WDIFF

draft-ietf-dhc-dhcpv6-19.txt --> draft-ietf-dhc-dhcpv6-20.txt

Internet Engineering Task Force J. Bound
INTERNET DRAFT Compaq
DHC Working Group M. Carney
Obsoletes: draft-ietf-dhc-dhcpv6-18.txt draft-ietf-dhc-dhcpv6-19.txt Sun Microsystems, Inc
C. Perkins
Nokia Research Center
R. Droms(ed.)
Cisco Systems
30 June
15 Oct 2001

Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
draft-ietf-dhc-dhcpv6-19.txt
draft-ietf-dhc-dhcpv6-20.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 dhcp-v6@bucknell.edu 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], 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 1

3. Background 1

4. Design Goals 3 2

5. Non-Goals 3

6. Terminology 4 3
6.1. IPv6 Terminology . . . . . . . . . . . . . . . . . . . . 4 3
6.2. DHCP Terminology . . . . . . . . . . . . . . . . . . . . 5

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

8. Overview Message Formats 10
8.1. How does a node know to use DHCP? DHCP Solicit Message Format . . . . . . . . . . . . 10
8.2. What if the client and server(s) are on different links? 10
8.3. How does a client request configuration parameters from
servers? . . . 11
8.2. DHCP Advertise Message Format . . . . . . . . . . . . . . 11
8.3. DHCP Request Message Format . . . . . . 11
8.4. How do clients and servers identify and manage addresses? 11
8.5. Can a client release its assigned addresses before the lease
expires? . . . . . . . . . 12
8.4. DHCP Confirm Message Format . . . . . . . . . . . . . . 12
8.6. What if the client determines one or more of its assigned
addresses are already being used by another client? . 12
8.7. How are clients notified of server configuration changes? 12

9. Message Formats 12
9.1.
8.5. DHCP Solicit Renew Message Format . . . . . . . . . . . . . . . 13
9.2. . 12
8.6. DHCP Advertise Rebind Message Format . . . . . . . . . . . . . . 13
9.3. . 12
8.7. DHCP Request Reply Message Format . . . . . . . . . . . . . . . 14
9.4. . 13
8.8. DHCP Confirm Release Message Format . . . . . . . . . . . . . . . 14
9.5. 13
8.9. DHCP Renew Decline Message Format . . . . . . . . . . . . . . . . 15
9.6. 13
8.10. DHCP Rebind Reconfigure-init Message Format . . . . . . . . . . 13

9. Relay messages 14
9.1. Relay-forward message . . . . . 15
9.7. DHCP Reply Message Format . . . . . . . . . . . . . 14
9.2. Relay-reply message . . . 15
9.8. DHCP Release Message Format . . . . . . . . . . . . . . . 16

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9.9. . 15

10. DHCP Decline Message Format unique identifier (DUID) 15
10.1. DUID contents . . . . . . . . . . . . . . . . 16
9.10. DHCP Reconfigure-init Message Format . . . . . . 15
10.2. DUID based on link-layer address plus time . . . . 17

10. Relay messages 17
10.1. Relay-forward message . . . 16
10.3. Vendor-assigned unique ID. . . . . . . . . . . . . . . . 17
10.2. Relay-reply message
10.4. Link-layer address . . . . . . . . . . . . . . . . . . . 18

11. DHCP unique identifier (DUID) 18

12. Identity association 18

13. 17

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11. Identity association 18

12. Selecting addresses for assignment to an IA 18

13. Reliability of Client Initiated Message Exchanges 19
13.1. Solicit

14. Message Validation validation 20
14.1. Use of Transaction-ID field . . . . . . . . . . . . . . . 19
13.2. Advertise Message Validation 21
14.2. Solicit message . . . . . . . . . . . . . . 19
13.3. Client Behavior . . . . . . . 21
14.3. Advertise message . . . . . . . . . . . . . . . 19
13.3.1. Creation and sending of the Solicit message . . . 19
13.3.2. Time out and retransmission of Solicit Messages . 20
13.3.3. Receipt of Advertise messages . 21
14.4. Request message . . . . . . . . . . 20
13.4. Server Behavior . . . . . . . . . . . 21
14.5. Confirm message . . . . . . . . . . 21
13.4.1. Receipt of Solicit messages . . . . . . . . . . . 21
13.4.2. Creation and sending of Advertise messages
14.6. Renew message . . . 21

14. DHCP Client-Initiated Configuration Exchange 22
14.1. Client Message Validation . . . . . . . . . . . . . . . . 23
14.2. Server Message Validation . . . 21
14.7. Rebind message . . . . . . . . . . . . . 23
14.3. Client Behavior . . . . . . . . 22
14.8. Decline messages . . . . . . . . . . . . . 24
14.3.1. Creation and sending of Request messages . . . . 24
14.3.2. Creation and sending of Confirm messages . . . 22
14.9. Release message . 25
14.3.3. Creation and sending of Renew messages . . . . . 26
14.3.4. Creation and sending of Rebind messages . . . . . 27
14.3.5. Receipt of Reply message in response to a Request,
Confirm, Renew or Rebind message . . . . . 28
14.3.6. Creation and sending of Release messages . . . . 29
14.3.7. Time out and retransmission of Release Messages . 30
14.3.8. Receipt of 22
14.10. Reply message in response to a Release
message . . . . . . . . . . . . . . . . . 30
14.3.9. Creation and sending of Decline messages . . . . 30
14.3.10. Time out and retransmission of Decline Messages . 31
14.3.11. Receipt of Reply message in response to a Release 22
14.11. Reconfigure-init message . . . . . . . . . . . . . . . . 22
14.12. Relay-forward message . 31
14.4. Server Behavior . . . . . . . . . . . . . . . . . 23
14.13. Relay-reply message . . . . 31
14.4.1. Receipt of Request messages . . . . . . . . . . . 32
14.4.2. Receipt of Confirm messages . . . . 23

15. DHCP Server Solicitation 23
15.1. Client Behavior . . . . . . . 32
14.4.3. Receipt of Renew messages . . . . . . . . . . . . 33
14.4.4. Receipt . . 23
15.1.1. Creation of Rebind Solicit messages . . . . . . . . . . . 34
14.4.5. Receipt 23
15.1.2. Transmission of Release messages . . . Solicit Messages . . . . . . . . 35
14.4.6. Sending 23
15.1.3. Receipt of Reply Advertise messages . . . . . . . . . . . . 36

15. DHCP Server-Initiated Configuration Exchange 36
15.1. Reconfigure-init Message Validation 25
15.2. Server Behavior . . . . . . . . . . . 36
15.2. Server Behavior . . . . . . . . . . 25
15.2.1. Receipt of Solicit messages . . . . . . . . . . . 36
15.2.1. Creation and sending of Reconfigure-init messages 36

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15.2.2. Time out Creation and retransmission transmission of Reconfigure-init Advertise messages . 26

16. DHCP Client-Initiated Configuration Exchange 26
16.1. Client Behavior . . . . . . . . . . . . . . . . 37
15.2.3. Receipt of Request messages . . . . . 27
16.1.1. Creation and transmission of Request messages . . 27
16.1.2. Creation and transmission of Confirm messages . . 28
16.1.3. Creation and transmission of Renew messages . . 37
15.3. Client Behavior . 29
16.1.4. Creation and transmission of Rebind messages . . 31
16.1.5. Receipt of Reply message in response to a Request,
Confirm, Renew or Rebind message . . . . . 32
16.1.6. Creation and transmission of Release messages . . 33
16.1.7. Receipt of Reply message in response to a Release
message . . . . . . . . . . . 38
15.3.1. Receipt of Reconfigure-init messages . . . . . . 38
15.3.2. 35
16.1.8. Creation and sending transmission of Request Decline messages . . . . 39
15.3.3. Time out and retransmission of Request messages . 39
15.3.4. 35
16.1.9. Receipt of Reply messages . . . . message in response to a Decline
message . . . . . . . . 39

16. Relay Behavior 39
16.1. Relaying of client messages . . . . . . . . . 36
16.2. Server Behavior . . . . . . 39
16.2. Relaying of server messages . . . . . . . . . . . . . . . 40

17. Authentication 36
16.2.1. Receipt of DHCP Request messages 40
17.1. DHCP threat model . . . . . . . . . . . 36
16.2.2. Receipt of Confirm messages . . . . . . . . . 40
17.2. Summary of DHCP authentication . . 37
16.2.3. Receipt of Renew messages . . . . . . . . . . . 41
17.3. Replay detection . . 38
16.2.4. Receipt of Rebind messages . . . . . . . . . . . 39
16.2.5. Receipt of Release messages . . . . . . . 41
17.4. Configuration token protocol . . . . 40
16.2.6. Receipt of Decline messages . . . . . . . . . . 42
17.5. Delayed authentication protocol . 40
16.2.7. Sending of Reply messages . . . . . . . . . . . . 42
17.5.1. Management issues in the delayed authentication
protocol 41

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17. DHCP Server-Initiated Configuration Exchange 41
17.1. Server Behavior . . . . . . . . . . . . . . . . . 42
17.5.2. Use of the Authentication option in the delayed
authentication protocol . . . . 41
17.1.1. Creation and transmission of Reconfigure-init
messages . . . . . 43
17.5.3. Message validation . . . . . . . . . . . . 41
17.1.2. Time out and retransmission of Reconfigure-init
messages . . . 44
17.5.4. Key utilization . . . . . . . . . . . . . . 42
17.1.3. Receipt of Request messages . . . 44
17.5.5. Client considerations for delayed authentication
protocol . . . . . . . . 42
17.2. Client Behavior . . . . . . . . . 44
17.5.6. Receiving Advertise messages . . . . . . . . . . 45
17.5.7. Server considerations for delayed authentication
protocol . . 43
17.2.1. Receipt of Reconfigure-init messages . . . . . . 43
17.2.2. Creation and sending of Request messages . . . . 44
17.2.3. Time out and retransmission of Request messages . 44
17.2.4. Receipt of Reply messages . . . . 46

18. DHCP options 46
18.1. Format of DHCP options . . . . . . . . 44

18. Relay Behavior 44
18.1. Relaying of client messages . . . . . . . . . 47
18.2. DHCP unique identifier option . . . . . . 45
18.2. Relaying of server messages . . . . . . . . 47
18.3. Identity association option . . . . . . . 45

19. Authentication of DHCP messages 45
19.1. DHCP threat model . . . . . . . . 47
18.4. Option request option . . . . . . . . . . . . 46
19.2. Security of messages sent between servers and relay agents 46
19.3. Summary of DHCP authentication . . . . . . 50
18.5. Client message option . . . . . . . 46
19.4. Replay detection . . . . . . . . . . . 50
18.6. Server message option . . . . . . . . . 47
19.5. Configuration token protocol . . . . . . . . . 51
18.7. Retransmission parameter option . . . . . 47
19.6. Delayed authentication protocol . . . . . . . . 51
18.8. DSTM Global IPv4 Address Option . . . . . 48
19.6.1. Management issues in the delayed authentication
protocol . . . . . . . . 51
18.9. Authentication option . . . . . . . . . . . . . . . . . . 52
18.10. Server unicast 48
19.6.2. Use of the Authentication option in the delayed
authentication protocol . . . . . . . . . 48
19.6.3. Message validation . . . . . . . . . 53
18.11. Domain Search Option . . . . . . 49
19.6.4. Key utilization . . . . . . . . . . . . 53
18.12. Domain Name Server Option . . . . . 49
19.6.5. Client considerations for delayed authentication
protocol . . . . . . . . . . . . 54

19. DHCP Client Implementor Notes 55
19.1. Primary Interface . . . . . 50
19.6.6. Server considerations for delayed authentication
protocol . . . . . . . . . . . . . . . 55
19.2. Advertise Message and Configuration Parameter Caching . . 55
19.3. Time out and retransmission variables 51

20. DHCP options 52
20.1. Format of DHCP options . . . . . . . . . . 55
19.4. Server Preference . . . . . . . 52
20.2. DHCP unique identifier option . . . . . . . . . . . . . 56

20. DHCP Server Implementor Notes 56
20.1. Client Bindings . 53
20.3. Identity association option . . . . . . . . . . . . . . . 53
20.4. Option request option . . . . . 56

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20.2. Reconfigure-init Considerations . . . . . . . . . . . . . 56
20.3. Server
20.5. Preference option . . . . . . . . . . . . . . . . . . . . 56
20.4. Request Message Transaction-ID Cache . . . . . . . . .
20.6. Elapsed Time . 57

21. DHCP Relay Implementor Notes 57

22. Security 57

23. Year 2000 considerations 57

24. IANA Considerations 57
24.1. DHCPv6 options . . . . . . . . . . . . . . . . . . . . . 57
24.2. Multicast addresses . . . . .
20.7. Client message option . . . . . . . . . . . . . . 58
24.3. Status codes . . . . 57
20.8. Server message option . . . . . . . . . . . . . . . . . . 58
24.4. Retransmission parameter option
20.9. DSTM Global IPv4 Address Option . . . . . . . . . . . . . 58
24.5.
20.10. Authentication option . . . . . . . . . . . . . . . . . . 58

25. Acknowledgments 59

A. Comparison between DHCPv4 and DHCPv6 59

B. Full Copyright Statement 61

C. Changes in this draft 61
C.1. Reconfigure-init .
20.11. Server unicast option . . . . . . . . . . . . . . . . . . 60
20.12. Domain Search Option . 62
C.2. Authentication . . . . . . . . . . . . . . . . . 60
20.13. Domain Name Server Option . . . . 62
C.3. Confirm message . . . . . . . . . . . . 61
20.14. Status Code Option . . . . . . . . . 62
C.4. Failure of Rebind message . . . . . . . . . . 61
20.15. Circuit-ID Option . . . . . . 63
C.5. Server behavior in response to Release message . . . . . 63
C.6. Client behavior when sending a Release message . . . . . 63
C.7. IA option . . . . 62
20.16. User Class Option . . . . . . . . . . . . . . . . . . . . 63
C.8. DSTM option . . . .
20.17. Vendor Class Option . . . . . . . . . . . . . . . . . . . 63
C.9. Server unicast option . . . . . . . . . . . . . . . . . . 64
C.10. Domain search option . . . . . . . . . . . . . . . . . . 64
C.11. DNS servers option . . . . . . . . . . . . . . . . . . . 64
C.12. DUID and IAID . . . . . . . . . . . . . . . .

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21. Security Considerations 65

22. Year 2000 considerations 65

23. IANA Considerations 65
23.1. Multicast addresses . . . . . . 64
C.13. Continuing to poll with Solicit . . . . . . . . . . . . . 64
C.14. Using 65
23.2. DHCPv6 without address assignment . . . . . . . . . 64
C.15. Potential crossing in flight of Request and Reconfigure-init
messages . . . . . . . . . . . . . . . . message types . . . . . . . 64

D. Open Issues for Working Group Discussion 64
D.1. Generation and use of DUID and IAID . . . . . . . . . . . 65
D.2. Address registration . . . . . . . . . .
23.3. DUID . . . . . . . . 65
D.3. Prefix advertisement . . . . . . . . . . . . . . . . . . 65
D.4. DHCP-DNS interaction . . . . . . . . . . . .
23.4. DHCPv6 options . . . . . . 65
D.5. Use of term "agent" . . . . . . . . . . . . . . . 66
23.5. Status codes . . . . 65
D.6. Additional options . . . . . . . . . . . . . . . . . . 66
23.6. Authentication option . 65
D.7. Operational parameters . . . . . . . . . . . . . . . . . 65 66

24. Acknowledgments 66

A. Comparison between DHCPv4 and DHCPv6 67

B. Full Copyright Statement 69

References 69

Chair's Address 68

Author's Address 68 71

Authors' Addresses 71

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1. Introduction

This document describes DHCP for IPv6 (DHCP), a UDP [18]
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]. DHCP is a stateful counterpart to
stateless autoconfiguration. Note that both stateful and stateless
autoconfiguration can be used concurrently in the same environment,
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 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] will find DHCP for IPv6
provides a superset of features, and benefits from the additional
features of IPv6 and freedom from BOOTP [5]-backward the constraints of backward
compatibility
constraints. with BOOTP [5]. For more information about the
differences between DHCP for IPv6 and DHCP for IPv4, see Appendix A.

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].

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

Related work in

The IPv6 that would best serve an Specification provides the base architecture and design of
IPv6. Related work in IPv6 that would best serve an implementor
to study is the IPv6 Specification [6], the IPv6 Addressing
Architecture [9], IPv6 Stateless Address Autoconfiguration [20], IPv6
Neighbor Discovery Processing [16], and Dynamic Updates to DNS [22].
These specifications enable DHCP to build upon the IPv6 work to provide

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provide both robust stateful autoconfiguration and autoregistration
of DNS Host Names.

The IPv6 Specification provides the base architecture and design of
IPv6. A key point for DHCP implementors to understand is that IPv6
requires that every link in the Internet have an MTU of 1280 octets
or greater (in IPv4 the requirement is 68 octets). This means that
a UDP packet of 536 octets will always pass through an internetwork
(less 40 octets for the IPv6 header), as long as there are no IP
options prior to the UDP header in the packet. But, IPv6 does not
support fragmentation at routers, so that fragmentation takes place
end-to-end between hosts. If a DHCP implementation needs to send a
packet greater than 1500 octets it can either fragment the UDP packet
into fragments of 1500 octets or less, or use Path MTU Discovery [11]
to determine the size of the packet that will traverse a network
path.

DHCP clients use Path MTU discovery when they have an address of
sufficient scope to reach the DHCP server. If a DHCP client does not
have such an address, that client MUST fragment its packets if the
resultant message size is greater than the minimum 1280 octets.

Path MTU Discovery for IPv6 is supported for both UDP and TCP and
can cause end-to-end fragmentation when the PMTU changes for a
destination.

The IPv6 Addressing Architecture specification [9] 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
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] (Addrconf) specifies procedures
by which a node may autoconfigure addresses based on router
advertisements [16], 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 addrconf stateless address
autoconfiguration is a design requirement of DHCP (see Section 4).

IPv6 Neighbor Discovery [16] is the node discovery protocol in IPv6
which replaces and enhances functions of ARP [17]. To understand
IPv6 and Addrconf stateless address autoconfiguration it is strongly
recommended that implementors understand IPv6 Neighbor Discovery.

Dynamic Updates to DNS [22] is a specification that supports the
dynamic update of DNS records for both IPv4 and IPv6. DHCP can use
the dynamic updates to DNS to integrate addresses and name space to

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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 autoconf [20]. address
autoconfiguration [20], 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.

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

- DHCP coexists with statically configured, non-participating nodes
and with existing network protocol implementations.

- 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].

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

- 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.

- How to manage a DHCP domain or DHCP server.

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

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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], IPv6 Addressing Architecture [9], and IPv6 Stateless
Address Autoconfiguration [20] 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).

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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.

link A communication facility or medium over
which nodes can communicate at the link
layer, i.e., the layer immediately below
IP. Examples are Ethernet (simple or
bridged); Token Ring; PPP links, X.25,
Frame Relay, or ATM networks; and Internet
(or higher) layer "tunnels", such as
tunnels over IPv4 or IPv6 itself.

link-layer identifier A link-layer identifier for an interface.
Examples include IEEE 802 addresses for
Ethernet or Token Ring network interfaces,
and E.164 addresses for ISDN links.

link-local address An IP 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.

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

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.

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6.2. DHCP Terminology

Terminology specific to DHCP can be found below.

abort status A status value returned to the
application that has invoked a DHCP
client operation, indicating anything
other than success.

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 server's information the server has about
the addresses in an IA and any other
configuration information assigned to
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.
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.

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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 Unique IDentifier for a client.

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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.

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.

7.1. Multicast Addresses

DHCP makes use of the following multicast addresses:

All DHCP Agents

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 those agents'

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address(es) for those agents. All agents (servers and
relays) are members of this multicast group.

All DHCP Servers

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] 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

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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.

7.3. DHCP message types

DHCP defines the following message types. More detail on these
message types can be found in Section 9. 8. Message types 0 and
TBD--255 13-255
are reserved and MUST be silently ignored. for future use. The message code for each message type
is shown with the message name.

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

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

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

CONFIRM (4) The DHCP Confirm (or 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

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assigned by the server to the client are
still valid.

RENEW (5) The DHCP Renew (or Renew) message is used by clients to
obtain 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
assigned the IA when the lease on an IA is
about to expire.

REBIND (6) The DHCP Rebind (or Rebind) message is used by clients to
obtain 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 clients
sends a Rebind message to all available DHCP
servers when the lease on an IA is about to
expire.

REPLY (7) The DHCP Reply (or Reply) message is used by servers
responding to Request, Confirm, Renew,
Rebind, Release and Decline messages. In the case of responding

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case of responding to a Request, Confirm,
Renew or Rebind message, the Reply contains
configuration parameters destined for the
client.

RELEASE (8) The DHCP Release (or Release) message is used by clients to
return one or more IP addresses to servers.

DECLINE (9) The DHCP Decline (or 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 (10) The DHCP Reconfigure-init (or
Reconfigure-init) 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.

RELAY-FORW (11) The DHCP Relay-forward (or 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.

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RELAY-REPL (12) The DHCP Relay-reply (or 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. Error Values Status Codes

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

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7.4.1. Generic Error Values Status Codes

The following symbolic names status codes in this section are used between client clients and server
implementations servers
to convey error status conditions. The following table contains the actual numeric values status
codes, the name for each name. 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
errors status codes are organized in logical groups.

_______________________________________________________________
|Error_Name___|Error_ID|_Description_________________________|_
|Success______|00______|_Success_____________________________|_
|UnspecFail___|16______|_Failure,_reason_unspecified_________|_
|AuthFailed___|17______|_Authentication_failed_or_nonexistent|_
|PoorlyFormed_|18______|_Poorly_formed_message_______________|_
|Unavail______|19______|_Addresses_unavailable_______________|_

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

7.4.2. Server-specific Error Values Status Codes

The following symbolic names status codes in this section are used by server implementations servers to convey error status
conditions to clients. The following table contains the
actual 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
---- ---- -----------
NoBinding 32 Client record (binding) unavailable
ConfNoMatch 33 Client record Confirm not match IA
RenwNoMatch 34 Client record Renew not match IA
RebdNoMatch 35 Client record Rebind not match IA
InvalidSource 36 Invalid Client IP address
NoServer 37 Relay cannot find Server Address
NoPrefixMatch 38 One or more prefixes of the addresses
in the IA is not valid for each name.
_______________________________________________________________
|Error_Name____|Error_ID|_Description________________________|_
|NoBinding_____|20______|_Client_record_(binding)_unavailable|_
|ConfNoMatch___|21______|_Client_record_Confirm_not_match_IA_|_

|RenwNoMatch___|22______|_Client_record_Renew_not_match_IA___|_
|RebdNoMatch___|23______|_Client_record_Rebind_not_match_IA__|_
|InvalidSource_|24______|_Invalid_Client_IP_address__________|_
|NoServer______|25______|_Relay_cannot_find_Server_Address___|_
|ICMPError_____|64______|_Server_unreachable_(ICMP_error)____|_ the link
from which the client message was received
ICMPError 64 Server unreachable (ICMP error)

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7.5. Configuration Variables

This section presents a table of client and server configuration
variables and the default or initial values for these variables. The
client-specific variables MAY be configured on the server

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 sec Initial Rebind timeout
REB_MAX_RT 600 secs Max Rebind 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

8. Message Formats

All DHCP messages sent between clients and MAY be
delivered to the client through servers share an identical
fixed format header and a variable format area for options. Not all
fields in the "DHCP Retransmission Parameter
Option" header are used in a Reply every message.

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

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_________________________________________________________________________
|Parameter__________|Default|_Description______________________________|_
|MIN_SOL_DELAY______|1______|_MIN_(secs)_to_delay_1st_mesg_____________|_
|MAX_SOL_DELAY______|5______|_MAX_(secs)_to_delay_1st_mesg_____________|_
|ADV_MSG_TIMEOUT____|500____|_SOL_Retrans_timer_(msecs)________________|_
|ADV_MSG_MAX________|30_____|_MAX_timer_value_(secs)___________________|_
|SOL_MAX_ATTEMPTS___|-1_____|_MAX_attempts_(-1_=_infinite)_____________|_
|REP_MSG_TIMEOUT____|250____|_Retrans_timer_(msecs)_for_Reply__________|_
|QRY_MSG_ATTEMPTS___|10_____|_MAX_Request/Confirm/Renew/Rebind_attempts|_
|REL_MSG_ATTEMPTS___|5______|_MAX_Release/Decline_attempts_____________|_
|RECREP_MSG_TIMEOUT_|2000___|_Retrans_timer_(msecs)____________________|_
|REC_MSG_ATTEMPTS___|10_____|_Reconfigure_attempts_____________________|_
|REC_THRESHOLD______|100____|_%_of_required_clients____________________|_
|SRVR_PREF_WAIT_____|2______|_Advertise_Collect_timer_(secs)___________|_

8. Overview

This section provides a general overview

The following diagram illustrates the DHCP message header:

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 interaction between fields in the functional entities DHCP
message header in each of DHCP. The overview is organized the DHCP messages. In these descriptions,
fields that are not used in a message are marked as "unused". All
unused fields in a
series of questions message MUST be transmitted as zeroes and answers. Details ignored
by the receiver of the message.

8.1. DHCP such as message
formats and retransmissions can be found in later sections of this
document.

8.1. How does a node know to use DHCP? Solicit Message Format

msg-type SOLICIT

transaction-ID An unconfigured node determines that it is to use DHCP for
configuration of an interface unsigned integer generated by detecting the presence (or absence)
of routers on the link. If router(s) are present, the node examines
router advertisements to determine if DHCP should be client used
to
configure the interface. If there are no routers present, then
the node identify this Solicit message.

server-address (unused) MUST use be 0

options See section 20.

8.2. DHCP Advertise Message Format

msg-type ADVERTISE

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

server-address The IP address of the server that generated this process can
message. The address must have sufficient scope
to be found in neighbor discovery [16] and stateless
autoconfiguration [20].

8.2. What if reachable from the client and server(s) are on different links?

Use of client.

options See section 20.

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8.3. DHCP relays
be set up on the client's link, because a client may only have a
link-local address. Relays receive messages from Request Message Format

msg-type REQUEST

transaction-ID An unsigned integer generated by the client and
forward them used
to some set identify this Request message.

server-address The IP address of servers within the DHCP domain. The
client message is forwarded verbatim as an option in server to which the this
message is directed, copied from an Advertise
message.

options See section 20.

8.4. DHCP Confirm Message Format

msg-type CONFIRM

transaction-ID An unsigned integer generated by the relay to the server. A relay will include one of its own
addresses (of sufficient scope) from the interface on client used
to identify this Confirm message.

server-address MUST be zero.

options See section 20.

8.5. DHCP Renew Message Format

msg-type RENEW

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

server-address The IP address of the client, as well as server to which this Renew
message is directed, which MUST be the prefix length address
of that address, in its
message to the server. Servers receiving server from which the forwarded traffic
use this information to aid IAs in selecting configuration parameters
appropriate to the client's link.

Servers use relays to forward messages to clients. The this message
intended for
were originally assigned.

options See section 20.

8.6. DHCP Rebind Message Format

msg-type REBIND

transaction-ID An unsigned integer generated by the client is carried as an option in the message used
to the identify this Rebind message.

server-address MUST be zero.

options See section 20.

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relay. The relay extracts

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 option and forwards
it to the client. Servers use the relay's

server-address The IP address as of the destination server. The address must
have sufficient scope to forward client-destined messages for final delivery be reachable from the
client.

options See section 20.

8.8. DHCP Release Message Format

msg-type RELEASE

transaction-ID An unsigned integer generated by the relay.

Relays forward client messages used
to servers using some combination identify this Release message.

server-address The IP address of the All DHCP Servers site-local multicast address, some other
(perhaps a combination) of site-local multicast addresses set up
within server that assigned the
addresses.

options See section 20.

8.9. DHCP domain to include Decline Message Format

msg-type DECLINE

transaction-ID An unsigned integer generated by the servers in that domain, or a
list of unicast addresses for servers. client used
to identify this Decline message.

server-address The network administrator
makes relay configuration decisions based upon the topological
requirements (scope) IP address of the DHCP domain they are managing. Note server that if assigned the
addresses.

options See section 20.

8.10. DHCP domain spans more than the site-local scope, then
the relays MUST be configured with global addresses for the client's
link so as to be reachable Reconfigure-init Message Format

msg-type RECONFIG-INIT

transaction-ID An unsigned integer generated by servers outside the relays' site-local
environment.

8.3. How does a client request configuration parameters from servers?

To request configuration parameters, the client forms a Request
message, and sends it server used
to identify this Reconfigure-init message.

server-address The IP address of the DHCP server either directly (the server is
on the same link as the client) or indirectly (through issuing the on-link
relay).
Reconfigure-init message. The client MAY include a Option Request Option 18.4 (ORO)
along with other options address must have
sufficient scope to request specific information be reachable from the
server. Note that the client MAY form multiple Request client.

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options See section 20.

9. Relay messages
and send each of them

Relay agents exchange messages with servers to different forward messages
between clients and servers that are not connected to request potentially
different information (perhaps based upon what was advertised) in
order to satisfy its needs. As a client's needs may change over time
(perhaps based upon an application's requirements), the client may
form additional Request messages to request additional information as
it is needed.

The server(s) respond with Reply messages containing the requested
configuration parameters, same link.
There are two relay messages, which can include status information
regarding share the information requested by 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-prefix |
| |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| | |
+-+-+-+-+-+-+-+-+ |
| client-return-address |
| |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| | |
+-+-+-+-+-+-+-+-+ |
. .
. options (variable number and length) .... .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

9.1. Relay-forward message

The Reply MAY
also include additional information.

8.4. How do clients and servers identify and manage addresses?

Servers and clients manage addresses following table defines the use of message fields in groups called "identity
associations." Each identity association (IA) is identified using a unique identifier.
Relay-forward message.

msg-type RELAY-FORW

link-prefix An identity association may contain one or
more IPv6 addresses. DHCP servers assign addresses address with a prefix that is assigned
to identity
associations. DHCP clients use the addresses in an identity
association to configure interfaces. There is always at least one
identity association per interface that a link from which the client wishes to configure.
Each address in should
be assigned an IA has its own preferred and valid lifetime. Over
time, address.

client-return-address The source address from the server may change IP datagram
in which the characteristics of message from the addresses in
an IA; for example, client was
received by changing the preferred or valid lifetime for
an address in the IA. The server may also add or delete addresses
from an IA; for example, deleting old addresses and adding new
addresses to renumber relay agent

options MUST include a client. A client can request "Client message option";
see section 20.7; MAY include other
options added by the current relay agent

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list

9.2. Relay-reply message

The following table defines the use of addresses assigned to an IA from message fields in a server through an exchange
of protocol messages.

8.5. Can
Relay-forward message.

msg-type RELAY-REPL

link-prefix An address with a client release its prefix that is assigned addresses before
to the lease
expires?

A client forms a Release message, including options identifying link from which the IA to client should
be released. assigned an address.

client-return-address The client sends the Release to source address from the server IP datagram
in which assigned the addresses to message from the client initially. If that
server cannot be reached after was
received by the relay agent

options MUST include a certain number of attempts (see "Server message option";
see section 7.5), the 20.8; MAY include other
options

10. DHCP unique identifier (DUID)

Each DHCP client can abandon the Release attempt. In this
case, has a DUID. DHCP servers use DUIDs to identify
clients for the address(es) selection of configuration parameters and in
the IA will be reclaimed by the server(s)
when the lifetimes on the addresses expire.

8.6. What if association of IAs with clients. See section 20.2 for the client determines one or more
representation of its assigned addresses
are already being used by another client?

If the client determines through a mechanism like Duplicate Address
Detection [20] that the address it was assigned by the server is
already DUID in use by another client, the client will send a Decline
message 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 server.

8.7. How are clients notified of server configuration changes?

There are two possibilities. Either the clients discover the new
information when they revisit the server(s) to request types defined in this document
as additional
configuration information/extend DUID types may be defined in the lifetime on future.

The DUID is carried in an address. or
through a server-initiated event known as 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 reconfigure event. DUID). The reconfiguration feature of DHCP offers network administrators
the opportunity to update configuration information on DUID must be unique
across all DHCP clients
whenever necessary. To signal the need clients, and it must also be consistent for the same
client reconfiguration, - that is, the server will unicast DUID used by a Reconfigure-init message to each client
individually. A Reconfigure-init is SHOULD NOT change over
time; for example, as a trigger which will cause result of network hardware reconfiguration.

The motivation for having more than one type of DUID is that the
client(s) DUID
must be globally unique, and must also be easy to initiate 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 standard Request/Reply exchange with the
server generated DUID in order to acquire the new or updated addresses.

9. Message Formats

Each DHCP message has an identical fixed format header; some messages
also allow such a variable format area for options. Not all fields in
the header are used in every message. In this section, every field device
is described for every message and fields that are not used in possible, so the DUID scheme must accommodate such devices.

10.1. DUID contents

A DUID consists of a
message are marked as "unused". All unused fields sixteen-bit type code represented in a message MUST
be transmitted as zeroes and ignored network
order, followed by the receiver a variable number of octets that make up the message.
actual identifier. A DUID can be no more than 256 octets long. The DHCP message header:
following types are currently defined:

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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. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | preference | transaction-ID Time (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hardware type (16 bits) | | client-link-local-address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (16 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| server-address |
| (16 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. options link-layer address (variable length) .
. .
| (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

9.1. DHCP Solicit Message Format

msg-type SOLICIT

preference (unused) MUST

The choice of network interface can be 0

transaction-ID An unsigned integer generated by completely arbitrary, as long
as that interface provides a unique link-layer address, and the
client same
DUID should be used in configuring all network interfaces connected
to identify this Solicit
message.

client-link-local-address The link-local 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 for which used to generate the client DUID is
using DHCP.

server-address (unused) removed. DHCP clients that do
not have any stable storage MUST be 0

options See section 18.

9.2. NOT use this type of DUID.

DHCP Advertise Message Format

msg-type ADVERTISE

preference An unsigned integer indicating a
server's willingness clients that use this DUID SHOULD attempt to provide
service configure the time
prior to generating the client. 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 not configured by the user prior
to generating the DUID. The use of a time source makes it unlikely
that 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. A DUID collision is

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transaction-ID An unsigned integer used to identify
this Advertise message. Copied from

very unlikely even if the client's Solicit message.

client-link-local-address 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. Vendor-assigned unique ID.

The IP link-local address vendor-assigned unique ID consists of an eight-octet
vendor-unique identifier, followed by the
client interface from which the client
issued the Solicit message.

server-address 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 IP address structure of the server that
generated this message. If VUID is left up to the DHCP
domain crosses site boundaries, then
this address vendor defining it, but
each device containing such a VUID MUST be globally-scoped.

options See section 18.

9.3. DHCP Request Message Format

msg-type REQUEST

preference (unused) unique to each device
that is using it, and MUST be 0

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

client-link-local-address The link-local address of the client
interface from which the client will
issue device at the Request message.

server-address The IP address 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 server to which vendor
in the domain name system, stored in canonical form. An example DUID
of this message 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 directed, copied
from an Advertise message.

options See section 18.

9.4. DHCP Confirm Message Format

msg-type CONFIRM

preference (unused) MUST be 0

transaction-ID An unsigned integer generated eight octets of VUID data, followed by the
client used to identify this Confirm
message.

client-link-local-address The link-local "example.com"
represented in ASCII.

10.4. Link-layer address

This type of DUID consists of a two octet network hardware type code,
followed by the client link-layer address of any one network interface from which that
is permanently connected to the DHCP client will
issue the Confirm message.

server-address device. The hardware
type MUST be zero. 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.

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options See section 18.

9.5. DHCP Renew Message Format

msg-type RENEW

preference (unused) MUST be

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

client-link-local-address The link-local 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 the client network interface from which the client will
issue the Renew message.

server-address The IP can be completely arbitrary, as
long as that interface provides a unique link-layer address of the server and
is permanently attached to the device on which
this Renew message the DUID is directed, which
MUST being
generated. The same DUID should be used in configuring all network
interfaces connected to the address device, regardless of the server from which interface's
link-layer address was used to generate the IAs in this message were
originally assigned.

options See section 18.

9.6. DHCP Rebind Message Format

msg-type REBIND

preference (unused) 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 0

transaction-ID An unsigned integer generated by the
client used by DHCP clients that cannot tell whether or not a
network interface is permanently attached to identify this Rebind
message.

client-link-local-address The link-local address of the client
interface from device on which the client will
issue the Rebind message.

server-address MUST be zero.

options See section 18.

9.7.
DHCP Reply Message Format

msg-type REPLY

preference client is running.

11. Identity association

An unsigned integer indicating "identity-association" (IA) is a
server's willingness to provide
service to the client.

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transaction-ID An unsigned integer used addresses. Each IA
consists of an IAID and a list of associated IPv6 addresses (the list
may be empty). A client associates an IA with one of its interfaces
and uses the IA to identify
this Reply message. Copied obtain IPv6 addresses for that interface from a
server.

See section 20.3 for the
client's Request, Confirm, Renew or
Rebind message.

client-link-local-address The link-local address representation of the
interface an IA in a DHCP message.

12. Selecting addresses for which assignment to an IA

A server selects addresses to be assigned to an IA according to the client is
using DHCP.

server-address The IP
address of assignment policies determined by the server.
If server administrator
and the DHCP domain crosses site
boundaries, then this address MUST be
globally-scoped.

options See section 18.

9.8. DHCP Release Message Format

msg-type RELEASE

preference (unused) MUST be 0

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

client-link-local-address The client's link-local address for server determines about the interface client
from the following sources:

- The link to which the client
will send the Release message.

server-address The IP address of is attached:

* If the server that
assigned receives the IA.

options See section 18.

9.9. DHCP Decline Message Format

msg-type DECLINE

preference (unused) MUST be 0

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

client-link-local-address The client's link-local
and the source address for in the interface from IP datagram in which the
message was received is a link-local address, then the client
will send
is on the Decline message.

server-address The IP address of same link to which the server that
assigned interface over which the addresses.
message was received is attached

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options See section 18.

9.10. DHCP Reconfigure-init Message Format

msg-type RECONFIG-INIT

preference (unused) MUST be 0

transaction-ID (unused) MUST be 0

client-link-local-address (unused) MUST be 0

server-address The

* If the server receives the message directly from the client
and the source address in the IP datagram in which the
message was received is not a link-local address, then the
client is on the link identified by the source address of in the
IP datagram

* If the DHCP server
issuing receives the Reconfigure-init message.
MUST be of sufficient scope message from a forwarding relay
agent, then the client is on the same link as the one to be
reachable
which the interface identified by all clients. the link-prefix field in
the message from the relay is attached

- The DUID supplied by the client

- Other information in options See section 18.

10. Relay messages

Relay agents exchange messages with servers to forward messages
between supplied by the client

- Other information in options supplied by the relay agent

13. Reliability of Client Initiated Message Exchanges

DHCP clients and servers that are not connected to responsible for reliable delivery of messages in the same link.

10.1. Relay-forward
client-initiated message

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 | prefix length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
| relay-address |
| |
| |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| options (variable number exchanges described in sections 15 and length) .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

msg-type RELAY-FORW

prefix-length The length of 16.
If a DHCP client fails to receive an expected response from a server,
the prefix in client must retransmit its message. This section describes the address
retransmission strategy to be used by clients in client-initiated
message exchanges.

The client begins the
"relay-address" field.

relay-address An address assigned message exchange by transmitting a message to
the interface through which
the server. The message from exchange terminates when either the client was received.

options MUST include
successfully receives the appropriate response or responses from a "Client message option"; see
section 18.5.

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10.2. Relay-reply
server or servers, or when the message

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 | prefix length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
| relay-address |
| |
| |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| options (variable number and length) .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

msg-type RELAY-REPL

prefix-length The length of the prefix in exchange is considered to have
failed according to the address in retransmission mechanism described below.

The client retransmission behavior is controlled and describe by five
variables:

RT Retransmission timeout

IRT Initial retransmission time

MRC Maximum retransmission count

MRT Maximum retransmission time

MRD Maximum retransmission duration

RAND Randomization factor

With each message transmission or retransmission, the
"relay-address" field.

relay-address An address identifying client sets RT
according to the interface through which rules given below. If RT expires before the message from
exchange terminates, the server should be forwarded;
copied from client recomputes RT and retransmits the "relay-forward"
message.

options MUST include a "Server message option"; see
section 18.6.

11. DHCP unique identifier (DUID)

Each DHCP client has a DUID.

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Each of configuration parameters and in the association computations of IAs 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. See section 18.2
The algorithm for the
representation of choosing a DUID in random number does not need to be
cryptographically sound. The algorithm SHOULD produce a different
sequence of numbers from each invocation of the DHCP message.

DISCUSSION:

The syntax, rules client.

RT for selecting and requirements the first message transmission is based on IRT:

RT = 2*IRT + RAND*IRT

RT for gloabl
uniqueness in DUIDs are TBD.

The DUID each subsequent message transmission is carried in based on the previous
value of RT:

RT = 2*RTprev + RAND*RTprev

MRT specifies 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 upper bound on the value of RT. If MRT has a DUID).

12. Identity association

An "identity-association" (IA) value
of 0, there is no upper limit on the value of RT. Otherwise:

if (RT > MRT)
RT = MRT + RAND*MRT

MRC specifies an upper bound on the number of times a construct through which client may
retransmit a server
and message. If MRC has a client can identify, group and manage IPv6 addresses. Each IA
consists value of an IAID and 0, the client MUST
continue to retransmit the original message until a list response is
received. Otherwise, the message exchange fails if the client
attempts to transmit the original message more than MRC times.

MRD specifies an upper bound on the length of associated IPv6 addresses (the list time a client may be empty). A
retransmit a message. If MRD has a value of 0, the client associates an IA with one MUST
continue to retransmit the original message until a response is
received. Otherwise, the message exchange fails if the client
attempts to transmit the original message more than MRD seconds.

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

14. Message validation

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

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.

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14.1. Use of Transaction-ID field

The "transaction-ID" field holds a value used by clients and uses the IA servers
to obtain IPv6 addresses for that interface from synchronize server responses to client messages. A client SHOULD
choose a
server.

See section 18.3 different transaction-ID for each new message it sends. A
client MUST leave the representation of an IA transaction-ID unchanged in retransmissions of
a DHCP message.

13. DHCP Server Solicitation

This section describes how a client locates servers. The behavior
of client and server implementations is discussed, along with the
messages they use.

13.1.

14.2. Solicit Message Validation message

Clients MUST silently discard any received Solicit messages.

Agents

Relay agents MUST silently discard any received Solicit messages if the
"client-link-local-address" field does not contain a valid link-local
address.

13.2. Advertise Message Validation

Servers MUST discard any received through port
546.

14.3. Advertise messages. message

Clients MUST discard any received Advertise messages that meet any of in which the
following criteria:

o The
"Transaction-ID" field value does not match the value the client used
in its Solicit message.

o The "client-link-local-address" field

Servers and relay agents MUST discard any received Advertise
messages.

14.4. 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'' field does not match the
link-local address any of the interface upon which the client sent addresses
used by the Solicit message.

13.3. Client Behavior server.

14.5. Confirm message

Clients use the Solicit MUST discard any received Confirm messages.

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

14.6. Renew message to discover

Clients MUST discard any received Renew messages.

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

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Servers MUST discard any received Renew message in which the client is attached.

13.3.1. Creation and sending value in
the ``server-address'' field does not match any of the Solicit message

The client sets addresses used
by the "msg-type" server.

14.7. Rebind message

Clients MUST discard any received Rebind messages.

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

14.8. Decline messages

Clients MUST discard any received Decline messages.

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

Servers MUST discard any received Decline message in which the value
in the ``server-address'' field to SOLICIT, and places does not match any of the
link-local address addresses
used by the server.

14.9. 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'' field does not match any of the interface it wishes to configure addresses
used by the server.

14.10. Reply message

Clients MUST discard any received Reply messages in which the
``transaction-ID'' field in the message does not match the
"client-link-local-address" field.

The client generates a transaction ID inserts this value used
in the
"transaction-ID" field. original message.

Servers and relay agents MUST discard any received Reply messages.

14.11. Reconfigure-init message

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

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The client includes a DUID option to identify itself to the server.
The client

Clients MUST include options for discard any IAs to which the client is
expecting to have Reconfigure-init messages that do not
contain an authentication option or that fail the server assign addresses. Because authentication
performed by the client
does not have client.

14.12. Relay-forward message

Clients MUST discard any IAs with addresses when sending a Solicit message,
all of the IAs received Relay-forward messages.

14.13. Relay-reply message

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

15. DHCP Server Solicitation

This section describes how a client locates servers.

15.1. 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. 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 options for any IAs to which it
wants the server to assign addresses. The client MAY choose not to
include any IAs in the Solicit message if it does not need to request
that any addresses be assigned. The client MAY include addresses in
the IAs as a hint to the server about addresses for which the client
may have 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. Transmission of Solicit Messages

The client sends the Solicit message to the All DHCP Agents All_DHCP_Agents
multicast address, destination port 547. address. The source port selection
can be arbitrary, although it SHOULD be possible using a client
configuration facility MUST use an IPv6 address assigned
to set a specific the interface for which the client is interested in obtaining
configuration information as the source port value.

13.3.2. Time out and retransmission address in the IP header of
the datagram carrying the Solicit Messages message.

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The client's first Solicit message on the interface MUST be delayed
by a random amount of time between transmitted on the interval of MIN_SOL_DELAY and
MAX_SOL_DELAY. This random delay desynchronizes clients which start
at link that the same time (e.g., after a power outage).
interface for which configuration information is being obtained
is attached to. The client waits ADV_MSG_TIMEOUT, collecting Advertise messages.
If no Advertise messages are received, SHOULD send the message through that
interface. The client retransmits MAY send the Solicit, message through another interface
attached to the same link if and doubles only if the ADV_MSG_TIMEOUT value. This process
continues until either one or more Advertise messages are received or
ADV_MSG_TIMEOUT reaches client is certain the ADV_MSG_MAX value. Thereafter, Solicits
the two interface are retransmitted every ADV_MSG_MAX until SOL_MAX_ATTEMPTS have been
made, at which time attached to the same link.

The first Solicit message from the client MAY choose to stop trying to DHCP
configure on the interface. An event external to DHCP is required
to restart 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 DHCP configuration process. A DHCP same time (e.g., after a power outage).

The client MAY,
alternatively, choose transmits the message according to continue sending Solicit messages at section 13, using the
ADV_MSG_MAX interval.

Default and initial values for MIN_SOL_DELAY, MAX_SOL_DELAY,
ADV_MSG_TIMEOUT, AND ADV_MSG_MAX are documented
following parameters:

IRT SOL_TIMEOUT

MRT SOL_MAX_RT

MRC 0

MRD 0

The mechanism in section 7.5.

13.3.3. Receipt 13 is modified as follows for use in the
transmission of Advertise messages

Upon Solicit messages. The message exchange is not
terminated by the receipt of one or more validated an Advertise messages, before SOL_TIMEOUT has
elapsed. Rather, the client
selects one or more collects Advertise messages based upon the following
criteria.

- Those until
SOL_TIMEOUT has elapsed. The first RT MUST be selected to be
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 the highest server a preference value (see section 19.4) are preferred over all other Advertise
messages.

- Within a group
of Advertise messages with the same server 255. The preference value, value is carried in the Preference option
(section 20.5). Any Solicit that does not include a Preference
option is considered to have a preference value of 0. If the client MAY select those servers whose
receives an Advertise messages advertise information message with a preference value of interest to 255, then
the client. For example, one server may 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 advertising 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 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.

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availability of IP addresses which have an address scope

15.1.3. Receipt of
interest to the client.

Once a client has selected Advertise message(s), the messages

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 MUST ignore any Advertise message that includes a Status
Code option containing the requirements of value AddrUnavail, with the client's
invoking user, exception that
the client MAY initiate a configuration exchange with display the server(s) immediately, associated status message to the user.

Upon receipt of one or MAY defer this exchange until later.

If more valid Advertise messages, the client needs to select an alternate server in the case that a
chosen server does not respond,
selects one or more Advertise messages based upon the client chooses following
criteria.

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

- Within a group of Advertise messages with the next highest same server
preference value. 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.

13.4. Server Behavior

For this discussion,

Once a client has selected Advertise message(s), the server is assumed to have been configured in
an implementation specific manner. This configuration is assumed to
contain all network topology client will
typically store information for the DHCP domain, as well about each server, such as any necessary authentication information.

13.4.1. Receipt of Solicit messages

If the server receives a Solicit message,
preference value, addresses advertised, when the client must be advertisement was
received, and so on. Depending on the
same link as requirements of the server. If user that
invoked the server receives a Relay-forward
message containing a Solicit message, DHCP client, the client must be on the
link to which MAY initiate a configuration
exchange with the prefix identified by server(s) immediately, or MAY defer this exchange
until later.

If the "relay-address" and
"prefix-length" fields client needs to select an alternate server in the Relay-forward message is assigned.
The case that a
chosen server records the "relay-address" field from the Relay-forward
message and extracts the solicit message from does not respond, the "client-message"
option.

If administrative policy permits client chooses the next server
according to respond to a client on
that link, the criteria given above.

15.2. 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. Receipt of Solicit messages

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

13.4.2.

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15.2.2. Creation and sending transmission of Advertise messages

The server sets the "msg-type" field to ADVERTISE and copies the
values
contents of the following fields transaction-ID field from the client's Solicit message
received from the client to the Advertise message:

o transaction-ID

o client-link-local-address

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one of its IP addresses (determined through administrator setting)
in the "server-address" field of the Advertise message. The server sets the "preference" field according
MAY add a Preference option to its
configuration information. See section 20.3 carry the preference value for a description the
Advertise message.

The server implementation SHOULD allow the setting of a server preference.
preference value by the administrator. The server preference value
MUST default to zero unless otherwise configured by the server
administrator.

The server MUST include IA options to in the Advertise message
containing any addresses that would be assigned to IAs contained in
the Solicit message from the client. If the Solicit message from the
client included no IAs, the server MUST not include any IAs in the
Advertise message. If the server will not assign any addresses to
IAs in a subsequent Request from the client, the server MAY choose to
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.

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.

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 "relay-address" source address field from the Relay-forward message.

If the Solicit message was received directly by the server, the
server unicasts the Advertise message directly to the client using
the "client-link-local-address" field value as the destination
address. The Advertise message MUST be unicast through the interface
on IP datagram in which
the Solicit Relay-forward message was received.

14.

16. 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

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system configuration process or when requested to do so by the
application layer.

The

16.1. Client Behavior

A client uses the following will use Request, Confirm, Renew and Rebind messages to initiate a configuration
event:

Request Obtain initial
acquire and confirm the validity of configuration information (from a information. The
client uses the server
identified address information from previous Advertise
message(s) for use in constructing Request and Renew message(s).
Note that a previously received Advertise message)
when the client has no assigned addresses

Confirm Confirm may request configuration information from one or
more servers at any time.

16.1.1. Creation and transmission of Request messages

If the validity client is using stateful address configuration and needs
either an initial set of assigned addresses or additional addresses, it
MUST send a Request message to obtain new addresses and other
configuration changes through information. The client includes one or more IAs in
the server from Request message, to which the
configuration information was obtained when the client's
assigned addresses may not be valid; for example, when
the client reboots or loses its connection to a link

Renew Extend the lease on an IA through the server that
originally assigned the IA

Rebind Extend the lease on an IA through any assigns new addresses. The
server willing then returns IA(s) to
extend the lease

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Release Release the lease on an IA client in a Reply message.

The client generates a transaction ID and release all of the
addresses contained inserts this value in the IA,

Decline Decline
"transaction-ID" field.

The client places the assignment address of one or more addresses the destination server in an
IA.

A client uses the Release/Reply message exchange
"server-address" field.

The client MUST include a DUID option to indicate identify itself to the
DHCP server that
server. The client adds any other appropriate options, including
one or more IA options (if the client will no longer be using is requesting that the server
assign it some network addresses). The list of addresses in each
included IA MUST be empty. If the released IA.

A client uses the Decline/Reply message exchange to indicate to is not requesting that the
DHCP
server that assign it any addresses, the client omits the IA option.

If the client has detected a source address that one or more addresses
assigned can be used by the server is already in use on
as a return address and the client's link.

14.1. Client Message Validation

Clients MUST silently discard any received client messages (Request,
Confirm, Renew, Rebind, Release or Decline messages).

Agents MUST discard any has received a Client Unicast
option (section 20.11) from the server, the client messages in which SHOULD unicast
the
"client-link-local-address" field does not contain a valid link-local
address.

Servers MUST discard any received client messages in which the
"options" field contains an authentication option, and the server
cannot successfully authenticate the client.

Servers MUST discard any received Request, Renew, Release or Decline Request message in which to the "server-address" field value does not match any
of server. Otherwise, the server's addresses.

14.2. Server Message Validation

Servers MUST silently discard any received server messages
(Advertise, Reply or Reconfigure-init messages).

Clients client MUST discard any server messages that meet any of the
following criteria:

o The "transaction-ID" field value in the server message does
not match the value send
the client used in its Request or Release
message.

o The "client-link-local-address" field value in the server message
does not match to the link-local All_DHCP_Agents multicast address. The
client MUST use an address of assigned to the interface from for which the
client sent is interested in its Request, Confirm, Renew, Rebind, Release
or Decline obtaining configuration information as the
source address in the IP header of the datagram carrying the Request
message.

o The server message contains an authentication option,

DISCUSSION:

Use of multicast and relay agents enables the
client's attempt to authenticate inclusion of
relay agent options in all messages sent by the message fails. client. The
server should enable the use of unicast only when relay
agent options will not be used.

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Relays MUST discard any Relay-reply message in which

If the
"client-link-local-address" in client multicasts the Request message, the encapsulated Reply message does
not contain a valid link-local address.

14.3. Client Behavior

A client will use Request, Confirm, Renew and Rebind messages to
acquire and confirm MUST be
transmitted on the validity of link that the interface for which configuration information. A
client may initiate such an exchange automatically in order to
acquire the necessary network parameters to communicate with nodes
off-link.
information is being obtained is attached to. The client uses SHOULD send
the server address information from
previous Advertise message(s) for use in constructing Request and
Renew message(s). Note message through that a client may request configuration
information from one or more servers at any time.

A interface. The client uses MAY send the Release message in
through another interface attached to the management of IAs when same link if and only if
the client has been instructed to release is certain the IA prior the two interface are attached to the IA
expiration time since it is no longer needed.

A same
link.

The client uses transmits the Decline message when according to section 13, using the
following parameters:

IRT REQ_TIMEOUT

MRT REQ_MAX_RT

MRC REQ_MAX_RC

MRD 0

If the message exchange fails, the client has determined
through DAD or some other method that MAY choose one or more of the addresses
assigned by
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

- Terminate the IA is already in use by a different
client.

14.3.1. configuration process and report failure

16.1.2. Creation and sending transmission of Request Confirm messages

Whenever a client has no valid may have moved to a new link, its IPv6 addresses
and other configuration information may no longer be valid. Examples
of sufficient scope to
communicate with times when a DHCP server, it client may send a Request message have moved to
obtain a new addresses. link include:

o The client includes one or more IAs in the
Request message, to which the server assigns new addresses. reboots

o The
server then returns IA(s) to the client in is physically disconnected from a Reply message. wired connection

o The client sets the "msg-type" field returns from sleep mode

o The client using a wireless technology changes cells

In any situation when a client may have moved to REQUEST, and places a new link, the link-local address
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 interface addresses with the status in the Reply message
it wishes returns to acquire
configuration information the client.

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The client sets the "client-link-local-address"
field. "msg-type" field to CONFIRM. 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 sets the "server-address" field. field to 0.

The client adds MUST include a DUID option to identify itself to the
server. The client adds any other approppriate appropriate options, including one or
more IA options (if the client is requesting that the server assign it confirm
the validity of some
network IPv6 addresses). The list of addresses in each included IA MUST
be empty. If the client is not requesting that the server assign it does include
any addresses, IA options, it MUST include the client omits list of addresses the IA option.

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currently has associated with that IA.

The client sends the Request Confirm message to the All DHCP Agents All_DHCP_Agents
multicast address, destination port 547. address. The source port selection
can be arbitrary, although it SHOULD be possible using a client
configuration facility to set a specific source port value.

The server will respond MUST use an IPv6 address assigned
to the Request message with a Reply
message. If no Reply message is received within REP_MSG_TIMEOUT
milliseconds, interface for which the client retransmits the Request with the same
transaction-ID, and doubles the REP_MSG_TIMEOUT value, and waits
again. The client continues this process until a Reply is received
or REQUEST_MSG_ATTEMPTS unsuccessful attempts have been made, at
which time the client MUST abort the interested in obtaining
configuration attempt. The
client SHOULD report the abort status to information as the application layer.

Default and initial values for REP_MSG_TIMEOUT and REQ_MSG_ATTEMPTS
are documented source address in section 7.5.

14.3.2. Creation and sending the IP header of
the datagram carrying the Confirm messages

Whenever a client may have moved to a new link, its IPv6 addresses
may no longer message.

The Confirm message MUST be valid. Examples of times when a client may have
moved to a new transmitted on the link include:

o The client reboots

o The client that the
interface for which configuration information is physically disconnected from a wired connection

o The client returns from sleep mode

o being obtained
is attached to. The client using a wireless technology changes cells

In any situation when a client may have moved to a new link, SHOULD send the
client MUST initiate a Confirm/Reply message exchange. through that
interface. The client
includes any IAs, along with MAY send the addresses associated with those IAs,
in its Confirm message. Any responding servers will indicate message through another interface
attached to the
acceptability of same link if and only if the addresses with client is certain the status in
the IA it returns two interface are attached to the client. same link.

The client sets transmits the "msg-type" field message according to CONFIRM, and places section 13, using the link-local address of
following parameters:

IRT CNF_TIMEOUT

MRT CNF_MAX_RT

MRC 0

MRD CNF_MAX_RD

If the interface it wishes to acquire
configuration information for client receives no responses before the message transmission
process as described in section 13 terminates, the "client-link-local-address"
field.

The client generates a transaction ID inserts this value in SHOULD
continue to use any IP addresses, using the
"transaction-ID" field.

The last known lifetimes for
those addresses, and SHOULD continue to use any other previously
obtained configuration parameters.

16.1.3. Creation and transmission of Renew messages

IPv6 addresses assigned to a client sets through an IA use the "server-address" field to 0. same
preferred and valid lifetimes as IPv6 addresses obtained through
stateless address autoconfiguration. The client adds a DUID option to identify itself server assigns preferred
and valid lifetimes to the server. The
client adds any appropriate options, including one or more IA options
(if IPv6 addresses it assigns to an IA. To
extend those lifetimes, the client is requesting that sends a Renew message to the
server confirm the validity of
some network addresses). If containing an "IA option" for the client does include any IA options, and its associated
addresses. The server determines new lifetimes for the addresses in

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it MUST include

the list IA according to the administrative configuration of the server.
The server may also add new addresses to the client currently has
associated with that IA. The client sends server may
remove addresses from the Confirm message to IA by setting the All DHCP Agents
multicast address, destination port 547. The source port selection
can be arbitrary, although it SHOULD be possible using a client
configuration facility to set a specific source port value.

Servers will respond preferred and valid
lifetimes of those addresses to zero.

The server controls the Confirm message with a Reply message. If
no Confirm message is received within REP_MSG_TIMEOUT milliseconds,
the client retransmits the Confirm with the same transaction-ID,
and doubles the REP_MSG_TIMEOUT value, and waits again. The client
continues this process until a Reply is received or QRY_MSG_ATTEMPTS
unsuccessful attempts have been made, at which time the client MUST
abort the configuration attempt. The client SHOULD report the abort
status to the application layer.

Default and initial values for REP_MSG_TIMEOUT and QRY_MSG_ATTEMPTS
are documented in section 7.5.

If the client receives no response to its Confirm message, it MAY
restart the configuration process by locating a DHCP server with an
Advertise message and sending a Request to that server, as described
in section 14.3.1.

14.3.3. Creation and sending of Renew messages

IPv6 addresses assigned to a client through an IA use the same
preferred and valid lifetimes as IPv6 addresses obtained through
stateless autoconfiguration. The server assigns preferred and valid
lifetimes to the IPv6 addresses it assigns to an IA. To extend those
lifetimes, the client sends a Request 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 server's administrative configuration. The server may also add
new addresses to the IA. The server remove addresses from the IA by
setting the preferred and valid lifetimes of those addresses to zero.

The server controls the time at which 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. If the server does not assign an
explicit value to T1 or T2 for an IA, T1 defaults to 0.5 times the
shortest preferred lifetime of any address assigned to the IA and
T2 defaults to 0.875 times the shortest preferred lifetime of any
address assigned to the IA.

At time T1 for an IA, the client initiates a Request/Reply 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 Request Renew message.

The client sends this Request message
to the All DHCP Agents multicast address.

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The client sets the "msg-type" field to RENEW, RENEW. The client generates a
transaction ID and places
the link-local address of the interface it wishes to acquire
configuration information for in the "client-link-local-address"
field.

The client generates a transaction ID inserts this value in the "transaction-ID" field.

The client places the address of the destination server in the
"server-address" field.

The client adds 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 lease on some IAs; note that the client may check the status of
other configuration parameters without asking for lease extensions).
If the client does include any IA options, it MUST include the list
of addresses the client currently has associated with that IA.

The client sends the Renew message to

If the All DHCP Agents multicast
address, destination port 547. The source port selection can
be arbitrary, although it SHOULD be possible using a client
configuration facility to set has a specific source port value.

The server will respond to address that can be used by the Renew message with server as
a Reply message.
If no Reply message is received within REP_MSG_TIMEOUT milliseconds,
the client retransmits the Renew with the same transaction-ID, return address and
doubles the REP_MSG_TIMEOUT value, and waits again. The client
continues this process until a Reply is has received or until time T2 is
reached (see section 14.3.4).

Default and initial values for REP_MSG_TIMEOUT are documented in
section 7.5.

14.3.4. Creation and sending of Rebind messages

At time T2 for an IA (which will only be reached if the server to
which a Client Unicast option
(section 20.11) from the Renew message was sent at time T1 has not responded), server, the client initiates a Rebind/Reply SHOULD unicast the Renew
message exchange. The client
includes an IA option with all addresses currently assigned to the IA
in its Rebind message. The server. Otherwise, the client sends this the Renew message
to the All DHCP
Agents All_DHCP_Agents multicast address. The client sets the "msg-type" field to REBIND, and places
the link-local MUST use an
address of assigned to the interface it wishes to acquire
configuration information for in which the "client-link-local-address"
field.

The client generates a transaction ID inserts this value is interested
in obtaining configuration information as the
"transaction-ID" field.

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

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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, using the
following parameters:

IRT REN_TIMEOUT

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MRT REP_MAX_RT

MRC 0

MRD 0

The mechanism in section 13 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), at which time the
client begins a Rebind message exchange.

16.1.4. 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 adds
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.

The client sets the "msg-type" field to REBIND. The client generates
a transaction ID 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 client does include any IA options (if the
client is requesting that the server extend the lease on some IAs;
note that the client may check the status of other configuration
parameters without asking for lease extensions), it MUST include the
list of addresses the client currently has associated with that IA.

The client sends the Rebind message to the All DHCP Agents All_DHCP_Agents
multicast
address, destination port 547. address. The source port selection can
be arbitrary, although it SHOULD be possible using a client
configuration facility to set a specific source port value.

The server will respond 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 with a Reply message.
If no Reply

The Rebind message MUST be transmitted on the link that the interface
for which configuration information is received within REP_MSG_TIMEOUT milliseconds, being obtained is attached
to. The client SHOULD send the message through that interface. The
client retransmits MAY send the Rebind with message through another interface attached to the
same transaction-ID, link if and
doubles only if the REP_MSG_TIMEOUT value, and waits again. The client
continues this process until a Reply is received.

Default and initial values for REP_MSG_TIMEOUT certain the the two interface
are documented attached to the same link.

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

IRT REB_TIMEOUT

MRT REB_MAX_RT

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MRC 0

MRD 0

The mechanism in section 7.5. 13 is modified as follows for use in the
transmission of Rebind messages. The message exchange is terminated
when the lease for the IA expires (see section 11), at which time the
client has several alternatives alternative actions to choose from if it receives no
response to its Rebind message. from:

- When the lease on the IA expires, 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

- Some addresses in the IA may have lifetimes that extend beyond
the lease of the IA, so the client may choose to continue to use
those addresses; once all of the addresses have expired, the
client may choose to locate a new DHCP 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

14.3.5.

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

Upon the receipt of a valid Reply message in response to a
Request, Confirm, Renew or Rebind message, the client extracts the
configuration information contained in the Reply. If the "status"
field contains a non-zero value, the client reports the error status
to the application layer. The client records MAY
choose to report any status code or message from the T1 and T2 times for each IA status code
option in the Reply message.

The client records any SHOULD perform duplicate address detection [20] on each of
the addresses included with in any IAs it receives in the Reply message. The client updates the preferred and valid
lifetimes for 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 16.1.8.

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

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has associated with the IA that are not included in the IA option
unchanged.

Management of the specific configuration information is detailed in
the definition of each option, in section 18. 20.

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

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client can use the addresses in the IA and ignore any messages that
do indicate a NoPrefixMatch status.

When the client receives an Unavail error 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 error 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 Conf_NoMatch error 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 lease for the addresses.

When the client receives a NoBinding error 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 Renw_NoMatch error 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 Unavail error 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.

When the client receives a NoBinding error 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 Rebd_NoMatch error 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 Unavail error 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.

14.3.6.

16.1.6. Creation and sending transmission of Release messages

The client sets the "msg-type" field to RELEASE, and places the
link-local address of the interface associated with the configuration
information it wishes to release in the "client-link-local-address"
field. RELEASE. The client generates
a transaction ID and places this value in the "transaction-ID" field.

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

The client adds 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 appropriate "status" field in the
options MUST be set to indicate the reason for the release.

If the

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The client is configured to MUST NOT use authentication, the client
generates any of the appropriate authentication option, and adds this option
to addresses in the "options" field. Note that IAs in the authentication option MUST be
message as the last option source address in the "options" field. See section 18.9 for more
details about Release message or in any
subsequently transmitted message.

If the authentication option.

The client sends has a source address that can be used by the server
as a return address and the client has received a Client Unicast
option (section 20.11) from the server, the client SHOULD unicast the
Release message to the All DHCP Agents server. Otherwise, the client MUST send the
Release message to the All_DHCP_Agents multicast address.

14.3.7. Time out 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 retransmission 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 Release Messages 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.

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.

If no Reply message is received within REP_MSG_TIMEOUT milliseconds,
the client retransmits the Release, doubles the REP_MSG_TIMEOUT
value, and waits again.

The client continues this process until a
Reply is received or REL_MSG_ATTEMPTS unsuccessful attempts have been
made, at which time transmits the client SHOULD abort message according to section 13, using the release attempt.
following parameters:

IRT REL_TIMEOUT

MRT 0

MRC REL_MAX_MRC

MRD 0

The client SHOULD return MUST abandon the abort status attempt to the application, release addresses if an
application initiated the release.

Default and initial values for REP_MSG_TIMEOUT
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 REL_MSG_ATTEMPTS
are documented 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 section 7.5. a Release message exchange as if it indicates an
error.

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Note that if the client fails to release the IA, the addresses
assigned to the IA will be reclaimed by the server when the lease
associated with it expires.

14.3.8.

16.1.7. 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, and SHOULD return the successful status to
the application layer, if an application initiated the release.

14.3.9.

16.1.8. Creation and sending transmission of Decline messages

The client sets the "msg-type" field to DECLINE, and places the
link-local address of the interface associated with the configuration

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information it wishes to decline in the "client-link-local-address"
field. 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 adds 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 released
MUST be included in the IAs. The appropriate "status" field in the
options MUST be set to indicate the reason for declining the address.

If the

The client is configured to MUST NOT use authentication, 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
generates has a source address that can be used by the appropriate authentication option, server
as a return address and adds this the client has received a Client Unicast
option
to (section 20.11) from the "options" field. Note that server, the authentication option MUST be client SHOULD unicast the last option in
Decline message to the "options" field. See section 18.9 for more
details about server. Otherwise, the authentication option.

The client MUST send the
Decline message to the All DHCP Agents All_DHCP_Agents multicast address.

14.3.10. Time out and retransmission of Decline Messages

If no Reply message is received within REP_MSG_TIMEOUT milliseconds,
the The client retransmits
MUST use an IPv6 address for the Decline, doubles interface to which the REP_MSG_TIMEOUT
value, IAs in the
Release message are assigned as the source address for the Decline
message.

DISCUSSION:

Use of multicast and waits again. relay agents enables the inclusion of
relay agent options in all messages sent by the client. The client continues this process until a
Reply
server should enable the use of unicast only when relay
agent options will not be used.

If the Decline message is received or REL_MSG_ATTEMPTS unsuccessful attempts have
been made, at which time multicast, it MUST be transmitted on the
link that the interface for which configuration information is being
obtained is attached to. The client SHOULD abort the attempt to
decline send the address. message through
that interface. The client SHOULD return MAY send the abort status message through another
interface attached to the application, same link if an application initiated the release.

Default and initial values for REP_MSG_TIMEOUT and REL_MSG_ATTEMPTS only if the client is
certain the the two interface are documented in attached to the same link.

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The client transmits the message according to section 7.5.

14.3.11. 13, 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.

16.1.9. Receipt of Reply message in response to a Release Decline message

Upon receipt of a valid Reply message, the client can consider the
Release
Decline event successful, and SHOULD return the successful status to
the application layer, if an application initiated the release.

14.4. successful.

16.2. Server Behavior

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

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14.4.1.

16.2.1. Receipt of Request messages

Upon the receipt of a valid

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

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

preference Enter the server's preference to
provide services to the client.

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

client-link-local

server address Enter One of the client-link-local address
from IP addresses assigned to the interface
through which the Request message. server address Enter received the IP address of message
from the server. client.

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When the server receives a Request and IA option is included the
client is requesting the configuration of a new IA by the server.
The server MUST take the clients IA from the client and associate a binding
for that client in an implementation-specific manner within the server's
configuration parameter database for DHCP clients. clients managed by the
server.

If the server finds that the prefix on one or more IP addresses in
any IA in the message fro 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 provide addresses to the client it SHOULD
send back an empty IA to the client with the status field set to Unavail.
AddrUnavail.

If the server can provide addresses to the client it MUST send back
the IA to the client with all fields entered and a status of Success,
and add the IA as a new client binding.

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

14.4.2.

16.2.2. Receipt of Confirm messages

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.

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

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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

preference Enter the server's preference to
provide services to the client.

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

client-link-local

server address Enter One of the client-link-local address
from IP addresses assigned to the interface
through which the Confirm message. server address Enter received the server's address. message
from the client.

When the server receives a Confirm and an IA option is included message, the client is requesting
confirmation that the addresses in the IA are configuration information it will use is valid.
The server SHOULD locate the clients binding for that client and verify compare the
information in the IA Confirm message from the client matches to the information stored
for
associated with that client.

If the server cannot find a client entry for this IA the server
SHOULD return an empty IA with status set to NoBinding.

If the server finds that determine if the information for in the client does not
match what Confirm
message is in the server's records for that client valid or invalid, the server
should MUST NOT send back an empty IA with status set a reply to Conf_NoMatch. the

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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 a that the information for the client does not
match to what is in the Confirm then binding for that client or the configuration
information is not valid, the server should
send back sends a Reply message containing
a Status Code option with the IA to 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 status set to success.

14.4.3. the value Success.

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

16.2.3. 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.

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.

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

preference Enter the server's preference to
provide services to the client.

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

client-link-local

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 empty IA with status set to NoBinding.

If the server finds that the addresses in the IA for the client do
not match the clients binding the server should return an empty IA
with status set to Renw_NoMatch. RenwNoMatch.

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If the server cannot Renew addresses for the client it SHOULD
send back an empty IA to the client with the status field set to Unavail.
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 lease times
and T1/T2 times if the default is not being used, and set status to
Success.

14.4.4.

16.2.4. 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.

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

preference Enter the server's preference to
provide services to the client.

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

client-link-local

server address Enter One of the client-link-local address
from IP addresses assigned to the interface
through which the Confirm message. server address Enter received the server's address.

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from the client.

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 empty IA with status set to NoBinding.

If the server finds that the addresses in the IA for the client do
not match the clients binding the server should return an empty IA
with status set to Rebd_NoMatch. RebdNoMatch.

If the server cannot Rebind addresses for the client it SHOULD
send back an empty IA to the client with the status field set to Unavail.
AddrUnavail.

DISCUSSION:

There is a significant difference between Renew and Rebind messages:
Because the Rebind Renew message is processed by a single server, the respnding

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responding server can actually change the addresses in the IA.
However, because multiple servers may
repsond respond to a Rebind, all they
can safely do is update T1, T2 (for the IA) and lifetimes (for
individual addresses).

14.4.5.

16.2.5. 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 IA, IAs, the server deletes
the addresses from the IAs and makes the addresses available for
assignment to other clients.

The server then generates a Reply message. If all of the IAs were
valid and the addresses successfully released,, released, the server sets the
"status" field to "Success". includes
a Status Code option with value Success. If any of the IAs were
invalid or if any of the addresses were not successfully released,
the server
releases none leaves all of the addresses IAs in the message and sets the "status"
field to "NoBinding"(section 7.4).

If the client successfully unchanged (the server
releases some but not all none of the addresses in an IA, any of the IA continues to exist IAs in the message) and holds
includes a Status Code option with value NoBinding. The server MUST
NOT include any other options in the remaining,
unreleased addresses. Reply message.

A client can send an option containing an IA with no listed addresses
to release implicitly all of the addresses in the IA.

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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.

14.4.6. Sending

16.2.6. Receipt of Reply Decline messages

If the Request, Confirm, Renew, Rebind or Release message

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

Upon the receipt of a valid Decline message, the server
unicasts examines the Reply message to
IAs and the link-local address addresses in the
"client-link-local-address" field. IAs for validity. If the message was originally received IAs in a Forward-request or
Forward-release the
message from are in a relay, binding for the server places client and the Reply
message 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.

The server then generates a Reply message. If all of the IAs were
valid and the addresses successfully declined,, the server includes

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a Status Code option with value Success. If any of the IAs were
invalid or if any of the addresses were not successfully declined,
the server leaves all of the IAs in the message unchanged (the server
releases none of the addresses in any of the IAs in the message) and
includes a Status Code option with value NoBinding. The server MUST
NOT include any other options in the Reply message.

A client can send an option containing an IA with no listed addresses
to decline implicitly all of the addresses in the IA.

16.2.7. Sending of Reply messages

If the Request, Confirm, Renew, Rebind, Release or Decline 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 Response-reply Relay-response message and unicasts copies the link-prefix 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 relay's source
address from the IP datagram in which the original message.

15. message was
received.

17. DHCP Server-Initiated Configuration Exchange

A server initiates a configuration exchange to force 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).

15.1. Reconfigure-init Message Validation

Agents MUST silently discard any received Reconfigure-init messages.

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

15.2. Server Behavior

A server sends a

17.1. Server Behavior

A server sends a Reconfigure-init message to cause a client to
initiate immediately a Request/Reply message exchange with the
server.

15.2.1.

17.1.1. Creation and sending transmission of Reconfigure-init messages

The server sets the "msg-type" field to RECONFIG-INIT. 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.

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The server MAY include an ORO option to inform the client of what
information has been changed or new information that has been added.

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In particular, the server specifies the IA option in the ORO if the
server wants the client to obtain new address information.

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 message.

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

The

A server unicasts the sends each Reconfigure-init message to one a single DHCP client,
using an IPv6 unicast address of sufficient scope belonging to the
DHCP client. The server may unicast Reconfigure-init messages to 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
concurrently; for example, to reliably reconfigure all known clients, client, the server will unicast unicasts a Reconfigure-init separate
message to each client.

After the The server sends may initiate the Reconfigure-init message, it waits reconfiguration
of multiple clients concurrently; for example, a
Request server may send
a Reconfigure-init message from those to additional clients confirming that each client has
received the Reconfigure-init and while previous
reconfiguration message exchanges are thus initiating still in progress.

The Reconfigure-init message causes the client to initiate a
Request/Reply
transaction message exchange with the server.

15.2.2. The server
interprets the receipt of a Request message from the client as
satisfying the Reconfigure-init message request.

17.1.2. Time out and retransmission of Reconfigure-init messages

If the server does not receive a Request message from the client
in RECREP_MSG_TIMEOUT milliseconds, the server retransmits
the Reconfigure-init 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. process for that client.

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

15.2.3.

17.1.3. Receipt of Request messages

The server generates and sends Reply message(s) to the client as
described in section 14.4.6, 16.2.7, including in the "options" field new
values for configuration parameters.

It is possible that the client may send a Request message after the
server has sent a Reconfigure-init but before the Reconfigure-init
is received by the client. In this case, the client's Request message from
the client may not include all of the IAs and requests for parameters

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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
Request message from the client.

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15.3.

17.2. Client Behavior

A client MUST always monitor UDP port 546 for Reconfigure-init
messages on interfaces upon 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.

15.3.1.

17.2.1. Receipt of Reconfigure-init messages

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

DISCUSSION:

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

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

It might be possible for a duplicate or retransmitted
Reconfigure-init to be sufficiently delayed (and
delivered out of order) to arrive at the client after
the Request/Reply exchange (initiated by the original
Reconfigure-init) has been completed. In this case, the

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client would initiate a redundant Request/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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15.3.2.

17.2.2. Creation and sending of Request messages

When responding to a Reconfigure-init, the client creates and
sends the Request message in exactly the same manner as outlined in
section 14.3.1 16.1.1 with the following difference:

IAs The client includes IA options containing the addresses the
client currently has assigned to those IAs for the interface
through which the Reconfigure-init message was received.

15.3.3.

17.2.3. Time out and retransmission of Request messages

The client uses the same variables and retransmission algorithm as it
does with Request messages generated as part of a client-initiated
configuration exchange. See section 14.3.1 16.1.1 for details.

15.3.4.

17.2.4. 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 15.2.3, 17.1.3, the Reply from the server may include
IAs and parameters that were not included in the Request message from
the client. The client MUST configure itself with all of the IAs and
parameters in the Reply from the server.

16.

18. 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 All_DHCP_Servers multicast address, or other multicast addresses
selected by the network administrator. If the Relay has not been
explicitly configured, it will MUST use the All DHCP Servers All_DHCP_Servers multicast
address as the default.

16.1.

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18.1. Relaying of client messages

When a Relay receives a valid client message, it constructs a
Relay-forward message. The relay places an address from with a prefix
assigned to the interface link on which the client message was received in the
"relay-address" field and the prefix length for that should be assigned an
address in the
"prefix-length" link-prefix field. This address will be used by the
server to
identify determine the link to from which the client is connected should be assigned
an address and other configuration information.

If the relay cannot use the address in the link-prefix field to
identify the interface through which the response to the client
will be used

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by forwarded, the relay to forward MUST include a circuit-id option (see
section 20.15)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 Advertise
message was received from the server back to client into the client. client-return-address
field in the Relay-forward message.

The relay constructs a "client-message" option 18.5 20.7 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 the Relay-forward message to the list
of server destination addresses that it has been configured with.

16.2.

18.2. Relaying of server messages

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

17.

19. 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
messages. A DHCP server MUST include an

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messages. A DHCP server MUST include an authentication option in
Reconfigure-init messages sent to clients.

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

17.1.

19.1. DHCP threat model

The threat to DHCP is inherently an insider threat (assuming a
properly configured network where DHCPv6 ports are blocked on the enterprise's
perimeter gateways.) 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

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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.

17.2.

19.2. 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]. The way in which IPsec
is employed by relay agents and servers is not specified in this
document.

19.3. 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.

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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.

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.

17.3.

19.4. 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]) can reduce the danger of replay attacks. This method
MUST be supported by all protocols.

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17.4.

19.5. 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.

17.5.

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19.6. 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.
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 [10] [11]
using the MD5 hash [19] is defined here.

17.5.1.

19.6.1. 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.

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17.5.2.

19.6.2. 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 or Confirm 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 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

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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.

The sender computes the MAC using the HMAC generation algorithm [10] [11]
and the MD5 hash function [19]. The entire DHCP message (except
as noted below),
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

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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.

17.5.3.

19.6.3. 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 [10]. [11]. The receiver
MUST set the 'MAC' field of the authentication option to all 0s for
computation of the MAC, and because a DHCP relay agent may alter
the values of the 'giaddr' and 'hops' fields in the DHCP message,
the contents of those two fields MUST also be set to zero for the
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.

17.5.4.

19.6.4. 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
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

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

17.5.5.

19.6.5. Client considerations for delayed authentication protocol

17.5.5.1.

19.6.5.1. 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 17.5. 19.6. The client does not include any authentication
information in the Authentication option.

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17.5.6.

19.6.5.2. 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 17.5.3. 19.6.3.

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

17.5.6.1. Sending Request, Confirm, Renew, Rebind or Release messages

If the client authenticated the Advertise message through which the
client selected the server, the client MUST generate authentication
information for subsequent Request, Confirm, Renew, Rebind or Release
messages sent to the server as described in section 17.5. When the
client sends a subsequent message, it MUST use the same secret used
by the server to generate the authentication information.

17.5.6.2. 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.

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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.

17.5.7. Server considerations for delayed authentication protocol

17.5.7.1. 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 17.5. 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.

17.5.7.2. 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 17.5.3. 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 14.4. The server
MUST include authentication information generated using the secret
identified in the received message as specified in section 17.5.

17.5.7.3. Sending Reconfigure-Init messages

The server MUST include authentication information in a
Reconfigure-Init message, generated as specified in section 17.5
using the secret the server initially selected for the client to
which the Reconfigure-Init message is to be sent.

18. 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 18.1.

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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18.1. 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 data in
this option in octets.

option-data The data for the option; the format of this data
depends on the definition of the option.

18.2. 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 len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DUID |
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

18.3. 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:

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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 | num-addrs |T| addr status | prefix length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 address |
| (16 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| preferred lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| valid lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T| addr status | prefix length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| IPv6 address |
| (16 octets) |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | preferred lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| pref. lifetime (cont.) | valid lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| valid lifetime (cont.) |T| addr status | prefix length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 address |
| (16 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_IA (1)

option-len Variable; equal to 24 + num-addrs*26

IA ID The unique identifier for this IA; chosen by
the client

T1 The time at which the client contacts the
server from which the addresses in client SHOULD inform any local users and
SHOULD log the IA event.

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were obtained to extend the lifetimes of

19.6.5.3. Sending Request, Confirm, Renew, Rebind or Release messages

If the
addresses assigned to client authenticated the IA.

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

T When set to 1, indicates that this address is
a "temporary address" [15]; when set to 0,
the address is not a temporary address.

IA status Status of the IA in this option.

num-addrs An unsigned integer giving the number of
addresses carried in this IA option (MAY be
zero).

addr status Status of the addresses in this IA.

prefix length Prefix length for this address.

IPv6 address An IPv6 address assigned to this IA.

preferred lifetime The preferred lifetime for selected the associated
IPv6 address.

valid lifetime The valid lifetime for server, the associated IPv6
address.

The "IPv6 address", "preferred lifetime" and "valid lifetime" fields
are repeated client MUST generate authentication
information for each address in the IA option (as determined by the
"num-addrs" field).

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

The 'T' bit identifies Release
messages sent to the associated address server as described in section 19.6. When the
client sends a temporary address.
If subsequent message, it MUST use the same secret used
by the server is configured to assign temporary addresses to generate the
client, authentication information.

19.6.5.4. Receiving Reply messages

If the server marks those temporary addresses with client authenticated the 'T'
bit. The number of temporary addresses assigned to Advertise it accepted, the client and
the lifetimes of those addresses is determined by
MUST validate the administrative
configuration of associated Reply message from the server. The 'T' bit only identifies an address
as a temporary address; identification of an address as ``temporary''
has no implication on
client MUST discard the lifetime of Reply if the extensibility of message fails to pass validation
and MAY log the
lifetime of validation failure. If the Reply fails to pass
validation, the client MUST restart the address.

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18.4. Option request 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-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| requested-option-code-1 | requested-option-code-2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_ORO (2)

option-len Variable; equal 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.

19.6.6. Server considerations for delayed authentication protocol

19.6.6.1. 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 twice the number of option codes
carried
client as specified in this option.

option-data A list section 19.6. The server MUST record the
identifier of the option codes secret selected for the options requested client and use that same
secret for validating subsequent messages with the client.

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

The server uses the secret identified in this option.

18.5. Client the 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_CLIENT_MSG | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DHCP client and validates
the message |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_CLIENT_MSG (3)

option-len Variable; equal as specified in section 19.6.3. If the message fails to
pass validation or the length of server does not know the secret identified by
the 'secret ID' field, the server MUST discard the forwarded DHCP
client message.

option-data The message received from and MAY
choose to log the client; forwarded
verbatim validation failure.

If the message passes the validation procedure, the server responds
to the server. specific message as described in section 16.2. The server
MUST include authentication information generated using the secret
identified in the received message as specified in section 19.6.

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18.6. 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_SERVER_MSG | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DHCP

19.6.6.3. Sending Reconfigure-Init messages

The server message |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_SERVER_MSG (4)

option-len Variable; equal to MUST include authentication information in a
Reconfigure-Init message, generated as specified in section 19.6
using the length of secret the forwarded DHCP server message.

option-data The message received from initially selected for the server; forwarded
verbatim client to
which the client.

18.7. Retransmission parameter Reconfigure-Init message is to be sent.

20. 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 20.1.

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.

20.1. 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_RETRANS_PARM option-code | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-data |
| (option-len octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_RETRANS_PARM (5)

option-len An unsigned integer giving the length of identifying the data in
this specific option
type carried in octets.

option-data TBD - The details of the operational parameters to
be set in the client

18.8. DSTM Global IPv4 Address Option

The DSTM Global IPv4 Address Option informs a client or server that
the Identity Association Option (IA) following this option will
contain an IPv4-Mapped IPv6 Address [9] in the case of a Client
receiving the option, or is a Request for an IPv4-Mapped IPv6 Address
from a client in option.

option-len An unsigned integer giving the case length of a DHCPv6 Server receiving the option.
The data in
this option can also provide a set in octets.

option-data The data for the option; the format of IPv6 addresses to be used as this data
depends on the
Tunnel Endpoint (TEP) to encapsulate an IPv6 packet within IPv6. definition of the option.

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This

20.2. DHCP unique identifier option can be

The DHCP unique identifier option is used with the Request, Reply, and Reconfigure-Init
Messages for cases where a server wants to assign carry a DUID. The format
for the DUID is keyed to clients
IPv4-Mapped IPv6 Addresses, thru mark the Option Request Option (ORO). 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_DSTM OPTION DUID | option-length option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tunnel End Point (TEP) DUID type | DUID | (If Present)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| (16 octets) |
. DUID (cont.) .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

20.3. Identity association option code OPTION_DSTM (7)

The identity association option length Variable: 0 or multiple of 16

tunnel end point IPv6 Address or addresses if Present

A DSTM IPv4 Global Address Option MUST only apply is used to carry an identity
association, the parameters associated with the IA following
this option.

18.9. Authentication option

The Authentication option carries authentication information and the addresses
assigned to
authenticate the identity and contents of IA.

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The format of the Authentication 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_AUTH OPTION IA | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IAID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T2 | option-length
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IA status | num-addrs |T| addr status | prefix length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol | Algorithm
| RDM IPv6 address |
| (16 octets) |
| | Replay detect.|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Replay Detection (64 bits) preferred lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Replay cont. valid lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T| addr status | prefix length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| IPv6 address |
| (16 octets) |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Auth. Info | preferred lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| pref. lifetime (cont.) | valid lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authentication Information valid lifetime (cont.) |T| addr status | prefix length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 address |
| (16 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_AUTH OPTION_IA (TBD)

option-len Variable; equal to 24 + num-addrs*26

IA ID The unique identifier for this IA; chosen by
the client

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option-length Variable

protocol

T1 The authentication protocol used time at which the client contacts the
server from which the addresses in
this authentication option

algorithm the IA
were obtained to extend the lifetimes of the
addresses assigned to the IA.

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

T When set to 1, indicates that this address is
a "temporary address" [15]; when set to 0,
the address is not a temporary address.

IA status Status of the IA in this option.

num-addrs An unsigned integer giving the number of
addresses carried in this IA option (MAY be
zero).

addr status Status of the
authentication protocol

RDM The replay detection method used addresses in this authentication option

Replay detection IA.

prefix length Prefix length for this address.

IPv6 address An IPv6 address assigned to this IA.

preferred lifetime The replay detection information preferred lifetime for the RDM

Authentication information associated
IPv6 address.

valid lifetime The authentication information,
as specified by valid lifetime for the protocol associated IPv6
address.

The "IPv6 address", "preferred lifetime" and
algorithm used "valid lifetime" fields
are repeated for each address in this authentication
option

18.10. Server unicast option

This the IA option is used (as determined by the
"num-addrs" field).

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

The 'T' bit identifies the associated address as a temporary address.
If the server is configured to send assign temporary addresses to a client the
client, the server marks those temporary addresses with the 'T'
bit. The number of temporary addresses assigned to inform the client it can send a Request, Renew, Confirm, Release, and Decline
the lifetimes of those addresses is determined by
unicasting directly to the server instead administrative
configuration of the ALL-DHCPv6-Agents
Multicast address as server. The 'T' bit only identifies an optimization, when the client address
as a temporary address; identification of an address as "temporary"
has no implication on the lifetime of sufficient scope to reach the server. extensibility of the
lifetime of the address.

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20.4. Option request 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_UNICAST OPTION_ORO | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| requested-option-code-1 | option-length requested-option-code-2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_UNICAST OPTION_ORO (TBD)

option-length 0

This option only applies

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

option-data A list of the
client.

18.11. Domain Search option codes for the options requested
in this option.

A client MAY include an Option

This Request option provides a list of domain names in a Solicit, Request,
Renew, Rebind or Confirm message to inform the server about options
the client can use wants the server to
resolve DNS names. send to the client.

20.5. Preference 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_DOMAIN_SEARCH_LIST OPTION_PREFERENCE | option-length option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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| Domain Search List |
| ... pref value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

msg type OPTION_DOMAIN_SEARCH_LIST
+-+-+-+-+-+-+-+-+

option-code OPTION_PREFERENCE (TBD)

option-length variable

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

So that the search list may

option-len MUST be encoded compactly and uniformly,
search strings in the search list are concatenated and encoded using 1

option-data The preference value for the technique described in section 4.1 of [13].

For use server in this specification, message.

A server MAY include a Preference option in an Advertise message to
control the compression pointer (see section
4.1.4 selection of [13]) refers to a server by the offset within client. See section 15.1.3
for the SearchString portion use of the option.

18.12. Domain Name Server Option

This Preference 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. by the client and the
interpretation of Preference option data value.

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20.6. 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_DNS_SERVERS | option_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| DNS server (IP address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| DNS server (IP address) |
| | OPTION_ELAPSED_TIME | option_len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... elapsed time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

msg-type OPTION_DNS_SERVERS
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_ELAPSED_TIME (TBD)

option-length variable

DNS server IPv6 address of a DNS name server for the
client to use.

option-len MUST be 2

option-data The DNS servers are listed in

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the order amount of preference for use by time since the client
resolver.

19. began its
current DHCP Client Implementor Notes transaction. This section provides helpful information for the client implementor
regarding their implementations. The text described here time is not part
of the protocol, but rather a discussion expressed in
hundredths of implementation features
we feel the implementor should consider during implementation.

19.1. Primary Interface

Since configuration parameters acquired through DHCP can be
interface-specific or more general, the client implementor SHOULD
provide a mechanism by which the client implementation can be
configured to specify which interface is the primary interface. The second (10^-2 seconds).

A client SHOULD always query the DHCP data associated with the primary
interface for non-interface specific configuration parameters. An
implementation MAY implement a list of interfaces which would be
scanned include an Elapsed Time option in order to satisfy the general request. In either case, the
first interface scanned is considered the primary interface.

By allowing the specification of a primary interface, the client
implementor identifies which interface is authoritative for
non-interface specific parameters, which prevents configuration
information ambiguity within the client implementation.

19.2. Advertise Message and Configuration Parameter Caching

If the hardware messages to indicate
how long the client is running on permits it, has been trying to complete a DHCP transaction.
Servers MAY use the implementor
SHOULD provide data value in this option as input to policy
controlling how a cache for Advertise messages and server responds to a cache of
configuration parameters received through DHCP. Providing these
caches prevents unnecessary client message.

20.7. 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_CLIENT_MSG | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DHCP traffic and client message |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_CLIENT_MSG (TBD)

option-len Variable; equal to the subsequent load
this generates on length of the servers. forwarded DHCP
client message.

option-data The implementor SHOULD provide a
configuration knob message received from the client; forwarded
verbatim to the server.

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20.8. Server message option

option-code OPTION_SERVER_MSG (TBD)

option-len Variable; equal to the amount length of time the cache(s) are
valid.

19.3. Time out and retransmission variables

Note that forwarded DHCP
server message.

option-data The message received from the client time out and retransmission variables outlined
in section 7.5 can be configured on server; forwarded
verbatim to the client.

20.9. DSTM Global IPv4 Address Option

The DSTM Global IPv4 Address Option informs a client or server and sent to that
the client
through Identity Association Option (IA) following this option will
contain an IPv4-Mapped IPv6 Address [9] in the use case of a Client
receiving the "DHCP Retransmission Parameter Option", which option, or is documented in section 18.7. A client implementation SHOULD be
able to reset these variables using the values from this option.

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19.4. Server Preference

A Address
from a client MUST wait for SRVR_PREF_WAIT seconds after sending in the case of a DHCP
Solicit message to collect Advertise messages and compare their
preferences (see section 20.3), unless it receives an Advertise
message with DHCPv6 Server receiving the option.
The option can also provide a preference set of 255. If IPv6 addresses to be used as the client receives
Tunnel Endpoint (TEP) to encapsulate an
Advertise message IPv6 packet within IPv6.

This option can be used with a preference of 255, then the client MAY act
immediately on that Advertise without waiting Request, Reply, and Reconfigure-Init
Messages for any more additional
Advertise messages.

20. cases where a server wants to assign to clients
IPv4-Mapped IPv6 Addresses, thru the Option Request Option (ORO).

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-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tunnel End Point (TEP) |
| (If Present) |
| (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option code OPTION_DSTM (TBD)

option length Variable: 0 or multiple of 16

tunnel end point IPv6 Address or addresses if Present

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Internet Draft DHCP Server Implementor Notes

This section provides helpful information for the server implementor.

20.1. Client Bindings IPv6 (-20) 15 Oct 2001

A server implementation DSTM IPv4 Global Address Option MUST use the IA's DUID and the prefix
specification from which the client sent its Request message(s) as an
index for finding configuration parameters assigned to the client.
While it isn't critical only apply to keep track of the other parameters
assigned IA following
this option.

20.10. Authentication option

The Authentication option carries authentication information to a client,
authenticate the server MUST keep track identity and contents of the addresses it
has assigned to an IA. DHCP messages. The server should periodically scan its bindings for addresses whose
leases have expired. When the server finds expired addresses, it
MUST delete use of
the assignment Authentication option is described in section 19.

The format of those addresses, thereby making these
addresses available to other clients. the Authentication option is:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_AUTH | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol | Algorithm | RDM | Replay detect.|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Replay Detection (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Replay cont. | Auth. Info |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Authentication Information |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_AUTH (TBD)

option-length Variable

protocol The client bindings MUST be stored authentication protocol used in
this authentication option

algorithm The algorithm used in the
authentication protocol

RDM The replay detection method used in non-volatile storage.
this authentication option

Replay detection The server implementation should provide policy knobs to control
whether or not the lifetimes on assigned addresses are renewable, and
by how long.

20.2. Reconfigure-init Considerations

A server implementation MUST provide an interface to the
administrator replay detection information for initiating reconfigure-init events.

20.3. Server Preference

The server implementation SHOULD allow the setting of a server
preference value by
the administrator. RDM

Authentication information The server preference
variable is an unsigned single octet value (0--255), with authentication information,
as specified by the lowest
preference being 0 protocol and the highest 255. Clients will choose higher
preference servers over those with lower preference values. If you
don't choose to implement this feature in your server, you MUST set
the server preference field to 0
algorithm used in the Advertise messages generated
by your server. this authentication
option

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20.4. Request Message Transaction-ID Cache

In order to improve performance, a server implementation MAY include
an in memory transaction-ID cache.

20.11. Server unicast option

This cache option is indexed used by client
binding and transaction-ID, and enables the a server to quickly
determine whether a Request is send to a retransmission or client to inform
the client it MAY send a new Request
without Request, Renew, Release, and Decline by
unicasting directly to the cost server instead of a database lookup. If the All_DHCPv6_Agents
Multicast address as an implementor chooses optimization, when the client as an address
of sufficient scope to reach the server.

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-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_UNICAST (TBD)

option-length 0

This option only applies to
implement the server address that sends this cache, then they SHOULD provide a configuration knob to tune the lifetime of the cache entries.

21. DHCP Relay Implementor Notes

A relay implementation SHOULD allow the specification of a list of
destination addresses for forwarded messages.
client.

20.12. Domain Search Option

This option provides a list MAY contain
any mixture of unicast addresses and multicast addresses.

If a relay receives an ICMP message in response to a DHCP message it
has forwarded, it SHOULD log this event.

22. Security

Section 17 describes domain names a threat model and an option that provides an
authentication framework to defend against that threat model.

23. Year 2000 considerations

Since all times are relative client can use 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_DOMAIN_SEARCH_LIST | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Domain Search List |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_DOMAIN_SEARCH_LIST (TBD)

option-length variable

Domain Search List The DNS domain search list the current time of the transaction,
there is no problem within the DHCPv6 protocol related client
should use to any
hardcoded dates or two-digit representation of resolve names.

So that the current year.

24. IANA Considerations

This document defines several new name spaces associated with DHCPv6 search list may be encoded compactly and DHCPv6 options. IANA is requested to manage uniformly,
search strings in the allocation of
values from these name spaces.

New values search list are concatenated and encoded using
the technique described in each section 4.1 of these name spaces should be approved by [13].

For use in this specification, the
process compression pointer (see section
4.1.4 of IETF Consensus [14].

24.1. DHCPv6 options

This document defines message types TBD [13]) refers to be received by UDP at port
numbers 546 and 547. Additional message types may be defined in the
future. offset within the SearchString portion
of the option.

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24.2. Multicast addresses

Section 7.1 lists several multicast addresses used by DHCP.
Additional multicast addresses may be defined in the future.

24.3. Status codes

Section 9.7 defines several status codes

20.13. Domain Name Server Option

This option provides a list of Domain Name System [13] that are a client
name resolver can use to be returned with
the Reply message. The non-zero values for these status codes that
are currently specified are shown in the table in section 7.4.

24.4. Retransmission parameter option access DNS services. There is a DHCPv6 option described must be at least
1 server listed in section 18.7, which allows
clients and servers to exchange values for some this 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_DNS_SERVERS | option_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| DNS server (IP address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| DNS server (IP address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_DNS_SERVERS (11)

option-length variable

DNS server IPv6 address of the timing
and retransmission parameters defined in section 7.5. Adding new
parameters in the future would require extending the values by which
the parameters are indicated in the DHCP option. Since there needs
to be a list kept, the default values for each parameter should also
be stored as part of the list.

24.5. Authentication option

Section 17 defines three new DNS name spaces associated with server for the
Authentication Option (section 18.9), which are
client to be created and
maintained by IANA: Protocol, Algorithm and RDM.

Initial values assigned from the Protocol name space use. The DNS servers are 0 (for the
configuration token Protocol in section 17.4) and 1 (for the delayed
authentication Protocol in section 17.5). Additional protocols may
be defined listed 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 order of preference for a particular protocol
should be specified along with use by the definition client
resolver.

20.14. Status Code Option

This option returns indications of status not related to a new Protocol.

For the configuration token Protocol, the Algorithm field MUST be
0, as described in section 17.4. For the delayed authentication
Protocol, the Algorithm value specific
option.

0 1 is assigned to 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_STATUS_CODE | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| status-code | status-message |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_STATUS_CODE (TBD)

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option-length variable

status-code The numeric code for the HMAC-MD5
generating function as status encoded in
this option. The status codes are defined in
section 17.5. Additional
algorithms for the delayed authentication protocol may 7.4.

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

20.15. Circuit-ID Option

This option provides a mechanism through which a relay agent can
identify the future.

The initial value of 0 network attachment point through which a message was
received from the RDM name space is assigned to the
use of a monotonically increasing DHCP client.

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_CIRCUIT_ID | option_length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Circuit-ID |
. .
. .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_CIRCUIT_ID (TBD)

option-length variable

Circuit-ID An opaque value as defined in section 17.3.
Additional replay detection methods may be defined in of arbitrary length; this
value must uniquely identify one of the future.
network attachments used by the relay agent

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25. Acknowledgments

Thanks to the DHC Working Group for their time and input into the
specification. Ralph Droms and Thomas Narten have had

20.16. User Class Option

This option is used by a major
role in shaping client to identify the continued improvement type or category 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
user or applications it represents. The information contained in
this option is an opaque field that represents the user class of
which the
Last Call process. Thanks also for client is a member. Based on this class, a DHCP server
selects the consistent input, ideas, and
review by (in alphabetical order) Brian Carpenter, Francis DuPont,
Ted Lemon, Jack McCann, Yakov Rekhter, Matt Thomas, Sue Thomson,
Bernie Volz and Phil Wells.

Thanks appropriate address pool to Steve Deering assign an address to the
client and Bob Hinden, who have consistently
taken the time to discuss appropriate configuration parameters.

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_USER_CLASS | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| user class data |
| . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code TBD

option-len Variable; If n user classes are carried
by the more complex parts option, the length of the IPv6
specifications.

Bill Arbaugh reviewed option
option-len = sum of each of the authentication mechanism described in
section 17. user class
lengths + 2*n.

option-data The Domain Search user classes carried by the client.

The user class option described in section 18.11 is based on may contain one or more instances of user class
data. Each instance of the
DHCPv4 domain search option, [1], and was reviewed by Bernard Aboba.

A. Comparison between DHCPv4 and DHCPv6

This appendix user class data is provided for readers who will find it useful to see
a model and architecture comparison between DHCPv4 [7, 2] formatted as follows:

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

The user class length is two octets long and DHCPv6.
There are three key reasons for specifies the differences:

o IPv6 inherently supports a new model and architecture for
communications and autoconfiguration length of addresses.

o DHCPv6 benefits from
the new IPv6 features.

o New features were added to support opaque user class data in network byte order.

Servers may interpret the expected evolution meanings of multiple class specifications
in an implementation dependent or configuration dependent manner,
and so the existence use of more complicated Internet network service
requirements.

IPv6 Architecture/Model Changes:

o The link-local address permits multiple classes by a node to have an address
immediately when DHCP client should be based
on the node boots, which means all clients have a
source IP address at all times to locate an on-link specific server or
relay.

o The need for BOOTP compatibility implementation and configuration which will
be used to process that User class option. Servers not equipped to
interpret the broadcast flag have been
removed.

o Multicast user class information sent by a client MUST ignore it
(although it may be reported).

20.17. Vendor Class Option

This option is used by clients and address scoping in IPv6 permit the design servers to exchange vendor-
specific information. The definition of
discovery packets that would inherently define their range by this information is vendor
specific. The vendor is indicated in the
multicast address for vendor class identifier
option. Servers not equipped to interpret the function required. vendor-specific

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o Stateful autoconfiguration has to coexist and integrate with
stateless autoconfiguration supporting Duplicate Address
Detection and the two IPv6 lifetimes,

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 facilitate the dynamic
renumbering of addresses and the management of those addresses.

o Multiple addresses per interface are inherently supported in
IPv6.

o Some DHCPv4 options are unnecessary now because the configuration
parameters operate without it, although
they may do so(and announce they are either obtained through IPv6 Neighbor Discovery or
the Service Location protocol [21].

DHCPv6 Architecture/Model Changes:

o 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_VENDOR_CLASS | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-data |
| . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code TBD

option-len Variable

option-data The message type information is an opaque object of
option-len octets, presumably interpreted
by vendor-specific code on the first octet clients and
servers

If a vendor potentially encodes more than one item of information
in this option, then the vendor SHOULD encode the packet.

o IPv6 Address allocations are now handled in a message option using
"Encapsulated vendor-specific options".

The Encapsulated vendor-specific options field SHOULD be encoded as
opposed a
sequence of code/length/value fields of identical syntax to the message header.

o Client/Server bindings DHCP
options field.

When encapsulated vendor-specific extensions are now mandatory and take advantage used, each of the client's link-local address to always permit communications
either directly from an on-link server, or from a off-link server
through an on-link relay.

o Servers are discovered by a client Solicit, followed by a server
Advertise message

o The client will know if the server
encapsulated options is on-link or off-link.

o The on-link relay may locate off-link server addresses from
system configuration or by the use of a site-wide multicast
packet.

o ACKs and NAKs are not used.

o formatted as follows.

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| opt_code | opt_len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-data |
| . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

opt_code The server assumes the client receives its responses unless it
receives a retransmission of the same client request. This
permits recovery in the case where the network has faulted.

o Clients can issue multiple, unrelated Request messages to code for the
same or different servers.

o encapsulated option

opt_len The function length of DHCPINFORM is inherent in the new packet design;
a client can request configuration parameters other than IPv6
addresses in the optional encapsulated option headers.

o Clients MUST listen to their UDP port

option-data The data area for the new
Reconfigure-init message from servers.

o New options have been defined.

With the changes just enumerated, we can support new user features,
including encapsulated option

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o Configuration

21. Security Considerations

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

22. Year 2000 considerations

Since all times are relative to the current time of Dynamic Updates the transaction,
there is no problem within the DHCPv6 protocol related to DNS

o Address deprecation, for dynamic renumbering.

o Relays can be preconfigured with server addresses, any
hardcoded dates or use two-digit representation of
multicast.

o Authentication

o Clients can ask for multiple IP addresses.

o Addresses can be reclaimed using the Reconfigure-init message.

o Integration between stateless and stateful address
autoconfiguration.

o Enabling relays to locate off-link servers.

B. Full Copyright Statement

23. IANA Considerations

This document defines several new name spaces associated with DHCPv6
and translations of it may be copied and furnished DHCPv6 options. IANA is requested 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 manage the allocation of any
kind, provided that
values from these name spaces, which are described in the above copyright notice and remainder
of this paragraph section. These name spaces 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 be managed separately
from the Internet Society
or other Internet organizations, except as needed for the purpose
of developing Internet standards in which case the procedures
for copyrights name spaces defined for DHCPv4 [7, 2].

New values 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 each of these name spaces should be
revoked approved by the Internet Society or its successors or assigns.

This document and
process of IETF consensus [14].

23.1. Multicast addresses

Section 7.1 defines 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.

C. Changes 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. DHCPv6 message types

IANA is requested to record the message types defined in this draft

This section describes 7.3.
IANA is requested to manage definition of additional message types in
the changes between this version future.

23.3. DUID

IANA is requested to record the DUID types defined in section 10.1.
IANA is requested to manage definition of additional DUID types in
the DHCPv6
specification and draft-ietf-dhc-dhcpv6-19.txt. future.

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C.1. Reconfigure-init

The client behavior in response

23.4. DHCPv6 options

IANA is requested to a Reconfigure-init message
described assign option-codes to the options defined
in section 15 has been changed. When the client receives
a Reconfigure-init message, 20.1. IANA is requested to manage the client goes into "Reconfigure"
mode. The client initiates a Request/Reply exchange definition of
additional DHCPv6 option-codes in which the
XID future.

23.5. Status codes

IANA is requested to record the status codes defined in client Request section 7.4.
IANA is independent requested to manage the definition of server Reconfigure-init XID.
The server waits for additional status codes
in the next Request message from future.

23.6. Authentication option

Section 19 defines three new name spaces associated with the client
Authentication Option (section 20.10), which are to
determine if the client has received the Reconfigure-init.

To avoid redundant Request/Reply messages exchanges, be created and
maintained by IANA: Protocol, Algorithm and RDM.

Initial values assigned from the client
ignores subsequent Reconfigure-init messages until it completes Protocol name space are 0 (for the
Request/Reply exchange.

Use of multicast for Reconfigure-init message delivery has been
removed:

- Multicast only saves, at most, 1/3 of
configuration token Protocol in section 19.5) and 1 (for the messages when
reconfiguring multiple clients

- Multicast might cause an implosion of Request messages;
additional complexity delayed
authentication Protocol in section 19.6). Additional protocols may
be defined in the client and 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 messages would
should be required to add delay to spread out Request messages

- Authentication specified along with the definition of multicast Reconfigure-init messages (where a
single message must be authenticated by multiple clients) is an
open problem

Text has been added clarifying that new Protocol.

For the ORO option applies to IAs as
well configuration token Protocol, the Algorithm field MUST be
0, as other options. The server may choose described in section 19.5. For the delayed authentication
Protocol, the Algorithm value 1 is assigned to omit the IA option
from HMAC-MD5
generating function as defined in section 19.6. Additional
algorithms for the ORO delayed authentication protocol may be defined in
the Reconfigure-init message.

The Reconfigure-delay option (used only by multicast
Reconfigure-init) has been removed. future.

The transaction ID feild in initial value of 0 from the Reconfigure-init message header RDM name space is
now marked assigned to the
use of a monotonically increasing value as "(unused) MUST defined in section 19.4.
Additional replay detection methods may be zero".

C.2. Authentication

DHCPv4-style authentication has been added defined in the future.

24. Acknowledgments

Thanks to this draft the DHC Working Group for their time and input into the
specification. Ralph Droms and Thomas Narten have had a major
role in
section 17.

C.3. Confirm message

The following DISCUSSION was removed from shaping the description 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
Confirm message:

DISCUSSION:
Last Call process. Thanks also for the consistent input, ideas, and
review by (in alphabetical order) Brian Carpenter, Francis DuPont,
Ted Lemon, Jack McCann, Yakov Rekhter, Matt Thomas, Sue Thomson,
Bernie Volz and Phil Wells.

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Internet Draft DHCP for IPv6 30 June (-20) 15 Oct 2001

This section used to allow servers

Thanks to change Steve Deering and Bob Hinden, who have consistently
taken the addresses
in an IA. Without some additional mechanism, servers
responding time to Confirm messages can't change safely
change the addresses in IAs (although they can change discuss the lifetimes), because servers may send back different
addresses.

C.4. Failure more complex parts of Rebind message

In section 14.3.4, the alternatives for client behavior in IPv6
specifications.

Bill Arbaugh reviewed the
case that authentication mechanism described in
section 19.

The Domain Search option described in section 20.12 is based on the client receives no response
DHCPv4 domain search option, [1], and was reviewed by Bernard Aboba.

A. Comparison between DHCPv4 and DHCPv6

This appendix is provided for readers who will find it useful to see
a Rebind message were
taken out of a DISCUSSION section model and made part of the spec. These
alternatives architecture comparison between DHCPv4 [7, 2] and DHCPv6.
There are really an implementation issue three key reasons for the differences:

o IPv6 inherently supports a new model and not part architecture for
communications and autoconfiguration of the addresses.

o DHCPv6 spec.

C.5. Server behavior in response to Release message

The following DISCUSSION was merged into benefits from the text describing server
behavior in response new IPv6 features.

o New features were added to a Release message in section 14.4.5:

DISCUSSION:

What is support the behavior of expected evolution and
the server relative to existence of more complicated Internet network service
requirements.

IPv6 Architecture/Model Changes:

o The link-local address permits a "partially
released" IA; i.e., node to have an IA for address
immediately when the node boots, which some but not means all
addresses are released?

Can clients have a client send an empty IA to release all addresses in
the IA?

If the IA becomes empty -
source IP address at all addresses are released - can
the times to locate an on-link server discard any record of or
relay.

o The need for BOOTP compatibility and the IA?

C.6. Client behavior when sending a Release message

Text has broadcast flag have been added to section 14.3.6 clarifying
removed.

o Multicast and address scoping in IPv6 permit the design of
discovery packets that a client MAY
(but not MUST) wait would inherently define their range by the
multicast address for a Reply to a Release message.

C.7. IA option

The format diagram the function required.

o Stateful autoconfiguration has been corrected to include the prefix length coexist and address status integrate with each address. PROPOSAL - use left-most bit
in
stateless address status to indicate whether an autoconfiguration supporting duplicate address is "temporary".

C.8. DSTM option

Definition of DSTM option has been updated to carry multiple
detection [20] and the two IPv6 address lifetimes, to facilitate
the dynamic renumbering of addresses as tunnel endpoints. and the management of those
addresses.

o Multiple addresses per interface are inherently supported in
IPv6.

o Some DHCPv4 options are unnecessary now because the configuration
parameters are either obtained through IPv6 Neighbor Discovery or
the Service Location protocol [21].

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C.9. Server unicast option

An option to allow clients to use unicast where possible has been
added

DHCPv6 Architecture/Model Changes:

o The message type is the first octet in section 18.10.

C.10. Domain search option

An option to pass a domain name search list to a client has been
added the packet.

o IPv6 Address allocations are now handled in section 18.11.

C.11. DNS servers option

An a message option as
opposed to pass a list the message header.

o Client/Server bindings are now mandatory and take advantage
of DNS options the link-local address of the client to always permit
communications either directly from an on-link server, or from a
off-link server through an on-link relay.

o Servers are discovered by a client has been added in
section 18.12.

C.12. DUID and IAID

The "DHCP unique identifier" is defined as Solicit, followed by a typed, variable length
value (see section 18.2). server
Advertise message

o The DUID client will know if the server is carried in an option. on-link or off-link.

o The
details of on-link relay may locate off-link server addresses from
system configuration or by the DUID use of a site-wide multicast
packet.

o ACKs and NAKs are TBD. not used.

o The "IA identifier" is defined as a 4 octet identifier, unique among
all IAIDs for IAs from a client.

C.13. Continuing to poll with Solicit

Text has been added to section 13.3.2 allowing a server assumes the client to continue
to send Solicit messages at low frequency indefinitely.

C.14. Using DHCPv6 without address assignment

Text has been added to section 14.3.1 allowing receives its responses unless it
receives a retransmission of the same client to send a
Solicit message containing no IAs to request other configuration
information without address assignment (equivalent to DHCPv4
DHCPINFORM).

C.15. Potential crossing request. This
permits recovery in flight of the case where the network has faulted.

o Clients can issue multiple, unrelated Request and Reconfigure-init messages

Text has been added to section 15 addressing the case
same or different servers.

o The function of DHCPINFORM is inherent in which the
client sends a Request after a server has sent new packet design;
a Reconfigure-init but
before the client receives can request configuration parameters other than IPv6
addresses in the Reconfigure-init.

D. Open Issues for Working Group Discussion

This section contains some items optional option headers.

o Clients MUST listen to their UDP port for discussion by the working group. new
Reconfigure-init message from servers.

o New options have been defined.

With the changes just enumerated, we can support new user features,
including

o Configuration of Dynamic Updates to DNS

o Address deprecation, for dynamic renumbering.

o Relays can be preconfigured with server addresses, or use of
multicast.

o Authentication

o Clients can ask for multiple IP addresses.

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D.1. Generation and use of DUID and IAID

Details for generation and use of DUID and IA identifiers is TBD.

D.2. Address registration

Should there be a way for a DHCP client to register stateless
autoconfig addresses with the server?

D.3. Prefix advertisement

Can a DHCP server advertise prefixes? This function might

o Addresses can be used
to provide managed temporary addresses - the server advertises a
prefix and the client then registers selected addresses with reclaimed using the DHCP
server.

D.4. DHCP-DNS interaction

Interaction among DHCP servers, clients and DNS servers should be
discussed in this document.

What is relationship Reconfigure-init message.

o Integration between DHCP-DNS for IPv4 (work-in-progress) stateless and stateful address
autoconfiguration.

o Enabling relays to locate off-link servers.

B. Full Copyright Statement

This document and
DHCP-DNS interaction requirements for IPv6?

D.5. Use translations of term "agent"

The term "agent", taken it may be copied and furnished to mean "relay agent
others, and derivative works that comment on or otherwise explain it
or server", assist in its implementation may be
confusing. "relay agent prepared, copied, published
and distributed, in whole or server" might be clearer.

D.6. Additional options

Which additional options should be included in part, without restriction of any
kind, provided that the above copyright notice and this base spec
document? How should we reserve space for "local options" (as paragraph
are included on all such copies and derivative works. However,
this document itself may not be modified in
DHCPv4)?

D.7. Operational parameters

Should servers have an option any way, such as by
removing the copyright notice or references to set operational parameters -
retransmission timeouts, number the Internet Society
or other Internet organizations, except as needed for the purpose
of retries - developing Internet standards in clients? 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.

References

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

Bound, Carney, Perkins, Droms (ed.) Expires 30 November 2001 [Page 65]

Internet Draft DHCP for IPv6 30 June 2001
Engineering Task Force, December 2000. Work in progress.

[2] S. Alexander and R. Droms. DHCP Options and BOOTP Vendor
Extensions. Request for Comments (Draft Standard) 2132,
Internet Engineering Task Force,
Extensions, March 1997. RFC 2132.

[3] S. Bradner. Key words for use in RFCs to Indicate Requirement
Levels. Request for Comments (Best Current Practice) 2119,
Internet Engineering Task Force,
Levels, March 1997. RFC 2119.

[4] S. Bradner and A. Mankin. The Recommendation for the IP Next
Generation Protocol. Request for Comments (Proposed Standard)
1752, Internet Engineering Task Force, Protocol, January 1995. RFC 1752.

[5] W. J. W.J. Croft and J. Gilmore. Bootstrap Protocol. Request for
Comments 951, Internet Engineering Task Force, Protocol, September 1985.
RFC 951.

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Internet Draft DHCP for IPv6 (-20) 15 Oct 2001

[6] S. Deering and R. Hinden. Internet Protocol, Version 6 (IPv6)
Specification. Request for Comments (Draft Standard) 2460,
Internet Engineering Task Force,
Specification, December 1998. RFC 2460.

[7] R. Droms. Dynamic Host Configuration Protocol. Request for
Comments (Draft Standard) 2131, Internet Engineering Task Force, Protocol, March 1997. RFC
2131.

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

[9] R. Hinden and S. Deering. IP Version 6 Addressing Architecture.
Request for Comments (Proposed Standard) 2373, Internet
Engineering Task Force, Architecture,
July 1998. RFC 2373.

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

[11] H. Krawczyk, M. Bellare, and R. Canetti. HMAC: Keyed-Hashing
for Message Authentication. Request for Comments
(Informational) 2104, Internet Engineering Task Force, Authentication, February 1997.

[11] J. McCann, S. Deering, and J. Mogul. Path MTU Discovery for
IP version 6. Request for Comments (Proposed Standard) 1981,
Internet Engineering Task Force, August 1996. RFC 2104.

[12] David L. Mills. Network Time Protocol (Version 3)
Specification, Implementation. Request for Comments (Draft
Standard) 1305, Internet Engineering Task Force, Implementation, March 1992. RFC 1305.

[13] P. V. P.V. Mockapetris. Domain names - implementation and
specification. Request for Comments (Standard) 1035, Internet
Engineering Task Force,
specification, November 1987. RFC 1035.

[14] T. Narten and H. Alvestrand. Guidelines for Writing an IANA
Considerations Section in RFCs. Request for Comments (Best
Current Practice) 2434, Internet Engineering Task Force, RFCs, October 1998.

Bound, Carney, Perkins, Droms (ed.) Expires 30 November 2001 [Page 66]

Internet Draft DHCP for IPv6 30 June 2001 RFC 2434.

[15] T. Narten and R. Draves. Privacy Extensions for Stateless
Address Autoconfiguration in IPv6. Request for Comments
(Proposed Standard) 3041, Internet Engineering Task Force, IPv6, January 2001. RFC 3041.

[16] T. Narten, E. Nordmark, and W. Simpson. Neighbor Discovery for
IP Version 6 (IPv6). Request for Comments (Draft Standard)
2461, Internet Engineering Task Force, (IPv6), December 1998. RFC 2461.

[17] D. C. D.C. Plummer. Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet address
for transmission on Ethernet hardware. Request for Comments
(Standard) 826, Internet Engineering Task Force, hardware, November 1982. RFC 826.

[18] J. Postel. User Datagram Protocol. Request for Comments
(Standard) 768, Internet Engineering Task Force, Protocol, August 1980. RFC 768.

[19] R. Rivest. The MD5 Message-Digest Algorithm. Request for
Comments (Informational) 1321, Internet Engineering Task Force, Algorithm, April 1992. RFC
1321.

[20] S. Thomson and T. Narten. IPv6 Stateless Address
Autoconfiguration. Request for Comments (Draft Standard) 2462,
Internet Engineering Task Force,
Autoconfiguration, December 1998. RFC 2462.

[21] J. Veizades, E. Guttman, C. Perkins, and S. Kaplan. Service
Location Protocol. Request for Comments (Proposed Standard)
2165, Internet Engineering Task Force, Protocol, June 1997. RFC 2165.

[22] P. Vixie, Ed., S. Thomson, Y. Rekhter, and J. Bound. Dynamic
Updates in the Domain Name System (DNS UPDATE). Request for
Comments (Proposed Standard) 2136, Internet Engineering Task
Force, UPDATE), April 1997. RFC
2136.

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Internet Draft DHCP for IPv6 30 June (-20) 15 Oct 2001

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

Author's Address

Authors' Addresses

Questions about this memo can be directed to:

Bound, Carney, Perkins, Droms (ed.) Expires 30 November 2001 15 Apr 2002 [Page 68] 71]

Internet Draft DHCP for IPv6 30 June (-20) 15 Oct 2001

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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