is set to 0.
 If the relay agent cannot use the address in the link-address field
 to identify the interface through which the response to the client
 will be relayed, the relay agent MUST include an Interface-id option
 (see section 22.18) in the Relay-forward message.  The server will
 include the Interface-id option in its Relay-reply message.  The
 relay agent fills in the link-address field as described in the
 previous paragraph regardless of whether the relay agent includes an
 Interface-id option in the Relay-forward message.

20.1.2. Relaying a Message from a Relay Agent

 If the message received by the relay agent is a Relay-forward message
 and the hop-count in the message is greater than or equal to
 HOP_COUNT_LIMIT, the relay agent discards the received message.
 The relay agent copies the source address from the IP datagram in
 which the message was received from the client into the peer-address
 field in the Relay-forward message and sets the hop-count field to
 the value of the hop-count field in the received message incremented
 by 1.

Droms, et al. Standards Track [Page 59] RFC 3315 DHCP for IPv6 July 2003

 If the source address from the IP datagram header of the received
 message is a global or site-local address (and the device on which
 the relay agent is running belongs to only one site), the relay agent
 sets the link-address field to 0; otherwise the relay agent sets the
 link-address field to a global or site-local address assigned to the
 interface on which the message was received, or includes an
 Interface-ID option to identify the interface on which the message
 was received.

20.2. Relaying a Relay-reply Message

 The relay agent processes any options included in the Relay-reply
 message in addition to the Relay Message option, and then discards
 those options.
 The relay agent extracts the message from the Relay Message option
 and relays it to the address contained in the peer-address field of
 the Relay-reply message.
 If the Relay-reply message includes an Interface-id option, the relay
 agent relays the message from the server to the client on the link
 identified by the Interface-id option.  Otherwise, if the
 link-address field is not set to zero, the relay agent relays the
 message on the link identified by the link-address field.

20.3. Construction of Relay-reply Messages

 A server uses a Relay-reply message to return a response to a client
 if the original message from the client was relayed to the server in
 a Relay-forward message or to send a Reconfigure message to a client
 if the server does not have an address it can use to send the message
 directly to the client.
 A response to the client MUST be relayed through the same relay
 agents as the original client message.  The server causes this to
 happen by creating a Relay-reply message that includes a Relay
 Message option containing the message for the next relay agent in the
 return path to the client.  The contained Relay-reply message
 contains another Relay Message option to be sent to the next relay
 agent, and so on.  The server must record the contents of the
 peer-address fields in the received message so it can construct the
 appropriate Relay-reply message carrying the response from the
 server.

Droms, et al. Standards Track [Page 60] RFC 3315 DHCP for IPv6 July 2003

 For example, if client C sent a message that was relayed by relay
 agent A to relay agent B and then to the server, the server would
 send the following Relay-Reply message to relay agent B:
 msg-type:       RELAY-REPLY
 hop-count:      1
 link-address:   0
 peer-address:   A
 Relay Message option, containing:
   msg-type:     RELAY-REPLY
   hop-count:    0
   link-address: address from link to which C is attached
   peer-address: C
   Relay Message option: <response from server>
 When sending a Reconfigure message to a client through a relay agent,
 the server creates a Relay-reply message that includes a Relay
 Message option containing the Reconfigure message for the next relay
 agent in the return path to the client.  The server sets the
 peer-address field in the Relay-reply message header to the address
 of the client, and sets the link-address field as required by the
 relay agent to relay the Reconfigure message to the client.  The
 server obtains the addresses of the client and the relay agent
 through prior interaction with the client or through some external
 mechanism.

21. Authentication of DHCP Messages

 Some network administrators may wish to provide authentication of the
 source and contents of DHCP messages.  For example, clients may be
 subject to denial of service attacks through the use of bogus DHCP
 servers, or may simply be misconfigured due to unintentionally
 instantiated DHCP servers.  Network administrators may wish to
 constrain the allocation of addresses to authorized hosts to avoid
 denial of service attacks in "hostile" environments where the network
 medium is not physically secured, such as wireless networks or
 college residence halls.
 The DHCP authentication mechanism is based on the design of
 authentication for DHCPv4 [4].

21.1. Security of Messages Sent Between Servers and Relay Agents

 Relay agents and servers that exchange messages securely use the
 IPsec mechanisms for IPv6 [7].  If a client message is relayed
 through multiple relay agents, each of the relay agents must have
 established independent, pairwise trust relationships.  That is, if
 messages from client C will be relayed by relay agent A to relay

Droms, et al. Standards Track [Page 61] RFC 3315 DHCP for IPv6 July 2003

 agent B and then to the server, relay agents A and B must be
 configured to use IPSec for the messages they exchange, and relay
 agent B and the server must be configured to use IPSec for the
 messages they exchange.
 Relay agents and servers that support secure relay agent to server or
 relay agent to relay agent communication use IPsec under the
 following conditions:
    Selectors        Relay agents are manually configured with the
                     addresses of the relay agent or server to which
                     DHCP messages are to be forwarded.  Each relay
                     agent and server that will be using IPsec for
                     securing DHCP messages must also be configured
                     with a list of the relay agents to which messages
                     will be returned.  The selectors for the relay
                     agents and servers will be the pairs of addresses
                     defining relay agents and servers that exchange
                     DHCP messages on the DHCPv6 UDP ports 546 and
                     547.
    Mode             Relay agents and servers use transport mode and
                     ESP. The information in DHCP messages is not
                     generally considered confidential, so encryption
                     need not be used (i.e., NULL encryption can be
                     used).
    Key management   Because the relay agents and servers are used
                     within an organization, public key schemes are
                     not necessary.  Because the relay agents and
                     servers must be manually configured, manually
                     configured key management may suffice, but does
                     not provide defense against replayed messages.
                     Accordingly, IKE with preshared secrets SHOULD be
                     supported.  IKE with public keys MAY be
                     supported.
    Security policy  DHCP messages between relay agents and servers
                     should only be accepted from DHCP peers as
                     identified in the local configuration.
    Authentication   Shared keys, indexed to the source IP address of
                     the received DHCP message, are adequate in this
                     application.
    Availability     Appropriate IPsec implementations are likely to
                     be available for servers and for relay agents in
                     more featureful devices used in enterprise and

Droms, et al. Standards Track [Page 62] RFC 3315 DHCP for IPv6 July 2003

                     core ISP networks.  IPsec is less likely to be
                     available for relay agents in low end devices
                     primarily used in the home or small office
                     markets.

21.2. Summary of DHCP Authentication

 Authentication of DHCP messages is accomplished through the use of
 the Authentication option (see section 22.11).  The authentication
 information carried in the Authentication option can be used to
 reliably identify the source of a DHCP message and to confirm that
 the contents of the DHCP message have not been tampered with.
 The Authentication option provides a framework for multiple
 authentication protocols.  Two such protocols are defined here.
 Other protocols defined in the future will be specified in separate
 documents.
 Any DHCP message MUST NOT include more than one Authentication
 option.
 The protocol field in the Authentication option identifies the
 specific protocol used to generate the authentication information
 carried in the option.  The algorithm field identifies a specific
 algorithm within the authentication protocol; for example, the
 algorithm field specifies the hash algorithm used to generate the
 message authentication code (MAC) in the authentication option.  The
 replay detection method (RDM) field specifies the type of replay
 detection used in the replay detection field.

21.3. Replay Detection

 The Replay Detection Method (RDM) field determines the type of replay
 detection used in the Replay Detection field.
 If the RDM field contains 0x00, the replay detection field MUST be
 set to the value of a monotonically increasing counter.  Using a
 counter value, such as the current time of day (for example, an NTP-
 format timestamp [9]), can reduce the danger of replay attacks.  This
 method MUST be supported by all protocols.

21.4. Delayed Authentication Protocol

 If the protocol field is 2, the message is using the "delayed
 authentication" mechanism.  In delayed authentication, the client
 requests authentication in its Solicit message, and the server
 replies with an Advertise message that includes authentication

Droms, et al. Standards Track [Page 63] RFC 3315 DHCP for IPv6 July 2003

 information.  This authentication information contains a nonce value
 generated by the source as a message authentication code (MAC) to
 provide message authentication and entity authentication.
 The use of a particular technique based on the HMAC protocol [8]
 using the MD5 hash [16] is defined here.

21.4.1. Use of the Authentication Option in the Delayed Authentication

      Protocol
 In a Solicit message, the client fills in the protocol, algorithm and
 RDM fields in the Authentication option with the client's
 preferences.  The client sets the replay detection field to zero and
 omits the authentication information field.  The client sets the
 option-len field to 11.
 In all other messages, the protocol and algorithm fields identify the
 method used to construct the contents of the authentication
 information field.  The RDM field identifies the method used to
 construct the contents of the replay detection field.
 The format of the Authentication information is:
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          DHCP realm                           |
  |                      (variable length)                        |
  .                                                               .
  .                                                               .
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                            key ID                             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  |                           HMAC-MD5                            |
  |                          (128 bits)                           |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    DHCP realm  The DHCP realm that identifies the key used to
                generate the HMAC-MD5 value.
    key ID      The key identifier that identified the key used to
                generate the HMAC-MD5 value.
    HMAC-MD5    The message authentication code generated by applying
                MD5 to the DHCP message using the key identified by
                the DHCP realm, client DUID, and key ID.

Droms, et al. Standards Track [Page 64] RFC 3315 DHCP for IPv6 July 2003

 The sender computes the MAC using the HMAC generation algorithm [8]
 and the MD5 hash function [16].  The entire DHCP message (setting the
 MAC field of the authentication option to zero), including the DHCP
 message header and the options field, is used as input to the HMAC-
 MD5 computation function.
 DISCUSSION:
    Algorithm 1 specifies the use of HMAC-MD5.  Use of a different
    technique, such as HMAC-SHA, will be specified as a separate
    protocol.
    The DHCP realm used to identify authentication keys is chosen to
    be unique among administrative domains.  Use of the DHCP realm
    allows DHCP administrators to avoid conflict in the use of key
    identifiers, and allows a host using DHCP to use authenticated
    DHCP while roaming among DHCP administrative domains.

21.4.2. Message Validation

 Any DHCP message that includes more than one authentication option
 MUST be discarded.
 To validate an incoming message, the receiver first checks that the
 value in the replay detection field is acceptable according to the
 replay detection method specified by the RDM field.  Next, the
 receiver computes the MAC as described in [8].  The entire DHCP
 message (setting the MAC field of the authentication option to 0) is
 used as input to the HMAC-MD5 computation function.  If the MAC
 computed by the receiver does not match the MAC contained in the
 authentication option, the receiver MUST discard the DHCP message.

21.4.3. Key Utilization

 Each DHCP client has a set of keys.  Each key is identified by <DHCP
 realm, client DUID, key id>.  Each key also has a lifetime.  The key
 may not be used past the end of its lifetime.  The client's keys are
 initially distributed to the client through some out-of-band
 mechanism.  The lifetime for each key is distributed with the key.
 Mechanisms for key distribution and lifetime specification are beyond
 the scope of this document.
 The client and server use one of the client's keys to authenticate
 DHCP messages during a session (until the next Solicit message sent
 by the client).

Droms, et al. Standards Track [Page 65] RFC 3315 DHCP for IPv6 July 2003

21.4.4. Client Considerations for Delayed Authentication Protocol

 The client announces its intention to use DHCP authentication by
 including an Authentication option in its Solicit message.  The
 server selects a key for the client based on the client's DUID.  The
 client and server use that key to authenticate all DHCP messages
 exchanged during the session.

21.4.4.1. Sending Solicit Messages

 When the client sends a Solicit message and wishes to use
 authentication, it includes an Authentication option with the desired
 protocol, algorithm and RDM as described in section 21.4.  The client
 does not include any replay detection or authentication information
 in the Authentication option.

21.4.4.2. Receiving Advertise Messages

 The client validates any Advertise messages containing an
 Authentication option specifying the delayed authentication protocol
 using the validation test described in section 21.4.2.
 Client behavior, if no Advertise messages include authentication
 information or pass the validation test, is controlled by local
 policy on the client.  According to client policy, the client MAY
 choose to respond to an Advertise message that has not been
 authenticated.
 The decision to set local policy to accept unauthenticated messages
 should be made with care.  Accepting an unauthenticated Advertise
 message can make the client vulnerable to spoofing and other attacks.
 If local users are not explicitly informed that the client has
 accepted an unauthenticated Advertise message, the users may
 incorrectly assume that the client has received an authenticated
 address and is not subject to DHCP attacks through unauthenticated
 messages.
 A client MUST be configurable to discard unauthenticated messages,
 and SHOULD be configured by default to discard unauthenticated
 messages if the client has been configured with an authentication key
 or other authentication information.  A client MAY choose to
 differentiate between Advertise messages with no authentication
 information and Advertise messages that do not pass the validation
 test; for example, a client might accept the former and discard the
 latter.  If a client does accept an unauthenticated message, the
 client SHOULD inform any local users and SHOULD log the event.

Droms, et al. Standards Track [Page 66] RFC 3315 DHCP for IPv6 July 2003

21.4.4.3. Sending Request, Confirm, Renew, Rebind, Decline or Release

        Messages
 If the client authenticated the Advertise message through which the
 client selected the server, the client MUST generate authentication
 information for subsequent Request, Confirm, Renew, Rebind or Release
 messages sent to the server, as described in section 21.4.  When the
 client sends a subsequent message, it MUST use the same key used by
 the server to generate the authentication information.

21.4.4.4. Sending Information-request Messages

 If the server has selected a key for the client in a previous message
 exchange (see section 21.4.5.1), the client MUST use the same key to
 generate the authentication information throughout the session.

21.4.4.5. Receiving Reply Messages

 If the client authenticated the Advertise it accepted, the client
 MUST validate the associated Reply message from the server.  The
 client MUST discard the Reply if the message fails to pass the
 validation test and MAY log the validation failure.  If the Reply
 fails to pass the validation test, the client MUST restart the DHCP
 configuration process by sending a Solicit message.
 If the client accepted an Advertise message that did not include
 authentication information or did not pass the validation test, the
 client MAY accept an unauthenticated Reply message from the server.

21.4.4.6. Receiving Reconfigure Messages

 The client MUST discard the Reconfigure if the message fails to pass
 the validation test and MAY log the validation failure.

21.4.5. Server Considerations for Delayed Authentication Protocol

 After receiving a Solicit message that contains an Authentication
 option, the server selects a key for the client, based on the
 client's DUID and key selection policies with which the server has
 been configured.  The server identifies the selected key in the
 Advertise message and uses the key to validate subsequent messages
 between the client and the server.

Droms, et al. Standards Track [Page 67] RFC 3315 DHCP for IPv6 July 2003

21.4.5.1. Receiving Solicit Messages and Sending Advertise Messages

 The server selects a key for the client and includes authentication
 information in the Advertise message returned to the client as
 specified in section 21.4.  The server MUST record the identifier of
 the key selected for the client and use that same key for validating
 subsequent messages with the client.

21.4.5.2. Receiving Request, Confirm, Renew, Rebind or Release Messages

        and Sending Reply Messages
 The server uses the key identified in the message and validates the
 message as specified in section 21.4.2.  If the message fails to pass
 the validation test or the server does not know the key identified by
 the 'key ID' field, the server MUST discard the message and MAY
 choose to log the validation failure.
 If the message passes the validation test, the server responds to the
 specific message as described in section 18.2.  The server MUST
 include authentication information generated using the key identified
 in the received message, as specified in section 21.4.

21.5. Reconfigure Key Authentication Protocol

 The Reconfigure key authentication protocol provides protection
 against misconfiguration of a client caused by a Reconfigure message
 sent by a malicious DHCP server.  In this protocol, a DHCP server
 sends a Reconfigure Key to the client in the initial exchange of DHCP
 messages.  The client records the Reconfigure Key for use in
 authenticating subsequent Reconfigure messages from that server.  The
 server then includes an HMAC computed from the Reconfigure Key in
 subsequent Reconfigure messages.
 Both the Reconfigure Key sent from the server to the client and the
 HMAC in subsequent Reconfigure messages are carried as the
 Authentication information in an Authentication option.  The format
 of the Authentication information is defined in the following
 section.
 The Reconfigure Key protocol is used (initiated by the server) only
 if the client and server are not using any other authentication
 protocol and the client and server have negotiated to use Reconfigure
 messages.

Droms, et al. Standards Track [Page 68] RFC 3315 DHCP for IPv6 July 2003

21.5.1. Use of the Authentication Option in the Reconfigure Key

      Authentication Protocol
 The following fields are set in an Authentication option for the
 Reconfigure Key Authentication Protocol:
    protocol    3
    algorithm   1
    RDM         0
 The format of the Authentication information for the Reconfigure Key
 Authentication Protocol is:
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |     Type      |                 Value (128 bits)              |
  +-+-+-+-+-+-+-+-+                                               |
  .                                                               .
  .                                                               .
  .                                               +-+-+-+-+-+-+-+-+
  |                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Type    Type of data in Value field carried in this option:
               1   Reconfigure Key value (used in Reply message).
               2   HMAC-MD5 digest of the message (used in Reconfigure
                   message).
    Value   Data as defined by field.

21.5.2. Server considerations for Reconfigure Key protocol

 The server selects a Reconfigure Key for a client during the
 Request/Reply, Solicit/Reply or Information-request/Reply message
 exchange.  The server records the Reconfigure Key and transmits that
 key to the client in an Authentication option in the Reply message.
 The Reconfigure Key is 128 bits long, and MUST be a cryptographically
 strong random or pseudo-random number that cannot easily be
 predicted.

Droms, et al. Standards Track [Page 69] RFC 3315 DHCP for IPv6 July 2003

 To provide authentication for a Reconfigure message, the server
 selects a replay detection value according to the RDM selected by the
 server, and computes an HMAC-MD5 of the Reconfigure message using the
 Reconfigure Key for the client.  The server computes the HMAC-MD5
 over the entire DHCP Reconfigure message, including the
 Authentication option; the HMAC-MD5 field in the Authentication
 option is set to zero for the HMAC-MD5 computation.  The server
 includes the HMAC-MD5 in the authentication information field in an
 Authentication option included in the Reconfigure message sent to the
 client.

21.5.3. Client considerations for Reconfigure Key protocol

 The client will receive a Reconfigure Key from the server in the
 initial Reply message from the server.  The client records the
 Reconfigure Key for use in authenticating subsequent Reconfigure
 messages.
 To authenticate a Reconfigure message, the client computes an
 HMAC-MD5 over the DHCP Reconfigure message, using the Reconfigure Key
 received from the server.  If this computed HMAC-MD5 matches the
 value in the Authentication option, the client accepts the
 Reconfigure message.

22. DHCP Options

 Options are used to carry additional information and parameters in
 DHCP messages.  Every option shares a common base format, as
 described in section 22.1.  All values in options are represented in
 network byte order.
 This document describes the DHCP options defined as part of the base
 DHCP specification.  Other options may be defined in the future in
 separate documents.
 Unless otherwise noted, each option may appear only in the options
 area of a DHCP message and may appear only once.  If an option does
 appear multiple times, each instance is considered separate and the
 data areas of the options MUST NOT be concatenated or otherwise
 combined.

Droms, et al. Standards Track [Page 70] RFC 3315 DHCP for IPv6 July 2003

22.1. Format of DHCP Options

 The format of DHCP options is:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          option-code          |           option-len          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          option-data                          |
    |                      (option-len octets)                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code   An unsigned integer identifying the specific option
                  type carried in this option.
    option-len    An unsigned integer giving the length of the
                  option-data field in this option in octets.
    option-data   The data for the option; the format of this data
                  depends on the definition of the option.
 DHCPv6 options are scoped by using encapsulation.  Some options apply
 generally to the client, some are specific to an IA, and some are
 specific to the addresses within an IA.  These latter two cases are
 discussed in sections 22.4 and 22.6.

22.2. Client Identifier Option

 The Client Identifier option is used to carry a DUID (see section 9)
 identifying a client between a client and a server.  The format of
 the Client Identifier option is:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        OPTION_CLIENTID        |          option-len           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                              DUID                             .
    .                        (variable length)                      .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code   OPTION_CLIENTID (1).
    option-len    Length of DUID in octets.

Droms, et al. Standards Track [Page 71] RFC 3315 DHCP for IPv6 July 2003

    DUID          The DUID for the client.

22.3. Server Identifier Option

 The Server Identifier option is used to carry a DUID (see section 9)
 identifying a server between a client and a server.  The format of
 the Server Identifier option is:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        OPTION_SERVERID        |          option-len           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                              DUID                             .
    .                        (variable length)                      .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code   OPTION_SERVERID (2).
    option-len    Length of DUID in octets.
    DUID          The DUID for the server.

22.4. Identity Association for Non-temporary Addresses Option

 The Identity Association for Non-temporary Addresses option (IA_NA
 option) is used to carry an IA_NA, the parameters associated with the
 IA_NA, and the non-temporary addresses associated with the IA_NA.
 Addresses appearing in an IA_NA option are not temporary addresses
 (see section 22.5).

Droms, et al. Standards Track [Page 72] RFC 3315 DHCP for IPv6 July 2003

 The format of the IA_NA option is:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          OPTION_IA_NA         |          option-len           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        IAID (4 octets)                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                              T1                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                              T2                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .                         IA_NA-options                         .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code          OPTION_IA_NA (3).
    option-len           12 + length of IA_NA-options field.
    IAID                 The unique identifier for this IA_NA; the
                         IAID must be unique among the identifiers for
                         all of this client's IA_NAs.  The number
                         space for IA_NA IAIDs is separate from the
                         number space for IA_TA IAIDs.
    T1                   The time at which the client contacts the
                         server from which the addresses in the IA_NA
                         were obtained to extend the lifetimes of the
                         addresses assigned to the IA_NA; T1 is a
                         time duration relative to the current time
                         expressed in units of seconds.
    T2                   The time at which the client contacts any
                         available server to extend the lifetimes of
                         the addresses assigned to the IA_NA; T2 is a
                         time duration relative to the current time
                         expressed in units of seconds.
    IA_NA-options        Options associated with this IA_NA.
 The IA_NA-options field encapsulates those options that are specific
 to this IA_NA.  For example, all of the IA Address Options carrying
 the addresses associated with this IA_NA are in the IA_NA-options
 field.

Droms, et al. Standards Track [Page 73] RFC 3315 DHCP for IPv6 July 2003

 An IA_NA option may only appear in the options area of a DHCP
 message.  A DHCP message may contain multiple IA_NA options.
 The status of any operations involving this IA_NA is indicated in a
 Status Code option in the IA_NA-options field.
 Note that an IA_NA has no explicit "lifetime" or "lease length" of
 its own.  When the valid lifetimes of all of the addresses in an
 IA_NA have expired, the IA_NA can be considered as having expired.
 T1 and T2 are included to give servers explicit control over when a
 client recontacts the server about a specific IA_NA.
 In a message sent by a client to a server, values in the T1 and T2
 fields indicate the client's preference for those parameters.  The
 client sets T1 and T2 to 0 if it has no preference for those values.
 In a message sent by a server to a client, the client MUST use the
 values in the T1 and T2 fields for the T1 and T2 parameters, unless
 those values in those fields are 0.  The values in the T1 and T2
 fields are the number of seconds until T1 and T2.
 The server selects the T1 and T2 times to allow the client to extend
 the lifetimes of any addresses in the IA_NA before the lifetimes
 expire, even if the server is unavailable for some short period of
 time.  Recommended values for T1 and T2 are .5 and .8 times the
 shortest preferred lifetime of the addresses in the IA that the
 server is willing to extend, respectively.  If the "shortest"
 preferred lifetime is 0xffffffff ("infinity"), the recommended T1 and
 T2 values are also 0xffffffff.  If the time at which the addresses in
 an IA_NA are to be renewed is to be left to the discretion of the
 client, the server sets T1 and T2 to 0.
 If a server receives an IA_NA with T1 greater than T2, and both T1
 and T2 are greater than 0, the server ignores the invalid values of
 T1 and T2 and processes the IA_NA as though the client had set T1 and
 T2 to 0.
 If a client receives an IA_NA with T1 greater than T2, and both T1
 and T2 are greater than 0, the client discards the IA_NA option and
 processes the remainder of the message as though the server had not
 included the invalid IA_NA option.
 Care should be taken in setting T1 or T2 to 0xffffffff ("infinity").
 A client will never attempt to extend the lifetimes of any addresses
 in an IA with T1 set to 0xffffffff.  A client will never attempt to
 use a Rebind message to locate a different server to extend the
 lifetimes of any addresses in an IA with T2 set to 0xffffffff.

Droms, et al. Standards Track [Page 74] RFC 3315 DHCP for IPv6 July 2003

22.5. Identity Association for Temporary Addresses Option

 The Identity Association for the Temporary Addresses (IA_TA) option
 is used to carry an IA_TA, the parameters associated with the IA_TA
 and the addresses associated with the IA_TA.  All of the addresses in
 this option are used by the client as temporary addresses, as defined
 in RFC 3041 [12].  The format of the IA_TA option is:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         OPTION_IA_TA          |          option-len           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        IAID (4 octets)                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .                         IA_TA-options                         .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code          OPTION_IA_TA (4).
    option-len           4 + length of IA_TA-options field.
    IAID                 The unique identifier for this IA_TA; the
                         IAID must be unique among the identifiers
                         for all of this client's IA_TAs.  The number
                         space for IA_TA IAIDs is separate from the
                         number space for IA_NA IAIDs.
    IA_TA-options        Options associated with this IA_TA.
 The IA_TA-Options field encapsulates those options that are specific
 to this IA_TA.  For example, all of the IA Address Options carrying
 the addresses associated with this IA_TA are in the IA_TA-options
 field.
 Each IA_TA carries one "set" of temporary addresses; that is, at most
 one address from each prefix assigned to the link to which the client
 is attached.
 An IA_TA option may only appear in the options area of a DHCP
 message.  A DHCP message may contain multiple IA_TA options.
 The status of any operations involving this IA_TA is indicated in a
 Status Code option in the IA_TA-options field.

Droms, et al. Standards Track [Page 75] RFC 3315 DHCP for IPv6 July 2003

 Note that an IA has no explicit "lifetime" or "lease length" of its
 own.  When the valid lifetimes of all of the addresses in an IA_TA
 have expired, the IA can be considered as having expired.
 An IA_TA option does not include values for T1 and T2.  A client MAY
 request that the lifetimes on temporary addresses be extended by
 including the addresses in a IA_TA option sent in a Renew or Rebind
 message to a server.  For example, a client would request an
 extension on the lifetime of a temporary address to allow an
 application to continue to use an established TCP connection.
 The client obtains new temporary addresses by sending an IA_TA option
 with a new IAID to a server.  Requesting new temporary addresses from
 the server is the equivalent of generating new temporary addresses as
 described in RFC 3041.  The server will generate new temporary
 addresses and return them to the client.  The client should request
 new temporary addresses before the lifetimes on the previously
 assigned addresses expire.
 A server MUST return the same set of temporary address for the same
 IA_TA (as identified by the IAID) as long as those addresses are
 still valid.  After the lifetimes of the addresses in an IA_TA have
 expired, the IAID may be reused to identify a new IA_TA with new
 temporary addresses.
 This option MAY appear in a Confirm message if the lifetimes on the
 temporary addresses in the associated IA have not expired.

22.6. IA Address Option

 The IA Address option is used to specify IPv6 addresses associated
 with an IA_NA or an IA_TA.  The IA Address option must be
 encapsulated in the Options field of an IA_NA or IA_TA option.  The
 Options field encapsulates those options that are specific to this
 address.

Droms, et al. Standards Track [Page 76] RFC 3315 DHCP for IPv6 July 2003

 The format of the IA Address option is:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          OPTION_IAADDR        |          option-len           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                         IPv6 address                          |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      preferred-lifetime                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        valid-lifetime                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                        IAaddr-options                         .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code   OPTION_IAADDR (5).
    option-len    24 + length of IAaddr-options field.
    IPv6 address  An IPv6 address.
    preferred-lifetime The preferred lifetime for the IPv6 address in
                  the option, expressed in units of seconds.
    valid-lifetime The valid lifetime for the IPv6 address in the
                  option, expressed in units of seconds.
    IAaddr-options Options associated with this address.
 In a message sent by a client to a server, values in the preferred
 and valid lifetime fields indicate the client's preference for those
 parameters.  The client may send 0 if it has no preference for the
 preferred and valid lifetimes.  In a message sent by a server to a
 client, the client MUST use the values in the preferred and valid
 lifetime fields for the preferred and valid lifetimes.  The values in
 the preferred and valid lifetimes are the number of seconds remaining
 in each lifetime.

Droms, et al. Standards Track [Page 77] RFC 3315 DHCP for IPv6 July 2003

 A client discards any addresses for which the preferred lifetime is
 greater than the valid lifetime.  A server ignores the lifetimes set
 by the client if the preferred lifetime is greater than the valid
 lifetime and ignores the values for T1 and T2 set by the client if
 those values are greater than the preferred lifetime.
 Care should be taken in setting the valid lifetime of an address to
 0xffffffff ("infinity"), which amounts to a permanent assignment of
 an address to a client.
 An IA Address option may appear only in an IA_NA option or an IA_TA
 option.  More than one IA Address Option can appear in an IA_NA
 option or an IA_TA option.
 The status of any operations involving this IA Address is indicated
 in a Status Code option in the IAaddr-options field.

22.7. Option Request Option

 The Option Request option is used to identify a list of options in a
 message between a client and a server.  The format of the Option
 Request option is:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           OPTION_ORO          |           option-len          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    requested-option-code-1    |    requested-option-code-2    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                              ...                              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code   OPTION_ORO (6).
    option-len    2 * number of requested options.
    requested-option-code-n The option code for an option requested by
                  the client.
 A client MAY include an Option Request option in a Solicit, Request,
 Renew, Rebind, Confirm or Information-request message to inform the
 server about options the client wants the server to send to the
 client.  A server MAY include an Option Request option in a
 Reconfigure option to indicate which options the client should
 request from the server.

Droms, et al. Standards Track [Page 78] RFC 3315 DHCP for IPv6 July 2003

22.8. Preference Option

 The Preference option is sent by a server to a client to affect the
 selection of a server by the client.
 The format of the Preference option is:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       OPTION_PREFERENCE       |          option-len           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  pref-value   |
    +-+-+-+-+-+-+-+-+
    option-code   OPTION_PREFERENCE (7).
    option-len    1.
    pref-value    The preference value for the server in this message.
 A server MAY include a Preference option in an Advertise message to
 control the selection of a server by the client.  See section 17.1.3
 for the use of the Preference option by the client and the
 interpretation of Preference option data value.

22.9. Elapsed Time Option

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      OPTION_ELAPSED_TIME      |           option-len          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          elapsed-time         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code   OPTION_ELAPSED_TIME (8).
    option-len    2.
    elapsed-time  The amount of time since the client began its
                  current DHCP transaction.  This time is expressed in
                  hundredths of a second (10^-2 seconds).
 A client MUST include an Elapsed Time option in messages to indicate
 how long the client has been trying to complete a DHCP message
 exchange.  The elapsed time is measured from the time at which the
 client sent the first message in the message exchange, and the

Droms, et al. Standards Track [Page 79] RFC 3315 DHCP for IPv6 July 2003

 elapsed-time field is set to 0 in the first message in the message
 exchange.  Servers and Relay Agents use the data value in this option
 as input to policy controlling how a server responds to a client
 message.  For example, the elapsed time option allows a secondary
 DHCP server to respond to a request when a primary server has not
 answered in a reasonable time.  The elapsed time value is an
 unsigned, 16 bit integer.  The client uses the value 0xffff to
 represent any elapsed time values greater than the largest time value
 that can be represented in the Elapsed Time option.

22.10. Relay Message Option

 The Relay Message option carries a DHCP message in a Relay-forward or
 Relay-reply message.
 The format of the Relay Message option is:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        OPTION_RELAY_MSG       |           option-len          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .                       DHCP-relay-message                      .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code   OPTION_RELAY_MSG (9)
    option-len    Length of DHCP-relay-message
    DHCP-relay-message In a Relay-forward message, the received
                  message, relayed verbatim to the next relay agent
                  or server; in a Relay-reply message, the message to
                  be copied and relayed to the relay agent or client
                  whose address is in the peer-address field of the
                  Relay-reply message

Droms, et al. Standards Track [Page 80] RFC 3315 DHCP for IPv6 July 2003

22.11. Authentication Option

 The Authentication option carries authentication information to
 authenticate the identity and contents of DHCP messages.  The use of
 the Authentication option is described in section 21.  The format of
 the Authentication option is:
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          OPTION_AUTH          |          option-len           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |   protocol    |   algorithm   |      RDM      |               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |
  |                                                               |
  |          replay detection (64 bits)           +-+-+-+-+-+-+-+-+
  |                                               |   auth-info   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |
  .                   authentication information                  .
  .                       (variable length)                       .
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code                  OPTION_AUTH (11)
    option-len                   11 + length of authentication
                                 information field
    protocol                     The authentication protocol used in
                                 this authentication option
    algorithm                    The algorithm used in the
                                 authentication protocol
    RDM                          The replay detection method used in
                                 this authentication option
    Replay detection             The replay detection information for
                                 the RDM
    authentication information   The authentication information,
                                 as specified by the protocol and
                                 algorithm used in this authentication
                                 option

Droms, et al. Standards Track [Page 81] RFC 3315 DHCP for IPv6 July 2003

22.12. Server Unicast Option

 The server sends this option to a client to indicate to the client
 that it is allowed to unicast messages to the server.  The format of
 the Server Unicast option is:
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          OPTION_UNICAST       |        option-len             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  |                       server-address                          |
  |                                                               |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code     OPTION_UNICAST (12).
    option-len      16.
    server-address  The IP address to which the client should send
                    messages delivered using unicast.
 The server specifies the IPv6 address to which the client is to send
 unicast messages in the server-address field.  When a client receives
 this option, where permissible and appropriate, the client sends
 messages directly to the server using the IPv6 address specified in
 the server-address field of the option.
 When the server sends a Unicast option to the client, some messages
 from the client will not be relayed by Relay Agents, and will not
 include Relay Agent options from the Relay Agents.  Therefore, a
 server should only send a Unicast option to a client when Relay
 Agents are not sending Relay Agent options.  A DHCP server rejects
 any messages sent inappropriately using unicast to ensure that
 messages are relayed by Relay Agents when Relay Agent options are in
 use.
 Details about when the client may send messages to the server using
 unicast are in section 18.

22.13. Status Code Option

 This option returns a status indication related to the DHCP message
 or option in which it appears.  The format of the Status Code option
 is:

Droms, et al. Standards Track [Page 82] RFC 3315 DHCP for IPv6 July 2003

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |       OPTION_STATUS_CODE      |         option-len            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          status-code          |                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
  .                                                               .
  .                        status-message                         .
  .                                                               .
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code          OPTION_STATUS_CODE (13).
    option-len           2 + length of status-message.
    status-code          The numeric code for the status encoded in
                         this option.  The status codes are defined in
                         section 24.4.
    status-message       A UTF-8 encoded text string suitable for
                         display to an end user, which MUST NOT be
                         null-terminated.
 A Status Code option may appear in the options field of a DHCP
 message and/or in the options field of another option.  If the Status
 Code option does not appear in a message in which the option could
 appear, the status of the message is assumed to be Success.

22.14. Rapid Commit Option

 The Rapid Commit option is used to signal the use of the two message
 exchange for address assignment.  The format of the Rapid Commit
 option is:
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |      OPTION_RAPID_COMMIT      |               0               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code     OPTION_RAPID_COMMIT (14).
    option-len      0.
 A client MAY include this option in a Solicit message if the client
 is prepared to perform the Solicit-Reply message exchange described
 in section 17.1.1.

Droms, et al. Standards Track [Page 83] RFC 3315 DHCP for IPv6 July 2003

 A server MUST include this option in a Reply message sent in response
 to a Solicit message when completing the Solicit-Reply message
 exchange.
 DISCUSSION:
    Each server that responds with a Reply to a Solicit that includes
    a Rapid Commit option will commit the assigned addresses in the
    Reply message to the client, and will not receive any confirmation
    that the client has received the Reply message.  Therefore, if
    more than one server responds to a Solicit that includes a Rapid
    Commit option, some servers will commit addresses that are not
    actually used by the client.
    The problem of unused addresses can be minimized, for example, by
    designing the DHCP service so that only one server responds to the
    Solicit or by using relatively short lifetimes for assigned
    addresses.

22.15. User Class Option

 The User Class option is used by a client to identify the type or
 category of user or applications it represents.
 The format of the User Class option is:
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       OPTION_USER_CLASS       |          option-len           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                          user-class-data                      .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code          OPTION_USER_CLASS (15).
    option-len           Length of user class data field.
    user-class-data      The user classes carried by the client.
 The information contained in the data area of this option is
 contained in one or more opaque fields that represent the user class
 or classes of which the client is a member.  A server selects
 configuration information for the client based on the classes
 identified in this option.  For example, the User Class option can be
 used to configure all clients of people in the accounting department

Droms, et al. Standards Track [Page 84] RFC 3315 DHCP for IPv6 July 2003

 with a different printer than clients of people in the marketing
 department.  The user class information carried in this option MUST
 be configurable on the client.
 The data area of the user class option MUST contain one or more
 instances of user class data.  Each instance of the user class data
 is formatted as follows:
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
    |        user-class-len         |          opaque-data          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
 The user-class-len is two octets long and specifies the length of the
 opaque user class data in network byte order.
 A server interprets the classes identified in this option according
 to its configuration to select the appropriate configuration
 information for the client.  A server may use only those user classes
 that it is configured to interpret in selecting configuration
 information for a client and ignore any other user classes.  In
 response to a message containing a User Class option, a server
 includes a User Class option containing those classes that were
 successfully interpreted by the server, so that the client can be
 informed of the classes interpreted by the server.

22.16. Vendor Class Option

 This option is used by a client to identify the vendor that
 manufactured the hardware on which the client is running.  The
 information contained in the data area of this option is contained in
 one or more opaque fields that identify details of the hardware
 configuration.  The format of the Vendor Class option is:
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      OPTION_VENDOR_CLASS      |           option-len          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       enterprise-number                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                       vendor-class-data                       .
    .                             . . .                             .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code          OPTION_VENDOR_CLASS (16).
    option-len           4 + length of vendor class data field.

Droms, et al. Standards Track [Page 85] RFC 3315 DHCP for IPv6 July 2003

    enterprise-number    The vendor's registered Enterprise Number as
                         registered with IANA [6].
    vendor-class-data    The hardware configuration of the host on
                         which the client is running.
 The vendor-class-data is composed of a series of separate items, each
 of which describes some characteristic of the client's hardware
 configuration.  Examples of vendor-class-data instances might include
 the version of the operating system the client is running or the
 amount of memory installed on the client.
 Each instance of the vendor-class-data is formatted as follows:
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
    |       vendor-class-len        |          opaque-data          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
 The vendor-class-len is two octets long and specifies the length of
 the opaque vendor class data in network byte order.

22.17. Vendor-specific Information Option

 This option is used by clients and servers to exchange
 vendor-specific information.
 The format of the Vendor-specific Information option is:
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      OPTION_VENDOR_OPTS       |           option-len          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       enterprise-number                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                          option-data                          .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code          OPTION_VENDOR_OPTS (17)
    option-len           4 + length of option-data field
    enterprise-number    The vendor's registered Enterprise Number as
                         registered with IANA [6].

Droms, et al. Standards Track [Page 86] RFC 3315 DHCP for IPv6 July 2003

    option-data          An opaque object of option-len octets,
                         interpreted by vendor-specific code on the
                         clients and servers
 The definition of the information carried in this option is vendor
 specific.  The vendor is indicated in the enterprise-number field.
 Use of vendor-specific information allows enhanced operation,
 utilizing additional features in a vendor's DHCP implementation.  A
 DHCP client that does not receive requested vendor-specific
 information will still configure the host device's IPv6 stack to be
 functional.
 The encapsulated vendor-specific options field MUST be encoded as a
 sequence of code/length/value fields of identical format to the DHCP
 options field.  The option codes are defined by the vendor identified
 in the enterprise-number field and are not managed by IANA.  Each of
 the encapsulated options is formatted as follows:
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          opt-code             |             option-len        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                          option-data                          .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    opt-code             The code for the encapsulated option.
    option-len           An unsigned integer giving the length of the
                         option-data field in this encapsulated option
                         in octets.
    option-data          The data area for the encapsulated option.
 Multiple instances of the Vendor-specific Information option may
 appear in a DHCP message.  Each instance of the option is interpreted
 according to the option codes defined by the vendor identified by the
 Enterprise Number in that option.

22.18. Interface-Id Option

 The relay agent MAY send the Interface-id option to identify the
 interface on which the client message was received.  If a relay agent
 receives a Relay-reply message with an Interface-id option, the relay
 agent relays the message to the client through the interface
 identified by the option.

Droms, et al. Standards Track [Page 87] RFC 3315 DHCP for IPv6 July 2003

 The format of the Interface ID option is:
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |      OPTION_INTERFACE_ID      |         option-len            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  .                                                               .
  .                         interface-id                          .
  .                                                               .
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code          OPTION_INTERFACE_ID (18).
    option-len           Length of interface-id field.
    interface-id         An opaque value of arbitrary length generated
                         by the relay agent to identify one of the
                         relay agent's interfaces.
 The server MUST copy the Interface-Id option from the Relay-Forward
 message into the Relay-Reply message the server sends to the relay
 agent in response to the Relay-Forward message.  This option MUST NOT
 appear in any message except a Relay-Forward or Relay-Reply message.
 Servers MAY use the Interface-ID for parameter assignment policies.
 The Interface-ID SHOULD be considered an opaque value, with policies
 based on exact match only; that is, the Interface-ID SHOULD NOT be
 internally parsed by the server.  The Interface-ID value for an
 interface SHOULD be stable and remain unchanged, for example, after
 the relay agent is restarted; if the Interface-ID changes, a server
 will not be able to use it reliably in parameter assignment policies.

22.19. Reconfigure Message Option

 A server includes a Reconfigure Message option in a Reconfigure
 message to indicate to the client whether the client responds with a
 Renew message or an Information-request message.  The format of this
 option is:
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |      OPTION_RECONF_MSG        |         option-len            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |    msg-type   |
  +-+-+-+-+-+-+-+-+

Droms, et al. Standards Track [Page 88] RFC 3315 DHCP for IPv6 July 2003

    option-code          OPTION_RECONF_MSG (19).
    option-len           1.
    msg-type             5 for Renew message, 11 for
                         Information-request message.
 The Reconfigure Message option can only appear in a Reconfigure
 message.

22.20. 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.  The default behavior, in the absence of this
 option, means unwillingness to accept Reconfigure messages, or
 instruction not to accept Reconfigure messages, for the client and
 server messages, respectively.  The following figure gives the format
 of the Reconfigure Accept option:
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |     OPTION_RECONF_ACCEPT      |               0               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    option-code   OPTION_RECONF_ACCEPT (20).
    option-len    0.

23. Security Considerations

 The threat to DHCP is inherently an insider threat (assuming a
 properly configured network where DHCPv6 ports are blocked on the
 perimeter gateways of the enterprise).  Regardless of the gateway
 configuration, however, the potential attacks by insiders and
 outsiders are the same.
 Use of manually configured preshared keys for IPsec between relay
 agents and servers does not defend against replayed DHCP messages.
 Replayed messages can represent a DOS attack through exhaustion of
 processing resources, but not through mis-configuration or exhaustion
 of other resources such as assignable addresses.
 One attack specific to a DHCP client is the establishment of a
 malicious server with the intent of providing incorrect configuration
 information to the client.  The motivation for doing so may be to

Droms, et al. Standards Track [Page 89] RFC 3315 DHCP for IPv6 July 2003

 mount a "man in the middle" attack that causes the client to
 communicate with a malicious server instead of a valid server for
 some service such as DNS or NTP.  The malicious server may also mount
 a denial of service attack through misconfiguration of the client
 that causes all network communication from the client to fail.
 There is another threat to DHCP clients from mistakenly or
 accidentally configured DHCP servers that answer DHCP client requests
 with unintentionally incorrect configuration parameters.
 A DHCP client may also be subject to attack through the receipt of a
 Reconfigure message from a malicious server that causes the client to
 obtain incorrect configuration information from that server.  Note
 that although a client sends its response (Renew or
 Information-request message) through a relay agent and, therefore,
 that response will only be received by servers to which DHCP messages
 are relayed, a malicious server could send a Reconfigure message to a
 client, followed (after an appropriate delay) by a Reply message that
 would be accepted by the client.  Thus, a malicious server that is
 not on the network path between the client and the server may still
 be able to mount a Reconfigure attack on a client.  The use of
 transaction IDs that are cryptographically sound and cannot easily be
 predicted will also reduce the probability that such an attack will
 be successful.
 The threat specific to a DHCP server is an invalid client
 masquerading as a valid client.  The motivation for this may be for
 theft of service, or to circumvent auditing for any number of
 nefarious purposes.
 The threat common to both the client and the server is the resource
 "denial of service" (DoS) attack.  These attacks typically involve
 the exhaustion of available addresses, or the exhaustion of CPU or
 network bandwidth, and are present anytime there is a shared
 resource.
 In the case where relay agents add additional options to Relay
 Forward messages, the messages exchanged between relay agents and
 servers may be used to mount a "man in the middle" or denial of
 service attack.
 This threat model does not consider the privacy of the contents of
 DHCP messages to be important.  DHCP is not used to exchange
 authentication or configuration information that must be kept secret
 from other networks nodes.

Droms, et al. Standards Track [Page 90] RFC 3315 DHCP for IPv6 July 2003

 DHCP authentication provides for authentication of the identity of
 DHCP clients and servers, and for the integrity of messages delivered
 between DHCP clients and servers.  DHCP authentication does not
 provide any privacy for the contents of DHCP messages.
 The Delayed Authentication protocol described in section 21.4 uses a
 secret key that is shared between a client and a server.  The use of
 a "DHCP realm" in the shared key allows identification of
 administrative domains so that a client can select the appropriate
 key or keys when roaming between administrative domains.  However,
 the Delayed Authentication protocol does not define any mechanism for
 sharing of keys, so a client may require separate keys for each
 administrative domain it encounters.  The use of shared keys may not
 scale well and does not provide for repudiation of compromised keys.
 This protocol is focused on solving the intradomain problem where the
 out-of-band exchange of a shared key is feasible.
 Because of the opportunity for attack through the Reconfigure
 message, a DHCP client MUST discard any Reconfigure message that does
 not include authentication or that does not pass the validation
 process for the authentication protocol.
 The Reconfigure Key protocol described in section 21.5 provides
 protection against the use of a Reconfigure message by a malicious
 DHCP server to mount a denial of service or man-in-the-middle attack
 on a client.  This protocol can be compromised by an attacker that
 can intercept the initial message in which the DHCP server sends the
 key to the client.
 Communication between a server and a relay agent, and communication
 between relay agents, can be secured through the use of IPSec, as
 described in section 21.1.  The use of manual configuration and
 installation of static keys are acceptable in this instance because
 relay agents and the server will belong to the same administrative
 domain and the relay agents will require other specific configuration
 (for example, configuration of the DHCP server address) as well as
 the IPSec configuration.

24. IANA Considerations

 This document defines several new name spaces associated with DHCPv6
 and DHCPv6 options:
  1. Message types
  1. Status codes
  1. DUID

Droms, et al. Standards Track [Page 91] RFC 3315 DHCP for IPv6 July 2003

  1. Option codes
 IANA has established a registry of values for each of these name
 spaces, which are described in the remainder of this section.  These
 name spaces will be managed by the IANA and all will be managed
 separately from the name spaces defined for DHCPv4.
 New multicast addresses, message types, status codes, and DUID types
 are assigned via Standards Action [11].
 New DHCP option codes are tentatively assigned after the
 specification for the associated option, published as an Internet
 Draft, has received expert review by a designated expert [11].  The
 final assignment of DHCP option codes is through Standards Action, as
 defined in RFC 2434 [11].
 This document also references three name spaces in section 21 that
 are associated with the Authentication Option (section 22.11).  These
 name spaces are defined by the authentication mechanism for DHCPv4 in
 RFC 3118 [4].
 The authentication name spaces currently registered by IANA will
 apply to both DHCPv6 and DHCPv4.  In the future, specifications that
 define new Protocol, Algorithm and RDM mechanisms will explicitly
 define whether the new mechanisms are used with DHCPv4, DHCPv6 or
 both.

24.1. Multicast Addresses

 Section 5.1 defines the following multicast addresses, which have
 been assigned by IANA for use by DHCPv6:
    All_DHCP_Relay_Agents_and_Servers address:   FF02::1:2
    All_DHCP_Servers address:                    FF05::1:3

Droms, et al. Standards Track [Page 92] RFC 3315 DHCP for IPv6 July 2003

24.2. DHCP Message Types

 IANA has recorded the following message types (defined in section
 5.3).  IANA will maintain the registry of DHCP message types.
    SOLICIT               1
    ADVERTISE             2
    REQUEST               3
    CONFIRM               4
    RENEW                 5
    REBIND                6
    REPLY                 7
    RELEASE               8
    DECLINE               9
    RECONFIGURE           10
    INFORMATION-REQUEST   11
    RELAY-FORW            12
    RELAY-REPL            13

Droms, et al. Standards Track [Page 93] RFC 3315 DHCP for IPv6 July 2003

24.3. DHCP Options

 IANA has recorded the following option-codes (as defined in section
 22).  IANA will maintain the registry of DHCP option codes.
    OPTION_CLIENTID       1
    OPTION_SERVERID       2
    OPTION_IA_NA          3
    OPTION_IA_TA          4
    OPTION_IAADDR         5
    OPTION_ORO            6
    OPTION_PREFERENCE     7
    OPTION_ELAPSED_TIME   8
    OPTION_RELAY_MSG      9
    OPTION_AUTH           11
    OPTION_UNICAST        12
    OPTION_STATUS_CODE    13
    OPTION_RAPID_COMMIT   14
    OPTION_USER_CLASS     15
    OPTION_VENDOR_CLASS   16
    OPTION_VENDOR_OPTS    17
    OPTION_INTERFACE_ID   18
    OPTION_RECONF_MSG     19
    OPTION_RECONF_ACCEPT  20

Droms, et al. Standards Track [Page 94] RFC 3315 DHCP for IPv6 July 2003

24.4. Status Codes

 IANA has recorded the status codes defined in the following table.
 IANA will manage the definition of additional status codes in the
 future.
 Name         Code Description
 ----------   ---- -----------
 Success         0 Success.
 UnspecFail      1 Failure, reason unspecified; this
                   status code is sent by either a client
                   or a server to indicate a failure
                   not explicitly specified in this
                   document.
 NoAddrsAvail    2 Server has no addresses available to assign to
                   the IA(s).
 NoBinding       3 Client record (binding) unavailable.
 NotOnLink       4 The prefix for the address is not appropriate for
                   the link to which the client is attached.
 UseMulticast    5 Sent by a server to a client to force the
                   client to send messages to the server.
                   using the All_DHCP_Relay_Agents_and_Servers
                   address.

24.5. DUID

 IANA has recorded the following DUID types (as defined in section
 9.1).  IANA will manage the definition of additional DUID types in
 the future.
    DUID-LLT                       1
    DUID-EN                        2
    DUID-LL                        3

25. Acknowledgments

 Thanks to the DHC Working Group and the members of the IETF for their
 time and input into the specification.  In particular, thanks also
 for the consistent input, ideas, and review by (in alphabetical
 order) Bernard Aboba, Bill Arbaugh, Thirumalesh Bhat, Steve Bellovin,
 A. K. Vijayabhaskar, Brian Carpenter, Matt Crawford, Francis Dupont,
 Richard Hussong, Kim Kinnear, Fredrik Lindholm, Tony Lindstrom, Josh
 Littlefield, Gerald Maguire, Jack McCann, Shin Miyakawa, Thomas
 Narten, Erik Nordmark, Jarno Rajahalme, Yakov Rekhter, Mark Stapp,
 Matt Thomas, Sue Thomson, Tatuya Jinmei and Phil Wells.

Droms, et al. Standards Track [Page 95] RFC 3315 DHCP for IPv6 July 2003

 Thanks to Steve Deering and Bob Hinden, who have consistently taken
 the time to discuss the more complex parts of the IPv6
 specifications.
 And, thanks to Steve Deering for pointing out at IETF 51 in London
 that the DHCPv6 specification has the highest revision number of any
 Internet Draft.

26. References

26.1. Normative References

 [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [2]  Crawford, M., "Transmission of IPv6 Packets over Ethernet
      Networks", RFC 2464, December 1998.
 [3]  Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
      Specification", RFC 2460, December 1998.
 [4]  Droms, R., Ed. and W. Arbaugh, Ed., "Authentication for DHCP
      Messages", RFC 3118, June 2001.
 [5]  Hinden, R. and S. Deering, "IP Version 6 Addressing
      Architecture", RFC 2373, July 1998.
 [6]  IANA.  Private Enterprise Numbers.
      http://www.iana.org/assignments/enterprise-numbers.html.
 [7]  Kent, S. and R. Atkinson, "Security Architecture for the
      Internet Protocol", RFC 2401, November 1998.
 [8]  Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-Hashing
      for Message Authentication", RFC 2104, February 1997.
 [9]  Mills, D., "Network Time Protocol (Version 3) Specification,
      Implementation", RFC 1305, March 1992.
 [10] Mockapetris, P., "Domain names - implementation and
      specification", RFC 1035, November 1987.
 [11] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
      Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
 [12] Narten, T. and R. Draves, "Privacy Extensions for Stateless
      Address Autoconfiguration in IPv6", RFC 3041, January 2001.

Droms, et al. Standards Track [Page 96] RFC 3315 DHCP for IPv6 July 2003

 [13] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for
      IP Version 6 (IPv6)", RFC 2461, December 1998.
 [14] Plummer, D.C., "Ethernet Address Resolution Protocol:  Or
      converting network protocol addresses to 48.bit Ethernet address
      for transmission on Ethernet hardware", STD 37, RFC 826,
      November 1982.
 [15] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August
      1980.
 [16] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April
      1992.
 [17] Thomson, S. and T. Narten, "IPv6 Stateless Address
      Autoconfiguration", RFC 2462, December 1998.

26.2. Informative References

 [18] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
      Extensions", RFC 2132, March 1997.
 [19] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
      March 1997.
 [20] R. Droms, Ed.  DNS Configuration options for DHCPv6.  April
      2002.  Work in Progress.
 [21] A. K. Vijayabhaskar.  Time Configuration Options for DHCPv6.
      May 2002.  Work in Progress.
 [22] Vixie, P., Ed., Thomson, S., Rekhter, Y. and J. Bound, "Dynamic
      Updates in the Domain Name System (DNS UPDATE)", RFC 2136, April
      1997.

Droms, et al. Standards Track [Page 97] RFC 3315 DHCP for IPv6 July 2003

A. Appearance of Options in Message Types

 The following table indicates with a "*" the options are allowed in
 each DHCP message type:
         Client Server IA_NA  Option Pref  Time Relay Auth. Server
           ID     ID   IA_TA  Request            Msg.       Unica.
 Solicit   *             *      *           *           *
 Advert.   *      *      *            *                 *
 Request   *      *      *      *           *           *
 Confirm   *             *      *           *           *
 Renew     *      *      *      *           *           *
 Rebind    *             *      *           *           *
 Decline   *      *      *      *           *           *
 Release   *      *      *      *           *           *
 Reply     *      *      *            *                 *     *
 Reconf.   *      *             *                       *
 Inform.   * (see note)         *           *           *
 R-forw.                                          *     *
 R-repl.                                          *     *
 NOTE:
    Only included in Information-Request messages that are sent
    in response to a Reconfigure (see section 19.4.3).
          Status  Rap. User  Vendor Vendor Inter. Recon. Recon.
           Code  Comm. Class Class  Spec.    ID    Msg.  Accept
 Solicit           *     *     *      *                    *
 Advert.    *            *     *      *                    *
 Request                 *     *      *                    *
 Confirm                 *     *      *
 Renew                   *     *      *                    *
 Rebind                  *     *      *                    *
 Decline                 *     *      *
 Release                 *     *      *
 Reply      *      *     *     *      *                    *
 Reconf.                                            *
 Inform.                 *     *      *                    *
 R-forw.                 *     *      *      *
 R-repl.                 *     *      *      *

Droms, et al. Standards Track [Page 98] RFC 3315 DHCP for IPv6 July 2003

B. Appearance of Options in the Options Field of DHCP Options

 The following table indicates with a "*" where options can appear in
 the options field of other options:
              Option  IA_NA/ IAADDR Relay  Relay
              Field   IA_TA         Forw.  Reply
 Client ID      *
 Server ID      *
 IA_NA/IA_TA    *
 IAADDR                 *
 ORO            *
 Preference     *
 Elapsed Time   *
 Relay Message                        *      *
 Authentic.     *
 Server Uni.    *
 Status Code    *       *       *
 Rapid Comm.    *
 User Class     *
 Vendor Class   *
 Vendor Info.   *
 Interf. ID                           *      *
 Reconf. MSG.   *
 Reconf. Accept *
 Note: "Relay Forw" / "Relay Reply" options appear in the options
 field of the message but may only appear in these messages.

Chair's Address

 The working group can be contacted via the current chair:
 Ralph Droms
 Cisco Systems
 1414 Massachusetts Avenue
 Boxborough, MA 01719
 Phone: (978) 936-1674
 EMail: rdroms@cisco.com

Droms, et al. Standards Track [Page 99] RFC 3315 DHCP for IPv6 July 2003

Authors' Addresses

 Jim Bound
 Hewlett Packard Corporation
 ZK3-3/W20
 110 Spit Brook Road
 Nashua, NH 03062-2698
 USA
 Phone:  +1 603 884 0062
 EMail:  Jim.Bound@hp.com
 Bernie Volz
 116 Hawkins Pond Road
 Center Harbor, NH  03226-3103
 USA
 Phone:  +1-508-259-3734
 EMail:  volz@metrocast.net
 Ted Lemon
 Nominum, Inc.
 950 Charter Street
 Redwood City, CA 94043
 USA
 EMail:  Ted.Lemon@nominum.com
 Charles E. Perkins
 Communications Systems Lab
 Nokia Research Center
 313 Fairchild Drive
 Mountain View, California 94043
 USA
 Phone:  +1-650 625-2986
 EMail:  charles.perkins@nokia.com
 Mike Carney
 Sun Microsystems, Inc
 17 Network Circle
 Menlo Park, CA 94025
 USA
 Phone:  +1-650-786-4171
 EMail:  michael.carney@sun.com

Droms, et al. Standards Track [Page 100] RFC 3315 DHCP for IPv6 July 2003

Full Copyright Statement

 Copyright (C) The Internet Society (2003).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Droms, et al. Standards Track [Page 101]

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