WDIFF

draft-ietf-dhc-dhcpv6-21.txt --> draft-ietf-dhc-dhcpv6-22.txt

Internet Engineering Task Force J. Bound
INTERNET DRAFT Compaq
DHC Working Group M. Carney
Obsoletes: draft-ietf-dhc-dhcpv6-20.txt draft-ietf-dhc-dhcpv6-21.txt Sun Microsystems, Inc
C. Perkins
Nokia Research Center
R. Droms(ed.)
Cisco Systems
21 Nov Dec 2001

Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
draft-ietf-dhc-dhcpv6-21.txt
draft-ietf-dhc-dhcpv6-22.txt

Status of This Memo

This document is a submission by the Dynamic Host Configuration
Working Group of the Internet Engineering Task Force (IETF). Comments
should be submitted to the dhcwg@ietf.org mailing list.

Distribution of this memo is unlimited.

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.

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

The list of current Internet-Drafts can be accessed at:
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at:
http://www.ietf.org/shadow.html.

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" [20], [23], and can be used separately
or concurrently with the latter to obtain configuration parameters.

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Contents

Status of This Memo i

Abstract i

1. Introduction 1

2. Requirements 2

3. Background 2

4. Design Goals 3

5. Non-Goals 3 4

6. Terminology 4
6.1. IPv6 Terminology . . . . . . . . . . . . . . . . . . . . 4
6.2. DHCP Terminology . . . . . . . . . . . . . . . . . . . . 5

7. DHCP Constants 6 7
7.1. Multicast Addresses . . . . . . . . . . . . . . . . . . . 7
7.2. UDP ports . . . . . . . . . . . . . . . . . . . . . . . . 7
7.3. DHCP message types . . . . . . . . . . . . . . . . . . . 7 8
7.4. Status Codes . . . . . . . . . . . . . . . . . . . . . . 9
7.4.1. Generic Status Codes . . . . . . . . . . . . . . 9
7.4.2. Server-specific Status Codes . . . . . . . . . . 9 11
7.5. Configuration Variables . . . . . . . . . . . . . . . . . 10 11

8. Message Formats 10 12
8.1. DHCP Solicit Message Format . . . . . . . . . . . . . . . 11 12
8.2. DHCP Advertise Message Format . . . . . . . . . . . . . . 11 12
8.3. DHCP Request Message Format . . . . . . . . . . . . . . . 12 13
8.4. DHCP Confirm Message Format . . . . . . . . . . . . . . . 12 13
8.5. DHCP Renew Message Format . . . . . . . . . . . . . . . . 12 13
8.6. DHCP Rebind Message Format . . . . . . . . . . . . . . . 12 14
8.7. DHCP Reply Message Format . . . . . . . . . . . . . . . . 13 14
8.8. DHCP Release Message Format . . . . . . . . . . . . . . . 13 14
8.9. DHCP Decline Message Format . . . . . . . . . . . . . . . 13 14
8.10. DHCP Reconfigure-init Reconfigure Message Format . . . . . . . . . . 13
8.11. Inform Message Format . . . . . . . 15
8.11. Information-Request Message Format . . . . . . . . . . . 14 15

9. Relay messages 14 16
9.1. Relay-forward message . . . . . . . . . . . . . . . . . . 14 16
9.2. Relay-reply message . . . . . . . . . . . . . . . . . . . 15 17

10. Representation and use of domain names 17

11. DHCP unique identifier (DUID) 15
10.1. 17
11.1. DUID contents . . . . . . . . . . . . . . . . . . . . . . 16
10.2. 18
11.2. DUID based on link-layer address plus time . . . . . . . 16
10.3. 18
11.3. Vendor-assigned unique ID. ID . . . . . . . . . . . . . . . 17
10.4. . 19

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11.4. Link-layer address . . . . . . . . . . . . . . . . . . . 18

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11. 20

12. Identity association 18

12. 20

13. Selecting addresses for assignment to an IA 19

13. 21

14. Management of temporary addresses 22

15. Reliability of Client Initiated Message Exchanges 19

14. 23

16. Message validation 21
14.1. 24
16.1. Use of Transaction-ID field . . . . . . . . . . . . . . . 21
14.2. 25
16.2. Solicit message . . . . . . . . . . . . . . . . . . . . . 21
14.3. 25
16.3. Advertise message . . . . . . . . . . . . . . . . . . . . 21
14.4. 25
16.4. Request message . . . . . . . . . . . . . . . . . . . . . 22
14.5. 25
16.5. Confirm message . . . . . . . . . . . . . . . . . . . . . 22
14.6. 25
16.6. Renew message . . . . . . . . . . . . . . . . . . . . . . 22
14.7. 26
16.7. Rebind message . . . . . . . . . . . . . . . . . . . . . 22
14.8. 26
16.8. Decline messages . . . . . . . . . . . . . . . . . . . . 22
14.9. 26
16.9. Release message . . . . . . . . . . . . . . . . . . . . . 23
14.10. 26
16.10. Reply message . . . . . . . . . . . . . . . . . . . . . . 23
14.11. Reconfigure-init 26
16.11. Reconfigure message . . . . . . . . . . . . . . . . 23
14.12. . . . 27
16.12. Inform message . . . . . . . . . . . . . . . . . . . . . 23
14.13. 27
16.13. Relay-forward message . . . . . . . . . . . . . . . . . . 23
14.14. 27
16.14. Relay-reply message . . . . . . . . . . . . . . . . . . . 23

15. 27

17. DHCP Server Solicitation 24
15.1. 27
17.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 24
15.1.1. 27
17.1.1. Creation of Solicit messages . . . . . . . . . . 24
15.1.2. 28
17.1.2. Transmission of Solicit Messages . . . . . . . . 24
15.1.3. 28
17.1.3. Receipt of Advertise messages . . . . . . . . . . 25
15.2. 29
17.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 26
15.2.1. 30
17.2.1. Receipt of Solicit messages . . . . . . . . . . . 26
15.2.2. 30
17.2.2. Creation and transmission of Advertise messages . 26

16. 30

18. DHCP Client-Initiated Configuration Exchange 27
16.1. 31
18.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 27
16.1.1. 31
18.1.1. Creation and transmission of Request messages . . 28
16.1.2. 31
18.1.2. Creation and transmission of Confirm messages . . 29
16.1.3. 33
18.1.3. Creation and transmission of Renew messages . . . 30
16.1.4. 34
18.1.4. Creation and transmission of Rebind messages . . 31
16.1.5. 35
18.1.5. Creation and Transmission of Inform messages . . 33
16.1.6. 36
18.1.6. Receipt of Reply message in response to a Request,
Confirm, Renew, Rebind or Inform message . 33
16.1.7. 37
18.1.7. Creation and transmission of Release messages . . 35
16.1.8. 39
18.1.8. Receipt of Reply message in response to a Release
message . . . . . . . . . . . . . . . . . 36
16.1.9. 40
18.1.9. Creation and transmission of Decline messages . . 36
16.1.10. 40
18.1.10. Receipt of Reply message in response to a Decline
message . . . . . . . . . . . . . . . . . 37
16.2. 41
18.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 38
16.2.1. 41
18.2.1. Receipt of Request messages . . . . . . . . . . . 38
16.2.2. 41
18.2.2. Receipt of Confirm messages . . . . . . . . . . . 39
16.2.3. 42

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18.2.3. Receipt of Renew messages . . . . . . . . . . . . 39
16.2.4. 43
18.2.4. Receipt of Rebind messages . . . . . . . . . . . 40
16.2.5. 44
18.2.5. Receipt of Inform messages . . . . . . . . . . . 41
16.2.6. 45
18.2.6. Receipt of Release messages . . . . . . . . . . . 42

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16.2.7. 45
18.2.7. Receipt of Decline messages . . . . . . . . . . . 42
16.2.8. 46
18.2.8. Receipt of Decline Information-Request messages . . . . . . . . . . . 43
16.2.9. 46
18.2.9. Sending of Reply messages . . . . . . . . . . . . 43

17. 46

19. DHCP Server-Initiated Configuration Exchange 43
17.1. 47
19.1. Server Behavior . . . . . . . . . . . . . . . . . . . . . 43
17.1.1. 47
19.1.1. Creation and transmission of Reconfigure-init Reconfigure messages 47
19.1.2. Time out and retransmission of Reconfigure
messages . . . . . . . . . . . . . . . . . 43
17.1.2. Time out and retransmission 48
19.1.3. Receipt of Reconfigure-init Renew messages . . . . . . . . . . . . . . . . . 44
17.1.3. 48
19.2. Receipt of Rebind Information-request messages . . . . . . . . . . . 44
17.2. 48
19.3. Client Behavior . . . . . . . . . . . . . . . . . . . . . 45
17.2.1. 49
19.3.1. Receipt of Reconfigure-init Reconfigure messages . . . . . . 45
17.2.2. . . . 49
19.3.2. Creation and sending of Rebind Renew messages . . . . . 46
17.2.3. 50
19.3.3. Creation and sending of Renew messages . . . . . 50
19.3.4. Time out and retransmission of Rebind Renew or
Information-request messages . 46
17.2.4. . . . . . . 50
19.3.5. Receipt of Reply messages . . . . . . . . . . . . 46

18. 50

20. Relay Behavior 46
18.1. 50
20.1. Relaying of client messages . . . . . . . . . . . . . . . 46
18.2. 50
20.2. Relaying of server messages . . . . . . . . . . . . . . . 47

19. 51

21. Authentication of DHCP messages 47
19.1. 51
21.1. DHCP threat model . . . . . . . . . . . . . . . . . . . . 48
19.2. 52
21.2. Security of messages sent between servers and relay agents 48
19.3. 52
21.3. Summary of DHCP authentication . . . . . . . . . . . . . 48
19.4. 52
21.4. Replay detection . . . . . . . . . . . . . . . . . . . . 49
19.5. 53
21.5. Configuration token protocol . . . . . . . . . . . . . . 49
19.6. 53
21.6. Delayed authentication protocol . . . . . . . . . . . . . 49
19.6.1. 54
21.6.1. Management issues in the delayed authentication
protocol . . . . . . . . . . . . . . . . . 50
19.6.2. 54
21.6.2. Use of the Authentication option in the delayed
authentication protocol . . . . . . . . . 50
19.6.3. 54
21.6.3. Message validation . . . . . . . . . . . . . . . 51
19.6.4. 55
21.6.4. Key utilization . . . . . . . . . . . . . . . . . 51
19.6.5. 55
21.6.5. Client considerations for delayed authentication
protocol . . . . . . . . . . . . . . . . . 52
19.6.6. 56
21.6.6. Server considerations for delayed authentication
protocol . . . . . . . . . . . . . . . . . 53

20. 58

22. DHCP options 54
20.1. 58
22.1. Format of DHCP options . . . . . . . . . . . . . . . . . 54
20.2. 59
22.2. DHCP unique identifier option . . . . . . . . . . . . . . 54
20.3. 59
22.3. Identity association option . . . . . . . . . . . . . . . 55
20.4. 60
22.4. IA Address option . . . . . . . . . . . . . . . . . . . . 56
20.5. 62
22.5. Requested Temporary Addresses (RTA) Option . . . . . . . 63
22.6. Option request option . . . . . . . . . . . . . . . . . . 57
20.6. 64
22.7. Preference option . . . . . . . . . . . . . . . . . . . . 58
20.7. 64

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22.8. Elapsed Time . . . . . . . . . . . . . . . . . . . . . . 58
20.8. 65
22.9. Client message option . . . . . . . . . . . . . . . . . . 58
20.9. 65
22.10. Server message option . . . . . . . . . . . . . . . . . . 59
20.10. 66
22.11. DSTM Global IPv4 Address Option . . . . . . . . . . . . . 59
20.11. 66
22.12. DSTM Tunnel EndPoint Option . . . . . . . . . . . . . . 67
22.13. Authentication option . . . . . . . . . . . . . . . . . . 60
20.12. 67
22.14. Server unicast option . . . . . . . . . . . . . . . . . . 61
20.13. 68
22.15. Domain Search Option . . . . . . . . . . . . . . . . . . 61

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20.14. 69
22.16. Domain Name Server Option . . . . . . . . . . . . . . . . 62
20.15. 70
22.17. Status Code Option . . . . . . . . . . . . . . . . . . . 63
20.16. 70
22.18. Circuit-ID Option . . . . . . . . . . . . . . . . . . . . 63
20.17. 71
22.19. User Class Option . . . . . . . . . . . . . . . . . . . . 64
20.18. 72
22.20. Vendor Class Option . . . . . . . . . . . . . . . . . . . 65

21. Security Considerations 66

22. Year 2000 considerations 66

23. IANA Considerations 66
23.1. Multicast addresses . . 72
22.21. SIP Servers Domain Name List . . . . . . . . . . . . . . 74
22.22. SIP Servers IPv6 Address List . . . . . . . 66
23.2. . . . . . . . 74

23. Security Considerations 75

24. Year 2000 considerations 75

25. IANA Considerations 75
25.1. Multicast addresses . . . . . . . . . . . . . . . . . . . 75
25.2. DHCPv6 message types . . . . . . . . . . . . . . . . . . 66
23.3. 75
25.3. DUID . . . . . . . . . . . . . . . . . . . . . . . . . . 67
23.4. 76
25.4. DHCPv6 options . . . . . . . . . . . . . . . . . . . . . 67
23.5. 76
25.5. Status codes . . . . . . . . . . . . . . . . . . . . . . 67
23.6. 76
25.6. Authentication option . . . . . . . . . . . . . . . . . . 67

24. 76

26. Acknowledgments 67 76

A. Full Copyright Statement 68 77

B. Appearance of Options in Message Types 78

C. Appearance of Options in the Options Field of DHCP Messages 79

References 68 79

Chair's Address 70 81

Authors' Addresses 70

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1. Introduction

This document describes DHCP for IPv6 (DHCP), a UDP [18] [20]
client/server protocol designed to reduce the cost of management
of IPv6 nodes in environments where network managers require more
control over the allocation of IPv6 addresses and configuration
of network stack parameters than that offered by "IPv6 Stateless
Address Autoconfiguration" [20]. [23]. DHCP is a stateful counterpart to
stateless autoconfiguration. Note that both stateful and stateless
autoconfiguration can be used concurrently in the same environment,

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leveraging the strengths of both mechanisms in order to reduce the
cost of ownership and management of network nodes.

DHCP reduces the cost of ownership by centralizing the management
of network resources such as IP addresses, routing information, OS
installation information, directory service information, and other
such information on a few DHCP servers, rather than distributing such
information in local configuration files among each all network node.
DHCP is designed to be easily extended to carry new configuration
parameters through the addition of new DHCP "options" defined to
carry this information.

Those readers familiar with DHCP for IPv4 [7] [8] will findDHCP find DHCP for
IPv6 provides a superset of features, the features of DHCP and benefits from
the additional

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backward compatibility with BOOTP [5]. [6].

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 [3]. [4].

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.

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 is includes the IPv6 Specification [6], [7], the IPv6 Addressing
Architecture [9], [10], IPv6 Stateless Address Autoconfiguration [20], [23],
IPv6 Neighbor Discovery Processing [16], [18], and Dynamic Updates to
DNS [21]. [24]. 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 [9] [10] 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. This means that a client can immediately use
its link-local address and a well-known multicast address to begin

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communications to discover neighbors on the link. For instance, a
client can send a Solicit message and locate a server or relay.

IPv6 Stateless Address Autoconfiguration [20] [23] specifies procedures
by which a node may autoconfigure addresses based on router
advertisements [16], [18], 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 (see Section 4).

IPv6 Neighbor Discovery [16] [18] is the node discovery protocol in IPv6
which replaces and enhances functions of ARP [17]. [19]. To understand

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IPv6 and stateless address autoconfiguration it is strongly
recommended that implementors understand IPv6 Neighbor Discovery.

Dynamic Updates to DNS [21] [24] 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. Design Goals

- DHCP is a mechanism rather than a policy. Network administrators
set their administrative policies through the configuration
parameters they place upon the DHCP servers in the DHCP domain
they're managing. DHCP is simply used to deliver parameters
according to that policy to each of the DHCP clients within the
domain.

- DHCP is compatible with IPv6 stateless address
autoconfiguration [20], [23], statically configured, non-participating
nodes and with existing network protocol implementations.

- DHCP does not require manual configuration of network parameters
on DHCP clients, except in cases where such configuration is
needed for security reasons. A node configuring itself using
DHCP should require no user intervention.

- DHCP does not require a server on each link. To allow for scale
and economy, DHCP must work across DHCP relays.

- DHCP clients can operate on a link without IPv6 routers present.

- DHCP will provide the ability to renumber network(s) when
required by network administrators [4]. [5].

- A DHCP client can make multiple, different requests for
configuration parameters when necessary from one or more DHCP
servers at any time.

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- DHCP will contain the appropriate time out and retransmission
mechanisms to efficiently operate in environments with high
latency and low bandwidth characteristics.

5. Non-Goals

This specification explicitly does not cover the following:

- Specification of a DHCP server to server protocol.

- How a DHCP server stores its DHCP data.

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- How to manage a DHCP domain or DHCP server.

- How a DHCP relay is configured or what sort of information it may
log.

6. Terminology

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

6.1. IPv6 Terminology

IPv6 terminology relevant to this specification from the IPv6
Protocol [6], [7], IPv6 Addressing Architecture [9], [10], and IPv6 Stateless
Address Autoconfiguration [20] [23] is included below.

address An IP layer identifier for an interface
or a set of interfaces.

unicast address An identifier for a single interface.
A packet sent to a unicast address is
delivered to the interface identified by
that 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.

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.

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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

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network interfaces, and E.164 addresses
for ISDN links.

link-local address An IPv6 address having link-only
scope, indicated by having the prefix
(FE80::0000/64), that can be used to
reach neighboring nodes attached to
the same link. Every interface has a
link-local address.

message A unit of data carried in a packet,
exchanged between DHCP agents and clients.

neighbor

neighbor A node attached to the same link.

node A device that implements IP.

packet An IP header plus payload.

prefix The initial bits of an address, or a
set of IP address 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.

6.2. DHCP Terminology

Terminology specific to DHCP can be found below.

agent address The address of a neighboring DHCP Agent
on the same link as the DHCP client.

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 and any other
configuration information assigned to

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the client. A binding is indexed by the
tuple <DUID, IAID>.

DHCP Dynamic Host Configuration Protocol
for IPv6. The terms DHCPv4 and DHCPv6
are used only in contexts where it is
necessary to avoid ambiguity.

configuration parameter An element of the configuration
information set on the server and
delivered to the client using DHCP.

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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 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 server (or server) A server is a node that responds to
requests from clients, and may or
may not be on the same link as the
client(s).

DHCP relay (or relay) A node that acts as an intermediary to
deliver DHCP messages between clients
and servers, and is on the same link as
a client.

DHCP agent (or agent) Either a DHCP server on the same link as
a client, or a DHCP relay.

DUID A DHCP Unique IDentifier for a client. client;
each DHCP client has exactly one DUID

Identity association (IA) A collection of addresses assigned to
a client. Each IA has an associated
IAID. An IA may have 0 or more addresses
associated with it.

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.

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message A unit of data carried in a packet,
exchanged between DHCP agents and
clients.

transaction-ID An unsigned integer to match responses
with replies initiated either by a
client or server.

7. DHCP Constants

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

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7.1. Multicast Addresses

DHCP makes use of the following multicast addresses:

All_DHCP_Agents address: FF02::1:2 This link-scoped multicast
address is used by clients to communicate with the
on-link agent(s) when they do not know the link-local
address(es) for those agents. All agents (servers and
relays) are members of this multicast group.

All_DHCP_Servers address: FF05::1:3 This site-scoped multicast
address is used by clients or relays to communicate
with server(s), either because they want to send
messages to all servers or because they do not know
the server(s) unicast address(es). Note that in order
for a client to use this address, it must have an
address of sufficient scope to be reachable by the
server(s). All servers within the site are members of
this multicast group.

7.2. UDP ports

DHCP uses the following destination UDP [18] [20] port numbers. While
source ports MAY be arbitrary, client implementations SHOULD permit
their specification through a local configuration parameter to
facilitate the use of DHCP through firewalls.

546 Client port. Used by servers as the destination port
for messages sent to clients and relays. Used by relay
agents as the destination port for messages sent to
clients.

547 Agent port. Used as the destination port by clients
for messages sent to agents. Used as the destination
port by relays for messages sent to servers.

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7.3. DHCP message types

DHCP defines the following message types. More detail on these
message types can be found in Section 8. Message types 0 and 13-255 not listed
here are reserved for future use. The message code for each message
type is shown with the message name.

SOLICIT (1) The Solicit message is used by clients to
locate servers.

ADVERTISE (2) The Advertise message is used by servers
responding to Solicits.

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REQUEST (3) The Request message is used by clients to
request configuration parameters from servers.

CONFIRM (4) The Confirm message is used by clients to
confirm that the addresses assigned to an IA
and the lifetimes for those addresses, as
well as the current configuration parameters
assigned by the server to the client are still
valid.

RENEW (5) The Renew message is used by clients to
update the addresses assigned to an IA and the
lifetimes for those addresses, as well as the
current configuration parameters assigned by
the server to the client. A client sends a
Renew message to the server that originally
populated the IA at time T1.

REBIND (6) The Rebind message is used by clients to extend
the lifetimes of addresses assigned to an IA,
as well as the current configuration parameters
assigned by the server to the client. A
client sends a Rebind message to all available
DHCP servers at time T2 only after the client
has been unable to contact the server that
originally populated the IA with a Rebind Renew
message.

REPLY (7) The Reply message is used by servers responding
to Request, Confirm, Renew, Rebind, Release and
Decline messages. In the case of responding to
a Request, Confirm, Renew or Rebind message,
the Reply contains configuration parameters
destined for the client.

RELEASE (8) The Release message is used by clients to
return
indicate to a server that the client will no
longer use one or more IP addresses to servers. in an IA.

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DECLINE (9) The Decline message is used by clients to
indicate that the client has determined that
one or more addresses in an IA are already
in use on the link to which the client is
connected.

RECONFIG-INIT

RECONFIGURE (10) The Reconfigure-init Reconfigure message is sent by server(s)
to inform client(s) that the server(s) has new
or updated configuration parameters, and that
the client(s) are to initiate a Request/Reply
transaction with the server(s) in order to
receive the updated information.

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INFORM

INFORMATION-REQUEST (11) The Inform Information-request message is sent
by clients to request configuration parameters
without the assignment of any IP addresses to
the client.

RELAY-FORW (12) The Relay-forward message is used by relays to
forward client messages to servers. The client
message is encapsulated in an option in the
Relay-forward message.

RELAY-REPL (13) The Relay-reply message is used by servers to
send messages to clients through a relay. The
server encapsulates the client message as an
option in the Relay-reply message, which the
relay extracts and forwards to the client.

7.4. Status Codes

This section describes status codes exchanged between DHCP
implementations. These status codes may appear in the Status Code
option or in the status field of an IA.

7.4.1. Generic Status Codes

The status codes in this section are used between clients and servers
to convey status conditions. The following table contains the status
codes, the name for each code (as used in this document) and a brief
description. Note that the numeric values do not start at 1, nor are
they consecutive. The status codes are organized in logical groups.

Name Code Description
---------- ---- -----------
Success 0 Success
UnspecFail 16 Failure, reason unspecified
AuthFailed 17 Authentication failed or nonexistent
PoorlyFormed 18 Poorly formed message
AddrUnavail 19 Addresses unavailable
OptionUnavail 20 Requested options unavailable

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7.4.2. Server-specific Status Codes

The status codes in this section are used by servers to convey status
conditions to clients. The following table contains the status
codes, the name for each code (as used in this document) and a brief
description. Note that the numeric values do not start at 1, nor are
they consecutive. The status codes are organized in logical groups.

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Name Code Description
---- ---- -----------
NoBinding 32 Client record (binding) unavailable
ConfNoMatch 33 Client record Confirm not doesn't match IA
RenwNoMatch 34 Client record Renew not doesn't match IA
RebdNoMatch 35 Client record Rebind not doesn't match IA
InvalidSource 36 Invalid Client IP address
NoServer
NoPrefixMatch 37 Relay cannot find Server Address
NoPrefixMatch 38 One or more prefixes of the addresses
in the IA is not valid for the link
from which the client message was received
ICMPError 64 Server unreachable (ICMP error)

7.5. Configuration Variables

This section presents a table of client and server configuration
variables and the default or initial values for these variables.

Parameter Default Description
-------------------------------------
MIN_SOL_DELAY 1 sec Min delay of first Solicit
MAX_SOL_DELAY 5 secs Max delay of first Solicit
SOL_TIMEOUT 500 msecs Initial Solicit timeout
SOL_MAX_RT 30 secs Max Solicit timeout value
REQ_TIMEOUT 250 msecs Initial Request timeout
REQ_MAX_RT 30 secs Max Request timeout value
REQ_MAX_RC 10 Max Request retry attempts
CNF_TIMEOUT 250 msecs Initial Confirm timeout
CNF_MAX_RT 1 sec Max Confirm timeout
CNF_MAX_RD 10 secs Max Confirm duration
REN_TIMEOUT 10 sec 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_TIMEOUT 500 ms Initial Inform timeout
INF_MAX_RT 30 secs Max Inform timeout value
REL_TIMEOUT 250 msecs Initial Release timeout
REL_MAX_RT 1 sec Max Release timeout
REL_MAX_RC 5 MAX Release/Decline attempts
DEC_TIMEOUT 250 msecs Initial Release timeout
DEC_MAX_RT 1 sec Max Release timeout
DEC_MAX_RC 5 MAX Release/Decline attempts

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8. Message Formats

All DHCP messages sent between clients and servers share an identical
fixed format header and a variable format area for options. Not all
fields in the header are used in every message.

All values in the message header and in options are in network byte order.

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The following diagram illustrates the format of DHCP message header: 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| server-address |
| (16 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. options .
. (variable) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The following sections describe the use of the fields in the DHCP
message header in each of the DHCP messages. In these descriptions,
fields that are not used in a message are marked as "unused". All
unused fields in a message MUST be transmitted as zeroes and ignored
by the receiver of the message.

8.1. DHCP Solicit Message Format

msg-type SOLICIT

transaction-ID An unsigned integer generated by the client used
to identify this Solicit message.

server-address (unused) (Unused) MUST be 0 zero

options See section 20. 22.

8.2. DHCP Advertise Message Format

msg-type ADVERTISE

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transaction-ID An unsigned integer used to identify this
Advertise message. Copied from the Solicit
message received from the client.

server-address The IP address of the server that generated this
message. The address must have sufficient scope
to be reachable from the client.

options See section 20.

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8.3. DHCP Request Message Format

msg-type REQUEST

transaction-ID An unsigned integer generated by the client used
to identify this Request message.

server-address The IP address of the server to which this
message is directed, copied from an Advertise
message.

options See section 20. 22.

8.4. DHCP Confirm Message Format

msg-type CONFIRM

transaction-ID An unsigned integer generated by the client used
to identify this Confirm message.

server-address MUST be zero.

options See section 20. 22.

8.5. DHCP Renew Message Format

msg-type RENEW

transaction-ID An unsigned integer generated by the client used
to identify this Renew message.

server-address The IP address of the server to which this Renew
message is directed, which MUST be the address
of the server from which the IAs in this message
were originally assigned.

options See section 20. 22.

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8.6. DHCP Rebind Message Format

msg-type REBIND

transaction-ID An unsigned integer generated by the client used
to identify this Rebind message.

server-address MUST be zero.

options See section 20.

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8.7. DHCP Reply Message Format

msg-type REPLY

transaction-ID An unsigned integer used to identify this
Reply message. Copied from the client Request,
Confirm, Renew or Rebind message received from
the client.

server-address The IP address of the server.

options See section 20. 22.

8.8. DHCP Release Message Format

msg-type RELEASE

transaction-ID An unsigned integer generated by the client used
to identify this Release message.

server-address The IP address of the server that assigned the
addresses.

options See section 20. 22.

8.9. DHCP Decline Message Format

msg-type DECLINE

transaction-ID An unsigned integer generated by the client used
to identify this Decline message.

server-address The IP address of the server that assigned the
addresses.

options See section 20. 22.

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8.10. DHCP Reconfigure-init Reconfigure Message Format

msg-type RECONFIG-INIT RECONFIG

transaction-ID An unsigned integer generated by the server used
to identify this Reconfigure-init Reconfigure message.

server-address The IP address of the DHCP server issuing the
Reconfigure-init
Reconfigure message. The address must have
sufficient scope to be reachable from the client.

options See section 20.

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8.11. DHCP Inform Information-Request Message Format

msg-type INFORM

transaction-ID An unsigned integer generated by the server client used
to identify this Inform message.

server-address MUST be zero. Contains IP address of server to which this
message is directed, or 0 if any server may
respond.

options See section 20. 22.

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9. Relay messages

Relay agents exchange messages with servers to forward messages
between clients and servers that are not connected to the same link.
There are two relay 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 | |
+-+-+-+-+-+-+-+-+ |
| link-address |
| |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| | |
+-+-+-+-+-+-+-+-+ |
| client-return-address |
| |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| | |
+-+-+-+-+-+-+-+-+ |
. .
. options (variable number and length) .... .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The following sections describe the use of the Relay message header.

9.1. Relay-forward message

The following table defines the use of message fields in a
Relay-forward message.

msg-type RELAY-FORW

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link-address An address with a prefix that is assigned
to the link from which the client should
be assigned an address.

client-return-address The IPv6 source address from the IP datagram in which the
message from the client was received by
the relay agent

options MUST include a "Client message option";
see section 20.8; 22.9; MAY include other
options added by the relay agent

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9.2. Relay-reply message

The following table defines the use of message fields in a
Relay-forward
Relay-reply message.

msg-type RELAY-REPL

link-address An address with a prefix that is assigned The link-address copied from the
Relay-forward message; used by the relay
agent to select the link from on which the
message is returned to the client should
be assigned an address.

client-return-address The source address from the IP datagram
in which the message from the client was
received by the relay agent

options MUST include a "Server message option";
see section 20.9; 22.10; MAY include other
options

10. Representation and use of domain names

So that domain names may be encoded uniformly and compactly, a
domain name or a list of domain names is encoded using the technique
described in sections 3.1 and 4.1.4 of RFC1035 [15]. Section 4.1.4
of RFC1035 describes how more than one domain name can be represented
in a list of domain names. For use in this specification, in a
list of domain names, the compression pointer (see section 4.1.4 of
RFC1035) refers to the offset within the list.

If a single domain name is being used by a vendor as a vendor
identifier, then the vendor MUST ensure that the domain name has not
previously been used by a different vendor.

11. DHCP unique identifier (DUID)

Each DHCP client has a DUID. DHCP servers use DUIDs to identify
clients for the selection of configuration parameters and in
the association of IAs with clients. See section 20.2 22.2 for the
representation of a DUID in a DHCP message.

Servers MUST treat DUIDs as opaque values and MUST only compare DUIDs
for equality. Servers MUST NOT in any other way interpret DUIDs.
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 options (e.g., messages
sent by servers need not include a DUID). The DUID must is designed to
be unique across all DHCP clients, and it must also be consistent for the same any specific

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client - that is, the DUID used by a client SHOULD NOT change over
time;
time, for example, as a result of network hardware reconfiguration.

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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.

10.1.

11.1. DUID contents

A DUID consists of a sixteen-bit type code represented in network
order, followed by a variable number of octets that make up the
actual identifier. A DUID can be no more than 256 octets long. The
following types are currently defined:

1 Link-layer address plus time
2 Vendor-assigned unique ID
3 Link-layer address

Formats for the variable field of the DUID for each of the above
types are shown below.

10.2.

11.2. DUID based on link-layer address plus time

This type of DUID consists of four octets containing a time value,
followed by a two octet network hardware type code, followed by
link-layer address of any one network interface that is connected
to the DHCP client 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 the section on ARP in RFC 826. Both the time and the
hardware type are stored in network order.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hardware type (16 bits) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
. .
. link-layer address (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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The choice of network interface can be completely arbitrary, as long
as that interface provides a unique link-layer address, and the same
DUID should be used in configuring all network interfaces connected

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to the device, regardless of which interface's link-layer address was
used to generate the DUID.

DHCP clients using this type of DUID MUST store the DUID in stable
storage, and MUST continue to use this DUID even if the network
interface used to generate the DUID is removed. DHCP clients that do
not have any stable storage MUST NOT use this type of DUID.

DHCP clients 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 (e.g., a real-time clock) in generating
the DUID, even if that time source is could not be configured by the user prior to
generating the DUID. The use of a time source makes it unlikely that
two identical DUIDs 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,
that two identical DUIDs will be generated. DUID. A DUID collision is very unlikely even
if the clocks haven't 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.

10.3.

11.3. Vendor-assigned unique ID. ID

The vendor-assigned unique ID consists of an eight-octet
vendor-unique identifier, followed by the vendor's registered domain
name.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VUID (64 bits) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. domain name (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The structure of the VUID is left up to the vendor defining it, but
each device containing such a VUID MUST be unique to each device
that is using it, and MUST be assigned to the device at the time of
manufacture and stored in some form of non-volatile storage. The
VUID SHOULD be recorded in non-erasable storage. The domain name
is simply any domain name that has been legally registered by the
vendor in the domain name system, system [14], stored in canonical form. An example DUID
of this type might look like this:

Bound, Carney, the form described
in section 10.

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An example DUID of this type might look like this:

+--+---+---+---+-+-+-+--+---+---+--+---+---+---+---+--+--+---+---+
|12|192|132|221|3|0|9|18|101|120|97|109|112|108|101|46|99|111|109|
+--+---+---+---+-+-+-+--+---+---+--+---+---+---+---+--+--+---+---+

This is eight octets of VUID data, followed by "example.com"
represented in ASCII.

10.4.

11.4. Link-layer address

This type of DUID consists of a two octet network hardware type code,
followed by the link-layer address of any one network interface that
is permanently connected to the DHCP client device. device and cannot be
removed. The hardware type MUST be a valid hardware type assigned by
the IANA as described in the section on ARP in RFC 826. The hardware
type is stored in network order.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 is being
generated. The same DUID 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.

This type of DUID is recommended for devices that have a
permanently-connected network interface with a link-layer address and
do not have nonvolatile, writable stable storage. This type of DUID
MUST NOT be used by DHCP clients that cannot tell whether or not a
network interface is permanently attached to the device on which the
DHCP client is running.

11.

12. Identity association

An "identity-association" (IA) is a construct through which a server
and a client can identify, group and manage IPv6 addresses. Each IA
consists of an IAID and associated configuration information.

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A client associates an must associate at least one distinct IA with one each of
its network interfaces and uses the that IA to obtain configuration
information from a server for that interface from interface. Other distinct IAs may
be associated with applications. 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
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 server. 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 and other parameters. The parameters are specified as DHCP

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options within the IA, and are associated with the addresses in the
IA and the interface to which the IA belongs. Other parameters that
are not associated with a particular interface may be specified in
the options section of a DHCP message, outside the scope of any IA.

Each address in an IA has a preferred lifetime and a valid lifetime,
as defined in RFC2462 [20]. [23]. 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 RFC2462.
An address whose valid lifetime has expired MAY be discarded from the
IA.

See section 20.3 22.3 for the representation of an IA in a DHCP message.

12.

13. 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 the following sources:

- The link to which the client 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 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 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

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client is on the link identified by the source address in the
IP datagram

* 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 is attached

- The DUID supplied by the client

- Other information in options supplied by the client

- Other information in options supplied by the relay agent

13. Reliability of Client Initiated Message Exchanges

DHCP clients are responsible

The addresses that the server selects for reliable delivery the client MUST be valid on
the link to which the interface is attached, regardless of messages the way in
which the
client-initiated message exchanges server selects the addresses.

14. Management of temporary addresses

A client may be assigned temporary addresses [17]. Clients and
servers simply label addresses as "temporary". DHCPv6 handling
of address lifetimes and lifetime extensions is no different for
temporary addresses. DHCPv6 says nothing about details of temporary
addresses like lifetimes, lifetime extensions, how clients use
temporary addresses, rules for generating successive temporary
addresses, etc.

In DHCP, temporary addresses are identified with T-bit set in the IA
Address Option(see section 22.4). A client may have zero or more
temporary addresses. Addresses with the T-bit set MUST be intended
for the client to use for the general purposes described in sections 15 RFC3041.
Addresses that otherwise have short lifetimes or are not intended to
be renewed by the server MUST NOT have the T-bit set.

Clients ask for temporary addresses and 16.
If servers assign them. When a DHCP
client fails to receive sends an expected response from IA to a server, the client lists all of the temporary
addresses it knows about and optionally indicates how many additional
temporary addresses it wants in the Requested Temporary Addresses
Option 22.5. The server compares the number of requested additional
temporary addresses against any previously allocated temporary
addresses for the IA that were not reported by the client in the
IA but still have some reasonable preferred lifetime left. If the
number of temporary addresses is less than the requested number, the
server adds additional temporary addresses to the IA to satisfy the
requested number (subject to server policy).

DISCUSSION:

It is important that the server include any allocated
temporary addresses that were not reported by the client as
it is possible the client never received an earlier Reply

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that contained these additional temporary addresses. If
the server did not consider these, a client must retransmit its message. This section describes the
retransmission that fails to
receive a server's reply might cause the server to allocate
many temporary addresses.

When the valid lifetime on a temporary address expires, both the
client and server silently discard the address from the IA. The
discarded address no longer counts against the client's allotment of
temporary addresses.

A server SHOULD NOT assign a client temporary addresses without the
client having specifically asked for it. The client is not obligated
to install address(es) that it receives and did not request and can
release any addresses it does not want.

The server MAY update the DNS for a temporary address as described in
section 4 of RFC3041, and MUST NOT update the DNS in any other way
for a temporary address.

15. 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 for use with the Solicit message (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 describe described by five 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

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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.
The algorithm for choosing a random number does not need to be
cryptographically sound. The algorithm SHOULD produce a different
sequence of numbers from each invocation of the DHCP client.

RT for the first message transmission is based on IRT:

RT = 2*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. If MRT has a value
of 0, there is no upper limit on the value of RT. Otherwise:

if (RT > MRT)

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RT = MRT + RAND*MRT

MRC specifies an upper bound on the number of times a client may
retransmit a message. If MRC has a value of 0, the client MUST
continue to retransmit the original message until a response is
received. Otherwise, the message exchange fails if once the client
attempts to transmit has
transmitted the original message more than MRC times.

MRD specifies an upper bound on the length of time a client may
retransmit a message. If MRD has a value of 0, the client MUST
continue to retransmit the original message until a response is
received. Otherwise, the message exchange fails if once the client
attempts to transmit has
transmitted the original message more than MRD seconds.

If both MRC and MRD are non-zero, the message exchange fails whenever
either of the conditions specified in the previous paragraph two paragraphs are
met.

Implementations SHOULD verify that for retransmissions that MRC,
MRT, and MRD are not all set to zero for any retransmission case.

14.

16. Message validation

Servers MUST discard any received messages that include
authentication information and fail the authentication check by the
server.

Clients

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Clients MUST discard any received messages that include
authentication information and fail the authentication check by the
client, except as noted in section 19.6.5.2.

14.1. 21.6.5.2.

16.1. Use of Transaction-ID field

The "transaction-ID" field holds a value used by clients and servers
to synchronize server responses to client messages. A client SHOULD
choose a different transaction-ID for each new message it sends. A
client MUST leave the transaction-ID unchanged in retransmissions of
a message.

14.2.

16.2. Solicit message

Clients MUST discard any received Solicit messages.

Relay agents MUST discard any Solicit messages received through port
546.

14.3.

16.3. Advertise message

Clients MUST discard any received Advertise messages in which the
"Transaction-ID" field value does not match the value the client used
in its Solicit message.

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Servers and relay agents MUST discard any received Advertise
messages.

14.4.

16.4. Request message

Clients MUST discard any received Request messages.

Relay agents MUST discard any Request messages received through port
546.

Servers MUST discard any received Request message in which the value
in the ``server-address'' "server-address" field does not match any of the addresses
used by the server.

14.5.

16.5. Confirm message

Clients MUST discard any received Confirm messages.

Relay agents MUST discard any Confirm messages received through port
546.

14.6.

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16.6. Renew message

Clients MUST discard any received Renew messages.

Relay agents MUST discard any Renew messages received through port
546.

Servers MUST discard any received Renew message in which the value in
the ``server-address'' "server-address" field does not match any of the addresses used
by the server.

14.7.

16.7. Rebind message

Clients MUST discard any received Rebind messages.

Relay agents MUST discard any Rebind messages received through port
546.

14.8.

16.8. Decline messages

Clients MUST discard any received Decline messages.

Relay agents MUST discard any Decline messages received through port
546.

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Servers MUST discard any received Decline message in which the value
in the ``server-address'' "server-address" field does not match any of the addresses
used by the server.

14.9.

16.9. Release message

Clients MUST discard any received Release messages.

Relay agents MUST discard any Release messages received through port
546.

Servers MUST discard any received Release message in which the value
in the ``server-address'' "server-address" field does not match any of the addresses
used by the server.

14.10.

16.10. Reply message

Clients MUST discard any received Reply messages in which the
``transaction-ID''
"transaction-ID" field in the message does not match the value used
in the original message.

Servers and relay agents MUST discard any received Reply messages.

14.11. Reconfigure-init

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16.11. Reconfigure message

Servers and relay agents MUST discard any received Reconfigure-init Reconfigure
messages.

Clients MUST discard any Reconfigure-init Reconfigure messages that do not contain an
authentication option or that fail the authentication performed by
the client.

14.12.

16.12. Inform message

Clients MUST discard any received Inform messages.

Relay agents MUST discard any Inform messages received through port
546.

14.13.

16.13. Relay-forward message

Clients MUST discard any received Relay-forward messages.

14.14.

16.14. Relay-reply message

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

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15.

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 configuration information, including 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 configuration information
to the IA respond to the client with an Advertise message. The
client then initiates a configuration exchange as described in
section 16.

15.1. 18.

17.1. Client Behavior

A client uses the Solicit message to discover DHCP servers configured
to serve addresses on the link to which the client is attached.

15.1.1.

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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.

The client MUST include a DUID option to identify itself to the
server. The client MUST include one or more 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 may have has a preference. The client MAY include an
Option Request Option in the Solicit message. The client MUST NOT
include any other options except those specifically allowed as
defined by specific options.

15.1.2.

17.1.2. Transmission of Solicit Messages

The client sends the Solicit message to the All_DHCP_Agents
multicast address. The client MUST use an IPv6 address assigned
to the interface for which the client is interested in obtaining
configuration information as the source address in the IP header of
the datagram carrying the Solicit message.

The Solicit message MUST be transmitted on the link that the
interface for which configuration information is being obtained
is attached to. The client SHOULD send the message through that
interface. The client MAY send the message through another interface
attached to the same link if and only if the client is certain the
two interface are attached to the same link.

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The first Solicit message from the client on the interface MUST
be delayed by a random amount of time between MIN_SOL_DELAY and
MAX_SOL_DELAY. This random delay desynchronizes clients which start
at the same time (e.g., after a power outage).

The client transmits the message according to section 13, 15, using the
following parameters:

IRT SOL_TIMEOUT

MRT SOL_MAX_RT

MRC 0

MRD 0

The mechanism in section 13 15 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 SOL_TIMEOUT has
elapsed. Rather, the client collects Advertise messages until
SOL_TIMEOUT has elapsed. The Also, the first RT MUST be selected to be

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strictly greater than SOL_TIMEOUT by choosing RAND to be strictly
greater than 0.

A client MUST collect Advertise messages for SOL_TIMEOUT seconds,
unless it receives an Advertise message with a preference value
of 255. The preference value is carried in the Preference option
(section 20.6). 22.7). Any Solicit that does not include a Preference
option is considered to have a preference value of 0. If the client
receives an Advertise message with a preference value of 255, then
the client MAY act immediately on that Advertise message without
waiting for any more 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 MAY SHOULD choose to restart the reconfiguration process
after some external event, such as user input, system restart, or
when the client is attached to a new link.

15.1.3.

17.1.3. Receipt of Advertise messages

The client MUST ignore any Advertise message that includes a Status
Code option containing the value AddrUnavail, 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.

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- Those Advertise messages with the highest server preference value
are preferred over all other Advertise messages.

- 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.

- 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. Depending on the requirements of the user that
invoked the DHCP client, the client MAY initiate a configuration
exchange with the server(s) immediately, or MAY defer this exchange
until later.

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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.

15.2.

17.2. Server Behavior

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

15.2.1.

17.2.1. Receipt of Solicit messages

The server determines the information about the client and its
location as described in section 12. 13. If administrative policy
permits the server to respond to the client, the server will generate
and send an Advertise message to the client.

15.2.2.

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
places one of its IP addresses (determined through administrator setting) in the "server-address" field of the
Advertise message. The administrator must be able to configure the
address used in the "server-address" field. 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

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MUST default to zero unless otherwise configured by the server
administrator.

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. The server MAY include some or
all of the IA options from the client in the Advertise message.

If the server will not assign any addresses to IAs in a subsequent
Request from the client, the server MAY SHOULD either send an Advertise
message to the client that includes only a status code option with
the status code set to AddrUnavail and a status message for the user
or discard not respond to the Advertise Solicit message.

The server MAY include other options the server will return to the
client in a subsequent Reply message. The information in these
options will be used by the client in the selection of a server if
the client receives more than one Advertise message. The server
SHOULD include options specifying values for options requested by the
client in an Option Request Option included in the Solicit message.

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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 through the interface on 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 "server-message" option. 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.

16.

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 or when requested to do so by the
application layer.

16.1.

18.1. Client Behavior

A client will use Request, Confirm, Renew, Rebind and Inform messages
to acquire and confirm the validity of configuration information.
The client uses the server address information and information about
IAs from previous Advertise messages for use in constructing Request
messages. Note that a client may request configuration information
from one or more servers at any time.

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16.1.1.

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, with addresses and
information about the IAs that were obtained from the server in a
previous Advertise 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 address of the destination server in the
"server-address" field.

The client MUST include a DUID 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

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assign it some network addresses). The list of addresses in each
included IA MUST include the addresses received by the client in a
previous Advertise message.

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 Client Server Unicast option (section 20.12) 22.14) from the server, the client
SHOULD unicast the Request message to the server. Otherwise, the
client MUST send the Request message to the All_DHCP_Agents multicast
address. The client MUST use an address assigned to the interface
for which the client is interested in obtaining configuration
information as the source address in the IP header of the datagram
carrying the Request message.

DISCUSSION:

Use of multicast and relay agents 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.

If the client multicasts the Request message, the message MUST be
transmitted on the link that the interface for which configuration
information is being obtained is attached to. The client SHOULD send
the message through that interface. The client MAY send the message
through another interface attached to the same link if and only if
the client is certain the the two interface are attached to the same
link.

The client transmits the message according to section 13, 15, using the
following parameters:

IRT REQ_TIMEOUT

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MRT REQ_MAX_RT

MRC REQ_MAX_RC

MRD 0

If the message exchange fails, the client MAY choose one of the
following actions:

- Select another server from a list of servers known to the client;
e. g., servers that responded with an Advertise message

- Initiate the server discovery process described in section 15 17

- Terminate the configuration process and report failure

16.1.2.

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18.1.2. Creation and transmission of Confirm messages

Whenever a client may have moved to a new link, its IPv6 addresses
and other configuration information may no longer be valid. Examples
of times when a client may have moved to a new link include:

o The client reboots

o The client is physically disconnected from a wired connection

o The client returns from sleep mode

o The client using a wireless technology changes links 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, along with the addresses associated with those IAs,
in its Confirm message. Any responding servers will indicate the
acceptability of the addresses 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 sets the "server-address" field to 0.

The client MUST include a DUID option to identify itself to the
server. The client adds any appropriate options, including one or
more IA options. The client MUST include the addresses the client
currently has associated with those IAs.

The client sends the Confirm message to the All_DHCP_Agents multicast
address. The client MUST use an IPv6 address that the client has
confirmed to be valid on the link to which it is currently attached
and that is assigned to the interface for which the client is
interested in obtaining

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address in the IP header of the datagram carrying the Confirm
message.

The Confirm message MUST be transmitted on the link that the
interface for which configuration information is being obtained
is attached to. The client SHOULD send the message through that
interface. The client MAY send the message through another interface
attached to the same link if and only if the client is certain the
the two interface are attached to the same link.

The client transmits the message according to section 13, 15, using the
following parameters:

IRT CNF_TIMEOUT

MRT CNF_MAX_RT

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MRC 0

MRD CNF_MAX_RD

If the client receives no responses before the message transmission
process as described in section 13 15 terminates, 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.

16.1.3.

18.1.3. Creation and transmission of Renew messages

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

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 address of the destination server in the
"server-address" field.

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The client MUST include a DUID option to identify itself to the
server. The client adds any appropriate options, including one or
more IA options (if the client is requesting that the server extend
the lifetimes of the addresses assigned to those IAs; note that the
client may check the status of other configuration parameters without
asking for lifetime extensions). If the The client does include any IA
options, it MUST include the list
of addresses the client currently has associated with that IA. the IAs in the
Renew message.

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 Client Server Unicast option (section 20.12) 22.14) from the server, the client
SHOULD unicast the Renew message to the server. Otherwise, the
client sends the Renew message to the All_DHCP_Agents multicast
address. The client MUST use an address assigned to the interface
for which the client is interested in obtaining configuration

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information as the source address in the IP header of the datagram
carrying the Renew message.

If the Renew message is multicast, it MUST be transmitted on the
link that the interface for which configuration information is being
obtained is attached to. The client SHOULD send the message through
that interface. The client MAY send the message through another
interface attached to the same link if and only if the client is
certain the the two interface are attached to the same link.

The client transmits the message according to section 13, 15, using the
following parameters:

IRT REN_TIMEOUT

MRT REP_MAX_RT

MRC 0

MRD 0

The mechanism in section 13 15 is modified as follows for use in the
transmission of Renew messages. The message exchange is terminated
when time T2 is reached (see section 16.1.4), 18.1.4), at which time the
client begins a Rebind message exchange.

16.1.4.

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. The client
includes an IA option with all addresses currently assigned to the
IA in its Rebind message. The client sends this message to the
All_DHCP_Agents multicast address.

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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 sets the "server-address" field to 0.

The client MUST include a DUID option to identify itself to the
server. The client adds any appropriate options, including one or
more IA options. If the The client does MUST include any IA options (if
the client is requesting that the server extend the lifetimes of
addresses assigned to those IAs; note that the client may check
the status of other configuration parameters without asking for
lifetime extensions), it MUST include the list list of addresses the
client currently has associated with that IA. the IAs in the Rebind message.

The client sends the Rebind message to the All_DHCP_Agents
multicast address. The client MUST use an IPv6 address assigned
to the interface for which the client is interested in obtaining
configuration information as the source address in the IP header of
the datagram carrying the Rebind message.

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The Rebind message MUST be transmitted on the link that the interface
for which configuration information is being obtained is attached
to. The client SHOULD send the message through that interface. The
client MAY send the message through another interface attached to the
same link if and only if the client is certain the the two interface
are attached to the same link.

The client transmits the message according to section 13, 15, using the
following parameters:

IRT REB_TIMEOUT

MRT REB_MAX_RT

MRC 0

MRD 0

The mechanism in section 13 15 is modified as follows for use in the
transmission of Rebind messages. The message exchange is terminated
when the lifetimes on of all of the addresses assigned to the IA expire
(see section 11), 12), at which time the client has several alternative
actions to choose from:

- 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

- 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

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16.1.5.

18.1.5. Creation and Transmission of Inform messages

The client uses an Inform message to obtain configuration information
without having addresses assigned to it. The client sets the
"msg-type" field to INFORM. The client generates a transaction ID and
inserts this value in the "transaction-ID" field.

The client sets the "server-address" field to 0.

The client MUST include a DUID option to identify itself to the
server. The client adds any appropriate options such as an ORO to
indicate to the server what configuration information the client is
interested in obtaining. The client MUST NOT include any IA options.

The client MUST use an IPv6 address assigned to the interface for
which the client is interested in obtaining configuration information
as the source address in the IP header of the datagram carrying the
Rebind message.

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If the client has an IPv6 address of sufficient scope, the client MAY
choose to send the Inform message to the Allmulticast All_DHCP_Servers multicast
address. Otherwise, the client MUST send the Inform message to the
All_DHCP_Agents multicast address.

The Inform message MUST be transmitted on the link that the interface
for which configuration information is being obtained is attached
to. The client SHOULD send the message through that interface. The
client MAY send the message through another interface attached to the
same link if and only if the client is certain the the two interface
are attached to the same link.

The client transmits the message according to section 13, 15, using the
following parameters:

IRT INF_TIMEOUT

MRT INF_MAX_RT

MRC 0

MRD 0

16.1.6.

18.1.6. Receipt of Reply message in response to a Request, Confirm,
Renew, Rebind or Inform message

Upon the receipt of a valid Reply message in response to a Request,
Confirm, Renew or Renew, Rebind or Inform message, the client extracts the
configuration 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.

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The client SHOULD perform duplicate address detection [20] [23] on each
of the addresses in any IAs it receives in the Reply message after
a Request message. 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 16.1.9. 18.1.9.

The client records the T1 and T2 times for each IA in the Reply
message. The client records any addresses included with IAs in
the Reply message. The client updates the preferred and valid
lifetimes for the addresses in the IA from the lifetime information
in the IA option. The client leaves any addresses that the client
has associated with the IA that are not included in the IA option
unchanged.

The client SHOULD respond to the server with a Release message for
any addresses in the Reply message that have a valid lifetime of 0.
The client constructs and transmits this message as described in
section 18.1.7.

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If the Reply was received in response to a Renew or Rebind message,
the client must update the information in any IA option contained in
the Reply message. The client adds any new addresses from the IA
option to the IA, updates lifetimes for existing addresses in the IA
from the IA option and discards any addresses with a lifetime of zero
in the IA option.

Management of the specific configuration information is detailed in
the definition of each option, in section 20. 22.

When the client receives a NoPrefixMatch status in an IA from the
server the client can assume it needs to send a Request to the server
to obtain appropriate addresses for the IA. If the client receives
any Reply messages that do not indicate a NoPrefixMatch status, the
client can use the addresses in the IA and ignore any messages that
do indicate a NoPrefixMatch status.

When the client receives an AddrUnavail status in an IA from the
server for a Request message the client will have to find a new
server to create an IA.

When the client receives a NoBinding status status in an IA from the server
for a Confirm message the client can assume it needs to send a
Request to reestablish an IA with the server.

When the client receives a ConfNoMatch status in an IA from the
server for a Confirm message the client can send a Renew message to
the server to extend the lifetimes of the addresses.

When the client receives a NoBinding status in an IA from the server
for a Renew message the client can assume it needs to send a Request
to reestablish an IA with the server.

When the client receives a RenwNoMatch status in an IA from the
server for a Renew message the client can assume it needs to send a
Request to reestablish an IA with the server.

When the client receives an AddrUnavail status in an IA from the
server for a Renew message the client can assume it needs to send a
Request to reestablish an IA with the server.

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When the client receives a NoBinding status in an IA from the server
for a Rebind message the client can assume it needs to send a Request
to reestablish an IA with the server or try another server.

When the client receives a RebdNoMatch status in an IA from the
server for a Rebind message the client can assume it needs to send a
Request to reestablish an IA with the server or try another server.

When the client receives an AddrUnavail status in an IA from the
server for a Rebind message the client can assume it needs to send a
Request to reestablish an IA with the server or try another server.

16.1.7.

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18.1.7. Creation and transmission of Release messages

The client sets the "msg-type" field to RELEASE. The client generates
a transaction ID and places this value in the "transaction-ID" field.

The client places the IP address of the server that allocated the
address(es) in the "server-address" field.

The client MUST include a DUID option to identify itself to the
server. The client includes options containing the IAs it is
releasing in the "options" field. The addresses to be released
MUST be included in the IAs. The client continues to use any other
addresses in the IA. IAs. The appropriate "status" field in the options
MUST be set to indicate the reason for the release.

The client MUST NOT use any of the addresses in the IAs in the
message as the source address in the Release message or in any
subsequently transmitted message.

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 Client Server Unicast option (section 20.12) 22.14) from the server, the client
SHOULD unicast the Release message to the server. Otherwise, the
client MUST send the Release message to the All_DHCP_Agents multicast
address. The client MUST use an address for the interface to which
the IAs in the Release message are assigned as the source address for
the Release message.

DISCUSSION:

Use of multicast and relay agents enables the inclusion of
relay agent options in all messages sent by the client. The
server MUST NOT enable the use of unicast for a client when
relay agent options are required for that client.

If the Release message is multicast, it MUST be transmitted on the
link that the interface for which configuration information is being
obtained is attached to. The client SHOULD send the message through
that interface. The client MAY send the message through another

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interface attached to the same link if and only if the client is
certain the the two interface are attached to the same link.

A client MAY choose to wait for a Reply message from the server in
response to the Release message. If the client does wait for a
Reply, the client MAY choose to retransmit the Release message.

The client transmits the message according to section 13, 15, using the
following parameters:

IRT REL_TIMEOUT

MRT 0

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MRC REL_MAX_MRC

MRD 0

The client MUST abandon the attempt to release addresses if the
Release message exchange fails.

The client MUST stop using all of the addresses in the IA(s) being
released as soon as the client begins the Release message exchange
process. If an IA is 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 IA, the addresses
assigned to the IA will be reclaimed by the server when the lifetime
of the address expires.

16.1.8.

18.1.8. Receipt of Reply message in response to a Release message

Upon receipt of a valid Reply message, the client can consider the
Release event successful.

16.1.9.

18.1.9. Creation and transmission of Decline messages

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 IP address of the server that allocated the
address(es) in the "server-address" field.

The client MUST include a DUID option to identify itself to the
server. The client includes options containing the IAs it is
declining in the "options" field. The addresses to be declined MUST
be included in the IAs. The client continues to use other addresses

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in the IAs. The appropriate "status" field in the options MUST be
set to indicate the reason for declining the address.

The client MUST NOT use any of the addresses in the IAs in the
message as the source address in the Decline message or in any
subsequently transmitted message.

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 Client Server Unicast option (section 20.12) 22.14) from the server, the client
SHOULD unicast the Decline message to the server. Otherwise, the
client MUST send the Decline message to the All_DHCP_Agents multicast
address. The client MUST use an IPv6 address for the interface to

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which the IAs in the Decline message are assigned as the source
address for the Decline message.

DISCUSSION:

If the Decline message is multicast, it MUST be transmitted on the
link that the interface for which configuration information is being
obtained is attached to. The client SHOULD send the message through
that interface. The client MAY send the message through another
interface attached to the same link if and only if the client is
certain the the two interface are attached to the same link.

The client transmits the message according to section 13, 15, using the
following parameters:

IRT DEC_TIMEOUT

MRT DEC_MAX_RT

MRC DEC_MAX_RC

MRD 0

The client MUST abandon the attempt to decline addresses if the
Decline message exchange fails.

16.1.10.

18.1.10. Receipt of Reply message in response to a Decline message

Upon receipt of a valid Reply message, the client can consider the
Decline event successful.

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16.2.

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.

16.2.1.

18.2.1. Receipt of Request messages

The server MAY choose to discard Request messages received via
unicast from a client to which the server has not sent a unicast
option.

When the server receives a Request and IA option(s) are included the client is requesting the
configuration of a new IA by the server. The server MUST take the

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IA from the client and associate a binding for that client in an
implementation-specific manner within the configuration parameter
database for DHCP clients managed by the server.

Upon the receipt of a valid Request message from a client the server
can respond to, (implementation-specific administrative policy
satisfied) the server scans the options field.

The server then constructs a Reply message and sends it to the
client.

The server SHOULD process each option for the client in an
implementation-specific manner. The server MUST construct a Reply
message containing the following values:

msg-type REPLY

transaction-ID The transaction-ID from the Request message.

server address One of the IP addresses assigned to the interface
through which the server received the message
from the client.

If the server finds that the prefix on one or more IP addresses in
any IA in the message from the client is not a valid prefix for the
link to which the client is connected, the server MUST return the IA
to the client with the status field set to NoPrefixMatch.

If the server cannot assign any addresses to any of the IAs in
the message from the client, the server SHOULD include the IAs in
the Reply message with the status field set to AddrUnavail and no
addresses in the IA.

For any IAs to which the server can assign addresses, server includes
the IA with addresses and other configuration parameters a status of
Success, and add the IA as a new client binding.

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The server adds options to the Reply message for any other
configuration information to be assigned to the client.

16.2.2.

18.2.2. Receipt of Confirm messages

When the server receives a Confirm message, the client is requesting
confirmation that the configuration information it will use is valid.
The server SHOULD locate the binding for that client and compare the
information in the Confirm message from the client to the information
associated with that client.

Upon the receipt of a valid Confirm message from a client the server
can respond to, (implementation-specific administrative policy
satisfied) the server scans the options field.

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If the server cannot determine if the information in the Confirm
message is valid or invalid, the server MUST NOT send a reply to the
client. For example, if the server does not have a binding for the
client, but the configuration information in the Confirm message
appears valid, the server does not reply.

If the server finds that the information for the client does not
match what is in the binding for that client or the configuration
information is not valid, the server sends a Reply message containing
a Status Code option with the value ConfNoMatch.

If the server finds that the information for the client does match
the information in the binding for that client, and the configuration
information is still valid, the server sends a Reply message
containing a Status Code option with the value Success.

The server SHOULD process each option for the client in an
implementation-specific manner. The server MUST construct a Reply
message containing the following values:

msg-type REPLY

transaction-ID The transaction-ID from the Confirm message.

server address One of the IP addresses assigned to the interface
through which the server received the message
from the client.

The Reply message from the server MUST contain a Status Code option
and MUST NOT include any other options.

16.2.3.

18.2.3. Receipt of Renew messages

The server MAY choose to discard Renew messages received via unicast
from a client to which the server has not sent a unicast option.

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Upon the receipt of a valid Renew message from a client the server
can respond to, (implementation-specific administrative policy
satisfied) the server scans the options field.

When the server receives a Renew and IA option from a client it
SHOULD locate the clients binding and verify the information in the
IA from the client matches the information stored for that client.

If the server cannot find a client entry for this IA the server
SHOULD return an IA containing no addresses with status set to
NoBinding.

If the server finds that the addresses in the IA for the client
do not match the client binding the server should return an IA
containing no addresses with status set to RenwNoMatch.

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If the server cannot Renew addresses for the client it SHOULD send
back an IA containing no addresses to the client with the status
field set to AddrUnavail.

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 if the default is not being used, and set status to
Success. 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 SHOULD process each option for the client in an
implementation-specific manner. The server MUST construct a Reply
message containing the following values:

msg-type REPLY

transaction-ID The transaction-ID from the Renew Confirm message.

server address One of the IP addresses assigned to the interface
through which the server received the message
from the client.

16.2.4.

18.2.4. Receipt of Rebind messages

Upon the receipt of a valid Rebind message from a client the server
can respond to, (implementation-specific administrative policy
satisfied) the server scans the options field.

When the server receives a Rebind and IA option from a client it
SHOULD locate the clients binding and verify the information in the
IA from the client matches the information stored for that client.

If the server cannot find a client entry for this IA the server
SHOULD return an IA containing no addresses with status set to
NoBinding.

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If the server finds that the addresses in the IA for the client
do not match the client binding the server should return an IA
containing no addresses with status set to RebdNoMatch.

If the server cannot Rebind addresses for the client it SHOULD send
back an IA containing no addresses to the client with the status
field set to AddrUnavail.

The server SHOULD process each option for the client in an
implementation-specific manner. The server MUST construct a Reply
message containing the following values:

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msg-type REPLY

transaction-ID The transaction-ID from the Rebind Confirm message.

server address One of the IP addresses assigned to the interface
through which the server received the message
from the client.

There is a significant difference between Renew and Rebind messages:
Because the Renew message is processed by a single server, the
responding server can actually change the addresses in the IA.
However, because multiple servers may respond to a Rebind, all they
can safely do is update T1, T2 (for the IA) and lifetimes (for
individual addresses).

16.2.5.

18.2.5. Receipt of Inform messages

When the server receives an Inform message, the client is requesting
configuration information that does not include the assignment of any
addresses. The server SHOULD determine all configuration parameters
appropriate to the client, based on the server configuration policies
known to the server.

Upon the receipt of a valid Inform message from a client the server
can respond to, (implementation-specific administrative policy
satisfied) the server scans the options field. The server then
constructs a Reply message and sends it to the client.

The server SHOULD process each option for the client in an
implementation-specific manner. The server MUST construct a Reply
message containing the following values:

msg-type REPLY

transaction-ID The transaction-ID from the Inforrm Confirm message.

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server address One of the IP addresses assigned to the interface
through which the server received the message
from the client.

The server adds options to the Reply message for all of the
configuration parameters to be returned to the client.

16.2.6.

18.2.6. Receipt of Release messages

The server MAY choose to discard Release messages received via
unicast from a client to which the server has not sent a unicast
option.

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.

If all of the IAs were valid and the addresses successfully released,
the The server generates ignores invalid addresses
(though it may choose to log an error if it finds an invalid
address).

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After all the addresses have been processed, the server generates a
Reply message and includes a Status Code option with value Success.
The server MUST NOT include any other options in the Reply message.

A server is not required to (but may choose to as an implementation
strategy) retain any record of an IA from which all of the addresses
have been released.

16.2.7.

18.2.7. Receipt of Decline messages

The server MAY choose to discard Decline messages received via
unicast from a client to which the server has not sent a unicast
option.

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 IA, the server deletes
the addresses from the IAs. 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.

If The server ignores invalid addresses (though it may
choose to log an error if it finds an invalid address).

After all of the IAs were valid and the addresses successfully declined, address have been processed, the server generates a
Reply message and includes a Status Code option with value Success.
The server MUST NOT include any other options in the Reply message.

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16.2.8.

18.2.8. Receipt of Decline Information-Request messages

Upon the receipt of a valid Inform message, the server determines the
appropriate configuration parameters and returns those parameters to
the client in a Reply message. The server MUST NOT include any IA
options in the Reply message.

16.2.9.

18.2.9. Sending of Reply messages

If the Request, Confirm, Renew, Rebind, Release, Decline or Inform
message from the client was originally received in a Relay-forward
message from a relay, the server places the Reply message in the
options field of a Relay-response message and copies the link-address
and client-return-address fields from the Relay-forward message into
the Relay-response message.

The server then unicasts the Reply or Relay-reply to the source
address from the IP datagram in which the original message was
received.

17.

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

17.1.

19.1. Server Behavior

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

17.1.1.

19.1.1. Creation and transmission of Reconfigure-init Reconfigure messages

The server sets the "msg-type" field to RECONFIG-INIT. RECONFIGURE. The server
generates a transaction-ID and inserts it in the "transaction-ID"
field. The server places its address (of appropriate scope) in the
"server-address" field.

The server MAY include an ORO 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 ORO if the
server wants the client to obtain new address information.

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The server MUST include an authentication option with the appropriate
settings and add that option as the last option in the "options"
field of the Reconfigure-init Reconfigure message.

The server MUST NOT include any other options in the Reconfigure-init Reconfigure
except as specifically allowed in the definition of individual
options.

A server sends each Reconfigure-init Reconfigure message to a single DHCP client,
using an IPv6 unicast address of sufficient scope belonging to the
DHCP client. The server may obtain the address of the client through
the information that the server has about clients that have been in
contact with the server, or the server may be configured with the
address of the client 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-init Reconfigure message to additional clients while previous
reconfiguration message exchanges are still in progress.

The Reconfigure-init Reconfigure message causes the client to initiate a
Rebind/Reply Renew/Reply
or Information-request/Reply message exchange with the server. The

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server interprets the receipt of a Rebind Renew or Information-request
message from the client as satisfying the
Reconfigure-init Reconfigure message
request.

17.1.2.

19.1.2. Time out and retransmission of Reconfigure-init Reconfigure messages

If the server does not receive a Rebind Renew or Information-request message
from the client in RECREP_MSG_TIMEOUT milliseconds, the server
retransmits the Reconfigure-init Reconfigure message, doubles the RECREP_MSG_TIMEOUT
value and waits again. The server continues this process until
REC_MSG_ATTEMPTS unsuccessful attempts have been made, at which point
the server SHOULD abort the reconfigure process for that client.

Default and initial values for RECREP_MSG_TIMEOUT and
REC_MSG_ATTEMPTS are documented in section 7.5.

17.1.3.

19.1.3. Receipt of Rebind Renew messages

The server generates and sends Reply message(s) to the client as
described in section 16.2.9, 18.2.9, including in the "options" field new
values for configuration parameters.

It is possible that the client may send a Rebind Renew message after the
server has sent a Reconfigure-init Reconfigure but before the Reconfigure-init Reconfigure is received
by the client. In this case, the Rebind Renew message from the client
may not include all of the IAs and requests for parameters to be
reconfigured by the server. To accommodate this scenario, the server
MAY choose to send a Reply with the IAs and other parameters

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reconfigured, even if those IAs and parameters were not in the
Rebind Renew
message from the client.

17.2. Client Behavior

A client MUST always monitor UDP port 546 for Reconfigure-init

19.2. Receipt of Information-request messages on interfaces upon which it

If the server has acquired DHCP parameters.
Since assigned addresses to one or more IAs that belong
to the results of a reconfiguration event may affect application
layer programs, responding client, the client SHOULD log these events, server MUST silently discard the
Information-request message.

The server generates and MAY notify
these programs of sends Reply message(s) to the change through an client as
described in section 18.2.9, including in the "options" field new
values for configuration parameters.

It is possible that the client may send an Information-request
message after the server has sent a Reconfigure but before
the Reconfigure is received by the client. In this case, the
Information-request message from the client may not include all of
the IAs and requests for parameters to be reconfigured by the server.
To accommodate this scenario, the server MAY choose to send a Reply
with the IAs and other parameters to be reconfigured, even if those
IAs and parameters were not in the Information-request message from
the client.

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19.3. Client Behavior

A client MUST always monitor UDP port 546 for Reconfigure messages
on interfaces for which it has acquired DHCP parameters. 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.

17.2.1.

19.3.1. Receipt of Reconfigure-init Reconfigure messages

Upon receipt of a valid Reconfigure-init Reconfigure message, the client initiates a Rebind/Reply
transaction with the server. While the
Rebind/Reply transaction is in progress,
the client silently discards any Reconfigure-init Reconfigure messages it receives.

If the client has IAs with addresses that have been assigned by the
server from which the Reconfigure message was received, the client
MUST respond with a Renew message. Otherwise, the client responds
with an Information-request message.

DISCUSSION:

The Reconfigure-init Reconfigure message acts as a trigger that signals the
client to complete a successful Rebind/Reply message exchange. Once
the client has received a Reconfigure-init, Reconfigure, the client proceeds
with the Rebind/Reply message exchange (retransmitting the Rebind Renew or
Information-request message if necessary); the client
ignores any additional Reconfigure-init Reconfigure messages (regardless
of the transaction ID in the Reconfigure-init Reconfigure message) until
the Rebind/Reply exchange is complete. Subsequent Reconfigure-init Reconfigure messages
(again independent of the transaction ID) cause the client
to initiate a new
Rebind/Reply exchange.

How does this mechanism work in the face of duplicated or
retransmitted Reconfigure-init Reconfigure messages? Duplicate messages
will be ignored because the client will begin the Rebind/Reply exchange
after the receipt of the first Reconfigure-init. Reconfigure. Retransmitted
messages will either trigger the Rebind/Reply exchange (if the first
Reconfigure-init
Reconfigure was not received by the client) or will be
ignored. The server can discontinue retransmission of
Reconfigure-init
Reconfigure messages to the client once the server receives
the Rebind Renew or Information-request message from the client.

It might be possible for a duplicate or retransmitted
Reconfigure-init
Reconfigure to be sufficiently delayed (and delivered out of
order) to arrive at the client after the Rebind/Reply exchange (initiated
by the original Reconfigure-init) Reconfigure) has been completed. In this
case, the client would initiate a redundant Rebind/Reply exchange. The
likelihood of delayed and out of order delivery is small
enough to be ignored. The consequence of the redundant
exchange is inefficiency rather than incorrect operation.

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The consequence of the redundant exchange is inefficiency
rather than incorrect operation.

17.2.2.

19.3.2. Creation and sending of Rebind Renew messages

When responding to a Reconfigure-init, Reconfigure, the client creates and sends
the Rebind Renew message in exactly the same manner as outlined in
section 16.1.1 18.1.3, with the following difference:

IAs The client includes exception: if the server included on ORO
option specifying the IA option, the client MUST include IA options
containing the addresses the client currently has assigned to those ALL IAs
for the interface through which the Reconfigure-init Reconfigure message was received.

17.2.3.

19.3.3. Creation and sending of Renew 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.

19.3.4. Time out and retransmission of Rebind Renew or Information-request
messages

The client uses the same variables and retransmission algorithm as it
does with Rebind or Information-request messages generated as part
of a client-initiated configuration exchange. See section 16.1.1 18.1.3
and 18.1.5 for details.

17.2.4.

19.3.5. Receipt of Reply messages

Upon the receipt of a valid Reply message, the client extracts the
contents of the "options" field, and sets (or resets) configuration
parameters appropriately. The client records and updates the
lifetimes for any addresses specified in IAs in the Reply message.
If the configuration parameters changed were requested by the
application layer, the client notifies the application layer of the
changes using an implementation-specific interface.

As discussed in section 17.1.3, the Reply from the server may include
IAs and parameters that were not included in the Rebind message from
the client. The client MUST configure itself with all of the IAs and
parameters in the Reply from the server.

18.

20. Relay Behavior

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

18.1.

20.1. Relaying of client messages

When a Relay receives a valid client message, it constructs a
Relay-forward message. The relay places an 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

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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.

If the relay cannot use the address in the link-address field to
identify the interface through which the response to the client
will be forwarded, the relay MUST include a circuit-id option (see
section 20.16)in 22.18)in the Relay-forward message. The server will include
the circuit-id option in its Relay-reply message.

The relay copies the source address from the IP datagram in which the
message was received from the client into the client-return-address
field in the Relay-forward message.

The relay constructs a "client-message" option 20.8 22.9 that contains
the entire message from the client in the data field of the
option. The relay places the "relay-message" option along with any
"relay-specific" options in the options field of the Relay-forward
message. The Relay then sends MUST send the Relay-forward message to the list
of server destination addresses that it has been configured with.

18.2. with and
MUST NOT send the message just to the server (if present) identified
in the server-address field in the client message.

20.2. Relaying of server messages

When the relay receives a Relay-reply message, it extracts the server
message from the "server-message" option. If the Relay-reply message
includes a circuit-id option, the relay forwards the message from the
server to the client on the link identified by the circuit-id option.
Otherwise, the relay forwards the message on the link identified
by the link-address field. In either case, the relay forwards the
message to the address in the client-return-address field in the
Relay-reply message.

19.

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.

Because of the risk of denial of service attacks against DHCP
clients, the use of authentication is mandated in Reconfigure-init Reconfigure
messages. A DHCP server MUST include an authentication option in
Reconfigure-init
Reconfigure messages sent to clients.

The DHCP authentication mechanism is based on the design of
authentication for DHCP for IPv4 [8].

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19.1.

The DHCP authentication mechanism is based on the design of
authentication for DHCP for IPv4 [9].

21.1. DHCP threat model

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.

The attack specific to a DHCP client is the possibility of the
establishment of a "rogue" server with the intent of providing
incorrect configuration information to the client. The motivation
for doing so may be to establish a "man in the middle" attack or it
may be for a "denial of service" attack.

There is another threat to DHCP clients from mistakenly or
accidentally configured DHCP servers that answer DHCP client requests
with unintentionally incorrect configuration parameters.

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 valid addresses, or the exhaustion of CPU or
network bandwidth, and are present anytime there is a shared
resource. In current practice, redundancy mitigates DoS attacks the
best.

19.2.

21.2. Security of messages sent between servers and relay agents

Relay agents and servers that choose to exchange messages securely
use the IPsec mechanisms for IPv6 [10]. [11]. The way in which IPsec
is employed by relay agents and servers is not specified in this
document.

19.3.

21.3. Summary of DHCP authentication

Authentication of DHCP messages is accomplished through the use of
the Authentication option. 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.

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Other protocols defined in the future will be specified in separate
documents.

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.

19.4.

21.4. 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 (e.g., an NTP-format
timestamp [12]) [13]) can reduce the danger of replay attacks. This method
MUST be supported by all protocols.

19.5.

21.5. Configuration token protocol

If the protocol field is 0, the authentication information field
holds a simple configuration token. The configuration token is an
opaque, unencoded value known to both the sender and receiver. The
sender inserts the configuration token in the DHCP message and the
receiver matches the token from the message to the shared token. If
the configuration option is present and the token from the message
does not match the shared token, the receiver MUST discard the
message.

Configuration token may be used to pass a plain-text configuration
token and provides only weak entity authentication and no message
authentication. This protocol is only useful for rudimentary
protection against inadvertently instantiated DHCP servers.

DISCUSSION:

The intent here is to pass a constant, non-computed token
such as a plain-text password. Other types of entity
authentication using computed tokens such as Kerberos
tickets or one-time passwords will be defined as separate
protocols.

19.6.

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21.6. Delayed authentication protocol

If the protocol field is 1, 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 information.

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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 [11] [12]
using the MD5 hash [19] [21] is defined here.

19.6.1.

21.6.1. Management issues in the delayed authentication protocol

The "delayed authentication" protocol does not attempt to address
situations where a client may roam from one administrative domain
to another, i.e. interdomain roaming. This protocol is focused on
solving the intradomain problem where the out-of-band exchange of a
shared secret is feasible.

19.6.2.

21.6.2. Use of the Authentication option in the delayed authentication
protocol

In a Solicit message, the Authentication option carries the Protocol,
Algorithm, RDM and Replay detection fields, but no Authentication
information.

In an Advertise, Request, Renew, Rebind Rebind, Confirm, Decline, Release
or Confirm Information-request message, the Authentication option carries
the Protocol, Algorithm, RDM and Replay detection fields and
Authentication information. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Secret ID (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC-MD5 (128 bits) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The

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The following definitions will be used in the description of the
authentication information for delayed authentication, algorithm 1:

Replay Detection - as defined by the RDM field
K - a secret value shared between the source and
destination of the message; each secret has a
unique identifier (secret ID)
secret ID - the unique identifier for the secret value
used to generate the MAC for this message
HMAC-MD5 - the MAC generating function.

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The sender computes the MAC using the HMAC generation algorithm [11] [12]
and the MD5 hash function [19]. [21]. The entire DHCP message (except
the MAC field of the authentication option itself), including the
DHCP message header and the options field, is used as input to the
HMAC-MD5 computation function. The 'secret ID' field MUST be set to
the identifier of the secret used to generate the MAC.

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.

Delayed authentication requires a shared secret key for each
client on each DHCP server with which that client may wish
to use the DHCP protocol. Each secret key has a unique
identifier that can be used by a receiver to determine which
secret was used to generate the MAC in the DHCP message.
Therefore, delayed authentication may not scale well in an
architecture in which a DHCP client connects to multiple
administrative domains.

19.6.3.

21.6.3. Message validation

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 [11]. [12]. The receiver
MUST set the 'MAC' field of the authentication option to all 0s for
computation of the MAC. If the MAC computed by the receiver does not
match the MAC contained in the authentication option, the receiver
MUST discard the DHCP message.

19.6.4.

21.6.4. Key utilization

Each DHCP client has a key, K. The client uses its key to encode
any messages it sends to the server and to authenticate and verify
any messages it receives from the server. The client's key SHOULD
be initially distributed to the client through some out-of-band

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mechanism, and SHOULD be stored locally on the client for use in all
authenticated DHCP messages. Once the client has been given its key,
it SHOULD use that key for all transactions even if the client's
configuration changes; e.g., if the client is assigned a new network
address.

Each DHCP server MUST know, or be able to obtain in a secure manner,
the keys for all authorized clients. If all clients use the same
key, clients can perform both entity and message authentication for
all messages received from servers. However, the sharing of keys
is strongly discouraged as it allows for unauthorized clients to
masquerade as authorized clients by obtaining a copy of the shared

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key. To authenticate the identity of individual clients, each client
MUST be configured with a unique key.

19.6.5.

21.6.5. Client considerations for delayed authentication protocol

19.6.5.1.

21.6.5.1. 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, RDM and replay detection field as described
in section 19.6. 21.6. The client does not include any authentication
information in the Authentication option.

19.6.5.2.

21.6.5.2. 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 19.6.3. 21.6.3.

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 a 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. 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

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unauthenticated message, the client SHOULD inform any local users and
SHOULD log the event.

19.6.5.3.

21.6.5.3. Sending Request, Confirm, Renew, Rebind Rebind, Decline or Release
messages

If the client authenticated the Advertise message through which the
client selected
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 21.6. When the
client sends a subsequent message, it MUST use the same secret used
by the server to generate the authentication information.

21.6.5.4. Sending Information-request messages

If the client has negotiated a secret with the server through a
previous message exchange, the client MUST use the same secret used
by the server to generate the authentication information. If the
client has not negotiated a secret with the server, the client MUST
use a secret that has been selected for the client through some
external mechanism.

21.6.5.5. 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 validation
and MAY log the validation failure. If the Reply fails to pass
validation, the client MUST restart the DHCP configuration process by
sending a Solicit message. The client MAY choose to remember which
server replied with a Reply message that failed to pass validation
and discard subsequent messages from that server.

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.

21.6.5.6. Receiving Reconfigure messages

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

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21.6.6. Server considerations for delayed authentication protocol

21.6.6.1. Receiving Solicit messages and Sending Advertise messages

The server selects a secret for the client and includes
authentication information in the Advertise message returned to the
client as specified in section 21.6. The server MUST record the
identifier of the secret selected for the client and use that same
secret for validating subsequent messages with the client.

21.6.6.2. Receiving Request, Confirm, Renew, Rebind or Release messages
and Sending Reply messages

The server uses the secret identified in the message and validates
the message as specified in section 21.6.3. If the message fails to
pass validation or the server does not know the secret identified by
the 'secret ID' field, the server MUST discard the message and MAY
choose to log the validation failure.

If the message passes the validation procedure, the server responds
to the specific message as described in section 18.2. The server
MUST include authentication information generated using the secret
identified in the received message as specified in section 21.6.

21.6.6.3. Sending Reconfigure messages

The server MUST include authentication information in a Reconfigure
message, generated as specified in section 21.6 using the secret the
server initially negotiated with the client to which the Reconfigure
message is to be sent.

If the server has not previously negotiated a secret with the client,
the server MUST use a secret that has been selected for the client
through some external mechanism.

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 is represented in
network order.

This document describes the DHCP options defined as part of the base
DHCP specification. Other options may be defined in the future in a
separate document.

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22.1. Format of DHCP options

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 22.3 and 22.4.

22.2. DHCP unique identifier option

The DHCP unique identifier option is used to carry a DUID. The format
for the DUID is keyed to mark the type of identifier and is of
variable length. The format of the DUID 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 DUID | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DUID type | DUID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
. DUID (cont.) .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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22.3. Identity association option

The identity association option is used to carry an identity
association, the parameters associated with the IA and the addresses
assigned to the IA.

The format of the IA 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 | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IAID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IA Status | |
+-+-+-+-+-+-+-+-+ |
. Options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_IA (TBD)

option-len See section 22.

IAID The unique identifier for this IA.

T1 The time at which the client contacts the
server from which the addresses in the IA
were obtained to extend the lifetimes of the
addresses assigned to the IA.

T2 The time at which the client contacts any
available server to extend the lifetimes of
the addresses assigned to the IA.

IA status Status of the IA in this option.

options Options associated with this IA.

The Options field encapsulates those options that are specific
to this IA. For example, all of the Address Options carrying the server,
addresses associated with this IA are in the client MUST generate authentication
information for subsequent Request, Confirm, Renew, Rebind Options field.

Note that an IA has no explicit "lifetime" or Release
messages sent to the server as described in section 19.6. "lease length" of
its own. When the
client sends a subsequent message, it MUST use the same secret used
by lifetimes of all of the server to generate addresses in an IA have
expired, the authentication information. IA can be considered as having expired. T1 and T2

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19.6.5.4. Receiving Reply messages

are included to pass
validation, the give servers explicit control over when a client MUST restart
recontacts the DHCP configuration process server about a specific IA.

In a message sent by
sending a Solicit message. The client MAY choose to remember which
server replied with a Reply message that failed to pass validation
and discard subsequent messages from that server.

19.6.6. Server considerations for delayed authentication protocol

19.6.6.1. Receiving Solicit messages T1 and Sending Advertise messages

The server selects a secret for
T2 fields indicate the client's preference for those parameters.
The client may send 0 if it has no preference for T1 and includes
authentication information in the Advertise T2. In a
message returned sent by a server to a client, the client as specified in section 19.6. The server MUST record use the
identifier of values
in the secret selected T1 and T2 fields for the client T1 and use that same
secret for validating subsequent messages with T2 parameters. The values in
the client.

19.6.6.2. Receiving Request, Confirm, Renew, Rebind or Release messages T1 and Sending Reply messages T2 fields are the number of seconds until T1 and T2.

The server uses the secret identified in MUST set the message T1 and validates T2 times to values that will allow
the message client to extend as specified appropriate the lifetimes of any addresses
in section 19.6.3. If the message fails to
pass validation or IA. If the server does not know the secret identified by intend for a client to extend the 'secret ID' field,
lifetimes of a particular address in an IA, the server MUST discard the message and MAY
choose set the
renewal time values to log occur after the validation failure.

If lifetimes on that address
expire.

T1 is the message passes time at which the validation procedure, client SHOULD begin the server responds lifetime
extension process by sending a Renew message to the specific message as described in section 16.2. The server
MUST include authentication information generated using that
originally assigned the secret
identified in addresses to the received message as specified in section 19.6.

19.6.6.3. Sending Reconfigure-Init messages

The server MUST include authentication information in a
Reconfigure-Init message, generated as specified in section 19.6
using IA. T2 is the secret time at which
the server initially selected client SHOULD start sending a Rebind message to any server. A
client MAY begin the lifetime extension process prior to T1 if it
needs additional addresses for some reason.

T1 and T2 are specified as unsigned integers that specify the client time
in seconds relative to the time at which the Reconfigure-Init message messages containing the
option is to be sent. received.

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20. DHCP options

Options are

22.4. IA Address option

The IA Address option is used to carry additional information and parameters
in DHCP messages. Every specify IPv6 addresses associated
with an IA. The IA Address option shares a common base format, as
described in section 20.1.

This document describes the DHCP options defined as part of the base
DHCP specification. Other options may must be defined encapsulated in the future in a
separate document.

20.1. Format
Options field of DHCP an Identity Association option. The Options field
encapsulates those options that are specific to this address.

The format of the IA Address option is:

option-code An unsigned integer identifying OPTION_IADDR (TBD)

option-len See section 22.

T When set to 1, indicates that this address is a
"temporary address" [17]; when set to 0, the specific option
type carried address
is not a temporary address.

addr status Status of this address in this option.

option-len IA.

prefix length Prefix length for this address.

IPv6 address An unsigned integer giving IPv6 address

preferred lifetime The preferred lifetime for the length of IPv6 address in
the option.

valid lifetime The valid lifetime for the data IPv6 address in
this the
option

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options Options associated with this address

In a message sent by a client to a server, values in octets.

option-data the preferred
and valid lifetime fields indicate the client's preference for those
parameters. The data client may send 0 if it has no preference for the option;
preferred and valid lifetimes. In a message sent by a server to a
client, the format of this data
depends on client MUST use the definition of 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.

One or more IA Address Options can appear anywhere in an IA option.

20.2. DHCP unique identifier option

22.5. Requested Temporary Addresses (RTA) Option

The DHCP unique identifier Requested Temporary Addresses (RTA) option is used by a client to carry
request a DUID. The format
for the DUID is keyed server to mark the type of identifier and is of
variable length. The format of the DUID option is: assign additional temporary addresses to an IA.

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 DUID OPTION_RTA | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DUID type | DUID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| num-requested |
. DUID (cont.) .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+

option-code OPTION_RTA (TBD)

option-len See section 22.

num-requested The number of additional temporary addresses the
client is requesting. This is an unsigned value.

This option MUST only be sent by a client and only in a Solicit,
Request, Renew, or Rebind message. It MUST only appear encapsulated
within an Identity association option. A client that does not need
any additional temporary addresses does not need to include this
option.

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20.3. Identity association option

The identity association option is used to carry an identity
association, the parameters associated with the IA and the addresses
assigned to the IA.

The format of the IA

22.6. 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 IA OPTION_ORO | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IAID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ requested-option-code-1 | T2 requested-option-code-2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IA Status | |
+-+-+-+-+-+-+-+-+ ... |
. Options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_IA OPTION_ORO (TBD)

option-len Variable; equal to 13 + number of bytes
required for ``options''

IAID See section 22.

requested-option-code-n The unique identifier option code for this IA; chosen an option requested by
the client.

A client

T1 The time at which the client contacts the
server from which the addresses in the IA
were obtained to extend the lifetimes of the
addresses assigned to the IA.

T2 The time at which the client contacts any
available server to extend the lifetimes of
the addresses assigned to the IA.

IA status Status of the IA in this option.

options Options associated with this IA

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The Options field carries those options that are specific to this
IA. This includes all of the Address Options to carry the addresses
associated with this IA.

Note that an IA has no explicit "lifetime" or "lease length" of
its own. When the lifetimes of all of the addresses in MAY include an IA have
expired, the IA can be considered as having expired. T1 and T2
are included to give servers explicit control over when Option Request option in a client
recontacts Solicit, Request,
Renew, Rebind or Confirm message to inform the server about a specific IA.

20.4. IA Address options
the client wants the server to send to the client.

22.7. Preference option

option-code OPTION_IADDR OPTION_PREFERENCE (TBD)

option-len See section 22.

pref value The number of bytes in preference value for the data area of this option

T When set to 1, indicates that server in this address is message.

A server MAY include a
"temporary address" [15]; when set Preference option in an Advertise message to 0, the address
is not a temporary address.

The 'T' bit identifies
control the associated address as selection of a temporary address. If the server is configured
to assign temporary addresses to the client, by the
server marks those temporary addresses with client. See section 17.1.3
for the 'T'
bit. The number use of temporary addresses assigned to the Preference option by the client and the lifetimes of those addresses is
determined by the administrative configuration
interpretation of
the server. The 'T' bit only identifies an address Preference option data value.

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as a temporary address; identification of an address
as "temporary" has no implication on the lifetime of
the extensibility of the lifetime

22.8. Elapsed Time

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 (TBD)

option-len See section 22.

elapsed time The amount of time since the address.

addr status Status of this address client began its
current DHCP transaction. This time is expressed in this IA.

prefix length Prefix length for this address.

IPv6 address An IPv6 address

preferred lifetime The preferred lifetime for the IPv6 address
hundredths of a second (10^-2 seconds).

A client MAY include an Elapsed Time option in messages to indicate
how long the option.

valid lifetime The valid lifetime for client has been trying to complete a DHCP transaction.
Servers and Relay Agents MAY use the IPv6 address data value in the
option

options Options associated with this address

The IA Address option is used
as input to specify IPv6 addresses associated
with an IA. It may only appear in an IA option.

The Options field carries those options that are specific policy controlling how a server responds to this
address.

20.5. Option request a client
message.

22.9. Client message 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_ORO OPTION_CLIENT_MSG | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| requested-option-code-1 | requested-option-code-2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
. DHCP client message .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_ORO OPTION_CLIENT_MSG (TBD)

option-len Variable; equal to twice the number of option codes
carried in this option.

option-data A list of See section 22.

DHCP client message The message received from the option codes for client;
forwarded verbatim to the options requested
in this option. server.

A client MAY include an Option Request option in relay agent forwards a Solicit, Request,
Renew, Rebind or Confirm message to inform the server about options
the from a client wants the server to send to a server as the client.
contents of a Client Message option in a Relay-forward message.

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20.6. Preference

22.10. Server message 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_PREFERENCE OPTION_SERVER_MSG | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| pref value |
+-+-+-+-+-+-+-+-+
. DHCP server message .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_PREFERENCE OPTION_SERVER_MSG (TBD)

option-len MUST be 1

option-data See section 22.

DHCP server message The preference value for message received from the server in this message. server;
forwarded verbatim to the client.

A server MAY include sends a Preference option in an Advertise DHCP message to
control the selection of be forwarded to a server by the client. See section 15.1.3
for the use of the Preference option by the client and the
interpretation of Preference option data value.

20.7. Elapsed Time

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 (TBD)

option-len MUST be 2

option-data The amount of time since by a relay
agent as the client began its
current DHCP transaction. This time is expressed in
hundredths contents of a second (10^-2 seconds).

A client MAY include an Elapsed Time Server Message option in messages to indicate
how long the client has been trying to complete a DHCP transaction.
Servers MAY use Relay-reply
message.

22.11. DSTM Global IPv4 Address Option

The DSTM Global IPv4 Address Option informs a client or server that
the data value Identity Association Option (IA) encapsulated in this option as input to policy
controlling how a server responds to a client message.

20.8. Client message option
contains or requests an IPv4-Mapped IPv6 Address [10], as used in the
``Dual Stack Transition Mechanism'' (DSTM) [3].

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_DSTM | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_DSTM (TBD)

option-len See section 22.

options Options associated with DSTM.

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One Identity Association Option MUST always be encapsulated within
the DSTM Global IPv4 Address Option options field and that Identity
Association MUST only be used for IPv4-Mapped IPv6 Addresses.

A DSTM Tunnel End Point Option MAY be encapsulated within the DSTM
Global IPv4 Address Option to specify one or more tunnel endpoints.

DISCUSSION:

By encapsulation the Identity Association Option within
the DSTM Global IPv4 Address Option, a server that does
not support the address type will simply ignore the entire
option and therefore not improperly allocate any addresses
to the Identity Association. This technique of using an
address typing option, SHOULD be used for other address
types that may be needed in the future.

22.12. DSTM Tunnel EndPoint Option

A DSTM Tunnel EndPoint Option can be used to provide a set of IPv6
addresses to be used as the Tunnel Endpoint (TEP) to encapsulate an
IPv6 packet within IPv6.

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_CLIENT_MSG OPTION_DSTM_TEP | option-len option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DHCP client message Tunnel End Point (TEP) |
| (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_CLIENT_MSG OPTION_DSTM_TEP (TBD)

option-len Variable; equal to the length of the forwarded DHCP
client message.

option-data The message received from the client; forwarded
verbatim to the server. See section 22.

tunnel end point IPv6 address or addresses.

A relay agent forwards a message from DSTM Tunnel EndPoint Option MUST NOT be used except when
encapsulated in a client DSTM Global IPv4 Address option.

22.13. Authentication option

The Authentication option carries authentication information to a server as
authenticate the identity and contents of a Client Message DHCP messages. The use of
the Authentication option is described in a Relay-forward message.

20.9. Server message section 21.

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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_SERVER_MSG OPTION_AUTH | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DHCP server message Protocol | Algorithm | RDM | Replay detect.|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Replay Detection (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Replay cont. | Auth. Info |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Authentication Information |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_SERVER_MSG OPTION_AUTH (TBD)

option-len Variable; equal to the length of the forwarded DHCP
server message.

option-data See section 22.

protocol The message received from authentication protocol used in
this authentication option

algorithm The algorithm used in the server; forwarded
verbatim to
authentication protocol

RDM The replay detection method used in
this authentication option

Replay detection The replay detection information for
the client.

A server sends a DHCP message to be forwarded to a client by a relay
agent RDM

Authentication information The authentication information,
as specified by the contents of a protocol and
algorithm used in this authentication
option

22.14. Server Message unicast option in a Relay-reply
message.

20.10. DSTM Global IPv4 Address Option

The DSTM Global IPv4 Address Option informs server MAY send this option to a client or server to indicate to the client
that is allowed to unicast messages to the Identity Association Option (IA) following server. When a client
receives this option will
contain an IPv4-Mapped IPv6 Address [9] in option, where permissible, the client MAY send messages
to the case of a Client
receiving server using the option, or is a Request for an IPv4-Mapped IPv6 Address address that the server specifies in the
server address field in this option.

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from a client in the case of a DHCPv6 Server receiving the option.
The option can also provide a set of IPv6 addresses to be used as

Details about when the
Tunnel Endpoint (TEP) client may send messages to encapsulate an IPv6 packet within IPv6.

This option can be used with the Request, Reply, and Reconfigure-Init
Messages for cases where a server wants to assign to clients
IPv4-Mapped IPv6 Addresses, thru the Option Request Option (ORO). using
unicast are in section 18.

option code OPTION_DSTM

option-code OPTION_UNICAST (TBD)

option length Variable: 0 or multiple of 16

tunnel end point IPv6 Address or addresses if Present

A DSTM IPv4 Global Address

option-len See section 22.

22.15. Domain Search Option MUST only apply to the IA following
this option.

20.11. Authentication option

The Authentication

This option carries authentication information to
authenticate the identity and contents provides a list of DHCP messages. The domain names a client can use of
the Authentication option is described in section 19.

The format of the Authentication option is: to
resolve DNS names.

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-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol | Algorithm | RDM | Replay detect.|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Replay Detection (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Replay cont. OPTION_DOMAIN_SEARCH_LIST | Auth. Info option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Domain Search List |
| Authentication Information |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_DOMAIN_SEARCH_LIST (TBD)

option-len See section 22.

Domain Search List The DNS domain search list the client
should use to resolve names.

The domain search list is stored in the option according to
section 10.

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option-code OPTION_AUTH (TBD)

option-length Variable

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

20.12.

22.16. Domain Name Server unicast option Option

This option is used by provides a server to send list of one or more IP addresses of DNS
servers to which a client to inform
the client it client's DNS resolver MAY send a Request, Renew, Release, and Decline by
unicasting directly to DNS [14] queries.
The DNS servers are listed in the server instead order of the All_DHCPv6_Agents
Multicast address as an optimization, when preference for use by the
client as an address
of sufficient scope to reach the server. resolver.

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_DNS_SERVERS | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| DNS server (IP address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| DNS server (IP address) |
| |
| option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_UNICAST (TBD)

option-length 0

This option only applies to the OPTION_DNS_SERVERS (11)

option-len See section 22.

DNS server IPv6 address that sends this to of a DNS name server for the
client.

20.13. Domain Search
client to use.

22.17. Status Code Option

This option provides a list of domain names returns a client can use status indication related to
resolve DNS names.

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in which it appears.

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_DOMAIN_SEARCH_LIST OPTION_STATUS_CODE | option-length option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Domain Search List status-code | status-message |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_DOMAIN_SEARCH_LIST OPTION_STATUS_CODE (TBD)

option-length variable

Domain Search List

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option-len See section 22.

status-code The DNS domain search list the client
should use to resolve names.

So that numeric code for the search list may be status encoded compactly and uniformly,
search strings in the search list
this option. The status codes are concatenated and encoded using
the technique described defined in
section 3.1 of [13].

For use in this specification, 7.4.

status-message A UTF-8 encoded text string, which MUST NOT
be null-terminated.

22.18. Circuit-ID Option

The relay agent MAY send the compression pointer (see section
4.1.4 of [13]) refers Circuit-ID option to identify the offset within the SearchString portion
of
circuit-id on which the option.

20.14. Domain Name Server Option

This option provides a list of Domain Name System [13] that a client
name resolver can use to access DNS services. There must be at least
1 server listed in this option. message was received.

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_DNS_SERVERS | option_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| DNS server (IP address) |
| | OPTION_CIRCUIT_ID | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| DNS server (IP address) |
| |
| Circuit-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_DNS_SERVERS (11) OPTION_CIRCUIT_ID (TBD)

option-len See section 22.

Circuit-ID An opaque value of arbitrary length generated
by the relay agent.

The server MUST copy the Circuit-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.

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option-length variable

DNS server IPv6 address of

22.19. User Class Option

This option is used by a DNS name server for the client to use. identify the type or category of
user or applications it represents. The DNS servers are listed information contained in
this option is an opaque field that represents the order user class of preference for use by
which the client
resolver.

20.15. Status Code Option

This option returns indications of status not related to is a specific
option.

0 1 2 3 member. The user class information carried in
this option MUST be configurable on the client.

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_USER_CLASS | option-length option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| status-code | status-message user class data |
| ... . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_STATUS_CODE (TBD)

option-length variable

status-code TBD

option-len See section 22.

user class data The numeric code for user classes carried by the status encoded in
this option. client.

The status codes are defined 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 | user class data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+

The user class len is two octets long and specifies the length of the
opaque user class data in
section 7.4.

status-message A UTF-8 encoded text string, network order.

Servers can interpret the meanings of multiple class specifications
in an implementation dependent or configuration dependent manner,
and so the use of multiple classes by a DHCP client should be based
on the specific server implementation and configuration which will
be used to process that User class option. Servers not equipped to
interpret the user class information sent by a client MUST NOT ignore it
(although it may be null-terminated.

20.16. Circuit-ID reported).

22.20. Vendor Class Option

This option provides a mechanism through which a relay agent can
identify is used by clients and servers to exchange
vendor-specific information. The definition of this information
is vendor specific. The vendor is indicated in the network attachment point through which a message was
received from vendor
class identifier option. Servers not equipped to interpret
the vendor-specific information sent by a client MUST ignore it
(although it may be reported). Clients which do not receive desired
vendor-specific information SHOULD make an attempt to operate without

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0 1 2 3 for IPv6 (-22) 21 Dec 2001

it, although they may do so (and announce they are doing so) in a
degraded mode.

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_CIRCUIT_ID OPTION_VENDOR_CLASS | option_length option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| vendor-id |
| Circuit-ID |
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-data |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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option-code OPTION_CIRCUIT_ID (TBD)

option-length variable

Circuit-ID An opaque value of arbitrary length; this
value must uniquely identify one of the
network attachments used by TBD

option-len See section 22.

vendor-id A domain name belonging to the relay agent

20.17. User Class Option

This option is vendor used by a client to
identify the type or category of
user or applications it represents. The information contained in
this option is an opaque field vendor that represents the user defined this vendor
class option.

option-data An opaque object of
which the client is a member. Based option-len octets,
presumably interpreted by vendor-specific
code on this class, a DHCP server
selects the appropriate address pool clients and servers

The vendor-id must adhere to assign an address the rules in section 10.

The Encapsulated vendor-specific options field MUST be encoded as
a sequence of code/length/value fields of identical format to the
client and
DHCP options field. Each of the appropriate configuration parameters. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_USER_CLASS opt-code | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| user class data option-data |
| . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code TBD

option-len Variable; If n user classes are carried
by the option, the length of

opt-code The code for the encapsulated option

option-len = sum of each of the user class
lengths + 2*n. See section 22.

option-data The user classes carried by the client.

The user class option may contain one or more instances of user class
data. Each instance of the user class data is formatted as follows:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
| user class1 len | user1 class data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+

The user class length is two octets long and specifies the length of
the opaque user class data in network byte order.

Servers may interpret the meanings of multiple class specifications
in an implementation dependent or configuration dependent manner,
and so area for the use of multiple classes by a DHCP client should be based encapsulated option

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on the specific server implementation and configuration which will
be used to process that User class option.

22.21. SIP Servers not equipped to
interpret the user class information sent by a client MUST ignore it
(although it may be reported).

20.18. Vendor Class Option Domain Name List

This option is used by clients and servers to exchange vendor-
specific information. The definition specifies a list of this information is vendor
specific. The vendor is indicated in the vendor class identifier
option. Servers not equipped fully-qualified domain names
to interpret the vendor-specific
information sent be used by a the SIP client MUST ignore it (although it may be
reported). Clients which do not receive desired vendor-specific
information to locate a SIP server (see
<draft-ietf-sip-srv-02.txt> [22] for more details.

The option MAY contain multiple domain names, but these SHOULD make an attempt refer
to operate without it, although
they may do so(and announce they are doing so) different SRV records, rather than different A records. Domain
names SHOULD be listed in a degraded mode. order of preference.

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_VENDOR_CLASS OPTION_SIP_SERVER_D | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-data SIP Server Domain Name List |
| . . . ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code TBD OPTION_SIP_SERVER_D (TBD)

option-len Variable

option-data See section 22.

SIP Server Domain List The information is an opaque object list of
option-len octets, presumably interpreted
by vendor-specific code on the clients and SIP servers

If a vendor potentially encodes more than one item of information
in this option, then the vendor SHOULD encode the client
should use (see section 10 for
encoding details).

22.22. SIP Servers IPv6 Address List

This option using
"Encapsulated vendor-specific options".

The Encapsulated vendor-specific options field SHOULD be encoded as specifies a
sequence of code/length/value fields list of identical syntax IPv6 addresses indicating
SIP outbound proxy servers available to the DHCP
options field.

When encapsulated vendor-specific extensions are used, each client (see
<draft-ietf-sip-srv-02.txt> [22] for more details. Servers SHOULD be
listed in order of the
encapsulated options is formatted as follows. preference.

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_SIP_SERVER_A | opt_len option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-data |
| . . . SIP Server (IP address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SIP Server (IP address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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Internet Draft DHCP for IPv6 (-22) 21 Nov Dec 2001

opt_code The code

option-code OPTION_SIP_SERVER_A (TBD)

option-len See section 22.

SIP Server IPv6 address of a SIP server for the encapsulated option

opt_len client to use.
The length of servers are listed in the encapsulated option

option-data The data area order of preference for the encapsulated option

21.
use by the client.

23. Security Considerations

Section 19 21 describes a threat model and an option that provides an
authentication framework to defend against that threat model.

22.

24. Year 2000 considerations

Since all times are relative to the current time of the transaction,
there is no problem within the DHCPv6 protocol related to any
hardcoded dates or two-digit representation of the current year.

23.

25. IANA Considerations

This document defines several new name spaces associated with DHCPv6
and DHCPv6 options. IANA is requested to manage the allocation of
values from these name spaces, which are described in the remainder
of this section. These name spaces are all to be managed separately
from the name spaces defined for DHCPv4 [7, [8, 2].

New values in each of these name spaces should be approved by the
process of IETF consensus [14].

23.1. [16].

25.1. Multicast addresses

Section 7.1 defines the following multicast addresses, which have
been assigned by IANA for use by DHCPv6:

All_DHCP_Agents address: FF02::1:2

All_DHCP_Servers address: FF05::1:3

IANA is requested to manage definition of additional multicast
addresses in the future.

23.2.

25.2. DHCPv6 message types

IANA is requested to record the message types defined in section 7.3.
IANA is requested to manage definition of additional message types in
the future.

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Internet Draft DHCP for IPv6 (-22) 21 Nov Dec 2001

23.3.

25.3. DUID

IANA is requested to record the DUID types defined in section 10.1. 11.1.
IANA is requested to manage definition of additional DUID types in
the future.

23.4.

25.4. DHCPv6 options

IANA is requested to assign option-codes to the options defined
in section 20.1. 22.1. IANA is requested to manage the definition of
additional DHCPv6 option-codes in the future.

23.5.

25.5. Status codes

IANA is requested to record the status codes defined in section 7.4.
IANA is requested to manage the definition of additional status codes
in the future.

23.6.

25.6. Authentication option

Section 19 21 defines three new name spaces associated with the
Authentication Option (section 20.11), 22.13), which are to be created and
maintained by IANA: Protocol, Algorithm and RDM.

Initial values assigned from the Protocol name space are 0 (for the
configuration token Protocol in section 19.5) 21.5) and 1 (for the delayed
authentication Protocol in section 19.6). 21.6). Additional protocols may
be defined in the future.

The Algorithm name space is specific to individual Protocols. That
is, each Protocol has its own Algorithm name space. The guidelines
for assigning Algorithm name space values for a particular protocol
should be specified along with the definition of a new Protocol.

For the configuration token Protocol, the Algorithm field MUST be
0, as described in section 19.5. 21.5. For the delayed authentication
Protocol, the Algorithm value 1 is assigned to the HMAC-MD5
generating function as defined in section 19.6. 21.6. Additional
algorithms for the delayed authentication protocol may be defined in
the future.

The initial value of 0 from the RDM name space is assigned to the
use of a monotonically increasing value as defined in section 19.4. 21.4.
Additional replay detection methods may be defined in the future.

24.

26. Acknowledgments

Thanks to the DHC Working Group for their time and input into
the specification. Ralph Droms and Thomas Narten have had a major In particular, thanks also for the consistent

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Internet Draft DHCP for IPv6 (-22) 21 Nov Dec 2001

role in shaping the continued improvement of the protocol by their
careful reviews. Many thanks to Matt Crawford, Erik Nordmark, Gerald
Maguire, and Mike Carney for their studied review as part of the
Last Call process. Thanks also for the consistent

input, ideas, and review by (in alphabetical order) Brian Carpenter,
Matt Crawford, Francis DuPont, Dupont, Ted Lemon, Josh Littlefield, Gerald
Maguire, Jack McCann, Thomas Narten, Erik Nordmark, Yakov Rekhter,
Mark Stapp, Matt Thomas, Sue Thomson, Bernie Volz and Phil Wells.

Thanks to Steve Deering and Bob Hinden, who have consistently
taken the time to discuss the more complex parts of the IPv6
specifications.

Bill Arbaugh reviewed the authentication mechanism described in
section 19. 21.

The Domain Search option described in section 20.13 22.15 is based on the
DHCPv4 domain search option, [1], and was reviewed by Bernard Aboba.

And, thanks to Steve Deering for pointing out at IETF 51 in London
that the DHCPv6 specification has (at least currently) the highest
revision number of any Internet Draft.

A. Full Copyright Statement

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.

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Internet Draft DHCP for IPv6 (-22) 21 Dec 2001

B. Appearance of Options in Message Types

The following table indicates with a "*" the options are allowed in
each DHCP message type:

DUID IA RTA ORO Pref Time Client Server DSTM DSTM
Forw. Forw. Addr Tunn
Solicit * * * *
Advert. * * * * * * *
Request * * * *
Confirm * * * *
Renew * * * *
Rebind * * * *
Decline * * * *
Release * * * *
Reply * * * * * * *
Reconf. * *
Inform. * *
R-forw. * *
R-repl. * *

Auth Server Domain Domain Status Circ. User Vendor
Unica. Search Server Code ID Class Class
Solicit * * *
Advert. * * *
Request * * *
Confirm * * *
Renew * * *
Rebind * * *
Decline * * * *
Release * * * *
Reply * * * * *
Reconf. *
Inform. * * *
R-forw. * *
R-repl. * *

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C. Appearance of Options in the Options Field of DHCP Messages

The following table indicates with a "*" where options can appear in
the options field or encapsulated in other options:

Option IA IAADDR RTA DSTM Client Server
Field Addr Forw. Forw.
Client msg. * *
Server msg. * *
DUID *
IA * *
IAADDR *
RTA *
ORO *
Pref *
Time *
Client Forw. *
Server Forw. *
DSTM Addr. *
DSTM Tunnel *
Authentic. *
Server Uni. *
Dom. Srch. *
Dom. Server *
Status Cod. * * *
Circ. ID * *
User Class *
Vend. Class *

References

[1] B. Aboba. DHCP Domain Search Option. Internet Draft, Internet
Engineering Task Force, December 2000. Work in progress.

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Internet Draft DHCP for IPv6 21 Nov 2001

[2] S. Alexander and R. Droms. DHCP Options and BOOTP Vendor
Extensions, March 1997. RFC 2132.

[3] J. Bound, L. Toutain, F. Dupont, O. Medina, A. Hossam, and
A. Durand. Dual Stack Transition Mechanism (DSTM). Internet
Draft, Internet Engineering Task Force, November 2001. Work in
progress.

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

[4]

[5] S. Bradner and A. Mankin. The Recommendation for the IP Next
Generation Protocol, January 1995. RFC 1752.

[5]

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Internet Draft DHCP for IPv6 (-22) 21 Dec 2001

[6] W.J. Croft and J. Gilmore. Bootstrap Protocol, September 1985.
RFC 951.

[6]

[7] S. Deering and R. Hinden. Internet Protocol, Version 6 (IPv6)
Specification, December 1998. RFC 2460.

[7]

[8] R. Droms. Dynamic Host Configuration Protocol, March 1997. RFC
2131.

[8]

[9] R. Droms and Droms, Editor, W. Arbaugh. Arbaugh, and Editor. Authentication for
DHCP Messages.
Internet Draft, Internet Engineering Task Force, January Messages, June 2001.
Work in progress.

[9] RFC 3118.

[10] R. Hinden and S. Deering. IP Version 6 Addressing Architecture,
July 1998. RFC 2373.

[10]

[11] S. Kent and R. Atkinson. Security Architecture for the Internet
Protocol, November 1998. RFC 2401.

[11]

[12] H. Krawczyk, M. Bellare, and R. Canetti. HMAC: Keyed-Hashing
for Message Authentication, February 1997. RFC 2104.

[12]

[13] David L. Mills. Network Time Protocol (Version 3)
Specification, Implementation, March 1992. RFC 1305.

[13]

[14] P.V. Mockapetris. Domain names - concepts and facilities,
November 1987. RFC 1034.

[15] P.V. Mockapetris. Domain names - implementation and
specification, November 1987. RFC 1035.

[14]

[16] T. Narten and H. Alvestrand. Guidelines for Writing an IANA
Considerations Section in RFCs, October 1998. RFC 2434.

[15]

[17] T. Narten and R. Draves. Privacy Extensions for Stateless
Address Autoconfiguration in IPv6, January 2001. RFC 3041.

[16]

[18] T. Narten, E. Nordmark, and W. Simpson. Neighbor Discovery for
IP Version 6 (IPv6), December 1998. RFC 2461.

[17]

[19] D.C. Plummer. Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet address
for transmission on Ethernet hardware, November 1982. RFC 826.

[18]

[20] J. Postel. User Datagram Protocol, August 1980. RFC 768.

[21] R. Rivest. The MD5 Message-Digest Algorithm, April 1992. RFC
1321.

[22] H. Schulzrinne and J. Rosenberg. SIP: Session Initiation
Protocol -- Locating SIP Servers. Internet Draft, Internet
Engineering Task Force, March 2001. Work in progress.

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Internet Draft DHCP for IPv6 (-22) 21 Nov Dec 2001

[19] R. Rivest. The MD5 Message-Digest Algorithm, April 1992. RFC
1321.

[20]

[23] S. Thomson and T. Narten. IPv6 Stateless Address
Autoconfiguration, December 1998. RFC 2462.

[21]

[24] P. Vixie, Ed., S. Thomson, Y. Rekhter, and J. Bound. Dynamic
Updates in the Domain Name System (DNS UPDATE), April 1997. RFC
2136.

Chair's Address

The working group can be contacted via the current chair:

Ralph Droms
Cisco Systems
300 Apollo Drive
Chelmsford, MA 01824

Phone: (978) 244-4733
E-mail: rdroms@cisco.com

Authors' Addresses

Questions about this memo can be directed to:

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Internet Draft DHCP for IPv6 (-22) 21 Nov Dec 2001

Authors' Addresses

Questions about this memo can be directed to:

Jim Bound
Compaq Computer Corporation
ZK3-3/W20
110 Spit Brook Road
Nashua, NH 03062-2698
USA
Phone: +1 603 884 0062
Email: Jim.Bound@compaq.com

Mike Carney
Sun Microsystems, Inc
Mail Stop: UMPK17-202
901 San Antonio Road
Palo Alto, CA 94303-4900
USA
Phone: +1-650-786-4171
Email: mwc@eng.sun.com

Charles E. Perkins
Communications Systems Lab
Nokia Research Center
313 Fairchild Drive
Mountain View, California 94043
USA
Phone: +1-650 625-2986
Email: charliep@iprg.nokia.com
Fax: +1 650 625-2502

Ralph Droms
Cisco Systems
300 Apollo Drive
Chelmsford, MA 01824
USA
Phone: +1 978 244 4733
Email: rdroms@cisco.com

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