Internet DRAFT - draft-dhcwg-dhc-rfc3315bis
draft-dhcwg-dhc-rfc3315bis
Dynamic Host Configuration (DHC) T. Mrugalski, Ed.
Internet-Draft M. Siodelski
Obsoletes: 3315,3633,3736,7083 (if ISC
approved) B. Volz, Ed.
Intended status: Standards Track A. Yourtchenko
Expires: August 26, 2015 Cisco
M. Richardson
SSW
S. Jiang
Huawei
T. Lemon
Nominum
February 22, 2015
Dynamic Host Configuration Protocol for IPv6 (DHCPv6) bis
draft-dhcwg-dhc-rfc3315bis-04
Abstract
The Dynamic Host Configuration Protocol for IPv6 (DHCP) enables DHCP
servers to pass configuration parameters such as IPv6 network
addresses to IPv6 nodes. It offers the capability of automatic
allocation of reusable network addresses and additional configuration
flexibility. This protocol is a stateful counterpart to "IPv6
Stateless Address Autoconfiguration" (RFC 4862), and can be used
separately or concurrently with the latter to obtain configuration
parameters.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on August 26, 2015.
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Table of Contents
1. Introduction and Overview . . . . . . . . . . . . . . . . . . 6
1.1. Protocols and Addressing . . . . . . . . . . . . . . . . 7
1.2. Client-server Exchanges Involving Two Messages . . . . . 7
1.3. Client-server Exchanges Involving Four Messages . . . . . 8
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1. IPv6 Terminology . . . . . . . . . . . . . . . . . . . . 10
4.2. DHCP Terminology . . . . . . . . . . . . . . . . . . . . 11
5. Operational Models . . . . . . . . . . . . . . . . . . . . . 14
5.1. Stateless DHCP . . . . . . . . . . . . . . . . . . . . . 14
5.2. DHCP for Non-Temporary Address Assignment . . . . . . . . 15
5.3. DHCP for Prefix Delegation . . . . . . . . . . . . . . . 15
5.4. DHCP for Customer Edge Routers . . . . . . . . . . . . . 18
5.5. DHCP for Temporary Addresses . . . . . . . . . . . . . . 18
6. DHCP Constants . . . . . . . . . . . . . . . . . . . . . . . 18
6.1. Multicast Addresses . . . . . . . . . . . . . . . . . . . 18
6.2. UDP Ports . . . . . . . . . . . . . . . . . . . . . . . . 19
6.3. DHCP Message Types . . . . . . . . . . . . . . . . . . . 19
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6.4. Status Codes . . . . . . . . . . . . . . . . . . . . . . 21
6.5. Transmission and Retransmission Parameters . . . . . . . 21
6.6. Representation of time values and "Infinity" as a time
value . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7. Client/Server Message Formats . . . . . . . . . . . . . . . . 22
8. Relay Agent/Server Message Formats . . . . . . . . . . . . . 23
8.1. Relay-forward Message . . . . . . . . . . . . . . . . . . 24
8.2. Relay-reply Message . . . . . . . . . . . . . . . . . . . 25
9. Representation and Use of Domain Names . . . . . . . . . . . 25
10. DHCP Unique Identifier (DUID) . . . . . . . . . . . . . . . . 25
10.1. DUID Contents . . . . . . . . . . . . . . . . . . . . . 26
10.2. DUID Based on Link-layer Address Plus Time, DUID-LLT . . 26
10.3. DUID Assigned by Vendor Based on Enterprise Number,
DUID-EN . . . . . . . . . . . . . . . . . . . . . . . . 28
10.4. DUID Based on Link-layer Address, DUID-LL . . . . . . . 29
11. Identity Association . . . . . . . . . . . . . . . . . . . . 30
11.1. Identity Associations for Address Assignment . . . . . . 30
11.2. Identity Associations for Prefix Delegation . . . . . . 30
12. Selecting Addresses for Assignment to an IA . . . . . . . . . 31
13. Management of Temporary Addresses . . . . . . . . . . . . . . 32
14. Transmission of Messages by a Client . . . . . . . . . . . . 33
14.1. Rate Limiting . . . . . . . . . . . . . . . . . . . . . 33
15. Reliability of Client Initiated Message Exchanges . . . . . . 34
16. Message Validation . . . . . . . . . . . . . . . . . . . . . 35
16.1. Use of Transaction IDs . . . . . . . . . . . . . . . . . 36
16.2. Solicit Message . . . . . . . . . . . . . . . . . . . . 36
16.3. Advertise Message . . . . . . . . . . . . . . . . . . . 36
16.4. Request Message . . . . . . . . . . . . . . . . . . . . 37
16.5. Confirm Message . . . . . . . . . . . . . . . . . . . . 37
16.6. Renew Message . . . . . . . . . . . . . . . . . . . . . 37
16.7. Rebind Message . . . . . . . . . . . . . . . . . . . . . 37
16.8. Decline Messages . . . . . . . . . . . . . . . . . . . . 38
16.9. Release Message . . . . . . . . . . . . . . . . . . . . 38
16.10. Reply Message . . . . . . . . . . . . . . . . . . . . . 38
16.11. Reconfigure Message . . . . . . . . . . . . . . . . . . 39
16.12. Information-request Message . . . . . . . . . . . . . . 39
16.13. Relay-forward Message . . . . . . . . . . . . . . . . . 39
16.14. Relay-reply Message . . . . . . . . . . . . . . . . . . 40
17. Client Source Address and Interface Selection . . . . . . . . 40
17.1. Address Assignment . . . . . . . . . . . . . . . . . . . 40
17.2. Prefix Delegation . . . . . . . . . . . . . . . . . . . 40
18. DHCP Server Solicitation . . . . . . . . . . . . . . . . . . 41
18.1. Client Behavior . . . . . . . . . . . . . . . . . . . . 41
18.1.1. Creation of Solicit Messages . . . . . . . . . . . . 41
18.1.2. Transmission of Solicit Messages . . . . . . . . . . 42
18.1.3. Receipt of Advertise Messages . . . . . . . . . . . 43
18.1.4. Receipt of Reply Message . . . . . . . . . . . . . . 44
18.2. Server Behavior . . . . . . . . . . . . . . . . . . . . 45
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18.2.1. Receipt of Solicit Messages . . . . . . . . . . . . 45
18.2.2. Creation and Transmission of Advertise Messages . . 45
18.2.3. Creation and Transmission of Reply Messages . . . . 47
18.3. Client behavior for Prefix Delegation . . . . . . . . . 47
18.4. Server Behavior for Prefix Delegation . . . . . . . . . 48
19. DHCP Client-Initiated Configuration Exchange . . . . . . . . 48
19.1. Client Behavior . . . . . . . . . . . . . . . . . . . . 49
19.1.1. Creation and Transmission of Request Messages . . . 49
19.1.2. Creation and Transmission of Confirm Messages . . . 50
19.1.3. Creation and Transmission of Renew Messages . . . . 52
19.1.4. Creation and Transmission of Rebind Messages . . . . 53
19.1.5. Creation and Transmission of Information-request
Messages . . . . . . . . . . . . . . . . . . . . . . 54
19.1.6. Creation and Transmission of Release Messages . . . 55
19.1.7. Creation and Transmission of Decline Messages . . . 56
19.1.8. Receipt of Reply Messages . . . . . . . . . . . . . 57
19.2. Server Behavior . . . . . . . . . . . . . . . . . . . . 59
19.2.1. Receipt of Request Messages . . . . . . . . . . . . 59
19.2.2. Receipt of Confirm Messages . . . . . . . . . . . . 60
19.2.3. Receipt of Renew Messages . . . . . . . . . . . . . 61
19.2.4. Receipt of Rebind Messages . . . . . . . . . . . . . 62
19.2.5. Receipt of Information-request Messages . . . . . . 62
19.2.6. Receipt of Release Messages . . . . . . . . . . . . 63
19.2.7. Receipt of Decline Messages . . . . . . . . . . . . 64
19.2.8. Transmission of Reply Messages . . . . . . . . . . . 64
19.3. Requesting Router Behavior for Prefix Delegation . . . . 65
19.4. Delegating Router Behavior for Prefix Delegation . . . . 66
20. DHCP Server-Initiated Configuration Exchange . . . . . . . . 67
20.1. Server Behavior . . . . . . . . . . . . . . . . . . . . 68
20.1.1. Creation and Transmission of Reconfigure Messages . 68
20.1.2. Time Out and Retransmission of Reconfigure Messages 69
20.2. Receipt of Renew or Rebind Messages . . . . . . . . . . 69
20.3. Receipt of Information-request Messages . . . . . . . . 69
20.4. Client Behavior . . . . . . . . . . . . . . . . . . . . 70
20.4.1. Receipt of Reconfigure Messages . . . . . . . . . . 70
20.4.2. Creation and Transmission of Renew or Rebind
Messages . . . . . . . . . . . . . . . . . . . . . . 71
20.4.3. Creation and Transmission of Information-request
Messages . . . . . . . . . . . . . . . . . . . . . . 71
20.4.4. Time Out and Retransmission of Renew, Rebind or
Information-request Messages . . . . . . . . . . . . 71
20.4.5. Receipt of Reply Messages . . . . . . . . . . . . . 71
20.5. Prefix Delegation Reconfiguration . . . . . . . . . . . 72
20.5.1. Delegating Router Behavior . . . . . . . . . . . . . 72
20.5.2. Requesting Router Behavior . . . . . . . . . . . . . 72
21. Relay Agent Behavior . . . . . . . . . . . . . . . . . . . . 72
21.1. Relaying a Client Message or a Relay-forward Message . . 72
21.1.1. Relaying a Message from a Client . . . . . . . . . . 73
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21.1.2. Relaying a Message from a Relay Agent . . . . . . . 73
21.1.3. Relay Agent Behavior with Prefix Delegation . . . . 74
21.2. Relaying a Relay-reply Message . . . . . . . . . . . . . 74
21.3. Construction of Relay-reply Messages . . . . . . . . . . 74
22. Authentication of DHCP Messages . . . . . . . . . . . . . . . 75
22.1. Security of Messages Sent Between Servers and Relay
Agents . . . . . . . . . . . . . . . . . . . . . . . . . 76
22.2. Summary of DHCP Authentication . . . . . . . . . . . . . 77
22.3. Replay Detection . . . . . . . . . . . . . . . . . . . . 77
22.4. Delayed Authentication Protocol . . . . . . . . . . . . 78
22.4.1. Use of the Authentication Option in the Delayed
Authentication Protocol . . . . . . . . . . . . . . 78
22.4.2. Message Validation . . . . . . . . . . . . . . . . . 80
22.4.3. Key Utilization . . . . . . . . . . . . . . . . . . 80
22.4.4. Client Considerations for Delayed Authentication
Protocol . . . . . . . . . . . . . . . . . . . . . . 80
22.4.4.1. Sending Solicit Messages . . . . . . . . . . . . 80
22.4.4.2. Receiving Advertise Messages . . . . . . . . . . 81
22.4.4.3. Sending Request, Confirm, Renew, Rebind, Decline
or Release Messages . . . . . . . . . . . . . . 81
22.4.4.4. Sending Information-request Messages . . . . . . 82
22.4.4.5. Receiving Reply Messages . . . . . . . . . . . . 82
22.4.4.6. Receiving Reconfigure Messages . . . . . . . . . 82
22.4.5. Server Considerations for Delayed Authentication
Protocol . . . . . . . . . . . . . . . . . . . . . . 82
22.4.5.1. Receiving Solicit Messages and Sending Advertise
Messages . . . . . . . . . . . . . . . . . . . . 82
22.4.5.2. Receiving Request, Confirm, Renew, Rebind or
Release Messages and Sending Reply Messages . . 83
22.5. Reconfigure Key Authentication Protocol . . . . . . . . 83
22.5.1. Use of the Authentication Option in the Reconfigure
Key Authentication Protocol . . . . . . . . . . . . 83
22.5.2. Server considerations for Reconfigure Key protocol . 84
22.5.3. Client considerations for Reconfigure Key protocol . 85
23. DHCP Options . . . . . . . . . . . . . . . . . . . . . . . . 85
23.1. Format of DHCP Options . . . . . . . . . . . . . . . . . 86
23.2. Client Identifier Option . . . . . . . . . . . . . . . . 86
23.3. Server Identifier Option . . . . . . . . . . . . . . . . 87
23.4. Identity Association for Non-temporary Addresses Option 88
23.5. Identity Association for Temporary Addresses Option . . 90
23.6. IA Address Option . . . . . . . . . . . . . . . . . . . 92
23.7. Option Request Option . . . . . . . . . . . . . . . . . 93
23.8. Preference Option . . . . . . . . . . . . . . . . . . . 94
23.9. Elapsed Time Option . . . . . . . . . . . . . . . . . . 95
23.10. Relay Message Option . . . . . . . . . . . . . . . . . . 95
23.11. Authentication Option . . . . . . . . . . . . . . . . . 96
23.12. Server Unicast Option . . . . . . . . . . . . . . . . . 97
23.13. Status Code Option . . . . . . . . . . . . . . . . . . . 98
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23.14. Rapid Commit Option . . . . . . . . . . . . . . . . . . 100
23.15. User Class Option . . . . . . . . . . . . . . . . . . . 101
23.16. Vendor Class Option . . . . . . . . . . . . . . . . . . 102
23.17. Vendor-specific Information Option . . . . . . . . . . . 104
23.18. Interface-Id Option . . . . . . . . . . . . . . . . . . 106
23.19. Reconfigure Message Option . . . . . . . . . . . . . . . 107
23.20. Reconfigure Accept Option . . . . . . . . . . . . . . . 107
23.21. Identity Association for Prefix Delegation Option . . . 108
23.22. IA Prefix Option . . . . . . . . . . . . . . . . . . . . 110
23.23. SOL_MAX_RT Option . . . . . . . . . . . . . . . . . . . 111
23.24. INF_MAX_RT Option . . . . . . . . . . . . . . . . . . . 112
24. Security Considerations . . . . . . . . . . . . . . . . . . . 113
25. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 116
26. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 116
27. References . . . . . . . . . . . . . . . . . . . . . . . . . 117
27.1. Normative References . . . . . . . . . . . . . . . . . . 117
27.2. Informative References . . . . . . . . . . . . . . . . . 119
Appendix A. Changes since RFC3315 . . . . . . . . . . . . . . . 120
Appendix B. Changes since RFC3633 . . . . . . . . . . . . . . . 123
Appendix C. Appearance of Options in Message Types . . . . . . . 123
Appendix D. Appearance of Options in the Options Field of DHCP
Options . . . . . . . . . . . . . . . . . . . . . . 124
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 125
1. Introduction and Overview
This document describes DHCP for IPv6 (DHCP), a client/server
protocol that provides managed configuration of devices.
DHCP can provide a device with addresses assigned by a DHCP server
and other configuration information, which are carried in options.
DHCP can be extended through the definition of new options to carry
configuration information not specified in this document.
DHCP is the "stateful address autoconfiguration protocol" and the
"stateful autoconfiguration protocol" referred to in "IPv6 Stateless
Address Autoconfiguration" [RFC4862].
This document also provides a mechanism for automated delegation of
IPv6 prefixes using DHCP. Through this mechanism, a delegating
router can delegate prefixes to requesting routers.
The operational models and relevant configuration information for
DHCPv4 [RFC2132][RFC2131] and DHCPv6 are sufficiently different that
integration between the two services is not included in this
document. [RFC3315] suggested that future work might be to extend
DHCPv6 to carry IPv4 address and configuration information. However,
the current consensus of the IETF is that DHCPv4 should be used
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rather than DHCPv6 when conveying IPv4 configuration information to
nodes. [RFC7341] describes a transport mechanism to carry DHCPv4
messages using the DHCPv6 protocol for the dynamic provisioning of
IPv4 address and configuration information across IPv6-only networks.
The remainder of this introduction summarizes DHCP, explaining the
message exchange mechanisms and example message flows. The message
flows in Section 1.2 and Section 1.3 are intended as illustrations of
DHCP operation rather than an exhaustive list of all possible client-
server interactions. Section 5 provides an overview of common
operational models. Section 18, Section 19, and Section 20 explain
client and server operation in detail.
1.1. Protocols and Addressing
Clients and servers exchange DHCP messages using UDP [RFC0768]. The
client uses a link-local address or addresses determined through
other mechanisms for transmitting and receiving DHCP messages.
A DHCP client sends most messages using a reserved, link-scoped
multicast destination address so that the client need not be
configured with the address or addresses of DHCP servers.
To allow a DHCP client to send a message to a DHCP server that is not
attached to the same link, a DHCP relay agent on the client's link
will relay messages between the client and server. The operation of
the relay agent is transparent to the client and the discussion of
message exchanges in the remainder of this section will omit the
description of message relaying by relay agents.
Once the client has determined the address of a server, it may under
some circumstances send messages directly to the server using
unicast.
1.2. Client-server Exchanges Involving Two Messages
When a DHCP client does not need to have a DHCP server assign it IP
addresses, the client can obtain configuration information such as a
list of available DNS servers [RFC3646] or NTP servers [RFC4075]
through a single message and reply exchanged with a DHCP server. To
obtain configuration information the client first sends an
Information-request message to the All_DHCP_Relay_Agents_and_Servers
multicast address. Servers respond with a Reply message containing
the configuration information for the client.
This message exchange assumes that the client requires only
configuration information and does not require the assignment of any
IPv6 addresses.
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When a server has IPv6 addresses and other configuration information
committed to a client, the client and server may be able to complete
the exchange using only two messages, instead of four messages as
described in the next section. In this case, the client sends a
Solicit message to the All_DHCP_Relay_Agents_and_Servers requesting
the assignment of addresses and other configuration information.
This message includes an indication that the client is willing to
accept an immediate Reply message from the server. The server that
is willing to commit the assignment of addresses to the client
immediately responds with a Reply message. The configuration
information and the addresses in the Reply message are then
immediately available for use by the client.
Each address assigned to the client has associated preferred and
valid lifetimes specified by the server. To request an extension of
the lifetimes assigned to an address, the client sends a Renew
message to the server. The server sends a Reply message to the
client with the new lifetimes, allowing the client to continue to use
the address without interruption.
1.3. Client-server Exchanges Involving Four Messages
To request the assignment of one or more IPv6 addresses, a client
first locates a DHCP server and then requests the assignment of
addresses and other configuration information from the server. The
client sends a Solicit message to the
All_DHCP_Relay_Agents_and_Servers address to find available DHCP
servers. Any server that can meet the client's requirements responds
with an Advertise message. The client then chooses one of the
servers and sends a Request message to the server asking for
confirmed assignment of addresses and other configuration
information. The server responds with a Reply message that contains
the confirmed addresses and configuration.
As described in the previous section, the client sends a Renew
message to the server to extend the lifetimes associated with its
addresses, allowing the client to continue to use those addresses
without interruption.
2. Requirements
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in [RFC2119].
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
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specific variable names, how their values change, and how their
settings influence protocol behavior are provided to demonstrate
protocol behavior. An implementation is not required to have them in
the exact form described here, so long as its external behavior is
consistent with that described in this document.
3. Background
The IPv6 Specification provides the base architecture and design of
IPv6. Related work in IPv6 that would best serve an implementor to
study includes the IPv6 Specification [RFC2460], the IPv6 Addressing
Architecture [RFC4291], IPv6 Stateless Address Autoconfiguration
[RFC4862], IPv6 Neighbor Discovery Processing [RFC4861], and Dynamic
Updates to DNS [RFC2136]. These specifications enable DHCP to build
upon the IPv6 work to provide both robust stateful autoconfiguration
and autoregistration of DNS Host Names.
The IPv6 Addressing Architecture specification [RFC4291] defines the
address scope that can be used in an IPv6 implementation, and the
various configuration architecture guidelines for network designers
of the IPv6 address space. Two advantages of IPv6 are that support
for multicast is required and nodes can create link-local addresses
during initialization. The availability of these features means that
a client can use its link-local address and a well-known multicast
address to discover and communicate with DHCP servers or relay agents
on its link.
IPv6 Stateless Address Autoconfiguration [RFC4862] specifies
procedures by which a node may autoconfigure addresses based on
router advertisements [RFC4861], and the use of a valid lifetime to
support renumbering of addresses on the Internet. In addition, the
protocol interaction by which a node begins stateless or stateful
autoconfiguration is specified. DHCP is one vehicle to perform
stateful autoconfiguration. Compatibility with stateless address
autoconfiguration is a design requirement of DHCP.
IPv6 Neighbor Discovery [RFC4861] is the node discovery protocol in
IPv6 which replaces and enhances functions of ARP [RFC0826]. To
understand IPv6 and stateless address autoconfiguration, it is
strongly recommended that implementors understand IPv6 Neighbor
Discovery.
Dynamic Updates to DNS [RFC2136] 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.
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4. Terminology
This section defines terminology specific to IPv6 and DHCP used in
this document.
4.1. IPv6 Terminology
IPv6 terminology relevant to this specification from the IPv6
Protocol [RFC2460], IPv6 Addressing Architecture [RFC4291], and IPv6
Stateless Address Autoconfiguration [RFC4862] is included below.
address An IP layer identifier for an interface or
a set of interfaces.
host Any node that is not a router.
IP Internet Protocol Version 6 (IPv6). The
terms IPv4 and IPv6 are used only in
contexts where it is necessary to avoid
ambiguity.
interface A node's attachment to a link.
link A communication facility or medium over
which nodes can communicate at the link
layer, i.e., the layer immediately below
IP. Examples are Ethernet (simple or
bridged); Token Ring; PPP links, X.25,
Frame Relay, or ATM networks; and Internet
(or higher) layer "tunnels", such as
tunnels over IPv4 or IPv6 itself.
link-layer identifier A link-layer identifier for an interface.
Examples include IEEE 802 addresses for
Ethernet or Token Ring network interfaces,
and E.164 addresses for ISDN links.
link-local address An IPv6 address having a link-only scope,
indicated by having the prefix (FE80::/10),
that can be used to reach neighboring nodes
attached to the same link. Every interface
has a link-local address.
multicast address An identifier for a set of interfaces
(typically belonging to different nodes).
A packet sent to a multicast address is
delivered to all interfaces identified by
that address.
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neighbor A node attached to the same link.
node A device that implements IP.
packet An IP header plus payload.
prefix The initial bits of an address, or a set of
IP addresses that share the same initial
bits.
prefix length The number of bits in a prefix.
router A node that forwards IP packets not
explicitly addressed to itself.
unicast address An identifier for a single interface. A
packet sent to a unicast address is
delivered to the interface identified by
that address.
4.2. DHCP Terminology
Terminology specific to DHCP can be found below.
allocatable resource (or resource). It is an address, a prefix
or any other allocatable resource that may
be defined in the future. Currently there
are three defined allocatable resources:
non-temporary addresses, temporary
addresses and delegated prefixes.
appropriate to the link An address is "appropriate to the link"
when the address is consistent with the
DHCP server's knowledge of the network
topology, prefix assignment and address
assignment policies.
binding A binding (or, client binding) is a group
of server data records containing the
information the server has about the
addresses in an IA or configuration
information explicitly assigned to the
client. Configuration information that has
been returned to a client through a policy
- for example, the information returned to
all clients on the same link - does not
require a binding. A binding containing
information about an IA is indexed by the
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tuple <DUID, IA-type, IAID> (where IA-type
is the type of address in the IA; for
example, temporary). A binding containing
configuration information for a client is
indexed by <DUID>.
configuration parameter An element of the configuration information
set on the server and delivered to the
client using DHCP. Such parameters may be
used to carry information to be used by a
node to configure its network subsystem and
enable communication on a link or
internetwork, for example.
delegating router: The router that acts as a DHCP server, and
is responding to the prefix request.
DHCP Dynamic Host Configuration Protocol for
IPv6. The terms DHCPv4 and DHCPv6 are used
only in contexts where it is necessary to
avoid ambiguity.
DHCP client (or client) A node that initiates requests on a link to
obtain configuration parameters from one or
more DHCP servers. Depending on the
purpose of the client, it may feature the
requesting router functionality, if it
supports prefix delegation.
DHCP domain A set of links managed by DHCP and operated
by a single administrative entity.
DHCP realm A name used to identify the DHCP
administrative domain from which a DHCP
authentication key was selected.
DHCP relay agent (or relay agent) A node that acts as an
intermediary to deliver DHCP messages
between clients and servers. In certain
configurations there may be more than one
relay agent between clients and servers, so
a relay agent may send DHCP messages to
another relay agent.
DHCP server (or server) A node that responds to requests from
clients, and may or may not be on the same
link as the client(s). Depending on its
capabilities, it may also feature the
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functionality of delegating router, if it
supports prefix delegation.
DUID A DHCP Unique IDentifier for a DHCP
participant; each DHCP client and server
has exactly one DUID. See Section 10 for
details of the ways in which a DUID may be
constructed.
IA Identity Association: A collection of
allocatable resources assigned to a client.
Each IA has an associated IAID. A client
may have more than one IA assigned to it;
for example, one for each of its
interfaces. Each IA holds one type of
address; for example, an identity
association for temporary addresses (IA_TA)
holds temporary addresses (see "identity
association for temporary addresses") and
identity association for prefix delegation
(IA_PD) holds delegated prefixes.
Throughout this document, "IA" is used to
refer to an identity association without
identifying the type of allocatable
resources in the IA. At the time of
writing this document, there are 3 IA types
defined: IA_NA, IA_TA and IA_PD. New IA
types may be defined in the future.
IAID Identity Association IDentifier: An
identifier for an IA, chosen by the client.
Each IA has an IAID, which is chosen to be
unique among IAIDs for IAs of a specific
type, belonging to that client.
IA_NA Identity association for Non-temporary
Addresses: An IA that carries assigned
addresses that are not temporary addresses
(see "identity association for temporary
addresses")
IA_TA Identity Association for Temporary
Addresses: An IA that carries temporary
addresses (see [RFC4941]).
IA_PD Identity Association for Prefix Delegation:
A collection of prefixes assigned to the
requesting router. Each IA_PD has an
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associated IAID. A requesting router may
have more than one IA_PD assigned to it;
for example, one for each of its
interfaces.
message A unit of data carried as the payload of a
UDP datagram, exchanged among DHCP servers,
relay agents and clients.
Reconfigure key A key supplied to a client by a server used
to provide security for Reconfigure
messages.
requesting router: The router that acts as a DHCP client and
is requesting prefix(es) to be assigned.
singleton option: An option that is allowed to appear only
once. Most options are singletons.
relaying A DHCP relay agent relays DHCP messages
between DHCP participants.
transaction ID An opaque value used to match responses
with replies initiated either by a client
or server.
5. Operational Models
This section describes some of the current most common DHCP
operational models. The described models are not mutually exclusive
and are sometimes used together. For example, a device may start in
stateful mode to obtain an address, and at a later time when an
application is started, request additional parameters using stateless
mode.
5.1. Stateless DHCP
Stateless DHCP [RFC3736] is used when DHCP is not used for obtaining
an allocatable resource, but a node (DHCP client) desires one or more
DHCP "other configuration" parameters, such as a list of DNS
recursive name servers or DNS domain search lists [RFC3646].
Stateless may be used when a node initially boots or at any time the
software on the node requires some missing or expired configuration
information that is available via DHCP.
This is the simplest and most basic operation for DHCP and requires a
client (and a server) to support only two messages - Information-
request and Reply. Note that DHCP servers and relay agents typically
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also need to support the Relay-Forw and Relay-Reply messages to
accommodate operation when clients and servers are not on the same
link.
5.2. DHCP for Non-Temporary Address Assignment
This model of operation was the original motivation for DHCP and is
the "stateful address autoconfiguration protocol" for IPv6 [RFC2462].
It is appropriate for situations where stateless address
autoconfiguration is not desired, because of network policy,
additional requirements (such as updating the DNS with forward or
reverse resource records), or client specific requirements (i.e.,
some prefixes are only available to some clients) which are not
possible using stateless address autoconfiguration.
The model of operation for non-temporary address assignment is as
follows. The server is provided with IPv6 prefixes from which it may
allocate addresses to clients, as well as any related network
topology information as to which prefixes are present on which links.
A client requests a non-temporary address to be assigned by the
server. The server allocates an address or addresses appropriate for
the link on which the client is connected. The server returns the
allocated address or addresses to the client.
Each address has an associated preferred and valid lifetime, which
constitutes an agreement about the length of time over which the
client is allowed to use the address. A client can request an
extension of the lifetimes on an address and is required to terminate
the use of an address if the valid lifetime of the address expires.
Typically clients request other configuration parameters, such as the
domain server addresses and search lists, when requesting addresses.
5.3. DHCP for Prefix Delegation
The prefix delegation mechanism, originally described in [RFC3633],
is another stateful mode of operation and intended for simple
delegation of prefixes from a delegating router (DHCP server) to
requesting routers (DHCP clients). It is appropriate for situations
in which the delegating router does not have knowledge about the
topology of the networks to which the requesting router is attached,
and the delegating router does not require other information aside
from the identity of the requesting router to choose a prefix for
delegation. For example, these options would be used by a service
provider to assign a prefix to a Customer Premise Equipment (CPE)
device acting as a router between the subscriber's internal network
and the service provider's core network.
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The design of this prefix delegation mechanism meets the requirements
for prefix delegation in [RFC3769].
The model of operation for prefix delegation is as follows. A
delegating router is provided IPv6 prefixes to be delegated to
requesting routers. Examples of ways in which the delegating router
may be provided these prefixes is given in Section 19.4. A
requesting router requests prefix(es) from the delegating router, as
described in Section 19.3. The delegating router chooses prefix(es)
for delegation, and responds with prefix(es) to the requesting
router. The requesting router is then responsible for the delegated
prefix(es). For example, the requesting router might assign a subnet
from a delegated prefix to one of its interfaces, and begin sending
router advertisements for the prefix on that link.
Each prefix has an associated valid and preferred lifetime, which
constitutes an agreement about the length of time over which the
requesting router is allowed to use the prefix. A requesting router
can request an extension of the lifetimes on a delegated prefix and
is required to terminate the use of a delegated prefix if the valid
lifetime of the prefix expires.
This prefix delegation mechanism would be appropriate for use by an
ISP to delegate a prefix to a subscriber, where the delegated prefix
would possibly be subnetted and assigned to the links within the
subscriber's network.
Figure 1 illustrates a network architecture in which prefix
delegation could be used.
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______________________ \
/ \ \
| ISP core network | \
\__________ ___________/ |
| |
+-------+-------+ |
| Aggregation | | ISP
| device | | network
| (delegating | |
| router) | |
+-------+-------+ |
| /
|DSL to subscriber /
|premises /
|
+------+------+ \
| CPE | \
| (requesting | \
| router) | |
+----+---+----+ |
| | | Subsciber
---+-------------+-----+ +-----+------ | Network
| | | |
+----+-----+ +-----+----+ +----+-----+ |
|Subscriber| |Subscriber| |Subscriber| /
| PC | | PC | | PC | /
+----------+ +----------+ +----------+ /
Figure 1: Prefix Delegation Newtork
In this example, the delegating router is configured with a set of
prefixes to be used for assignment to customers at the time of each
customer's first connection to the ISP service. The prefix
delegation process begins when the requesting router requests
configuration information through DHCP. The DHCP messages from the
requesting router are received by the delegating router in the
aggregation device. When the delegating router receives the request,
it selects an available prefix or prefixes for delegation to the
requesting router. The delegating router then returns the prefix or
prefixes to the requesting router.
The requesting router subnets the delegated prefix and assigns the
longer prefixes to links in the subscriber's network. In a typical
scenario based on the network shown in Figure 1, the requesting
router subnets a single delegated /48 prefix into /64 prefixes and
assigns one /64 prefix to each of the links in the subscriber
network.
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The prefix delegation options can be used in conjunction with other
DHCP options carrying other configuration information to the
requesting router. The requesting router may, in turn, provide DHCP
service to hosts attached to the internal network. For example, the
requesting router may obtain the addresses of DNS and NTP servers
from the ISP delegating router, and then pass that configuration
information on to the subscriber hosts through a DHCP server in the
requesting router.
5.4. DHCP for Customer Edge Routers
The DHCP requirements and network architecture for Customer Edge
Routers are described in [RFC7084]. This model of operation combines
address assignment (see Section 5.2) and prefix delegation (see
Section 5.3). In general, this model assumes that a single set of
transactions between the client and server will assign or extend the
client's non-temporary addresses and delegated prefixes.
5.5. DHCP for Temporary Addresses
Temporary addresses were originally introduced to avoid privacy
concerns with stateless address autoconfiguration, which based
64-bits of the address on the EUI-64 (see [RFC3041] and [RFC4941]).
They were added to DHCP to provide complementary support when
stateful address assignment is used.
Temporary address assignment works mostly like non-temporary address
assignment (see Section 5.2), however these addresses are generally
intended to be used for a short period of time and not to have their
lifetimes extended, though they can be if required.
6. DHCP Constants
This section describes various program and networking constants used
by DHCP.
6.1. Multicast Addresses
DHCP makes use of the following multicast addresses:
All_DHCP_Relay_Agents_and_Servers (FF02::1:2) A link-scoped
multicast address used by a client to communicate
with neighboring (i.e., on-link) relay agents and
servers. All servers and relay agents are members of
this multicast group.
All_DHCP_Servers (FF05::1:3) A site-scoped multicast address used by
a relay agent to communicate with servers, either
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because the relay agent wants to send messages to all
servers or because it does not know the unicast
addresses of the servers. Note that in order for a
relay agent to use this address, it must have an
address of sufficient scope to be reachable by the
servers. All servers within the site are members of
this multicast group.
6.2. UDP Ports
Clients listen for DHCP messages on UDP port 546. Servers and relay
agents listen for DHCP messages on UDP port 547.
6.3. DHCP Message Types
DHCP defines the following message types. More detail on these
message types can be found in Section 7 and Section 8. Message types
not listed here are reserved for future use. The numeric encoding
for each message type is shown in parentheses.
SOLICIT (1) A client sends a Solicit message to locate servers.
ADVERTISE (2) A server sends an Advertise message to indicate that
it is available for DHCP service, in response to a
Solicit message received from a client.
REQUEST (3) A client sends a Request message to request
configuration parameters, including IP addresses,
from a specific server.
CONFIRM (4) A client sends a Confirm message to any available
server to determine whether the addresses it was
assigned are still appropriate to the link to which
the client is connected.
RENEW (5) A client sends a Renew message to the server that
originally provided the client's addresses and
configuration parameters to extend the lifetimes on
the addresses assigned to the client and to update
other configuration parameters.
REBIND (6) A client sends a Rebind message to any available
server to extend the lifetimes on the addresses
assigned to the client and to update other
configuration parameters; this message is sent after
a client receives no response to a Renew message.
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REPLY (7) A server sends a Reply message containing assigned
addresses and configuration parameters in response to
a Solicit, Request, Renew, Rebind message received
from a client. A server sends a Reply message
containing configuration parameters in response to an
Information-request message. A server sends a Reply
message in response to a Confirm message confirming
or denying that the addresses assigned to the client
are appropriate to the link to which the client is
connected. A server sends a Reply message to
acknowledge receipt of a Release or Decline message.
RELEASE (8) A client sends a Release message to the server that
assigned addresses to the client to indicate that the
client will no longer use one or more of the assigned
addresses.
DECLINE (9) A client sends a Decline message to a server to
indicate that the client has determined that one or
more addresses assigned by the server are already in
use on the link to which the client is connected.
RECONFIGURE (10) A server sends a Reconfigure message to a client to
inform the client that the server has new or updated
configuration parameters, and that the client is to
initiate a Renew/Reply or Information-request/Reply
transaction with the server in order to receive the
updated information.
INFORMATION-REQUEST (11) A client sends an Information-request
message to a server to request configuration
parameters without the assignment of any IP addresses
to the client.
RELAY-FORW (12) A relay agent sends a Relay-forward message to relay
messages to servers, either directly or through
another relay agent. The received message, either a
client message or a Relay-forward message from
another relay agent, is encapsulated in an option in
the Relay-forward message.
RELAY-REPL (13) A server sends a Relay-reply message to a relay agent
containing a message that the relay agent delivers to
a client. The Relay-reply message may be relayed by
other relay agents for delivery to the destination
relay agent.
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The server encapsulates the client message as an
option in the Relay-reply message, which the relay
agent extracts and relays to the client.
6.4. Status Codes
DHCPv6 uses status codes to communicate the success or failure of
operations requested in messages from clients and servers, and to
provide additional information about the specific cause of the
failure of a message. The specific status codes are defined in
Section 23.12.
If the Status Code option does not appear in a message in which the
option could appear, the status of the message is assumed to be
Success.
6.5. Transmission and Retransmission Parameters
This section presents a table of values used to describe the message
transmission behavior of clients and servers.
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+-----------------+-----------+-------------------------------------+
| Parameter | Default | Description |
+-----------------+-----------+-------------------------------------+
| SOL_MAX_DELAY | 1 sec | Max delay of first Solicit |
| SOL_TIMEOUT | 1 sec | Initial Solicit timeout |
| SOL_MAX_RT | 3600 secs | Max Solicit timeout value |
| REQ_TIMEOUT | 1 sec | Initial Request timeout |
| REQ_MAX_RT | 30 secs | Max Request timeout value |
| REQ_MAX_RC | 10 | Max Request retry attempts |
| CNF_MAX_DELAY | 1 sec | Max delay of first Confirm |
| CNF_TIMEOUT | 1 sec | Initial Confirm timeout |
| CNF_MAX_RT | 4 secs | Max Confirm timeout |
| CNF_MAX_RD | 10 secs | Max Confirm duration |
| REN_TIMEOUT | 10 secs | Initial Renew timeout |
| REN_MAX_RT | 600 secs | Max Renew timeout value |
| REB_TIMEOUT | 10 secs | Initial Rebind timeout |
| REB_MAX_RT | 600 secs | Max Rebind timeout value |
| INF_MAX_DELAY | 1 sec | Max delay of first Information- |
| | | request |
| INF_TIMEOUT | 1 sec | Initial Information-request timeout |
| INF_MAX_RT | 3600 secs | Max Information-request timeout |
| | | value |
| REL_TIMEOUT | 1 sec | Initial Release timeout |
| REL_MAX_RC | 4 | MAX Release retry attempts |
| DEC_TIMEOUT | 1 sec | Initial Decline timeout |
| DEC_MAX_RC | 4 | Max Decline retry attempts |
| REC_TIMEOUT | 2 secs | Initial Reconfigure timeout |
| REC_MAX_RC | 8 | Max Reconfigure attempts |
| HOP_COUNT_LIMIT | 32 | Max hop count in a Relay-forward |
| | | message |
+-----------------+-----------+-------------------------------------+
6.6. Representation of time values and "Infinity" as a time value
All time values for lifetimes, T1 and T2 are unsigned integers. The
value 0xffffffff is taken to mean "infinity" when used as a lifetime
(as in [RFC4861]) or a value for T1 or T2.
7. Client/Server Message Formats
All DHCP messages sent between clients and servers share an identical
fixed format header and a variable format area for options.
All values in the message header and in options are in network byte
order.
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Options are stored serially in the options field, with no padding
between the options. Options are byte-aligned but are not aligned in
any other way such as on 2 or 4 byte boundaries.
The following diagram illustrates the format of DHCP messages sent
between clients and servers:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | transaction-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. options .
. (variable) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Client/Server message format
msg-type Identifies the DHCP message type; the
available message types are listed in
Section 6.3.
transaction-id The transaction ID for this message exchange.
options Options carried in this message; options are
described in Section 23.
8. Relay Agent/Server Message Formats
Relay agents exchange messages with servers to relay messages between
clients and servers that are not connected to the same link.
All values in the message header and in options are in network byte
order.
Options are stored serially in the options field, with no padding
between the options. Options are byte-aligned but are not aligned in
any other way such as on 2 or 4 byte boundaries.
There are two relay agent messages, which share the following format:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | hop-count | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
| link-address |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
| peer-address |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
. .
. options (variable number and length) .... .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Relay Agent/Server message format
The following sections describe the use of the Relay Agent message
header.
8.1. Relay-forward Message
The following table defines the use of message fields in a Relay-
forward message.
msg-type RELAY-FORW
hop-count Number of relay agents that have relayed this
message.
link-address An address that will be used by the server to
identify the link on which the client is
located. This is typically global, site-
scoped or ULA [RFC4193], but see discussion
in Section 21.1.1.
peer-address The address of the client or relay agent from
which the message to be relayed was received.
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options MUST include a "Relay Message option" (see
Section 23.10); MAY include other options
added by the relay agent.
8.2. Relay-reply Message
The following table defines the use of message fields in a Relay-
reply message.
msg-type RELAY-REPL
hop-count Copied from the Relay-forward message
link-address Copied from the Relay-forward message
peer-address Copied from the Relay-forward message
options MUST include a "Relay Message option"; see
Section 23.10; MAY include other options
9. Representation and Use of Domain Names
So that domain names may be encoded uniformly, a domain name or a
list of domain names is encoded using the technique described in
section 3.1 of [RFC1035]. A domain name, or list of domain names, in
DHCP MUST NOT be stored in compressed form, as described in section
4.1.4 of [RFC1035].
10. DHCP Unique Identifier (DUID)
Each DHCP client and server has a DUID. DHCP servers use DUIDs to
identify clients for the selection of configuration parameters and in
the association of IAs with clients. DHCP clients use DUIDs to
identify a server in messages where a server needs to be identified.
See Section 23.2 and Section 23.3 for the representation of a DUID in
a DHCP message.
Clients and servers MUST treat DUIDs as opaque values and MUST only
compare DUIDs for equality. Clients and servers MUST NOT in any
other way interpret DUIDs. Clients and servers MUST NOT restrict
DUIDs to the types defined in this document, as additional DUID types
may be defined in the future.
The DUID is carried in an option because it may be variable length
and because it is not required in all DHCP messages. The DUID is
designed to be unique across all DHCP clients and servers, and stable
for any specific client or server - that is, the DUID used by a
client or server SHOULD NOT change over time if at all possible; for
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example, a device's DUID should not change as a result of a change in
the device's network hardware.
The motivation for having more than one type of DUID is that the DUID
must be globally unique, and must also be easy to generate. The sort
of globally-unique identifier that is easy to generate for any given
device can differ quite widely. Also, some devices may not contain
any persistent storage. Retaining a generated DUID in such a device
is not possible, so the DUID scheme must accommodate such devices.
10.1. DUID Contents
A DUID consists of a two-octet type code represented in network byte
order, followed by a variable number of octets that make up the
actual identifier. The length of the DUID (not including the type
code) is at least 1 octet and at most 128 octets. The following
types are currently defined:
+------+------------------------------------------------------+
| Type | Description |
+------+------------------------------------------------------+
| 1 | Link-layer address plus time |
| 2 | Vendor-assigned unique ID based on Enterprise Number |
| 3 | Link-layer address |
| 4 | Universally Unique IDentifier (UUID) - see [RFC6355] |
+------+------------------------------------------------------+
Formats for the variable field of the DUID for the first 3 of the
above types are shown below. The fourth type, DUID-UUID [RFC6355],
can be used in situations where there is a UUID stored in a device's
firmware settings.
10.2. DUID Based on Link-layer Address Plus Time, DUID-LLT
This type of DUID consists of a two octet type field containing the
value 1, a two octet hardware type code, four octets containing a
time value, followed by link-layer address of any one network
interface that is connected to the DHCP device at the time that the
DUID is generated. The time value is the time that the DUID is
generated represented in seconds since midnight (UTC), January 1,
2000, modulo 2^32. The hardware type MUST be a valid hardware type
assigned by the IANA as described in [RFC0826]. Both the time and
the hardware type are stored in network byte order. The link-layer
address is stored in canonical form, as described in [RFC2464].
The following diagram illustrates the format of a DUID-LLT:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | hardware type (16 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| time (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. link-layer address (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: DUID-LLT format
The choice of network interface can be completely arbitrary, as long
as that interface provides a globally unique link-layer address for
the link type, and the same DUID-LLT SHOULD be used in configuring
all network interfaces connected to the device, regardless of which
interface's link-layer address was used to generate the DUID-LLT.
Clients and servers using this type of DUID MUST store the DUID-LLT
in stable storage, and MUST continue to use this DUID-LLT even if the
network interface used to generate the DUID-LLT is removed. Clients
and servers that do not have any stable storage MUST NOT use this
type of DUID.
Clients and servers that use this DUID SHOULD attempt to configure
the time prior to generating the DUID, if that is possible, and MUST
use some sort of time source (for example, a real-time clock) in
generating the DUID, even if that time source could not be configured
prior to generating the DUID. The use of a time source makes it
unlikely that two identical DUID-LLTs will be generated if the
network interface is removed from the client and another client then
uses the same network interface to generate a DUID-LLT. A collision
between two DUID-LLTs is very unlikely even if the clocks have not
been configured prior to generating the DUID.
This method of DUID generation is recommended for all general purpose
computing devices such as desktop computers and laptop computers, and
also for devices such as printers, routers, and so on, that contain
some form of writable non-volatile storage.
Despite our best efforts, it is possible that this algorithm for
generating a DUID could result in a client identifier collision. A
DHCP client that generates a DUID-LLT using this mechanism MUST
provide an administrative interface that replaces the existing DUID
with a newly-generated DUID-LLT.
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10.3. DUID Assigned by Vendor Based on Enterprise Number, DUID-EN
This form of DUID is assigned by the vendor to the device. It
consists of the vendor's registered Private Enterprise Number as
maintained by IANA [IANA-PEN] followed by a unique identifier
assigned by the vendor. The following diagram summarizes the
structure of a DUID-EN:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | enterprise-number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| enterprise-number (contd) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
. identifier .
. (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: DUID-EN format
The source of the identifier is left up to the vendor defining it,
but each identifier part of each DUID-EN MUST be unique to the device
that is using it, and MUST be assigned to the device no later than at
the first usage and stored in some form of non-volatile storage.
This typically means being assigned during manufacture process in
case of physical devices or when the image is created or booted for
the first time in case of virtual machines. The generated DUID
SHOULD be recorded in non-erasable storage. The enterprise-number is
the vendor's registered Private Enterprise Number as maintained by
IANA [IANA-PEN]. The enterprise-number is stored as an unsigned 32
bit number.
An example DUID of this type might look like this:
+---+---+---+---+---+---+---+---+
| 0 | 2 | 0 | 0 | 0 | 9| 12|192|
+---+---+---+---+---+---+---+---+
|132|211| 3 | 0 | 9 | 18|
+---+---+---+---+---+---+
Figure 6: DUID-EN example
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This example includes the two-octet type of 2, the Enterprise Number
(9), followed by eight octets of identifier data
(0x0CC084D303000912).
10.4. DUID Based on Link-layer Address, DUID-LL
This type of DUID consists of two octets containing the DUID type 3,
a two octet network hardware type code, followed by the link-layer
address of any one network interface that is permanently connected to
the client or server device. For example, a host that has a network
interface implemented in a chip that is unlikely to be removed and
used elsewhere could use a DUID-LL. The hardware type MUST be a
valid hardware type assigned by the IANA, as described in [RFC0826].
The hardware type is stored in network byte order. The link-layer
address is stored in canonical form, as described in [RFC2464]. The
following diagram illustrates the format of a DUID-LL:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 3 | hardware type (16 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. link-layer address (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: DUID-LL format
The choice of network interface can be completely arbitrary, as long
as that interface provides a unique link-layer address and is
permanently attached to the device on which the DUID-LL is being
generated. The same DUID-LL SHOULD be used in configuring all
network interfaces connected to the device, regardless of which
interface's link-layer address was used to generate the DUID.
DUID-LL is recommended for devices that have a permanently-connected
network interface with a link-layer address, and do not have
nonvolatile, writable stable storage. DUID-LL MUST NOT be used by
DHCP clients or servers that cannot tell whether or not a network
interface is permanently attached to the device on which the DHCP
client is running.
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11. Identity Association
An "identity-association" (IA) is a construct through which a server
and a client can identify, group, and manage a set of related IPv6
addresses or delegated prefixes. Each IA consists of an IAID and
associated configuration information.
The IAID uniquely identifies the IA and must be chosen to be unique
among the IAIDs for that IA type on the client. The IAID is chosen
by the client. For any given use of an IA by the client, the IAID
for that IA MUST be consistent across restarts of the DHCP client.
The client may maintain consistency either by storing the IAID in
non-volatile storage or by using an algorithm that will consistently
produce the same IAID as long as the configuration of the client has
not changed. There may be no way for a client to maintain
consistency of the IAIDs if it does not have non-volatile storage and
the client's hardware configuration changes. If the client uses only
one IAID, it can use a well-known value, e.g., zero.
11.1. Identity Associations for Address Assignment
A client must associate at least one distinct IA with each of its
network interfaces for which it is to request the assignment of IPv6
addresses from a DHCP server. The client uses the IAs assigned to an
interface to obtain configuration information from a server for that
interface. Each IA must be associated with exactly one interface.
The configuration information in an IA consists of one or more IPv6
addresses along with the times T1 and T2 for the IA. See
Section 22.4 for the representation of an IA in a DHCP message.
Each address in an IA has a preferred lifetime and a valid lifetime,
as defined in [RFC4862]. The lifetimes are transmitted from the DHCP
server to the client in the IA option. The lifetimes apply to the
use of IPv6 addresses, as described in section 5.5.4 of [RFC4862].
11.2. Identity Associations for Prefix Delegation
An IA_PD is different from an IA for address assignment, in that it
does not need to be associated with exactly one interface. One IA_PD
can be associated with the requesting router, with a set of
interfaces or with exactly one interface. A requesting router must
create at least one distinct IA_PD. It may associate a distinct
IA_PD with each of its downstream network interfaces and use that
IA_PD to obtain a prefix for that interface from the delegating
router.
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The configuration information in an IA_PD consists of one or more
IPv6 prefixes along with the times T1 and T2 for the IA_PD. See
Section 23.21 for the representation of an IA_PD 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 some combination of the following sources:
- The link to which the client is attached. The server determines
the link as follows:
* If the server receives the message directly from the client and
the source address in the IP datagram in which the message was
received is a link-local address, then the client is on the
same link to which the interface over which the message was
received is attached.
* If the server receives the message from a forwarding relay
agent, then the client is on the same link as the one to which
the interface, identified by the link-address field in the
message from the relay agent, is attached. According to
[RFC6221], the server MUST ignore any link-address field whose
value is zero. The link address field referes to the link-
address field of the Relay-Forward message, and the link-
address fields in any Relay-Forward messages that may be nested
within the Relay-Forward message.
* If the server receives the message directly from the client and
the source address in the IP datagram in which the message was
received is not a link-local address, then the client is on the
link identified by the source address in the IP datagram (note
that this situation can occur only if the server has enabled
the use of unicast message delivery by the client and the
client has sent a message for which unicast delivery is
allowed).
- The DUID supplied by the client.
- Other information in options supplied by the client, e.g. IA
Address options that include the client's requests for specific
addresses.
- Other information in options supplied by the relay agent.
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Any address assigned by a server that is based on an EUI-64
identifier MUST include an interface identifier with the "u"
(universal/local) and "g" (individual/group) bits of the interface
identifier set appropriately, as indicated in section 2.5.1 of
[RFC4291].
A server MUST NOT assign an address that is otherwise reserved for
some other purpose. For example, a server MUST NOT assign reserved
anycast addresses, as defined in [RFC2526], from any subnet.
13. Management of Temporary Addresses
A client may request the assignment of temporary addresses (see
[RFC4941] for the definition of temporary addresses). DHCPv6
handling of address assignment is no different for temporary
addresses.
Clients ask for temporary addresses and servers assign them.
Temporary addresses are carried in the Identity Association for
Temporary Addresses (IA_TA) option (see Section 23.5). Each IA_TA
option contains at most one temporary address for each of the
prefixes on the link to which the client is attached.
The lifetime of the assigned temporary address is set in the IA
Address Option (see Section 23.6) with in the IA_TA option. It is
RECOMMENDED to set short lifetimes, typically shorter than
TEMP_VALID_LIFETIME and TEMP_PREFERRED_LIFETIME (see Section 5,
[RFC4941].
The IAID number space for the IA_TA option IAID number space is
separate from the IA_NA option IAID number space.
A DHCPv6 server implementation MAY generate temporary addresses
referring to the algorithm defined in Section 3.2.1, [RFC4941], with
additional condition that the new address is not duplicated with any
assigned addresses.
The server MAY update the DNS for a temporary address, as described
in section 4 of [RFC4941].
On the clients, by default, temporary addresses are preferred in
source address selection, according to Rule 7, [RFC6724]. However,
this policy is overridable.
One of the most important properties of temporary address is
unlinkability of different actions over time. So, it is NOT
RECOMMENDED for a client to renew expired temporary addresses, though
DHCPv6 provides such possibility (see Section 23.5).
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14. Transmission of Messages by a Client
Unless otherwise specified in this document, or in a document that
describes how IPv6 is carried over a specific type of link (for link
types that do not support multicast), a client sends DHCP messages to
the All_DHCP_Relay_Agents_and_Servers.
A client uses multicast to reach all servers or an individual server.
An individual server is indicated by specifying that server's DUID in
a Server Identifier option (see Section 23.3) in the client's message
(all servers will receive this message but only the indicated server
will respond). All servers are indicated by not supplying this
option.
A client may send some messages directly to a server using unicast,
as described in Section 23.12.
14.1. Rate Limiting
In order to avoid prolonged message bursts that may be caused by
possible logic loops, a DHCPv6 client MUST limit the rate of DHCPv6
messages it transmits. One example is that a client obtains an
address, but does not like the response; it reverts back to Solicit
procedure, discovers the same (sole) server, requests an address and
gets the same address as before (the server still has the lease that
was requested just previously). This loops can repeat infinitely if
there is not a quit/stop mechanism. Therefore, a client must not
initiate transmissions too frequently.
A recommended method for implementing the rate limiting function is a
token bucket, limiting the average rate of transmission to a certain
number in a certain time. This method of bounding burstiness also
guarantees that the long-term transmission rate will not exceed.
TRT Transmission Rate Limit
The Transmission Rate Limit parameter (TRT) SHOULD be configurable.
A possible default could be 20 packets in 20 seconds.
For a device that has multiple interfaces, the limit MUST be enforced
on a per interface basis.
Rate limiting of forwarded DHCPv6 messages and server-side messages
are out of scope of this specification.
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15. Reliability of Client Initiated Message Exchanges
DHCP clients are responsible for reliable delivery of messages in the
client-initiated message exchanges described in Section 18 and
Section 19. If a DHCP client fails to receive an expected response
from a server, the client must retransmit its message. This section
describes the retransmission strategy to be used by clients in
client-initiated message exchanges.
Note that the procedure described in this section is slightly
modified when used with the Solicit message. The modified procedure
is described in Section 18.1.2.
The client begins the message exchange by transmitting a message to
the server. The message exchange terminates when either the client
successfully receives the appropriate response or responses from a
server or servers, or when the message exchange is considered to have
failed according to the retransmission mechanism described below.
The client retransmission behavior is controlled and described by the
following variables:
RT Retransmission timeout
IRT Initial retransmission time
MRC Maximum retransmission count
MRT Maximum retransmission time
MRD Maximum retransmission duration
RAND Randomization factor
With each message transmission or retransmission, the client sets RT
according to the rules given below. If RT expires before the message
exchange terminates, the client recomputes RT and retransmits the
message.
Each of the computations of a new RT include a randomization factor
(RAND), which is a random number chosen with a uniform distribution
between -0.1 and +0.1. The randomization factor is included to
minimize synchronization of messages transmitted by DHCP clients.
The algorithm for choosing a random number does not need to be
cryptographically sound. The algorithm SHOULD produce a different
sequence of random numbers from each invocation of the DHCP client.
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RT for the first message transmission is based on IRT:
RT = IRT + RAND*IRT
RT for each subsequent message transmission is based on the previous
value of RT:
RT = 2*RTprev + RAND*RTprev
MRT specifies an upper bound on the value of RT (disregarding the
randomization added by the use of RAND). If MRT has a value of 0,
there is no upper limit on the value of RT. Otherwise:
if (RT > MRT)
RT = MRT + RAND*MRT
MRC specifies an upper bound on the number of times a client may
retransmit a message. Unless MRC is zero, the message exchange fails
once the client has transmitted the message MRC times.
MRD specifies an upper bound on the length of time a client may
retransmit a message. Unless MRD is zero, the message exchange fails
once MRD seconds have elapsed since the client first transmitted the
message.
If both MRC and MRD are non-zero, the message exchange fails whenever
either of the conditions specified in the previous two paragraphs are
met.
If both MRC and MRD are zero, the client continues to transmit the
message until it receives a response.
A client is not expected to listen for a response during the entire
period between transmission of Solicit or Information-request
messages.
16. Message Validation
Clients and servers might get messages that contain options not
allowed to appear in the received message. For example, an IA option
is not allowed to appear in an Information-request message. Clients
and servers MAY choose either to extract information from such a
message if the information is of use to the recipient, or to ignore
such message completely and just drop it.
A server MUST discard any Solicit, Confirm, Rebind or Information-
request messages it receives with a unicast destination address.
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Message validation based on DHCP authentication is discussed in
Section 22.4.2.
If a server receives a message that contains options it should not
contain (such as an Information-request message with an IA option),
is missing options that it should contain, or is otherwise not valid,
it MAY send a Reply (or Advertise as appropriate) with a Server
Identifier option, a Client Identifier option if one was included in
the message and a Status Code option with status UnSpecFail.
A client or server MUST silently discary and yreceived DHCPv6
messages with an unknown message type.
16.1. Use of Transaction IDs
The "transaction-id" field holds a value used by clients and servers
to synchronize server responses to client messages. A client SHOULD
generate a random number that cannot easily be guessed or predicted
to use as the transaction ID for each new message it sends. Note
that if a client generates easily predictable transaction
identifiers, it may become more vulnerable to certain kinds of
attacks from off-path intruders. A client MUST leave the transaction
ID unchanged in retransmissions of a message.
16.2. Solicit Message
Clients MUST discard any received Solicit messages.
Servers MUST discard any Solicit messages that do not include a
Client Identifier option or that do include a Server Identifier
option.
16.3. Advertise Message
Clients MUST discard any received Advertise message that meets any of
the following conditions:
- the message does not include a Server Identifier option.
- the message does not include a Client Identifier option.
- the contents of the Client Identifier option does not match the
client's DUID.
- the "transaction-id" field value does not match the value the
client used in its Solicit message.
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Servers and relay agents MUST discard any received Advertise
messages.
16.4. Request Message
Clients MUST discard any received Request messages.
Servers MUST discard any received Request message that meets any of
the following conditions:
- the message does not include a Server Identifier option.
- the contents of the Server Identifier option do not match the
server's DUID.
- the message does not include a Client Identifier option.
16.5. Confirm Message
Clients MUST discard any received Confirm messages.
Servers MUST discard any received Confirm messages that do not
include a Client Identifier option or that do include a Server
Identifier option.
16.6. Renew Message
Clients MUST discard any received Renew messages.
Servers MUST discard any received Renew message that meets any of the
following conditions:
- the message does not include a Server Identifier option.
- the contents of the Server Identifier option does not match the
server's identifier.
- the message does not include a Client Identifier option.
16.7. Rebind Message
Clients MUST discard any received Rebind messages.
Servers MUST discard any received Rebind messages that do not include
a Client Identifier option or that do include a Server Identifier
option.
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16.8. Decline Messages
Clients MUST discard any received Decline messages.
Servers MUST discard any received Decline message that meets any of
the following conditions:
- the message does not include a Server Identifier option.
- the contents of the Server Identifier option does not match the
server's identifier.
- the message does not include a Client Identifier option.
16.9. Release Message
Clients MUST discard any received Release messages.
Servers MUST discard any received Release message that meets any of
the following conditions:
- the message does not include a Server Identifier option.
- the contents of the Server Identifier option does not match the
server's identifier.
- the message does not include a Client Identifier option.
16.10. Reply Message
Clients MUST discard any received Reply message that meets any of the
following conditions:
- the message does not include a Server Identifier option.
- the "transaction-id" field in the message does not match the value
used in the original message.
If the client included a Client Identifier option in the original
message, the Reply message MUST include a Client Identifier option
and the contents of the Client Identifier option MUST match the DUID
of the client; OR, if the client did not include a Client Identifier
option in the original message, the Reply message MUST NOT include a
Client Identifier option.
Servers and relay agents MUST discard any received Reply messages.
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16.11. Reconfigure Message
Servers and relay agents MUST discard any received Reconfigure
messages.
Clients MUST discard any Reconfigure message that meets any of the
following conditions:
- the message was not unicast to the client.
- the message does not include a Server Identifier option.
- the message does not include a Client Identifier option that
contains the client's DUID.
- the message does not contain a Reconfigure Message option.
- the Reconfigure Message option msg-type is not a valid value.
- the message includes any IA options and the msg-type in the
Reconfigure Message option is INFORMATION-REQUEST.
- the message does not include DHCP authentication:
* the message does not contain an authentication option.
* the message does not pass the authentication validation
performed by the client.
16.12. Information-request Message
Clients MUST discard any received Information-request messages.
Servers MUST discard any received Information-request message that
meets any of the following conditions:
- The message includes a Server Identifier option and the DUID in
the option does not match the server's DUID.
- The message includes an IA option.
16.13. Relay-forward Message
Clients MUST discard any received Relay-forward messages.
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16.14. Relay-reply Message
Clients and servers MUST discard any received Relay-reply messages.
17. Client Source Address and Interface Selection
Client's behavior is different depending on the purpose of the
configuration.
17.1. Address Assignment
When a client sends a DHCP message to the
All_DHCP_Relay_Agents_and_Servers address, it SHOULD send the message
through the interface for which configuration information is being
requested. However, the client MAY send the message through another
interface if the interface is a logical interface without direct link
attachement or the client is certain that two interfaces are attached
to the same link.
When a client sends a DHCP message directly to a server using unicast
(after receiving the Server Unicast option from that server), the
source address in the header of the IPv6 datagram MUST be an address
assigned to the interface for which the client is interested in
obtaining configuration and which is suitable for use by the server
in responding to the client.
17.2. Prefix Delegation
Delegated prefixes are not associated with a particular interface in
the same way as addresses are for address assignment, and mentioned
above.
When a client (acting as requesting router) sends a DHCP message for
the purpose of prefix delegation, it SHOULD be sent on the interface
associated with the upstream router (ISP network). The upstream
interface is typically determined by configuration. This rule
applies even in the case where a separate IA_PD is used for each
downstream interface.
When a requesting router sends a DHCP message directly to a
delegating router using unicast (after receiving the Server Unicast
option from that delegating router), the source address SHOULD be an
address from the upstream interface and which is suitable for use by
the delegating router in responding to the requesting router.
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18. DHCP Server Solicitation
This section describes how a client locates servers that will assign
addresses and delegated prefixes to IAs belonging to the client.
The client is responsible for creating IAs and requesting that a
server assign IPv6 addresses and delegated prefixes to the IAs. The
client first creates the IAs and assigns IAIDs to them. The client
then transmits a Solicit message containing the IA options describing
the IAs. The client MUST NOT be using any of the addresses or
delegated prefixes for which it tries to obtain the bindings by
sending the Solicit message. In particular, if the client had some
valid bindings and has chosen to start the server solicitation
process to obtain the bindings from a different server, the client
MUST stop using the addresses and delegated prefixes for the bindings
it had obtained from the previous server, and which it is now trying
to obtain from a new server.
Servers that can assign addresses or delegated prefixes to the IAs
respond to the client with an Advertise message. The client then
initiates a configuration exchange as described in Section 19.
If the client will accept a Reply message with committed address
assignments and other resources in response to the Solicit message,
the client includes a Rapid Commit option (see Section 23.14) in the
Solicit message.
18.1. Client Behavior
A client uses the Solicit message to discover DHCP servers configured
to assign addresses or return other configuration parameters on the
link to which the client is attached.
18.1.1. 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 Client Identifier option to identify itself
to the server. The client includes IA options for any IAs to which
it wants the server to assign addresses. The client MAY include
addresses in the IAs as a hint to the server about addresses for
which the client has a preference. The client MUST NOT include any
other options in the Solicit message, except as specifically allowed
in the definition of individual options.
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The client uses IA_NA options to request the assignment of non-
temporary addresses and uses IA_TA options to request the assignment
of temporary addresses. Either IA_NA or IA_TA options, or a
combination of both, can be included in DHCP messages.
The client MUST include an Option Request option (see Section 23.7)
to request the SOL_MAX_RT option (see Section 23.23) and any other
options the client is interested in receiving. The client MAY
additionally include instances of those options that are identified
in the Option Request option, with data values as hints to the server
about parameter values the client would like to have returned.
The client includes a Reconfigure Accept option (see Section 23.20)
if the client is willing to accept Reconfigure messages from the
server.
18.1.2. Transmission of Solicit Messages
The first Solicit message from the client on the interface MUST be
delayed by a random amount of time between 0 and SOL_MAX_DELAY. In
the case of a Solicit message transmitted when DHCP is initiated by
IPv6 Neighbor Discovery, the delay gives the amount of time to wait
after IPv6 Neighbor Discovery causes the client to invoke the
stateful address autoconfiguration protocol (see section 5.5.3 of
[RFC4862]). This random delay desynchronizes clients which start at
the same time (for example, after a power outage).
The client transmits the message according to Section 15, using the
following parameters:
IRT SOL_TIMEOUT
MRT SOL_MAX_RT
MRC 0
MRD 0
If the client has included a Rapid Commit option in its Solicit
message, the client terminates the waiting process as soon as a Reply
message with a Rapid Commit option is received.
If the client is waiting for an Advertise message, the mechanism in
Section 15 is modified as follows for use in the transmission of
Solicit messages. The message exchange is not terminated by the
receipt of an Advertise before the first RT has elapsed. Rather, the
client collects Advertise messages until the first RT has elapsed.
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Also, the first RT MUST be selected to be strictly greater than IRT
by choosing RAND to be strictly greater than 0.
A client MUST collect Advertise messages for the first RT seconds,
unless it receives an Advertise message with a preference value of
255. The preference value is carried in the Preference option
(Section 23.8). Any Advertise that does not include a Preference
option is considered to have a preference value of 0. If the client
receives an Advertise message that includes a Preference option with
a preference value of 255, the client immediately begins a client-
initiated message exchange (as described in Section 19) by sending a
Request message to the server from which the Advertise message was
received. If the client receives an Advertise message that does not
include a Preference option with a preference value of 255, the
client continues to wait until the first RT elapses. If the first RT
elapses and the client has received an Advertise message, the client
SHOULD continue with a client-initiated message exchange by sending a
Request message.
If the client does not receive any Advertise messages before the
first RT has elapsed, it begins the retransmission mechanism
described in Section 15. The client terminates the retransmission
process as soon as it receives any Advertise message, and the client
acts on the received Advertise message without waiting for any
additional Advertise messages.
A DHCP client SHOULD choose MRC and MRD to be 0. If the DHCP client
is configured with either MRC or MRD set to a value other than 0, it
MUST stop trying to configure the interface if the message exchange
fails. After the DHCP client stops trying to configure the
interface, it SHOULD restart the reconfiguration process after some
external event, such as user input, system restart, or when the
client is attached to a new link.
18.1.3. Receipt of Advertise Messages
The client MUST process SOL_MAX_RT and INF_MAX_RT options in an
Advertise message, even if the message contains a Status Code option
indicating a failure, and the Advertise message will be discarded by
the client.
The client MUST ignore any IAs in an Advertise message that include a
Status Code option containing the value NoAddrsAvail, with the
exception that the client MAY display the associated status message
to the user.
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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.
- 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.
In practice, this means that the client will maintain independent
per-IA state machines per each selected server.
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.
18.1.4. Receipt of Reply Message
If the client includes a Rapid Commit option in the Solicit message,
it will expect a Reply message that includes a Rapid Commit option in
response. The client discards any Reply messages it receives that do
not include a Rapid Commit option. If the client receives a valid
Reply message that includes a Rapid Commit option, it processes the
message as described in Section 19.1.8. If it does not receive such
a Reply message and does receive a valid Advertise message, the
client processes the Advertise message as described in
Section 18.1.3.
If the client subsequently receives a valid Reply message that
includes a Rapid Commit option, it either:
- processes the Reply message as described in Section 19.1.8, and
discards any Reply messages received in response to the Request
message, or
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- processes any Reply messages received in response to the Request
message and discards the Reply message that includes the Rapid
Commit option.
18.2. Server Behavior
A server sends an Advertise message in response to valid Solicit
messages it receives to announce the availability of the server to
the client.
18.2.1. Receipt of Solicit Messages
The server determines the information about the client and its
location as described in Section 12 and checks its administrative
policy about responding to the client. If the server is not
permitted to respond to the client, the server discards the Solicit
message. For example, if the administrative policy for the server is
that it may only respond to a client that is willing to accept a
Reconfigure message, if the client does not include a Reconfigure
Accept option (see Section 23.20) in the Solicit message, the servers
discard the Solicit message.
If the client has included a Rapid Commit option in the Solicit
message and the server has been configured to respond with committed
address assignments and other resources, the server responds to the
Solicit with a Reply message as described in Section 18.2.3.
Otherwise, the server ignores the Rapid Commit option and processes
the remainder of the message as if no Rapid Commit option were
present.
18.2.2. Creation and Transmission of Advertise Messages
The server sets the "msg-type" field to ADVERTISE and copies the
contents of the transaction-id field from the Solicit message
received from the client to the Advertise message. The server
includes its server identifier in a Server Identifier option and
copies the Client Identifier from the Solicit message into the
Advertise message.
The server MAY add a Preference option to carry the preference value
for the Advertise message. The server implementation SHOULD allow
the setting of a server preference value by the administrator. The
server preference value MUST default to zero unless otherwise
configured by the server administrator.
The server includes a Reconfigure Accept option if the server wants
to require that the client accept Reconfigure messages.
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The server includes options the server will return to the client in a
subsequent Reply message. The information in these options may be
used by the client in the selection of a server if the client
receives more than one Advertise message. If the client has included
an Option Request option in the Solicit message, the server includes
options in the Advertise message containing configuration parameters
for all of the options identified in the Option Request option that
the server has been configured to return to the client. The server
MAY return additional options to the client if it has been configured
to do so. The server must be aware of the recommendations on packet
sizes and the use of fragmentation in section 5 of [RFC2460].
If the Solicit message from the client included one or more IA
options, the server MUST include IA options in the Advertise message
containing any addresses that would be assigned to IAs contained in
the Solicit message from the client. If the client has included
addresses in the IAs in the Solicit message, the server uses those
addresses as hints about the addresses the client would like to
receive.
If the server will not assign any addresses to any IAs in a
subsequent Request from the client, the server MUST send an Advertise
message to the client that includes only a Status Code option with
code NoAddrsAvail and a status message for the user, a Server
Identifier option with the server's DUID, a Client Identifier option
with the client's DUID, and (optionally) SOL_MAX_RT and/or INF_MAX_RT
options. The server SHOULD include other stateful IA options (like
IA_PD) and other configuration options in the Advertise 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 on the link from which the Solicit message was received.
If the Solicit message was received in a Relay-forward message, the
server constructs a Relay-reply message with the Advertise message in
the payload of a "relay-message" option. If the Relay-forward
messages included an Interface-id option, the server copies that
option to the Relay-reply message. The server unicasts the Relay-
reply message directly to the relay agent using the address in the
source address field from the IP datagram in which the Relay-forward
message was received.
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18.2.3. Creation and Transmission of Reply Messages
The server MUST commit the assignment of any addresses or other
configuration information message before sending a Reply message to a
client in response to a Solicit message.
DISCUSSION:
When using the Solicit-Reply message exchange, the server commits
the assignment of any addresses before sending the Reply message.
The client can assume it has been assigned the addresses in the
Reply message and does not need to send a Request message for
those addresses.
Typically, servers that are configured to use the Solicit-Reply
message exchange will be deployed so that only one server will
respond to a Solicit message. If more than one server responds,
the client will only use the addresses from one of the servers,
while the addresses from the other servers will be committed to
the client but not used by the client.
The server includes a Rapid Commit option in the Reply message to
indicate that the Reply is in response to a Solicit message.
The server includes a Reconfigure Accept option if the server wants
to require that the client accept Reconfigure messages.
The server produces the Reply message as though it had received a
Request message, as described in Section 19.2.1. The server
transmits the Reply message as described in Section 19.2.8.
18.3. Client behavior for Prefix Delegation
The requesting router creates and transmits a Solicit message as
described in Section 18.1.1 and Section 18.1.2. The client creates
an IA_PD and assigns it an IAID. The client MUST include the IA_PD
option in the Solicit message.
The client processes any received Advertise messages as described in
Section 18.1.3. The client MAY choose to consider the presence of
advertised prefixes in its decision about which delegating router to
respond to.
The client MUST ignore any IA_PDs in an Advertise message that
include a Status Code option containing the value NoPrefixAvail, with
the exception that the client MAY display the associated status
message to the user and SHOULD process SOL_MAX_RT and INF_MAX_RT
options.
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18.4. Server Behavior for Prefix Delegation
The server sends an Advertise message to the requesting router in the
same way as described in Section 18.2.2. If the message contains an
IA_PD option and the delegating router is configured to delegate
prefix(es) to the requesting router, the delegating router selects
the prefix(es) to be delegated to the requesting router. The
mechanism through which the delegating router selects prefix(es) for
delegation is not specified in this document. Examples of ways in
which the server might select prefix(es) for a client include: static
assignment based on subscription to an ISP; dynamic assignment from a
pool of available prefixes; selection based on an external authority
such as a RADIUS server using the Framed-IPv6-Prefix option as
described in [RFC3162].
If the client includes an IA_PD Prefix option in the IA_PD option in
its Solicit message, the server MAY choose to use the information in
that option to select the prefix(es) or prefix size to be delegated
to the client.
The server sends an Advertise message to the requesting router in the
same way as described in Section 18.2.2. The server MUST include an
IA_PD option, identifying any prefix(es) that the server will
delegate to the client.
If the server will not assign any prefixes to an IA_PD in a
subsequent Request from the requesting router, the server MUST send
an Advertise message to the client that includes the IA_PD with no
prefixes in the IA_PD and a Status Code option in the IA_PD
containing status code NoPrefixAvail and a status message for the
user, a Server Identifier option with the server's DUID and a Client
Identifier option with the client's DUID. The server SHOULD include
other stateful IA options (like IA_NA) and other configuration
options in the Advertise message.
19. DHCP Client-Initiated Configuration Exchange
A client initiates a message exchange with a server or servers to
acquire or update configuration information of interest. The client
may initiate the configuration exchange as part of the operating
system configuration process, when requested to do so by the
application layer, when required by Stateless Address
Autoconfiguration or as required to extend the lifetime of
address(es) or/and delegated prefix(es), using Renew and Rebind
messages.
According to a terminology for the prefix delegation, a client
requesting a delegation of a prefix is referred to as a requesting
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router and a server delegating the prefix is referred to as a
delegating router. The requesting router and the delegating router
use the IA_PD Prefix option to exchange information about prefix(es)
in much the same way as IA Address options are used for assigned
addresses. Typically, a single DHCP session is used to exchange
information about addresses and prefixes, i.e. IA_NA and IA_PD
options are carried in the same message.
19.1. Client Behavior
A client uses Request, Renew, Rebind, Release and Decline messages
during the normal life cycle of addresses. It uses Confirm to
validate addresses when it may have moved to a new link. It uses
Information-Request messages when it needs configuration information
but no addresses.
If the client has a source address of sufficient scope that can be
used by the server as a return address, and the client has received a
Server Unicast option (Section 23.12) from the server, the client
SHOULD unicast any Request, Renew, Release and Decline messages to
the server.
DISCUSSION:
Use of unicast may avoid delays due to the relaying of messages by
relay agents, as well as avoid overhead and duplicate responses by
servers due to the delivery of client messages to multiple
servers. Requiring the client to relay all DHCP messages through
a relay agent enables the inclusion of relay agent options in all
messages sent by the client. The server should enable the use of
unicast only when relay agent options will not be used.
19.1.1. Creation and Transmission of Request Messages
The client uses a Request message to populate IAs with addresses and
obtain other configuration information. The client includes one or
more IA options in the Request message. The server then returns
addresses and other information about the IAs to the client in IA
options in a Reply message.
The client generates a transaction ID and inserts this value in the
"transaction-id" field.
The client places the identifier of the destination server in a
Server Identifier option.
The client MUST include a Client Identifier option to identify itself
to the server. The client adds any other appropriate options,
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including one or more IA options (if the client is requesting that
the server assign it some network addresses).
The client MUST include an Option Request option (see Section 23.7)
to indicate the options the client is interested in receiving. The
client MAY include options with data values as hints to the server
about parameter values the client would like to have returned.
The client includes a Reconfigure Accept option (see Section 23.20)
indicating whether or not the client is willing to accept Reconfigure
messages from the server.
The client transmits the message according to Section 15, using the
following parameters:
IRT REQ_TIMEOUT
MRT REQ_MAX_RT
MRC REQ_MAX_RC
MRD 0
If the message exchange fails, the client takes an action based on
the client's local policy. Examples of actions the client might take
include:
- Select another server from a list of servers known to the client;
for example, servers that responded with an Advertise message.
- Initiate the server discovery process described in Section 18.
- Terminate the configuration process and report failure.
19.1.2. Creation and Transmission of Confirm Messages
Whenever a client may have moved to a new link, the prefixes/
addresses assigned to the interfaces on that link may no longer be
appropriate for the link to which the client is attached. Examples
of times when a client may have moved to a new link include:
o The client reboots.
o The client is physically connected to a wired connection.
o The client returns from sleep mode.
o The client using a wireless technology changes access points.
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In any situation when a client may have moved to a new link, the
client SHOULD initiate a Confirm/Reply message exchange. The client
includes any IAs assigned to the interface that may have moved to a
new link, along with the addresses associated with those IAs, in its
Confirm message. Any responding servers will indicate whether those
addresses are appropriate for the link to which the client is
attached with the status in the Reply message it returns to the
client.
One example when this rule may not be followed is when the client
does not store its leases in stable storage and experiences a reboot.
It may simply not retain any information, so it does not know what to
confirm. In such case client MUST restart server discovery process
as described in Section 18.1.1.
The client sets the "msg-type" field to CONFIRM. The client
generates a transaction ID and inserts this value in the
"transaction-id" field.
The client MUST include a Client Identifier option to identify itself
to the server. The client includes IA options for all of the IAs
assigned to the interface for which the Confirm message is being
sent. The IA options include all of the addresses the client
currently has associated with those IAs. The client SHOULD set the
T1 and T2 fields in any IA_NA options, and the preferred-lifetime and
valid-lifetime fields in the IA Address options to 0, as the server
will ignore these fields.
The first Confirm message from the client on the interface MUST be
delayed by a random amount of time between 0 and CNF_MAX_DELAY. The
client transmits the message according to Section 15, using the
following parameters:
IRT CNF_TIMEOUT
MRT CNF_MAX_RT
MRC 0
MRD CNF_MAX_RD
If the client receives no responses before the message transmission
process terminates, as described in Section 15, 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.
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19.1.3. Creation and Transmission of Renew Messages
To extend the valid and preferred lifetimes for the addresses
associated with an IA, the client sends a Renew message to the server
from which the client obtained the addresses in the IA containing an
IA option for the IA. The client includes IA Address options in the
IA option for the addresses associated with the IA. The server
determines new lifetimes for the addresses in the IA according to the
administrative configuration of the server. The server may also add
new addresses to the IA. The server may remove addresses from the IA
by setting the preferred and valid lifetimes of those addresses to
zero.
The server controls the time at which the client contacts the server
to extend the lifetimes on assigned addresses through the T1 and T2
parameters assigned to an IA.
At time T1 for an IA, the client initiates a Renew/Reply message
exchange to extend the lifetimes on any addresses in the IA. The
client includes an IA option with all addresses currently assigned to
the IA in its Renew message.
If T1 or T2 is set to 0 by the server (for an IA_NA) or there are no
T1 or T2 times (for an IA_TA), the client may send a Renew or Rebind
message, respectively, at the client's discretion.
The client sets the "msg-type" field to RENEW. The client generates
a transaction ID and inserts this value in the "transaction-id"
field.
The client places the identifier of the destination server in a
Server Identifier option.
The client MUST include a Client Identifier option to identify itself
to the server. The client adds any appropriate options, including
one or more IA options. The client MUST include the list of
addresses the client currently has associated with the IAs in the
Renew message.
The client MUST include an Option Request option (see Section 23.7)
to indicate the options the client is interested in receiving. The
client MAY include options with data values as hints to the server
about parameter values the client would like to have returned.
The client transmits the message according to Section 15, using the
following parameters:
IRT REN_TIMEOUT
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MRT REN_MAX_RT
MRC 0
MRD Remaining time until T2
The message exchange is terminated when time T2 is reached (see
Section 19.1.4), at which time the client begins a Rebind message
exchange.
19.1.4. Creation and Transmission of Rebind Messages
At time T2 for an IA (which will only be reached if the server to
which the Renew message was sent at time T1 has not responded), the
client initiates a Rebind/Reply message exchange with any available
server. The client includes an IA option with all addresses
currently assigned to the IA in its Rebind message.
The client sets the "msg-type" field to REBIND. The client generates
a transaction ID and inserts this value in the "transaction-id"
field.
The client MUST include a Client Identifier option to identify itself
to the server. The client adds any appropriate options, including
one or more IA options. The client MUST include the list of
addresses the client currently has associated with the IAs in the
Rebind message.
The client MUST include an Option Request option (see Section 23.7)
to indicate the options the client is interested in receiving. The
client MAY include options with data values as hints to the server
about parameter values the client would like to have returned.
The client transmits the message according to Section 15, using the
following parameters:
IRT REB_TIMEOUT
MRT REB_MAX_RT
MRC 0
MRD Remaining time until valid lifetimes of all addresses have
expired
The message exchange is terminated when the valid lifetimes of all
the addresses assigned to the IA expire (see Section 11), at which
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time the client has several alternative actions to choose from; for
example:
- The client may choose to use a Solicit message to locate a new
DHCP server and send a Request for the expired IA to the new
server.
- The client may have other addresses in other IAs, so the client
may choose to discard the expired IA and use the addresses in the
other IAs.
19.1.5. Creation and Transmission of Information-request Messages
The client uses an Information-request message to obtain
configuration information without having addresses assigned to it.
The client sets the "msg-type" field to INFORMATION-REQUEST. The
client generates a transaction ID and inserts this value in the
"transaction-id" field.
The client SHOULD include a Client Identifier option to identify
itself to the server. If the client does not include a Client
Identifier option, the server will not be able to return any client-
specific options to the client, or the server may choose not to
respond to the message at all. The client MUST include a Client
Identifier option if the Information-Request message will be
authenticated.
The client MUST include an Option Request option (see Section 23.7)
to request the INF_MAX_RT option (see Section 23.24) and any other
options the client is interested in receiving. The client MAY
include options with data values as hints to the server about
parameter values the client would like to have returned.
The first Information-request message from the client on the
interface MUST be delayed by a random amount of time between 0 and
INF_MAX_DELAY. The client transmits the message according to
Section 15, using the following parameters:
IRT INF_TIMEOUT
MRT INF_MAX_RT
MRC 0
MRD 0
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19.1.6. Creation and Transmission of Release Messages
To release one or more addresses, a client sends a Release message to
the server.
The client sets the "msg-type" field to RELEASE. The client
generates a transaction ID and places this value in the "transaction-
id" field.
The client places the identifier of the server that allocated the
address(es) in a Server Identifier option.
The client MUST include a Client Identifier option to identify itself
to the server. The client includes options containing the IAs for
the addresses it is releasing in the "options" field. The addresses
to be released MUST be included in the IAs. Any addresses for the
IAs the client wishes to continue to use MUST NOT be added to the
IAs.
The client MUST NOT use any of the addresses it is releasing as the
source address in the Release message or in any subsequently
transmitted message.
Because Release messages may be lost, the client should retransmit
the Release if no Reply is received. However, there are scenarios
where the client may not wish to wait for the normal retransmission
timeout before giving up (e.g., on power down). Implementations
SHOULD retransmit one or more times, but MAY choose to terminate the
retransmission procedure early.
The client transmits the message according to Section 15, using the
following parameters:
IRT REL_TIMEOUT
MRT 0
MRC REL_MAX_RC
MRD 0
The client MUST stop using all of the addresses being released as
soon as the client begins the Release message exchange process. If
addresses are released but the Reply from a DHCP server is lost, the
client will retransmit the Release message, and the server may
respond with a Reply indicating a status of NoBinding. Therefore,
the client does not treat a Reply message with a status of NoBinding
in a Release message exchange as if it indicates an error.
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Note that if the client fails to release the addresses, each address
assigned to the IA will be reclaimed by the server when the valid
lifetime of that address expires.
19.1.7. Creation and Transmission of Decline Messages
If a client detects that one or more addresses assigned to it by a
server are already in use by another node, the client sends a Decline
message to the server to inform it that the address is suspect.
The client sets the "msg-type" field to DECLINE. The client
generates a transaction ID and places this value in the "transaction-
id" field.
The client places the identifier of the server that allocated the
address(es) in a Server Identifier option.
The client MUST include a Client Identifier option to identify itself
to the server. The client includes options containing the IAs for
the addresses it is declining in the "options" field. The addresses
to be declined MUST be included in the IAs. Any addresses for the
IAs the client wishes to continue to use should not be in added to
the IAs.
The client MUST NOT use any of the addresses it is declining as the
source address in the Decline message or in any subsequently
transmitted message.
The client transmits the message according to Section 15, using the
following parameters:
IRT DEC_TIMEOUT
MRT 0
MRC DEC_MAX_RC
MRD 0
If addresses are declined but the Reply from a DHCP server is lost,
the client will retransmit the Decline message, and the server may
respond with a Reply indicating a status of NoBinding. Therefore,
the client does not treat a Reply message with a status of NoBinding
in a Decline message exchange as if it indicates an error.
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19.1.8. Receipt of Reply Messages
Upon the receipt of a valid Reply message in response to a Solicit
(with a Rapid Commit option), Request, Confirm, Renew, Rebind or
Information-request message, the client extracts the configuration
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 [RFC4862] on
each of the addresses in any IAs it receives in the Reply message
before using that address for traffic. If any of the addresses are
found to be in use on the link, the client sends a Decline message to
the server as described in Section 19.1.7.
If the Reply was received in response to a Solicit (with a Rapid
Commit option), Request, Renew or Rebind message, the client updates
the information it has recorded about IAs from the IA options
contained in the Reply message:
- Record T1 and T2 times.
- Add any new addresses in the IA option to the IA as recorded by
the client.
- Update lifetimes for any addresses in the IA option that the
client already has recorded in the IA.
- Discard any addresses from the IA, as recorded by the client, that
have a valid lifetime of 0 in the IA Address option.
- Leave unchanged any information about addresses the client has
recorded in the IA but that were not included in the IA from the
server.
Management of the specific configuration information is detailed in
the definition of each option in Section 23.
If the client receives a Reply message with a Status Code containing
UnspecFail, the server is indicating that it was unable to process
the message due to an unspecified failure condition. If the client
retransmits the original message to the same server to retry the
desired operation, the client MUST limit the rate at which it
retransmits the message and limit the duration of the time during
which it retransmits the message (see Section 14.1).
When the client receives a Reply message with a Status Code option
with the value UseMulticast, the client records the receipt of the
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message and sends subsequent messages to the server through the
interface on which the message was received using multicast. The
client resends the original message using multicast.
When the client receives a NotOnLink status from the server in
response to a Confirm message, the client performs DHCP server
solicitation, as described in Section 18, and client-initiated
configuration as described in Section 19. If the client receives any
Reply messages that do not indicate a NotOnLink status, the client
can use the addresses in the IA and ignore any messages that indicate
a NotOnLink status.
When the client receives a NotOnLink status from the server in
response to a Solicit (with a Rapid Commit option) or a Request, the
client can either re-issue the Request without specifying any
addresses or restart the DHCP server discovery process (see
Section 18).
The client examines the status code in each IA individually. If the
status code is NoAddrsAvail, the client has received no usable
addresses in the IA and may choose to try obtaining addresses for the
IA from another server. The client uses addresses and other
information from any IAs that do not contain a Status Code option
with the NoAddrsAvail code. If the client receives no addresses in
any of the IAs, it may either try another server (perhaps restarting
the DHCP server discovery process) or use the Information-request
message to obtain other configuration information only.
Whenever a client restarts the DHCP server discovery process or
selects an alternate server, as described in Section 18.1.3, the
client SHOULD stop using all the addresses and delegated prefixes for
which it has the bindings and try to obtain all required adresses and
prefixes from the new server. This facilitates the client using a
single state machine for all bindings.
When the client receives a Reply message in response to a Renew or
Rebind message, the client examines each IA independently. For each
IA in the original Renew or Rebind message, the client:
- sends a Request message if the IA contained a Status Code option
with the NoBinding status (and does not send any additional Renew/
Rebind messages)
- sends a Renew/Rebind if the IA is not in the Reply message
- otherwise accepts the information in the IA
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When the client receives a valid Reply message in response to a
Release message, the client considers the Release event completed,
regardless of the Status Code option(s) returned by the server.
When the client receives a valid Reply message in response to a
Decline message, the client considers the Decline event completed,
regardless of the Status Code option(s) returned by the server.
19.2. Server Behavior
For this discussion, the Server is assumed to have been configured in
an implementation specific manner with configuration of interest to
clients.
In most instances, the server will send a Reply in response to a
client message. This Reply message MUST always contain the Server
Identifier option containing the server's DUID and the Client
Identifier option from the client message if one was present.
In most Reply messages, the server includes options containing
configuration information for the client. The server must be aware
of the recommendations on packet sizes and the use of fragmentation
in section 5 of [RFC2460]. If the client included an Option Request
option in its message, the server includes options in the Reply
message containing configuration parameters for all of the options
identified in the Option Request option that the server has been
configured to return to the client. The server MAY return additional
options to the client if it has been configured to do so.
19.2.1. Receipt of Request Messages
When the server receives a Request message via unicast from a client
to which the server has not sent a unicast option, the server
discards the Request message and responds with a Reply message
containing a Status Code option with the value UseMulticast, a Server
Identifier option containing the server's DUID, the Client Identifier
option from the client message, and no other options.
When the server receives a valid Request message, the server creates
the bindings for that client according to the server's policy and
configuration information and records the IAs and other information
requested by the client.
The server constructs a Reply message by setting the "msg-type" field
to REPLY, and copying the transaction ID from the Request message
into the transaction-id field.
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The server MUST include a Server Identifier option containing the
server's DUID and the Client Identifier option from the Request
message in the Reply message.
If the server finds that the prefix on one or more IP addresses in
any IA in the message from the client is not appropriate for the link
to which the client is connected, the server MUST return the IA to
the client with a Status Code option with the value NotOnLink.
If the server cannot assign any addresses to an IA in the message
from the client, the server MUST include the IA in the Reply message
with no addresses in the IA and a Status Code option in the IA
containing status code NoAddrsAvail.
For any IAs to which the server can assign addresses, the server
includes the IA with addresses and other configuration parameters,
and records the IA as a new client binding.
The server includes a Reconfigure Accept option if the server wants
to require that the client accept Reconfigure messages.
The server includes other options containing configuration
information to be returned to the client as described in
Section 19.2.
If the server finds that the client has included an IA in the Request
message for which the server already has a binding that associates
the IA with the client, the client has resent a Request message for
which it did not receive a Reply message. The server either resends
a previously cached Reply message or sends a new Reply message.
19.2.2. Receipt of Confirm Messages
When the server receives a Confirm message, the server determines
whether the addresses in the Confirm message are appropriate for the
link to which the client is attached. If all of the addresses in the
Confirm message pass this test, the server returns a status of
Success. If any of the addresses do not pass this test, the server
returns a status of NotOnLink. If the server is unable to perform
this test (for example, the server does not have information about
prefixes on the link to which the client is connected), or there were
no addresses in any of the IAs sent by the client, the server MUST
NOT send a reply to the client.
The server ignores the T1 and T2 fields in the IA options and the
preferred-lifetime and valid-lifetime fields in the IA Address
options.
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The server constructs a Reply message by setting the "msg-type" field
to REPLY, and copying the transaction ID from the Confirm message
into the transaction-id field.
The server MUST include a Server Identifier option containing the
server's DUID and the Client Identifier option from the Confirm
message in the Reply message. The server includes a Status Code
option indicating the status of the Confirm message.
19.2.3. Receipt of Renew Messages
When the server receives a Renew message via unicast from a client to
which the server has not sent a unicast option, the server discards
the Renew message and responds with a Reply message containing a
Status Code option with the value UseMulticast, a Server Identifier
option containing the server's DUID, the Client Identifier option
from the client message, and no other options.
When the server receives a Renew message that contains an IA option
from a client, it locates the client's binding and verifies that the
information in the IA from the client matches the information stored
for that client.
If the server cannot find a client entry for the IA the server
returns the IA containing no addresses with a Status Code option set
to NoBinding in the Reply message.
If the server finds that any of the addresses are not appropriate for
the link to which the client is attached, the server returns the
address to the client with lifetimes of 0.
If the server finds the addresses in the IA for the client then the
server sends back the IA to the client with new lifetimes and T1/T2
times. The server may choose to change the list of addresses and the
lifetimes of addresses in IAs that are returned to the client.
The server constructs a Reply message by setting the "msg-type" field
to REPLY, and copying the transaction ID from the Renew message into
the transaction-id field.
The server MUST include a Server Identifier option containing the
server's DUID and the Client Identifier option from the Renew message
in the Reply message.
The server includes other options containing configuration
information to be returned to the client as described in
Section 19.2.
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19.2.4. Receipt of Rebind Messages
When the server receives a Rebind message that contains an IA option
from a client, it locates the client's binding and verifies that the
information in the IA from the client matches the information stored
for that client.
If the server cannot find a client entry for the IA and the server
determines that the addresses in the IA are not appropriate for the
link to which the client's interface is attached according to the
server's explicit configuration information, the server MAY send a
Reply message to the client containing the client's IA, with the
lifetimes for the addresses in the IA set to zero. This Reply
constitutes an explicit notification to the client that the addresses
in the IA are no longer valid. In this situation, if the server does
not send a Reply message it discards the Rebind message.
If the server finds that any of the addresses are no longer
appropriate for the link to which the client is attached, the server
returns the address to the client with lifetimes of 0.
If the server finds the addresses in the IA for the client then the
server SHOULD send back the IA to the client with new lifetimes and
T1/T2 times.
The server constructs a Reply message by setting the "msg-type" field
to REPLY, and copying the transaction ID from the Rebind message into
the transaction-id field.
The server MUST include a Server Identifier option containing the
server's DUID and the Client Identifier option from the Rebind
message in the Reply message.
The server includes other options containing configuration
information to be returned to the client as described in
Section 19.2.
19.2.5. Receipt of Information-request Messages
When the server receives an Information-request message, the client
is requesting configuration information that does not include the
assignment of any addresses. The server determines all configuration
parameters appropriate to the client, based on the server
configuration policies known to the server.
The server constructs a Reply message by setting the "msg-type" field
to REPLY, and copying the transaction ID from the Information-request
message into the transaction-id field.
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The server MUST include a Server Identifier option containing the
server's DUID in the Reply message. If the client included a Client
Identification option in the Information-request message, the server
copies that option to the Reply message.
The server includes options containing configuration information to
be returned to the client as described in Section 19.2.
If the Information-request message received from the client did not
include a Client Identifier option, the server SHOULD respond with a
Reply message containing any configuration parameters that are not
determined by the client's identity. If the server chooses not to
respond, the client may continue to retransmit the Information-
request message indefinitely.
19.2.6. Receipt of Release Messages
When the server receives a Release message via unicast from a client
to which the server has not sent a unicast option, the server
discards the Release message and responds with a Reply message
containing a Status Code option with value UseMulticast, a Server
Identifier option containing the server's DUID, the Client Identifier
option from the client message, and no other options.
Upon the receipt of a valid Release message, the server examines the
IAs and the addresses in the IAs for validity. If the IAs in the
message are in a binding for the client, and the addresses in the IAs
have been assigned by the server to those IAs, the server deletes the
addresses from the IAs and makes the addresses available for
assignment to other clients. The server ignores addresses not
assigned to the IA, although it may choose to log an error.
After all the addresses have been processed, the server generates a
Reply message and includes a Status Code option with value Success, a
Server Identifier option with the server's DUID, and a Client
Identifier option with the client's DUID. For each IA in the Release
message for which the server has no binding information, the server
adds an IA option using the IAID from the Release message, and
includes a Status Code option with the value NoBinding in the IA
option. No other options are included in the IA option.
A server may choose to retain a record of assigned addresses and IAs
after the lifetimes on the addresses have expired to allow the server
to reassign the previously assigned addresses to a client.
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19.2.7. Receipt of Decline Messages
When the server receives a Decline message via unicast from a client
to which the server has not sent a unicast option, the server
discards the Decline message and responds with a Reply message
containing a Status Code option with the value UseMulticast, a Server
Identifier option containing the server's DUID, the Client Identifier
option from the client message, and no other options.
Upon the receipt of a valid Decline message, the server examines the
IAs and the addresses in the IAs for validity. If the IAs in the
message are in a binding for the client, and the addresses in the IAs
have been assigned by the server to those IAs, the server deletes the
addresses from the IAs. The server ignores addresses not assigned to
the IA (though it may choose to log an error if it finds such an
address).
The client has found any addresses in the Decline messages to be
already in use on its link. Therefore, the server SHOULD mark the
addresses declined by the client so that those addresses are not
assigned to other clients, and MAY choose to make a notification that
addresses were declined. Local policy on the server determines when
the addresses identified in a Decline message may be made available
for assignment.
After all the addresses have been processed, the server generates a
Reply message and includes a Status Code option with the value
Success, a Server Identifier option with the server's DUID, and a
Client Identifier option with the client's DUID. For each IA in the
Decline message for which the server has no binding information, the
server adds an IA option using the IAID from the Decline message and
includes a Status Code option with the value NoBinding in the IA
option. No other options are included in the IA option.
19.2.8. Transmission of Reply Messages
If the original message was received directly by the server, the
server unicasts the Reply message directly to the client using the
address in the source address field from the IP datagram in which the
original message was received. The Reply message MUST be unicast
through the interface on which the original message was received.
If the original message was received in a Relay-forward message, the
server constructs a Relay-reply message with the Reply message in the
payload of a Relay Message option (see Section 23.10). If the Relay-
forward messages included an Interface-id option, the server copies
that option to the Relay-reply message. The server unicasts the
Relay-reply message directly to the relay agent using the address in
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the source address field from the IP datagram in which the Relay-
forward message was received.
19.3. Requesting Router Behavior for Prefix Delegation
The requesting router uses a Request message to populate IA_PDs with
prefixes. The requesting router includes one or more IA_PD options
in the Request message. The delegating router then returns the
prefixes for the IA_PDs to the requesting router in IA_PD options in
a Reply message.
The requesting router includes IA_PD options in any Renew, or Rebind
messages sent by the requesting router. The IA_PD option includes
all of the prefixes the requesting router currently has associated
with that IA_PD.
In some circumstances the requesting router may need verification
that the delegating router still has a valid binding for the
requesting router. Examples of times when a requesting router may
ask for such verification include:
o The requesting router reboots.
o The requesting router's upstream link flaps.
o The requesting router is physically disconnected from a wired
connection.
If such verification is needed the requesting router MUST initiate a
Rebind/Reply message exchange as described in section Section 19.1.4,
with the exception that the retransmission parameters should be set
as for the Confirm message, described in Section 19.1.2. The
requesting router includes any IA_PDs, along with prefixes associated
with those IA_PDs in its Rebind message.
Each prefix has valid and preferred lifetimes whose durations are
specified in the IA_PD Prefix option for that prefix. The requesting
router uses Renew and Rebind messages to request the extension of the
lifetimes of a delegated prefix.
The requesting router uses a Release message to return a delegated
prefix to a delegating router. The prefixes to be released MUST be
included in the IA_PDs.
The Confirm and Decline message types are not used with Prefix
Delegation.
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Upon the receipt of a valid Reply message, for each IA_PD the
requesting router assigns a subnet from each of the delegated
prefixes to each of the links to which the associated interfaces are
attached.
When the Delegating Router delegates prefixes to a Requesting Router,
the Requesting Router has sole authority for assignment of those
prefixes, and the Delegating Router MUST NOT assign any prefixes from
that delegated prefix to any of its own links.
When a requesting router subnets a delegated prefix, it must assign
additional bits to the prefix to generate unique, longer prefixes.
For example, if the requesting router in Figure 1 were delegated
3FFE:FFFF:0::/48, it might generate 3FFE:FFFF:0:1::/64 and
3FFE:FFFF:0:2::/64 for assignment to the two links in the subscriber
network. If the requesting router were delegated 3FFE:FFFF:0::/48
and 3FFE:FFFF:5::/48, it might assign 3FFE:FFFF:0:1::/64 and
3FFE:FFFF:5:1::/64 to one of the links, and 3FFE:FFFF:0:2::/64 and
3FFE:FFFF:5:2::/64 for assignment to the other link.
If the requesting router assigns a delegated prefix to a link to
which the router is attached, and begins to send router
advertisements for the prefix on the link, the requesting router MUST
set the valid lifetime in those advertisements to be no later than
the valid lifetime specified in the IA_PD Prefix option. A
requesting router MAY use the preferred lifetime specified in the
IA_PD Prefix option.
Handling of Status Codes options in received Reply messages is
described in section Section 19.1.8. The NoPrefixAvail Status Code
is handled in the same manner as the NoAddrsAvail Status Code.
19.4. Delegating Router Behavior for Prefix Delegation
When a delegating router receives a Request message from a requesting
router that contains an IA_PD option, and the delegating router is
authorized to delegate prefix(es) to the requesting router, the
delegating router selects the prefix(es) to be delegated to the
requesting router. The mechanism through which the delegating router
selects prefix(es) for delegation is not specified in this document.
Section 18.4 gives examples of ways in which a delegating router
might select the prefix(es) to be delegated to a requesting router.
A delegating router examines the prefix(es) identified in IA_PD
Prefix options (in an IA_PD option) in Renew and Rebind messages and
responds according to the current status of the prefix(es). The
delegating router returns IA_PD Prefix options (within an IA_PD
option) with updated lifetimes for each valid prefix in the message
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from the requesting router. If the delegating router finds that any
of the prefixes are not in the requesting router's binding entry, the
delegating router returns the prefix to the requesting router with
lifetimes of 0.
The delegating router behaves as follows when it cannot find a
binding for the requesting router's IA_PD:
Renew message: If the delegating router cannot find a binding
for the requesting router's IA_PD the delegating
router returns the IA_PD containing no prefixes
with a Status Code option set to NoBinding in the
Reply message.
Rebind message: If the delegating router cannot find a binding
for the requesting router's IA_PD and the
delegating router determines that the prefixes in
the IA_PD are not appropriate for the link to
which the requesting router's interface is
attached according to the delegating routers
explicit configuration, the delegating router MAY
send a Reply message to the requesting router
containing the IA_PD with the lifetimes of the
prefixes in the IA_PD set to zero. This Reply
constitutes an explicit notification to the
requesting router that the prefixes in the IA_PD
are no longer valid. If the delegating router is
unable to determine if the prefix is not
appropriate for the link, the Rebind message is
discarded.
A delegating router may mark any prefix(es) in IA_PD Prefix options
in a Release message from a requesting router as "available",
dependent on the mechanism used to acquire the prefix, e.g., in the
case of a dynamic pool.
The delegating router MUST include an IA_PD Prefix option or options
(in an IA_PD option) in Reply messages sent to a requesting router.
20. 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.
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20.1. Server Behavior
A server sends a Reconfigure message to cause a client to initiate
immediately a Renew/Reply or Information-request/Reply message
exchange with the server.
20.1.1. Creation and Transmission of Reconfigure Messages
The server sets the "msg-type" field to RECONFIGURE. The server sets
the transaction-id field to 0. The server includes a Server
Identifier option containing its DUID and a Client Identifier option
containing the client's DUID in the Reconfigure message.
The server MAY include an Option Request option to inform the client
of what information has been changed or new information that has been
added. In particular, the server specifies the IA option in the
Option Request option if the server wants the client to obtain new
address information. If the server identifies the IA option in the
Option Request option, the server MUST include an IA option to
identify each IA that is to be reconfigured on the client. The IA
options included by the server MUST NOT contain any options.
Because of the risk of denial of service attacks against DHCP
clients, the use of a security mechanism is mandated in Reconfigure
messages. The server MUST use DHCP authentication in the Reconfigure
message.
The server MUST include a Reconfigure Message option (defined in
Section 23.19) to select whether the client responds with a Renew
message, a Rebind message, or an Information-Request message.
The server MUST NOT include any other options in the Reconfigure
except as specifically allowed in the definition of individual
options.
A server sends each Reconfigure message to a single DHCP client,
using an IPv6 unicast address of sufficient scope belonging to the
DHCP client. If the server does not have an address to which it can
send the Reconfigure message directly to the client, the server uses
a Relay-reply message (as described in Section 21.3) to send the
Reconfigure message to a relay agent that will relay the message to
the client. The server may obtain the address of the client (and the
appropriate relay agent, if required) through the information the
server has about clients that have been in contact with the server,
or through some external agent.
To reconfigure more than one client, the server unicasts a separate
message to each client. The server may initiate the reconfiguration
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of multiple clients concurrently; for example, a server may send a
Reconfigure message to additional clients while previous
reconfiguration message exchanges are still in progress.
The Reconfigure message causes the client to initiate a Renew/Reply,
a Rebind/Reply, or Information-request/Reply message exchange with
the server. The server interprets the receipt of a Renew, a Rebind,
or Information-request message (whichever was specified in the
original Reconfigure message) from the client as satisfying the
Reconfigure message request.
20.1.2. Time Out and Retransmission of Reconfigure Messages
If the server does not receive a Renew, Rebind, or Information-
request message from the client in REC_TIMEOUT milliseconds, the
server retransmits the Reconfigure message, doubles the REC_TIMEOUT
value and waits again. The server continues this process until
REC_MAX_RC unsuccessful attempts have been made, at which point the
server SHOULD abort the reconfigure process for that client.
Default and initial values for REC_TIMEOUT and REC_MAX_RC are
documented in Section 6.5.
20.2. Receipt of Renew or Rebind Messages
In response to a Renew message, the server generates and sends a
Reply message to the client as described in Section 19.2.3 and
Section 19.2.8, including options for configuration parameters.
In response to a Rebind message, the server generates and sends a
Reply message to the client as described in Section 19.2.4 and
Section 19.2.8, including options for configuration parameters.
The server MAY include options containing the IAs and new values for
other configuration parameters in the Reply message, even if those
IAs and parameters were not requested in the Renew or Rebind message
from the client.
20.3. Receipt of Information-request Messages
The server generates and sends a Reply message to the client as
described in Section 19.2.5 and Section 19.2.8, including options for
configuration parameters.
The server MAY include options containing new values for other
configuration parameters in the Reply message, even if those
parameters were not requested in the Information-request message from
the client.
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20.4. Client Behavior
A client receives Reconfigure messages sent to the UDP port 546 on
interfaces for which it has acquired configuration information
through DHCP. These messages may be sent at any time. Since the
results of a reconfiguration event may affect application layer
programs, the client SHOULD log these events, and MAY notify these
programs of the change through an implementation-specific interface.
20.4.1. Receipt of Reconfigure Messages
Upon receipt of a valid Reconfigure message, the client responds with
either a Renew message, a Rebind message, or an Information-request
message as indicated by the Reconfigure Message option (as defined in
Section 23.19). The client ignores the transaction-id field in the
received Reconfigure message. While the transaction is in progress,
the client discards any Reconfigure messages it receives.
DISCUSSION:
The Reconfigure message acts as a trigger that signals the client
to complete a successful message exchange. Once the client has
received a Reconfigure, the client proceeds with the message
exchange (retransmitting the Renew or Information-request message
if necessary); the client ignores any additional Reconfigure
messages until the exchange is complete. Subsequent Reconfigure
messages cause the client to initiate a new exchange.
How does this mechanism work in the face of duplicated or
retransmitted Reconfigure messages? Duplicate messages will be
ignored because the client will begin the exchange after the
receipt of the first Reconfigure. Retransmitted messages will
either trigger the exchange (if the first Reconfigure was not
received by the client) or will be ignored. The server can
discontinue retransmission of Reconfigure messages to the client
once the server receives the Renew or Information-request message
from the client.
It might be possible for a duplicate or retransmitted Reconfigure
to be sufficiently delayed (and delivered out of order) to arrive
at the client after the exchange (initiated by the original
Reconfigure) has been completed. In this case, the client would
initiate a redundant exchange. The likelihood of delayed and out
of order delivery is small enough to be ignored. The consequence
of the redundant exchange is inefficiency rather than incorrect
operation.
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20.4.2. Creation and Transmission of Renew or Rebind Messages
When responding to a Reconfigure, the client creates and sends the
Renew message in exactly the same manner as outlined in
Section 19.1.3, with the exception that the client copies the Option
Request option and any IA options from the Reconfigure message into
the Renew message. The client MUST include a Server Identifier
option in the Renew message, identifying the server with which the
client most recently communicated.
When responding to a Reconfigure, the client creates and sends the
Rebind message in exactly the same manner as outlined in
Section 19.1.4, with the exception that the client copies the Option
Request option and any IA options from the Reconfigure message into
the Rebind message.
If a client is currently sending Rebind messages, as described in
Section 19.1.3, the client ignores any received Reconfigure messages.
20.4.3. Creation and Transmission of Information-request Messages
When responding to a Reconfigure, the client creates and sends the
Information-request message in exactly the same manner as outlined in
Section 19.1.5, with the exception that the client includes a Server
Identifier option with the identifier from the Reconfigure message to
which the client is responding.
20.4.4. Time Out and Retransmission of Renew, Rebind or Information-
request Messages
The client uses the same variables and retransmission algorithm as it
does with Renew, Rebind, or Information-request messages generated as
part of a client-initiated configuration exchange. See
Section 19.1.3, Section 19.1.4, and Section 19.1.5 for details. If
the client does not receive a response from the server by the end of
the retransmission process, the client ignores and discards the
Reconfigure message.
20.4.5. Receipt of Reply Messages
Upon the receipt of a valid Reply message, the client processes the
options and sets (or resets) configuration parameters appropriately.
The client records and updates the lifetimes for any addresses
specified in IAs in the Reply message.
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20.5. Prefix Delegation Reconfiguration
This section describes prefix delegation in Reconfigure message
exchanges.
20.5.1. Delegating Router Behavior
The delegating router initiates a configuration message exchange with
a requesting router, as described in Section 20, by sending a
Reconfigure message (acting as a DHCP server) to the requesting
router, as described in Section 20.1. The delegating router
specifies the IA_PD option in the Option Request option to cause the
requesting router to include an IA_PD option to obtain new
information about delegated prefix(es).
20.5.2. Requesting Router Behavior
The requesting router responds to a Reconfigure message, acting as a
DHCP client, received from a delegating router as described in
Section 20.4 The requesting router MUST include the IA_PD Prefix
option(s) (in an IA_PD option) for prefix(es) that have been
delegated to the requesting router by the delegating router from
which the Reconfigure message was received.
21. Relay Agent Behavior
The relay agent MAY be configured to use a list of destination
addresses, which MAY include unicast addresses, the All_DHCP_Servers
multicast address, or other addresses selected by the network
administrator. If the relay agent has not been explicitly
configured, it MUST use the All_DHCP_Servers multicast address as the
default.
If the relay agent relays messages to the All_DHCP_Servers multicast
address or other multicast addresses, it sets the Hop Limit field to
32.
If the relay agent receives a message other than Relay-forward and
Relay-reply and the relay agent does not recognize its message type,
it MUST forward them as described in Section 21.1.1.
21.1. Relaying a Client Message or a Relay-forward Message
A relay agent relays both messages from clients and Relay-forward
messages from other relay agents. When a relay agent receives a
valid message (for a definition of a valid message, see Section 4.1
of [RFC7283]) to be relayed, it constructs a new Relay-forward
message. The relay agent copies the source address from the header
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of the IP datagram in which the message was received to the peer-
address field of the Relay-forward message. The relay agent copies
the received DHCP message (excluding any IP or UDP headers) into a
Relay Message option in the new message. The relay agent adds to the
Relay-forward message any other options it is configured to include.
[RFC6221] defines a Lightweight DHCPv6 Relay Agent (LDRA) that allows
Relay Agent Information to be inserted by an access node that
performs a link- layer bridging (i.e., non-routing) function.
21.1.1. Relaying a Message from a Client
If the relay agent received the message to be relayed from a client,
the relay agent places a global, ULA [RFC4193] or site-scoped address
with a prefix assigned to the link on which the client should be
assigned an address in the link-address field. (It is possible for
the relay to use link local address instead, but that is not
recommended as it would require additional information to be provided
in the server configuration. See Section 3.2 of
[I-D.ietf-dhc-topo-conf] for detailed discussion.) This address will
be used by the server to determine the link from which the client
should be assigned an address and other configuration information.
The hop-count in the Relay-forward message is set to 0.
If the relay agent cannot use the address in the link-address field
to identify the interface through which the response to the client
will be relayed, the relay agent MUST include an Interface-id option
(see Section 23.18) in the Relay-forward message. The server will
include the Interface-id option in its Relay-reply message. The
relay agent fills in the link-address field as described in the
previous paragraph regardless of whether the relay agent includes an
Interface-id option in the Relay-forward message.
21.1.2. Relaying a Message from a Relay Agent
If the message received by the relay agent is a Relay-forward message
and the hop-count in the message is greater than or equal to
HOP_COUNT_LIMIT, the relay agent discards the received message.
The relay agent copies the source address from the IP datagram in
which the message was received from the relay agent into the peer-
address field in the Relay-forward message and sets the hop-count
field to the value of the hop-count field in the received message
incremented by 1.
If the source address from the IP datagram header of the received
message is a global or site-scoped address (and the device on which
the relay agent is running belongs to only one site), the relay agent
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sets the link-address field to 0; otherwise the relay agent sets the
link-address field to a global or site-scoped address assigned to the
interface on which the message was received, or includes an
Interface-ID option to identify the interface on which the message
was received.
21.1.3. Relay Agent Behavior with Prefix Delegation
A relay agent forwards messages containing Prefix Delegation options
in the same way as described earlier in this section.
If a delegating router communicates with a requesting router through
a relay agent, the delegating router may need a protocol or other
out-of-band communication to configure routing information for
delegated prefixes on any router through which the requesting router
may forward traffic.
21.2. Relaying a Relay-reply Message
The relay agent processes any options included in the Relay-reply
message in addition to the Relay Message option, and then discards
those options.
The relay agent extracts the message from the Relay Message option
and relays it to the address contained in the peer-address field of
the Relay-reply message. Relay agents MUST NOT modify the message.
If the Relay-reply message includes an Interface-id option, the relay
agent relays the message from the server to the client on the link
identified by the Interface-id option. Otherwise, if the link-
address field is not set to zero, the relay agent relays the message
on the link identified by the link-address field.
If the relay agent receives a Relay-reply message, it MUST process
the message as defined above, regardless of the type of message
encapsulated in the Relay Message option.
21.3. Construction of Relay-reply Messages
A server uses a Relay-reply message to return a response to a client
if the original message from the client was relayed to the server in
a Relay-forward message or to send a Reconfigure message to a client
if the server does not have an address it can use to send the message
directly to the client.
A response to the client MUST be relayed through the same relay
agents as the original client message. The server causes this to
happen by creating a Relay-reply message that includes a Relay
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Message option containing the message for the next relay agent in the
return path to the client. The contained Relay-reply message
contains another Relay Message option to be sent to the next relay
agent, and so on. The server must record the contents of the peer-
address fields in the received message so it can construct the
appropriate Relay-reply message carrying the response from the
server.
For example, if client C sent a message that was relayed by relay
agent A to relay agent B and then to the server, the server would
send the following Relay-Reply message to relay agent B:
msg-type: RELAY-REPLY
hop-count: 1
link-address: 0
peer-address: A
Relay Message option, containing:
msg-type: RELAY-REPLY
hop-count: 0
link-address: address from link to which C is attached
peer-address: C
Relay Message option: <response from server>
Figure 8: Relay-reply Example
When sending a Reconfigure message to a client through a relay agent,
the server creates a Relay-reply message that includes a Relay
Message option containing the Reconfigure message for the next relay
agent in the return path to the client. The server sets the peer-
address field in the Relay-reply message header to the address of the
client, and sets the link-address field as required by the relay
agent to relay the Reconfigure message to the client. The server
obtains the addresses of the client and the relay agent through prior
interaction with the client or through some external mechanism.
22. 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.
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The DHCP authentication mechanism is based on the design of
authentication for DHCPv4 [RFC3118].
22.1. Security of Messages Sent Between Servers and Relay Agents
Relay agents and servers that exchange messages securely use the
IPsec mechanisms for IPv6 [RFC4301]. If a client message is relayed
through multiple relay agents, each of the relay agents must have
established independent, pairwise trust relationships. That is, if
messages from client C will be relayed by relay agent A to relay
agent B and then to the server, relay agents A and B must be
configured to use IPsec for the messages they exchange, and relay
agent B and the server must be configured to use IPsec for the
messages they exchange.
Relay agents and servers that support secure relay agent to server or
relay agent to relay agent communication use IPsec under the
following conditions:
Selectors Relay agents are manually configured with the
addresses of the relay agent or server to
which DHCP messages are to be forwarded.
Each relay agent and server that will be
using IPsec for securing DHCP messages must
also be configured with a list of the relay
agents to which messages will be returned.
The selectors for the relay agents and
servers will be the pairs of addresses
defining relay agents and servers that
exchange DHCP messages on DHCPv6 UDP port
547.
Mode Relay agents and servers use transport mode
and ESP. The information in DHCP messages is
not generally considered confidential, so
encryption need not be used (i.e., NULL
encryption can be used).
Key management Because the relay agents and servers are used
within an organization, public key schemes
are not necessary. Because the relay agents
and servers must be manually configured,
manually configured key management may
suffice, but does not provide defense against
replayed messages. Accordingly, IKE with
preshared secrets SHOULD be supported. IKE
with public keys MAY be supported.
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Security policy DHCP messages between relay agents and
servers should only be accepted from DHCP
peers as identified in the local
configuration.
Authentication Shared keys, indexed to the source IP address
of the received DHCP message, are adequate in
this application.
Availability Appropriate IPsec implementations are likely
to be available for servers and for relay
agents in more featureful devices used in
enterprise and core ISP networks. IPsec is
less likely to be available for relay agents
in low end devices primarily used in the home
or small office markets.
22.2. Summary of DHCP Authentication
Authentication of DHCP messages is accomplished through the use of
the Authentication option (see Section 23.11). The authentication
information carried in the Authentication option can be used to
reliably identify the source of a DHCP message and to confirm that
the contents of the DHCP message have not been tampered with.
The Authentication option provides a framework for multiple
authentication protocols. Two such protocols are defined here.
Other protocols defined in the future will be specified in separate
documents.
Any DHCP message MUST NOT include more than one Authentication
option.
The protocol field in the Authentication option identifies the
specific protocol used to generate the authentication information
carried in the option. The algorithm field identifies a specific
algorithm within the authentication protocol; for example, the
algorithm field specifies the hash algorithm used to generate the
message authentication code (MAC) in the authentication option. The
replay detection method (RDM) field specifies the type of replay
detection used in the replay detection field.
22.3. Replay Detection
The Replay Detection Method (RDM) field determines the type of replay
detection used in the Replay Detection field.
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If the RDM field contains 0x00, the replay detection field MUST be
set to the value of a strictly monotonically increasing counter.
Using a counter value, such as the current time of day (for example,
an NTP-format timestamp [RFC5905]), can reduce the danger of replay
attacks. This method MUST be supported by all protocols.
22.4. Delayed Authentication Protocol
If the protocol field is 2, the message is using the "delayed
authentication" mechanism. In delayed authentication, the client
requests authentication in its Solicit message, and the server
replies with an Advertise message that includes authentication
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.
Note that the delayed authentication protocol cannot work with
2-message exchange model. This protocol uses Solicit/Advertise
exchange as the key and server selection process. So, real DHCPv6
procedures can only be made in the follow-up messages.
The use of a particular technique based on the HMAC protocol
[RFC2104] using the MD5 hash [RFC1321] is defined here.
22.4.1. Use of the Authentication Option in the Delayed Authentication
Protocol
In a Solicit message, the client fills in the protocol, algorithm and
RDM fields in the Authentication option with the client's
preferences. The client sets the replay detection field to zero and
omits the authentication information field. The client sets the
option-len field to 11.
In all other messages, the protocol and algorithm fields identify the
method used to construct the contents of the authentication
information field. The RDM field identifies the method used to
construct the contents of the replay detection field.
The format of the Authentication information is:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DHCP realm |
| (variable length) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| key ID (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC-MD5 |
| (128 bits) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Authentication information format
DHCP realm The DHCP realm that identifies the key used
to generate the HMAC-MD5 value. This is a
domain name encoded as described in
Section 9.
key ID The key identifier that identified the key
used to generate the HMAC-MD5 value.
HMAC-MD5 The message authentication code generated by
applying MD5 to the DHCP message using the
key identified by the DHCP realm, client
DUID, and key ID.
The sender computes the MAC using the HMAC generation algorithm
[RFC2104] and the MD5 hash function [RFC1321]. The entire DHCP
message (setting the MAC field of the authentication option to zero),
including the DHCP message header and the options field, is used as
input to the HMAC-MD5 computation function.
DISCUSSION:
Algorithm 1 specifies the use of HMAC-MD5. Use of a different
technique, such as HMAC-SHA, will be specified as a separate
protocol.
The DHCP realm used to identify authentication keys is chosen to
be unique among administrative domains. Use of the DHCP realm
allows DHCP administrators to avoid conflict in the use of key
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identifiers, and allows a host using DHCP to use authenticated
DHCP while roaming among DHCP administrative domains.
22.4.2. Message Validation
Any DHCP message that includes more than one authentication option
MUST be discarded.
To validate an incoming message, the receiver first checks that the
value in the replay detection field is acceptable according to the
replay detection method specified by the RDM field. If no replay is
detected, then the receiver computes the MAC as described in
[RFC2104]. The entire DHCP message (setting the MAC field of the
authentication option to 0) is used as input to the HMAC-MD5
computation function. If the MAC computed by the receiver does not
match the MAC contained in the authentication option, the receiver
MUST discard the DHCP message.
22.4.3. Key Utilization
Each DHCP client has a set of keys. Each key is identified by <DHCP
realm, client DUID, key id>. Each key also has a lifetime. The key
may not be used past the end of its lifetime. The client's keys are
initially distributed to the client through some out-of-band
mechanism. The lifetime for each key is distributed with the key.
Mechanisms for key distribution and lifetime specification are beyond
the scope of this document.
The client and server use one of the client's keys to authenticate
DHCP messages during a session (until the next Solicit message sent
by the client).
22.4.4. Client Considerations for Delayed Authentication Protocol
The client announces its intention to use DHCP authentication by
including an Authentication option in its Solicit message. The
server selects a key for the client based on the client's DUID. The
client and server use that key to authenticate all DHCP messages
exchanged during the session.
22.4.4.1. Sending Solicit Messages
When the client sends a Solicit message and wishes to use
authentication, it includes an Authentication option with the desired
protocol, algorithm and RDM as described in Section 22.4. The client
does not include any replay detection or authentication information
in the Authentication option.
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22.4.4.2. Receiving Advertise Messages
The client validates any Advertise messages containing an
Authentication option specifying the delayed authentication protocol
using the validation test described in Section 22.4.2.
The Client behavior is defined by local policy, as detailed below.
If the client requires that Advertise messages be authenticated, then
it MUST ignore Advertise messages that do not include authentication
information, or for which the client has no matching key, or that do
not pass the validation test.
Local policy MAY also prefer authenticated Advertise messages, in
which case the client SHOULD attempt to validate all Advertise
messages for which the client has a matching key. Messages for which
the client has a key, but which do not pass the validation test MUST
be rejected, even if the client would otherwise accept the same
message without the Authentication option.
In all cases, messages for which the client does not have a matching
key should be treated as if they have no Authentication option.
When the decision to accept unauthenticated message is made, it
should be made with care. Accepting an unauthenticated Advertise
message can make the client vulnerable to spoofing and other attacks.
Policies and actions which were depending upon Authentication MUST
NOT be executed. Local users SHOULD be informed that the client has
accepted an unauthenticated Advertise message.
A client MUST be configurable to discard unauthenticated messages,
and SHOULD be configured by default to discard unauthenticated
messages if the client has been configured with an authentication key
or other authentication information.
A client MAY choose to differentiate between Advertise messages with
no authentication information and Advertise messages that do not pass
the validation test; for example, a client might accept the former
and discard the latter. If a client does accept an unauthenticated
message, the client SHOULD inform any local users and SHOULD log the
event.
22.4.4.3. Sending Request, Confirm, Renew, Rebind, Decline or Release
Messages
If the client authenticated the Advertise message through which the
client selected the server, the client MUST generate authentication
information for subsequent Request, Confirm, Renew, Rebind or Release
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messages sent to the server, as described in Section 22.4. When the
client sends a subsequent message, it MUST use the same key used by
the server to generate the authentication information.
22.4.4.4. Sending Information-request Messages
If the server has selected a key for the client in a previous message
exchange (see Section 22.4.5.1), the client MUST use the same key to
generate the authentication information throughout the session.
22.4.4.5. Receiving Reply Messages
If the client authenticated the Advertise it accepted, the client
MUST validate the associated Reply message from the server. The
client MUST ignore and discard the Reply if the message fails to pass
the validation test and MAY log the validation failure.
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.
22.4.4.6. Receiving Reconfigure Messages
The client MUST discard the Reconfigure if the message fails to pass
the validation test and MAY log the validation failure.
22.4.5. Server Considerations for Delayed Authentication Protocol
After receiving a Solicit message that contains an Authentication
option, the server selects a key for the client, based on the
client's DUID and key selection policies with which the server has
been configured. The server identifies the selected key in the
Advertise message and uses the key to validate subsequent messages
between the client and the server.
22.4.5.1. Receiving Solicit Messages and Sending Advertise Messages
The server selects a key for the client and includes authentication
information in the Advertise message returned to the client as
specified in Section 22.4. The server MUST record the identifier of
the key selected for the client and use that same key for validating
subsequent messages with the client.
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22.4.5.2. Receiving Request, Confirm, Renew, Rebind or Release Messages
and Sending Reply Messages
The server uses the key identified in the message and validates the
message as specified in Section 22.4.2. If the message fails to pass
the validation test or the server does not know the key identified by
the 'key ID' field, the server MUST discard the message and MAY
choose to log the validation failure. If the server receives a
client message without an authentication option while the server has
previously sent authentication information in the same session, it
MUST discard the message and MAY choose to log the validation
failure, because the client violates the definition in
Section 22.4.4.3.
If the message passes the validation test, the server responds to the
specific message as described in Section 19.2. The server MUST
include authentication information generated using the key identified
in the received message, as specified in Section 22.4.
22.5. Reconfigure Key Authentication Protocol
The Reconfigure key authentication protocol provides protection
against misconfiguration of a client caused by a Reconfigure message
sent by a malicious DHCP server. In this protocol, a DHCP server
sends a Reconfigure Key to the client in the initial exchange of DHCP
messages. The client records the Reconfigure Key for use in
authenticating subsequent Reconfigure messages from that server. The
server then includes an HMAC computed from the Reconfigure Key in
subsequent Reconfigure messages.
Both the Reconfigure Key sent from the server to the client and the
HMAC in subsequent Reconfigure messages are carried as the
Authentication information in an Authentication option. The format
of the Authentication information is defined in the following
section.
The Reconfigure Key protocol is used (initiated by the server) only
if the client and server are not using any other authentication
protocol and the client and server have negotiated to use Reconfigure
messages.
22.5.1. Use of the Authentication Option in the Reconfigure Key
Authentication Protocol
The following fields are set in an Authentication option for the
Reconfigure Key Authentication Protocol:
protocol 3
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algorithm 1
RDM 0
The format of the Authentication information for the Reconfigure Key
Authentication Protocol is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Value (128 bits) |
+-+-+-+-+-+-+-+-+ |
. .
. .
. +-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: RKAP Authentication Information
Type Type of data in Value field carried in this
option:
1 Reconfigure Key value (used in Reply
message).
2 HMAC-MD5 digest of the message (used in
Reconfigure message).
Value Data as defined by the Type field.
22.5.2. Server considerations for Reconfigure Key protocol
The server selects a Reconfigure Key for a client during the Request/
Reply, Solicit/Reply or Information-request/Reply message exchange.
The server records the Reconfigure Key and transmits that key to the
client in an Authentication option in the Reply message.
The Reconfigure Key is 128 bits long, and MUST be a cryptographically
strong random or pseudo-random number that cannot easily be
predicted.
To provide authentication for a Reconfigure message, the server
selects a replay detection value according to the RDM selected by the
server, and computes an HMAC-MD5 of the Reconfigure message using the
Reconfigure Key for the client. The server computes the HMAC-MD5
over the entire DHCP Reconfigure message, including the
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Authentication option; the HMAC-MD5 field in the Authentication
option is set to zero for the HMAC-MD5 computation. The server
includes the HMAC-MD5 in the authentication information field in an
Authentication option included in the Reconfigure message sent to the
client.
22.5.3. Client considerations for Reconfigure Key protocol
The client will receive a Reconfigure Key from the server in the
initial Reply message from the server. The client records the
Reconfigure Key for use in authenticating subsequent Reconfigure
messages.
To authenticate a Reconfigure message, the client computes an HMAC-
MD5 over the DHCP Reconfigure message, using the Reconfigure Key
received from the server. If this computed HMAC-MD5 matches the
value in the Authentication option, the client accepts the
Reconfigure message.
23. 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 23.1. All values in options are represented in
network byte order.
This document describes the DHCP options defined as part of the base
DHCP specification. Other options may be defined in the future in
separate documents. See [RFC7227] for guidelines regarding new
options definition.
Unless otherwise noted, each option may appear only in the options
area of a DHCP message and may appear only once. If an option does
appear multiple times, each instance is considered separate and the
data areas of the options MUST NOT be concatenated or otherwise
combined.
Options that are allowed to appear only once are called singleton
options. The only non-singleton options defined in this document are
IA_NA (see Section 23.4), IA_TA (see Section 23.5), and IA_PD (see
Section 23.21) options. Also, IAAddress (see Section 23.6) and
IAPrefix (see Section 23.22) may appear in their respective IA
options more than once.
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23.1. Format of DHCP Options
The format of DHCP options is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-code | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-data |
| (option-len octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: Option Format
option-code An unsigned integer identifying the specific
option type carried in this option.
option-len An unsigned integer giving the length of the
option-data field in this option in octets.
option-data The data for the option; the format of this
data depends on the definition of the option.
DHCPv6 options are scoped by using encapsulation. Some options apply
generally to the client, some are specific to an IA, and some are
specific to the addresses within an IA. These latter two cases are
discussed in Section 23.4 and Section 23.6.
23.2. Client Identifier Option
The Client Identifier option is used to carry a DUID (see Section 10)
identifying a client between a client and a server. The format of
the Client Identifier option is:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_CLIENTID | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. DUID .
. (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: Client Identifier Option Format
option-code OPTION_CLIENTID (1).
option-len Length of DUID in octets.
DUID The DUID for the client.
23.3. Server Identifier Option
The Server Identifier option is used to carry a DUID (see Section 10)
identifying a server between a client and a server. The format of
the Server Identifier option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_SERVERID | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. DUID .
. (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: Server Identifier Option Format
option-code OPTION_SERVERID (2).
option-len Length of DUID in octets.
DUID The DUID for the server.
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23.4. Identity Association for Non-temporary Addresses Option
The Identity Association for Non-temporary Addresses option (IA_NA
option) is used to carry an IA_NA, the parameters associated with the
IA_NA, and the non-temporary addresses associated with the IA_NA.
Addresses appearing in an IA_NA option are not temporary addresses
(see Section 23.5).
The format of the IA_NA option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_IA_NA | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IAID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. IA_NA-options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: Identity Association for Non-temporary Addresses Option
Format
option-code OPTION_IA_NA (3).
option-len 12 + length of IA_NA-options field.
IAID The unique identifier for this IA_NA; the
IAID must be unique among the identifiers for
all of this client's IA_NAs. The number
space for IA_NA IAIDs is separate from the
number space for IA_TA IAIDs.
T1 The time at which the client contacts the
server from which the addresses in the IA_NA
were obtained to extend the lifetimes of the
addresses assigned to the IA_NA; T1 is a time
duration relative to the current time
expressed in units of seconds.
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T2 The time at which the client contacts any
available server to extend the lifetimes of
the addresses assigned to the IA_NA; T2 is a
time duration relative to the current time
expressed in units of seconds.
IA_NA-options Options associated with this IA_NA.
The IA_NA-options field encapsulates those options that are specific
to this IA_NA. For example, all of the IA Address Options carrying
the addresses associated with this IA_NA are in the IA_NA-options
field.
Each IA_NA carries one "set" of non-temporary addresses; that is, at
most one address from each prefix assigned to the link to which the
client is attached.
An IA_NA option may only appear in the options area of a DHCP
message. A DHCP message may contain multiple IA_NA options.
The status of any operations involving this IA_NA is indicated in a
Status Code option in the IA_NA-options field.
Note that an IA_NA has no explicit "lifetime" or "lease length" of
its own. When the valid lifetimes of all of the addresses in an
IA_NA have expired, the IA_NA can be considered as having expired.
T1 and T2 are included to give servers explicit control over when a
client recontacts the server about a specific IA_NA.
In a message sent by a client to a server, values in the T1 and T2
fields indicate the client's preference for those parameters. The
client sets T1 and T2 to 0 if it has no preference for those values.
In a message sent by a server to a client, the client MUST use the
values in the T1 and T2 fields for the T1 and T2 parameters, unless
those values in those fields are 0. The values in the T1 and T2
fields are the number of seconds until T1 and T2.
The server selects the T1 and T2 times to allow the client to extend
the lifetimes of any addresses in the IA_NA before the lifetimes
expire, even if the server is unavailable for some short period of
time. Recommended values for T1 and T2 are .5 and .8 times the
shortest preferred lifetime of the addresses in the IA that the
server is willing to extend, respectively. If the "shortest"
preferred lifetime is 0xffffffff ("infinity"), the recommended T1 and
T2 values are also 0xffffffff. If the time at which the addresses in
an IA_NA are to be renewed is to be left to the discretion of the
client, the server sets T1 and T2 to 0.
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If a server receives an IA_NA with T1 greater than T2, and both T1
and T2 are greater than 0, the server ignores the invalid values of
T1 and T2 and processes the IA_NA as though the client had set T1 and
T2 to 0.
If a client receives an IA_NA with T1 greater than T2, and both T1
and T2 are greater than 0, the client discards the IA_NA option and
processes the remainder of the message as though the server had not
included the invalid IA_NA option.
Care should be taken in setting T1 or T2 to 0xffffffff ("infinity").
A client will never attempt to extend the lifetimes of any addresses
in an IA with T1 set to 0xffffffff. A client will never attempt to
use a Rebind message to locate a different server to extend the
lifetimes of any addresses in an IA with T2 set to 0xffffffff.
This option MAY appear in a Confirm message if the lifetimes on the
non-temporary addresses in the associated IA have not expired.
23.5. Identity Association for Temporary Addresses Option
The Identity Association for the Temporary Addresses (IA_TA) option
is used to carry an IA_TA, the parameters associated with the IA_TA
and the addresses associated with the IA_TA. All of the addresses in
this option are used by the client as temporary addresses, as defined
in [RFC4941]. The format of the IA_TA option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_IA_TA | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IAID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. IA_TA-options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: Identity Association for Temporary Addresses Option Format
option-code OPTION_IA_TA (4).
option-len 4 + length of IA_TA-options field.
IAID The unique identifier for this IA_TA; the
IAID must be unique among the identifiers for
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all of this client's IA_TAs. The number
space for IA_TA IAIDs is separate from the
number space for IA_NA IAIDs.
IA_TA-options Options associated with this IA_TA.
The IA_TA-Options field encapsulates those options that are specific
to this IA_TA. For example, all of the IA Address Options carrying
the addresses associated with this IA_TA are in the IA_TA-options
field.
Each IA_TA carries one "set" of temporary addresses.
An IA_TA option may only appear in the options area of a DHCP
message. A DHCP message may contain multiple IA_TA options.
The status of any operations involving this IA_TA is indicated in a
Status Code option in the IA_TA-options field.
Note that an IA has no explicit "lifetime" or "lease length" of its
own. When the valid lifetimes of all of the addresses in an IA_TA
have expired, the IA can be considered as having expired.
An IA_TA option does not include values for T1 and T2. A client MAY
request that the lifetimes on temporary addresses be extended by
including the addresses in a IA_TA option sent in a Renew or Rebind
message to a server. For example, a client would request an
extension on the lifetime of a temporary address to allow an
application to continue to use an established TCP connection.
The client obtains new temporary addresses by sending an IA_TA option
with a new IAID to a server. Requesting new temporary addresses from
the server is the equivalent of generating new temporary addresses as
described in [RFC4941]. The server will generate new temporary
addresses and return them to the client. The client should request
new temporary addresses before the lifetimes on the previously
assigned addresses expire.
A server MUST return the same set of temporary address for the same
IA_TA (as identified by the IAID) as long as those addresses are
still valid. After the lifetimes of the addresses in an IA_TA have
expired, the IAID may be reused to identify a new IA_TA with new
temporary addresses.
This option MAY appear in a Confirm message if the lifetimes on the
temporary addresses in the associated IA have not expired.
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23.6. IA Address Option
The IA Address option is used to specify IPv6 addresses associated
with an IA_NA or an IA_TA. The IA Address option must be
encapsulated in the Options field of an IA_NA or IA_TA option. The
Options fields of the IA_NA or IA_TA option encapsulates those
options that are specific to this address.
The format of the IA Address option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_IAADDR | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| preferred-lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| valid-lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. IAaddr-options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: IA Address Option Format
option-code OPTION_IAADDR (5).
option-len 24 + length of IAaddr-options field.
IPv6 address An IPv6 address.
preferred-lifetime The preferred lifetime for the IPv6 address
in the option, expressed in units of seconds.
valid-lifetime The valid lifetime for the IPv6 address in
the option, expressed in units of seconds.
IAaddr-options Options associated with this address.
In a message sent by a client to a server, values in the preferred
and valid lifetime fields indicate the client's preference for those
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parameters. The client may send 0 if it has no preference for the
preferred and valid lifetimes. If a client wishes to express its
lifetimes preferences and does not have the knowledge to populate the
IPv6 address field, it can use unspecified address (::). It is up to
a server to honor or ignore these preferences.
In a message sent by a server to a client, the client MUST use the
values in the preferred and valid lifetime fields for the preferred
and valid lifetimes. The values in the preferred and valid lifetimes
are the number of seconds remaining in each lifetime.
A client discards any addresses for which the preferred lifetime is
greater than the valid lifetime. A server ignores the lifetimes set
by the client if the preferred lifetime is greater than the valid
lifetime and ignores the values for T1 and T2 set by the client if
those values are greater than the preferred lifetime.
Care should be taken in setting the valid lifetime of an address to
0xffffffff ("infinity"), which amounts to a permanent assignment of
an address to a client.
More than one IA Address Option can appear in an IA_NA option or an
IA_TA option.
The status of any operations involving this IA Address is indicated
in a Status Code option in the IAaddr-options field, as specified in
Section 23.13.
23.7. Option Request Option
The Option Request option is used to identify a list of options in a
message between a client and a server. The format of the Option
Request option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_ORO | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| requested-option-code-1 | requested-option-code-2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: Option Request Option Format
option-code OPTION_ORO (6).
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option-len 2 * number of requested options.
requested-option-code-n The option code for an option requested
by the client.
A client MAY include an Option Request option in a Solicit, Request,
Renew, Rebind, Confirm or Information-request message to inform the
server about options the client wants the server to send to the
client. A server MAY include an Option Request option in a
Reconfigure message to indicate which options the client should
request from the server. If there is a need to request encapsulated
options, top-level Option Request option MUST be used for that
purpose. There is no need request IAADDR or IAPREFIX.
23.8. Preference Option
The Preference option is sent by a server to a client to affect the
selection of a server by the client.
The format of the Preference option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_PREFERENCE | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| pref-value |
+-+-+-+-+-+-+-+-+
Figure 18: Preference Option Format
option-code OPTION_PREFERENCE (7).
option-len 1.
pref-value The preference value for the server in this
message.
A server MAY include a Preference option in an Advertise message to
control the selection of a server by the client. See Section 18.1.3
for the use of the Preference option by the client and the
interpretation of Preference option data value.
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23.9. Elapsed Time Option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_ELAPSED_TIME | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| elapsed-time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19: Elapsed Time Option Format
option-code OPTION_ELAPSED_TIME (8).
option-len 2.
elapsed-time The amount of time since the client began its
current DHCP transaction. This time is
expressed in hundredths of a second (10^-2
seconds).
A client MUST include an Elapsed Time option in messages to indicate
how long the client has been trying to complete a DHCP message
exchange. The elapsed time is measured from the time at which the
client sent the first message in the message exchange, and the
elapsed-time field is set to 0 in the first message in the message
exchange. Servers and Relay Agents use the data value in this option
as input to policy controlling how a server responds to a client
message. For example, the elapsed time option allows a secondary
DHCP server to respond to a request when a primary server has not
answered in a reasonable time. The elapsed time value is an
unsigned, 16 bit integer. The client uses the value 0xffff to
represent any elapsed time values greater than the largest time value
that can be represented in the Elapsed Time option.
23.10. Relay Message Option
The Relay Message option carries a DHCP message in a Relay-forward or
Relay-reply message.
The format of the Relay Message option is:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_RELAY_MSG | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. DHCP-relay-message .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: Relay Message Option Format
option-code OPTION_RELAY_MSG (9)
option-len Length of DHCP-relay-message
DHCP-relay-message In a Relay-forward message, the received
message, relayed verbatim to the next relay
agent or server; in a Relay-reply message,
the message to be copied and relayed to the
relay agent or client whose address is in the
peer-address field of the Relay-reply message
23.11. Authentication Option
The Authentication option carries authentication information to
authenticate the identity and contents of DHCP messages. The use of
the Authentication option is described in Section 22. The format of
the Authentication option is:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_AUTH | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| protocol | algorithm | RDM | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
| replay detection (64 bits) +-+-+-+-+-+-+-+-+
| | auth-info |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
. authentication information .
. (variable length) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: Authentication Option Format
option-code OPTION_AUTH (11).
option-len 11 + length of authentication information
field.
protocol The authentication protocol used in this
authentication option.
algorithm The algorithm used in the authentication
protocol.
RDM The replay detection method used in this
authentication option.
Replay detection The replay detection information for the RDM.
authentication information The authentication information, as
specified by the protocol and algorithm used
in this authentication option.
23.12. Server Unicast Option
The server sends this option to a client to indicate to the client
that it is allowed to unicast messages to the server. The format of
the Server Unicast option is:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_UNICAST | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| server-address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22: Server Unicast Option Format
option-code OPTION_UNICAST (12).
option-len 16.
server-address The IP address to which the client should
send messages delivered using unicast.
The server specifies the IPv6 address to which the client is to send
unicast messages in the server-address field. When a client receives
this option, where permissible and appropriate, the client sends
messages directly to the server using the IPv6 address specified in
the server-address field of the option.
When the server sends a Unicast option to the client, some messages
from the client will not be relayed by Relay Agents, and will not
include Relay Agent options from the Relay Agents. Therefore, a
server should only send a Unicast option to a client when Relay
Agents are not sending Relay Agent options. A DHCP server rejects
any messages sent inappropriately using unicast to ensure that
messages are relayed by Relay Agents when Relay Agent options are in
use.
Details about when the client may send messages to the server using
unicast are in Section 19.
23.13. Status Code Option
This option returns a status indication related to the DHCP message
or option in which it appears. The format of the Status Code option
is:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_STATUS_CODE | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| status-code | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
. .
. status-message .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 23: Status Code Option Format
option-code OPTION_STATUS_CODE (13).
option-len 2 + length of status-message.
status-code The numeric code for the status encoded in
this option.
status-message A UTF-8 encoded text string suitable for
display to an end user, which MUST NOT be
null-terminated.
A Status Code option may appear in the options field of a DHCP
message and/or in the options field of another option. If the Status
Code option does not appear in a message in which the option could
appear, the status of the message is assumed to be Success.
The status-codes values previously defined by [RFC3315] and [RFC3633]
are:
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+---------------+------+--------------------------------------------+
| Name | Code | Description |
+---------------+------+--------------------------------------------+
| Success | 0 | Success. |
| UnspecFail | 1 | Failure, reason unspecified; this status |
| | | code is sent by either a client or a |
| | | server to indicate a failure not |
| | | explicitly specified in this document. |
| NoAddrsAvail | 2 | Server has no addresses available to |
| | | assign to the IA(s). |
| NoBinding | 3 | Client record (binding) unavailable. |
| NotOnLink | 4 | The prefix for the address is not |
| | | appropriate for the link to which the |
| | | client is attached. |
| UseMulticast | 5 | Sent by a server to a client to force the |
| | | client to send messages to the server |
| | | using the |
| | | All_DHCP_Relay_Agents_and_Servers address. |
| NoPrefixAvail | 6 | Delegating router has no prefixes |
| | | available to assign to the IAPD(s). |
+---------------+------+--------------------------------------------+
23.14. Rapid Commit Option
The Rapid Commit option is used to signal the use of the two message
exchange for address assignment. The format of the Rapid Commit
option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_RAPID_COMMIT | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 24: Rapid Commit Option Format
option-code OPTION_RAPID_COMMIT (14).
option-len 0.
A client MAY include this option in a Solicit message if the client
is prepared to perform the Solicit-Reply message exchange described
in Section 18.1.1.
A server MUST include this option in a Reply message sent in response
to a Solicit message when completing the Solicit-Reply message
exchange.
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DISCUSSION:
Each server that responds with a Reply to a Solicit that includes
a Rapid Commit option will commit the assigned addresses in the
Reply message to the client, and will not receive any confirmation
that the client has received the Reply message. Therefore, if
more than one server responds to a Solicit that includes a Rapid
Commit option, some servers will commit addresses that are not
actually used by the client.
The problem of unused addresses can be minimized, for example, by
designing the DHCP service so that only one server responds to the
Solicit or by using relatively short lifetimes for assigned
addresses, or the DHCP client initiatively releases unused
addresses using the Release message.
23.15. User Class Option
The User Class option is used by a client to identify the type or
category of user or applications it represents.
The format of the User Class option is:
0 1 2 3
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 .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 25: User Class Option Format
option-code OPTION_USER_CLASS (15).
option-len Length of user class data field.
user-class-data The user classes carried by the client.
The information contained in the data area of this option is
contained in one or more opaque fields that represent the user class
or classes of which the client is a member. A server selects
configuration information for the client based on the classes
identified in this option. For example, the User Class option can be
used to configure all clients of people in the accounting department
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with a different printer than clients of people in the marketing
department. The user class information carried in this option MUST
be configurable on the client.
The data area of the user class option MUST contain one or more
instances of user class data. Each instance of the user class data
is formatted as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
| user-class-len | opaque-data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
Figure 26: User Class Data Format
The user-class-len is two octets long and specifies the length of the
opaque user class data in network byte order.
A server interprets the classes identified in this option according
to its configuration to select the appropriate configuration
information for the client. A server may use only those user classes
that it is configured to interpret in selecting configuration
information for a client and ignore any other user classes. In
response to a message containing a User Class option, a server
includes a User Class option containing those classes that were
successfully interpreted by the server, so that the client can be
informed of the classes interpreted by the server.
23.16. Vendor Class Option
This option is used by a client to identify the vendor that
manufactured the hardware on which the client is running. The
information contained in the data area of this option is contained in
one or more opaque fields that identify details of the hardware
configuration. The format of the Vendor Class option is:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_VENDOR_CLASS | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| enterprise-number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. vendor-class-data .
. . . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 27: Vendor Class Option Format
option-code OPTION_VENDOR_CLASS (16).
option-len 4 + length of vendor class data field.
enterprise-number The vendor's registered Enterprise Number as
registered with IANA [IANA-PEN].
vendor-class-data The hardware configuration of the host on
which the client is running.
The vendor-class-data is composed of a series of separate items, each
of which describes some characteristic of the client's hardware
configuration. Examples of vendor-class-data instances might include
the version of the operating system the client is running or the
amount of memory installed on the client.
Each instance of the vendor-class-data is formatted as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
| vendor-class-len | opaque-data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
Figure 28: Vendor Class Data Format
The vendor-class-len is two octets long and specifies the length of
the opaque vendor class data in network byte order.
Servers and clients MUST NOT include more than one instance of
OPTION_VENDOR_CLASS with the same Enterprise Number. Each instance
of OPTION_VENDOR_CLASS can carry multiple sub-options.
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23.17. Vendor-specific Information Option
This option is used by clients and servers to exchange vendor-
specific information.
The format of the Vendor-specific Information option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_VENDOR_OPTS | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| enterprise-number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. option-data .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 29: Vendor-specific Information Option Format
option-code OPTION_VENDOR_OPTS (17).
option-len 4 + length of option-data field.
enterprise-number The vendor's registered Enterprise Number as
registered with IANA [IANA-PEN].
option-data An opaque object, interpreted by vendor-
specific code on the clients and servers.
The definition of the information carried in this option is vendor
specific. The vendor is indicated in the enterprise-number field.
Use of vendor-specific information allows enhanced operation,
utilizing additional features in a vendor's DHCP implementation. A
DHCP client that does not receive requested vendor-specific
information will still configure the host device's IPv6 stack to be
functional.
The encapsulated vendor-specific options field MUST be encoded as a
sequence of code/length/value fields of identical format to the DHCP
options field. The option codes are defined by the vendor identified
in the enterprise-number field and are not managed by IANA. Each of
the encapsulated options is formatted as follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| opt-code | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. option-data .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 30: Vendor-specific Options Format
opt-code The code for the encapsulated option.
option-len An unsigned integer giving the length of the
option-data field in this encapsulated option
in octets.
option-data The data area for the encapsulated option.
Multiple instances of the Vendor-specific Information option may
appear in a DHCP message. Each instance of the option is interpreted
according to the option codes defined by the vendor identified by the
Enterprise Number in that option. Servers and clients MUST NOT send
more than one instance of Vendor-specific Information option with the
same Enterprise Number. Each instanf of Vendor-specific Information
option MAY contain multiple encapsulated options.
A client that is interested in receiving a Vendor-specific
Information Option:
- MUST specify the Vendor-specific Information Option in an Option
Request Option.
- MAY specify an associated Vendor Class Option.
- MAY specify the Vendor-specific Information Option with any data.
Severs only return the Vendor-specific Information Options if
specified in Option Request Options from clients and:
- MAY use the Enterprise Numbers in the associated Vendor Class
Options to restrict the set of Enterprise Numbers in the Vendor-
specific Information Options returned.
- MAY return all configured Vendor-specific Information Options.
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- MAY use other information in the packet or in its configuration to
determine which set of Enterprise Numbers in the Vendor-specific
Information Options to return.
23.18. Interface-Id Option
The relay agent MAY send the Interface-id option to identify the
interface on which the client message was received. If a relay agent
receives a Relay-reply message with an Interface-id option, the relay
agent relays the message to the client through the interface
identified by the option.
The format of the Interface ID option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_INTERFACE_ID | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. interface-id .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 31: Interface-ID Option Format
option-code OPTION_INTERFACE_ID (18).
option-len Length of interface-id field.
interface-id An opaque value of arbitrary length generated
by the relay agent to identify one of the
relay agent's interfaces.
The server MUST copy the Interface-Id option from the Relay-forward
message into the Relay-reply message the server sends to the relay
agent in response to the Relay-forward message. This option MUST NOT
appear in any message except a Relay-forward or Relay-reply message.
Servers MAY use the Interface-ID for parameter assignment policies.
The Interface-ID SHOULD be considered an opaque value, with policies
based on exact match only; that is, the Interface-ID SHOULD NOT be
internally parsed by the server. The Interface-ID value for an
interface SHOULD be stable and remain unchanged, for example, after
the relay agent is restarted; if the Interface-ID changes, a server
will not be able to use it reliably in parameter assignment policies.
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23.19. Reconfigure Message Option
A server includes a Reconfigure Message option in a Reconfigure
message to indicate to the client whether the client responds with a
Renew message, a Rebind message, or an Information-request message.
The format of this option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_RECONF_MSG | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type |
+-+-+-+-+-+-+-+-+
Figure 32: Reconfigure Message Option Format
option-code OPTION_RECONF_MSG (19).
option-len 1.
msg-type 5 for Renew message, 6 for Rebind, 11 for
Information-request message.
The Reconfigure Message option can only appear in a Reconfigure
message.
23.20. Reconfigure Accept Option
A client uses the Reconfigure Accept option to announce to the server
whether the client is willing to accept Reconfigure messages, and a
server uses this option to tell the client whether or not to accept
Reconfigure messages. The default behavior, in the absence of this
option, means unwillingness to accept Reconfigure messages, or
instruction not to accept Reconfigure messages, for the client and
server messages, respectively. The following figure gives the format
of the Reconfigure Accept option:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_RECONF_ACCEPT | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 33: Reconfigure Accept Option Format
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option-code OPTION_RECONF_ACCEPT (20).
option-len 0.
23.21. Identity Association for Prefix Delegation Option
The IA_PD option is used to carry a prefix delegation identity
association, the parameters associated with the IA_PD and the
prefixes associated with it.
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_PD | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IAID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. IA_PD-options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 34: Identity Association for Prefix Delegation Option Format
option-code OPTION_IA_PD (25).
option-length 12 + length of IA_PD-options field.
IAID The unique identifier for this IA_PD; the
IAID must be unique among the identifiers for
all of this requesting router's IA_PDs.
T1 The time at which the requesting router
should contact the delegating router from
which the prefixes in the IA_PD were obtained
to extend the lifetimes of the prefixes
delegated to the IA_PD; T1 is a time duration
relative to the current time expressed in
units of seconds.
T2 The time at which the requesting router
should contact any available delegating
router to extend the lifetimes of the
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prefixes assigned to the IA_PD; T2 is a time
duration relative to the current time
expressed in units of seconds.
IA_PD-options Options associated with this IA_PD.
The IA_PD-options field encapsulates those options that are specific
to this IA_PD. For example, all of the IA_PD Prefix Options carrying
the prefixes associated with this IA_PD are in the IA_PD-options
field.
An IA_PD option may only appear in the options area of a DHCP
message. A DHCP message may contain multiple IA_PD options.
The status of any operations involving this IA_PD is indicated in a
Status Code option in the IA_PD-options field.
Note that an IA_PD has no explicit "lifetime" or "lease length" of
its own. When the valid lifetimes of all of the prefixes in a IA_PD
have expired, the IA_PD can be considered as having expired. T1 and
T2 are included to give delegating routers explicit control over when
a requesting router should contact the delegating router about a
specific IA_PD.
In a message sent by a requesting router to a delegating router,
values in the T1 and T2 fields indicate the requesting router's
preference for those parameters. The requesting router sets T1 and
T2 to zero if it has no preference for those values. In a message
sent by a delegating router to a requesting router, the requesting
router MUST use the values in the T1 and T2 fields for the T1 and T2
parameters. The values in the T1 and T2 fields are the number of
seconds until T1 and T2.
The delegating router selects the T1 and T2 times to allow the
requesting router to extend the lifetimes of any prefixes in the
IA_PD before the lifetimes expire, even if the delegating router is
unavailable for some short period of time. Recommended values for T1
and T2 are .5 and .8 times the shortest preferred lifetime of the
prefixes in the IA_PD that the delegating router is willing to
extend, respectively. If the time at which the prefixes in an IA_PD
are to be renewed is to be left to the discretion of the requesting
router, the delegating router sets T1 and T2 to 0.
If a delegating router receives an IA_PD with T1 greater than T2, and
both T1 and T2 are greater than 0, the delegating router ignores the
invalid values of T1 and T2 and processes the IA_PD as though the
requesting router had set T1 and T2 to 0.
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If a requesting router receives an IA_PD with T1 greater than T2, and
both T1 and T2 are greater than 0, the requesting router discards the
IA_PD option and processes the remainder of the message as though the
requesting router had not included the IA_PD option.
23.22. IA Prefix Option
The IA_PD Prefix option is used to specify IPv6 address prefixes
associated with an IA_PD. The IA_PD Prefix option must be
encapsulated in the IA_PD-options field of an IA_PD 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_IAPREFIX | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| preferred-lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| valid-lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| prefix-length | |
+-+-+-+-+-+-+-+-+ IPv6 prefix |
| (16 octets) |
| |
| |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | .
+-+-+-+-+-+-+-+-+ .
. IAprefix-options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 35: IA Prefix Option Format
option-code OPTION_IAPREFIX (26).
option-length 25 + length of IAprefix-options field.
preferred-lifetime The recommended preferred lifetime for the
IPv6 prefix in the option, expressed in units
of seconds. A value of 0xFFFFFFFF represents
infinity.
valid-lifetime The valid lifetime for the IPv6 prefix in the
option, expressed in units of seconds. A
value of 0xFFFFFFFF represents infinity.
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prefix-length Length for this prefix in bits.
IPv6-prefix An IPv6 prefix.
IAprefix-options Options associated with this prefix.
In a message sent by a requesting router to a delegating router, the
values in the fields can be used to indicate the requesting router's
preference for those values. The requesting router may send a value
of zero to indicate no preference. A requesting router may set the
IPv6 prefix field to zero and a given value in the prefix-length
field to indicate a preference for the size of the prefix to be
delegated.
In a message sent by a delegating router the preferred and valid
lifetimes should be set to the values of AdvPreferredLifetime and
AdvValidLifetime as specified in section 6.2.1, "Router Configuration
Variables" of [RFC2461], unless administratively configured.
A requesting router discards any prefixes for which the preferred
lifetime is greater than the valid lifetime. A delegating router
ignores the lifetimes set by the requesting router if the preferred
lifetime is greater than the valid lifetime and ignores the values
for T1 and T2 set by the requesting router if those values are
greater than the preferred lifetime.
The values in the preferred and valid lifetimes are the number of
seconds remaining for each lifetime.
An IA_PD Prefix option may appear only in an IA_PD option. More than
one IA_PD Prefix Option can appear in a single IA_PD option.
The status of any operations involving this IA_PD Prefix option is
indicated in a Status Code option in the IAprefix-options field.
23.23. SOL_MAX_RT Option
A DHCP server sends the SOL_MAX_RT option to a client to override the
default value of SOL_MAX_RT. The value of SOL_MAX_RT in the option
replaces the default value defined in Section 6.5. One use for the
SOL_MAX_RT option is to set a longer value for SOL_MAX_RT, which
reduces the Solicit traffic from a client that has not received a
response to its Solicit messages.
The format of the SOL_MAX_RT option is:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-code | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SOL_MAX_RT value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 36: SOL_MAX_RT Option Format
option-code OPTION_SOL_MAX_RT (82).
option-len 4.
SOL_MAX_RT value Overriding value for SOL_MAX_RT in seconds;
MUST be in range: 60 <= "value" <= 86400 (1
day).
A DHCP client MUST include the SOL_MAX_RT option code in any Option
Request option (see Section 23.7) it sends.
The DHCP server MAY include the SOL_MAX_RT option in any response it
sends to a client that has included the SOL_MAX_RT option code in an
Option Request option. The SOL_MAX_RT option is sent in the main
body of the message to client, not as an encapsulated option in,
e.g., an IA_NA, IA_TA, or IA_PD option.
A DHCP client MUST ignore any SOL_MAX_RT option values that are less
than 60 or more than 86400.
If a DHCP client receives a message containing a SOL_MAX_RT option
that has a valid value for SOL_MAX_RT, the client MUST set its
internal SOL_MAX_RT parameter to the value contained in the
SOL_MAX_RT option. This value of SOL_MAX_RT is then used by the
retransmission mechanism defined in Section 15 and Section 18.1.2.
Updated SOL_MAX_RT value applies only to the network interface on
which the client received SOL_MAX_RT option.
23.24. INF_MAX_RT Option
A DHCP server sends the INF_MAX_RT option to a client to override the
default value of INF_MAX_RT. The value of INF_MAX_RT in the option
replaces the default value defined in Section 6.5. One use for the
INF_MAX_RT option is to set a longer value for INF_MAX_RT, which
reduces the Information-request traffic from a client that has not
received a response to its Information-request messages.
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The format of the INF_MAX_RT 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-code | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INF_MAX_RT value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 37: INF_MAX_RT Option Format
option-code OPTION_INF_MAX_RT (83).
option-len 4.
SOL_MAX_RT value Overriding value for INF_MAX_RT in seconds;
MUST be in range: 60 <= "value" <= 86400 (1
day).
A DHCP client MUST include the INF_MAX_RT option code in any Option
Request option (see Section 23.7) it sends.
The DHCP server MAY include the INF_MAX_RT option in any response it
sends to a client that has included the INF_MAX_RT option code in an
Option Request option. The INF_MAX_RT option is sent in the main
body of the message to client, not as an encapsulated option in,
e.g., an IA_NA, IA_TA, or IA_PD option.
A DHCP client MUST ignore any INF_MAX_RT option values that are less
than 60 or more than 86400.
If a DHCP client receives a message containing an INF_MAX_RT option
that has a valid value for INF_MAX_RT, the client MUST set its
internal INF_MAX_RT parameter to the value contained in the
INF_MAX_RT option. This value of INF_MAX_RT is then used by the
retransmission mechanism defined in Section 15 and Section 19.1.5.
Updated INF_MAX_RT value applies only to the network interface on
which the client received INF_MAX_RT option.
24. Security Considerations
The threat to DHCP is inherently an insider threat (assuming a
properly configured network where DHCPv6 ports are blocked on the
perimeter gateways of the enterprise). Regardless of the gateway
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configuration, however, the potential attacks by insiders and
outsiders are the same.
Use of manually configured preshared keys for IPsec between relay
agents and servers does not defend against replayed DHCP messages.
Replayed messages can represent a DOS attack through exhaustion of
processing resources, but not through mis-configuration or exhaustion
of other resources such as assignable addresses.
One attack specific to a DHCP client is the establishment of a
malicious server with the intent of providing incorrect configuration
information to the client. The motivation for doing so may be to
mount a "man in the middle" attack that causes the client to
communicate with a malicious server instead of a valid server for
some service such as DNS or NTP. The malicious server may also mount
a denial of service attack through misconfiguration of the client
that causes all network communication from the client to fail.
A malicious DHCP server might cause a client to set its SOL_MAX_RT
and INF_MAX_RT parameters to an unreasonably high value with the
SOL_MAX_RT and INF_MAX_RT options, which may cause an undue delay in
a client completing its DHCP protocol transaction in the case no
other valid response is received. Assuming the client also receives
a response from a valid DHCP server, large values for SOL_MAX_RT and
INF_MAX_RT will not have any effect.
There is another threat to DHCP clients from mistakenly or
accidentally configured DHCP servers that answer DHCP client requests
with unintentionally incorrect configuration parameters.
A DHCP client may also be subject to attack through the receipt of a
Reconfigure message from a malicious server that causes the client to
obtain incorrect configuration information from that server. Note
that although a client sends its response (Renew or Information-
request message) through a relay agent and, therefore, that response
will only be received by servers to which DHCP messages are relayed,
a malicious server could send a Reconfigure message to a client,
followed (after an appropriate delay) by a Reply message that would
be accepted by the client. Thus, a malicious server that is not on
the network path between the client and the server may still be able
to mount a Reconfigure attack on a client. The use of transaction
IDs that are cryptographically sound and cannot easily be predicted
will also reduce the probability that such an attack will be
successful.
The threat specific to a DHCP server is an invalid client
masquerading as a valid client. The motivation for this may be for
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theft of service, or to circumvent auditing for any number of
nefarious purposes.
The threat common to both the client and the server is the resource
"denial of service" (DoS) attack. These attacks typically involve
the exhaustion of available addresses, or the exhaustion of CPU or
network bandwidth, and are present anytime there is a shared
resource.
In the case where relay agents add additional options to Relay
Forward messages, the messages exchanged between relay agents and
servers may be used to mount a "man in the middle" or denial of
service attack.
This threat model does not consider the privacy of the contents of
DHCP messages to be important. DHCP is not used to exchange
authentication or configuration information that must be kept secret
from other networks nodes.
DHCP authentication provides for authentication of the identity of
DHCP clients and servers, and for the integrity of messages delivered
between DHCP clients and servers. DHCP authentication does not
provide any privacy for the contents of DHCP messages.
The Delayed Authentication protocol described in Section 22.4 uses a
secret key that is shared between a client and a server. The use of
a "DHCP realm" in the shared key allows identification of
administrative domains so that a client can select the appropriate
key or keys when roaming between administrative domains. However,
the Delayed Authentication protocol does not define any mechanism for
sharing of keys, so a client may require separate keys for each
administrative domain it encounters. The use of shared keys may not
scale well and does not provide for repudiation of compromised keys.
This protocol is focused on solving the intradomain problem where the
out-of-band exchange of a shared key is feasible.
Because of the opportunity for attack through the Reconfigure
message, a DHCP client MUST discard any Reconfigure message that does
not include authentication or that does not pass the validation
process for the authentication protocol.
The Reconfigure Key protocol described in Section 22.5 provides
protection against the use of a Reconfigure message by a malicious
DHCP server to mount a denial of service or man-in-the-middle attack
on a client. This protocol can be compromised by an attacker that
can intercept the initial message in which the DHCP server sends the
key to the client.
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Communication between a server and a relay agent, and communication
between relay agents, can be secured through the use of IPsec, as
described in Section 22.1. The use of manual configuration and
installation of static keys are acceptable in this instance because
relay agents and the server will belong to the same administrative
domain and the relay agents will require other specific configuration
(for example, configuration of the DHCP server address) as well as
the IPsec configuration.
A rogue delegating router can issue bogus prefixes to a requesting
router. This may cause denial of service due to unreachability.
A malicious requesting router may be able to mount a denial of
service attack by repeated requests for delegated prefixes that
exhaust the delegating router's available prefixes.
To guard against attacks through prefix delegation, requesting
routers and delegating routers SHOULD use DHCP authentication as
described in Section 22. For point to point links, where one trusts
that there is no man in the middle, or one trusts layer two
authentication, DHCP authentication or IPsec may not be necessary.
Because a requesting router and delegating routers must each have at
least one assigned IPv6 address, the routers may be able to use IPsec
for authentication of DHCPv6 messages. The details of using IPsec
for DHCPv6 are under development.
Networks configured with delegated prefixes should be configured to
preclude intentional or inadvertent inappropriate advertisement of
these prefixes.
25. IANA Considerations
This document does not define any new DHCPv6 name spaces or
definitions.
IANA is requested to update the http://www.iana.org/assignments/
dhcpv6-parameters/dhcpv6-parameters.xhtml page to add a reference to
this document for definitions previously created by [RFC3315],
[RFC3633], and [RFC7083].
26. Acknowledgments
The following people are authors of the original RFC 3315: Ralph
Droms, Jim Bound, Bernie Volz, Ted Lemon, Charles Perkins, and Mike
Carney. The following people are authors of the original RFC 3633:
Ole Troan and Ralph Droms. This document is merely a refinement of
their work and would not be possible without their original work.
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A number of additional people have contributed to identifying issues
with RFC 3315 and RFC 3633 and proposed resolutions to these issues
as reflected in this document (in no particular order): Ole Troan,
Robert Marks, Leaf Yeh, Tim Winters, Michelle Cotton, Pablo Armando,
John Brzozowski, Suresh Krishnan, Hideshi Enokihara, Alexandru
Petrescu, Yukiyo Akisada, Tatuya Jinmei, Fred Templin. With special
thanks to Ralph Droms for answering many questions related to the
original RFC 3315 work.
The following acknowledgements are from the original RFC 3315 and RFC
3633:
Thanks to the DHC Working Group and the members of the IETF for their
time and input into the specification. In particular, thanks also
for the consistent input, ideas, and review by (in alphabetical
order) Bernard Aboba, Bill Arbaugh, Thirumalesh Bhat, Steve Bellovin,
A. K. Vijayabhaskar, Brian Carpenter, Matt Crawford, Steve Deering,
Francis Dupont, Dave Forster, Brian Haberman, Richard Hussong, Tatuya
Jinmei, Kim Kinnear, Fredrik Lindholm, Tony Lindstrom, Josh
Littlefield, Gerald Maguire, Jack McCann, Shin Miyakawa, Thomas
Narten, Erik Nordmark, Jarno Rajahalme, Yakov Rekhter, Pekka Savola,
Mark Stapp, Matt Thomas, Sue Thomson, Tatuya Jinmei, Bernie Volz,
Trevor Warwick, Phil Wells and Toshi Yamasaki.
Thanks to Steve Deering and Bob Hinden, who have consistently taken
the time to discuss the more complex parts of the IPv6
specifications.
And, thanks to Steve Deering for pointing out at IETF 51 in London
that the DHCPv6 specification has the highest revision number of any
Internet Draft.
27. References
27.1. Normative References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", STD 37,
RFC 826, November 1982.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
[RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)",
RFC 2136, April 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December
1998.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, December 1998.
[RFC2526] Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast
Addresses", RFC 2526, March 1999.
[RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP
Messages", RFC 3118, June 2001.
[RFC3646] Droms, R., "DNS Configuration options for Dynamic Host
Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
December 2003.
[RFC4075] Kalusivalingam, V., "Simple Network Time Protocol (SNTP)
Configuration Option for DHCPv6", RFC 4075, May 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
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[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010.
[RFC6221] Miles, D., Ooghe, S., Dec, W., Krishnan, S., and A.
Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, May
2011.
[RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based
DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, August
2011.
[RFC6724] Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, September 2012.
[RFC7083] Droms, R., "Modification to Default Values of SOL_MAX_RT
and INF_MAX_RT", RFC 7083, November 2013.
[RFC7227] Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and
S. Krishnan, "Guidelines for Creating New DHCPv6 Options",
BCP 187, RFC 7227, May 2014.
[RFC7283] Cui, Y., Sun, Q., and T. Lemon, "Handling Unknown DHCPv6
Messages", RFC 7283, July 2014.
27.2. Informative References
[I-D.ietf-dhc-topo-conf]
Lemon, T. and T. Mrugalski, "Customizing DHCP
Configuration on the Basis of Network Topology", draft-
ietf-dhc-topo-conf-04 (work in progress), January 2015.
[IANA-PEN]
IANA, "Private Enterprise Numbers registry
http://www.iana.org/assignments/enterprise-numbers", .
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992.
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[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, February
1997.
[RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[RFC3041] Narten, T. and R. Draves, "Privacy Extensions for
Stateless Address Autoconfiguration in IPv6", RFC 3041,
January 2001.
[RFC3162] Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6", RFC
3162, August 2001.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC3736] Droms, R., "Stateless Dynamic Host Configuration Protocol
(DHCP) Service for IPv6", RFC 3736, April 2004.
[RFC3769] Miyakawa, S. and R. Droms, "Requirements for IPv6 Prefix
Delegation", RFC 3769, June 2004.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
Requirements for IPv6 Customer Edge Routers", RFC 7084,
November 2013.
[RFC7341] Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I.
Farrer, "DHCPv4-over-DHCPv6 (DHCP 4o6) Transport", RFC
7341, August 2014.
Appendix A. Changes since RFC3315
1. Incorporated RFC3315 errata (ids: 294, 1373, 2928, 1815, 3577,
2509, 295).
2. Partially incorporated RFC3315 errata id 2472 (place other IA
options if NoAddrsAvail is sent in Advertise).
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3. Clarified section 21.4.1 of RFC3315 by defining length of "key
ID" field and specifying that 'DHCP realm' is Domain Name
encoded as per section 8 of RFC3315. Ticket #43.
4. Added DUID-UUID and reference to RFC6355. Ticket #54.
5. Specified a minimum length for the DUID in section "9.1. DUID
Contents". Ticket #39.
6. Removed the use of term "sub-options" from section "19.1.1.
Creation and Transmission of Reconfigure Messages". Ticket #40.
7. Added text to section 22.6 "IA Address Option" about the usage
of unspecified address to express the client hints for Preferred
and Valid lifetimes. Ticket #45.
8. Updated text in 21.4.2 of RFC3315 ("Message Validation") as
suggested in section 3.1 of draft-ietf-dhc-dhcpv6-clarify-auth-
01. Ticket #87.
9. Merged RFC7083, "Modification to Default Values of SOL_MAX_RT
and INF_MAX_RT", into this document. Ticket #51.
10. Incorporated RFC3315 errata (id 2471), into section 17.1.3.
Ticket #25.
11. Added text that relay agents MUST NOT modify the relayed message
to section 20.1.2. Ticket #57.
12. Modified the text in section 21.4.4.5, Receiving Reply Messages,
to remove special treatment of a Reply validation failure
(client ignores message). Ticket #89.
13. Appendix C updated: Authentication option is no longer allowed
in Relay-forward and Relay-reply messages, ORO is no longer
allowed in Confirm, Release and Decline messages; Preference
option is no longer allowed in Reply messages (only in
Advertise). Ticket #10.
14. Removed "silently" from several instances of "silently ignores"
or "silently" discards. It is up to software vendor if and how
to log such events (debug log message, event log, message pop-up
etc.). Ticket #50.
15. Clarified that: there should be no more that one instance of
Vendor Class option with a given Enterprise Number; that one
instance of Vendor Class can contain multiple encapsulated
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options; the same applies to Vendor Specific Information option.
Ticket #22.
16. Clarified relay agent definition. Ticket #12.
17. Changed REL_MAX_RC and DEC_MAX_RC defaults from 5 to 4 and added
retry to parameter description. Ticket #84.
18. Clarify handling process for Vendor-specific Information Option
and Vendor Class Option. Ticket #20.
19. Replace "monotonic" with "strictly monotonic" in Section 21.3.
Ticket #11.
20. Incorporate everything of RFC 6644, except for Security
Considerations Section, which has already covered in a more
abstracted way. Ticket #55 & #56.
21. Clarify the server behavior process when a client violates
Delayed Authentication Protocol, in Section 21.4. Ticket #90.
22. Updated titles of sections 19.4.2. and 19.4.4. to include Rebind
messages.
23. Applied many of the review comments from a review done by Fred
Templin in August 2006. Ticket #14.
24. Reworded the first paragraph of Section 15 to relax the "SHOULD"
requirement to drop the messages which contain the options not
expected in the current message. Ticket #17.
25. Changed WG to DHC, added keywords
26. Loosened requirements for DUID-EN, so that DUID type can be used
for virtual machines. Ticket #16.
27. Clarified that IA may contain other resources than just address.
Ticket #93.
28. Clarified that most options are singletons (i.e. can appear only
once). Ticket #83.
29. Merged sections 1 (Ticket #96), 2 (Ticket #97), 3 (Ticket #98),
4 (Ticket #99), 6 (Ticket #101), 8 (Ticket #103), 9 (Ticket
#104), 10 (Ticket #105), 11 (Ticket #106), 13 (Ticket #108), 14
(Ticket #109), 15 (Ticket #110), 16 (Ticket #111), 17 (Ticket
#112) and 19 (Ticket #113) from RFC3633 (Prefix Delegation).
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30. Clarified that encapsulated options must be requested using top
level ORO (ticket #38).
31. Clarified that configuration for interface X should be requested
over interface X (ticket #48).
32. CONFIRM is now an optional message (MUST send Confirm eased to
SHOULD) (ticket #120).
33. Added reference to RFC7227: DHCPv6 Option Guidelines (ticket
#121).
34. Added new section 5 providing an overview of DHCPv6 operational
modes and removed two prefix delegation sections from section 1.
See tickets #53, #100, and #102.
35. Addressed ticket #115 - don't use DHCPv6 for DHCPv4
configuration.
36. Revised IANA Considerations based on ticket #117.
37. Updated IAID description in the terminology with the
clarification that the IAID is unique among IAs of a specific
type, rather than globally unique among all IAs (ticket #94).
38. Merged Section 12 from RFC3633 (ticket #107)
39. Clarified behavior for unknown messages (RFC7283), ticket #58.
40. Addressed tickets #123 and #126, and clarified that the client
SHOULD abandon its bindings when restarts the server
solicitation.
41. Clarified link-address field usage, ticket #73.
Appendix B. Changes since RFC3633
1. Incorporated RFC3633 errata (ids: 248, 1880, 2468, 2469, 2470,
3736)
2. ...
Appendix C. Appearance of Options in Message Types
The following table indicates with a "*" the options are allowed in
each DHCP message type:
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Client Server IA_NA IA_PD Option Pref Elap. Relay Auth. Server
ID ID IA_TA Request Time Msg. Unicast
Solicit * * * * * *
Advert. * * * * * *
Request * * * * * * *
Confirm * * * *
Renew * * * * * * *
Rebind * * * * * *
Decline * * * * * *
Release * * * * * *
Reply * * * * * *
Reconf. * * * *
Inform. * (see note) * * *
R-forw. *
R-repl. *
NOTE:
Only included in Information-request messages that are sent in
response to a Reconfigure (see Section 20.4.3).
Status Rap. User Vendor Vendor Inter. Recon. Recon. SOL_MAX_RT
Code Comm. Class Class Spec. ID Msg. Accept INF_MAX_RT
Solicit * * * * *
Advert. * * * * * *
Request * * * *
Confirm * * *
Renew * * * *
Rebind * * * *
Decline * * *
Release * * *
Reply * * * * * * *
Reconf. *
Inform. * * * *
R-forw. * * * *
R-repl. * * * *
Appendix D. Appearance of Options in the Options Field of DHCP Options
The following table indicates with a "*" where options can appear in
the options field of other options:
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Option IA_NA/ Relay Relay
Field IA_TA IAADDR IA_PD IAPREFIX Forw. Reply
Client ID *
Server ID *
IA_NA/IA_TA *
IAADDR *
IA_PD *
IAPREFIX *
ORO *
Preference *
Elapsed Time *
Relay Message * *
Authentic. *
Server Uni. *
Status Code * * *
Rapid Comm. *
User Class *
Vendor Class *
Vendor Info. * * *
Interf. ID * *
Reconf. MSG. *
Reconf. Accept *
Note: "Relay Forw" / "Relay Reply" options appear in the options
field of the message but may only appear in these messages.
Authors' Addresses
Tomek Mrugalski (editor)
Internet Systems Consortium, Inc.
950 Charter Street
Redwood City, CA 94063
USA
Email: tomasz.mrugalski@gmail.com
Marcin Siodelski
Internet Systems Consortium, Inc.
950 Charter St.
Redwood City, CA 94063
USA
Email: msiodelski@gmail.com
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Bernie Volz (editor)
Cisco Systems, Inc.
1414 Massachusetts Ave
Boxborough, MA 01719
USA
Email: volz@cisco.com
Andrew Yourtchenko
Cisco Systems, Inc.
De Kleetlaan, 7
Diegem B-1831
Belgium
Email: ayourtch@cisco.com
Michael C. Richardson
Sandelman Software Works
470 Dawson Avenue
Ottawa, ON K1Z 5V7
CA
Email: mcr+ietf@sandelman.ca
URI: http://www.sandelman.ca/
Sheng Jiang
Huawei Technologies Co., Ltd
Q14, Huawei Campus, No.156 Beiqing Road
Hai-Dian District, Beijing, 100095
P.R. China
Email: jiangsheng@huawei.com
Ted Lemon
Nominum, Inc.
950 Charter St.
Redwood City, CA 94043
USA
Email: Ted.Lemon@nominum.com
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