One document matched: draft-ietf-dhc-rfc3315bis-00.xml
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<rfc category="std" docName="draft-ietf-dhc-rfc3315bis-00" ipr="pre5378Trust200902"
obsoletes="3315,3633,3736,7083">
<front>
<title abbrev="RFC 3315 bis">Dynamic Host Configuration Protocol for IPv6 (DHCPv6) bis</title>
<author fullname="Tomek Mrugalski" initials="T." role="editor" surname="Mrugalski">
<organization abbrev="ISC">Internet Systems Consortium, Inc.</organization>
<address>
<postal>
<street>950 Charter Street</street>
<city>Redwood City</city>
<region>CA</region>
<code>94063</code>
<country>USA</country>
</postal>
<email>tomasz.mrugalski@gmail.com</email>
</address>
</author>
<author fullname="Marcin Siodelski" initials="M" surname="Siodelski">
<organization abbrev="ISC">Internet Systems Consortium, Inc.</organization>
<address>
<postal>
<street>950 Charter St.</street>
<city>Redwood City</city>
<region>CA</region>
<code>94063</code>
<country>USA</country>
</postal>
<email>msiodelski@gmail.com</email>
</address>
</author>
<author fullname="Bernie Volz" initials="B" surname="Volz">
<organization abbrev="Cisco">Cisco Systems, Inc.</organization>
<address>
<postal>
<street>1414 Massachusetts Ave</street>
<city>Boxborough, MA 01719</city>
<region></region>
<code></code>
<country>USA</country>
</postal>
<email>volz@cisco.com</email>
</address>
</author>
<author fullname="Andrew Yourtchenko" initials="A" surname="Yourtchenko">
<organization abbrev="Cisco">Cisco Systems, Inc.</organization>
<address>
<postal>
<street>De Kleetlaan, 7</street>
<city>Diegem</city>
<code>B-1831</code>
<country>Belgium</country>
</postal>
<email>ayourtch@cisco.com</email>
</address>
</author>
<author initials="M." surname="Richardson" fullname="Michael C. Richardson">
<organization abbrev="SSW">Sandelman Software Works</organization>
<address>
<postal>
<street>470 Dawson Avenue</street>
<city>Ottawa</city>
<region>ON</region>
<code>K1Z 5V7</code>
<country>CA</country>
</postal>
<email>mcr+ietf@sandelman.ca</email>
<uri>http://www.sandelman.ca/</uri>
</address>
</author>
<author fullname="Sheng Jiang" initials="S." surname="Jiang">
<organization abbrev="Huawei">Huawei Technologies Co., Ltd</organization>
<address>
<postal>
<street>Q14, Huawei Campus, No.156 Beiqing Road</street>
<city>Hai-Dian District, Beijing, 100095</city>
<country>P.R. China</country>
</postal>
<email>jiangsheng@huawei.com</email>
</address>
</author>
<author fullname="Ted Lemon" initials="T" surname="Lemon">
<organization abbrev="Nominum">Nominum, Inc.</organization>
<address>
<postal>
<street>950 Charter St.</street>
<city>Redwood City</city>
<region>CA</region>
<code>94043</code>
<country>USA</country>
</postal>
<email>Ted.Lemon@nominum.com</email>
</address>
</author>
<date year="2015"/>
<area>Internet</area>
<workgroup>Dynamic Host Configuration (DHC)</workgroup>
<keyword>DHCPv6</keyword>
<keyword>IPv6</keyword>
<keyword>DHCP</keyword>
<!-- SECTION 0: Abstract -->
<abstract>
<t>
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.
</t>
</abstract>
</front>
<middle>
<section title="Introduction and Overview">
<!-- 1, line 230-->
<t>This document describes DHCP for IPv6 (DHCP), a client/server
protocol that provides managed configuration of devices.</t>
<t>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.</t>
<t>DHCP is the "stateful address autoconfiguration protocol" and the
"stateful autoconfiguration protocol" referred to in "IPv6 Stateless
Address Autoconfiguration" <xref target="RFC4862"/>.</t>
<t>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.</t>
<t>The operational models and relevant configuration information for
DHCPv4 <xref target="RFC2132"/><xref target="RFC2131"/> and DHCPv6
are sufficiently different that integration between the two
services is not included in this document. <xref target="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 rather than
DHCPv6 when conveying IPv4 configuration information to
nodes. <xref target="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.</t>
<t>The remainder of this introduction summarizes DHCP, explaining the
message exchange mechanisms and example message flows. The message flows
in <xref target='RFC3315-1.2'/> and <xref target='RFC3315-1.3'/> are intended
as illustrations of DHCP operation
rather than an exhaustive list of all possible client-server
interactions. <xref target='OpModes'/> provides an overview of common
operational models. <xref target='RFC3315-17'/>, <xref target='RFC3315-18'/>, and
<xref target='RFC3315-19'/> explain client and server
operation in detail.</t>
<section title="Protocols and Addressing">
<!-- 1.1, line 260-->
<t>Clients and servers exchange DHCP messages using UDP <xref
target="RFC0768"/>. The client uses a link-local address or addresses
determined through other mechanisms for transmitting and receiving
DHCP messages.</t>
<t>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.</t>
<t>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.</t>
<t>Once the client has determined the address of a server, it may
under some circumstances send messages directly to the server using
unicast.</t>
</section>
<!-- ends: "1.1 from line 260-->
<section anchor='RFC3315-1.2' title="Client-server Exchanges Involving Two Messages">
<!-- 1.2, line 284-->
<t>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 <xref target="RFC3646"/> or NTP
servers <xref target="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.</t>
<t>This message exchange assumes that the client requires only
configuration information and does not require the assignment of any
IPv6 addresses.</t>
<t>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.</t>
<t>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.</t>
</section>
<!-- ends: "1.2 from line 284-->
<section anchor='RFC3315-1.3' title="Client-server Exchanges Involving Four Messages">
<!-- 1.3, line 323-->
<t>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.</t>
<t>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.</t>
</section>
<!-- ends: "1.3 from line 323-->
</section>
<!-- ends: "1 from line 230-->
<section title="Requirements">
<!-- 2, line 343-->
<t>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 <xref
target="RFC2119"/>.</t>
<t>This document also makes use of internal conceptual variables to
describe protocol behavior and external variables that an implementation
must allow system administrators to change. The specific variable names,
how their values change, and how their settings influence protocol
behavior are provided to demonstrate protocol behavior. An
implementation is not required to have them in the exact form described
here, so long as its external behavior is consistent with that described
in this document.</t>
</section>
<!-- ends: "2 from line 343-->
<section title="Background">
<!-- 3, line 360-->
<t>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 <xref target="RFC2460"/>, the IPv6
Addressing Architecture <xref target="RFC4291"/>, IPv6 Stateless Address
Autoconfiguration <xref target="RFC4862"/>, IPv6 Neighbor Discovery
Processing <xref target="RFC4861"/>, and Dynamic Updates to DNS <xref
target="RFC2136"/>. These specifications enable DHCP to build upon the
IPv6 work to provide both robust stateful autoconfiguration and
autoregistration of DNS Host Names.</t>
<t>The IPv6 Addressing Architecture specification <xref
target="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.</t>
<t>IPv6 Stateless Address Autoconfiguration <xref target="RFC4862"/>
specifies procedures by which a node may autoconfigure addresses based
on router advertisements <xref target="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.</t>
<t>IPv6 Neighbor Discovery <xref target="RFC4861"/> is the node
discovery protocol in IPv6 which replaces and enhances functions of ARP
<xref target="RFC0826"/>. To understand IPv6 and stateless address
autoconfiguration, it is strongly recommended that implementors
understand IPv6 Neighbor Discovery.</t>
<t>Dynamic Updates to DNS <xref target="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.</t>
</section>
<!-- ends: "3 from line 360-->
<section title="Terminology">
<!-- 4, line 402-->
<t>This section defines terminology specific to IPv6 and DHCP used in
this document.</t>
<section title="IPv6 Terminology">
<!-- 4.1, line 408-->
<t>IPv6 terminology relevant to this specification from the IPv6
Protocol <xref target="RFC2460"/>, IPv6 Addressing Architecture <xref
target="RFC4291"/>, and IPv6 Stateless Address Autoconfiguration <xref
target="RFC4862"/> is included below.</t>
<t>
<list hangIndent="26" style="hanging">
<t hangText="address">An IP layer identifier for an interface or a set of
interfaces.</t>
<t hangText="host">Any node that is not a router.</t>
<t hangText="IP"> Internet Protocol Version 6 (IPv6). The terms IPv4 and IPv6 are
used only in contexts where it is necessary to avoid ambiguity.</t>
<t hangText="interface"> A node's attachment to a link.</t>
<t hangText="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.</t>
<t hangText="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.</t>
<t hangText="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.</t>
<t hangText="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.</t>
<t hangText="neighbor"> A node attached to the same link.</t>
<t hangText="node"> A device that implements IP.</t>
<t hangText="packet"> An IP header plus payload.</t>
<t hangText="prefix"> The initial bits of an address, or a set of IP addresses
that share the same initial bits.</t>
<t hangText="prefix length"> The number of bits in a prefix.</t>
<t hangText="router"> A node that forwards IP packets not explicitly addressed to
itself.</t>
<t hangText="unicast address"> An identifier for a single interface. A packet sent
to a unicast address is delivered to the interface identified by that
address.</t>
</list>
</t>
</section>
<!-- ends: "4.1 from line 408-->
<section title="DHCP Terminology">
<!-- 4.2, line 478-->
<t>Terminology specific to DHCP can be found below.</t>
<t>
<list hangIndent="26" style="hanging">
<t hangText="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.</t>
<t hangText="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.</t>
<t hangText="binding"> A binding (or, client binding) is a group of server data
records containing the information the server has about the addresses
in an IA or configuration information explicitly assigned to the
client. Configuration information that has been returned to a client
through a policy - for example, the information returned to all
clients on the same link - does not require a binding. A binding
containing information about an IA is indexed by the tuple <DUID,
IA-type, IAID> (where IA-type is the type of address in the IA; for
example, temporary). A binding containing configuration information
for a client is indexed by <DUID>. </t>
<t hangText="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.</t>
<t hangText="delegating router:">The router that acts as a
DHCP server, and is responding to the prefix request.</t>
<t hangText="DHCP">Dynamic Host Configuration Protocol for IPv6. The terms DHCPv4
and DHCPv6 are used only in contexts where it is necessary to avoid
ambiguity.</t>
<t hangText="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.</t>
<t hangText="DHCP domain"> A set of links managed by DHCP and operated by a single
administrative entity.</t>
<t hangText="DHCP realm"> A name used to identify the DHCP administrative domain
from which a DHCP authentication key was selected.</t>
<t hangText="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.</t>
<t hangText="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 functionality of delegating router,
if it supports prefix delegation.</t>
<t hangText="DUID"> A DHCP Unique IDentifier for a DHCP participant; each DHCP
client and server has exactly one DUID. See <xref target='RFC3315-9'/> for details of
the ways in which a DUID may be constructed.</t>
<t hangText="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.</t>
<t hangText="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.</t>
<t hangText="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")</t>
<t hangText="IA_TA">Identity Association for Temporary Addresses: An IA that
carries temporary addresses (see <xref target="RFC4941"/>).</t>
<t hangText="IA_PD"> Identity Association for Prefix Delegation:
A collection of prefixes assigned to the requesting
router. Each IA_PD has an associated IAID. A requesting
router may have more than one IA_PD assigned to it; for
example, one for each of its interfaces.</t>
<!-- tomek: Should this text mention delegating/requesting
routers instead of clients and servers? -->
<t hangText="message"> A unit of data carried as the payload of a UDP datagram,
exchanged among DHCP servers, relay agents and clients.</t>
<t hangText="Reconfigure key"> A key supplied to a client by a server used to
provide security for Reconfigure messages.</t>
<t hangText="requesting router:">The router that acts as a
DHCP client and is requesting prefix(es) to be assigned.</t>
<t hangText="singleton option:">An option that is allowed to appear only once.
Most options are singletons.</t>
<t hangText="relaying"> A DHCP relay agent relays DHCP messages between DHCP
participants.</t>
<t hangText="transaction ID"> An opaque value used to match responses with replies
initiated either by a client or server.</t>
</list>
</t>
</section>
<!-- ends: "4.2 from line 478-->
</section>
<!-- ends: "4 from line 402-->
<section anchor='OpModes' title="Operational Models">
<t>
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.
</t>
<section anchor='OpModes-Stateless' title="Stateless DHCP">
<t>
Stateless DHCP <xref target='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 <xref target='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.
</t>
<t>
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 also need to support
the Relay-Forw and Relay-Reply messages to accommodate
operation when clients and servers are not on the same link.
</t>
</section>
<section anchor='OpModes-NA'
title="DHCP for Non-Temporary Address Assignment">
<t>
This model of operation was the original motivation for
DHCP and is the "stateful address autoconfiguration
protocol" for IPv6 <xref target='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.
</t>
<t>
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.
</t>
<t>
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.
</t>
<t>
Typically clients request other configuration parameters,
such as the domain server addresses and search lists, when
requesting addresses.
</t>
</section>
<section anchor='OpModes-PD' title="DHCP for Prefix Delegation">
<t>
The prefix delegation mechanism, originally described in
<xref target='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.
</t>
<t>
The design of this prefix delegation mechanism meets the
requirements for prefix delegation in <xref target='RFC3769'/>.
</t>
<t>
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 <xref target='pd-client-initated-server'/>. A requesting
router requests prefix(es) from the delegating router, as
described in <xref target='pd-client-initiated-client'/>. 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.
</t>
<t>
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.
</t>
<t>
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.
</t>
<t>
<xref target='FigISPNetwork'/> illustrates a network
architecture in which prefix delegation could be used.
</t>
<figure align="center" anchor="FigISPNetwork"
title="Prefix Delegation Newtork">
<preamble/>
<artwork align="left">
<![CDATA[
______________________ \
/ \ \
| ISP core network | \
\__________ ___________/ |
| |
+-------+-------+ |
| Aggregation | | ISP
| device | | network
| (delegating | |
| router) | |
+-------+-------+ |
| /
|DSL to subscriber /
|premises /
|
+------+------+ \
| CPE | \
| (requesting | \
| router) | |
+----+---+----+ |
| | | Subsciber
---+-------------+-----+ +-----+------ | Network
| | | |
+----+-----+ +-----+----+ +----+-----+ |
|Subscriber| |Subscriber| |Subscriber| /
| PC | | PC | | PC | /
+----------+ +----------+ +----------+ /
]]>
</artwork>
<postamble/>
</figure>
<t>
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.
</t>
<t>
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 <xref target='FigISPNetwork'/>, 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.
</t>
<t>
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.
</t>
</section>
<section anchor='OpModes-CPE'
title="DHCP for Customer Edge Routers">
<t>
The DHCP requirements and network architecture for
Customer Edge Routers are described in <xref
target='RFC7084'/>. This model of operation combines
address assignment (see <xref target='OpModes-NA'/>)
and prefix delegation (see <xref target='OpModes-PD'/>).
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.
</t>
</section>
<section anchor='OpModes-TA'
title="DHCP for Temporary Addresses">
<t>
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
<xref target='RFC3041'/> and <xref target='RFC4941'/>).
They were added to DHCP to provide complementary support
when stateful address assignment is used.
</t>
<t>
Temporary address assignment works mostly like non-temporary
address assignment (see <xref target='OpModes-NA'/>), 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.
</t>
</section>
</section>
<section title="DHCP Constants">
<!-- 5, line 597-->
<t>This section describes various program and networking constants used
by DHCP.</t>
<section anchor="mutlicastAddr" title="Multicast Addresses">
<!-- 5.1, line 603-->
<t>DHCP makes use of the following multicast addresses:</t>
<t>
<list hangIndent="16" style="hanging">
<t hangText="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.</t>
<t hangText="All_DHCP_Servers (FF05::1:3)"> A site-scoped multicast address used
by a relay agent to communicate with servers, either because the relay
agent wants to send messages to all servers or because it does not
know the unicast addresses of the servers. Note that in order for a
relay agent to use this address, it must have an address of sufficient
scope to be reachable by the servers. All servers within the site are
members of this multicast group.</t>
</list>
</t>
</section>
<!-- ends: "5.1 from line 603-->
<section title="UDP Ports">
<!-- 5.2, line 628-->
<t>Clients listen for DHCP messages on UDP port 546. Servers and relay
agents listen for DHCP messages on UDP port 547.</t>
</section>
<!-- ends: "5.2 from line 628-->
<section anchor='RFC3315-5.3' title="DHCP Message Types">
<!-- 5.3, line 634-->
<t>DHCP defines the following message types. More detail on these
message types can be found in <xref target='RFC3315-6'/> and <xref target='RFC3315-7'/>. Message types not
listed here are reserved for future use. The numeric encoding for each
message type is shown in parentheses.</t>
<t>
<list hangIndent="16" style="hanging">
<t hangText="SOLICIT (1)"> A client sends a Solicit message to locate servers.</t>
<t hangText="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.</t>
<t hangText="REQUEST (3)"> A client sends a Request message to request
configuration parameters, including IP addresses, from a specific
server.</t>
<t hangText="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.</t>
<t hangText="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.</t>
<t hangText="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.</t>
<t hangText="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.</t>
<t hangText="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.</t>
<t hangText="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.</t>
<t hangText="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. </t>
<t hangText="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.</t>
<t hangText="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.</t>
<t hangText="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.</t>
<t>The server encapsulates the client message as an option in the
Relay-reply message, which the relay agent extracts and relays to the
client.</t>
</list>
</t>
</section>
<!-- ends: "5.3 from line 634-->
<section title="Status Codes">
<!-- 5.4, line 733-->
<t>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
<xref target='RFC3315-22.12'/>.</t>
<t>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.</t>
</section>
<!-- ends: "5.4 from line 733-->
<section anchor='RFC3315-5.5' title="Transmission and Retransmission Parameters">
<!-- 5.5, line 743-->
<t>This section presents a table of values used to describe the
message transmission behavior of clients and servers.</t>
<texttable>
<ttcol>Parameter</ttcol>
<ttcol>Default</ttcol>
<ttcol>Description</ttcol>
<c>SOL_MAX_DELAY</c>
<c>1 sec</c>
<c>Max delay of first Solicit</c>
<c>SOL_TIMEOUT</c>
<c>1 sec</c>
<c>Initial Solicit timeout</c>
<c>SOL_MAX_RT</c>
<c>3600 secs</c>
<c>Max Solicit timeout value</c>
<c>REQ_TIMEOUT</c>
<c>1 sec</c>
<c>Initial Request timeout</c>
<c>REQ_MAX_RT</c>
<c>30 secs</c>
<c>Max Request timeout value</c>
<c>REQ_MAX_RC</c>
<c>10</c>
<c>Max Request retry attempts</c>
<c>CNF_MAX_DELAY</c>
<c>1 sec</c>
<c>Max delay of first Confirm</c>
<c>CNF_TIMEOUT</c>
<c>1 sec</c>
<c>Initial Confirm timeout</c>
<c>CNF_MAX_RT</c>
<c>4 secs</c>
<c>Max Confirm timeout</c>
<c>CNF_MAX_RD</c>
<c>10 secs</c>
<c>Max Confirm duration</c>
<c>REN_TIMEOUT</c>
<c>10 secs</c>
<c>Initial Renew timeout</c>
<c>REN_MAX_RT</c>
<c>600 secs</c>
<c>Max Renew timeout value</c>
<c>REB_TIMEOUT</c>
<c>10 secs</c>
<c>Initial Rebind timeout</c>
<c>REB_MAX_RT</c>
<c>600 secs</c>
<c>Max Rebind timeout value</c>
<c>INF_MAX_DELAY</c>
<c>1 sec</c>
<c>Max delay of first Information-request</c>
<c>INF_TIMEOUT</c>
<c>1 sec</c>
<c>Initial Information-request timeout</c>
<c>INF_MAX_RT</c>
<c>3600 secs</c>
<c>Max Information-request timeout value</c>
<c>REL_TIMEOUT</c>
<c>1 sec</c>
<c>Initial Release timeout</c>
<c>REL_MAX_RC</c>
<c>4</c>
<c>MAX Release retry attempts</c>
<c>DEC_TIMEOUT</c>
<c>1 sec</c>
<c>Initial Decline timeout</c>
<c>DEC_MAX_RC</c>
<c>4</c>
<c>Max Decline retry attempts</c>
<c>REC_TIMEOUT</c>
<c>2 secs</c>
<c>Initial Reconfigure timeout</c>
<c>REC_MAX_RC</c>
<c>8</c>
<c>Max Reconfigure attempts</c>
<c>HOP_COUNT_LIMIT</c>
<c>32</c>
<c>Max hop count in a Relay-forward message</c>
</texttable>
</section>
<!-- ends: "5.5 from line 743-->
<section title='Representation of time values and "Infinity" as a time value'>
<t>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 <xref target="RFC4861"/>) or a value for T1 or T2.</t>
</section>
<!-- ends: "5.6 -->
</section>
<!-- ends: "5 from line 597-->
<section anchor='RFC3315-6' title="Client/Server Message Formats">
<!-- 6, line 786-->
<t>All DHCP messages sent between clients and servers share an identical
fixed format header and a variable format area for options.</t>
<t>All values in the message header and in options are in network byte
order.</t>
<t>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.</t>
<t>The following diagram illustrates the format of DHCP messages sent
between clients and servers:</t>
<figure align="center" anchor="FigClientServerMsg"
title="Client/Server message format">
<preamble/>
<artwork align="left">
<![CDATA[
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) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t>
<list hangIndent="24" style="hanging">
<t hangText=" msg-type">Identifies the DHCP message type; the
available message types are listed in <xref target='RFC3315-5.3'/>.
</t>
<t hangText=" transaction-id">The transaction ID for this message exchange.</t>
<t hangText=" options">Options carried in this message; options are
described in <xref target='RFC3315-22'/>.
</t>
</list>
</t>
</section>
<!-- ends: "6 from line 786-->
<section anchor='RFC3315-7' title="Relay Agent/Server Message Formats">
<!-- 7, line 825-->
<t>Relay agents exchange messages with servers to relay messages between
clients and servers that are not connected to the same link.</t>
<t>All values in the message header and in options are in network byte
order.</t>
<t>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.</t>
<t>There are two relay agent messages, which share the following
format:</t>
<figure align="center" anchor="FigRelayServerMsg"
title="Relay Agent/Server message format">
<preamble/>
<artwork align="left">
<![CDATA[
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) .... .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t>The following sections describe the use of the Relay Agent message
header.</t>
<section title="Relay-forward Message">
<!-- 7.1, line 868-->
<t>The following table defines the use of message fields in a
Relay-forward message.</t>
<t>
<list hangIndent="24" style="hanging">
<t hangText=" msg-type">RELAY-FORW</t>
<t hangText=" hop-count">Number of relay agents that have relayed this
message.</t>
<t hangText=" 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 <xref target="RFC4193"/>,
but see discussion in <xref target="relaying-from-client" />.</t>
<t hangText=" peer-address">The address of the client or relay agent from which
the message to be relayed was received.</t>
<t hangText=" options">MUST include a "Relay Message option" (see <xref target='RFC3315-22.10'/>);
MAY include other options added by the relay agent.</t>
</list>
</t>
</section>
<!-- ends: "7.1 from line 868-->
<section title="Relay-reply Message">
<!-- 7.2, line 892-->
<t>The following table defines the use of message fields in a
Relay-reply message.</t>
<t>
<list hangIndent="24" style="hanging">
<t hangText=" msg-type">RELAY-REPL</t>
<t hangText=" hop-count">Copied from the Relay-forward message</t>
<t hangText=" link-address">Copied from the Relay-forward message</t>
<t hangText=" peer-address">Copied from the Relay-forward message</t>
<t hangText=" options">MUST include a "Relay Message option"; see <xref target='RFC3315-22.10'/>;
MAY include other options</t>
</list>
</t>
</section>
<!-- ends: "7.2 from line 892-->
</section>
<!-- ends: "7 from line 825-->
<section anchor='RFC3315-8' title="Representation and Use of Domain Names">
<!-- 8, line 912-->
<t>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 <xref target="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 <xref target="RFC1035"/>.</t>
</section>
<!-- ends: "8 from line 912-->
<section anchor='RFC3315-9' title="DHCP Unique Identifier (DUID)">
<!-- 9, line 921-->
<t>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
<xref target='RFC3315-22.2'/> and <xref target='RFC3315-22.3'/> for
the representation of a DUID in a DHCP message.</t>
<t>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.</t>
<t>The DUID is carried in an option because it may be variable length
and because it is not required in all DHCP messages. The DUID is
designed to be unique across all DHCP clients and servers, and stable
for any specific client or server - that is, the DUID used by a client
or server SHOULD NOT change over time if at all possible; for example, a
device's DUID should not change as a result of a change in the device's
network hardware.</t>
<t>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.</t>
<section anchor='RFC3315-9.1' title="DUID Contents">
<!-- 9.1, line 953-->
<t>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:</t>
<texttable>
<ttcol>Type</ttcol><ttcol>Description</ttcol>
<c>1</c><c>Link-layer address plus time</c>
<c>2</c><c>Vendor-assigned unique ID based on Enterprise Number</c>
<c>3</c><c>Link-layer address</c>
<c>4</c><c>Universally Unique IDentifier (UUID) - see <xref target="RFC6355"/></c>
</texttable>
<!-- Alternative, but multiple spaces are ignored
<t>
1 Link-layer address plus time<vspace blankLines='0'/>
2 Vendor-assigned unique ID based on Enterprise Number<vspace blankLines='0'/>
3 Link-layer address
</t>
-->
<!-- Altnerative, but results in blank lines between entries
<t>
<list hangIndent="12" style="hanging">
<t hangText="1">Link-layer address plus time</t>
<t hangText="2">Vendor-assigned unique ID based on Enterprise Number</t>
<t hangText="3">Link-layer address</t>
</list>
</t>
-->
<t>Formats for the variable field of the DUID for the first 3 of the
above types are shown below. The fourth type, DUID-UUID <xref target="RFC6355"/>, can
be used in situations where there is a UUID stored in a device's firmware settings.
</t>
</section>
<!-- ends: "9.1 from line 953-->
<section title="DUID Based on Link-layer Address Plus Time, DUID-LLT">
<!-- 9.2, line 972-->
<t>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 <xref target="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 <xref
target="RFC2464"/>.</t>
<t>The following diagram illustrates the format of a DUID-LLT:</t>
<figure align="center" anchor="FigDUIDLLT"
title="DUID-LLT format">
<preamble/>
<artwork align="left">
<![CDATA[
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) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
</section>
<!-- ends: "9.2 from line 972-->
<section title="DUID Assigned by Vendor Based on Enterprise Number, DUID-EN">
<!-- 9.3, line 1038-->
<t>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 <xref target="IANA-PEN"/> followed by a unique
identifier assigned by the vendor. The following diagram summarizes
the structure of a DUID-EN:</t>
<figure align="center" anchor="FigDUIDEN"
title="DUID-EN format">
<preamble/>
<artwork align="left">
<![CDATA[
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) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t>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 <xref target="IANA-PEN"/>. The enterprise-number
is stored as an unsigned 32 bit number.</t>
<t>An example DUID of this type might look like this:</t>
<figure align="center" anchor="FigDUIDENExample"
title="DUID-EN example">
<preamble/>
<artwork align="left">
<![CDATA[
+---+---+---+---+---+---+---+---+
| 0 | 2 | 0 | 0 | 0 | 9| 12|192|
+---+---+---+---+---+---+---+---+
|132|211| 3 | 0 | 9 | 18|
+---+---+---+---+---+---+
]]>
</artwork>
<postamble/>
</figure>
<t>This example includes the two-octet type of 2, the Enterprise
Number (9), followed by eight octets of identifier data
(0x0CC084D303000912).</t>
</section>
<!-- ends: "9.3 from line 1038-->
<section title="DUID Based on Link-layer Address, DUID-LL">
<!-- 9.4, line 1084-->
<t>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 <xref
target="RFC0826"/>. The hardware type is stored in network byte order.
The link-layer address is stored in canonical form, as described in
<xref target="RFC2464"/>. The following diagram illustrates
the format of a DUID-LL:</t>
<figure align="center" anchor="FigDUIDLL"
title="DUID-LL format">
<preamble/>
<artwork align="left">
<![CDATA[
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) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t>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.</t>
<t>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.</t>
</section>
<!-- ends: "9.4 from line 1084-->
</section>
<!-- ends: "9 from line 921-->
<section anchor='RFC3315-10' title="Identity Association">
<!-- 10, line 1125-->
<t>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.</t>
<t>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.</t>
<section anchor='RFC3315-10.1' title="Identity Associations for Address Assignment">
<t>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.
</t>
<t>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.</t>
<t>Each address in an IA has a preferred lifetime and a valid lifetime,
as defined in <xref target="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 <xref target="RFC4862"/>.
</t>
</section>
<section anchor='RFC3315-10.2' title="Identity Associations for Prefix Delegation">
<t>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.</t>
<t>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
<xref target="IA_PD-option"/> for the representation of an IA_PD in a DHCP message.
</t>
</section>
</section>
<!-- ends: "10 from line 1125-->
<section anchor='RFC3315-11' title="Selecting Addresses for Assignment to an IA">
<!-- 11, line 1159-->
<t>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:
<list hangIndent="3" style="hanging">
<t hangText="-"> The link to which the client is attached. The server determines the
link as follows:
<list hangIndent="3" style="hanging">
<t hangText="*"> 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.</t>
<t hangText="*"> 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 <xref target="RFC6221"></xref>, 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.</t>
<t hangText="*"> 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).</t>
</list></t>
<t hangText="-"> The DUID supplied by the client.</t>
<t hangText="-"> Other information in options supplied by the client, e.g. IA
Address options that include the client's requests for specific addresses.</t>
<t hangText="-"> Other information in options supplied by the relay agent.</t>
</list></t>
<t>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
<xref target="RFC4291"/>.</t>
<t>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 <xref target="RFC2526"/>, from any subnet.</t>
</section>
<!-- ends: "11 from line 1159-->
<section title="Management of Temporary Addresses">
<!-- 12, line 1217-->
<t>A client may request the assignment of temporary addresses (see
<xref target="RFC4941"/> for the definition of temporary
addresses). DHCPv6 handling of address assignment is no different for
temporary addresses.</t>
<t>Clients ask for temporary addresses and servers assign them.
Temporary addresses are carried in the Identity Association for
Temporary Addresses (IA_TA) option (see <xref target='RFC3315-22.5'/>). Each IA_TA option
contains at most one temporary address for each of the prefixes on the
link to which the client is attached.</t>
<t>The lifetime of the assigned temporary address is set in the IA Address Option
(see <xref target='RFC3315-22.6'/>) 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, <xref target='RFC4941'/>.</t>
<t>The IAID number space for the IA_TA option IAID number space is
separate from the IA_NA option IAID number space.</t>
<t>A DHCPv6 server implementation MAY generate temporary addresses
referring to the algorithm defined in Section 3.2.1, <xref target='RFC4941'/>,
with additional condition that the new address is not duplicated with any assigned addresses. </t>
<t>The server MAY update the DNS for a temporary address, as described
in section 4 of <xref target="RFC4941"/>.</t>
<t>On the clients, by default, temporary addresses are preferred in source address selection,
according to Rule 7, <xref target='RFC6724'/>. However, this policy is overridable.</t>
<t>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 <xref target='RFC3315-22.5'/>).</t>
</section>
<!-- ends: "12 from line 1217-->
<section title="Transmission of Messages by a Client">
<!-- 13, line 1239-->
<t>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.</t>
<t>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 <xref target='RFC3315-22.3'/>) in the client's message (all
servers will receive this message but only the indicated server will
respond). All servers are indicated by not supplying this option.</t>
<t>A client may send some messages directly to a server using unicast,
as described in <xref target='RFC3315-22.12'/>.</t>
<section anchor='rate-limit' title="Rate Limiting">
<t>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.</t>
<t>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.</t>
<t>
<list hangIndent="11" style="hanging">
<t hangText=" TRT">Transmission Rate Limit</t>
</list>
The Transmission Rate Limit parameter (TRT) SHOULD be configurable.
A possible default could be 20 packets in 20 seconds.</t>
<t>For a device that has multiple interfaces, the limit MUST be
enforced on a per interface basis.</t>
<t>Rate limiting of forwarded DHCPv6 messages and server-side
messages are out of scope of this specification.</t>
</section>
</section>
<!-- ends: "13 from line 1239-->
<section anchor='RFC3315-14' title="Reliability of Client Initiated Message Exchanges">
<!-- 14, line 1258-->
<t>DHCP clients are responsible for reliable delivery of messages in the
client-initiated message exchanges described in
<xref target='RFC3315-17'/> and <xref target='RFC3315-18'/>. If a
DHCP client fails to receive an expected response from a server, the
client must retransmit its message. This section describes the
retransmission strategy to be used by clients in client-initiated
message exchanges.</t>
<t>Note that the procedure described in this section is slightly
modified when used with the Solicit message. The modified procedure is
described in <xref target='RFC3315-17.1.2'/>.</t>
<t>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.</t>
<t>The client retransmission behavior is controlled and described by the
following variables:
<list hangIndent="11" style="hanging">
<t hangText=" RT"> Retransmission timeout</t>
<t hangText=" IRT"> Initial retransmission time</t>
<t hangText=" MRC"> Maximum retransmission count</t>
<t hangText=" MRT"> Maximum retransmission time</t>
<t hangText=" MRD"> Maximum retransmission duration</t>
<t hangText=" RAND"> Randomization factor</t>
</list></t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>RT for the first message transmission is based on IRT:</t>
<figure>
<artwork>
RT = IRT + RAND*IRT
</artwork>
</figure>
<t>RT for each subsequent message transmission is based on the previous
value of RT:</t>
<figure>
<artwork>
RT = 2*RTprev + RAND*RTprev
</artwork>
</figure>
<t>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:</t>
<figure>
<artwork>
if (RT > MRT)
RT = MRT + RAND*MRT
</artwork>
</figure>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>If both MRC and MRD are zero, the client continues to transmit the
message until it receives a response.</t>
<!-- New text from section 6 of RFC7083 -->
<t>A client is not expected to listen for a response during the entire
period between transmission of Solicit or Information-request
messages.</t>
</section>
<!-- ends: "14 from line 1258-->
<section title="Message Validation">
<!-- 15, line 1345-->
<t>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.</t>
<t>A server MUST discard any Solicit, Confirm, Rebind or
Information-request messages it receives with a unicast destination
address.</t>
<t>Message validation based on DHCP authentication is discussed in
<xref target='RFC3315-21.4.2'/>.</t>
<t>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.</t>
<!-- Applied text from Section 5 of RFC7283 -->
<t>A client or server MUST silently discard any received DHCPv6
messages with an unknown message type.</t>
<section title="Use of Transaction IDs">
<!-- 15.1, line 1370-->
<t>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.</t>
</section>
<!-- ends: "15.1 from line 1370-->
<section title="Solicit Message">
<!-- 15.2, line 1382-->
<t>Clients MUST discard any received Solicit messages.</t>
<t>Servers MUST discard any Solicit messages that do not include a
Client Identifier option or that do include a Server Identifier
option.</t>
</section>
<!-- ends: "15.2 from line 1382-->
<section title="Advertise Message">
<!-- 15.3, line 1391-->
<t>Clients MUST discard any received Advertise message that meets any
of the following conditions:
<list hangIndent="3" style="hanging">
<t hangText="-"> the message does not include a Server Identifier option.</t>
<t hangText="-"> the message does not include a Client Identifier option.</t>
<t hangText="-"> the contents of the Client Identifier option does not match the
client's DUID.</t>
<t hangText="-"> the "transaction-id" field value does not match the value the
client used in its Solicit message.</t>
</list></t>
<t>Servers and relay agents MUST discard any received Advertise
messages.</t>
</section>
<!-- ends: "15.3 from line 1391-->
<section title="Request Message">
<!-- 15.4, line 1416-->
<t>Clients MUST discard any received Request messages.</t>
<t>Servers MUST discard any received Request message that meets any of
the following conditions:
<list hangIndent="3" style="hanging">
<t hangText="-"> the message does not include a Server Identifier option.</t>
<t hangText="-"> the contents of the Server Identifier option do not match the
server's DUID.</t>
<t hangText="-"> the message does not include a Client Identifier option.</t>
</list></t>
</section>
<!-- ends: "15.4 from line 1416-->
<section title="Confirm Message">
<!-- 15.5, line 1436-->
<t>Clients MUST discard any received Confirm messages.</t>
<t>Servers MUST discard any received Confirm messages that do not
include a Client Identifier option or that do include a Server
Identifier option.</t>
</section>
<!-- ends: "15.5 from line 1436-->
<section title="Renew Message">
<!-- 15.6, line 1445-->
<t>Clients MUST discard any received Renew messages.</t>
<t>Servers MUST discard any received Renew message that meets any of
the following conditions:
<list hangIndent="3" style="hanging">
<t hangText="-"> the message does not include a Server Identifier option.</t>
<t hangText="-"> the contents of the Server Identifier option does not match the
server's identifier.</t>
<t hangText="-"> the message does not include a Client Identifier option.</t>
</list></t>
</section>
<!-- ends: "15.6 from line 1445-->
<section title="Rebind Message">
<!-- 15.7, line 1465-->
<t>Clients MUST discard any received Rebind messages.</t>
<t>Servers MUST discard any received Rebind messages that do not
include a Client Identifier option or that do include a Server
Identifier option.</t>
</section>
<!-- ends: "15.7 from line 1465-->
<section title="Decline Messages">
<!-- 15.8, line 1474-->
<t>Clients MUST discard any received Decline messages.</t>
<t>Servers MUST discard any received Decline message that meets any of
the following conditions:
<list hangIndent="3" style="hanging">
<t hangText="-"> the message does not include a Server Identifier option.</t>
<t hangText="-"> the contents of the Server Identifier option does not match the
server's identifier.</t>
<t hangText="-"> the message does not include a Client Identifier option.</t>
</list></t>
</section>
<!-- ends: "15.8 from line 1474-->
<section title="Release Message">
<!-- 15.9, line 1494-->
<t>Clients MUST discard any received Release messages.</t>
<t>Servers MUST discard any received Release message that meets any of
the following conditions:
<list hangIndent="3" style="hanging">
<t hangText="-"> the message does not include a Server Identifier option.</t>
<t hangText="-"> the contents of the Server Identifier option does not match the
server's identifier.</t>
<t hangText="-"> the message does not include a Client Identifier option.</t>
</list></t>
</section>
<!-- ends: "15.9 from line 1494-->
<section title="Reply Message">
<!-- 15.10, line 1514-->
<t>Clients MUST discard any received Reply message that meets any of
the following conditions:
<list hangIndent="3" style="hanging">
<t hangText="-"> the message does not include a Server Identifier option.</t>
<t hangText="-"> the "transaction-id" field in the message does not match the
value used in the original message.</t>
</list></t>
<t>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.</t>
<t>Servers and relay agents MUST discard any received Reply
messages.</t>
</section>
<!-- ends: "15.10 from line 1514-->
<section title="Reconfigure Message">
<!-- 15.11, line 1538-->
<t>Servers and relay agents MUST discard any received Reconfigure
messages.</t>
<t>Clients MUST discard any Reconfigure message that meets any of the
following conditions:
<list hangIndent="3" style="hanging">
<t hangText="-"> the message was not unicast to the client.</t>
<t hangText="-"> the message does not include a Server Identifier option.</t>
<t hangText="-"> the message does not include a Client Identifier option that
contains the client's DUID.</t>
<t hangText="-"> the message does not contain a Reconfigure Message option.</t>
<t hangText="-"> the Reconfigure Message option msg-type is not a valid value.</t>
<t hangText="-"> the message includes any IA options and the msg-type in the
Reconfigure Message option is INFORMATION-REQUEST.</t>
<t hangText="-"> the message does not include DHCP authentication:
<list hangIndent="3" style="hanging">
<t hangText="*"> the message does not contain an authentication option.</t>
<t hangText="*"> the message does not pass the authentication validation performed
by the client.</t>
</list></t>
</list></t>
</section>
<!-- ends: "15.11 from line 1538-->
<section title="Information-request Message">
<!-- 15.12, line 1578-->
<t>Clients MUST discard any received Information-request messages.</t>
<t>Servers MUST discard any received Information-request message that
meets any of the following conditions:
<list hangIndent="3" style="hanging">
<t hangText="-"> The message includes a Server Identifier option and the DUID in
the option does not match the server's DUID.</t>
<t hangText="-"> The message includes an IA option.</t>
</list></t>
</section>
<!-- ends: "15.12 from line 1578-->
<section title="Relay-forward Message">
<!-- 15.13, line 1595-->
<t>Clients MUST discard any received Relay-forward messages.</t>
</section>
<!-- ends: "15.13 from line 1595-->
<section title="Relay-reply Message">
<!-- 15.14, line 1600-->
<t>Clients and servers MUST discard any received Relay-reply
messages.</t>
</section>
<!-- ends: "15.14 from line 1600-->
</section>
<!-- ends: "15 from line 1345-->
<section title="Client Source Address and Interface Selection">
<!-- 16, line 1605-->
<t>Client's behavior is different depending on the purpose of the
configuration.</t>
<section title="Address Assignment">
<t>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.
<!-- tomek: ok, this is a bit confusing. The intention is to say:
- if you want to configure interface X, send you packets over X
- you may send it over Y, if you're sure X and Y are connected to the same
link
- if you're doing weird stuff with virtual interfaces, that's fine,
just be careful, ok?
-->
<!-- tomek: removed this sentence. Source address selection is not covered
by DHCPv6. -->
<!-- The client MUST use a link-local address assigned to the interface
for which it is requesting configuration information as the source
address in the header of the IPv6 datagram. --></t>
<t>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.</t>
</section>
<section title="Prefix Delegation">
<t>Delegated prefixes are not associated with a particular
interface in the same way as addresses are for address
assignment, and mentioned above.</t>
<t>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.</t>
<t>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.</t>
</section>
</section>
<!-- ends: "16 from line 1605-->
<section anchor='RFC3315-17' title="DHCP Server Solicitation">
<!-- 17, line 1625-->
<t>This section describes how a client locates servers that will assign
addresses and delegated prefixes to IAs belonging to the client.</t>
<t>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.</t>
<t>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 <xref target='RFC3315-18'/>.</t>
<t>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 <xref target='RFC3315-22.14'/>) in the Solicit
message.</t>
<section title="Client Behavior">
<!-- 17.1, line 1644-->
<t>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.</t>
<section anchor='RFC3315-17.1.1' title="Creation of Solicit Messages">
<!-- 17.1.1, line 1651-->
<t>The client sets the "msg-type" field to SOLICIT. The client
generates a transaction ID and inserts this value in the
"transaction-id" field.</t>
<t>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.</t>
<t>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.</t>
<t>The client MUST include an Option Request option (see
<xref target='RFC3315-22.7'/>) to request the SOL_MAX_RT option
(see <xref target='SOL_MAX_RT_option'/>) 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.</t>
<t>The client includes a Reconfigure Accept option (see
<xref target='RFC3315-22.20'/>) if the client is willing to accept
Reconfigure messages from the server.</t>
</section>
<!-- ends: "17.1.1 from line 1651-->
<section anchor='RFC3315-17.1.2' title="Transmission of Solicit Messages">
<!-- 17.1.2, line 1682-->
<t>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
<xref target="RFC4862"/>). This random delay desynchronizes clients which start at
the same time (for example, after a power outage).</t>
<t>The client transmits the message according to <xref target='RFC3315-14'/>, using
the following parameters:
<list hangIndent="11" style="hanging">
<t hangText=" IRT"> SOL_TIMEOUT</t>
<t hangText=" MRT"> SOL_MAX_RT</t>
<t hangText=" MRC"> 0</t>
<t hangText=" MRD"> 0</t>
</list></t>
<t>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.</t>
<t>If the client is waiting for an Advertise message, the mechanism
in <xref target='RFC3315-14'/> 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.
Also, the first RT MUST be selected to be strictly greater than IRT
by choosing RAND to be strictly greater than 0.</t>
<t>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 (<xref target='RFC3315-22.8'/>). 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 <xref target='RFC3315-18'/>) 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.</t>
<t>If the client does not receive any Advertise messages before the
first RT has elapsed, it begins the retransmission mechanism
described in <xref target='RFC3315-14'/>. 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.</t>
<t>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.</t>
</section>
<!-- ends: "17.1.2 from line 1682-->
<section anchor='RFC3315-17.1.3' title="Receipt of Advertise Messages">
<!-- 17.1.3, line 1750-->
<!-- The new paragraph to introduce the requirement stated in first
paragraph of section 6. of RFC7083. -->
<t>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.</t>
<!-- todo: Update this paragraph with NoPrefixAvail status code when
RFC3633 is merged -->
<t>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.</t>
<t>Upon receipt of one or more valid Advertise messages, the client
selects one or more Advertise messages based upon the following
criteria.
<list hangIndent="3" style="hanging">
<t hangText="-"> Those Advertise messages with the highest server preference
value are preferred over all other Advertise messages.</t>
<t hangText="-"> 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.</t>
<t hangText="-"> 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.</t>
</list></t>
<t>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.</t>
<t>In practice, this means that the client will maintain
independent per-IA state machines per each selected server.</t>
<t>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.</t>
</section>
<!-- ends: "17.1.3 from line 1750-->
<section title="Receipt of Reply Message">
<!-- 17.1.4, line 1790-->
<t>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 <xref target='RFC3315-18.1.8'/>. 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
<xref target='RFC3315-17.1.3'/>.</t>
<t>If the client subsequently receives a valid Reply
message that includes a Rapid Commit option, it either:</t>
<t><list hangIndent="3" style="hanging">
<t hangText="-"> processes the Reply message as described in
<xref target='RFC3315-18.1.8'/>, and
discards any Reply messages received in response to the Request
message, or</t>
<t hangText="-"> processes any Reply messages received in response to the Request
message and discards the Reply message that includes the Rapid
Commit option.</t>
</list></t>
</section>
<!-- ends: "17.1.4 from line 1790-->
</section>
<!-- ends: "17.1 from line 1644-->
<section title="Server Behavior">
<!-- 17.2, line 1816-->
<t>A server sends an Advertise message in response to valid Solicit
messages it receives to announce the availability of the server to the
client.</t>
<section title="Receipt of Solicit Messages">
<!-- 17.2.1, line 1823-->
<t>The server determines the information about the client and its
location as described in <xref target='RFC3315-11'/> 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 <xref target='RFC3315-22.20'/>) in the
Solicit message, the servers discard the Solicit message.</t>
<t>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 <xref target='RFC3315-17.2.3'/>.
Otherwise, the server ignores the Rapid Commit option and
processes the remainder of the message as if no Rapid Commit
option were present.</t>
</section>
<!-- ends: "17.2.1 from line 1823-->
<section anchor="RFC3315-17.2.2" title="Creation and Transmission of Advertise Messages">
<!-- 17.2.2, line 1844-->
<t>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.</t>
<t>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.</t>
<t>The server includes a Reconfigure Accept option if the server
wants to require that the client accept Reconfigure messages.</t>
<t>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 <xref target='RFC2460'/>.</t>
<t>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.</t>
<!-- This paragraph has been updated with the changes from section
6 of RFC7083 -->
<!-- Also, partially applied RFC3315 errata 2472, to include other IA
options if NoAddrsAvail status code is sent. Do not apply the part
of errata that mandates sending NoAddrsAvail encapsulated in IA -->
<t>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.</t>
<t>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.</t>
<t>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.</t>
</section>
<!-- ends: "17.2.2 from line 1844-->
<section anchor='RFC3315-17.2.3' title="Creation and Transmission of Reply Messages">
<!-- 17.2.3, line 1906-->
<t>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.</t>
<t>DISCUSSION:</t>
<t><list style="empty">
<t>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.</t>
<t>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.</t>
</list></t>
<t>The server includes a Rapid Commit option in the Reply message to
indicate that the Reply is in response to a Solicit message.</t>
<t>The server includes a Reconfigure Accept option if the server
wants to require that the client accept Reconfigure messages.</t>
<t>The server produces the Reply message as though it had received a
Request message, as described in <xref target='RFC3315-18.2.1'/>. The server
transmits the Reply message as described in <xref target='RFC3315-18.2.8'/>.</t>
</section>
<!-- ends: "17.2.3 from line 1906-->
</section>
<section anchor="pd-solicit-client"
title="Client behavior for Prefix Delegation">
<t>The requesting router creates and transmits a Solicit
message as described in <xref target="RFC3315-17.1.1"/> and
<xref target="RFC3315-17.1.2"/>. The client creates an IA_PD
and assigns it an IAID. The client MUST include the IA_PD
option in the Solicit message.</t>
<t>The client processes any received Advertise messages as
described in <xref target="RFC3315-17.1.3"/>. The client MAY
choose to consider the presence of advertised prefixes in its
decision about which delegating router to respond to.</t>
<t>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.</t>
</section>
<section anchor="pd-solicit-server"
title="Server Behavior for Prefix Delegation">
<t>The server sends an Advertise message to the requesting
router in the same way as described in <xref
target="RFC3315-17.2.2"/>. 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 <xref target="RFC3162" pageno="false" />.</t>
<t>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.</t>
<t>The server sends an Advertise message to the
requesting router in the same way as described in
<xref target="RFC3315-17.2.2"/>. The server
MUST include an IA_PD option,
identifying any prefix(es) that the server will
delegate to the client.</t>
<t>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.</t>
</section>
<!-- ends: "17.2 from line 1816-->
</section>
<!-- ends: "17 from line 1625-->
<section anchor='RFC3315-18' title="DHCP Client-Initiated Configuration Exchange">
<!-- 18, line 1942-->
<t>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.</t>
<t>According to a terminology for the prefix delegation, a client requesting a
delegation of a prefix is referred to as a requesting 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.</t>
<section title="Client Behavior">
<!-- 18.1, line 1953-->
<t>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.</t>
<t>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 (<xref target='RFC3315-22.12'/>) from the server, the client
SHOULD unicast any Request, Renew, Release and Decline messages to the
server.</t>
<t>DISCUSSION:</t>
<t><list style="empty">
<t>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.</t>
</list></t>
<section title="Creation and Transmission of Request Messages">
<!-- 18.1.1, line 1981-->
<t>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.</t>
<t>The client generates a transaction ID and inserts this value in
the "transaction-id" field.</t>
<t>The client places the identifier of the destination server in a
Server Identifier option.</t>
<t>The client MUST include a Client Identifier option to identify
itself to the server. The client adds any other appropriate options,
including one or more IA options (if the client is requesting that
the server assign it some network addresses).</t>
<t>The client MUST include an Option Request option (see
<xref target='RFC3315-22.7'/>) 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.</t>
<t>The client includes a Reconfigure Accept option (see
<xref target='RFC3315-22.20'/>) indicating whether or not the client is willing to accept
Reconfigure messages from the server.</t>
<t>The client transmits the message according to <xref target='RFC3315-14'/>, using
the following parameters:
<list hangIndent="11" style="hanging">
<t hangText=" IRT"> REQ_TIMEOUT</t>
<t hangText=" MRT"> REQ_MAX_RT</t>
<t hangText=" MRC"> REQ_MAX_RC</t>
<t hangText=" MRD"> 0</t>
</list></t>
<t>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:
<list hangIndent="3" style="hanging">
<t hangText="-"> Select another server from a list of servers known to the
client; for example, servers that responded with an Advertise
message.</t>
<t hangText="-"> Initiate the server discovery process described in
<xref target='RFC3315-17'/>.</t>
<t hangText="-"> Terminate the configuration process and report failure.</t>
</list></t>
</section>
<!-- ends: "18.1.1 from line 1981-->
<section anchor='RFC3315-18.1.2' title="Creation and Transmission of Confirm Messages">
<!-- 18.1.2, line 2037-->
<t>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:
<list hangIndent="3" style="hanging">
<t hangText="o"> The client reboots.</t>
<t hangText="o"> The client is physically connected to a wired connection.</t>
<t hangText="o"> The client returns from sleep mode.</t>
<t hangText="o"> The client using a wireless technology changes access
points.</t>
</list></t>
<t>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.</t>
<t>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 <xref target="RFC3315-17.1.1"/>.</t>
<t>The client sets the "msg-type" field to CONFIRM. The client
generates a transaction ID and inserts this value in the
"transaction-id" field.</t>
<t>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.</t>
<t>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 <xref target='RFC3315-14'/>, using the
following parameters:
<list hangIndent="11" style="hanging">
<t hangText=" IRT"> CNF_TIMEOUT</t>
<t hangText=" MRT"> CNF_MAX_RT</t>
<t hangText=" MRC"> 0</t>
<t hangText=" MRD"> CNF_MAX_RD</t>
</list></t>
<t>If the client receives no responses before the message
transmission process terminates, as described in <xref target='RFC3315-14'/>, 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.</t>
</section>
<!-- ends: "18.1.2 from line 2037-->
<section anchor='RFC3315-18.1.3' title="Creation and Transmission of Renew Messages">
<!-- 18.1.3, line 2100-->
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>The client sets the "msg-type" field to RENEW. The client
generates a transaction ID and inserts this value in the
"transaction-id" field.</t>
<t>The client places the identifier of the destination server in a
Server Identifier option.</t>
<t>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.</t>
<t>The client MUST include an Option Request option (see
<xref target='RFC3315-22.7'/>) 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.</t>
<t>The client transmits the message according to <xref target='RFC3315-14'/>, using
the following parameters:
<list hangIndent="11" style="hanging">
<t hangText=" IRT"> REN_TIMEOUT</t>
<t hangText=" MRT"> REN_MAX_RT</t>
<t hangText=" MRC"> 0</t>
<t hangText=" MRD"> Remaining time until T2</t>
</list></t>
<t>The message exchange is terminated
when time T2 is reached (see <xref target='RFC3315-18.1.4'/>), at which time the
client begins a Rebind message exchange.</t>
</section>
<!-- ends: "18.1.3 from line 2100-->
<section anchor='RFC3315-18.1.4' title="Creation and Transmission of Rebind Messages">
<!-- 18.1.4, line 2160-->
<t>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.</t>
<t>The client sets the "msg-type" field to REBIND. The client
generates a transaction ID and inserts this value in the
"transaction-id" field.</t>
<t>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.</t>
<t>The client MUST include an Option Request option (see
<xref target='RFC3315-22.7'/>) 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.</t>
<t>The client transmits the message according to <xref target='RFC3315-14'/>, using
the following parameters:
<list hangIndent="11" style="hanging">
<t hangText=" IRT"> REB_TIMEOUT</t>
<t hangText=" MRT"> REB_MAX_RT</t>
<t hangText=" MRC"> 0</t>
<t hangText=" MRD"> Remaining time until valid lifetimes of all addresses have
expired</t>
</list></t>
<t>The message exchange is terminated when the valid lifetimes of
all the addresses assigned to the IA expire (see <xref target='RFC3315-10'/>), at
which time the client has several alternative actions to choose
from; for example:
<list hangIndent="3" style="hanging">
<t hangText="-"> 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.</t>
<t hangText="-"> 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.</t>
</list></t>
</section>
<!-- ends: "18.1.4 from line 2160-->
<section anchor='RFC3315-18.1.5' title="Creation and Transmission of Information-request Messages">
<!-- 18.1.5, line 2215-->
<t>The client uses an Information-request message to obtain
configuration information without having addresses assigned to
it.</t>
<t>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.</t>
<t>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.</t>
<t>The client MUST include an Option Request option (see
<xref target='RFC3315-22.7'/>) to request the INF_MAX_RT option
(see <xref target='INF_MAX_RT_option'/>) 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.</t>
<t>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
<xref target='RFC3315-14'/>, using the following parameters:
<list hangIndent="11" style="hanging">
<t hangText=" IRT"> INF_TIMEOUT</t>
<t hangText=" MRT"> INF_MAX_RT</t>
<t hangText=" MRC"> 0</t>
<t hangText=" MRD"> 0</t>
</list></t>
</section>
<!-- ends: "18.1.5 from line 2215-->
<section title="Creation and Transmission of Release Messages">
<!-- 18.1.6, line 2251-->
<t>To release one or more addresses, a client sends a Release
message to the server.</t>
<t>The client sets the "msg-type" field to RELEASE. The client
generates a transaction ID and places this value in the
"transaction-id" field.</t>
<t>The client places the identifier of the server that allocated the
address(es) in a Server Identifier option.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>The client transmits the message according to <xref target='RFC3315-14'/>, using
the following parameters:
<list hangIndent="11" style="hanging">
<t hangText=" IRT"> REL_TIMEOUT</t>
<t hangText=" MRT"> 0</t>
<t hangText=" MRC"> REL_MAX_RC</t>
<t hangText=" MRD"> 0</t>
</list></t>
<t>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.</t>
<t>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.</t>
</section>
<!-- ends: "18.1.6 from line 2251-->
<section anchor='RFC3315-18.1.7' title="Creation and Transmission of Decline Messages">
<!-- 18.1.7, line 2304-->
<t>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.</t>
<t>The client sets the "msg-type" field to DECLINE. The client
generates a transaction ID and places this value in the
"transaction-id" field.</t>
<t>The client places the identifier of the server that allocated the
address(es) in a Server Identifier option.</t>
<t>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.</t>
<t>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.</t>
<t>The client transmits the message according to <xref target='RFC3315-14'/>, using
the following parameters:
<list hangIndent="11" style="hanging">
<t hangText=" IRT"> DEC_TIMEOUT</t>
<t hangText=" MRT"> 0</t>
<t hangText=" MRC"> DEC_MAX_RC</t>
<t hangText=" MRD"> 0</t>
</list></t>
<t>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.</t>
</section>
<!-- ends: "18.1.7 from line 2304-->
<section anchor='RFC3315-18.1.8' title="Receipt of Reply Messages">
<!-- 18.1.8, line 2345-->
<t>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.</t>
<t>The client SHOULD perform duplicate address detection <xref
target="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
<xref target='RFC3315-18.1.7'/>.</t>
<t>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:
<list hangIndent="3" style="hanging">
<t hangText="-"> Record T1 and T2 times.</t>
<t hangText="-"> Add any new addresses in the IA option to the IA as recorded by
the client.</t>
<t hangText="-"> Update lifetimes for any addresses in the IA option that the
client already has recorded in the IA.</t>
<t hangText="-"> Discard any addresses from the IA, as recorded by the client,
that have a valid lifetime of 0 in the IA Address option.</t>
<t hangText="-"> Leave unchanged any information about addresses the client has
recorded in the IA but that were not included in the IA from the
server.</t>
</list></t>
<t>Management of the specific configuration information is detailed
in the definition of each option in <xref target='RFC3315-22'/>.</t>
<t>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 <xref target='rate-limit'/>).</t>
<t>When the client receives a Reply message with a Status Code
option with the value UseMulticast, the client records the receipt
of the 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.</t>
<t>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 <xref target='RFC3315-17'/>, and client-initiated configuration as described in
<xref target='RFC3315-18'/>. 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.</t>
<t>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 <xref target='RFC3315-17'/>).</t>
<t>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.</t>
<t>Whenever a client restarts the DHCP server discovery process
or selects an alternate server, as described in
<xref target="RFC3315-17.1.3"/>, 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.</t>
<t>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:
<list hangIndent="3" style="hanging">
<t hangText="-"> 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)</t>
<t hangText="-"> sends a Renew/Rebind if the IA is not in the Reply message</t>
<t hangText="-"> otherwise accepts the information in the IA</t>
</list></t>
<t>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.</t>
<t>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.</t>
</section>
<!-- ends: "18.1.8 from line 2345-->
</section>
<!-- ends: "18.1 from line 1953-->
<section anchor='RFC3315-18.2' title="Server Behavior">
<!-- 18.2, line 2455-->
<t>For this discussion, the Server is assumed to have been configured
in an implementation specific manner with configuration of interest to
clients.</t>
<t>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.</t>
<t>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 <xref target="RFC2460"></xref>. 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.</t>
<section anchor='RFC3315-18.2.1' title="Receipt of Request Messages">
<!-- 18.2.1, line 2477-->
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>The server includes a Reconfigure Accept option if the server
wants to require that the client accept Reconfigure messages.</t>
<t>The server includes other options containing configuration
information to be returned to the client as described in
<xref target='RFC3315-18.2'/>.</t>
<t>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.</t>
</section>
<!-- ends: "18.2.1 from line 2477-->
<section title="Receipt of Confirm Messages">
<!-- 18.2.2, line 2527-->
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
</section>
<!-- ends: "18.2.2 from line 2527-->
<section anchor='RFC3315-18.2.3' title="Receipt of Renew Messages">
<!-- 18.2.3, line 2554-->
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>The server includes other options containing configuration
information to be returned to the client as described in
<xref target='RFC3315-18.2'/>.</t>
</section>
<!-- ends: "18.2.3 from line 2554-->
<section anchor='RFC3315-18.2.4' title="Receipt of Rebind Messages">
<!-- 18.2.4, line 2594-->
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>The server includes other options containing configuration
information to be returned to the client as described in
<xref target='RFC3315-18.2'/>.</t>
</section>
<!-- ends: "18.2.4 from line 2594-->
<section anchor='RFC3315-18.2.5' title="Receipt of Information-request Messages">
<!-- 18.2.5, line 2634-->
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>The server includes options
containing configuration information to be returned to the client as
described in <xref target='RFC3315-18.2'/>.</t>
<t>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.</t>
</section>
<!-- ends: "18.2.5 from line 2634-->
<section title="Receipt of Release Messages">
<!-- 18.2.6, line 2663-->
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
</section>
<!-- ends: "18.2.6 from line 2663-->
<section title="Receipt of Decline Messages">
<!-- 18.2.7, line 2694-->
<t>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.</t>
<t>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).</t>
<t>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.</t>
<t>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.</t>
</section>
<!-- ends: "18.2.7 from line 2694-->
<section anchor='RFC3315-18.2.8' title="Transmission of Reply Messages">
<!-- 18.2.8, line 2729-->
<t>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.</t>
<t>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 <xref target='RFC3315-22.10'/>). 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 the source address field from the IP datagram in which
the Relay-forward message was received.</t>
</section>
<!-- ends: "18.2.8 from line 2729-->
</section>
<!-- ends: "18.2 -->
<section anchor='pd-client-initiated-client'
title="Requesting Router Behavior for Prefix Delegation">
<t>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.</t>
<t>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.</t>
<t>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:</t>
<t><list style="symbols">
<t>The requesting router reboots.</t>
<t>The requesting router's upstream link flaps.</t>
<t>The requesting router is physically disconnected from a
wired connection.</t>
</list></t>
<t>If such verification is needed the requesting router MUST
initiate a Rebind/Reply message exchange as described in
section <xref target="RFC3315-18.1.4"/>, with the exception
that the retransmission parameters should be set as for the
Confirm message, described in <xref target="RFC3315-18.1.2"/>.
The requesting router includes any IA_PDs, along with
prefixes associated with those IA_PDs in its Rebind
message.</t>
<t>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.</t>
<t>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.</t>
<t>The Confirm and Decline message types are not used with
Prefix Delegation.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>Handling of Status Codes options in received Reply messages
is described in section <xref target="RFC3315-18.1.8"/>. The
NoPrefixAvail Status Code is handled in the same manner as the
NoAddrsAvail Status Code.</t>
</section>
<section anchor='pd-client-initated-server'
title="Delegating Router Behavior for Prefix Delegation">
<t>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. <xref target="pd-solicit-server"
pageno="false"/> gives examples of ways in which a delegating
router might select the prefix(es) to be delegated to a
requesting router.</t>
<t>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 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.</t>
<t>The delegating router behaves as follows when it cannot
find a binding for the requesting router's IA_PD:</t>
<t><list style="hanging" hangIndent='20'>
<t hangText="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.</t>
<t hangText="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.</t>
</list>
</t>
<t>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.</t>
<t>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.</t>
</section>
</section>
<!-- ends: "18 from line 1942-->
<section anchor='RFC3315-19' title="DHCP Server-Initiated Configuration Exchange">
<!-- 19, line 2751-->
<t>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.</t>
<section anchor='RFC3315-19.1' title="Server Behavior">
<!-- 19.1, line 2762-->
<t>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.</t>
<section title="Creation and Transmission of Reconfigure Messages">
<!-- 19.1.1, line 2769-->
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>The server MUST include a Reconfigure Message option (defined in
<xref target='RFC3315-22.19'/>) to select whether the client responds with a Renew
message, a Rebind message, or an Information-Request message.</t>
<t>The server MUST NOT include any other options in the Reconfigure
except as specifically allowed in the definition of individual
options.</t>
<t>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 <xref target='RFC3315-20.3'/>) 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.</t>
<t>To reconfigure more than one client, the server unicasts a
separate message to each client. The server may initiate the
reconfiguration of multiple clients concurrently; for example, a
server may send a Reconfigure message to additional clients while
previous reconfiguration message exchanges are still in
progress.</t>
<t>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.</t>
</section>
<!-- ends: "19.1.1 from line 2769-->
<section title="Time Out and Retransmission of Reconfigure Messages">
<!-- 19.1.2, line 2824-->
<t>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.</t>
<t>Default and initial values for REC_TIMEOUT and REC_MAX_RC are
documented in <xref target='RFC3315-5.5'/>.</t>
</section>
<!-- ends: "19.1.2 from line 2824-->
</section>
<!-- ends: "19.1 from line 2762-->
<section title="Receipt of Renew or Rebind Messages">
<!-- 19.2, line 2837-->
<t>In response to a Renew message, the server generates
and sends a Reply message to the client as
described in <xref target='RFC3315-18.2.3'/> and
<xref target='RFC3315-18.2.8'/>, including options for
configuration parameters.</t>
<t>In response to a Rebind message, the server generates and sends a
Reply message to the client as described in <xref target='RFC3315-18.2.4'/>
and <xref target='RFC3315-18.2.8'/>, including options
for configuration parameters.</t>
<t>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.</t>
</section>
<!-- ends: "19.2 from line 2837-->
<section title="Receipt of Information-request Messages">
<!-- 19.3, line 2849-->
<t>The server generates and sends a Reply message to the client as
described in <xref target='RFC3315-18.2.5'/> and
<xref target='RFC3315-18.2.8'/>, including options for
configuration parameters.</t>
<t>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.</t>
</section>
<!-- ends: "19.3 from line 2849-->
<section anchor='RFC3315-19.4' title="Client Behavior">
<!-- 19.4, line 2861-->
<t>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.</t>
<section title="Receipt of Reconfigure Messages">
<!-- 19.4.1, line 2871-->
<t>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
<xref target='RFC3315-22.19'/>). 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.</t>
<t>DISCUSSION:</t>
<t><list style="empty">
<t>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.</t>
<t>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.</t>
<t>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.</t>
</list></t>
</section>
<!-- ends: "19.4.1 from line 2871-->
<section title="Creation and Transmission of Renew or Rebind Messages">
<!-- 19.4.2, line 2913-->
<t>When responding to a Reconfigure, the client creates and sends
the Renew message in exactly the same manner as outlined in
<xref target='RFC3315-18.1.3'/>, 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.</t>
<t>When responding to a Reconfigure, the client creates and sends the
Rebind message in exactly the same manner as outlined in
<xref target='RFC3315-18.1.4'/>, with the exception that the client copies the
Option Request option and any IA options from the Reconfigure message
into the Rebind message.</t>
<t>If a client is currently sending Rebind messages, as described in
<xref target='RFC3315-18.1.3'/>, the client ignores any received
Reconfigure messages.</t>
</section>
<!-- ends: "19.4.2 from line 2913-->
<section anchor='RFC3315-19.4.3' title="Creation and Transmission of Information-request Messages">
<!-- 19.4.3, line 2922-->
<t>When responding to a Reconfigure, the client creates and sends
the Information-request message in exactly the same manner as
outlined in <xref target='RFC3315-18.1.5'/>, with the exception that the client
includes a Server Identifier option with the identifier from the
Reconfigure message to which the client is responding.</t>
</section>
<!-- ends: "19.4.3 from line 2922-->
<section title="Time Out and Retransmission of Renew, Rebind or Information-request Messages">
<!-- 19.4.4, line 2931-->
<t>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
<xref target='RFC3315-18.1.3'/>, <xref target='RFC3315-18.1.4'/>, and <xref target='RFC3315-18.1.5'/>
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.</t>
</section>
<!-- ends: "19.4.4 from line 2931-->
<section title="Receipt of Reply Messages">
<!-- 19.4.5, line 2942-->
<t>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.</t>
</section>
<!-- ends: "19.4.5 from line 2942-->
</section>
<!-- ends: "19.4 from line 2861-->
<!-- begins: RFC3633 Section 13: Prefix Delegation reconfiguration -->
<section anchor="sipd" title="Prefix Delegation Reconfiguration">
<t>This section describes prefix delegation in Reconfigure
message exchanges.</t>
<section anchor="sipd-server" title="Delegating Router Behavior">
<t>The delegating router initiates a configuration message
exchange with a requesting router, as described in <xref target='RFC3315-19'/>,
by sending a Reconfigure message (acting as a DHCP server)
to the requesting router, as described in <xref target='RFC3315-19.1'/>.
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).</t>
</section>
<section anchor="sipd-client" title="Requesting Router Behavior">
<t>The requesting router responds to a Reconfigure message,
acting as a DHCP client, received from a delegating router
as described in <xref target='RFC3315-19.4'/>
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.</t>
</section>
</section>
<!-- ends: RFC3633 Section 13: Prefix Delegation reconfiguration -->
</section>
<!-- ends: "19 from line 2751-->
<section title="Relay Agent Behavior">
<!-- 20, line 2950-->
<t>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.</t>
<t>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.</t>
<!-- Applied text from Section 4.2 of RFC7283 -->
<t>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 <xref
target="relaying-from-client" />.</t>
<section title="Relaying a Client Message or a Relay-forward Message">
<!-- 20.1, line 2964-->
<t>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 <xref
target="RFC7283"/>) to be relayed, it constructs a new Relay-forward message. The
<!-- Applied text from Section 4.1 of RFC7283 -->
relay agent copies the source address from the header 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.</t>
<t><xref target="RFC6221"></xref> 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.</t>
<section anchor="relaying-from-client" title="Relaying a Message from a Client">
<!-- 20.1.1, line 2979-->
<t>If the relay agent received the message to be relayed from a
client, the relay agent places a global, ULA <xref target="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 <xref target="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.</t>
<t>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 <xref target='RFC3315-22.18'/>) 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.</t>
</section>
<!-- ends: "20.1.1 from line 2979-->
<section title="Relaying a Message from a Relay Agent">
<!-- 20.1.2, line 2999-->
<t>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.</t>
<t>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.</t>
<t>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 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.</t>
</section>
<!-- ends: "20.1.2 from line 2999-->
<!-- begins: RFC3633 Section 14: Relay agent behavior -->
<section title="Relay Agent Behavior with Prefix Delegation">
<t>A relay agent forwards messages containing Prefix Delegation
options in the same way as described earlier in this section.</t>
<t>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.</t>
</section>
<!-- ends: RFC3633 Section 14: Relay agent behavior -->
</section>
<!-- ends: "20.1 from line 2964-->
<section title="Relaying a Relay-reply Message">
<!-- 20.2, line 3021-->
<t>The relay agent processes any options included in the Relay-reply
message in addition to the Relay Message option, and then discards
those options.</t>
<t>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.</t>
<t>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.</t>
<!-- Applied text from Section 4.3 of RFC7283 -->
<t>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.</t>
</section>
<!-- ends: "20.2 from line 3021-->
<section anchor='RFC3315-20.3' title="Construction of Relay-reply Messages">
<!-- 20.3, line 3040-->
<t>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.</t>
<t>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 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.</t>
<t>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:</t>
<figure align="center" anchor="FigRelayExample"
title="Relay-reply Example">
<preamble/>
<artwork align="left">
<![CDATA[
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>
]]>
</artwork>
<postamble/>
</figure>
<t>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.</t>
</section>
<!-- ends: "20.3 from line 3040-->
</section>
<!-- ends: "20 from line 2950-->
<section anchor='RFC3315-21' title="Authentication of DHCP Messages">
<!-- 21, line 3092-->
<t>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.</t>
<t>The DHCP authentication mechanism is based on the design of
authentication for DHCPv4 <xref target="RFC3118"/>.</t>
<section anchor='RFC3315-21.1' title="Security of Messages Sent Between Servers and Relay Agents">
<!-- 21.1, line 3108-->
<t>Relay agents and servers that exchange messages securely use the
IPsec mechanisms for IPv6 <xref target="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.</t>
<t>Relay agents and servers that support secure relay agent to server
or relay agent to relay agent communication use IPsec under the
following conditions:
<list hangIndent="24" style="hanging">
<t hangText=" 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.</t>
<t hangText=" 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).</t>
<t hangText=" 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.</t>
<t hangText=" Security policy"> DHCP messages between relay agents and servers
should only be accepted from DHCP peers as identified in the local
configuration.</t>
<t hangText=" Authentication"> Shared keys, indexed to the source IP address of the
received DHCP message, are adequate in this application.</t>
<t hangText=" 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.</t>
</list></t>
</section>
<!-- ends: "21.1 from line 3108-->
<section title="Summary of DHCP Authentication">
<!-- 21.2, line 3172-->
<t>Authentication of DHCP messages is accomplished through the use of
the Authentication option (see <xref target='RFC3315-22.11'/>). 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.</t>
<t>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.</t>
<t>Any DHCP message MUST NOT include more than one Authentication
option.</t>
<t>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.</t>
</section>
<!-- ends: "21.2 from line 3172-->
<section title="Replay Detection">
<!-- 21.3, line 3198-->
<t>The Replay Detection Method (RDM) field determines the type of
replay detection used in the Replay Detection field.</t>
<t>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 <xref target="RFC5905"/>), can reduce the danger
of replay attacks. This method MUST be supported by all protocols.</t>
</section>
<!-- ends: "21.3 from line 3198-->
<section anchor='RFC3315-21.4' title="Delayed Authentication Protocol">
<!-- 21.4, line 3210-->
<t>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.</t>
<t>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.</t>
<t>The use of a particular technique based on the HMAC protocol <xref
target="RFC2104"/> using the MD5 hash <xref target="RFC1321"/> is
defined here.</t>
<section title="Use of the Authentication Option in the Delayed Authentication Protocol">
<!-- 21.4.1, line 3226-->
<t>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.</t>
<t>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.</t>
<t>The format of the Authentication information is:</t>
<figure align="center" anchor="FigAuthInfo"
title="Authentication information format">
<preamble/>
<artwork align="left">
<![CDATA[
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) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" 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
<xref target='RFC3315-8'/>.</t>
<t hangText=" key ID"> The key identifier that identified the key used to
generate the HMAC-MD5 value.</t>
<t hangText=" 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.</t>
</list></t>
<t>The sender computes the MAC using the HMAC generation algorithm
<xref target="RFC2104"/> and the MD5 hash function <xref
target="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.</t>
<t>DISCUSSION:</t>
<t><list style="empty">
<t>Algorithm 1 specifies the use of HMAC-MD5. Use of a different
technique, such as HMAC-SHA, will be specified as a separate
protocol.</t>
<t>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 identifiers,
and allows a host using DHCP to use authenticated DHCP while roaming
among DHCP administrative domains.</t>
</list></t>
</section>
<!-- ends: "21.4.1 from line 3226-->
<section anchor='RFC3315-21.4.2' title="Message Validation">
<!-- 21.4.2, line 3294-->
<t>Any DHCP message that includes more than one authentication
option MUST be discarded.</t>
<t>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
<xref target="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.</t>
</section>
<!-- ends: "21.4.2 from line 3294-->
<section title="Key Utilization">
<!-- 21.4.3, line 3309-->
<t>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.</t>
<t>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).</t>
</section>
<!-- ends: "21.4.3 from line 3309-->
<section title="Client Considerations for Delayed Authentication Protocol">
<!-- 21.4.4, line 3324-->
<t>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.</t>
<section title="Sending Solicit Messages">
<!-- 21.4.4.1, line 3333-->
<t>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 <xref target='RFC3315-21.4'/>.
The client does not include any replay detection or authentication
information in the Authentication option.</t>
</section>
<!-- ends: "21.4.4.1 from line 3333-->
<section title="Receiving Advertise Messages">
<!-- 21.4.4.2, line 3342-->
<t>The client validates any Advertise messages containing an
Authentication option specifying the delayed authentication
protocol using the validation test described in
<xref target='RFC3315-21.4.2'/>.</t>
<t>The Client behavior is defined by local policy, as detailed below. </t>
<t>
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.
</t>
<t>
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. </t>
<t> In all cases, messages for which the client does not have a matching key
should be treated as if they have no Authentication option.
</t>
<t>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. </t>
<t>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.
</t>
<t> 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.</t>
</section>
<!-- ends: "21.4.4.2 from line 3342-->
<section anchor='RFC3315-21.4.4.3' title="Sending Request, Confirm, Renew, Rebind, Decline or Release Messages">
<!-- 21.4.4.3, line 3374-->
<t>If the client authenticated the Advertise message through which
the client selected the server, the client MUST generate
authentication information for subsequent Request, Confirm, Renew,
Rebind or Release messages sent to the server, as described in
<xref target='RFC3315-21.4'/>. When the client sends a subsequent message, it MUST
use the same key used by the server to generate the authentication
information.</t>
</section>
<!-- ends: "21.4.4.3 from line 3374-->
<section title="Sending Information-request Messages">
<!-- 21.4.4.4, line 3385-->
<t>If the server has selected a key for the client in a previous
message exchange (see <xref target='RFC3315-21.4.5.1'/>), the client MUST use the
same key to generate the authentication information throughout the
session.</t>
</section>
<!-- ends: "21.4.4.4 from line 3385-->
<section title="Receiving Reply Messages">
<!-- 21.4.4.5, line 3392-->
<t>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.</t>
<t>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.</t>
</section>
<!-- ends: "21.4.4.5 from line 3392-->
<section title="Receiving Reconfigure Messages">
<!-- 21.4.4.6, line 3406-->
<t>The client MUST discard the Reconfigure if the message fails to
pass the validation test and MAY log the validation failure.</t>
</section>
<!-- ends: "21.4.4.6 from line 3406-->
</section>
<!-- ends: "21.4.4 from line 3324-->
<section title="Server Considerations for Delayed Authentication Protocol">
<!-- 21.4.5, line 3412-->
<t>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.</t>
<section anchor='RFC3315-21.4.5.1' title="Receiving Solicit Messages and Sending Advertise Messages">
<!-- 21.4.5.1, line 3422-->
<t>The server selects a key for the client and includes
authentication information in the Advertise message returned to
the client as specified in <xref target='RFC3315-21.4'/>. 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.</t>
</section>
<!-- ends: "21.4.5.1 from line 3422-->
<section title="Receiving Request, Confirm, Renew, Rebind or Release Messages and Sending Reply Messages">
<!-- 21.4.5.2, line 3431-->
<t>The server uses the key identified in the message and validates
the message as specified in <xref target='RFC3315-21.4.2'/>. 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 <xref target='RFC3315-21.4.4.3'/>.</t>
<t>If the message passes the validation test, the server responds
to the specific message as described in <xref target='RFC3315-18.2'/>. The server
MUST include authentication information generated using the key
identified in the received message, as specified in
<xref target='RFC3315-21.4'/>.</t>
</section>
<!-- ends: "21.4.5.2 from line 3431-->
</section>
<!-- ends: "21.4.5 from line 3412-->
</section>
<!-- ends: "21.4 from line 3210-->
<section anchor='RFC3315-21.5' title="Reconfigure Key Authentication Protocol">
<!-- 21.5, line 3446-->
<t>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.</t>
<t>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.</t>
<t>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.</t>
<section title="Use of the Authentication Option in the Reconfigure Key Authentication Protocol">
<!-- 21.5.1, line 3470-->
<t>The following fields are set in an Authentication option for the
Reconfigure Key Authentication Protocol:
<list hangIndent="14" style="hanging">
<t hangText=" protocol"> 3</t>
<t hangText=" algorithm"> 1</t>
<t hangText=" RDM"> 0</t>
</list>
</t>
<t>The format of the Authentication information for the Reconfigure
Key Authentication Protocol is:</t>
<figure align="center" anchor="FigRKAPAuthInfo"
title="RKAP Authentication Information">
<preamble/>
<artwork align="left">
<![CDATA[
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) |
+-+-+-+-+-+-+-+-+ |
. .
. .
. +-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="20" style="hanging">
<t hangText=" Type"> Type of data in Value field carried in this option:
<list hangIndent="8" style="hanging">
<t hangText=" 1"> Reconfigure Key value (used in Reply message).</t>
<t hangText=" 2"> HMAC-MD5 digest of the message (used in Reconfigure
message).</t>
</list>
</t>
<t hangText=" Value"> Data as defined by the Type field.</t>
</list></t>
</section>
<!-- ends: "21.5.1 from line 3470-->
<section title="Server considerations for Reconfigure Key protocol">
<!-- 21.5.2, line 3508-->
<t>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.</t>
<t>The Reconfigure Key is 128 bits long, and MUST be a
cryptographically strong random or pseudo-random number that cannot
easily be predicted.</t>
<t>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
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.</t>
</section>
<!-- ends: "21.5.2 from line 3508-->
<section title="Client considerations for Reconfigure Key protocol">
<!-- 21.5.3, line 3532-->
<t>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.</t>
<t>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.</t>
</section>
<!-- ends: "21.5.3 from line 3532-->
</section>
<!-- ends: "21.5 from line 3446-->
</section>
<!-- ends: "21 from line 3092-->
<section anchor='RFC3315-22' title="DHCP Options">
<!-- 22, line 3547-->
<t>Options are used to carry additional information and parameters in
DHCP messages. Every option shares a common base format, as described in
<xref target='RFC3315-22.1'/>. All values in options are represented in network byte
order.</t>
<t>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 <xref target="RFC7227"/> for guidelines regarding
new options definition.</t>
<t>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.</t>
<t>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 <xref target="RFC3315-22.4"/>),
IA_TA (see <xref target="RFC3315-22.5"/>), and
IA_PD (see <xref target="IA_PD-option"/>) options.
Also, IAAddress (see <xref target="RFC3315-22.6"/>) and
IAPrefix (see <xref target="IAPREFIX-option"/>) may appear in their
respective IA options more than once.</t>
<section anchor='RFC3315-22.1' title="Format of DHCP Options">
<!-- 22.1, line 3566-->
<t>The format of DHCP options is:</t>
<figure align="center" anchor="FigOptions"
title="Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> An unsigned integer identifying the specific option
type carried in this option.</t>
<t hangText=" option-len"> An unsigned integer giving the length of the option-data
field in this option in octets.</t>
<t hangText=" option-data"> The data for the option; the format of this data
depends on the definition of the option.</t>
</list></t>
<t>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 <xref target='RFC3315-22.4'/> and <xref target='RFC3315-22.6'/>.</t>
</section>
<!-- ends: "22.1 from line 3566-->
<section anchor='RFC3315-22.2' title="Client Identifier Option">
<!-- 22.2, line 3597-->
<t>The Client Identifier option is used to carry a DUID (see
<xref target='RFC3315-9'/>) identifying a client between a client
and a server. The format of the Client Identifier option is:</t>
<figure align="center" anchor="FigOption1"
title="Client Identifier Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_CLIENTID (1).</t>
<t hangText=" option-len"> Length of DUID in octets.</t>
<t hangText=" DUID"> The DUID for the client.</t>
</list></t>
</section>
<!-- ends: "22.2 from line 3597-->
<section anchor='RFC3315-22.3' title="Server Identifier Option">
<!-- 22.3, line 3623-->
<t>The Server Identifier option is used to carry a DUID (see
<xref target='RFC3315-9'/>) identifying a server between a client
and a server. The format of the Server Identifier option is:</t>
<figure align="center" anchor="FigOption2"
title="Server Identifier Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_SERVERID (2).</t>
<t hangText=" option-len"> Length of DUID in octets.</t>
<t hangText=" DUID"> The DUID for the server.</t>
</list></t>
</section>
<!-- ends: "22.3 from line 3623-->
<section anchor='RFC3315-22.4' title="Identity Association for Non-temporary Addresses Option">
<!-- 22.4, line 3649-->
<t>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.</t>
<t>Addresses appearing in an IA_NA option are not temporary addresses
(see <xref target='RFC3315-22.5'/>).</t>
<t>The format of the IA_NA option is:</t>
<figure align="center" anchor="FigOption3"
title="Identity Association for Non-temporary Addresses Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_IA_NA (3).</t>
<t hangText=" option-len"> 12 + length of IA_NA-options field.</t>
<t hangText=" 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.</t>
<t hangText=" 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.</t>
<t hangText=" 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.</t>
<t hangText=" IA_NA-options"> Options associated with this IA_NA.</t>
</list></t>
<t>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.</t>
<t>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.</t>
<t>An IA_NA option may only appear in the options area of a DHCP
message. A DHCP message may contain multiple IA_NA options.</t>
<t>The status of any operations involving this IA_NA is indicated in a
Status Code option in the IA_NA-options field.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>This option MAY appear in a Confirm message if the lifetimes on the
non-temporary addresses in the associated IA have not expired.</t>
</section>
<!-- ends: "22.4 from line 3649-->
<section anchor='RFC3315-22.5' title="Identity Association for Temporary Addresses Option">
<!-- 22.5, line 3761-->
<t>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 <xref target="RFC4941"/>. The format of the IA_TA option
is:</t>
<figure align="center" anchor="FigOption4"
title="Identity Association for Temporary Addresses Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_IA_TA (4).</t>
<t hangText=" option-len"> 4 + length of IA_TA-options field.</t>
<t hangText=" IAID"> The unique identifier for this IA_TA; the IAID must be unique
among the identifiers for all of this client's IA_TAs. The number
space for IA_TA IAIDs is separate from the number space for IA_NA
IAIDs.</t>
<t hangText=" IA_TA-options"> Options associated with this IA_TA.</t>
</list></t>
<t>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.</t>
<t>Each IA_TA carries one "set" of temporary addresses.</t>
<t>An IA_TA option may only appear in the options area of a DHCP
message. A DHCP message may contain multiple IA_TA options.</t>
<t>The status of any operations involving this IA_TA is indicated in a
Status Code option in the IA_TA-options field.</t>
<t>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.</t>
<t>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.</t>
<t>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 <xref target="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.</t>
<t>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.</t>
<t>This option MAY appear in a Confirm message if the lifetimes on the
temporary addresses in the associated IA have not expired.</t>
</section>
<!-- ends: "22.5 from line 3761-->
<section anchor='RFC3315-22.6' title="IA Address Option">
<!-- 22.6, line 3840-->
<t>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.</t>
<t>The format of the IA Address option is:</t>
<figure align="center" anchor="FigOption5"
title="IA Address Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_IAADDR (5).</t>
<t hangText=" option-len"> 24 + length of IAaddr-options field.</t>
<t hangText=" IPv6 address"> An IPv6 address.</t>
<t hangText=" preferred-lifetime"> The preferred lifetime for the IPv6 address in
the option, expressed in units of seconds.</t>
<t hangText=" valid-lifetime"> The valid lifetime for the IPv6 address in the
option, expressed in units of seconds.</t>
<t hangText=" IAaddr-options"> Options associated with this address.</t>
</list></t>
<t>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
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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>More than one IA Address Option can appear in an IA_NA option
or an IA_TA option.</t>
<t>The status of any operations involving this IA Address is indicated
in a Status Code option in the IAaddr-options field, as specified
in <xref target='RFC3315-22.13'/>.</t>
</section>
<!-- ends: "22.6 from line 3840-->
<section anchor='RFC3315-22.7' title="Option Request Option">
<!-- 22.7, line 3912-->
<t>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:</t>
<figure align="center" anchor="FigOption6"
title="Option Request Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_ORO (6).</t>
<t hangText=" option-len"> 2 * number of requested options.</t>
<t hangText=" requested-option-code-n"> The option code for an option requested by
the client.</t>
</list></t>
<t>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.</t>
</section>
<!-- ends: "22.7 from line 3912-->
<section anchor='RFC3315-22.8' title="Preference Option">
<!-- 22.8, line 3945-->
<t>The Preference option is sent by a server to a client to affect the
selection of a server by the client.</t>
<t>The format of the Preference option is:</t>
<figure align="center" anchor="FigOption7"
title="Preference Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 |
+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_PREFERENCE (7).</t>
<t hangText=" option-len"> 1.</t>
<t hangText=" pref-value"> The preference value for the server in this message.</t>
</list></t>
<t>A server MAY include a Preference option in an Advertise message to
control the selection of a server by the client. See <xref target='RFC3315-17.1.3'/>
for the use of the Preference option by the client and the
interpretation of Preference option data value.</t>
</section>
<!-- ends: "22.8 from line 3945-->
<section title="Elapsed Time Option">
<!-- 22.9, line 3974-->
<figure align="center" anchor="FigOption8"
title="Elapsed Time Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_ELAPSED_TIME (8).</t>
<t hangText=" option-len"> 2.</t>
<t hangText=" 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).</t>
</list></t>
<t>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.</t>
</section>
<!-- ends: "22.9 from line 3974-->
<section anchor='RFC3315-22.10' title="Relay Message Option">
<!-- 22.10, line 4009-->
<t>The Relay Message option carries a DHCP message in a Relay-forward
or Relay-reply message.</t>
<t>The format of the Relay Message option is:</t>
<figure align="center" anchor="FigOption9"
title="Relay Message Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_RELAY_MSG (9)</t>
<t hangText=" option-len"> Length of DHCP-relay-message</t>
<t hangText=" 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</t>
</list></t>
</section>
<!-- ends: "22.10 from line 4009-->
<section anchor='RFC3315-22.11' title="Authentication Option">
<!-- 22.11, line 4042-->
<t>The Authentication option carries authentication information to
authenticate the identity and contents of DHCP messages. The use of
the Authentication option is described in <xref target='RFC3315-21'/>. The format of
the Authentication option is:</t>
<figure align="center" anchor="FigOption11"
title="Authentication Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_AUTH (11).</t>
<t hangText=" option-len"> 11 + length of authentication information field.</t>
<t hangText=" protocol"> The authentication protocol used in this authentication
option.</t>
<t hangText=" algorithm"> The algorithm used in the authentication protocol.</t>
<t hangText=" RDM"> The replay detection method used in this authentication
option.</t>
<t hangText=" Replay detection"> The replay detection information for the RDM.</t>
<t hangText=" authentication information">The authentication information, as
specified by the protocol and algorithm used in this authentication
option.</t>
</list></t>
</section>
<!-- ends: "22.11 from line 4042-->
<section anchor='RFC3315-22.12' title="Server Unicast Option">
<!-- 22.12, line 4089-->
<t>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:</t>
<figure align="center" anchor="FigOption12"
title="Server Unicast Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_UNICAST (12).</t>
<t hangText=" option-len"> 16.</t>
<t hangText=" server-address"> The IP address to which the client should send
messages delivered using unicast.</t>
</list></t>
<t>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.</t>
<t>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.</t>
<t>Details about when the client may send messages to the server using
unicast are in <xref target='RFC3315-18'/>.</t>
</section>
<!-- ends: "22.12 from line 4089-->
<section anchor='RFC3315-22.13' title="Status Code Option">
<!-- 22.13, line 4134-->
<t>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:</t>
<figure align="center" anchor="FigOption13"
title="Status Code Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_STATUS_CODE (13).</t>
<t hangText=" option-len"> 2 + length of status-message.</t>
<t hangText=" status-code"> The numeric code for the status encoded in
this option.</t>
<t hangText=" status-message"> A UTF-8 encoded text string suitable for display to
an end user, which MUST NOT be null-terminated.</t>
</list></t>
<t>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.</t>
<t>The status-codes values previously defined by <xref target="RFC3315"/>
and <xref target="RFC3633"/> are:</t>
<texttable>
<ttcol>Name</ttcol>
<ttcol align="right">Code</ttcol>
<ttcol>Description</ttcol>
<c>Success</c><c>0</c><c>Success.</c>
<c>UnspecFail</c><c>1</c><c>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.</c>
<c>NoAddrsAvail</c><c>2</c><c>Server has no addresses available
to assign to the IA(s).</c>
<c>NoBinding</c><c>3</c><c>Client record (binding) unavailable.</c>
<c>NotOnLink</c><c>4</c><c>The prefix for the address is not
appropriate for the link to which the client is attached.</c>
<c>UseMulticast</c><c>5</c><c>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.</c>
<c>NoPrefixAvail</c><c>6</c><c>Delegating router has no prefixes
available to assign to the IAPD(s).</c>
</texttable>
</section>
<!-- ends: "22.13 from line 4134-->
<section anchor='RFC3315-22.14' title="Rapid Commit Option">
<!-- 22.14, line 4172-->
<t>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:</t>
<figure align="center" anchor="FigOption14"
title="Rapid Commit Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_RAPID_COMMIT (14).</t>
<t hangText=" option-len"> 0.</t>
</list></t>
<t>A client MAY include this option in a Solicit message if the client
is prepared to perform the Solicit-Reply message exchange described in
<xref target='RFC3315-17.1.1'/>.</t>
<t>A server MUST include this option in a Reply message sent in
response to a Solicit message when completing the Solicit-Reply
message exchange.</t>
<t>DISCUSSION:</t>
<t><list style="empty">
<t>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.</t>
<t>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.
</t>
</list></t>
</section>
<!-- ends: "22.14 from line 4172-->
<section title="User Class Option">
<!-- 22.15, line 4217-->
<t>The User Class option is used by a client to identify the type or
category of user or applications it represents.</t>
<t>The format of the User Class option is:</t>
<figure align="center" anchor="FigOption15"
title="User Class Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_USER_CLASS (15).</t>
<t hangText=" option-len"> Length of user class data field.</t>
<t hangText=" user-class-data"> The user classes carried by the client.</t>
</list></t>
<t>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
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.</t>
<t>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:</t>
<figure align="center" anchor="FigOption15Data"
title="User Class Data Format">
<preamble/>
<artwork align="left">
<![CDATA[
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
| user-class-len | opaque-data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t>The user-class-len is two octets long and specifies the length of
the opaque user class data in network byte order.</t>
<t>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.</t>
</section>
<!-- ends: "22.15 from line 4217-->
<section title="Vendor Class Option">
<!-- 22.16, line 4276-->
<t>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:</t>
<figure align="center" anchor="FigOption16"
title="Vendor Class Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 .
. . . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_VENDOR_CLASS (16).</t>
<t hangText=" option-len"> 4 + length of vendor class data field.</t>
<t hangText=" enterprise-number"> The vendor's registered Enterprise Number as
registered with IANA <xref target="IANA-PEN"/>.</t>
<t hangText=" vendor-class-data"> The hardware configuration of the host on which
the client is running.</t>
</list></t>
<t>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.</t>
<t>Each instance of the vendor-class-data is formatted as follows:</t>
<figure align="center" anchor="FigOption16Data"
title="Vendor Class Data Format">
<preamble/>
<artwork align="left">
<![CDATA[
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
| vendor-class-len | opaque-data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t>The vendor-class-len is two octets long and specifies the length of
the opaque vendor class data in network byte order.</t>
<t>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.</t>
</section>
<!-- ends: "22.16 from line 4276-->
<section title="Vendor-specific Information Option">
<!-- 22.17, line 4325-->
<t>This option is used by clients and servers to exchange
vendor-specific information.</t>
<t>The format of the Vendor-specific Information option is:</t>
<figure align="center" anchor="FigOption17"
title="Vendor-specific Information Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_VENDOR_OPTS (17).</t>
<t hangText=" option-len"> 4 + length of option-data field.</t>
<t hangText=" enterprise-number"> The vendor's registered Enterprise Number as
registered with IANA <xref target="IANA-PEN"/>.</t>
<t hangText=" option-data"> An opaque object, interpreted by
vendor-specific code on the clients and servers.</t>
</list></t>
<t>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.</t>
<t>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:</t>
<figure align="center" anchor="FigOption17Data"
title="Vendor-specific Options Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" opt-code"> The code for the encapsulated option.</t>
<t hangText=" option-len"> An unsigned integer giving the length of the option-data
field in this encapsulated option in octets.</t>
<t hangText=" option-data"> The data area for the encapsulated option.</t>
</list></t>
<t>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.</t>
<t>A client that is interested in receiving a Vendor-specific Information Option:
</t>
<t><list hangIndent="3" style="hanging">
<t hangText="-"> MUST specify the Vendor-specific Information Option in an
Option Request Option.</t>
<t hangText="-"> MAY specify an associated Vendor Class Option.</t>
<t hangText="-"> MAY specify the Vendor-specific Information Option with any
data.</t>
</list></t>
<t>Severs only return the Vendor-specific Information Options if specified in
Option Request Options from clients and:</t>
<t><list hangIndent="3" style="hanging">
<t hangText="-"> 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.</t>
<t hangText="-"> MAY return all configured Vendor-specific Information Options.</t>
<t hangText="-"> 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.</t>
</list> </t>
</section>
<!-- ends: "22.17 from line 4325-->
<section anchor='RFC3315-22.18' title="Interface-Id Option">
<!-- 22.18, line 4396-->
<t>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.</t>
<t>The format of the Interface ID option is:</t>
<figure align="center" anchor="FigOption18"
title="Interface-ID Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_INTERFACE_ID (18).</t>
<t hangText=" option-len"> Length of interface-id field.</t>
<t hangText=" interface-id"> An opaque value of arbitrary length generated by the
relay agent to identify one of the relay agent's interfaces.</t>
</list></t>
<t>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.</t>
<t>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.</t>
</section>
<!-- ends: "22.18 from line 4396-->
<section anchor='RFC3315-22.19' title="Reconfigure Message Option">
<!-- 22.19, line 4440-->
<t>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:</t>
<figure align="center" anchor="FigOption19"
title="Reconfigure Message Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 |
+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_RECONF_MSG (19).</t>
<t hangText=" option-len"> 1.</t>
<t hangText=" msg-type"> 5 for Renew message, 6 for Rebind,
11 for Information-request message.</t>
</list></t>
<t>The Reconfigure Message option can only appear in a Reconfigure
message.</t>
</section>
<!-- ends: "22.19 from line 4440-->
<section anchor='RFC3315-22.20' title="Reconfigure Accept Option">
<!-- 22.20, line 4468-->
<t>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:</t>
<figure align="center" anchor="FigOption20"
title="Reconfigure Accept Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_RECONF_ACCEPT (20).</t>
<t hangText=" option-len"> 0.</t>
</list></t>
</section>
<!-- ends: "22.20 from line 4468-->
<!-- begins: merged section 9. and 10. from RFC3633 -->
<section anchor="IA_PD-option"
title="Identity Association for Prefix Delegation Option">
<t>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.</t>
<figure align="center" anchor="FigOption25"
title="Identity Association for Prefix Delegation Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t>
<list style="hanging" hangIndent='24'>
<t hangText=" option-code">OPTION_IA_PD (25).</t>
<t hangText=" option-length">12 + length of IA_PD-options
field.</t>
<t hangText=" 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.</t>
<t hangText=" 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.</t>
<t hangText=" T2">The time at which the requesting router
should contact any available delegating router to extend
the lifetimes of the prefixes assigned to the IA_PD; T2 is
a time duration relative to the current time expressed in
units of seconds.</t>
<t hangText=" IA_PD-options">Options associated with this
IA_PD.</t>
</list>
</t>
<t>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.</t>
<t>An IA_PD option may only appear in the options area of a DHCP
message. A DHCP message may contain multiple IA_PD options.</t>
<t>The status of any operations involving this IA_PD is indicated
in a Status Code option in the IA_PD-options field.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
</section>
<section anchor='IAPREFIX-option' title="IA Prefix Option">
<t>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.</t>
<figure align="center" anchor="FigOption26"
title="IA Prefix Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t>
<list style="hanging" hangIndent='24'>
<t hangText=" option-code">OPTION_IAPREFIX (26).</t>
<t hangText=" option-length">25 + length of
IAprefix-options field.</t>
<t hangText=" preferred-lifetime">The recommended
preferred lifetime for the IPv6 prefix in the option,
expressed in units of seconds. A value of 0xFFFFFFFF
represents infinity.</t>
<t hangText=" valid-lifetime">The valid lifetime for the
IPv6 prefix in the option, expressed in units of
seconds. A value of 0xFFFFFFFF represents infinity.</t>
<t hangText=" prefix-length">Length for this prefix in
bits.</t>
<t hangText=" IPv6-prefix">An IPv6 prefix.</t>
<t hangText=" IAprefix-options">Options associated with
this prefix.</t>
</list>
</t>
<t>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.</t>
<t>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 <xref
target="RFC2461"/>, unless administratively configured.</t>
<t>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.</t>
<t>The values in the preferred and valid lifetimes are the
number of seconds remaining for each lifetime.</t>
<t>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.</t>
<t>The status of any operations involving this IA_PD Prefix
option is indicated in a Status Code option in the
IAprefix-options field.</t>
</section>
<!-- ends: merged section 9. and 10. from RFC3633 -->
<!-- Merging section 4. from RFC7083 (SOL_MAX_RT option) -->
<section anchor='SOL_MAX_RT_option' title="SOL_MAX_RT Option">
<t>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 <xref target='RFC3315-5.5'/>.
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. </t>
<t>The format of the SOL_MAX_RT option is:</t>
<figure align="center" anchor="FigOption82"
title="SOL_MAX_RT Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_SOL_MAX_RT (82).</t>
<t hangText=" option-len"> 4.</t>
<t hangText=" SOL_MAX_RT value"> Overriding value for SOL_MAX_RT
in seconds; MUST be in range: 60 <= "value" <= 86400 (1 day).</t>
</list></t>
<!-- The following paragraphs have been merged from section 7 and 8
of RFC7083 -->
<t>A DHCP client MUST include the SOL_MAX_RT option code in any Option
Request option (see <xref target='RFC3315-22.7'/>) it sends.</t>
<t>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.</t>
<t>A DHCP client MUST ignore any SOL_MAX_RT option values
that are less than 60 or more than 86400.</t>
<t>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 <xref target='RFC3315-14'/>
and <xref target='RFC3315-17.1.2'/>.</t>
<t>Updated SOL_MAX_RT value applies only to the network interface on
which the client received SOL_MAX_RT option.</t>
</section>
<!-- ends: merged section 4. from RFC7083 -->
<section anchor='INF_MAX_RT_option' title="INF_MAX_RT Option">
<t>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 <xref target='RFC3315-5.5'/>.
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.</t>
<t>The format of the INF_MAX_RT option is:</t>
<figure align="center" anchor="FigOption83"
title="INF_MAX_RT Option Format">
<preamble/>
<artwork align="left">
<![CDATA[
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]>
</artwork>
<postamble/>
</figure>
<t><list hangIndent="24" style="hanging">
<t hangText=" option-code"> OPTION_INF_MAX_RT (83).</t>
<t hangText=" option-len"> 4.</t>
<t hangText=" SOL_MAX_RT value"> Overriding value for INF_MAX_RT
in seconds; MUST be in range: 60 <= "value" <= 86400 (1 day).</t>
</list></t>
<!-- The following paragraphs have been merged from section 7 of RFC7083 -->
<t>A DHCP client MUST include the INF_MAX_RT option code in any Option
Request option (see <xref target='RFC3315-22.7'/>) it sends.</t>
<t>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.</t>
<t>A DHCP client MUST ignore any INF_MAX_RT option values
that are less than 60 or more than 86400.</t>
<t>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 <xref target='RFC3315-14'/>
and <xref target='RFC3315-18.1.5'/>.</t>
<t>Updated INF_MAX_RT value applies only to the network interface on
which the client received INF_MAX_RT option.</t>
</section>
<!-- ends: merged section 5. from RFC7083 -->
</section>
<!-- ends: "22 from line 3547-->
<section title="Security Considerations">
<!-- 23, line 4492-->
<t>The threat to DHCP is inherently an insider threat (assuming a
properly configured network where DHCPv6 ports are blocked on the
perimeter gateways of the enterprise). Regardless of the gateway
configuration, however, the potential attacks by insiders and outsiders
are the same.</t>
<t>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.</t>
<t>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.</t>
<!-- Merged from the section 10 of RFC7083. -->
<t>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.</t>
<t>There is another threat to DHCP clients from mistakenly or
accidentally configured DHCP servers that answer DHCP client requests
with unintentionally incorrect configuration parameters.</t>
<t>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.</t>
<t>The threat specific to a DHCP server is an invalid client
masquerading as a valid client. The motivation for this may be for theft
of service, or to circumvent auditing for any number of nefarious
purposes.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>The Delayed Authentication protocol described in <xref target='RFC3315-21.4'/> 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.</t>
<t>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.</t>
<t>The Reconfigure Key protocol described in <xref target='RFC3315-21.5'/> 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.</t>
<t>Communication between a server and a relay agent, and communication
between relay agents, can be secured through the use of IPsec, as
described in <xref target='RFC3315-21.1'/>. 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.</t>
<t>A rogue delegating router can issue bogus prefixes to a requesting
router. This may cause denial of service due to unreachability.</t>
<t>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.</t>
<t>To guard against attacks through prefix delegation, requesting
routers and delegating routers SHOULD use DHCP authentication as
described in <xref target='RFC3315-21'/>.
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.</t>
<t>Networks configured with delegated prefixes should be configured to
preclude intentional or inadvertent inappropriate advertisement of these
prefixes.</t>
</section>
<!-- ends: "23 from line 4492-->
<section title="IANA Considerations">
<!-- 24, line 4595-->
<t>This document does not define any new DHCPv6 name spaces or definitions.</t>
<t>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
<xref target="RFC3315"/>, <xref target="RFC3633"/>, and <xref target="RFC7083"/>.
</t>
</section>
<!-- ends: "24 from line 4595-->
<section title="Acknowledgments">
<!-- 25, line 4764-->
<t>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.</t>
<t>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.</t>
<t>The following acknowledgements are from the original RFC 3315 and RFC 3633:</t>
<t>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.</t>
<t>Thanks to Steve Deering and Bob Hinden, who have consistently taken
the time to discuss the more complex parts of the IPv6
specifications.</t>
<t>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.</t>
</section>
<!-- ends: "25 from line 4764-->
</middle>
<back>
<references title="Normative References">
<?rfc include='reference.RFC.3646'?>
<?rfc include='reference.RFC.4075'?>
<?rfc include='reference.RFC.2136'?>
<!-- Vixie, P., Ed., Thomson, S., Rekhter, Y. and J. Bound, "DynamicUpdates in the Domain Name System (DNS UPDATE)", RFC 2136, April
1997. -->
<?rfc include='reference.RFC.2119'?>
<!-- Bradner, S., "Key words for use in RFCs to Indicate RequirementLevels", BCP 14, RFC 2119, March 1997. -->
<?rfc include='reference.RFC.2460'?>
<!-- Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)Specification", RFC 2460, December 1998. -->
<?rfc include='reference.RFC.2464'?>
<!-- Crawford, M., "Transmission of IPv6 Packets over EthernetNetworks", RFC 2464, December 1998. -->
<?rfc include='reference.RFC.4291'?>
<!-- Hinden, R. and S. Deering, "IP Version 6 AddressingArchitecture", RFC 4291, February 2006. -->
<?rfc include='reference.RFC.3118'?>
<!-- Droms, R., Ed. and W. Arbaugh, Ed., "Authentication forDHCP Messages", RFC 3118, June 2001. -->
<?rfc include='reference.RFC.4301'?>
<!-- Kent, S. and R. Atkinson, "Security Architecture for the Internet Protocol", RFC 4301, December 2005. -->
<?rfc include='reference.RFC.5905'?>
<!-- Mills, D., "Network Time Protocol Version 4: Protocol and Algorithms Specification", RFC 5905, June 2010. -->
<?rfc include='reference.RFC.5226'?>
<!-- Narten, T. and H. Alvestrand, "Guidelines for Writing an IANAConsiderations Section in RFCs", BCP 26, RFC 5226, May 2008.
-->
<?rfc include='reference.RFC.1035'?>
<!-- Mockapetris, P., "Domain names - implementation andspecification", RFC 1035, November 1987. -->
<?rfc include='reference.RFC.4861'?>
<!-- Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery forIP Version 6 (IPv6)", RFC 4861, September 2007. -->
<?rfc include='reference.RFC.4941'?>
<!-- Narten, T. and R. Draves, "Privacy Extensions for StatelessAddress Autoconfiguration in IPv6", RFC 4941, . -->
<?rfc include='reference.RFC.0768'?>
<!-- Postel, J., "User Datagram Protocol", STD 6, RFC 768, August 1980. -->
<?rfc include='reference.RFC.0826'?>
<!-- Plummer, D.C., "Ethernet Address Resolution Protocol: Orconverting network protocol addresses to 48.bit Ethernet addressfor
transmission on Ethernet hardware", STD 37, RFC 826, November1982. -->
<?rfc include='reference.RFC.4862'?>
<!-- Thomson, S. and T. Narten, "IPv6 Stateless AddressAutoconfiguration", RFC 4862, September 2007. -->
<?rfc include='reference.RFC.2131'?>
<!-- Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March1997. -->
<?rfc include='reference.RFC.2132'?>
<!-- Alexander, S. and R. Droms, "DHCP Options and BOOTP VendorExtensions", RFC 2132, March 1997. -->
<?rfc include='reference.RFC.6355'?>
<?rfc include='reference.RFC.6724'?>
<?rfc include='reference.RFC.2526'?>
<!-- Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast Addresses", RFC 2526, March 1999. -->
<?rfc include='reference.RFC.2461'?>
<?rfc include='reference.RFC.7227'?>
<?rfc include='reference.RFC.6221'?>
<?rfc include='reference.RFC.7083'?>
<?rfc include='reference.RFC.7283'?>
</references>
<references title="Informative References">
<reference anchor="IANA-PEN">
<front>
<title>Private Enterprise Numbers registry
http://www.iana.org/assignments/enterprise-numbers</title>
<author>
<organization>IANA</organization>
</author>
<date />
</front>
</reference>
<?rfc include='reference.RFC.1321'?>
<!--Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April1992. -->
<?rfc include='reference.RFC.2104'?>
<!--Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-Hashingfor Message Authentication", RFC 2104, February 1997. -->
<?rfc include='reference.RFC.3769'?>
<?rfc include='reference.RFC.3162'?>
<?rfc include='reference.RFC.7084'?>
<?rfc include='reference.RFC.3736'?>
<?rfc include='reference.RFC.3633'?>
<?rfc include='reference.RFC.2462'?>
<?rfc include='reference.RFC.3041'?>
<?rfc include='reference.RFC.3315'?>
<?rfc include='reference.RFC.4193'?>
<?rfc include='reference.RFC.7341'?>
<?rfc include='reference.I-D.ietf-dhc-topo-conf'?>
</references>
<!-- Let's briefly document relevant changes against 3315 here -->
<section title="Changes since RFC3315">
<t>
<list style="numbers">
<t>Incorporated RFC3315 errata (ids: 294, 1373, 2928, 1815, 3577,
2509, 295).</t>
<t>Partially incorporated RFC3315 errata id 2472 (place other IA options
if NoAddrsAvail is sent in Advertise).</t>
<t>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.</t>
<t>Added DUID-UUID and reference to RFC6355. Ticket #54.</t>
<t>Specified a minimum length for the DUID in section "9.1. DUID Contents".
Ticket #39.</t>
<t>Removed the use of term "sub-options" from section "19.1.1. Creation and
Transmission of Reconfigure Messages". Ticket #40.</t>
<t>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.</t>
<t>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.</t>
<t>Merged RFC7083, "Modification to Default Values of SOL_MAX_RT and
INF_MAX_RT", into this document. Ticket #51.</t>
<t>Incorporated RFC3315 errata (id 2471), into section 17.1.3. Ticket #25.</t>
<t>Added text that relay agents MUST NOT modify the relayed message to section
20.1.2. Ticket #57.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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 options; the same applies to Vendor Specific
Information option. Ticket #22.</t>
<t>Clarified relay agent definition. Ticket #12.</t>
<t>Changed REL_MAX_RC and DEC_MAX_RC defaults from 5 to 4 and added retry to
parameter description. Ticket #84.</t>
<t>Clarify handling process for Vendor-specific Information Option
and Vendor Class Option. Ticket #20.</t>
<t>Replace "monotonic" with "strictly monotonic" in Section 21.3.
Ticket #11.</t>
<t>Incorporate everything of RFC 6644, except for Security
Considerations Section, which has already covered in a more
abstracted way. Ticket #55 & #56.</t>
<t>Clarify the server behavior process when a client violates
Delayed Authentication Protocol, in Section 21.4. Ticket #90.</t>
<t>Updated titles of sections 19.4.2. and 19.4.4. to include Rebind
messages.</t>
<t>Applied many of the review comments from a review done by Fred
Templin in August 2006. Ticket #14.</t>
<t>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.</t>
<t>Changed WG to DHC, added keywords</t>
<t>Loosened requirements for DUID-EN, so that DUID type can be used
for virtual machines. Ticket #16.</t>
<t>Clarified that IA may contain other resources than just address.
Ticket #93.</t>
<t>Clarified that most options are singletons (i.e. can appear only
once). Ticket #83.</t>
<t>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).</t>
<t>Clarified that encapsulated options must be requested using
top level ORO (ticket #38).</t>
<t>Clarified that configuration for interface X should be requested
over interface X (ticket #48).</t>
<t>CONFIRM is now an optional message (MUST send Confirm eased to
SHOULD) (ticket #120).</t>
<t>Added reference to RFC7227: DHCPv6 Option Guidelines (ticket #121).
</t>
<t>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.</t>
<t>Addressed ticket #115 - don't use DHCPv6 for DHCPv4 configuration.</t>
<t>Revised IANA Considerations based on ticket #117.</t>
<t>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).</t>
<t>Merged Section 12 from RFC3633 (ticket #107)</t>
<t>Clarified behavior for unknown messages (RFC7283), ticket #58.</t>
<t>Addressed tickets #123 and #126, and clarified that the client
SHOULD abandon its bindings when restarts the server solicitation.</t>
<t>Clarified link-address field usage, ticket #73.</t>
</list>
</t>
</section>
<!-- Let's briefly document relevant changes against 3633 here -->
<section title="Changes since RFC3633">
<t>
<list style="numbers">
<t>Incorporated RFC3633 errata (ids: 248, 1880, 2468, 2469, 2470, 3736)</t>
<t>...</t>
</list>
</t>
</section>
<!-- ** This should be an appendix tag but that does not yet seem to work! -->
<!-- tomek: I managed to get it work. The trick was to move section from <middle>
to <back> -->
<section title="Appearance of Options in Message Types">
<t>The following table indicates with a "*" the options are allowed in
each DHCP message type:</t>
<figure>
<artwork>
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. *
</artwork>
</figure>
<t>NOTE:</t>
<t>Only included in Information-request messages that are sent in
response to a Reconfigure (see <xref target='RFC3315-19.4.3'/>).</t>
<figure>
<artwork>
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. * * * *
</artwork>
</figure>
</section>
<!-- ** This should be an appendix tag but that does not yet seem to work! -->
<section title="Appearance of Options in the Options Field of DHCP Options">
<t>The following table indicates with a "*" where options can appear
in the options field of other options:</t>
<figure>
<artwork>
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 *
</artwork>
</figure>
<t>Note: "Relay Forw" / "Relay Reply" options appear in the options
field of the message but may only appear in these messages.</t>
</section>
</back>
</rfc>
<!-- generated from file samples/rfc3315.nroff with nroff2xml 0.0.2 by Tomek Mrugalski -->
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