Network Working Group R. Droms, Ed.
Request for Comments: 3315 Cisco
Category: Standards Track J. Bound
Hewlett Packard
B. Volz
EriCsson
T. Lemon
Nominum
C. Perkins
Nokia Research Center
M. Carney
Sun Microsystems
July 2003
Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
The Dynamic Host Configuration Protocol for IPv6 (DHCP) enables DHCP
servers to pass configuration parameters sUCh as IPv6 network
addresses to IPv6 nodes. It offers the capability of automatic
allocation of reusable network addresses and additional configuration
flexibility. This protocol is a stateful counterpart to "IPv6
Stateless Address Autoconfiguration" (RFC2462), and can be used
separately or concurrently with the latter to oBTain configuration
parameters.
Table of Contents
1. Introduction and Overview . . . . . . . . . . . . . . . . . . 5
1.1. Protocols and Addressing . . . . . . . . . . . . . . . 6
1.2. Client-server Exchanges Involving Two Messages . . . . 6
1.3. Client-server Exchanges Involving Four Messages. . . . 7
2. Requirements. . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Background. . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. IPv6 Terminology . . . . . . . . . . . . . . . . . . . 9
4.2. DHCP Terminology . . . . . . . . . . . . . . . . . . . 10
5. DHCP Constants. . . . . . . . . . . . . . . . . . . . . . . . 12
5.1. Multicast Addresses. . . . . . . . . . . . . . . . . . 13
5.2. UDP Ports. . . . . . . . . . . . . . . . . . . . . . . 13
5.3. DHCP Message Types . . . . . . . . . . . . . . . . . . 13
5.4. Status Codes . . . . . . . . . . . . . . . . . . . . . 15
5.5. Transmission and Retransmission Parameters . . . . . . 16
5.6 Representation of time values and "Infinity" as a time
value. . . . . . . . . . . . . . . . . . . . . . . . . 16
6. Client/Server Message Formats . . . . . . . . . . . . . . . . 16
7. Relay Agent/Server Message Formats. . . . . . . . . . . . . . 17
7.1. Relay-forward Message. . . . . . . . . . . . . . . . . 18
7.2. Relay-reply Message. . . . . . . . . . . . . . . . . . 19
8. Representation and Use of Domain Names. . . . . . . . . . . . 19
9. DHCP Unique Identifier (DUID) . . . . . . . . . . . . . . . . 19
9.1. DUID Contents. . . . . . . . . . . . . . . . . . . . . 20
9.2. DUID Based on Link-layer Address Plus Time [DUID-LLT]. 20
9.3. DUID Assigned by Vendor Based on Enterprise Number
[DUID-EN]. . . . . . . . . . . . . . . . . . . . . . . 22
9.4. DUID Based on Link-layer Address [DUID-LL] . . . . . . 22
10. Identity Association. . . . . . . . . . . . . . . . . . . . . 23
11. Selecting Addresses for Assignment to an IA . . . . . . . . . 24
12. Management of Temporary Addresses . . . . . . . . . . . . . . 25
13. Transmission of Messages by a Client. . . . . . . . . . . . . 25
14. Reliability of Client Initiated Message Exchanges . . . . . . 26
15. Message Validation. . . . . . . . . . . . . . . . . . . . . . 27
15.1. Use of Transaction IDs . . . . . . . . . . . . . . . . 28
15.2. Solicit Message. . . . . . . . . . . . . . . . . . . . 28
15.3. Advertise Message. . . . . . . . . . . . . . . . . . . 28
15.4. Request Message. . . . . . . . . . . . . . . . . . . . 29
15.5. Confirm Message. . . . . . . . . . . . . . . . . . . . 29
15.6. Renew Message. . . . . . . . . . . . . . . . . . . . . 29
15.7. Rebind Message . . . . . . . . . . . . . . . . . . . . 29
15.8. Decline Messages . . . . . . . . . . . . . . . . . . . 30
15.9. Release Message. . . . . . . . . . . . . . . . . . . . 30
15.10. Reply Message. . . . . . . . . . . . . . . . . . . . . 30
15.11. Reconfigure Message. . . . . . . . . . . . . . . . . . 31
15.12. Information-request Message. . . . . . . . . . . . . . 31
15.13. Relay-forward Message. . . . . . . . . . . . . . . . . 31
15.14. Relay-reply Message. . . . . . . . . . . . . . . . . . 31
16. Client Source Address and Interface Selection . . . . . . . . 32
17. DHCP Server Solicitation. . . . . . . . . . . . . . . . . . . 32
17.1. Client Behavior. . . . . . . . . . . . . . . . . . . . 32
17.1.1. Creation of Solicit Messages . . . . . . . . . 32
17.1.2. Transmission of Solicit Messages . . . . . . . 33
17.1.3. Receipt of Advertise Messages. . . . . . . . . 35
17.1.4. Receipt of Reply Message . . . . . . . . . . . 35
17.2. Server Behavior. . . . . . . . . . . . . . . . . . . . 36
17.2.1. Receipt of Solicit Messages . . . . . . . . . 36
17.2.2. Creation and Transmission of Advertise Messages 36
17.2.3. Creation and Transmission of Reply Messages. . 38
18. DHCP Client-Initiated Configuration Exchange. . . . . . . . . 38
18.1. Client Behavior. . . . . . . . . . . . . . . . . . . . 39
18.1.1. Creation and Transmission of Request Messages. 39
18.1.2. Creation and Transmission of Confirm Messages. 40
18.1.3. Creation and Transmission of Renew Messages. . 41
18.1.4. Creation and Transmission of Rebind Messages . 43
18.1.5. Creation and Transmission of Information-
request Messages . . .. . . . . . . . . . . . 44
18.1.6. Creation and Transmission of Release Messages. 44
18.1.7. Creation and Transmission of Decline Messages. 46
18.1.8. Receipt of Reply Messages. . . . . . . . . . . 46
18.2. Server Behavior. . . . . . . . . . . . . . . . . . . . 48
18.2.1. Receipt of Request Messages. . . . . . . . . . 49
18.2.2. Receipt of Confirm Messages. . . . . . . . . . 50
18.2.3. Receipt of Renew Messages. . . . . . . . . . . 51
18.2.4. Receipt of Rebind Messages . . . . . . . . . . 51
18.2.5. Receipt of Information-request Messages. . . . 52
18.2.6. Receipt of Release Messages. . . . . . . . . . 53
18.2.7. Receipt of Decline Messages. . . . . . . . . . 53
18.2.8. Transmission of Reply Messages . . . . . . . . 54
19. DHCP Server-Initiated Configuration Exchange. . . . . . . . . 54
19.1. Server Behavior. . . . . . . . . . . . . . . . . . . . 55
19.1.1. Creation and Transmission of Reconfigure
Messages . . . . . . . . . . . . . . . . . . . 55
19.1.2. Time Out and Retransmission of Reconfigure
Messages . . . . . . . . . . . . . . . . . . . 56
19.2. Receipt of Renew Messages. . . . . . . . . . . . . . . 56
19.3. Receipt of Information-request Messages. . . . . . . . 56
19.4. Client Behavior. . . . . . . . . . . . . . . . . . . . 57
19.4.1. Receipt of Reconfigure Messages. . . . . . . . 57
19.4.2. Creation and Transmission of Renew Messages. . 58
19.4.3. Creation and Transmission of Information-
request Messages . . . . . . . . . . . . . . . 58
19.4.4. Time Out and Retransmission of Renew or
Information-request Messages . . . . . . . . . 58
19.4.5. Receipt of Reply Messages. . . . . . . . . . . 58
20. Relay Agent Behavior. . . . . . . . . . . . . . . . . . . . . 58
20.1. Relaying a Client Message or a Relay-forward Message . 59
20.1.1. Relaying a Message from a Client . . . . . . . 59
20.1.2. Relaying a Message from a Relay Agent. . . . . 59
20.2. Relaying a Relay-reply Message . . . . . . . . . . . . 60
20.3. Construction of Relay-reply Messages . . . . . . . . . 60
21. Authentication of DHCP Messages . . . . . . . . . . . . . . . 61
21.1. Security of Messages Sent Between Servers and Relay
Agents . . . . . . . . . . . . . . . . . . . . . . . 61
21.2. Summary of DHCP Authentication . . . . . . . . . . . . 63
21.3. Replay Detection . . . . . . . . . . . . . . . . . . . 63
21.4. Delayed Authentication Protocol. . . . . . . . . . . . 63
21.4.1. Use of the Authentication Option in the Delayed
Authentication Protocol. . . . . . . . . . . . 64
21.4.2. Message Validation . . . . . . . . . . . . . . 65
21.4.3. Key Utilization . . . . . . . . . . . . . . . 65
21.4.4. Client Considerations for Delayed Authentication
Protocol . . . . . . . . . . . . . . . . . . . 66
21.4.5. Server Considerations for Delayed Authentication
Protocol . . . . . . . . . . . . . . . . . . . 67
21.5. Reconfigure Key Authentication Protocol. . . . . . . . 68
21.5.1. Use of the Authentication Option in the
Reconfigure Key Authentication Protocol. . . . 69
21.5.2. Server considerations for Reconfigure Key
protocol . . . . . . . . . . . . . . . . . . . 69
21.5.3. Client considerations for Reconfigure Key
protocol . . . . . . . . . . . . . . . . . . . 70
22. DHCP Options. . . . . . . . . . . . . . . . . . . . . . . . . 70
22.1. Format of DHCP Options . . . . . . . . . . . . . . . . 71
22.2. Client Identifier Option . . . . . . . . . . . . . . . 71
22.3. Server Identifier Option . . . . . . . . . . . . . . . 72
22.4. Identity Association for Non-temporary Addresses Option 72
22.5. Identity Association for Temporary Addresses Option. . 75
22.6. IA Address Option. . . . . . . . . . . . . . . . . . . 76
22.7. Option Request Option. . . . . . . . . . . . . . . . . 78
22.8. Preference Option. . . . . . . . . . . . . . . . . . . 79
22.9. Elapsed Time Option. . . . . . . . . . . . . . . . . . 79
22.10. Relay Message Option . . . . . . . . . . . . . . . . . 80
22.11. Authentication Option. . . . . . . . . . . . . . . . . 81
22.12. Server Unicast Option. . . . . . . . . . . . . . . . . 82
22.13. Status Code Option . . . . . . . . . . . . . . . . . . 82
22.14. Rapid Commit Option. . . . . . . . . . . . . . . . . . 83
22.15. User Class Option. . . . . . . . . . . . . . . . . . . 84
22.16. Vendor Class Option. . . . . . . . . . . . . . . . . . 85
22.17. Vendor-specific Information Option . . . . . . . . . . 86
22.18. Interface-Id Option. . . . . . . . . . . . . . . . . . 87
22.19. Reconfigure Message Option . . . . . . . . . . . . . . 88
22.20. Reconfigure Accept Option. . . . . . . . . . . . . . . 89
23. Security Considerations . . . . . . . . . . . . . . . . . . . 89
24. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 91
24.1. Multicast Addresses. . . . . . . . . . . . . . . . . . 92
24.2. DHCP Message Types . . . . . . . . . . . . . . . . . . 93
24.3. DHCP Options . . . . . . . . . . . . . . . . . . . . . 94
24.4. Status Codes . . . . . . . . . . . . . . . . . . . . . 95
24.5. DUID . . . . . . . . . . . . . . . . . . . . . . . . . 95
25. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 95
26. References. . . . . . . . . . . . . . . . . . . . . . . . . . 96
26.1. Normative References . . . . . . . . . . . . . . . . . 96
26.2. Informative References . . . . . . . . . . . . . . . . 97
A. Appearance of Options in Message Types . . . . . . . . . . . . 98
B. Appearance of Options in the Options Field of DHCP Options . . 99
Chair"s Address . . . . . . . . . . . . . . . . . . . . . . . . . 99
Authors" Addresses. . . . . . . . . . . . . . . . . . . . . . . . 100
Full Copyright Statement. . . . . . . . . . . . . . . . . . . . . 101
1. Introduction and Overview
This document describes DHCP for IPv6 (DHCP), a client/server
protocol that provides managed configuration of devices.
DHCP can provide a device with addresses assigned by a DHCP server
and other configuration information, which are carried in options.
DHCP can be extended through the definition of new options to carry
configuration information not specified in this document.
DHCP is the "stateful address autoconfiguration protocol" and the
"stateful autoconfiguration protocol" referred to in "IPv6 Stateless
Address Autoconfiguration" [17].
The operational models and relevant configuration information for
DHCPv4 [18][19] and DHCPv6 are sufficiently different that
integration between the two services is not included in this
document. If there is sufficient interest and demand, integration
can be specified in a document that extends DHCPv6 to carry IPv4
addresses and configuration information.
The remainder of this introduction summarizes DHCP, eXPlaining the
message exchange mechanisms and example message flows. The message
flows in sections 1.2 and 1.3 are intended as illustrations of DHCP
operation rather than an exhaustive list of all possible
client-server interactions. Sections 17, 18, and 19 explain client
and server operation in detail.
1.1. Protocols and Addressing
Clients and servers exchange DHCP messages using UDP [15]. The
client uses a link-local address or addresses determined through
other mechanisms for transmitting and receiving DHCP messages.
DHCP servers receive messages from clients using a reserved,
link-scoped multicast address. A DHCP client transmits most messages
to this reserved multicast address, so that the client need not be
configured with the address or addresses of DHCP servers.
To allow a DHCP client to send a message to a DHCP server that is not
attached to the same link, a DHCP relay agent on the client"s link
will relay messages between the client and server. The operation of
the relay agent is transparent to the client and the discussion of
message exchanges in the remainder of this section will omit the
description of message relaying by relay agents.
Once the client has determined the address of a server, it may under
some circumstances send messages directly to the server using
unicast.
1.2. Client-server Exchanges Involving Two Messages
When a DHCP client does not need to have a DHCP server assign it IP
addresses, the client can obtain configuration information such as a
list of available DNS servers [20] or NTP servers [21] through a
single message and reply exchanged with a DHCP server. To obtain
configuration information the client first sends an
Information-Request message to the All_DHCP_Relay_Agents_and_Servers
multicast address. Servers respond with a Reply message containing
the configuration information for the client.
This message exchange assumes that the client requires only
configuration information and does not require the assignment of any
IPv6 addresses.
When a server has IPv6 addresses and other configuration information
committed to a client, the client and server may be able to complete
the exchange using only two messages, instead of four messages as
described in the next section. In this case, the client sends a
Solicit message to the All_DHCP_Relay_Agents_and_Servers requesting
the assignment of addresses and other configuration information.
This message includes an indication that the client is willing to
accept an immediate Reply message from the server. The server that
is willing to commit the assignment of addresses to the client
immediately responds with a Reply message. The configuration
information and the addresses in the Reply message are then
immediately available for use by the client.
Each address assigned to the client has associated preferred and
valid lifetimes specified by the server. To request an extension of
the lifetimes assigned to an address, the client sends a Renew
message to the server. The server sends a Reply message to the
client with the new lifetimes, allowing the client to continue to use
the address without interruption.
1.3. Client-server Exchanges Involving Four Messages
To request the assignment of one or more IPv6 addresses, a client
first locates a DHCP server and then requests the assignment of
addresses and other configuration information from the server. The
client sends a Solicit message to the
All_DHCP_Relay_Agents_and_Servers address to find available DHCP
servers. Any server that can meet the client"s requirements responds
with an Advertise message. The client then chooses one of the
servers and sends a Request message to the server aSKINg for
confirmed assignment of addresses and other configuration
information. The server responds with a Reply message that contains
the confirmed addresses and configuration.
As described in the previous section, the client sends a Renew
message to the server to extend the lifetimes associated with its
addresses, allowing the client to continue to use those addresses
without interruption.
2. Requirements
The keyWords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in [1].
This document also makes use of internal conceptual variables to
describe protocol behavior and external variables that an
implementation must allow system administrators to change. The
specific variable names, how their values change, and how their
settings influence protocol behavior are provided to demonstrate
protocol behavior. An implementation is not required to have them in
the exact form described here, so long as its external behavior is
consistent with that described in this document.
3. Background
The IPv6 Specification provides the base architecture and design of
IPv6. Related work in IPv6 that would best serve an implementor to
study includes the IPv6 Specification [3], the IPv6 Addressing
Architecture [5], IPv6 Stateless Address Autoconfiguration [17], IPv6
Neighbor Discovery Processing [13], and Dynamic Updates to DNS [22].
These specifications enable DHCP to build upon the IPv6 work to
provide both robust stateful autoconfiguration and autoregistration
of DNS Host Names.
The IPv6 Addressing Architecture specification [5] defines the
address scope that can be used in an IPv6 implementation, and the
various configuration architecture guidelines for network designers
of the IPv6 address space. Two advantages of IPv6 are that support
for multicast is required and nodes can create link-local addresses
during initialization. The availability of these features means that
a client can use its link-local address and a well-known multicast
address to discover and communicate with DHCP servers or relay agents
on its link.
IPv6 Stateless Address Autoconfiguration [17] specifies procedures by
which a node may autoconfigure addresses based on router
advertisements [13], and the use of a valid lifetime to support
renumbering of addresses on the Internet. In addition, the protocol
interaction by which a node begins stateless or stateful
autoconfiguration is specified. DHCP is one vehicle to perform
stateful autoconfiguration. Compatibility with stateless address
autoconfiguration is a design requirement of DHCP.
IPv6 Neighbor Discovery [13] is the node discovery protocol in IPv6
which replaces and enhances functions of ARP [14]. To understand
IPv6 and stateless address autoconfiguration, it is strongly
recommended that implementors understand IPv6 Neighbor Discovery.
Dynamic Updates to DNS [22] is a specification that supports the
dynamic update of DNS records for both IPv4 and IPv6. DHCP can use
the dynamic updates to DNS to integrate addresses and name space to
not only support autoconfiguration, but also autoregistration in
IPv6.
4. Terminology
This sections defines terminology specific to IPv6 and DHCP used in
this document.
4.1. IPv6 Terminology
IPv6 terminology relevant to this specification from the IPv6
Protocol [3], IPv6 Addressing Architecture [5], and IPv6 Stateless
Address Autoconfiguration [17] is included below.
address An IP layer identifier for an interface
or a set of interfaces.
host Any node that is not a router.
IP Internet Protocol Version 6 (IPv6). The
terms IPv4 and IPv6 are used only in
contexts where it is necessary to avoid
ambiguity.
interface A node"s attachment to a link.
link A communication facility or medium over
which nodes can communicate at the link
layer, i.e., the layer immediately
below IP. Examples are Ethernet (simple
or bridged); Token Ring; PPP links,
X.25, Frame Relay, or ATM networks; and
Internet (or higher) layer "tunnels",
such as tunnels over IPv4 or IPv6
itself.
link-layer identifier A link-layer identifier for an
interface. Examples include IEEE 802
addresses for Ethernet or Token Ring
network interfaces, and E.164 addresses
for ISDN links.
link-local address An IPv6 address having a link-only
scope, indicated by having the prefix
(FE80::/10), that can be used to reach
neighboring nodes attached to the same
link. Every interface has a link-local
address.
multicast address An identifier for a set of interfaces
(typically belonging to different
nodes). A packet sent to a multicast
address is delivered to all interfaces
identified by that address.
neighbor A node attached to the same link.
node A device that implements IP.
packet An IP header plus payload.
prefix The initial bits of an address, or a
set of IP addresses that share the same
initial bits.
prefix length The number of bits in a prefix.
router A node that forwards IP packets not
explicitly addressed to itself.
unicast address An identifier for a single interface.
A packet sent to a unicast address is
delivered to the interface identified by
that address.
4.2. DHCP Terminology
Terminology specific to DHCP can be found below.
appropriate to the link An address is "appropriate to the link"
when the address is consistent with the
DHCP server"s knowledge of the network
topology, prefix assignment and address
assignment policies.
binding A binding (or, client binding) is a
group of server data records containing
the information the server has about
the addresses in an IA or configuration
information explicitly assigned to the
client. Configuration information that
has been returned to a client through a
policy - for example, the information
returned to all clients on the same
link - does not require a binding. A
binding containing information about
an IA is indexed by the tuple <DUID,
IA-type, IAID> (where IA-type is the
type of address in the IA; for example,
temporary). A binding containing
configuration information for a client
is indexed by <DUID>.
configuration parameter An element of the configuration
information set on the server and
delivered to the client using DHCP.
Such parameters may be used to carry
information to be used by a node to
configure its network subsystem and
enable communication on a link or
internetwork, for example.
DHCP Dynamic Host Configuration Protocol
for IPv6. The terms DHCPv4 and DHCPv6
are used only in contexts where it is
necessary to avoid ambiguity.
DHCP client (or client) A node that initiates requests on a link
to obtain configuration parameters from
one or more DHCP servers.
DHCP domain A set of links managed by DHCP and
operated by a single administrative
entity.
DHCP realm A name used to identify the DHCP
administrative domain from which a DHCP
authentication key was selected.
DHCP relay agent (or relay agent) A node that acts as an
intermediary to deliver DHCP messages
between clients and servers, and is on
the same link as the client.
DHCP server (or server) A node that responds to requests from
clients, and may or may not be on the
same link as the client(s).
DUID A DHCP Unique IDentifier for a DHCP
participant; each DHCP client and server
has exactly one DUID. See section 9 for
details of the ways in which a DUID may
be constructed.
Identity association (IA) A collection of addresses assigned to
a client. Each IA has an associated
IAID. A client may have more than one
IA assigned to it; for example, one for
each of its interfaces.
Each IA holds one type of address;
for example, an identity association
for temporary addresses (IA_TA) holds
temporary addresses (see "identity
association for temporary addresses").
Throughout this document, "IA" is used
to refer to an identity association
without identifying the type of
addresses in the IA.
Identity association identifier (IAID) An identifier for an IA,
chosen by the client. Each IA has an
IAID, which is chosen to be unique among
all IAIDs for IAs belonging to that
client.
Identity association for non-temporary addresses (IA_NA) An IA
that carries assigned addresses that are
not temporary addresses (see "identity
association for temporary addresses")
Identity association for temporary addresses (IA_TA) An IA that
carries temporary addresses (see RFC
3041 [12]).
message A unit of data carried as the payload
of a UDP datagram, exchanged among DHCP
servers, relay agents and clients.
Reconfigure key A key supplied to a client by a server
used to provide security for Reconfigure
messages.
relaying A DHCP relay agent relays DHCP messages
between DHCP participants.
transaction ID An opaque value used to match responses
with replies initiated either by a
client or server.
5. DHCP Constants
This section describes various program and networking constants used
by DHCP.
5.1. Multicast Addresses
DHCP makes use of the following multicast addresses:
All_DHCP_Relay_Agents_and_Servers (FF02::1:2) A link-scoped
multicast address used by a client to communicate with
neighboring (i.e., on-link) relay agents and servers.
All servers and relay agents are members of this
multicast group.
All_DHCP_Servers (FF05::1:3) A site-scoped multicast address used
by a relay agent to communicate with servers, either
because the relay agent wants to send messages to
all servers or because it does not know the unicast
addresses of the servers. Note that in order for
a relay agent to use this address, it must have an
address of sufficient scope to be reachable by the
servers. All servers within the site are members of
this multicast group.
5.2. UDP Ports
Clients listen for DHCP messages on UDP port 546. Servers and relay
agents listen for DHCP messages on UDP port 547.
5.3. DHCP Message Types
DHCP defines the following message types. More detail on these
message types can be found in sections 6 and 7. Message types not
listed here are reserved for future use. The numeric encoding for
each message type is shown in parentheses.
SOLICIT (1) A client sends a Solicit message to locate
servers.
ADVERTISE (2) A server sends an Advertise message to indicate
that it is available for DHCP service, in
response to a Solicit message received from a
client.
REQUEST (3) A client sends a Request message to request
configuration parameters, including IP
addresses, from a specific server.
CONFIRM (4) A client sends a Confirm message to any
available server to determine whether the
addresses it was assigned are still appropriate
to the link to which the client is connected.
RENEW (5) A client sends a Renew message to the server
that originally provided the client"s addresses
and configuration parameters to extend the
lifetimes on the addresses assigned to the
client and to update other configuration
parameters.
REBIND (6) A client sends a Rebind message to any
available server to extend the lifetimes on the
addresses assigned to the client and to update
other configuration parameters; this message is
sent after a client receives no response to a
Renew message.
REPLY (7) A server sends a Reply message containing
assigned addresses and configuration parameters
in response to a Solicit, Request, Renew,
Rebind message received from a client. A
server sends a Reply message containing
configuration parameters in response to an
Information-request message. A server sends a
Reply message in response to a Confirm message
confirming or denying that the addresses
assigned to the client are appropriate to the
link to which the client is connected. A
server sends a Reply message to acknowledge
receipt of a Release or Decline message.
RELEASE (8) A client sends a Release message to the server
that assigned addresses to the client to
indicate that the client will no longer use one
or more of the assigned addresses.
DECLINE (9) A client sends a Decline message to a server to
indicate that the client has determined that
one or more addresses assigned by the server
are already in use on the link to which the
client is connected.
RECONFIGURE (10) A server sends a Reconfigure message to a
client to inform the client that the server has
new or updated configuration parameters, and
that the client is to initiate a Renew/Reply
or Information-request/Reply transaction with
the server in order to receive the updated
information.
INFORMATION-REQUEST (11) A client sends an Information-request
message to a server to request configuration
parameters without the assignment of any IP
addresses to the client.
RELAY-FORW (12) A relay agent sends a Relay-forward message
to relay messages to servers, either directly
or through another relay agent. The received
message, either a client message or a
Relay-forward message from another relay
agent, is encapsulated in an option in the
Relay-forward message.
RELAY-REPL (13) A server sends a Relay-reply message to a relay
agent containing a message that the relay
agent delivers to a client. The Relay-reply
message may be relayed by other relay agents
for delivery to the destination relay agent.
The server encapsulates the client message as
an option in the Relay-reply message, which the
relay agent extracts and relays to the client.
5.4. Status Codes
DHCPv6 uses status codes to communicate the success or failure of
operations requested in messages from clients and servers, and to
provide additional information about the specific cause of the
failure of a message. The specific status codes are defined in
section 24.4.
5.5. Transmission and Retransmission Parameters
This section presents a table of values used to describe the message
transmission behavior of clients and servers.
Parameter Default Description
-------------------------------------
SOL_MAX_DELAY 1 sec Max delay of first Solicit
SOL_TIMEOUT 1 sec Initial Solicit timeout
SOL_MAX_RT 120 secs Max Solicit timeout value
REQ_TIMEOUT 1 sec Initial Request timeout
REQ_MAX_RT 30 secs Max Request timeout value
REQ_MAX_RC 10 Max Request retry attempts
CNF_MAX_DELAY 1 sec Max delay of first Confirm
CNF_TIMEOUT 1 sec Initial Confirm timeout
CNF_MAX_RT 4 secs Max Confirm timeout
CNF_MAX_RD 10 secs Max Confirm duration
REN_TIMEOUT 10 secs Initial Renew timeout
REN_MAX_RT 600 secs Max Renew timeout value
REB_TIMEOUT 10 secs Initial Rebind timeout
REB_MAX_RT 600 secs Max Rebind timeout value
INF_MAX_DELAY 1 sec Max delay of first Information-request
INF_TIMEOUT 1 sec Initial Information-request timeout
INF_MAX_RT 120 secs Max Information-request timeout value
REL_TIMEOUT 1 sec Initial Release timeout
REL_MAX_RC 5 MAX Release attempts
DEC_TIMEOUT 1 sec Initial Decline timeout
DEC_MAX_RC 5 Max Decline attempts
REC_TIMEOUT 2 secs Initial Reconfigure timeout
REC_MAX_RC 8 Max Reconfigure attempts
HOP_COUNT_LIMIT 32 Max hop count in a Relay-forward message
5.6 Representation of time values and "Infinity" as a time value
All time values for lifetimes, T1 and T2 are unsigned integers. The
value 0xffffffff is taken to mean "infinity" when used as a lifetime
(as in RFC2461 [17]) or a value for T1 or T2.
6. Client/Server Message Formats
All DHCP messages sent between clients and servers share an identical
fixed format header and a variable format area for options.
All values in the message header and in options are in network byte
order.
Options are stored serially in the options field, with no padding
between the options. Options are byte-aligned but are not aligned in
any other way such as on 2 or 4 byte boundaries.
The following diagram illustrates the format of DHCP messages sent
between clients and servers:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
msg-type transaction-id
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

. options .
. (variable) .

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
msg-type Identifies the DHCP message type; the
available message types are listed in
section 5.3.
transaction-id The transaction ID for this message exchange.
options Options carried in this message; options are
described in section 22.
7. Relay Agent/Server Message Formats
Relay agents exchange messages with servers to relay messages between
clients and servers that are not connected to the same link.
All values in the message header and in options are in network byte
order.
Options are stored serially in the options field, with no padding
between the options. Options are byte-aligned but are not aligned in
any other way such as on 2 or 4 byte boundaries.
There are two relay agent messages, which share the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
msg-type hop-count
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

link-address

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

peer-address

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. options (variable number and length) .... .

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The following sections describe the use of the Relay Agent message
header.
7.1. Relay-forward Message
The following table defines the use of message fields in a Relay-
forward message.
msg-type RELAY-FORW
hop-count Number of relay agents that have relayed this
message.
link-address A global or site-local address that will be used by
the server to identify the link on which the client
is located.
peer-address The address of the client or relay agent from which
the message to be relayed was received.
options MUST include a "Relay Message option" (see
section 22.10); MAY include other options added by
the relay agent.
7.2. Relay-reply Message
The following table defines the use of message fields in a
Relay-reply message.
msg-type RELAY-REPL
hop-count Copied from the Relay-forward message
link-address Copied from the Relay-forward message
peer-address Copied from the Relay-forward message
options MUST include a "Relay Message option"; see
section 22.10; MAY include other options
8. Representation and Use of Domain Names
So that domain names may be encoded uniformly, a domain name or a
list of domain names is encoded using the technique described in
section 3.1 of RFC1035 [10]. A domain name, or list of domain
names, in DHCP MUST NOT be stored in compressed form, as described in
section 4.1.4 of RFC1035.
9. DHCP Unique Identifier (DUID)
Each DHCP client and server has a DUID. DHCP servers use DUIDs to
identify clients for the selection of configuration parameters and in
the association of IAs with clients. DHCP clients use DUIDs to
identify a server in messages where a server needs to be identified.
See sections 22.2 and 22.3 for the representation of a DUID in a DHCP
message.
Clients and servers MUST treat DUIDs as opaque values and MUST only
compare DUIDs for equality. Clients and servers MUST NOT in any
other way interpret DUIDs. Clients and servers MUST NOT restrict
DUIDs to the types defined in this document, as additional DUID types
may be defined in the future.
The DUID is carried in an option because it may be variable length
and because it is not required in all DHCP messages. The DUID is
designed to be unique across all DHCP clients and servers, and stable
for any specific client or server - that is, the DUID used by a
client or server SHOULD NOT change over time if at all possible; for
example, a device"s DUID should not change as a result of a change in
the device"s network hardware.
The motivation for having more than one type of DUID is that the DUID
must be globally unique, and must also be easy to generate. The sort
of globally-unique identifier that is easy to generate for any given
device can differ quite widely. Also, some devices may not contain
any persistent storage. Retaining a generated DUID in such a device
is not possible, so the DUID scheme must accommodate such devices.
9.1. DUID Contents
A DUID consists of a two-octet type code represented in network byte
order, followed by a variable number of octets that make up the
actual identifier. A DUID can be no more than 128 octets long (not
including the type code). The following types are currently defined:
1 Link-layer address plus time
2 Vendor-assigned unique ID based on Enterprise Number
3 Link-layer address
Formats for the variable field of the DUID for each of the above
types are shown below.
9.2. DUID Based on Link-layer Address Plus Time [DUID-LLT]
This type of DUID consists of a two octet type field containing the
value 1, a two octet hardware type code, four octets containing a
time value, followed by link-layer address of any one network
interface that is connected to the DHCP device at the time that the
DUID is generated. The time value is the time that the DUID is
generated represented in seconds since midnight (UTC), January 1,
2000, modulo 2^32. The hardware type MUST be a valid hardware type
assigned by the IANA as described in RFC826 [14]. Both the time and
the hardware type are stored in network byte order. The link-layer
address is stored in canonical form, as described in RFC2464 [2].
The following diagram illustrates the format of a DUID-LLT:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 hardware type (16 bits)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
time (32 bits)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. link-layer address (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The choice of network interface can be completely arbitrary, as long
as that interface provides a globally unique link-layer address for
the link type, and the same DUID-LLT SHOULD be used in configuring
all network interfaces connected to the device, regardless of which
interface"s link-layer address was used to generate the DUID-LLT.
Clients and servers using this type of DUID MUST store the DUID-LLT
in stable storage, and MUST continue to use this DUID-LLT even if the
network interface used to generate the DUID-LLT is removed. Clients
and servers that do not have any stable storage MUST NOT use this
type of DUID.
Clients and servers that use this DUID SHOULD attempt to configure
the time prior to generating the DUID, if that is possible, and MUST
use some sort of time source (for example, a real-time clock) in
generating the DUID, even if that time source could not be configured
prior to generating the DUID. The use of a time source makes it
unlikely that two identical DUID-LLTs will be generated if the
network interface is removed from the client and another client then
uses the same network interface to generate a DUID-LLT. A collision
between two DUID-LLTs is very unlikely even if the clocks have not
been configured prior to generating the DUID.
This method of DUID generation is recommended for all general purpose
computing devices such as desktop computers and laptop computers, and
also for devices such as printers, routers, and so on, that contain
some form of writable non-volatile storage.
Despite our best efforts, it is possible that this algorithm for
generating a DUID could result in a client identifier collision. A
DHCP client that generates a DUID-LLT using this mechanism MUST
provide an administrative interface that replaces the existing DUID
with a newly-generated DUID-LLT.
9.3. DUID Assigned by Vendor Based on Enterprise Number [DUID-EN]
This form of DUID is assigned by the vendor to the device. It
consists of the vendor"s registered Private Enterprise Number as
maintained by IANA [6] followed by a unique identifier assigned by
the vendor. The following diagram summarizes the structure of a
DUID-EN:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2 enterprise-number
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
enterprise-number (contd)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. identifier .
. (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The source of the identifier is left up to the vendor defining it,
but each identifier part of each DUID-EN MUST be unique to the device
that is using it, and MUST be assigned to the device at the time it
is manufactured and stored in some form of non-volatile storage. The
generated DUID SHOULD be recorded in non-erasable storage. The
enterprise-number is the vendor"s registered Private Enterprise
Number as maintained by IANA [6]. The enterprise-number is stored as
an unsigned 32 bit number.
An example DUID of this type might look like this:
+---+---+---+---+---+---+---+---+
0 2 0 0 0 9 12192
+---+---+---+---+---+---+---+---+
132221 3 0 9 18
+---+---+---+---+---+---+
This example includes the two-octet type of 2, the Enterprise Number
(9), followed by eight octets of identifier data
(0x0CC084D303000912).
9.4. DUID Based on Link-layer Address [DUID-LL]
This type of DUID consists of two octets containing the DUID type 3,
a two octet network hardware type code, followed by the link-layer
address of any one network interface that is permanently connected to
the client or server device. For example, a host that has a network
interface implemented in a chip that is unlikely to be removed and
used elsewhere could use a DUID-LL. The hardware type MUST be a
valid hardware type assigned by the IANA, as described in RFC826
[14]. The hardware type is stored in network byte order. The
link-layer address is stored in canonical form, as described in RFC
2464 [2]. The following diagram illustrates the format of a DUID-LL:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3 hardware type (16 bits)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. link-layer address (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The choice of network interface can be completely arbitrary, as long
as that interface provides a unique link-layer address and is
permanently attached to the device on which the DUID-LL is being
generated. The same DUID-LL SHOULD be used in configuring all
network interfaces connected to the device, regardless of which
interface"s link-layer address was used to generate the DUID.
DUID-LL is recommended for devices that have a permanently-connected
network interface with a link-layer address, and do not have
nonvolatile, writable stable storage. DUID-LL MUST NOT be used by
DHCP clients or servers that cannot tell whether or not a network
interface is permanently attached to the device on which the DHCP
client is running.
10. Identity Association
An "identity-association" (IA) is a construct through which a server
and a client can identify, group, and manage a set of related IPv6
addresses. Each IA consists of an IAID and associated configuration
information.
A client must associate at least one distinct IA with each of its
network interfaces for which it is to request the assignment of IPv6
addresses from a DHCP server. The client uses the IAs assigned to an
interface to obtain configuration information from a server for that
interface. Each IA must be associated with exactly one interface.
The IAID uniquely identifies the IA and must be chosen to be unique
among the IAIDs on the client. The IAID is chosen by the client.
For any given use of an IA by the client, the IAID for that IA MUST
be consistent across restarts of the DHCP client. The client may
maintain consistency either by storing the IAID in non-volatile
storage or by using an algorithm that will consistently produce the
same IAID as long as the configuration of the client has not changed.
There may be no way for a client to maintain consistency of the IAIDs
if it does not have non-volatile storage and the client"s hardware
configuration changes.
The configuration information in an IA consists of one or more IPv6
addresses along with the times T1 and T2 for the IA. See section
22.4 for the representation of an IA in a DHCP message.
Each address in an IA has a preferred lifetime and a valid lifetime,
as defined in RFC2462 [17]. The lifetimes are transmitted from the
DHCP server to the client in the IA option. The lifetimes apply to
the use of IPv6 addresses, as described in section 5.5.4 of RFC2462.
11. Selecting Addresses for Assignment to an IA
A server selects addresses to be assigned to an IA according to the
address assignment policies determined by the server administrator
and the specific information the server determines about the client
from some combination of the following sources:
- The link to which the client is attached. The server determines
the link as follows:
* If the server receives the message directly from the client and
the source address in the IP datagram in which the message was
received is a link-local address, then the client is on the
same link to which the interface over which the message was
received is attached.
* If the server receives the message from a forwarding relay
agent, then the client is on the same link as the one to which
the interface, identified by the link-address field in the
message from the relay agent, is attached.
* If the server receives the message directly from the client and
the source address in the IP datagram in which the message was
received is not a link-local address, then the client is on the
link identified by the source address in the IP datagram (note
that this situation can occur only if the server has enabled
the use of unicast message delivery by the client and the
client has sent a message for which unicast delivery is
allowed).
- The DUID supplied by the client.
- Other information in options supplied by the client.
- Other information in options supplied by the relay agent.
Any address assigned by a server that is based on an EUI-64
identifier MUST include an interface identifier with the "u"
(universal/local) and "g" (individual/group) bits of the interface
identifier set appropriately, as indicated in section 2.5.1 of RFC
2373 [5].
A server MUST NOT assign an address that is otherwise reserved for
some other purpose. For example, a server MUST NOT assign reserved
anycast addresses, as defined in RFC2526, from any subnet.
12. Management of Temporary Addresses
A client may request the assignment of temporary addresses (see RFC
3041 [12] for the definition of temporary addresses). DHCPv6
handling of address assignment is no different for temporary
addresses. DHCPv6 says nothing about details of temporary addresses
like lifetimes, how clients use temporary addresses, rules for
generating successive temporary addresses, etc.
Clients ask for temporary addresses and servers assign them.
Temporary addresses are carried in the Identity Association for
Temporary Addresses (IA_TA) option (see section 22.5). Each IA_TA
option contains at most one temporary address for each of the
prefixes on the link to which the client is attached.
The IAID number space for the IA_TA option IAID number space is
separate from the IA_NA option IAID number space.
The server MAY update the DNS for a temporary address, as described
in section 4 of RFC3041.
13. Transmission of Messages by a Client
Unless otherwise specified in this document, or in a document that
describes how IPv6 is carried over a specific type of link (for link
types that do not support multicast), a client sends DHCP messages to
the All_DHCP_Relay_Agents_and_Servers.
A client uses multicast to reach all servers or an individual server.
An individual server is indicated by specifying that server"s DUID in
a Server Identifier option (see section 22.3) in the client"s message
(all servers will receive this message but only the indicated server
will respond). All servers are indicated by not supplying this
option.
A client may send some messages directly to a server using unicast,
as described in section 22.12.
14. Reliability of Client Initiated Message Exchanges
DHCP clients are responsible for reliable delivery of messages in the
client-initiated message exchanges described in sections 17 and 18.
If a DHCP client fails to receive an expected response from a server,
the client must retransmit its message. This section describes the
retransmission strategy to be used by clients in client-initiated
message exchanges.
Note that the procedure described in this section is slightly
modified when used with the Solicit message. The modified procedure
is described in section 17.1.2.
The client begins the message exchange by transmitting a message to
the server. The message exchange terminates when either the client
successfully receives the appropriate response or responses from a
server or servers, or when the message exchange is considered to have
failed according to the retransmission mechanism described below.
The client retransmission behavior is controlled and described by the
following variables:
RT Retransmission timeout
IRT Initial retransmission time
MRC Maximum retransmission count
MRT Maximum retransmission time
MRD Maximum retransmission duration
RAND Randomization factor
With each message transmission or retransmission, the client sets RT
according to the rules given below. If RT expires before the message
exchange terminates, the client recomputes RT and retransmits the
message.
Each of the computations of a new RT include a randomization factor
(RAND), which is a random number chosen with a uniform distribution
between -0.1 and +0.1. The randomization factor is included to
minimize synchronization of messages transmitted by DHCP clients.
The algorithm for choosing a random number does not need to be
cryptographically sound. The algorithm SHOULD produce a different
sequence of random numbers from each invocation of the DHCP client.
RT for the first message transmission is based on IRT:
RT = IRT + RAND*IRT
RT for each subsequent message transmission is based on the previous
value of RT:
RT = 2*RTprev + RAND*RTprev
MRT specifies an upper bound on the value of RT (disregarding the
randomization added by the use of RAND). If MRT has a value of 0,
there is no upper limit on the value of RT. Otherwise:
if (RT > MRT)
RT = MRT + RAND*MRT
MRC specifies an upper bound on the number of times a client may
retransmit a message. Unless MRC is zero, the message exchange fails
once the client has transmitted the message MRC times.
MRD specifies an upper bound on the length of time a client may
retransmit a message. Unless MRD is zero, the message exchange fails
once MRD seconds have elapsed since the client first transmitted the
message.
If both MRC and MRD are non-zero, the message exchange fails whenever
either of the conditions specified in the previous two paragraphs are
met.
If both MRC and MRD are zero, the client continues to transmit the
message until it receives a response.
15. Message Validation
Clients and servers SHOULD discard any messages that contain options
that are not allowed to appear in the received message. For example,
an IA option is not allowed to appear in an Information-request
message. Clients and servers MAY choose to extract information from
such a message if the information is of use to the recipient.
A server MUST discard any Solicit, Confirm, Rebind or
Information-request messages it receives with a unicast destination
address.
Message validation based on DHCP authentication is discussed in
section 21.4.2.
If a server receives a message that contains options it should not
contain (such as an Information-request message with an IA option),
is missing options that it should contain, or is otherwise not valid,
it MAY send a Reply (or Advertise as appropriate) with a Server
Identifier option, a Client Identifier option if one was included in
the message and a Status Code option with status UnSpecFail.
15.1. Use of Transaction IDs
The "transaction-id" field holds a value used by clients and servers
to synchronize server responses to client messages. A client SHOULD
generate a random number that cannot easily be guessed or predicted
to use as the transaction ID for each new message it sends. Note
that if a client generates easily predictable transaction
identifiers, it may become more vulnerable to certain kinds of
attacks from off-path intruders. A client MUST leave the transaction
ID unchanged in retransmissions of a message.
15.2. Solicit Message
Clients MUST discard any received Solicit messages.
Servers MUST discard any Solicit messages that do not include a
Client Identifier option or that do include a Server Identifier
option.
15.3. Advertise Message
Clients MUST discard any received Advertise messages that meet any of
the following conditions:
- the message does not include a Server Identifier option.
- the message does not include a Client Identifier option.
- the contents of the Client Identifier option does not match the
client"s DUID.
- the "transaction-id" field value does not match the value the
client used in its Solicit message.
Servers and relay agents MUST discard any received Advertise
messages.
15.4. Request Message
Clients MUST discard any received Request messages.
Servers MUST discard any received Request message that meet any of
the following conditions:
- the message does not include a Server Identifier option.
- the contents of the Server Identifier option do not match the
server"s DUID.
- the message does not include a Client Identifier option.
15.5. Confirm Message
Clients MUST discard any received Confirm messages.
Servers MUST discard any received Confirm messages that do not
include a Client Identifier option or that do include a Server
Identifier option.
15.6. Renew Message
Clients MUST discard any received Renew messages.
Servers MUST discard any received Renew message that meets any of the
following conditions:
- the message does not include a Server Identifier option.
- the contents of the Server Identifier option does not match the
server"s identifier.
- the message does not include a Client Identifier option.
15.7. Rebind Message
Clients MUST discard any received Rebind messages.
Servers MUST discard any received Rebind messages that do not include
a Client Identifier option or that do include a Server Identifier
option.
15.8. Decline Messages
Clients MUST discard any received Decline messages.
Servers MUST discard any received Decline message that meets any of
the following conditions:
- the message does not include a Server Identifier option.
- the contents of the Server Identifier option does not match the
server"s identifier.
- the message does not include a Client Identifier option.
15.9. Release Message
Clients MUST discard any received Release messages.
Servers MUST discard any received Release message that meets any of
the following conditions:
- the message does not include a Server Identifier option.
- the contents of the Server Identifier option does not match the
server"s identifier.
- the message does not include a Client Identifier option.
15.10. Reply Message
Clients MUST discard any received Reply message that meets any of the
following conditions:
- the message does not include a Server Identifier option.
- the "transaction-id" field in the message does not match the value
used in the original message.
If the client included a Client Identifier option in the original
message, the Reply message MUST include a Client Identifier option
and the contents of the Client Identifier option MUST match the DUID
of the client; OR, if the client did not include a Client Identifier
option in the original message, the Reply message MUST NOT include a
Client Identifier option.
Servers and relay agents MUST discard any received Reply messages.
15.11. Reconfigure Message
Servers and relay agents MUST discard any received Reconfigure
messages.
Clients MUST discard any Reconfigure messages that meets any of the
following conditions:
- the message was not unicast to the client.
- the message does not include a Server Identifier option.
- the message does not include a Client Identifier option that
contains the client"s DUID.
- the message does not contain a Reconfigure Message option and the
msg-type must be a valid value.
- the message includes any IA options and the msg-type in the
Reconfigure Message option is INFORMATION-REQUEST.
- the message does not include DHCP authentication:
* the message does not contain an authentication option.
* the message does not pass the authentication validation
performed by the client.
15.12. Information-request Message
Clients MUST discard any received Information-request messages.
Servers MUST discard any received Information-request message that
meets any of the following conditions:
- The message includes a Server Identifier option and the DUID in
the option does not match the server"s DUID.
- The message includes an IA option.
15.13. Relay-forward Message
Clients MUST discard any received Relay-forward messages.
15.14. Relay-reply Message
Clients and servers MUST discard any received Relay-reply messages.
16. Client Source Address and Interface Selection
When a client sends a DHCP message to the
All_DHCP_Relay_Agents_and_Servers address, it SHOULD send the message
through the interface for which configuration information is being
requested. However, the client MAY send the message through another
interface attached to the same link, if and only if the client is
certain the two interfaces are attached to the same link. The client
MUST use a link-local address assigned to the interface for which it
is requesting configuration information as the source address in the
header of the IP datagram.
When a client sends a DHCP message directly to a server using unicast
(after receiving the Server Unicast option from that server), the
source address in the header of the IP datagram MUST be an address
assigned to the interface for which the client is interested in
obtaining configuration and which is suitable for use by the server
in responding to the client.
17. DHCP Server Solicitation
This section describes how a client locates servers that will assign
addresses to IAs belonging to the client.
The client is responsible for creating IAs and requesting that a
server assign IPv6 addresses to the IA. The client first creates an
IA and assigns it an IAID. The client then transmits a Solicit
message containing an IA option describing the IA. Servers that can
assign addresses to the IA respond to the client with an Advertise
message. The client then initiates a configuration exchange as
described in section 18.
If the client will accept a Reply message with committed address
assignments and other resources in response to the Solicit message,
the client includes a Rapid Commit option (see section 22.14) in the
Solicit message.
17.1. Client Behavior
A client uses the Solicit message to discover DHCP servers configured
to assign addresses or return other configuration parameters on the
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