Internet Engineering Task Force J. Bound
INTERNET DRAFT Compaq
DHC Working Group M. Carney
Obsoletes: draft-ietf-dhc-dhcpv6-19.txt Sun Microsystems, Inc
C. Perkins
Nokia Research Center
R. Droms(ed.)
Cisco Systems
15 Oct 2001
Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
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 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 2
5. Non-Goals 3
6. Terminology 3
6.1. IPv6 Terminology . . . . . . . . . . . . . . . . . . . . 3
6.2. DHCP Terminology . . . . . . . . . . . . . . . . . . . . 5
7. DHCP Constants 6
7.1. Multicast Addresses . . . . . . . . . . . . . . . . . . . 6
7.2. UDP ports . . . . . . . . . . . . . . . . . . . . . . . . 6
7.3. DHCP message types . . . . . . . . . . . . . . . . . . . 7
7.4. Status Codes . . . . . . . . . . . . . . . . . . . . . . 8
7.4.1. Generic Status Codes . . . . . . . . . . . . . . 9
7.4.2. Server-specific Status Codes . . . . . . . . . . 9
7.5. Configuration Variables . . . . . . . . . . . . . . . . . 10
8. Message Formats 10
8.1. DHCP Solicit Message Format . . . . . . . . . . . . . . . 11
8.2. DHCP Advertise Message Format . . . . . . . . . . . . . . 11
8.3. DHCP Request Message Format . . . . . . . . . . . . . . . 12
8.4. DHCP Confirm Message Format . . . . . . . . . . . . . . . 12
8.5. DHCP Renew Message Format . . . . . . . . . . . . . . . . 12
8.6. DHCP Rebind Message Format . . . . . . . . . . . . . . . 12
8.7. DHCP Reply Message Format . . . . . . . . . . . . . . . . 13
8.8. DHCP Release Message Format . . . . . . . . . . . . . . . 13
8.9. DHCP Decline Message Format . . . . . . . . . . . . . . . 13
8.10. DHCP Reconfigure-init Message Format . . . . . . . . . . 13
9. Relay messages 14
9.1. Relay-forward message . . . . . . . . . . . . . . . . . . 14
9.2. Relay-reply message . . . . . . . . . . . . . . . . . . . 15
10. DHCP unique identifier (DUID) 15
10.1. DUID contents . . . . . . . . . . . . . . . . . . . . . . 15
10.2. DUID based on link-layer address plus time . . . . . . . 16
10.3. Vendor-assigned unique ID. . . . . . . . . . . . . . . . 17
10.4. Link-layer address . . . . . . . . . . . . . . . . . . . 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
14. Message validation 20
14.1. Use of Transaction-ID field . . . . . . . . . . . . . . . 21
14.2. Solicit message . . . . . . . . . . . . . . . . . . . . . 21
14.3. Advertise message . . . . . . . . . . . . . . . . . . . . 21
14.4. Request message . . . . . . . . . . . . . . . . . . . . . 21
14.5. Confirm message . . . . . . . . . . . . . . . . . . . . . 21
14.6. Renew message . . . . . . . . . . . . . . . . . . . . . . 21
14.7. Rebind message . . . . . . . . . . . . . . . . . . . . . 22
14.8. Decline messages . . . . . . . . . . . . . . . . . . . . 22
14.9. Release message . . . . . . . . . . . . . . . . . . . . . 22
14.10. Reply message . . . . . . . . . . . . . . . . . . . . . . 22
14.11. Reconfigure-init message . . . . . . . . . . . . . . . . 22
14.12. Relay-forward message . . . . . . . . . . . . . . . . . . 23
14.13. Relay-reply message . . . . . . . . . . . . . . . . . . . 23
15. DHCP Server Solicitation 23
15.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 23
15.1.1. Creation of Solicit messages . . . . . . . . . . 23
15.1.2. Transmission of Solicit Messages . . . . . . . . 23
15.1.3. Receipt of Advertise messages . . . . . . . . . . 25
15.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 25
15.2.1. Receipt of Solicit messages . . . . . . . . . . . 25
15.2.2. Creation and transmission of Advertise messages . 26
16. DHCP Client-Initiated Configuration Exchange 26
16.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 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 . . . 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 . . . . . . . . . . . . . . . . . 35
16.1.8. Creation and transmission of Decline messages . . 35
16.1.9. Receipt of Reply message in response to a Decline
message . . . . . . . . . . . . . . . . . 36
16.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 36
16.2.1. Receipt of Request messages . . . . . . . . . . . 36
16.2.2. Receipt of Confirm messages . . . . . . . . . . . 37
16.2.3. Receipt of Renew messages . . . . . . . . . . . . 38
16.2.4. Receipt of Rebind messages . . . . . . . . . . . 39
16.2.5. Receipt of Release messages . . . . . . . . . . . 40
16.2.6. Receipt of Decline messages . . . . . . . . . . . 40
16.2.7. Sending of Reply messages . . . . . . . . . . . . 41
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17. DHCP Server-Initiated Configuration Exchange 41
17.1. Server Behavior . . . . . . . . . . . . . . . . . . . . . 41
17.1.1. Creation and transmission of Reconfigure-init
messages . . . . . . . . . . . . . . . . . 41
17.1.2. Time out and retransmission of Reconfigure-init
messages . . . . . . . . . . . . . . . . . 42
17.1.3. Receipt of Request messages . . . . . . . . . . . 42
17.2. Client Behavior . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . 44
18. Relay Behavior 44
18.1. Relaying of client messages . . . . . . . . . . . . . . . 45
18.2. Relaying of server messages . . . . . . . . . . . . . . . 45
19. Authentication of DHCP messages 45
19.1. DHCP threat model . . . . . . . . . . . . . . . . . . . . 46
19.2. Security of messages sent between servers and relay agents 46
19.3. Summary of DHCP authentication . . . . . . . . . . . . . 46
19.4. Replay detection . . . . . . . . . . . . . . . . . . . . 47
19.5. Configuration token protocol . . . . . . . . . . . . . . 47
19.6. Delayed authentication protocol . . . . . . . . . . . . . 48
19.6.1. Management issues in the delayed authentication
protocol . . . . . . . . . . . . . . . . . 48
19.6.2. Use of the Authentication option in the delayed
authentication protocol . . . . . . . . . 48
19.6.3. Message validation . . . . . . . . . . . . . . . 49
19.6.4. Key utilization . . . . . . . . . . . . . . . . . 49
19.6.5. Client considerations for delayed authentication
protocol . . . . . . . . . . . . . . . . . 50
19.6.6. Server considerations for delayed authentication
protocol . . . . . . . . . . . . . . . . . 51
20. DHCP options 52
20.1. Format of DHCP options . . . . . . . . . . . . . . . . . 52
20.2. DHCP unique identifier option . . . . . . . . . . . . . . 53
20.3. Identity association option . . . . . . . . . . . . . . . 53
20.4. Option request option . . . . . . . . . . . . . . . . . . 56
20.5. Preference option . . . . . . . . . . . . . . . . . . . . 56
20.6. Elapsed Time . . . . . . . . . . . . . . . . . . . . . . 57
20.7. Client message option . . . . . . . . . . . . . . . . . . 57
20.8. Server message option . . . . . . . . . . . . . . . . . . 58
20.9. DSTM Global IPv4 Address Option . . . . . . . . . . . . . 58
20.10. Authentication option . . . . . . . . . . . . . . . . . . 59
20.11. Server unicast option . . . . . . . . . . . . . . . . . . 60
20.12. Domain Search Option . . . . . . . . . . . . . . . . . . 60
20.13. Domain Name Server Option . . . . . . . . . . . . . . . . 61
20.14. Status Code Option . . . . . . . . . . . . . . . . . . . 61
20.15. Circuit-ID Option . . . . . . . . . . . . . . . . . . . . 62
20.16. User Class Option . . . . . . . . . . . . . . . . . . . . 63
20.17. Vendor Class Option . . . . . . . . . . . . . . . . . . . 63
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21. Security Considerations 65
22. Year 2000 considerations 65
23. IANA Considerations 65
23.1. Multicast addresses . . . . . . . . . . . . . . . . . . . 65
23.2. DHCPv6 message types . . . . . . . . . . . . . . . . . . 65
23.3. DUID . . . . . . . . . . . . . . . . . . . . . . . . . . 65
23.4. DHCPv6 options . . . . . . . . . . . . . . . . . . . . . 66
23.5. Status codes . . . . . . . . . . . . . . . . . . . . . . 66
23.6. Authentication option . . . . . . . . . . . . . . . . . . 66
24. Acknowledgments 66
A. Comparison between DHCPv4 and DHCPv6 67
B. Full Copyright Statement 69
References 69
Chair's Address 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 the constraints of backward
compatibility 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
The IPv6 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
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provide both robust stateful autoconfiguration and autoregistration
of DNS Host Names.
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] 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 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 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. Design Goals
- DHCP is a mechanism rather than a policy. Network administrators
set their administrative policies through the configuration
parameters they place upon the DHCP servers in the DHCP domain
they're managing. DHCP is simply used to deliver parameters
according to that policy to each of the DHCP clients within the
domain.
- DHCP is compatible with IPv6 stateless address
autoconfiguration [20], 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 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.
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 IPv6 address having link-only
scope, indicated by having the prefix
(FE80::0000/64), that can be used to reach
neighboring nodes attached to the same
link. Every interface has a link-local
address.
message A unit of data carried in a packet,
exchanged between DHCP agents and clients.
neighbor 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.
agent address The address of a neighboring DHCP Agent
on the same link as the DHCP client.
binding A binding (or, client binding) is a
group of server data records containing
the information the server has about
the addresses in an IA and any other
configuration information assigned to
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.
DHCP client (or client) A node that initiates requests on a link
to obtain configuration parameters from
one or more DHCP servers.
DHCP domain A set of links managed by DHCP and
operated by a single administrative
entity.
DHCP server (or server) A server is a node that responds to
requests from clients, and may or
may not be on the same link as the
client(s).
DHCP relay (or relay) A node that acts as an intermediary to
deliver DHCP messages between clients
and servers, and is on the same link as
a client.
DHCP agent (or agent) Either a DHCP server on the same link as
a client, or a DHCP relay.
DUID A DHCP Unique IDentifier for a client.
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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 address: FF02::1:2 This link-scoped multicast
address is used by clients to communicate with the
on-link agent(s) when they do not know the link-local
address(es) for those agents. All agents (servers and
relays) are members of this multicast group.
All_DHCP_Servers address: FF05::1:3 This site-scoped multicast
address is used by clients or relays to communicate
with server(s), either because they want to send
messages to all servers or because they do not know
the server(s) unicast address(es). Note that in order
for a client to use this address, it must have an
address of sufficient scope to be reachable by the
server(s). All servers within the site are members of
this multicast group.
7.2. UDP ports
DHCP uses the following destination UDP [18] 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 8. Message types 0 and 13-255
are reserved for future use. The message code for each message type
is shown with the message name.
SOLICIT (1) The Solicit message is used by clients to
locate servers.
ADVERTISE (2) The Advertise message is used by servers
responding to Solicits.
REQUEST (3) The Request message is used by clients
to request configuration parameters from
servers.
CONFIRM (4) The Confirm message is used by clients to
confirm that the addresses assigned to an IA
and the lifetimes for those addresses, as
well as the current configuration parameters
assigned by the server to the client are
still valid.
RENEW (5) The Renew message is used by clients to
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 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 Reply message is used by servers
responding to Request, Confirm, Renew,
Rebind, Release and Decline messages. In the
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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 Release message is used by clients to
return one or more IP addresses to servers.
DECLINE (9) The Decline message is used by clients to
indicate that the client has determined that
one or more addresses in an IA are already
in use on the link to which the client is
connected.
RECONFIG-INIT (10) The 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 Relay-forward message is used by relays
to forward client messages to servers. The
client message is encapsulated in an option
in the Relay-forward message.
RELAY-REPL (12) The Relay-reply message is used by servers
to send messages to clients through a relay.
The server encapsulates the client message
as an option in the Relay-reply message,
which the relay extracts and forwards to the
client.
7.4. Status Codes
This section describes status codes exchanged between DHCP
implementations. These status codes may appear in the Status Code
option or in the status field of an IA.
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7.4.1. Generic Status Codes
The status codes in this section are used between clients and servers
to convey status conditions. The following table contains the status
codes, the name for each code (as used in this document) and a brief
description. Note that the numeric values do not start at 1, nor are
they consecutive. The status codes are organized in logical groups.
Name Code Description
---------- ---- -----------
Success 0 Success
UnspecFail 16 Failure, reason unspecified
AuthFailed 17 Authentication failed or nonexistent
PoorlyFormed 18 Poorly formed message
AddrUnavail 19 Addresses unavailable
OptionUnavail 20 Requested options unavailable
7.4.2. Server-specific Status Codes
The status codes in this section are used by servers to convey status
conditions to clients. The following table contains the status
codes, the name for each code (as used in this document) and a brief
description. Note that the numeric values do not start at 1, nor are
they consecutive. The status codes are organized in logical groups.
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 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.
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 servers share an identical
fixed format header and a variable format area for options. Not all
fields in the header are used in every message.
All values in the message header and in options are in network byte
order.
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The following diagram illustrates the 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 fields in the DHCP
message header in each of the DHCP messages. In these descriptions,
fields that are not used in a message are marked as "unused". All
unused fields in a message MUST be transmitted as zeroes and ignored
by the receiver of the message.
8.1. DHCP Solicit Message Format
msg-type SOLICIT
transaction-ID An unsigned integer generated by the client used
to identify this Solicit message.
server-address (unused) MUST be 0
options See section 20.
8.2. DHCP Advertise Message Format
msg-type ADVERTISE
transaction-ID An unsigned integer used to identify this
Advertise message. Copied from the Solicit
message received from the client.
server-address The IP address of the server that generated this
message. The address must have sufficient scope
to be reachable from the client.
options See section 20.
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8.3. DHCP Request Message Format
msg-type REQUEST
transaction-ID An unsigned integer generated by the client used
to identify this Request message.
server-address The IP address of the server to which 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 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 client used
to identify this Renew message.
server-address The IP address of the server to which this Renew
message is directed, which MUST be the address
of the server from which the IAs in this message
were originally assigned.
options See section 20.
8.6. DHCP Rebind Message Format
msg-type REBIND
transaction-ID An unsigned integer generated by the client used
to identify this Rebind message.
server-address MUST be zero.
options See section 20.
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8.7. DHCP Reply Message Format
msg-type REPLY
transaction-ID An unsigned integer used to identify this
Reply message. Copied from the client Request,
Confirm, Renew or Rebind message received from
the client.
server-address The IP address of the server. The address must
have sufficient scope to 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 client used
to identify this Release message.
server-address The IP address of the server that assigned the
addresses.
options See section 20.
8.9. DHCP Decline Message Format
msg-type DECLINE
transaction-ID An unsigned integer generated by the client used
to identify this Decline message.
server-address The IP address of the server that assigned the
addresses.
options See section 20.
8.10. DHCP Reconfigure-init Message Format
msg-type RECONFIG-INIT
transaction-ID An unsigned integer generated by the server used
to identify this Reconfigure-init message.
server-address The IP address of the DHCP server issuing the
Reconfigure-init message. The address must have
sufficient scope to be reachable from the client.
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options See section 20.
9. Relay messages
Relay agents exchange messages with servers to forward messages
between clients and servers that are not connected to the same link.
There are two relay messages, which share the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | |
+-+-+-+-+-+-+-+-+ |
| link-prefix |
| |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| | |
+-+-+-+-+-+-+-+-+ |
| client-return-address |
| |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| | |
+-+-+-+-+-+-+-+-+ |
. .
. options (variable number and length) .... .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The following sections describe the use of the Relay message header.
9.1. Relay-forward message
The following table defines the use of message fields in a
Relay-forward message.
msg-type RELAY-FORW
link-prefix An address with a prefix that is assigned
to the link from which the client should
be assigned an address.
client-return-address The source address from the IP datagram
in which the message from the client was
received by the relay agent
options MUST include a "Client message option";
see section 20.7; MAY include other
options added by the relay agent
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9.2. Relay-reply message
The following table defines the use of message fields in a
Relay-forward message.
msg-type RELAY-REPL
link-prefix An address with a prefix that is assigned
to the link from which the client should
be assigned an address.
client-return-address The source address from the IP datagram
in which the message from the client was
received by the relay agent
options MUST include a "Server message option";
see section 20.8; MAY include other
options
10. DHCP unique identifier (DUID)
Each DHCP client has a DUID. DHCP servers use DUIDs to identify
clients for the selection of configuration parameters and in
the association of IAs with clients. See section 20.2 for the
representation of a DUID in a DHCP message.
Servers MUST treat DUIDs as opaque values and must only compare DUIDs
for equality. Servers MUST NOT in any other way interpret DUIDs.
Servers MUST NOT restrict DUIDs to the types defined in this document
as additional DUID types may be defined in the future.
The DUID is carried in an option because it may be variable length
and because it is not required in all DHCP options (e.g., messages
sent by servers need not include a DUID). The DUID must be unique
across all DHCP clients, and it must also be consistent for the same
client - that is, the DUID used by a client SHOULD NOT change over
time; for example, as a result of network hardware reconfiguration.
The motivation for having more than one type of DUID is that the DUID
must be globally unique, and must also be easy to generate. The sort
of globally-unique identifier that is easy to generate for any given
device can differ quite widely. Also, some devices may not contain
any persistent storage. Retaining a generated DUID in such a device
is not possible, so the DUID scheme must accommodate such devices.
10.1. DUID contents
A DUID consists of a sixteen-bit type code represented in network
order, followed by a variable number of octets that make up the
actual identifier. A DUID can be no more than 256 octets long. The
following types are currently defined:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 the same
DUID should be used in configuring all network interfaces connected
to the device, regardless of which interface's link-layer address was
used to generate the DUID.
DHCP clients using this type of DUID MUST store the DUID in stable
storage, and MUST continue to use this DUID even if the network
interface used to generate the DUID is removed. DHCP clients that do
not have any stable storage MUST NOT use this type of DUID.
DHCP clients that use this DUID SHOULD attempt to configure the time
prior to generating the DUID, if that is possible, and MUST use some
sort of time source (e.g., a real-time clock) in generating the
DUID, even if that time source is 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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very unlikely even if the clocks haven't been configured prior to
generating the DUID.
This method of DUID generation is recommended for all general purpose
computing devices such as desktop computers and laptop computers, and
also for devices such as printers, routers, and so on, that contain
some form of writable non-volatile storage.
10.3. Vendor-assigned unique ID.
The vendor-assigned unique ID consists of an eight-octet
vendor-unique identifier, followed by the vendor's registered domain
name.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VUID (64 bits) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. domain name (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The structure of the VUID is left up to the vendor defining it, but
each device containing such a VUID MUST be unique to each device
that is using it, and MUST be assigned to the device at the time of
manufacture and stored in some form of non-volatile storage. The
VUID SHOULD be recorded in non-erasable storage. The domain name is
simply any domain name that has been legally registered by the vendor
in the domain name system, stored in canonical form. An example DUID
of this type might look like this:
+--+---+---+---+-+-+-+--+---+---+--+---+---+---+---+--+--+---+---+
|12|192|132|221|3|0|9|18|101|120|97|109|112|108|101|46|99|111|109|
+--+---+---+---+-+-+-+--+---+---+--+---+---+---+---+--+--+---+---+
This is eight octets of VUID data, followed by "example.com"
represented in ASCII.
10.4. Link-layer address
This type of DUID consists of a two octet network hardware type code,
followed by the link-layer address of any one network interface that
is permanently connected to the DHCP client device. The hardware
type MUST be a valid hardware type assigned by the IANA as described
in the section on ARP in RFC 826. The hardware type is stored in
network order.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hardware type (16 bits) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
. .
. link-layer address (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The choice of network interface can be completely arbitrary, as
long as that interface provides a unique link-layer address and
is permanently attached to the device on which the DUID is being
generated. The same DUID should be used in configuring all network
interfaces connected to the device, regardless of which interface's
link-layer address was used to generate the DUID.
This type of DUID is recommended for devices that have a
permanently-connected network interface with a link-layer address and
do not have nonvolatile, writable stable storage. This type of DUID
MUST NOT be used by DHCP clients that cannot tell whether or not a
network interface is permanently attached to the device on which the
DHCP client is running.
11. Identity association
An "identity-association" (IA) is a construct through which a server
and a client can identify, group and manage IPv6 addresses. Each IA
consists of an IAID and 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 obtain IPv6 addresses for that interface from a
server.
See section 20.3 for the representation of an IA in a DHCP message.
12. Selecting addresses for assignment to an IA
A server selects addresses to be assigned to an IA according to the
address assignment policies determined by the server administrator
and the specific information the server determines about the client
from the following sources:
- The link to which the client is attached:
* If the server receives the message directly from the client
and the source address in the IP datagram in which the
message was received is a link-local address, then the client
is on the same link to which the interface over which the
message was received is attached
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* 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
* 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-prefix field in
the message from the relay is attached
- The DUID supplied by the client
- Other information in options supplied by the client
- Other information in options supplied by the relay agent
13. Reliability of Client Initiated Message Exchanges
DHCP clients are responsible for reliable delivery of messages in the
client-initiated message exchanges described in sections 15 and 16.
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.
The client begins the message exchange by transmitting a message to
the server. The message exchange terminates when either the client
successfully receives the appropriate response or responses from a
server or servers, or when the message exchange is considered to have
failed according to the retransmission mechanism described below.
The client retransmission behavior is controlled and describe 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 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.
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Each of the computations of a new RT include a randomization factor
(RAND), which is a random number chosen with a uniform distribution
between -0.1 and +0.1. The randomization factor is included to
minimize synchronization of messages transmitted by DHCP clients.
The algorithm for choosing a random number does not need to be
cryptographically sound. The algorithm SHOULD produce a different
sequence of numbers from each invocation of the DHCP client.
RT for the first message transmission is based on IRT:
RT = 2*IRT + RAND*IRT
RT for each subsequent message transmission is based on the previous
value of RT:
RT = 2*RTprev + RAND*RTprev
MRT specifies an upper bound on the value of RT. If MRT has a value
of 0, there is no upper limit on the value of RT. Otherwise:
if (RT > MRT)
RT = MRT + RAND*MRT
MRC specifies an upper bound on the number of times a client may
retransmit a message. If MRC has a value of 0, the client MUST
continue to retransmit the original message until a response is
received. Otherwise, the message exchange fails if the client
attempts to transmit the original message more than MRC times.
MRD specifies an upper bound on the length of time a client may
retransmit a message. If MRD has a value of 0, the client MUST
continue to retransmit the original message until a response is
received. Otherwise, the message exchange fails if 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 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 servers
to synchronize server responses to client messages. A client SHOULD
choose a different transaction-ID for each new message it sends. A
client MUST leave the transaction-ID unchanged in retransmissions of
a message.
14.2. Solicit message
Clients MUST discard any received Solicit messages.
Relay agents MUST discard any Solicit messages received through port
546.
14.3. Advertise message
Clients MUST discard any received Advertise messages in which the
"Transaction-ID" field value does not match the value the client used
in its Solicit message.
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 any of the addresses
used by the server.
14.5. Confirm message
Clients MUST discard any received Confirm messages.
Relay agents MUST discard any Confirm messages received through port
546.
14.6. Renew message
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 value in
the ``server-address'' field does not match any of the addresses used
by the 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 does not match any of the 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 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 value used
in the 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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Clients MUST discard any Reconfigure-init messages that do not
contain an authentication option or that fail the authentication
performed by the client.
14.12. Relay-forward message
Clients MUST discard any received Relay-forward messages.
14.13. Relay-reply message
Clients and servers MUST 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
multicast address. The client MUST use an IPv6 address assigned
to the interface for which the client is interested in obtaining
configuration information as the source address in the IP header of
the datagram carrying the Solicit message.
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The Solicit message MUST be transmitted on the link that the
interface for which configuration information is being obtained
is attached to. The client SHOULD send the message through that
interface. The client MAY send the message through another interface
attached to the same link if and only if the client is certain the
the two interface are attached to the same link.
The first Solicit message from the client on the interface MUST
be delayed by a random amount of time between MIN_SOL_DELAY and
MAX_SOL_DELAY. This random delay desynchronizes clients which start
at the same time (e.g., after a power outage).
The client transmits the message according to section 13, using the
following parameters:
IRT SOL_TIMEOUT
MRT SOL_MAX_RT
MRC 0
MRD 0
The mechanism in section 13 is modified as follows for use in the
transmission of Solicit messages. The message exchange is not
terminated by the receipt of an Advertise before SOL_TIMEOUT has
elapsed. Rather, the client collects Advertise messages until
SOL_TIMEOUT has elapsed. The 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 a preference value
of 255. The preference 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
receives an Advertise message with a preference value of 255, then
the client MAY act immediately on that Advertise message without
waiting for any more additional Advertise messages.
A DHCP client SHOULD choose MRC and MRD to be 0. If the DHCP client
is configured with either MRC or MRD set to a value other than
0, it MUST stop trying to configure the interface if the message
exchange fails. After the DHCP client stops trying to configure the
interface, it MAY 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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15.1.3. Receipt of Advertise messages
The client MUST ignore any Advertise message that includes a Status
Code option containing the value AddrUnavail, with the exception that
the client MAY display the associated status message to the user.
Upon receipt of one or more valid Advertise messages, the client
selects one or more Advertise messages based upon the following
criteria.
- Those Advertise messages with the highest server preference value
are preferred over all other Advertise messages.
- Within a group of Advertise messages with the same server
preference value, a client MAY select those servers whose
Advertise messages advertise information of interest to the
client. For example, the client may choose a server that
returned an advertisement with configuration options of interest
to the client.
- The client MAY choose a less-preferred server if that server has
a better set of advertised parameters, such as the available
addresses advertised in IAs.
Once a client has selected Advertise message(s), the client will
typically store information about each server, such as server
preference value, addresses advertised, when the advertisement was
received, and so on. Depending on the requirements of the user that
invoked the DHCP client, the client MAY initiate a configuration
exchange with the server(s) immediately, or MAY defer this exchange
until later.
If the client needs to select an alternate server in the case that a
chosen server does not respond, the client chooses the next server
according to the criteria given above.
15.2. 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.
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15.2.2. Creation and transmission of Advertise messages
The server sets the "msg-type" field to ADVERTISE and copies the
contents of the transaction-ID field from the Solicit message
received from the client to the Advertise message. The server places
one of its IP addresses (determined through administrator setting)
in the "server-address" field of the Advertise message. The server
MAY add a Preference option to carry the preference value for the
Advertise message.
The server implementation SHOULD allow the setting of a server
preference value by the administrator. The server preference value
MUST default to zero unless otherwise configured by the server
administrator.
The server MUST include IA options in the Advertise message
containing any addresses that would be assigned to IAs contained in
the Solicit message from the client. If the 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 source address field from the IP datagram in which
the Relay-forward message was received.
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.
16.1. Client Behavior
A client will use Request, Confirm, Renew and Rebind messages to
acquire and confirm the validity of configuration information. The
client uses the server address information from previous Advertise
message(s) for use in constructing Request and Renew message(s).
Note that a client may request configuration information from one or
more servers at any time.
16.1.1. Creation and transmission of Request messages
If the client is using stateful address configuration and needs
either an initial set of addresses or additional addresses, it
MUST send a Request message to obtain new addresses and other
configuration information. The client includes one or more IAs in
the Request message, to which the server assigns new addresses. The
server then returns IA(s) to the client in a Reply message.
The client generates a transaction ID and inserts this value in the
"transaction-ID" field.
The client places the address of the destination server in the
"server-address" field.
The client MUST include a DUID option to identify itself to the
server. The client adds any other appropriate options, including
one or more IA options (if the client is requesting that the server
assign it some network addresses). The list of addresses in each
included IA MUST be empty. If the client is not requesting that the
server assign it any addresses, the client omits the IA option.
If the client 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 Request message to the server. Otherwise, the client MUST send
the Request message to the All_DHCP_Agents multicast address. The
client MUST use an address assigned to the interface for which the
client is interested in obtaining configuration information as the
source address in the IP header of the datagram carrying the Request
message.
DISCUSSION:
Use of multicast and relay agents enables the inclusion of
relay agent options in all messages sent by the client. The
server should enable the use of unicast only when relay
agent options will not be used.
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If the client multicasts the Request message, the message MUST be
transmitted on the link that the interface for which configuration
information is being obtained is attached to. The client SHOULD send
the message through that interface. The client MAY send the message
through another interface attached to the same link if and only if
the client is certain the the two interface are attached to the same
link.
The client transmits the message according to section 13, using the
following parameters:
IRT REQ_TIMEOUT
MRT REQ_MAX_RT
MRC REQ_MAX_RC
MRD 0
If the message exchange fails, the client MAY choose one of the
following actions:
- Select another server from a list of servers known to the client;
e. g., servers that responded with an Advertise message
- Initiate the server discovery process described in section 15
- Terminate the configuration process and report failure
16.1.2. Creation and transmission of Confirm messages
Whenever a client may have moved to a new link, its IPv6 addresses
and other configuration information may no longer be valid. Examples
of times when a client may have moved to a new link include:
o The client reboots
o The client is physically disconnected from a wired connection
o The client returns from sleep mode
o The client using a wireless technology changes cells
In any situation when a client may have moved to a new link, the
client MUST initiate a Confirm/Reply message exchange. The client
includes any IAs, along with the addresses associated with those IAs,
in its Confirm message. Any responding servers will indicate the
acceptability of the addresses with the status in the Reply message
it returns to the client.
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The client sets the "msg-type" field to CONFIRM. The client generates
a transaction ID and inserts this value in the "transaction-ID"
field.
The client sets the "server-address" field to 0.
The client MUST include a DUID option to identify itself to the
server. The client adds any appropriate options, including one or
more IA options (if the client is requesting that the server confirm
the validity of some IPv6 addresses). 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 Confirm message to the All_DHCP_Agents
multicast address. The client MUST use an IPv6 address assigned
to the interface for which the client is interested in obtaining
configuration information as the source address in the IP header of
the datagram carrying the Confirm message.
The Confirm message MUST be transmitted on the link that the
interface for which configuration information is being obtained
is attached to. The client SHOULD send the message through that
interface. The client MAY send the message through another interface
attached to the same link if and only if the client is certain the
the two interface are attached to the same link.
The client transmits the message according to section 13, using the
following parameters:
IRT CNF_TIMEOUT
MRT CNF_MAX_RT
MRC 0
MRD CNF_MAX_RD
If the client receives no responses before the message transmission
process as described in section 13 terminates, the client SHOULD
continue to use any IP addresses, using the last known lifetimes for
those addresses, and SHOULD continue to use any other previously
obtained configuration parameters.
16.1.3. Creation and transmission 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 address 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 Renew message to the
server containing an "IA option" for the IA and its associated
addresses. The server determines new lifetimes for the addresses in
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the IA according to the administrative configuration of the server.
The server may also add new addresses to the IA. The server may
remove addresses from the IA by setting the preferred and valid
lifetimes of those addresses to zero.
The server controls the time at which the client contacts the server
to extend the lifetimes on assigned addresses through the T1 and
T2 parameters assigned to an IA. 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 Renew/Reply message
exchange to extend the lifetimes on any addresses in the IA. The
client includes an IA option with all addresses currently assigned to
the IA in its Renew message.
The client sets the "msg-type" field to RENEW. The client generates a
transaction ID and inserts this value in the "transaction-ID" field.
The client places the address of the destination server in the
"server-address" field.
The client MUST include a DUID option to identify itself to the
server. The client adds any appropriate options, including one or
more IA options (if the client is requesting that the server extend
the 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.
If the client 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 Renew
message to the server. Otherwise, the client sends the Renew message
to the All_DHCP_Agents multicast address. The client MUST use an
address assigned to the interface for which the client is interested
in obtaining configuration information as the source address in the
IP header of the datagram carrying the Renew message.
If the Renew message is multicast, it MUST be transmitted on the
link that the interface for which configuration information is being
obtained is attached to. The client SHOULD send the message through
that interface. The client MAY send the message through another
interface attached to the same link if and only if the client is
certain the the two interface are attached to the same link.
The client transmits the message according to section 13, 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
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
multicast address. The client MUST use an IPv6 address assigned
to the interface for which the client is interested in obtaining
configuration information as the source address in the IP header of
the datagram carrying the Rebind message.
The Rebind message MUST be transmitted on the link that the interface
for which configuration information is being obtained is attached
to. The client SHOULD send the message through that interface. The
client MAY send the message through another interface attached to the
same link if and only if the client is certain the the two interface
are attached to the same link.
The client transmits the message according to section 13, using the
following parameters:
IRT REB_TIMEOUT
MRT REB_MAX_RT
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MRC 0
MRD 0
The mechanism in section 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 alternative actions to choose 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
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. The client MAY
choose to report any status code or message from the status code
option in the Reply message.
The client SHOULD perform duplicate address detection [20] on each of
the addresses in any IAs it receives in the Reply message. If any of
the addresses are found to be in use on the link, the client sends a
Decline message to the server as described in section 16.1.8.
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
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 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 AddrUnavail status in an IA from the
server for a Request message the client will have to find a new
server to create an IA.
When the client receives a NoBinding status status in an IA from the
server for a Confirm message the client can assume it needs to send a
Request to reestablish an IA with the server.
When the client receives a ConfNoMatch status in an IA from the
server for a Confirm message the client can send a Renew message to
the server to extend the lease for the addresses.
When the client receives a NoBinding status in an IA from the server
for a Renew message the client can assume it needs to send a Request
to reestablish an IA with the server.
When the client receives a RenwNoMatch status in an IA from the
server for a Renew message the client can assume it needs to send a
Request to reestablish an IA with the server.
When the client receives an AddrUnavail status in an IA from the
server for a Renew message the client can assume it needs to send a
Request to reestablish an IA with the server.
When the client receives a NoBinding status in an IA from the server
for a Rebind message the client can assume it needs to send a Request
to reestablish an IA with the server or try another server.
When the client receives a RebdNoMatch status in an IA from the
server for a Rebind message the client can assume it needs to send a
Request to reestablish an IA with the server or try another server.
When the client receives an AddrUnavail status in an IA from the
server for a Rebind message the client can assume it needs to send a
Request to reestablish an IA with the server or try another server.
16.1.6. Creation and transmission of Release messages
The client sets the "msg-type" field to RELEASE. The client generates
a transaction ID and places this value in the "transaction-ID" field.
The client places the IP address of the server that allocated the
address(es) in the "server-address" field.
The client MUST include a DUID option to identify itself to the
server. The client includes options containing the IAs it is
releasing in the "options" field. The addresses to be released
MUST be included in the IAs. The appropriate "status" field in the
options MUST be set to indicate the reason for the release.
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The client MUST NOT use any of the addresses in the IAs in the
message as the source address in the Release message or in any
subsequently transmitted message.
If the client has a source address 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 server. Otherwise, the client MUST send the
Release message to the All_DHCP_Agents multicast address. The client
MUST use an address for the interface to which the IAs in the Release
message are assigned as the source address for the Release message.
DISCUSSION:
Use of multicast and relay agents enables the inclusion of
relay agent options in all messages sent by the client. The
server should enable the use of unicast only when relay
agent options will not be used.
If the Release message is multicast, it MUST be transmitted on the
link that the interface for which configuration information is being
obtained is attached to. The client SHOULD send the message through
that interface. The client MAY send the message through another
interface attached to the same link if and only if the client is
certain the the two interface are attached to the same link.
A client MAY choose to wait for a Reply message from the server in
response to the Release message. If the client does wait for a
Reply, the client MAY choose to retransmit the Release message.
The client transmits the message according to section 13, using the
following parameters:
IRT REL_TIMEOUT
MRT 0
MRC REL_MAX_MRC
MRD 0
The client MUST abandon the attempt to release addresses if the
Release message exchange fails.
The client MUST stop using all of the addresses in the IA(s) being
released as soon as the client begins the Release message exchange
process. If an IA is released but the Reply from a DHCP server
is lost, the client will retransmit the Release message, and the
server may respond with a Reply indicating a status of "Nobinding".
Therefore, the client does not treat a Reply message with a status
of "Nobinding" in a Release message exchange as if it indicates an
error.
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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.
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.
16.1.8. Creation and transmission of Decline messages
The client sets the "msg-type" field to DECLINE. The client generates
a transaction ID and places this value in the "transaction-ID" field.
The client places the IP address of the server that allocated the
address(es) in the "server-address" field.
The client MUST include a DUID option to identify itself to the
server. The client includes options containing the IAs it is
declining in the "options" field. The addresses to be 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.
The client MUST NOT use any of the addresses in the IAs in the
message as the source address in the Decline message or in any
subsequently transmitted message.
If the client has a source address 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
Decline message to the server. Otherwise, the client MUST send the
Decline message to the All_DHCP_Agents multicast address. The client
MUST use an IPv6 address for the interface to which the IAs in the
Release message are assigned as the source address for the Decline
message.
DISCUSSION:
Use of multicast and relay agents enables the inclusion of
relay agent options in all messages sent by the client. The
server should enable the use of unicast only when relay
agent options will not be used.
If the Decline message is multicast, it MUST be transmitted on the
link that the interface for which configuration information is being
obtained is attached to. The client SHOULD send the message through
that interface. The client MAY send the message through another
interface attached to the same link if and only if the client is
certain the the two interface are attached to the same link.
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The client transmits the message according to section 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 Decline message
Upon receipt of a valid Reply message, the client can consider the
Decline event 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.
16.2.1. Receipt of Request messages
The server MAY choose to discard Request messages received via
unicast from a client to which the server has not sent a unicast
option.
Upon the receipt of a valid Request message from a client the server
can respond to, (implementation-specific administrative policy
satisfied) the server scans the options field.
The server then constructs a Reply message and sends it to the
client.
The server SHOULD process each option for the client in an
implementation-specific manner. The server MUST construct a Reply
message containing the following values:
msg-type REPLY
transaction-ID The transaction-ID from the Request message.
server address One of the IP addresses assigned to the interface
through which the server received the message
from the client.
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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 IA from the client and associate a binding
for that client in an implementation-specific manner within the
configuration parameter database for DHCP clients managed by the
server.
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
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.
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.
The server SHOULD process each option for the client in an
implementation-specific manner. The server MUST construct a Reply
message containing the following values:
msg-type REPLY
transaction-ID The transaction-ID from the Confirm message.
server address One of the IP addresses assigned to the interface
through which the server received the message
from the client.
When the server receives a Confirm message, the client is requesting
confirmation that the configuration information it will use is valid.
The server SHOULD locate the binding for that client and compare the
information in the Confirm message from the client to the information
associated with that client.
If the server cannot determine if the information in the Confirm
message is valid or invalid, the server MUST NOT send a reply to the
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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 that the information for the client does not
match what is in the binding for that client or the configuration
information is not valid, the server sends a Reply message containing
a Status Code option with the value ConfNoMatch.
If the server finds that the information for the client does match
the information in the binding for that client, and the configuration
information is still valid, the server sends a Reply message
containing a Status Code option with the value Success.
The 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
transaction-ID The transaction-ID from the Confirm message.
server address One of the IP addresses assigned to the interface
through which the server received the message
from the client.
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 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
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.
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
transaction-ID The transaction-ID from the Confirm message.
server address One of the IP addresses assigned to the interface
through which the server received the message
from the client.
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 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
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.
There is a significant difference between Renew and Rebind messages:
Because the Renew message is processed by a single server, the
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responding server can actually change the addresses in the IA.
However, because multiple servers may respond to a Rebind, all they
can safely do is update T1, T2 (for the IA) and lifetimes (for
individual addresses).
16.2.5. Receipt of Release messages
The server MAY choose to discard Release messages received via
unicast from a client to which the server has not sent a unicast
option.
Upon the receipt of a valid Release message, the server examines the
IAs and the addresses in the IAs for validity. If the IAs in the
message are in a binding for the client and the addresses in the IAs
have been assigned by the server to those IAs, the server deletes
the addresses from the IAs and makes the addresses available for
assignment to other clients.
The server then generates a Reply message. If all of the IAs were
valid and the addresses successfully released, the server 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 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 release implicitly all of the addresses in the IA.
A server is not required to (but may choose to as an implementation
strategy) retain any record of an IA from which all of the addresses
have been released.
16.2.6. Receipt of Decline messages
The server MAY choose to discard Decline messages received via
unicast from a client to which the server has not sent a unicast
option.
Upon the receipt of a valid Decline message, the server examines the
IAs and the addresses in the IAs for validity. If the IAs in the
message are in a binding for the client and the addresses in the IAs
have been assigned by the server to those IA, the server deletes
the addresses from the IAs. The server SHOULD mark the addresses
declined by the client so that those addresses are not assigned to
other clients, and MAY choose to make a notification that addresses
were declined.
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 Relay-response message and 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 source
address from the IP datagram in which the original message was
received.
17. DHCP Server-Initiated Configuration Exchange
A server initiates a configuration exchange to cause DHCP clients
to obtain new addresses and other configuration information. For
example, an administrator may use a server-initiated configuration
exchange when links in the DHCP domain are to be renumbered. Other
examples include changes in the location of directory servers,
addition of new services such as printing, and availability of new
software (system or application).
17.1. Server Behavior
A server sends a Reconfigure-init message to cause a client to
initiate immediately a Request/Reply message exchange with the
server.
17.1.1. Creation and 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.
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.
A server sends each Reconfigure-init message to a single DHCP client,
using an IPv6 unicast address of sufficient scope belonging to the
DHCP client. The server may obtain the address of the client through
the information that the server has about clients that have been in
contact with the server, or the server may be configured with the
address of the client through some external agent.
To reconfigure more than one client, the server unicasts a separate
message to each client. The server may initiate the reconfiguration
of multiple clients concurrently; for example, a server may send
a Reconfigure-init message to additional clients while previous
reconfiguration message exchanges are still in progress.
The Reconfigure-init message causes the client to initiate a
Request/Reply message exchange with the server. 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 for that client.
Default and initial values for RECREP_MSG_TIMEOUT and
REC_MSG_ATTEMPTS are documented in section 7.5.
17.1.3. Receipt of Request messages
The server generates and sends Reply message(s) to the client as
described in section 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 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.
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.
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 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 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.
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 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.
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 16.1.1 for details.
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 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.
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 multicast address, or other multicast addresses
selected by the network administrator. If the Relay has not been
explicitly configured, it MUST use the All_DHCP_Servers multicast
address as the default.
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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 with a prefix
assigned to the link on which the client should be assigned an
address in the link-prefix field. This address will be used by the
server to determine the link from which the client should be assigned
an address and other configuration information.
If the relay cannot use the address in the link-prefix field to
identify the interface through which the response to the client
will be forwarded, the relay MUST include a circuit-id option (see
section 20.15)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
message was received from the client into the client-return-address
field in the Relay-forward message.
The relay constructs a "client-message" option 20.7 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.
18.2. Relaying of server messages
When the relay receives a Relay-reply message, it extracts the server
message from the "server-message" option. If the Relay-reply message
includes a circuit-id option, the relay forwards the message from the
server to the client on the link identified by the circuit-id option.
Otherwise, the relay forwards the message on the link identified
by the link-prefix option. In either case, the relay forwards the
message to the address in the client-return-address field in the
Relay-reply message.
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
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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].
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
perimeter gateways of the enterprise). Regardless of the gateway
configuration, however, the potential attacks by insiders and
outsiders are the same.
The attack specific to a DHCP client is the possibility of the
establishment of a "rogue" server with the intent of providing
incorrect configuration information to the client. The motivation
for doing so may be to establish a "man in the middle" attack or it
may be for a "denial of service" attack.
There is another threat to DHCP clients from mistakenly or
accidentally configured DHCP servers that answer DHCP client requests
with unintentionally incorrect configuration parameters.
The threat specific to a DHCP server is an invalid client
masquerading as a valid client. The motivation for this may be for
"theft of service", or to circumvent auditing for any number of
nefarious purposes.
The threat common to both the client and the server is the resource
"denial of service" (DoS) attack. These attacks typically involve
the exhaustion of valid addresses, or the exhaustion of CPU or
network bandwidth, and are present anytime there is a shared
resource. In current practice, redundancy mitigates DoS attacks the
best.
19.2. 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.
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.
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.
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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 [11]
using the MD5 hash [19] is defined here.
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.
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 [11]
and the MD5 hash function [19]. The entire DHCP message (except
the MAC field of the authentication option itself), including the
DHCP message header and the options field, is used as input to the
HMAC-MD5 computation function. The 'secret ID' field MUST be set to
the identifier of the secret used to generate the MAC.
DISCUSSION:
Algorithm 1 specifies the use of HMAC-MD5. Use of a
different technique, such as HMAC-SHA, will be specified as
a separate protocol.
Delayed authentication requires a shared secret key for each
client on each DHCP server with which that client may wish
to use the DHCP protocol. Each secret key has a unique
identifier that can be used by a receiver to determine which
secret was used to generate the MAC in the DHCP message.
Therefore, delayed authentication may not scale well in an
architecture in which a DHCP client connects to multiple
administrative domains.
19.6.3. Message validation
To validate an incoming message, the receiver first checks that
the value in the replay detection field is acceptable according
to the replay detection method specified by the RDM field. Next,
the receiver computes the MAC as described in [11]. The receiver
MUST set the 'MAC' field of the authentication option to all 0s for
computation of the MAC. If the MAC computed by the receiver does not
match the MAC contained in the authentication option, the receiver
MUST discard the DHCP message.
19.6.4. 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.
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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.
19.6.5. Client considerations for delayed authentication protocol
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 19.6. The client does not include any authentication
information in the Authentication option.
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 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.
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19.6.5.3. 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 19.6. When the
client sends a subsequent message, it MUST use the same secret used
by the server to generate the authentication information.
19.6.5.4. Receiving Reply messages
If the client authenticated the Advertise it accepted, the client
MUST validate the associated Reply message from the server. The
client MUST discard the Reply if the message fails to pass validation
and MAY log the validation failure. If the Reply fails to pass
validation, the client MUST restart the DHCP configuration process by
sending a Solicit message. The client MAY choose to remember which
server replied with a Reply message that failed to pass validation
and discard subsequent messages from that server.
If the client accepted an Advertise message that did not include
authentication information or did not pass the validation test, the
client MAY accept an unauthenticated Reply message from the server.
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 the
client as specified in section 19.6. The server MUST record the
identifier of the secret selected for the client and use that same
secret for validating subsequent messages with the client.
19.6.6.2. Receiving Request, Confirm, Renew, Rebind or Release messages
and Sending Reply messages
The server uses the secret identified in the message and validates
the message as specified in section 19.6.3. If the message fails to
pass validation or the server does not know the secret identified by
the 'secret ID' field, the server MUST discard the message and MAY
choose to log the validation failure.
If the message passes the validation procedure, the server responds
to the specific message as described in section 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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19.6.6.3. Sending Reconfigure-Init messages
The server MUST include authentication information in a
Reconfigure-Init message, generated as specified in section 19.6
using the secret the server initially selected for the client to
which the 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-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.
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20.2. DHCP unique identifier option
The DHCP unique identifier option is used to carry a DUID. The format
for the DUID is keyed to mark the type of identifier and is of
variable length. The format of the DUID option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION DUID | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DUID type | DUID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
. DUID (cont.) .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
20.3. Identity association option
The identity association option is used to carry an identity
association, the parameters associated with the IA and the addresses
assigned to the IA.
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The format of the IA option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION IA | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IAID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IA status | 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 (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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T1 The time at which the client contacts the
server from which the addresses in the IA
were obtained to extend the lifetimes of the
addresses assigned to the IA.
T2 The time at which the client contacts any
available server to extend the lifetimes of
the addresses assigned to the IA.
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 the associated
IPv6 address.
valid lifetime The valid lifetime for the associated IPv6
address.
The "IPv6 address", "preferred lifetime" and "valid lifetime" fields
are repeated for each address in the IA option (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 assign temporary addresses to the
client, the server marks those temporary addresses with the 'T'
bit. The number of temporary addresses assigned to the client and
the lifetimes of those addresses is determined by the administrative
configuration of the server. The 'T' bit only identifies an address
as a temporary address; identification of an address as "temporary"
has no implication on the lifetime of the 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_ORO | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| requested-option-code-1 | requested-option-code-2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_ORO (TBD)
option-len Variable; equal to twice the number of option codes
carried in this option.
option-data A list of the option codes for the options requested
in this option.
A client MAY include an Option Request option in a Solicit, Request,
Renew, Rebind or Confirm message to inform the server about options
the client wants the server to 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_PREFERENCE | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| pref value |
+-+-+-+-+-+-+-+-+
option-code OPTION_PREFERENCE (TBD)
option-len MUST be 1
option-data The preference value for the server in this message.
A server MAY include a Preference option in an Advertise message to
control the selection of a server by the client. See section 15.1.3
for the use of the Preference 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_ELAPSED_TIME | option_len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| elapsed time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_ELAPSED_TIME (TBD)
option-len MUST be 2
option-data The amount of time since the client began its
current DHCP transaction. This time is expressed in
hundredths of a second (10^-2 seconds).
A client MAY include an Elapsed Time option in messages to indicate
how long the client has been trying to complete a DHCP transaction.
Servers MAY use the data value in this option as input to policy
controlling how a server responds to a 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 client message |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_CLIENT_MSG (TBD)
option-len Variable; equal to the length of the forwarded DHCP
client message.
option-data The message received from the client; forwarded
verbatim to the server.
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20.8. 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 server message |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_SERVER_MSG (TBD)
option-len Variable; equal to the length of the forwarded DHCP
server message.
option-data The message received from the server; forwarded
verbatim to the client.
20.9. 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 the case of a DHCPv6 Server receiving the option.
The option can also provide a set of IPv6 addresses to be used as the
Tunnel Endpoint (TEP) to encapsulate an IPv6 packet within IPv6.
This option can be used with the Request, Reply, and Reconfigure-Init
Messages for cases where a server wants to assign to clients
IPv4-Mapped IPv6 Addresses, thru the Option Request Option (ORO).
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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A DSTM IPv4 Global Address Option MUST only apply to the IA following
this option.
20.10. Authentication option
The Authentication option carries authentication information to
authenticate the identity and contents of DHCP messages. The use of
the Authentication option is described in section 19.
The format of the Authentication option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_AUTH | option-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 authentication protocol used in
this authentication option
algorithm The algorithm used in the
authentication protocol
RDM The replay detection method used in
this authentication option
Replay detection The replay detection information for
the RDM
Authentication information The authentication information,
as specified by the protocol and
algorithm used in this authentication
option
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20.11. Server unicast option
This option is used by a server to send to a client to inform
the client it MAY send a Request, Renew, Release, and Decline by
unicasting directly to the server instead of the All_DHCPv6_Agents
Multicast address as an 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 the server address that sends this to the
client.
20.12. Domain Search Option
This option provides a list of domain names a 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 client
should use to resolve names.
So that the search list may be encoded compactly and uniformly,
search strings in the search list are concatenated and encoded using
the technique described in section 4.1 of [13].
For use in this specification, the compression pointer (see section
4.1.4 of [13]) refers to the offset within the SearchString portion
of the option.
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20.13. Domain Name Server Option
This option provides a list of Domain Name System [13] that a client
name resolver can use to access DNS services. There must be at least
1 server listed in this option.
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 a DNS name server for the
client to use. The DNS servers are listed in
the order of preference for use by the client
resolver.
20.14. Status Code Option
This option returns indications of status not related to a specific
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_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 status encoded in
this option. The status codes are defined in
section 7.4.
status-message A UTF-8 encoded text string, which MUST NOT
be null-terminated.
20.15. Circuit-ID Option
This option provides a mechanism through which a relay agent can
identify the network attachment point through which a message was
received from a 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 of arbitrary length; this
value must uniquely identify one of the
network attachments used by the relay agent
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20.16. User Class Option
This option is used by a client to identify the type or category of
user or applications it represents. The information contained in
this option is an opaque field that represents the user class of
which the client is a member. Based on this class, a DHCP server
selects the appropriate address pool to assign an address to the
client and the 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 option, the length of the option
option-len = sum of each of the user class
lengths + 2*n.
option-data The user classes carried by the client.
The user class option may contain one or more instances of user class
data. Each instance of the user class data is formatted as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
| user class1 len | user1 class data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
The user class length is two octets long and specifies the length of
the opaque user class data in network byte order.
Servers may interpret the meanings of multiple class specifications
in an implementation dependent or configuration dependent manner,
and so the use of multiple classes by a DHCP client should be based
on the specific server implementation and configuration which will
be used to process that User class option. Servers not equipped to
interpret the user class information sent by a client MUST ignore it
(although it may be reported).
20.17. Vendor Class Option
This option is used by clients and servers to exchange vendor-
specific information. The definition of this information is vendor
specific. The vendor is indicated in the vendor class identifier
option. Servers not equipped to interpret the vendor-specific
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information sent by a client MUST ignore it (although it may be
reported). Clients which do not receive desired vendor-specific
information SHOULD make an attempt to operate without it, although
they may do so(and announce they are doing so) in a degraded mode.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_VENDOR_CLASS | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-data |
| . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code TBD
option-len Variable
option-data The information is an opaque object of
option-len octets, presumably interpreted
by vendor-specific code on the clients and
servers
If a vendor potentially encodes more than one item of information
in this option, then the vendor SHOULD encode the option using
"Encapsulated vendor-specific options".
The Encapsulated vendor-specific options field SHOULD be encoded as a
sequence of code/length/value fields of identical syntax to the DHCP
options field.
When encapsulated vendor-specific extensions are used, each of the
encapsulated options is formatted as follows.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| opt_code | opt_len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-data |
| . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
opt_code The code for the encapsulated option
opt_len The length of the encapsulated option
option-data The data area for the encapsulated option
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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 the transaction,
there is no problem within the DHCPv6 protocol related to any
hardcoded dates or two-digit representation of the current year.
23. IANA Considerations
This document defines several new name spaces associated with DHCPv6
and DHCPv6 options. IANA is requested to manage the allocation of
values from these name spaces, which are described in the remainder
of this section. These name spaces are all to be managed separately
from the name spaces defined for DHCPv4 [7, 2].
New values in each of these name spaces should be approved by the
process of IETF consensus [14].
23.1. Multicast addresses
Section 7.1 defines the following multicast addresses, which have
been assigned by IANA for use by DHCPv6:
All_DHCP_Agents address: FF02::1:2
All_DHCP_Servers address: FF05::1:3
IANA is requested to manage definition of additional multicast
addresses in the future.
23.2. DHCPv6 message types
IANA is requested to record the message types defined in section 7.3.
IANA is requested to manage definition of additional message types in
the future.
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 future.
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23.4. DHCPv6 options
IANA is requested to assign option-codes to the options defined
in section 20.1. IANA is requested to manage the definition of
additional DHCPv6 option-codes in the future.
23.5. Status codes
IANA is requested to record the status codes defined in section 7.4.
IANA is requested to manage the definition of additional status codes
in the future.
23.6. Authentication option
Section 19 defines three new name spaces associated with the
Authentication Option (section 20.10), which are to be created and
maintained by IANA: Protocol, Algorithm and RDM.
Initial values assigned from the Protocol name space are 0 (for the
configuration token Protocol in section 19.5) and 1 (for the delayed
authentication Protocol in section 19.6). Additional protocols may
be defined in the future.
The Algorithm name space is specific to individual Protocols. That
is, each Protocol has its own Algorithm name space. The guidelines
for assigning Algorithm name space values for a particular protocol
should be specified along with the definition of a new Protocol.
For the configuration token Protocol, the Algorithm field MUST be
0, as described in section 19.5. For the delayed authentication
Protocol, the Algorithm value 1 is assigned to the HMAC-MD5
generating function as defined in section 19.6. Additional
algorithms for the delayed authentication protocol may be defined in
the future.
The initial value of 0 from the RDM name space is assigned to the
use of a monotonically increasing value as defined in section 19.4.
Additional replay detection methods may be defined in the future.
24. Acknowledgments
Thanks to the DHC Working Group for their time and input into the
specification. Ralph Droms and Thomas Narten have had a major
role in shaping the continued improvement of the protocol by their
careful reviews. Many thanks to Matt Crawford, Erik Nordmark, Gerald
Maguire, and Mike Carney for their studied review as part of the
Last Call process. Thanks also for the consistent input, ideas, and
review by (in alphabetical order) Brian Carpenter, Francis DuPont,
Ted Lemon, Jack McCann, Yakov Rekhter, Matt Thomas, Sue Thomson,
Bernie Volz and Phil Wells.
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Thanks to Steve Deering and Bob Hinden, who have consistently
taken the time to discuss the more complex parts of the IPv6
specifications.
Bill Arbaugh reviewed the authentication mechanism described in
section 19.
The Domain Search option described in section 20.12 is based on the
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 model and architecture comparison between DHCPv4 [7, 2] and DHCPv6.
There are three key reasons for the differences:
o IPv6 inherently supports a new model and architecture for
communications and autoconfiguration of addresses.
o DHCPv6 benefits from the new IPv6 features.
o New features were added to support the expected evolution and
the existence of more complicated Internet network service
requirements.
IPv6 Architecture/Model Changes:
o The link-local address permits a node to have an address
immediately when the node boots, which means all clients have a
source IP address at all times to locate an on-link server or
relay.
o The need for BOOTP compatibility and the broadcast flag have been
removed.
o Multicast and address scoping in IPv6 permit the design of
discovery packets that would inherently define their range by the
multicast address for the function required.
o Stateful autoconfiguration has to coexist and integrate with
stateless address autoconfiguration supporting duplicate address
detection [20] and the two IPv6 address lifetimes, 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 are either obtained through IPv6 Neighbor Discovery or
the Service Location protocol [21].
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DHCPv6 Architecture/Model Changes:
o The message type is the first octet in the packet.
o IPv6 Address allocations are now handled in a message option as
opposed to the message header.
o Client/Server bindings are now mandatory and take advantage
of 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 Solicit, followed by a server
Advertise message
o The client will know if the server 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 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 the
same or different servers.
o The function of DHCPINFORM is inherent in the new packet design;
a client can request configuration parameters other than IPv6
addresses in the optional option headers.
o Clients MUST listen to their UDP port 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
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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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
Copyright (C) The Internet Society (2001). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However,
this document itself may not be modified in any way, such as by
removing the copyright notice or references to the Internet Society
or other Internet organizations, except as needed for the purpose
of developing Internet standards in which case the procedures
for copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
References
[1] B. Aboba. DHCP Domain Search Option. Internet Draft, Internet
Engineering Task Force, December 2000. Work in progress.
[2] S. Alexander and R. Droms. DHCP Options and BOOTP Vendor
Extensions, March 1997. RFC 2132.
[3] S. Bradner. Key words for use in RFCs to Indicate Requirement
Levels, March 1997. RFC 2119.
[4] S. Bradner and A. Mankin. The Recommendation for the IP Next
Generation Protocol, January 1995. RFC 1752.
[5] W.J. Croft and J. Gilmore. Bootstrap Protocol, September 1985.
RFC 951.
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[6] S. Deering and R. Hinden. Internet Protocol, Version 6 (IPv6)
Specification, December 1998. RFC 2460.
[7] R. Droms. Dynamic Host Configuration 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,
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, February 1997. RFC 2104.
[12] David L. Mills. Network Time Protocol (Version 3)
Specification, Implementation, March 1992. RFC 1305.
[13] P.V. Mockapetris. Domain names - implementation and
specification, November 1987. RFC 1035.
[14] T. Narten and H. Alvestrand. Guidelines for Writing an IANA
Considerations Section in RFCs, October 1998. RFC 2434.
[15] T. Narten and R. Draves. Privacy Extensions for Stateless
Address Autoconfiguration in IPv6, January 2001. RFC 3041.
[16] T. Narten, E. Nordmark, and W. Simpson. Neighbor Discovery for
IP Version 6 (IPv6), December 1998. RFC 2461.
[17] D.C. Plummer. Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet address
for transmission on Ethernet hardware, November 1982. RFC 826.
[18] J. Postel. User Datagram Protocol, August 1980. RFC 768.
[19] R. Rivest. The MD5 Message-Digest Algorithm, April 1992. RFC
1321.
[20] S. Thomson and T. Narten. IPv6 Stateless Address
Autoconfiguration, December 1998. RFC 2462.
[21] J. Veizades, E. Guttman, C. Perkins, and S. Kaplan. Service
Location 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), April 1997. RFC
2136.
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Chair's Address
The working group can be contacted via the current chair:
Ralph Droms
Cisco Systems
300 Apollo Drive
Chelmsford, MA 01824
Phone: (978) 244-4733
E-mail: rdroms@cisco.com
Authors' Addresses
Questions about this memo can be directed to:
Bound, Carney, Perkins, Droms (ed.) Expires 15 Apr 2002 [Page 71]
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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
Bound, Carney, Perkins, Droms (ed.) Expires 15 Apr 2002 [Page 72]
