Dynamic Host Configuration Protocol for IPv6
(DHCPv6) bisInternet Systems Consortium,
Inc.950 Charter StreetRedwood CityCA94063USAtomasz.mrugalski@gmail.comInternet Systems Consortium,
Inc.950 Charter St.Redwood CityCA94063USAmsiodelski@gmail.comCisco Systems, Inc.1414 Massachusetts AveBoxborough, MA 01719USAvolz@cisco.comCisco Systems, Inc.De Kleetlaan, 7DiegemB-1831Belgiumayourtch@cisco.comSandelman Software Works470 Dawson AvenueOttawaONK1Z 5V7CAmcr+ietf@sandelman.cahttp://www.sandelman.ca/Huawei Technologies Co.,
LtdQ14, Huawei Campus, No.156 Beiqing RoadHai-Dian District, Beijing, 100095P.R. Chinajiangsheng@huawei.comNominum, Inc.800 Bridge St.Redwood CityCA94043USATed.Lemon@nominum.comUniversity of New Hampshire, Interoperability Lab (UNH-IOL)Durham, NHUSAtwinters@iol.unh.edu
Internet
Dynamic Host Configuration (DHC)DHCPv6IPv6DHCPThis document describes the Dynamic Host Configuration Protocol for
IPv6 (DHCPv6): an extensible mechanism for configuring hosts with
network configuration parameters, IP addresses, and prefixes. Parameters
can be provided statelessly, or in combination with stateful assignment
of one or more IPv6 addresses and/or IPv6 prefixes. DHCPv6 can operate
either in place of or in addition to stateless address autoconfiguration
(SLAAC).This document updates the text from RFC 3315, the original DHCPv6
specification, and incorporates the stateless DHCPv6 extensions (RFC
3736) and prefix delegation (RFC 3633), clarifying the interactions
between these modes of operation (RFC 7550) and providing a mechanism
for throttling DHCPv6 clients when DHCPv6 service is not available (RFC
7083). As such, this document obsoletes RFC3315, RFC3633, RFC3736,
RFC7083, RFC7550.This document describes DHCP for IPv6 (DHCPv6), a client/server
protocol that provides managed configuration of devices. Relay agent
functionality is also defined for enabling communication between clients
and servers that are not on the same link.DHCPv6 can provide a device with addresses assigned by a DHCPv6
server and other configuration information, which are carried in
options. DHCPv6 can be extended through the definition of new options to
carry configuration information not specified in this document.DHCPv6 is the "stateful address autoconfiguration protocol" and the
"stateful autoconfiguration protocol" referred to in "IPv6 Stateless
Address Autoconfiguration" .This document also provides a mechanism for automated delegation of
IPv6 prefixes using DHCPv6. Through this mechanism, a delegating router
can delegate prefixes to requesting routers. Use of this mechanism is
specified as part of the and by .DHCPv6 can also provide only other configuration options
(i.e., no addresses or prefixes). That implies that the
server doesn't have to track any state, and thus the mode is called
stateless DHCPv6. Mechanisms necessary to support stateless DHCPv6 are
much smaller than to support stateful DHCPv6.The remainder of this introduction summarizes relation to the
previous DHCPv6 standards ,
clarifies the stance with regards to DHCPv4 . More detailed description of the message
exchange mechanisms and example message flows in and are
intended as illustrations of DHCP operation rather than an exhaustive
list of all possible client-server interactions. provides an overview of common operational
models. explains client
and server operation in detail.The initial specification of DHCPv6 was defined in and a number of follow up extensions
published over the years. Several notable extensions were published:
prefix delegation , stateless , update to SOL_MAX_RT and INF_MAX_RT option
values and harmonization between
addresses and prefixes support .
Understanding a protocol which definition is spread between large
number of documents may be cumbersome. Furthermore, a significant
operational experience has been gained over the years and certain
small elements of the protocol have been reworked. This document
provides a unified, corrected and cleaned up definition of the DHCPv6
that also covers all erratas filled against older RFCs. As such, it
obsoletes a number of aforementioned RFCs. There is a small number of
mechanisms that were obsoleted. They are listed in .The operational models and relevant configuration information for
DHCPv4
and DHCPv6 are sufficiently different that integration between the two
services is not included in this document. 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.
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.Clients and servers exchange DHCP messages using UDP . The client uses a link-local address or
addresses determined through other mechanisms for transmitting and
receiving DHCP messages.A DHCP client sends most messages using a reserved, link-scoped
multicast destination address so that the client need not be
configured with the address or addresses of DHCP servers.To allow a DHCP client to send a message to a DHCP server that is
not attached to the same link, a DHCP relay agent on the client's link
will relay messages between the client and server. The operation of
the relay agent is transparent to the client and the discussion of
message exchanges in the remainder of this section will omit the
description of message relaying by relay agents.Once the client has determined the address of a server, it may
under some circumstances send messages directly to the server using
unicast.When a DHCP client does not need to have a DHCP server assign it IP
addresses or delegated prefixes, the client can obtain configuration information such as a
list of available DNS servers or NTP
servers through a single message and
reply exchange with a DHCP server. To obtain configuration
information the client first sends an Information-request message to
the All_DHCP_Relay_Agents_and_Servers multicast address. Servers
respond with a Reply message containing the configuration information
for the client.This message exchange assumes that the client requires only
configuration information and does not require the assignment of any
IPv6 addresses or delegated prefixes.When a server has IPv6 addresses and/or delegated prefixes 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/or delegated prefixes 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 and/or
delegated prefixes to the client immediately responds with a Reply
message. The configuration information and the addresses and/or
delegated prefixes in the Reply message are then
immediately available for use by the client.Each address or delegated prefix 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 or delegated prefix, 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 or
delegated prefix without interruption.To request the assignment of one or more IPv6 addresses and/or delegated prefixes, a client
first locates a DHCP server and then requests the assignment of
addresses and/or delegated prefixes 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/or delegated prefixes and other configuration information. The
server responds with a Reply message that contains the confirmed
addresses, delegated prefixes, and configuration.As described in the previous section, the client sends a Renew
message to the server to extend the lifetimes associated with its
addresses and/or delegated prefixes, allowing the client to continue to use those addresses
and/or delegated prefixes without interruption.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in .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.The IPv6 Specification provides the base architecture and design of
IPv6. Related work in IPv6 that would best serve an implementer to study
includes the IPv6 Specification , the IPv6
Addressing Architecture , IPv6 Stateless
Address Autoconfiguration , IPv6 Neighbor
Discovery Processing , and Dynamic Updates
to DNS . These specifications enable DHCP
to build upon the IPv6 work to provide both robust stateful
autoconfiguration and autoregistration of DNS Host Names.The IPv6 Addressing Architecture specification defines the address scope that can be used in
an IPv6 implementation, and the various configuration architecture
guidelines for network designers of the IPv6 address space. Two
advantages of IPv6 are that support for multicast is required and nodes
can create link-local addresses during initialization. The availability
of these features means that a client can use its link-local address and
a well-known multicast address to discover and communicate with DHCP
servers or relay agents on its link.IPv6 Stateless Address Autoconfiguration specifies procedures by which a node may
autoconfigure addresses based on router advertisements , and the use of a valid lifetime to support
renumbering of addresses on the Internet. In addition, the protocol
interaction by which a node begins stateless or stateful
autoconfiguration is specified. DHCP is one vehicle to perform stateful
autoconfiguration. Compatibility with stateless address
autoconfiguration is a design requirement of DHCP.IPv6 Neighbor Discovery is the node
discovery protocol in IPv6 which replaces and enhances functions of ARP
. To understand IPv6 and stateless address
autoconfiguration, it is strongly recommended that implementers
understand IPv6 Neighbor Discovery.Dynamic Updates to DNS 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.This section defines terminology specific to IPv6 and DHCP used in
this document.IPv6 terminology relevant to this specification from the IPv6
Protocol , IPv6 Addressing Architecture
, and IPv6 Stateless Address
Autoconfiguration is included
below.An IP layer identifier for an interface or a
set of interfaces.Any node that is not a router.Internet Protocol Version 6 (IPv6). The terms
IPv4 and IPv6 are used only in contexts where it is necessary to
avoid ambiguity.A node's attachment to a 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 and PPPoE links, X.25, Frame Relay, or ATM networks; and
Internet (or higher) layer "tunnels", such as tunnels over IPv4 or
IPv6 itself.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.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.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.A node attached to the same link.A device that implements IP.An IP header plus payload.The initial bits of an address, or a set of
IP addresses that share the same initial bits.The number of bits in a prefix.A node that forwards IP packets not
explicitly addressed to itself.An identifier for a single
interface. A packet sent to a unicast address is delivered to the
interface identified by that address.Terminology specific to DHCP can be found below.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.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>.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.The router that acts as a DHCP
server, and is responding to the prefix request.Dynamic Host Configuration Protocol for IPv6.
The terms DHCPv4 and DHCPv6 are used only in contexts where it is
necessary to avoid ambiguity.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.A set of links managed by DHCP and
operated by a single administrative entity.A name used to identify the DHCP
administrative domain from which a DHCP authentication key was
selected.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.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.A DHCP Unique IDentifier for a DHCP
participant; each DHCP client and server has exactly one DUID. See
for details of the ways in which
a DUID may be constructed.Identity Association: A collection of leases
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 a lease 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.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.Identity association for Non-temporary
Addresses: An IA that carries assigned addresses that are not
temporary addresses (see "identity association for temporary
addresses")Identity Association for Temporary Addresses:
An IA that carries temporary addresses (see ).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.It is an address assigned by the DHCP server
to the client or a delegated prefix assigned by the delegating
router to the requesting router. Leases are carried in the IA
Address or IA Prefix options within the IA_NA/IA_TA and IA_PD
options respectively.A unit of data carried as the payload of a
UDP datagram, exchanged among DHCP servers, relay agents and
clients.A key supplied to a client by a
server used to provide security for Reconfigure messages.The router that acts as a DHCP
client and is requesting prefix(es) to be assigned.An option that is allowed to appear
only once. Most options are singletons.A DHCP relay agent relays DHCP messages
between DHCP participants.Another attempt to send the same
DHCP message by a client or server, as a result of not
receiving a valid response to the previously sent messages.
The retransmitted message is typically modified prior to sending,
as required by the DHCP specifications. In particular, the
client updates the value of the Elapsed Time option in the
retransmitted message.An option conveyed in a DHCP
message directly, i.e. not encapsulated in any other option, as
described in Section 9 of .An opaque value used to match
responses with replies initiated either by a client or server.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.This document assumes that the DHCP servers and the client,
communicating with the servers via specific interface, belong to a
single provisioning domain.Stateless DHCP is used when DHCP is
not used for obtaining a lease, 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 . Stateless may be used when a node initially
boots or at any time the software on the node requires some missing or
expired configuration information that is available via DHCP.This is the simplest and most basic operation for DHCP and requires
a client (and a server) to support only two messages -
Information-request and Reply. Note that DHCP servers and relay agents
typically also need to support the Relay-Forw and Relay-Reply messages
to accommodate operation when clients and servers are not on the same
link.This model of operation was the original motivation for DHCP and is
the "stateful address autoconfiguration protocol" for IPv6 . It is appropriate for situations where
stateless address autoconfiguration is not desired, because of network
policy, additional requirements (such as updating the DNS with forward
or reverse resource records), or client specific requirements (i.e.,
some prefixes are only available to some clients) which are not
possible using stateless address autoconfiguration.The model of operation for non-temporary address assignment is as
follows. The server is provided with IPv6 prefixes from which it may
allocate addresses to clients, as well as any related network topology
information as to which prefixes are present on which links. A client
requests a non-temporary address to be assigned by the server. The
server allocates an address or addresses appropriate for the link on
which the client is connected. The server returns the allocated
address or addresses to the client.Each address has an associated preferred and valid lifetime, which
constitutes an agreement about the length of time over which the
client is allowed to use the address. A client can request an
extension of the lifetimes on an address and is required to terminate
the use of an address if the valid lifetime of the address
expires.Typically clients request other configuration parameters, such as
the domain server addresses and search lists, when requesting
addresses.The prefix delegation mechanism, originally described in , 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 Edge Router device acting as
a router between the subscriber's internal network and the service
provider's core network.The design of this prefix delegation mechanism meets the
requirements for prefix delegation in .The model of operation for prefix delegation is as follows. A
delegating router is provided IPv6 prefixes to be delegated to
requesting routers. A requesting router requests prefix(es) from the
delegating router, as described in . The delegating router chooses
prefix(es) for delegation, and responds with prefix(es) to the
requesting router. The requesting router is then responsible for the
delegated prefix(es). For example, the requesting router might assign
a subnet from a delegated prefix to one of its interfaces, and begin
sending router advertisements for the prefix on that link.Each prefix has an associated valid and preferred lifetime, which
constitutes an agreement about the length of time over which the
requesting router is allowed to use the prefix. A requesting router
can request an extension of the lifetimes on a delegated prefix and is
required to terminate the use of a delegated prefix if the valid
lifetime of the prefix expires.This prefix delegation mechanism is 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. and describe in detail such use. illustrates a network
architecture in which prefix delegation could be used.The DHCP requirements and network architecture for Customer Edge
Routers are described in . This model of
operation combines address assignment (see ) and prefix delegation (see ). 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.In this example, the delegating router is configured with a set of
prefixes to be used for assignment to customers at the time of each
customer's first connection to the ISP service. The prefix delegation
process begins when the requesting router requests configuration
information through DHCP. The DHCP messages from the requesting router
are received by the delegating router in the aggregation device. When
the delegating router receives the request, it selects an available
prefix or prefixes for delegation to the requesting router. The
delegating router then returns the prefix or prefixes to the
requesting router.The requesting router subnets the delegated prefix and assigns the
longer prefixes to links in the subscriber's network. In a typical
scenario based on the network shown in , 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.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.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.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 and
). They were added to DHCP to provide
complementary support when stateful address assignment is used.Temporary address assignment works mostly like non-temporary
address assignment (see ), 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.This section describes various program and networking constants used
by DHCP.DHCP makes use of the following multicast addresses: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.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 on the interfaces which are within the site.Clients listen for DHCP messages on UDP port 546. Servers and relay
agents listen for DHCP messages on UDP port 547.DHCP defines the following message types. More detail on these
message types can be found in and
. Additional message types are
defined in , ,
, , . Additional message types may be defined in
the future. The numeric encoding for each message type is
shown in parentheses.A client sends a Solicit message to
locate servers.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.A client sends a Request message to
request configuration parameters, including IP addresses, from a
specific server.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.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.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.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.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.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.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.A client sends an
Information-request message to a server to request configuration
parameters without the assignment of any IP addresses to the
client.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.A server sends a Relay-reply message
to a relay agent containing a message that the relay agent
delivers to a client. The Relay-reply message may be relayed by
other relay agents for delivery to the destination relay
agent.The server encapsulates the client message as an option in the
Relay-reply message, which the relay agent extracts and relays to
the client.DHCP 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 .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.This section presents a table of values used to describe the
message transmission behavior of clients and servers.ParameterDefaultDescriptionSOL_MAX_DELAY1 secMax delay of first SolicitSOL_TIMEOUT1 secInitial Solicit timeoutSOL_MAX_RT3600 secsMax Solicit timeout valueREQ_TIMEOUT1 secInitial Request timeoutREQ_MAX_RT30 secsMax Request timeout valueREQ_MAX_RC10Max Request retry attemptsCNF_MAX_DELAY1 secMax delay of first ConfirmCNF_TIMEOUT1 secInitial Confirm timeoutCNF_MAX_RT4 secsMax Confirm timeoutCNF_MAX_RD10 secsMax Confirm durationREN_TIMEOUT10 secsInitial Renew timeoutREN_MAX_RT600 secsMax Renew timeout valueREB_TIMEOUT10 secsInitial Rebind timeoutREB_MAX_RT600 secsMax Rebind timeout valueINF_MAX_DELAY1 secMax delay of first Information-requestINF_TIMEOUT1 secInitial Information-request timeoutINF_MAX_RT3600 secsMax Information-request timeout valueREL_TIMEOUT1 secInitial Release timeoutREL_MAX_RC4MAX Release retry attemptsDEC_TIMEOUT1 secInitial Decline timeoutDEC_MAX_RC4Max Decline retry attemptsREC_TIMEOUT2 secsInitial Reconfigure timeoutREC_MAX_RC8Max Reconfigure attemptsHOP_COUNT_LIMIT32Max hop count in a Relay-forward messageAll 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 ) or a value for T1 or T2.All DHCP messages sent between clients and servers share an identical
fixed format header and a variable format area for options.All values in the message header and in options are in network byte
order.Options are stored serially in the options field, with no padding
between the options. Options are byte-aligned but are not aligned in any
other way such as on 2 or 4 byte boundaries.The following diagram illustrates the format of DHCP messages sent
between clients and servers:Identifies the DHCP message type; the
available message types are listed in .The transaction ID for this message
exchange.Options carried in this message; options
are described in .Relay agents exchange messages with servers to relay messages between
clients and servers that are not connected to the same link.All values in the message header and in options are in network byte
order.Options are stored serially in the options field, with no padding
between the options. Options are byte-aligned but are not aligned in any
other way such as on 2 or 4 byte boundaries.There are two relay agent messages, which share the following
format:The following sections describe the use of the Relay Agent message
header.The following table defines the use of message fields in a
Relay-forward message.RELAY-FORWNumber of relay agents that have
relayed this message.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 , but see discussion in .The address of the client or relay
agent from which the message to be relayed was received.MUST include a "Relay Message option"
(see ); MAY include other
options added by the relay agent.The following table defines the use of message fields in a
Relay-reply message.RELAY-REPLCopied from the Relay-forward
messageCopied from the Relay-forward
messageCopied from the Relay-forward
messageMUST include a "Relay Message option";
see ; MAY include other
optionsSo 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 . 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 .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 and
for the representation of a DUID in a DHCP message.Clients and servers MUST treat DUIDs as opaque values and MUST only
compare DUIDs for equality. Clients and servers MUST NOT in any other
way interpret DUIDs. Clients and servers MUST NOT restrict DUIDs to the
types defined in this document, as additional DUID types may be defined
in the future.The DUID is carried in an option because it may be variable length
and because it is not required in all DHCP messages. The DUID is
designed to be unique across all DHCP clients and servers, and stable
for any specific client or server - that is, the DUID used by a client
or server SHOULD NOT change over time if at all possible; for example, a
device's DUID should not change as a result of a change in the device's
network hardware. The stability of the DUID includes changes to virtual
interfaces, such as logical PPP (over Ethernet) interfaces that may
come and go in Customer Premise Equipment routers.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.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:TypeDescription1Link-layer address plus time2Vendor-assigned unique ID based on Enterprise Number3Link-layer address4Universally Unique IDentifier (UUID) - see Formats for the variable field of the DUID for the first 3 of the
above types are shown below. The fourth type, DUID-UUID , can be used in situations where there is a
UUID stored in a device's firmware settings.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 . 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 .The following diagram illustrates the format of a DUID-LLT:The choice of network interface can be completely arbitrary, as
long as that interface provides a globally unique link-layer address
for the link type, and the same DUID-LLT SHOULD be used in configuring
all network interfaces connected to the device, regardless of which
interface's link-layer address was used to generate the DUID-LLT.Clients and servers using this type of DUID MUST store the DUID-LLT
in stable storage, and MUST continue to use this DUID-LLT even if the
network interface used to generate the DUID-LLT is removed. Clients
and servers that do not have any stable storage MUST NOT use this type
of DUID.Clients and servers that use this DUID SHOULD attempt to configure
the time prior to generating the DUID, if that is possible, and MUST
use some sort of time source (for example, a real-time clock) in
generating the DUID, even if that time source could not be configured
prior to generating the DUID. The use of a time source makes it
unlikely that two identical DUID-LLTs will be generated if the network
interface is removed from the client and another client then uses the
same network interface to generate a DUID-LLT. A collision between two
DUID-LLTs is very unlikely even if the clocks have not been configured
prior to generating the DUID.This method of DUID generation is recommended for all general
purpose computing devices such as desktop computers and laptop
computers, and also for devices such as printers, routers, and so on,
that contain some form of writable non-volatile storage.Despite our best efforts, it is possible that this algorithm for
generating a DUID could result in a client identifier collision. A
DHCP client that generates a DUID-LLT using this mechanism MUST
provide an administrative interface that replaces the existing DUID
with a newly-generated DUID-LLT.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 followed by a
unique identifier assigned by the vendor. The following diagram
summarizes the structure of a DUID-EN: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
. The enterprise-number is stored as an
unsigned 32 bit number.An example DUID of this type might look like this:This example includes the two-octet type of 2, the Enterprise
Number (9), followed by eight octets of identifier data
(0x0CC084D303000912).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 . The hardware type is stored in network byte
order. The link-layer address is stored in canonical form, as
described in . The following diagram
illustrates the format of a DUID-LL:The choice of network interface can be completely arbitrary, as
long as that interface provides a unique link-layer address and is
permanently attached to the device on which the DUID-LL is being
generated. The same DUID-LL SHOULD be used in configuring all network
interfaces connected to the device, regardless of which interface's
link-layer address was used to generate the DUID.DUID-LL is recommended for devices that have a
permanently-connected network interface with a link-layer address, and
do not have nonvolatile, writable stable storage. DUID-LL MUST NOT be
used by DHCP clients or servers that cannot tell whether or not a
network interface is permanently attached to the device on which the
DHCP client is running.An "identity-association" (IA) is a construct through which a server
and a client can identify, group, and manage a set of related IPv6
addresses or delegated prefixes. Each IA consists of an IAID and
associated configuration information.The IAID uniquely identifies the IA and must be chosen to be unique
among the IAIDs for that IA type on the client. The IAID is chosen by
the client. For any given use of an IA by the client, the IAID for that
IA MUST be consistent across restarts of the DHCP client. The client may
maintain consistency either by storing the IAID in non-volatile storage
or by using an algorithm that will consistently produce the same IAID as
long as the configuration of the client has not changed. There may be no
way for a client to maintain consistency of the IAIDs if it does not
have non-volatile storage and the client's hardware configuration
changes. If the client uses only one IAID, it can use a well-known
value, e.g., zero.If the client wishes to obtain a distinctly new address or prefix and
deprecate the existing one, the client sends a Release message
to the server for the IAs using the original IAID. Then the client creates
a new IAID, to be used in future Request messages to obtain new IAs.A client must associate at least one distinct IA with each of its
network interfaces for which it is to request the assignment of IPv6
addresses from a DHCP server. The client uses the IAs assigned to an
interface to obtain configuration information from a server for that
interface. Each IA must be associated with exactly one interface.The configuration information in an IA consists of one or more IPv6
addresses along with the times T1 and T2 for the IA. See for the representation of an IA in a
DHCP message.Each address in an IA has a preferred lifetime and a valid
lifetime, as defined in . 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 .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.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 for the representation of an IA_PD in a
DHCP message.A server selects addresses to be assigned to an IA_NA according to
the address assignment policies determined by the server administrator
and the specific information the server determines about the client
from some combination of the following sources: The link to which the client is attached. The
server determines the link as follows: If the server receives the message directly
from the client and the source address in the IP datagram in
which the message was received is a link-local address, then
the client is on the same link to which the interface over
which the message was received is attached.If the server receives the message from a
forwarding relay agent, then the client is on the same link as
the one to which the interface, identified by the link-address
field in the message from the relay agent, is attached.
According to , the server MUST
ignore any link-address field whose value is zero. The link
address field refers to the link-address field of the
Relay-Forward message, and the link-address fields in any
Relay-Forward messages that may be nested within the
Relay-Forward message.If the server receives the message directly
from the client and the source address in the IP datagram in
which the message was received is not a link-local address,
then the client is on the link identified by the source
address in the IP datagram (note that this situation can occur
only if the server has enabled the use of unicast message
delivery by the client and the client has sent a message for
which unicast delivery is allowed).The DUID supplied by the client.Other information in options supplied by the
client, e.g. IA Address options that include the client's requests
for specific addresses.Other information in options supplied by the relay
agent.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 .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 , from
any subnet.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 .A client may request the assignment of temporary addresses (see
for the definition of temporary
addresses). DHCP handling of address assignment is no different for
temporary addresses.Clients ask for temporary addresses and servers assign them.
Temporary addresses are carried in the Identity Association for
Temporary Addresses (IA_TA) option (see ). Each IA_TA option contains at most one
temporary address for each of the prefixes on the link to which the
client is attached.The lifetime of the assigned temporary address is set in the IA
Address Option (see ) 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, .The IAID number space for the IA_TA option IAID number space is
separate from the IA_NA option IAID number space.A DHCP server implementation MAY generate temporary addresses
referring to the algorithm defined in Section 3.2.1, , with additional condition that the new
address is not duplicated with any assigned addresses.The server MAY update the DNS for a temporary address, as described
in section 4 of .On the clients, by default, temporary addresses are preferred in
source address selection, according to Rule 7, . However, this policy is overridable.One of the most important properties of temporary address is
unlinkability of different actions over time. So, it is NOT
RECOMMENDED for a client to renew expired temporary addresses, though
DHCP provides such possibility (see ).Unless otherwise specified in this document, or in a document that
describes how IPv6 is carried over a specific type of link (for link
types that do not support multicast), a client sends DHCP messages to
the All_DHCP_Relay_Agents_and_Servers.A client uses multicast to reach all servers or an individual server.
An individual server is indicated by specifying that server's DUID in a
Server Identifier option (see ) in
the client's message (all servers will receive this message but only the
indicated server will respond). All servers are indicated by not
supplying this option.A client may send some messages directly to a server using unicast,
as described in .In order to avoid prolonged message bursts that may be caused by
possible logic loops, a DHCP client MUST limit the rate of DHCP
messages it transmits. One example is that a client obtains an
address, but does not like the response; it reverts back to Solicit
procedure, discovers the same (sole) server, requests an address and
gets the same address as before (the server still has the lease that
was requested just previously). This loops can repeat infinitely if
there is not a quit/stop mechanism. Therefore, a client must not
initiate transmissions too frequently.A recommended method for implementing the rate limiting function is
a token bucket, limiting the average rate of transmission to a certain
number in a certain time. This method of bounding burstiness also
guarantees that the long-term transmission rate will not exceed.Transmission Rate Limit The Transmission Rate Limit parameter (TRT) SHOULD be
configurable. A possible default could be 20 packets in 20
seconds.For a device that has multiple interfaces, the limit MUST be
enforced on a per interface basis.Rate limiting of forwarded DHCP messages and server-side messages
are out of scope of this specification.In certain cases, T1 and/or T2 time may be set to zero. Currently
there are three such cases: 1. a client received an IA_NA option with
a zero value; 2. a client received an IA_PD option with a zero value;
3. a client received an IA_TA option (which does not contain T1 and T2
fields and are not generally renewed). Additional cases may appear in
the future. This is an indication that the transmission times are left
at the client's discretion. They are not completely discretionary,
though.When T1 and/or T2 times are set to zero, the client MUST choose a
time to avoid packet storms. In particular, it MUST NOT transmit
immediately. If the client received multiple IA containers, it SHOULD
pick renew and/or rebind transmission times so all IA containers are
handled in one exchange, if possible. Client MUST choose the
transmission times to not violate rate limiting restrictions, defined
in .DHCP clients are responsible for reliable delivery of messages in the
client-initiated message exchanges described in . If a DHCP client fails to
receive an expected response from a server, the client must retransmit
its message. This section describes the retransmission strategy to be
used by clients in client-initiated message exchanges.Note that the procedure described in this section is slightly
modified when used with the Solicit message. The modified procedure is
described in .The client begins the message exchange by transmitting a message to
the server. The message exchange terminates when either the client
successfully receives the appropriate response or responses from a
server or servers, or when the message exchange is considered to have
failed according to the retransmission mechanism described below.The client MUST update an "elapsed-time" value within an Elapsed
Time option (see ) in the
retransmitted message. In some cases, the client may also need to modify
values in the IA Address or IA Prefix options, if a valid lifetime for
any of the client's leases expires before retransmission. Thus, whenever
this document refers to a "retransmission" of a client's message, it
refers to both modifying the original message and sending this new message
instance to the server. The retransmitting client MUST NOT resend the
original message to the server, i.e. the client MUST update all options
in the retransmitted message, for which such update is required by the
protocol (e.g. Elapsed Time option).The client retransmission behavior is controlled and described by the
following variables: Retransmission timeoutInitial retransmission timeMaximum retransmission countMaximum retransmission timeMaximum retransmission durationRandomization factorWith each message transmission or retransmission, the client sets RT
according to the rules given below. If RT expires before the message
exchange terminates, the client recomputes RT and retransmits the
message.Each of the computations of a new RT include a randomization factor
(RAND), which is a random number chosen with a uniform distribution
between -0.1 and +0.1. The randomization factor is included to minimize
synchronization of messages transmitted by DHCP clients.The algorithm for choosing a random number does not need to be
cryptographically sound. The algorithm SHOULD produce a different
sequence of random numbers from each invocation of the DHCP client.RT for the first message transmission is based on IRT:RT for each subsequent message transmission is based on the previous
value of RT: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: MRT)
RT = MRT + RAND*MRT
]]>MRC specifies an upper bound on the number of times a client may
retransmit a message. Unless MRC is zero, the message exchange fails
once the client has transmitted the message MRC times.MRD specifies an upper bound on the length of time a client may
retransmit a message. Unless MRD is zero, the message exchange fails
once MRD seconds have elapsed since the client first transmitted the
message.If both MRC and MRD are non-zero, the message exchange fails whenever
either of the conditions specified in the previous two paragraphs are
met.If both MRC and MRD are zero, the client continues to transmit the
message until it receives a response.A client is not expected to listen for a response during the entire
period between transmission of Solicit or Information-request
messages.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.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.Clients, relay agents and servers MUST NOT discard messages that
contain unknown options (or instances of vendor options with unknown
enterprise-numbers). These should be ignored as if they weren't
present.A server MUST discard any Solicit, Confirm, Rebind or
Information-request messages it receives with a unicast destination
address.A client or server MUST silently discard any received DHCP messages
with an unknown message type.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.Clients MUST discard any received Solicit messages.Servers MUST discard any Solicit messages that do not include a
Client Identifier option or that do include a Server Identifier
option.Clients MUST discard any received Advertise message that meets any
of the following conditions: the message does not include a Server Identifier
option.the message does not include a Client Identifier
option.the contents of the Client Identifier option does
not match the client's DUID.the "transaction-id" field value does not match
the value the client used in its Solicit message.Servers and relay agents MUST discard any received Advertise
messages.Clients MUST discard any received Request messages.Servers MUST discard any received Request message that meets any of
the following conditions: the message does not include a Server Identifier
option.the contents of the Server Identifier option do
not match the server's DUID.the message does not include a Client Identifier
option.Clients MUST discard any received Confirm messages.Servers MUST discard any received Confirm messages that do not
include a Client Identifier option or that do include a Server
Identifier option.Clients MUST discard any received Renew messages.Servers MUST discard any received Renew message that meets any of
the following conditions: the message does not include a Server Identifier
option.the contents of the Server Identifier option does
not match the server's identifier.the message does not include a Client Identifier
option.Clients MUST discard any received Rebind messages.Servers MUST discard any received Rebind messages that do not
include a Client Identifier option or that do include a Server
Identifier option.Clients MUST discard any received Decline messages.Servers MUST discard any received Decline message that meets any of
the following conditions: the message does not include a Server Identifier
option.the contents of the Server Identifier option does
not match the server's identifier.the message does not include a Client Identifier
option.Clients MUST discard any received Release messages.Servers MUST discard any received Release message that meets any of
the following conditions: the message does not include a Server Identifier
option.the contents of the Server Identifier option does
not match the server's identifier.the message does not include a Client Identifier
option.Clients MUST discard any received Reply message that meets any of
the following conditions: the message does not include a Server Identifier
option.the "transaction-id" field in the message does not
match the value used in the original message.If the client included a Client Identifier option in the original
message, the Reply message MUST include a Client Identifier option and
the contents of the Client Identifier option MUST match the DUID of
the client; OR, if the client did not include a Client Identifier
option in the original message, the Reply message MUST NOT include a
Client Identifier option.Servers and relay agents MUST discard any received Reply
messages.Servers and relay agents MUST discard any received Reconfigure
messages.Clients MUST discard any Reconfigure message that meets any of the
following conditions: the message was not unicast to the client.the message does not include a Server Identifier
option.the message does not include a Client Identifier
option that contains the client's DUID.the message does not contain a Reconfigure Message
option.the Reconfigure Message option msg-type is not a
valid value.the message includes any IA options and the
msg-type in the Reconfigure Message option is
INFORMATION-REQUEST.the message does not include DHCP authentication:
the message does not contain an authentication
option.the message does not pass the authentication
validation performed by the client.Clients MUST discard any received Information-request messages.Servers MUST discard any received Information-request message that
meets any of the following conditions: The message includes a Server Identifier option
and the DUID in the option does not match the server's DUID.The message includes an IA option.Clients MUST discard any received Relay-forward messages.Clients and servers MUST discard any received Relay-reply
messages.Client's behavior is different depending on the purpose of the
configuration.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
attachment or the client is certain that two interfaces are attached
to the same link. When a client sends a DHCP message directly to a server using
unicast (after receiving the Server Unicast option from that server),
the source address in the header of the IPv6 datagram MUST be an
address assigned to the interface for which the client is interested
in obtaining configuration and which is suitable for use by the server
in responding to the client.Delegated prefixes are not associated with a particular interface
in the same way as addresses are for address assignment, and mentioned
above.When a client (acting as requesting router) sends a DHCP message
for the purpose of prefix delegation, it SHOULD be sent on the
interface associated with the upstream router (ISP network). The
upstream interface is typically determined by configuration. This rule
applies even in the case where a separate IA_PD is used for each
downstream interface.When a requesting router sends a DHCP message directly to a
delegating router using unicast (after receiving the Server Unicast
option from that delegating router), the source address SHOULD be an
address from the upstream interface and which is suitable for use by
the delegating router in responding to the requesting router.A client initiates a message exchange with a server or servers to
acquire or update configuration information of interest.A DHCP client that does not need to have a DHCP server assign it IP
addresses or delegated prefixes, can obtain configuration information
such as a list of available DNS servers or
NTP servers through a single message and
reply exchange with a DHCP server. To obtain configuration
information the client first sends an Information-request message
(see ) to the All_DHCP_Relay_Agents_and_Servers
multicast address. Servers respond with a Reply message containing
the configuration information for the client (see ).To request the assignment of one or more IPv6 addresses or delegated
prefixes, a client first locates a DHCP server and then requests the
assignment of addresses and other configuration information from the
server. The client does it by sending the Solicit message
(see ) to the
All_DHCP_Relay_Agents_and_Servers multicast address and collecting
Advertise messages from the servers which respond to the client's
message and selects a server from which it wants to obtain configuration
information. This process is referred to as server discovery or server
solicitation. When the client has selected the server it sends a Request
message to this server as described in the .A client willing to perform the Solicit-Reply message
exchange described in includes a Rapid
Commit option (see ) in its
Solicit message.The client has many reasons to initiate the configuration exchange:
as part of the operating system configuration/bootstrap process, when requested to do so by the application layer (through an
operating system specific API), when required by Stateless Address Autoconfiguration (as defined
in ) or as required to extend the lifetime of address(es) and/or
delegated prefix(es), using Renew and Rebind messages.A server may initiate a message exchange with a client by sending a
Reconfigure message to cause the client to send a Renew, Rebind or
Information-request message to refresh its configuration information as
soon as the Reconfigure message is received by the client.The client is responsible for creating IAs and requesting that a
server assign IPv6 addresses and/or 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.If the client will accept a Reply message with committed leases
assignments and other resources in response to the Solicit message, the
client includes a Rapid Commit option (see ) in the Solicit message.Servers that can assign addresses or delegated prefixes to the IAs
respond to the client with an Advertise message or Reply message if the
client included a Rapid Commit option and the server is configured to
accept it.If the server responds with an Advertise message, the client initiates
a configuration exchange as described in .Requesting router and 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.A client uses the Solicit message to discover DHCP servers
configured to assign leases or return other configuration parameters
on the link to which the client is attached.A client uses Request, Renew, Rebind, Release and Decline messages
during the normal life cycle of addresses and delegated prefixes. When
a client detects it may have moved to a new link, it uses Confirm if
it only has addresses and Rebind if it has delegated prefixes (and
addresses). It uses Information-request messages when it needs
configuration information but no addresses and no prefixes.When a client requests multiple IA option types in a Solicit,
Request, Renew, or Rebind, it is possible
that the available server(s) may only be configured to offer a subset
of them. When possible, the client SHOULD use the best configuration
available and continue to request the additional IAs in subsequent
messages (). This allows the client to maintain
a single session and state machine. In practice, especially in the
case of handling IA_NA and IA_PD requests (),
this situation should be rare or a temporary operational error.
Thus, it is more likely for the client to get all configuration if
it continues, in each subsequent configuration exchange, to request
all the configuration information it is programmed to try to obtain,
including any stateful configuration options for which no results
were returned in previous message exchanges.Upon receipt of a Reconfigure message from the server, a client
responds with a Renew, Rebind or an Information-request message as
indicated by the Reconfigure Message option. The server sends IAs
and/or other configuration information to the client in a Reply
message.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 () from the
server, the client SHOULD unicast any Request, Renew, Release and
Decline messages to the server.DISCUSSION:Use of unicast may avoid delays due to the relaying of messages
by relay agents, as well as avoid overhead and duplicate responses
by servers due to the delivery of client messages to multiple
servers. However, 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.The client sets the "msg-type" field to SOLICIT. The client
generates a transaction ID and inserts this value in the
"transaction-id" field.The client MUST include a Client Identifier option to identify
itself to the server. The client includes IA options for any IAs to
which it wants the server to assign leases.The client MUST include an Elapsed Time option (see
) to indicate how long the client has
been trying to complete the current DHCP message exchange.The client MAY include addresses in the IA_NA and IA_TA options
as hints to the server about the addresses for which the client has
a preference.The client MAY include values in the IA Prefix option
encapsulated within IA_PD option as hints for the delegated prefix
and/or prefix length 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.The client uses IA_NA options to request the assignment of
non-temporary addresses, IA_TA options to request the assignment of
temporary addresses and IA_PD options to request prefix delegation.
Either IA_NA, IA_TA or IA_PD options, or a combination of all, can
be included in DHCP messages. In addition, multiple instances of any
IA option type can be included.The client MUST include an Option Request option (see ) to request the SOL_MAX_RT option (see
) and any other options the
client is interested in receiving. The client MAY additionally
include instances of those options that are identified in the Option
Request option, with data values as hints to the server about
parameter values the client would like to have returned.The client includes a Reconfigure Accept option (see ) if the client is willing to accept
Reconfigure messages from the server.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
). This random delay desynchronizes
clients which start at the same time (for example, after a power
outage).The client transmits the message according to , using the following parameters: SOL_TIMEOUTSOL_MAX_RT00A client that wishes to use the Rapid Commit 2-message exchange
includes a Rapid Commit option in its Solicit message.
The client may receive a number of different replies from
different servers. The client will make note of any Advertise
messages that it receives. The client will discard any Reply
messages that do not contain the Rapid Commit option.
Upon receipt of a valid Reply with the Rapid Commit option,
the client processes the message as described in
At the end of the first RT period, if no suitable Reply
messages are received, but the client has valid Advertise
messages, then the client processes the Advertise as
described in .If the client subsequently receives a valid Reply message that
includes a Rapid Commit option, it either:processes the Reply message as described in
, and discards any Reply
messages received in response to the Request message, orprocesses any Reply messages received in
response to the Request message and discards the Reply message
that includes the Rapid Commit option.If the client is waiting for an Advertise message, the mechanism
in 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.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 (). 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 ) by
sending a Request message to the server from which the Advertise
message was received. If the client receives an Advertise message
that does not include a Preference option with a preference value of
255, the client continues to wait until the first RT elapses. If the
first RT elapses and the client has received an Advertise message,
the client SHOULD continue with a client-initiated message exchange
by sending a Request message.If the client does not receive any Advertise messages before the
first RT has elapsed, it begins the retransmission mechanism
described in . The client
terminates the retransmission process as soon as it receives any
Advertise message, and the client acts on the received Advertise
message without waiting for any additional Advertise messages.A DHCP client SHOULD choose MRC and MRD to be 0. If the DHCP
client is configured with either MRC or MRD set to a value other
than 0, it MUST stop trying to configure the interface if the
message exchange fails. After the DHCP client stops trying to
configure the interface, it SHOULD restart the reconfiguration
process after some external event, such as user input, system
restart, or when the client is attached to a new link.The client uses a Request message to populate IAs with leases and
obtain other configuration information. The client includes one or
more IA options in the Request message. The server then returns
leases and other information about the IAs to the client in IA
options in a Reply message.The client generates a transaction ID and inserts this value in
the "transaction-id" field.The client places the identifier of the destination server in a
Server Identifier option.The client MUST include a Client Identifier option to identify
itself to the server. The client adds any other appropriate options,
including one or more IA options.The client MUST include an Elapsed Time option (see
) to indicate how long the client has
been trying to complete the current DHCP message exchange.The client MUST include an Option Request option (see ) to request the SOL_MAX_RT option (see
) and any other options the
client is interested in receiving. The client MAY additionally
include instances of those options that are identified in the Option
Request option, with data values as hints to the server about
parameter values the client would like to have returned.The client includes a Reconfigure Accept option (see ) indicating whether or not the client
is willing to accept Reconfigure messages from the server.The client transmits the message according to , using the following parameters: REQ_TIMEOUTREQ_MAX_RTREQ_MAX_RC0If the message exchange fails, the client takes an action based
on the client's local policy. Examples of actions the client might
take include: Select another server from a list of servers
known to the client; for example, servers that responded with an
Advertise message.Initiate the server discovery process described
in .Terminate the configuration process and report
failure.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: The client reboots (and has no stable storage or
persisted DHCP state).The client is physically connected to a wired
connection.The client returns from sleep mode.The client using a wireless technology changes
access points.In any situation when a client may have moved to a new link and
the client does not have any delegated prefixes obtained from the
DHCP server from which it has obtained the addresses, 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.If the client has any valid delegated prefixes obtained from the
DHCP server from which it has obtained the addresses, the client
initiates Rebind/Reply exchange as described in instead of sending the
Confirm message.The client sets the "msg-type" field to CONFIRM. The client
generates a transaction ID and inserts this value in the
"transaction-id" field.The client MUST include a Client Identifier option to identify
itself to the server.The client MUST include an Elapsed Time option (see
) to indicate how long the client has
been trying to complete the current DHCP message exchange.The client includes IA options for all of the
IAs assigned to the interface for which the Confirm message is being
sent. The IA options include all of the addresses the client
currently has associated with those IAs. The client SHOULD set the
T1 and T2 fields in any IA_NA options and the preferred-lifetime and
valid-lifetime fields in the IA Address options to 0, as the server
will ignore these fields.The first Confirm message from the client on the interface MUST
be delayed by a random amount of time between 0 and CNF_MAX_DELAY.
The client transmits the message according to , using the following parameters: CNF_TIMEOUTCNF_MAX_RT0CNF_MAX_RDIf the client receives no responses before the message
transmission process terminates, as described in , 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.To extend the valid and preferred lifetimes for the leases
assigned to the IAs and obtain new addresses or delegated prefixes
for IAs, the client sends a Renew message to the server from which
the leases were obtained, which includes IA options for the IAs
whose lease lifetimes are to be extended. The client includes IA
Address options within IA_NA and IA_TA options for the addresses
assigned to the IAs. The client includes IA Prefix options within
IA_PD options for the delegated prefixes assigned to the IAs. The
server determines new lifetimes for the leases according to the
administrative configuration of the server. The server may also add
leases to the IAs. The server can remove leases from the IAs by
returning IA Address options (for IA_NA and IA_TA) and IA Prefix
options (for IA_PD) with preferred and valid lifetimes set to 0.The server controls the time at which the client contacts the
server to extend the lifetimes on assigned leases through the T1 and
T2 parameters assigned to an IA. However, as the client
Renews/Rebinds all IAs from the server at the same time, the client
MUST select a T1 and T2 time from all IA options, which will
guarantee that the client will send Renew/Rebind messages not later
than at the T1/T2 times associated with any of the client's bindings
(earliest T1/T2).At time T1, the client initiates a Renew/Reply message exchange
to extend the lifetimes on any leases in the IA.If T1 or T2 had been set to 0 by the server (for an IA_NA or
IA_PD) or there are no T1 or T2 times (for an IA_TA) in a previous
Reply, the client may send a Renew or Rebind message, respectively,
at the client's discretion. The client MUST follow the rules defined
in .If the client is sending a Renew message in response to a
Reconfigure message from the server, the client copies IA options
from the Reconfigure message into the Renew message.The client sets the "msg-type" field to RENEW. The client
generates a transaction ID and inserts this value in the
"transaction-id" field.The client MUST include a Server Identifier option in the Renew
message, identifying the server with which the client most recently
communicated.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 an Elapsed Time option (see
) to indicate how long the client has
been trying to complete the current DHCP message exchange.For IAs to which leases have been assigned, the client includes a
corresponding IA option containing an IA Address option for each
address assigned to the IA and IA Prefix option for each prefix
assigned to the IA. The client MUST NOT include addresses and
prefixes in any IA option that the client did not obtain from the
server or that are no longer valid (that have a valid lifetime of
0).The client MAY include an IA option for each binding it desires
but has been unable to obtain. In this case, if the client includes
the IA_PD option to request prefix delegation, the client MAY
include the IA Prefix option encapsulated within the IA_PD option,
with the IPv6 prefix field set to 0 and the "prefix-length" field
set to the desired length of the prefix to be delegated. The server
MAY use this value as a hint for the prefix length. The client
SHOULD NOT include IA Prefix option with the IPv6 prefix field set
to 0 unless it is supplying a hint for the prefix length.When the client is responding to a Reconfigure, the client copies
the Option Request option from the Reconfigure message into the
Renew message. Otherwise, the client includes Option Request option
(see ) to request the SOL_MAX_RT
option (see ) and any other
options the client is interested in receiving. The client MAY
include options with data values as hints to the server about
parameter values the client would like to have returned.The client transmits the message according to , using the following parameters: REN_TIMEOUTREN_MAX_RT0Remaining time until earliest T2The message exchange is terminated when earliest time T2 is
reached. If the client is responding to a Reconfigure, the client
ignores and discards the Reconfigure message. In this case, the
client continues to operate as if Reconfigure message was not
received, i.e. it uses T1/T2 times associated with the client's
leases to determine when it should send Renew or Rebind to the
server. If the terminated Renew exchange was not initiated as a
result of receiving a Reconfigure message, the client begins a
Rebind message exchange (see )
when the earliest time T2 is reached.At time T2 (which will only be reached if the server to which the
Renew message was sent starting at time T1 has not responded), the
client initiates a Rebind/Reply message exchange with any available
server.The client constructs the Rebind message as described in with the following differences:
The client sets the "msg-type" field to
REBIND.The client does not include the Server
Identifier option in the Rebind message.The client transmits the message according to , using the following parameters: REB_TIMEOUTREB_MAX_RT0Remaining time until valid lifetimes of all
leases in all IAs have expiredIf all leases for an IA have expired, the client may choose to
include this IA in subsequent Rebind messages to indicate that the
client is interested in assignment of the leases to this IA.The message exchange is terminated when the valid lifetimes of
all leases across all IAs have expired, at which time the client
uses the Solicit message to locate a new DHCP server and sends a
Request for the expired IAs to the new server. If the terminated
Rebind exchange was initiated as a result of receiving a Reconfigure
message, the client ignores and discards the Reconfigure
message.The client uses an Information-request message to obtain
configuration information without having addresses and/or delegated
prefixes assigned to it.The client sets the "msg-type" field to INFORMATION-REQUEST. The
client generates a transaction ID and inserts this value in the
"transaction-id" field.The client SHOULD include a Client Identifier option to identify
itself to the server. If the client does not include a Client
Identifier option, the server will not be able to return any
client-specific options to the client, or the server may choose not
to respond to the message at all.The client MUST include an Elapsed Time option (see
) to indicate how long the client has
been trying to complete the current DHCP message exchange.The client MUST include an Option Request option (see ) to request the INF_MAX_RT option (see
), the Information
Refresh Time 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.When responding to a Reconfigure, the client includes a Server
Identifier option with the identifier from the Reconfigure message
to which the client is responding.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 , using the following parameters: INF_TIMEOUTINF_MAX_RT00To release one or more leases, a client sends a Release message
to the server.The client sets the "msg-type" field to RELEASE. The client
generates a transaction ID and places this value in the
"transaction-id" field.The client places the identifier of the server that allocated the
lease(s) in a Server Identifier option.The client MUST include a Client Identifier option to identify
itself to the server.The client MUST include an Elapsed Time option (see
) to indicate how long the client has
been trying to complete the current DHCP message exchange.The client includes options containing the IAs
for the leases it is releasing in the "options" field. The leases to
be released MUST be included in the IAs. Any leases for the IAs the
client wishes to continue to use MUST NOT be added to the IAs.The client MUST NOT use any of the addresses it is releasing as
the source address in the Release message or in any subsequently
transmitted message.Because Release messages may be lost, the client should
retransmit the Release if no Reply is received. However, there are
scenarios where the client may not wish to wait for the normal
retransmission timeout before giving up (e.g., on power down).
Implementations SHOULD retransmit one or more times, but MAY choose
to terminate the retransmission procedure early.The client transmits the message according to , using the following parameters: REL_TIMEOUT0REL_MAX_RC0The client MUST stop using all of the leases being released
before the client begins the Release message exchange process. For
an address, this means the address MUST have been removed from the
interface. For a delegated prefix, this means the prefix MUST have
been advertised with a Preferred Lifetime and a Valid Lifetime of
zero in a Router Advertisement message as described in Section
5.5.3, (e) of - also see L-13 in
Section 4.3 of .If leases 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.Note that if the client fails to release the lease, each lease
assigned to the IA will be reclaimed by the server when the valid
lifetime of that lease expires.If a client detects that one or more addresses assigned to it by
a server are already in use by another node, the client sends a
Decline message to the server to inform it that the address is
suspect.The Decline message is not used in prefix delegation and thus the
client MUST NOT include IA_PD options in the Decline message.The client sets the "msg-type" field to DECLINE. The client
generates a transaction ID and places this value in the
"transaction-id" field.The client places the identifier of the server that allocated the
address(es) in a Server Identifier option.The client MUST include a Client Identifier option to identify
itself to the server.The client MUST include an Elapsed Time option (see
) to indicate how long the client has
been trying to complete the current DHCP message exchange.The client includes options containing the IAs
for the addresses it is declining in the "options" field. The
addresses to be declined MUST be included in the IAs. Any addresses
for the IAs the client wishes to continue to use should not be in
added to the IAs.The client MUST NOT use any of the addresses it is declining as
the source address in the Decline message or in any subsequently
transmitted message.The client transmits the message according to , using the following parameters: DEC_TIMEOUT0DEC_MAX_RC0If 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.The client SHOULD NOT send a Release message for other bindings
it may have received just because it sent a Decline message. The
client SHOULD retain the non-conflicting bindings. The client SHOULD
treat the failure to acquire a binding as a result of the conflict,
to be equivalent to not having received the binding, insofar as it
behaves when sending Renew and Rebind messages.The client MUST process SOL_MAX_RT and INF_MAX_RT options in an
Advertise message, even if the message contains a Status Code option
indicating a failure, and the Advertise message will be discarded by
the client.The client MUST ignore any Advertise message that contains no
addresses (IAADDR options encapsulated in IA_NA or IA_TA options)
and no delegated prefixes (IAPREFIX options encapsulated in IA_PD
options) with the exception that the client: MUST process an included SOL_MAX_RT option
andMUST process an included INF_MAX_RT option.A client can display any associated status message(s) to the user
or activity log.The client ignoring this Advertise message MUST NOT restart the
Solicit retransmission timer.Upon receipt of one or more valid Advertise messages, the client
selects one or more Advertise messages based upon the following
criteria. Those Advertise messages with the highest server
preference value are preferred over all other Advertise
messages.Within a group of Advertise messages with the
same server preference value, a client MAY select those servers
whose Advertise messages advertise information of interest to
the client.The client MAY choose a less-preferred server if
that server has a better set of advertised parameters, such as
the available set of IAs, as well as the set of other
configuration options advertised.Once a client has selected Advertise message(s), the client will
typically store information about each server, such as server
preference value, addresses advertised, when the advertisement was
received, and so on.In practice, this means that the client will maintain independent
per-IA state machines per each selected server.If the client needs to select an alternate server in the case
that a chosen server does not respond, the client chooses the next
server according to the criteria given above.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
top-level Status Code option if present.If the client receives a Reply message with a status code of
UnspecFail, the server is indicating that it was unable to process
the client's 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 ).If the client receives a Reply message with a status code of
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.Otherwise (no status code or another status code), the client
processes the Reply as described below based on the original message
for which the Reply was received.The client MAY choose to report any status code or message from
the Status Code option in the Reply message.If 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 message without specifying any
addresses or restart the DHCP server discovery process (see ).If the Reply was received in response to a Solicit (with a
Rapid Commit option), Request, Renew, or Rebind message, the
client updates the information it has recorded about IAs from the
IA options contained in the Reply message: Record T1 and T2 times, if appropriate for the
IA type.Add any new leases in the IA option to the IA
as recorded by the client.Update lifetimes for any leases in the IA
option that the client already has recorded in the IA.Discard any leases from the IA, as recorded by
the client, that have a valid lifetime of 0 in the IA Address
or IA Prefix option.Leave unchanged any information about leases
the client has recorded in the IA but that were not included
in the IA from the server.If the client can operate with the addresses and/or prefixes
obtained from the server: The client uses the addresses, delegated
prefixes, and other information from any IAs that do not
contain a Status Code option with the NoAddrsAvail or
NoPrefixAvail status code. The client MAY include the IAs for
which it received the NoAddrsAvail or NoPrefixAvail status
code, with no addresses or prefixes, in subsequent Renew and
Rebind messages sent to the server, to retry obtaining the
addresses or prefixes for these IAs.The client MUST perform duplicate address
detection as per Section 5.4, which
does list some exceptions, on each of the
received addresses in any IAs, on which it has not performed
duplicate address detection during processing of any of the
previous Reply messages from the server. The client performs
the duplicate address detection before using the received
addresses for the traffic. If any of the addresses are found
to be in use on the link, the client sends a Decline message
to the server for those addresses as described in .For each IAADDR, which does not have any
associated reachability information, in order avoid the
problems described in , hosts
MUST NOT assume that any addresses are reachable on-link as a
result of receiving an IA_NA or IA_TA. Addresses obtained from
IA_NA or IA_TA MUST NOT be used to form an implicit prefix
with a length other than 128.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, with the following exception: the requesting router MUST
NOT assign any delegated prefixes or subnets from the delegated
prefix(es) to the link through which it received the DHCP message
from the delegating router (see
for exceptions).
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
2001:db8:0::/48, it might generate 2001:db8:0:1::/64 and
2001:db8:0:2::/64 for assignment to the two links in the subscriber
network. If the requesting router were delegated 2001:db8:0::/48
and 2001:db8:5::/48, it might assign 2001:db8:0:1::/64 and
2001:db8:5:1::/64 to one of the links, and 2001:db8:0:2::/64 and
2001:db8:5:2::/64 for assignment to the other link.
If the requesting router assigns a delegated prefix to a link to
which the router is attached, and begins to send router
advertisements for the prefix on the link, the requesting router MUST
set the valid lifetime in those advertisements to be no later than
the valid lifetime specified in the IA_PD Prefix option. A
requesting router MAY use the preferred lifetime specified in the
IA_PD Prefix option.Management of the specific configuration information is
detailed in the definition of each option in .When a client had received a configuration option in earlier
Reply, then sent Renew, Rebind or Information-Request and that
requested option does not appear in in the Reply any more, it MUST
stop using the received configuration information. In other words,
client should behave as if it never received this option at all and
return to whatever default state regarding that configuration
information was. If there is no viable way to stop using the
information, the values received/configured from the option MAY
persist if there are no other sources for that data and they have no
external impact. For example, a client that previously received
Client FQDN option and used it to set up its hostname is allowed to
continue using it if there is no reasonable way for a host to unset
its hostname and it has no external impact. As a counter example, a
client that used to receive an NTP server address from the DHCP
server and does not receive it any more, MUST stop using the
configured NTP server IPv6 address. The client SHOULD be open to
other sources of the same configuration information. This behavior
does not apply to any IA containers, as their processing is
described in detail in other parts of this document.If the Reply message contains any IAs, but the client finds no
usable addresses and/or delegated prefixes in any of these IAs,
the client may either try another server (perhaps restarting the
DHCP server discovery process) or use the Information-request
message to obtain other configuration information only.When the client receives a Reply message in response to a Renew
or Rebind message, the client: Sends a Request message if any of the IAs in
the Reply message contains the NoBinding status code. The
client places IA options in this message for only those IAs
for which the server returned the NoBinding status code in the
Reply message. The client continues to use other bindings for
which the server did not return an error.Sends a Renew/Rebind if any of the IAs are not
in the Reply message, but in this case the client MUST limit
the rate at which it sends these messages, to avoid the
Renew/Rebind storm.Otherwise accepts the information in the
IA.Whenever a client restarts the DHCP server discovery process or
selects an alternate server, as described in , the client SHOULD stop using all
the addresses and delegated prefixes for which it has bindings and
try to obtain all required leases from the new server. This
facilitates the client using a single state machine for all
bindings.When the client receives a valid Reply message in response to a
Release message, the client considers the Release event completed,
regardless of the Status Code option(s) returned by the
server.When the client receives a valid Reply message in response to a
Decline message, the client considers the Decline event completed,
regardless of the Status Code option(s) returned by the
server.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 , and client-initiated
configuration, as described in . If the client receives
any Reply messages that indicate a success status (explicit or
implicit), the client can use the addresses in the IA and ignore
any messages that indicate a NotOnLink status.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.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 ). The
client ignores the transaction-id field in the received Reconfigure
message. While the transaction is in progress, the client discards
any Reconfigure messages it receives.DISCUSSION:The Reconfigure message acts as a trigger that signals the
client to complete a successful message exchange. Once the
client has received a Reconfigure, the client proceeds with the
message exchange (retransmitting the Renew or
Information-request message if necessary); the client ignores
any additional Reconfigure messages until the exchange is
complete. Subsequent Reconfigure messages cause the client to
initiate a new exchange.How does this mechanism work in the face of duplicated or
retransmitted Reconfigure messages? Duplicate messages will be
ignored because the client will begin the exchange after the
receipt of the first Reconfigure. Retransmitted messages will
either trigger the exchange (if the first Reconfigure was not
received by the client) or will be ignored. The server can
discontinue retransmission of Reconfigure messages to the client
once the server receives the Renew, Rebind or
Information-request message from the client.It might be possible for a duplicate or retransmitted
Reconfigure to be sufficiently delayed (and delivered out of
order) to arrive at the client after the exchange (initiated by
the original Reconfigure) has been completed. In this case, the
client would initiate a redundant exchange. The likelihood of
delayed and out of order delivery is small enough to be ignored.
The consequence of the redundant exchange is inefficiency rather
than incorrect operation.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:The requesting router reboots.The requesting router's upstream link flaps.The requesting router is physically disconnected from a wired
connection.If such verification is needed the requesting router MUST
initiate a Rebind/Reply message exchange as described in , with the exception that the
retransmission parameters should be set as for the Confirm message,
described in . The requesting
router includes any IA_PDs, along with prefixes associated with
those IA_PDs in its Rebind message.For this discussion, the Server is assumed to have been configured
in an implementation specific manner with configuration of interest to
clients.A server sends Advertise message in response to valid Solicit
messages it receives to announce the availability of the server to the
client.In most instances, the server will send a Reply in response to a
Request, Confirm, Renew, Rebind, Decline and Information-request
messages sent by a client. The server will also send a Reply in
response to a Solicit with a Rapid Commit option, when the server is
configured to respond with committed lease assignments.This Reply message MUST always contain the Server Identifier option
containing the server's DUID and the Client Identifier option from the
client message if one was present.In most reply messages, the server includes options containing
configuration information for the client. The server must be aware of
the recommendations on packet sizes and the use of fragmentation in
section 5 of . 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.The server MAY initiate a configuration exchange, by sending
Reconfigure messages, to cause DHCP clients to obtain new addresses,
prefixes 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.When a client receives a Reconfigure message from the server, the
client sends Renew, Rebind or Information-request message as indicated
by the as indicated by the Reconfigure Message option (as defined in
). The server sends IAs and/or
other configuration information to the client in a Reply message. 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 client's message.The server determines the information about the client and its
location as described in 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 ) in the Solicit message, the servers
discard the Solicit message.If the server is permitted to respond to the client, the client
has not included a Rapid Commit option in the Solicit message or
the server has not been configured to respond with committed assignment
of leases and other resources, the server sends an Advertise
message to the client as described in .
If the client has included a Rapid Commit option in the Solicit
message and the server has been configured to respond with committed
assignments of leases and other resources, the server responds to the
Solicit with a Reply message. The server MUST commit the assignment
of any addresses and delegated prefixes or other configuration
information before sending a Reply message to a client. In this case
the server includes a Rapid Commit option in the Reply message to
indicate that the Reply is in response to a Solicit message.DISCUSSION:When using the Solicit-Reply message exchange, the server
commits the assignment of any leases before sending the Reply
message. The client can assume it has been assigned the leases
in the Reply message and does not need to send a Request message
for those addresses.Typically, servers that are configured to use the
Solicit-Reply message exchange will be deployed so that only one
server will respond to a Solicit message. If more than one
server responds, the client will only use the leases from one of
the servers, while the leases from the other servers will be
committed to the client but not used by the client.The server includes a Reconfigure Accept option if the
server is configured to use reconfigure mechanism (see ). Sending this option
back to the client may useful using server selection process.The server produces the Reply message as though it had received a
Request message, as described in . The server transmits the Reply
message as described in .When the server receives a Request message via unicast from a
client to which the server has not sent a unicast option (or is not
currently configured to send a unicast option to the client), the
server discards the Request message and responds with a Reply
message containing a Status Code option with the value UseMulticast,
a Server Identifier option containing the server's DUID, the Client
Identifier option from the client message, and no other options.When the server receives a valid Request message, the server
creates the bindings for that client according to the server's
policy and configuration information and records the IAs and other
information requested by the client.The server constructs a Reply message by setting the "msg-type"
field to REPLY, and copying the transaction ID from the Request
message into the transaction-id field.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.The server examines all IAs in the message from the client.For each IA_NA and IA_TA in the Request message the server
checks if the prefixes on included IP addresses are appropriate for
the link to which the client is connected. If any of the prefixes on
the included IP addresses is not appropriate for the link to which
the client is connected, the server MUST return the IA to the client
with a Status Code option with the value NotOnLink. If the server
does not send the NotOnLink status code but it cannot assign any IP
addresses to an IA, the server MUST return the IA in the Reply
message with no addresses in the IA and a Status Code option
containing status code NoAddrsAvail.For any IA_PD in the Request message, to which the server cannot
assign any delegated prefixes, the server MUST return the IA_PD
option in the Reply message with the Status Code option containing
status code NoPrefixAvail.The server MAY assign different addresses and/or delegated
prefixes to an IA than included in the IA within the Request message
sent by the client.For all IAs to which the server can assign addresses or delegated
prefixes, the server includes the IAs with addresses (for IA_NA and
IA_TA), prefixes (for IA_PD) and other configuration parameters, and
records the IA as a new client binding. The server MUST NOT include
any addresses or delegated prefixes in the IA which the server does
not assign to the client.The T1/T2 times set in each applicable IA option for a Reply MUST
be the same values across all IAs. The server MUST determine the
T1/T2 times across all of the applicable client's bindings in the
Reply. This facilitates the client being able to renew all of the
bindings at the same time.The server MAY include a Reconfigure Accept option. New
server implementations are discouraged from sending
Reconfigure Accept option, as it does not convey any
additional information. If the reconfigure mechanism is
supported, the server is supposed to send Authentication
option with Reconfigure Key (see for details). However, it is
still allowed to send Reconfigure Accept option to maintain
backward compatibility with servers that implement .The server includes other options containing configuration
information to be returned to the client as described in .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 server sends a new Reply
message with existing bindings, possibly with updated lifetimes. The
server may update the bindings according to its local policies, but
the server SHOULD generate the response again and not simply
retransmit previously sent information, even if the transaction-id
matches previous transmission. The server MUST NOT cache its
responses.When the server receives a Confirm message, the server determines
whether the addresses in the Confirm message are appropriate for the
link to which the client is attached. If all of the addresses in the
Confirm message pass this test, the server returns a status of
Success. If any of the addresses do not pass this test, the server
returns a status of NotOnLink. If the server is unable to perform
this test (for example, the server does not have information about
prefixes on the link to which the client is connected), or there
were no addresses in any of the IAs sent by the client, the server
MUST NOT send a Reply to the client.The server ignores the T1 and T2 fields in the IA options and the
preferred-lifetime and valid-lifetime fields in the IA Address
options.The server constructs a Reply message by setting the "msg-type"
field to REPLY, and copying the transaction ID from the Confirm
message into the transaction-id field.The server MUST include a Server Identifier option containing the
server's DUID and the Client Identifier option from the Confirm
message in the Reply message. The server includes a Status Code
option indicating the status of the Confirm message.When the server receives a Renew message via unicast from a
client to which the server has not sent a unicast option (or is not
currently configured to send a unicast option to the client), 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.For each IA in the Renew message from a client, the server
locates the client's binding and verifies that the information in
the IA from the client matches the information stored for that
client.If the server finds the client entry for the IA, the server sends
back the IA to the client with new lifetimes and, if applicable,
T1/T2 times. If the server is unable to extend the lifetimes of an
address or delegated prefix in the IA, the server MAY choose not to
include the IA Address or IA Prefix option for this address or
delegated prefix. If the server chooses to include the IA Address or
IA Prefix option for such an address or delegated prefix, the server
SHOULD set T1 and T2 to the valid lifetime for the IA option unless
the server also includes other addresses or delegated prefix which
the server is able to extend.The server may choose to change the list of addresses or
delegated prefixes and the lifetimes in IAs that are returned to the
client.If the server finds that any of the addresses in the IA are not
appropriate for the link to which the client is attached, the server
returns the address to the client with lifetimes of 0.If the server finds that any of the delegated prefixes in the IA
are not appropriate for the link to which the client is attached,
the server returns the delegated prefix to the client with lifetimes
of 0.For each IA for which the server cannot find a client entry, the
server has the following choices depending on the server's policy
and configuration information: If the server is configured to create new
bindings as a result of processing Renew messages, the server
SHOULD create a binding and return the IA with assigned
addresses or delegated prefixes with lifetimes and, if
applicable, T1/T2 times and other information requested by the
client. If the client included the IA Prefix option within the
IA_PD option with zero value in the "IPv6 prefix" field and
non-zero value in the "prefix-length" field, the server MAY use
the "prefix-length" value as a hint for the length of the
prefixes to be assigned (see
for further details on prefix length hints).If the server is configured to create new
bindings as a result of processing Renew messages, but the
server will not assign any leases to an IA, the server returns
the IA option containing a Status Code option with the
NoAddrsAvail or NoPrefixAvail status code and a status message
for a user.If the server does not support creation of new
bindings for the client sending a Renew message, or if this
behavior is disabled according to the server's policy or
configuration information, the server returns the IA option
containing a Status Code option with the NoBinding status code
and a status message for a user.The server constructs a Reply message by setting the "msg-type"
field to REPLY and copying the transaction ID from the Renew message
into the "transaction-id" field.The server MUST include a Server Identifier option containing the
server's DUID and the Client Identifier option from the Renew
message in the Reply message.The server includes other options containing configuration
information to be returned to the client as described in .The server MAY include options containing the IAs and values for
other configuration parameters, even if those parameters were not
requested in the Renew message.The T1/T2 times set in each applicable IA option for a Reply MUST
be the same values across all IAs. The server MUST determine the
T1/T2 times across all of the applicable client's bindings in the
Reply. This facilitates the client being able to renew all of the
bindings at the same time.When the server receives a Rebind message that contains an IA
option from a client, it locates the client's binding and verifies
that the information in the IA from the client matches the
information stored for that client.If the server finds the client entry for the IA and the server
determines that the addresses or delegated prefixes in the IA are
appropriate for the link to which the client's interface is attached
according to the server's explicit configuration information, the
server SHOULD send back the IA to the client with new lifetimes and,
if applicable, T1/T2 times. If the server is unable to extend the
lifetimes of an address in the IA, the server MAY choose not to
include the IA Address option for this address. If the server is
unable to extend the lifetimes of a delegated prefix in the IA, the
server MAY choose not to include the IA Prefix option for this
prefix.If the server finds that the client entry for the IA and any of
the addresses or delegated prefixes are no longer appropriate for
the link to which the client's interface is attached according to
the server's explicit configuration information, the server returns
the address or delegated prefix to the client with lifetimes of
0.If the server cannot find a client entry for the IA, the server
checks if the IA contains addresses (for IA_NA and IA_TA) or
delegated prefixes (for IA_PD). The server checks if the addresses
and delegated prefixes are appropriate for the link to which the
client's interface is attached according to the server's explicit
configuration information. For any address which is not appropriate
for the link to which the client's interface is attached, the server
MAY include the IA Address option with the lifetimes of 0. For any
delegated prefix which is not appropriate for the link to which the
client's interface is attached, the server MAY include the IA Prefix
option with the lifetimes of 0. The Reply with lifetimes of 0
constitutes an explicit notification to the client that the specific
addresses and delegated prefixes are no longer valid and MUST NOT be
used by the client. If the server chooses to not include any IAs
containing IA Address or IA Prefix options with lifetimes of 0 and
the server does not include any other IAs with leases and/or status
codes, the server does not send a Reply message. In this situation
the server silently discards the Rebind message.Otherwise, for each IA for which the server cannot find a client
entry, the server has the following choices depending on the
server's policy and configuration information: If the server is configured to create new
bindings as a result of processing Rebind messages (also see the
note about the Rapid Commit option below), the server SHOULD
create a binding and return the IA with allocated leases with
lifetimes and, if applicable, T1/T2 times and other information
requested by the client. The server MUST NOT return any
addresses or delegated prefixes in the IA which the server does
not assign to the client.If the server is configured to create new
bindings as a result of processing Rebind messages, but the
server will not assign any leases to an IA, the server returns
the IA option containing a Status Code option with the
NoAddrsAvail or NoPrefixAvail status code and a status message
for a user.If the server does not support creation of new
bindings for the client sending a Rebind message, or if this
behavior is disabled according to the server's policy or
configuration information, the server returns the IA option
containing a Status Code option with the NoBinding status code
and a status message for a user.When the server creates new bindings for the IA, it is possible
that other servers also create bindings as a result of receiving the
same Rebind message. This is the same issue as in the Discussion
under "Rapid Commit Option"; see . Therefore, the server SHOULD only
create new bindings during processing of a Rebind message if the
server is configured to respond with a Reply message to a Solicit
message containing the Rapid Commit option.The server constructs a Reply message by setting the "msg-type"
field to REPLY and copying the transaction ID from the Rebind
message into the "transaction-id" field.The server MUST include a Server Identifier option containing the
server's DUID and the Client Identifier option from the Rebind
message in the Reply message.The server includes other options containing configuration
information to be returned to the client as described in .The server MAY include options containing the IAs and values for
other configuration parameters, even if those IAs and parameters
were not requested in the Rebind message.The T1/T2 times set in each applicable IA option for a Reply MUST
be the same values across all IAs. The server MUST determine the
T1/T2 times across all of the applicable client's bindings in the
Reply. This facilitates the client being able to renew all of the
bindings at the same time.When the server receives an Information-request message, the
client is requesting configuration information that does not include
the assignment of any leases. The server determines all
configuration parameters appropriate to the client, based on the
server configuration policies known to the server.The server constructs a Reply message by setting the "msg-type"
field to REPLY, and copying the transaction ID from the
Information-request message into the transaction-id field.The server MUST include a Server Identifier option containing the
server's DUID in the Reply message. If the client included a Client
Identification option in the Information-request message, the server
copies that option to the Reply message.The server includes options containing configuration information
to be returned to the client as described in . The server MAY include additional
options that were not requested by the client in the
Information-request message.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.The server constructs a Reply message by setting the "msg-type"
field to REPLY, and copying the transaction ID from the Release
message into the transaction-id field.When the server receives a Release message via unicast from a
client to which the server has not sent a unicast option (or is not
currently configured to send a unicast option to the client), the
server discards the Release message and responds with a Reply
message containing a Status Code option with value UseMulticast, a
Server Identifier option containing the server's DUID, the Client
Identifier option from the client message, and no other options.Upon the receipt of a valid Release message, the server examines
the IAs and the leases in the IAs for validity. If the IAs in the
message are in a binding for the client, and the leases in the IAs
have been assigned by the server to those IAs, the server deletes
the leases from the IAs and makes the leases available for
assignment to other clients. The server ignores leases not assigned
to the IA, although it may choose to log an error.After all the leases have been processed, the server generates a
Reply message and includes a Status Code option with value Success,
a Server Identifier option with the server's DUID, and a Client
Identifier option with the client's DUID. For each IA in the Release
message for which the server has no binding information, the server
adds an IA option using the IAID from the Release message, and
includes a Status Code option with the value NoBinding in the IA
option. No other options are included in the IA option.A server may choose to retain a record of assigned leases and IAs
after the lifetimes on the leases have expired to allow the server
to reassign the previously assigned leases to a client.When the server receives a Decline message via unicast from a
client to which the server has not sent a unicast option (or is not
currently configured to send a unicast option to the client), the
server discards the Decline message and responds with a Reply
message containing a Status Code option with the value UseMulticast,
a Server Identifier option containing the server's DUID, the Client
Identifier option from the client message, and no other options.Upon the receipt of a valid Decline message, the server examines
the IAs and the addresses in the IAs for validity. If the IAs in the
message are in a binding for the client, and the addresses in the
IAs have been assigned by the server to those IAs, the server
deletes the addresses from the IAs. The server ignores addresses not
assigned to the IA (though it may choose to log an error if it finds
such an address).The client has found any addresses in the Decline messages to be
already in use on its link. Therefore, the server SHOULD mark the
addresses declined by the client so that those addresses are not
assigned to other clients, and MAY choose to make a notification
that addresses were declined. Local policy on the server determines
when the addresses identified in a Decline message may be made
available for assignment.After all the addresses have been processed, the server generates
a Reply message by setting the "msg-type" field to REPLY, and
copying the transaction ID from the Decline message into the
transaction-id field. The client 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.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 option from the Solicit message into
the Advertise message.The server MAY add a Preference option to carry the preference
value for the Advertise message. The server implementation SHOULD
allow the setting of a server preference value by the administrator.
The server preference value MUST default to zero unless otherwise
configured by the server administrator.The server includes a Reconfigure Accept option if the server
wants to indicate it supports Reconfigure mechanism. This
information may be used by the client during server
selection process.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. The server MUST include
options in the Advertise message containing configuration parameters
for all of the options identified in the Option Request option in the Solicit message
that the server has been configured to return to the client. If the
Option Request option includes a container option the server MUST include all
the options that are eligible to be encapsulated in the container. The Option
Request option MAY be used to signal support for a feature even when that option is
encapsulated as in the case of the Prefix Excluded option .
In this case, special processing is required by the server.
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 .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 and/or delegated prefixes that would be
assigned to IAs contained in the Solicit message from the client. If
the client has included addresses in the IA in the Solicit message,
the server MAY use those addresses as hints about the addresses that
the client would like to receive. If the client has included IA
Prefix option in the IA_PD, the server MAY use the prefix contained
in the IPv6 prefix field and/or the prefix length contained in the
"prefix-length" field as a hints about the prefixes the client would
like to receive. If the server is not going to assign an address or
delegated prefix received as a hint in the Solicit message, the
server MUST NOT include this address or delegated prefix in the
Advertise messageIf the server will not assign any addresses to an IA (IA_NA or
IA_IA) in subsequent Request from the client, the server MUST
include the IA in the Advertise message with no addresses in the IA
and a Status Code option encapsulated in the IA containing status
code NoAddrsAvail.If the server will not assign any prefixes to an IA_PD in
subsequent Request from the client, the server MUST include the
IA_PD in the Advertise message with no prefixes in the IA and a
Status Code option encapsulated in the IA_PD containing status code
NoPrefixAvail.If the Solicit message was received directly by the server, the
server unicasts the Advertise message directly to the client using
the address in the source address field from the IP datagram in
which the Solicit message was received. The Advertise message MUST
be unicast on the link from which the Solicit message was
received.If the Solicit message was received in a Relay-forward message,
the server constructs a Relay-reply message with the Advertise
message in the payload of a "relay-message" option. If the
Relay-forward messages included an Interface-id option, the server
copies that option to the Relay-reply message. The server unicasts
the Relay-reply message directly to the relay agent using the
address in the source address field from the IP datagram in which
the Relay-forward message was received.If the original message was received directly by the server, the
server unicasts the Reply message directly to the client using the
address in the source address field from the IP datagram in which
the original message was received. The Reply message MUST be unicast
through the interface on which the original message was
received.If the original message was received in a Relay-forward message,
the server constructs a Relay-reply message with the Reply message
in the payload of a Relay Message option (see ). 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.The server sets the "msg-type" field to RECONFIGURE. The server
sets the transaction-id field to 0. The server includes a Server
Identifier option containing its DUID and a Client Identifier option
containing the client's DUID in the Reconfigure message.The server MAY include an Option Request option to inform the
client of what information has been changed or new information that
has been added. In particular, the server specifies the IA option in
the Option Request option if the server wants the client to obtain
new address information. If the server identifies the IA option in
the Option Request option, the server MUST include an IA option to
identify each IA that is to be reconfigured on the client. The IA
options included by the server MUST NOT contain any options.Because of the risk of denial of service attacks against DHCP
clients, the use of a security mechanism is mandated in Reconfigure
messages. The server MUST use DHCP authentication in the Reconfigure
message.The server MUST include a Reconfigure Message option (defined in
) to select whether the client
responds with a Renew message, a Rebind message, or an
Information-request message.The server MUST NOT include any other options in the Reconfigure
except as specifically allowed in the definition of individual
options.A server sends each Reconfigure message to a single DHCP client,
using an IPv6 unicast address of sufficient scope belonging to the
DHCP client. If the server does not have an address to which it can
send the Reconfigure message directly to the client, the server uses
a Relay-reply message (as described in ) to send the Reconfigure message to a
relay agent that will relay the message to the client. The server
may obtain the address of the client (and the appropriate relay
agent, if required) through the information the server has about
clients that have been in contact with the server, or through some
external agent.To reconfigure more than one client, the server unicasts a
separate message to each client. The server may initiate the
reconfiguration of multiple clients concurrently; for example, a
server may send a Reconfigure message to additional clients while
previous reconfiguration message exchanges are still in
progress.The Reconfigure message causes the client to initiate a
Renew/Reply, a Rebind/Reply, or Information-request/Reply message
exchange with the server. The server interprets the receipt of a
Renew, a Rebind, or Information-request message (whichever was
specified in the original Reconfigure message) from the client as
satisfying the Reconfigure message request.If the server does not receive a Renew, Rebind, or
Information-request message from the client in REC_TIMEOUT
milliseconds, the server retransmits the Reconfigure message,
doubles the REC_TIMEOUT value and waits again. The server continues
this process until REC_MAX_RC unsuccessful attempts have been made,
at which point the server SHOULD abort the reconfigure process for
that client.Default and initial values for REC_TIMEOUT and REC_MAX_RC are
documented in .The relay agent MAY be configured to use a list of destination
addresses, which MAY include unicast addresses, the All_DHCP_Servers
multicast address, or other addresses selected by the network
administrator. If the relay agent has not been explicitly configured, it
MUST use the All_DHCP_Servers multicast address as the default.If the relay agent relays messages to the All_DHCP_Servers multicast
address or other multicast addresses, it sets the Hop Limit field to
32.If the relay agent receives a message other than Relay-forward and
Relay-reply and the relay agent does not recognize its message type, it
MUST forward them as described in .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 ) to be relayed, it constructs a new
Relay-forward message. The
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. 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.If the relay agent received the message to be relayed from a
client, the relay agent places a global, ULA 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. If not addresses of other scopes
are available the relay agent may fill in the link-address field
with a link-local address from the interface the original message
was received on. That is not recommended as it requires additional
information to be provided in the server configuration. See Section
3.2 of for detailed
discussion.This address will be used by the server to determine the link
from which the client should be assigned an address and other
configuration information. The hop-count in the Relay-forward
message is set to 0.If the relay agent cannot use the address in the link-address
field to identify the interface through which the response to the
client will be relayed, the relay agent MUST include an Interface-id
option (see ) 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.If the message received by the relay agent is a Relay-forward
message and the hop-count in the message is greater than or equal to
HOP_COUNT_LIMIT, the relay agent discards the received message.The relay agent copies the source address from the IP datagram in
which the message was received from the relay agent into the
peer-address field in the Relay-forward message and sets the
hop-count field to the value of the hop-count field in the received
message incremented by 1.If the source address from the IP datagram header of the received
message is a global or site-scoped address (and the device on which
the relay agent is running belongs to only one site), the relay
agent 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.A relay agent forwards messages containing Prefix Delegation
options in the same way as described earlier in this section.If a delegating router communicates with a requesting router
through a relay agent, the delegating router may need a protocol or
other out-of-band communication to configure routing information for
delegated prefixes on any router through which the requesting router
may forward traffic.The relay agent processes any options included in the Relay-reply
message in addition to the Relay Message option, and then discards
those options.The relay agent extracts the message from the Relay Message option
and relays it to the address contained in the peer-address field of
the Relay-reply message. Relay agents MUST NOT modify the message.If the Relay-reply message includes an Interface-id option, the
relay agent relays the message from the server to the client on the
link identified by the Interface-id option. Otherwise, if the
link-address field is not set to zero, the relay agent relays the
message on the link identified by the link-address field.If the relay agent receives a Relay-reply message, it MUST process
the message as defined above, regardless of the type of message
encapsulated in the Relay Message option.A server uses a Relay-reply message to return a response to a
client if the original message from the client was relayed to the
server in a Relay-forward message or to send a Reconfigure message to
a client if the server does not have an address it can use to send the
message directly to the client.A response to the client MUST be relayed through the same relay
agents as the original client message. The server causes this to
happen by creating a Relay-reply message that includes a Relay Message
option containing the message for the next relay agent in the return
path to the client. The contained Relay-reply message contains another
Relay Message option to be sent to the next relay agent, and so on.
The server must record the contents of the peer-address fields in the
received message so it can construct the appropriate Relay-reply
message carrying the response from the server.For example, if client C sent a message that was relayed by relay
agent A to relay agent B and then to the server, the server would send
the following Relay-reply message to relay agent B:
]]>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.Within this document, two security mechanisms are introduced for the
authentication of DHCP messages: security of messages sent between
servers and relay agents using IPsec, and protection against
misconfiguration of a client caused by a Reconfigure message sent by a
malicious DHCP server. The delayed authentication protocol, defined in
, has been obsoleted by this document, due
to lack of usage.Relay agents and servers that exchange messages securely use the
IPsec mechanisms for IPv6 . If a client
message is relayed through multiple relay agents, each of the relay
agents must have established independent, pairwise trust
relationships. That is, if messages from client C will be relayed by
relay agent A to relay agent B and then to the server, relay agents A
and B must be configured to use IPsec for the messages they exchange,
and relay agent B and the server must be configured to use IPsec for
the messages they exchange.Relay agents and servers that support secure relay agent to server
or relay agent to relay agent communication use IPsec under the
following conditions: 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 UDP port 547.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).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.DHCP messages between relay
agents and servers should only be accepted from DHCP peers as
identified in the local configuration.Shared keys, indexed to the source
IP address of the received DHCP message, are adequate in this
application.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.Authentication of DHCP messages is accomplished through the use of
the Authentication option (see ).
The authentication information carried in the Authentication option
can be used to reliably identify the source of a DHCP message and to
confirm that the contents of the DHCP message have not been tampered
with.The Authentication option provides a framework for multiple
authentication protocols. One such protocol, the Reconfigure key
authentication protocol , is defined in . Other protocols defined in the future
will be specified in separate documents.Any DHCP message MUST NOT include more than one Authentication
option.The protocol field in the Authentication option identifies the
specific protocol used to generate the authentication information
carried in the option. The algorithm field identifies a specific
algorithm within the authentication protocol; for example, the
algorithm field specifies the hash algorithm used to generate the
message authentication code (MAC) in the authentication option. The
replay detection method (RDM) field specifies the type of replay
detection used in the replay detection field. has defined the delayed
authentication protocol. But it is obsoleted by this document, due to
lack of usage.The Replay Detection Method (RDM) field determines the type of
replay detection used in the Replay Detection field.If the RDM field contains 0x00, the replay detection field MUST be
set to the value of a strictly monotonically increasing counter. Using
a counter value, such as the current time of day (for example, an
NTP-format timestamp ), can reduce the
danger of replay attacks. This method MUST be supported by all
protocols.The Reconfigure key authentication protocol provides protection
against misconfiguration of a client caused by a Reconfigure message
sent by a malicious DHCP server. In this protocol, a DHCP server sends
a Reconfigure Key to the client in the initial exchange of DHCP
messages. The client records the Reconfigure Key for use in
authenticating subsequent Reconfigure messages from that server. The
server then includes an HMAC computed from the Reconfigure Key in
subsequent Reconfigure messages.Both the Reconfigure Key sent from the server to the client and the
HMAC in subsequent Reconfigure messages are carried as the
Authentication information in an Authentication option. The format of
the Authentication information is defined in the following
section.The Reconfigure Key protocol is used (initiated by the server) only
if the client and server are not using any other authentication
protocol and the client and server have negotiated to use Reconfigure
messages.The following fields are set in an Authentication option for the
Reconfigure Key Authentication Protocol: 310The format of the Authentication information for the Reconfigure
Key Authentication Protocol is:Type of data in Value field carried in
this option: Reconfigure Key value (used in Reply
message).HMAC-MD5 digest of the message (used in
Reconfigure message).Data as defined by the Type field.The server selects a Reconfigure Key for a client during the
Request/Reply, Solicit/Reply or Information-request/Reply message
exchange. The server records the Reconfigure Key and transmits that
key to the client in an Authentication option in the Reply
message.The Reconfigure Key is 128 bits long, and MUST be a
cryptographically strong random or pseudo-random number that cannot
easily be predicted.To provide authentication for a Reconfigure message, the server
selects a replay detection value according to the RDM selected by
the server, and computes an HMAC-MD5 of the Reconfigure message
using the Reconfigure Key for the client. The server computes the
HMAC-MD5 over the entire DHCP Reconfigure message, including the
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.The client will receive a Reconfigure Key from the server in the
initial Reply message from the server. The client records the
Reconfigure Key for use in authenticating subsequent Reconfigure
messages.To authenticate a Reconfigure message, the client computes an
HMAC-MD5 over the DHCP Reconfigure message, using the Reconfigure
Key received from the server. If this computed HMAC-MD5 matches the
value in the Authentication option, the client accepts the
Reconfigure message.Options are used to carry additional information and parameters in
DHCP messages. Every option shares a common base format, as described in
. All values in options are
represented in network byte order.This document describes the DHCP options defined as part of the base
DHCP specification. Other options may be defined in the future in
separate documents. See for guidelines regarding
new options definition. See for additional
information about a registry maintained by IANA.Unless otherwise noted, each option may appear only in the options
area of a DHCP message and may appear only once. If an option does
appear multiple times, each instance is considered separate and the data
areas of the options MUST NOT be concatenated or otherwise combined.Options that are allowed to appear only once are called singleton
options. The only non-singleton options defined in this document are
IA_NA (see ), IA_TA (see ), and IA_PD (see ) options. Also, IAAddress (see ) and IAPrefix (see ) may appear in their respective IA
options more than once.The format of DHCP options is:An unsigned integer identifying the
specific option type carried in this option.An unsigned integer giving the length
of the option-data field in this option in octets.The data for the option; the format
of this data depends on the definition of the option.DHCP 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 and .The Client Identifier option is used to carry a DUID (see ) identifying a client between a client and
a server. The format of the Client Identifier option is:OPTION_CLIENTID (1).Length of DUID in octets.The DUID for the client.The Server Identifier option is used to carry a DUID (see ) identifying a server between a client and
a server. The format of the Server Identifier option is:OPTION_SERVERID (2).Length of DUID in octets.The DUID for the server.The Identity Association for Non-temporary Addresses option (IA_NA
option) is used to carry an IA_NA, the parameters associated with the
IA_NA, and the non-temporary addresses associated with the IA_NA.Addresses appearing in an IA_NA option are not temporary addresses
(see ).The format of the IA_NA option is:OPTION_IA_NA (3).12 + length of IA_NA-options
field.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.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.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.Options associated with this
IA_NA.The IA_NA-options field encapsulates those options that are
specific to this IA_NA. For example, all of the IA Address Options
carrying the addresses associated with this IA_NA are in the
IA_NA-options field.Each IA_NA carries one "set" of non-temporary addresses; that is,
at most one address from each prefix assigned to the link to which the
client is attached.An IA_NA option may only appear in the options area of a DHCP
message. A DHCP message may contain multiple IA_NA options.The status of any operations involving this IA_NA is indicated in a
Status Code option in the IA_NA-options field.Note that an IA_NA has no explicit "lifetime" or "lease length" of
its own. When the valid lifetimes of all of the addresses in an IA_NA
have expired, the IA_NA can be considered as having expired. T1 and T2
are included to give servers explicit control over when a client
recontacts the server about a specific IA_NA.In a message sent by a client to a server, the T1 and T2 fields
SHOULD be set to 0. The server MUST ignore any values in these fields
in messages received from a client.In a message sent by a server to a client, the client MUST use the
values in the T1 and T2 fields for the T1 and T2 parameters, unless
those values in those fields are 0. The values in the T1 and T2 fields
are the number of seconds until T1 and T2.The server selects the T1 and T2 times to allow the client to
extend the lifetimes of any addresses in the IA_NA before the
lifetimes expire, even if the server is unavailable for some short
period of time. Recommended values for T1 and T2 are .5 and .8 times
the shortest preferred lifetime of the addresses in the IA that the
server is willing to extend, respectively. If the "shortest" preferred
lifetime is 0xffffffff ("infinity"), the recommended T1 and T2 values
are also 0xffffffff. If the time at which the addresses in an IA_NA
are to be renewed is to be left to the discretion of the client, the
server sets T1 and T2 to 0. The client MUST follow the rules defined
in .If a server receives an IA_NA with T1 greater than T2, and both T1
and T2 are greater than 0, the server ignores the invalid values of T1
and T2 and processes the IA_NA as though the client had set T1 and T2
to 0.If a client receives an IA_NA with T1 greater than T2, and both T1
and T2 are greater than 0, the client discards the IA_NA option and
processes the remainder of the message as though the server had not
included the invalid IA_NA option.Care should be taken in setting T1 or T2 to 0xffffffff
("infinity"). A client will never attempt to extend the lifetimes of
any addresses in an IA with T1 set to 0xffffffff. A client will never
attempt to use a Rebind message to locate a different server to extend
the lifetimes of any addresses in an IA with T2 set to 0xffffffff.This option MAY appear in a Confirm message if the lifetimes on the
non-temporary addresses in the associated IA have not expired.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 . The format of the IA_TA option
is:OPTION_IA_TA (4).4 + length of IA_TA-options field.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.Options associated with this
IA_TA.The IA_TA-Options field encapsulates those options that are
specific to this IA_TA. For example, all of the IA Address Options
carrying the addresses associated with this IA_TA are in the
IA_TA-options field.Each IA_TA carries one "set" of temporary addresses.An IA_TA option may only appear in the options area of a DHCP
message. A DHCP message may contain multiple IA_TA options.The status of any operations involving this IA_TA is indicated in a
Status Code option in the IA_TA-options field.Note that an IA has no explicit "lifetime" or "lease length" of its
own. When the valid lifetimes of all of the addresses in an IA_TA have
expired, the IA can be considered as having expired.An IA_TA option does not include values for T1 and T2. A client MAY
request that the lifetimes on temporary addresses be extended by
including the addresses in a IA_TA option sent in a Renew or Rebind
message to a server. For example, a client would request an extension
on the lifetime of a temporary address to allow an application to
continue to use an established TCP connection.The client obtains new temporary addresses by sending an IA_TA
option with a new IAID to a server. Requesting new temporary addresses
from the server is the equivalent of generating new temporary
addresses as described in . The server
will generate new temporary addresses and return them to the client.
The client should request new temporary addresses before the lifetimes
on the previously assigned addresses expire.A server MUST return the same set of temporary address for the same
IA_TA (as identified by the IAID) as long as those addresses are still
valid. After the lifetimes of the addresses in an IA_TA have expired,
the IAID may be reused to identify a new IA_TA with new temporary
addresses.This option MAY appear in a Confirm message if the lifetimes on the
temporary addresses in the associated IA have not expired.The IA Address option is used to specify IPv6 addresses associated
with an IA_NA or an IA_TA. The IA Address option must be encapsulated
in the Options field of an IA_NA or IA_TA option. The Options fields
of the IA_NA or IA_TA option encapsulates those options that are
specific to this address.The format of the IA Address option is:OPTION_IAADDR (5).24 + length of IAaddr-options
field.An IPv6 address.The preferred lifetime for the
IPv6 address in the option, expressed in units of seconds.The valid lifetime for the IPv6
address in the option, expressed in units of seconds.Options associated with this
address.In a message sent by a client to a server, the preferred and valid
lifetime fields SHOULD be set to 0. The server MUST ignore any
received values.The client SHOULD NOT send the IA Address option with unspecified
address (::).In a message sent by a server to a client, the client MUST use the
values in the preferred and valid lifetime fields for the preferred
and valid lifetimes. The values in the preferred and valid lifetimes
are the number of seconds remaining in each lifetime.A client discards any addresses for which the preferred lifetime is
greater than the valid lifetime. A server ignores the lifetimes set by
the client if the preferred lifetime is greater than the valid
lifetime and ignores the values for T1 and T2 set by the client if
those values are greater than the preferred lifetime.Care should be taken in setting the valid lifetime of an address to
0xffffffff ("infinity"), which amounts to a permanent assignment of an
address to a client.More than one IA Address Option can appear in an IA_NA option or an
IA_TA option.The status of any operations involving this IA Address is indicated
in a Status Code option in the IAaddr-options field, as specified in
.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:OPTION_ORO (6).2 * number of requested options.The option code for an
option requested by the client.A client MAY include an Option Request option in a Solicit,
Request, Renew, Rebind, Confirm or Information-request message to
inform the server about options the client wants the server to send to
the client. A server MAY include an Option Request option in a
Reconfigure message to indicate which options the client should
request from the server. The Option Request option MUST NOT include the
following options: Server Identifier, Client Identifier, IA_NA, IA_PD, IA_TA,
Option Request, Elapsed Time, Preference, Relay Message, Authentication,
Server Unicast, Rapid Commit, User Class, Interface-Id, Reconfigure Message, and
Reconfigure Accept. Other top-level Options MUST appear in the Option Request
option or the will not be sent by the server. Only container options MUST appear
in the Option Request, options encapsulated in the container MUST NOT by in the
Option Request, see as an example of container options.
The exception to this is the Option Request option MAY be used to signal support
for a feature even when that option is encapsulated as in the case of the
Prefix Excluded option .
The Preference option is sent by a server to a client to affect the
selection of a server by the client.The format of the Preference option is:OPTION_PREFERENCE (7).1.The preference value for the server in
this message.A server MAY include a Preference option in an Advertise message to
control the selection of a server by the client. See for the use of the Preference option
by the client and the interpretation of Preference option data
value.OPTION_ELAPSED_TIME (8).2.The amount of time since the client
began its current DHCP transaction. This time is expressed in
hundredths of a second (10^-2 seconds).A client MUST include an Elapsed Time option in messages to
indicate how long the client has been trying to complete a DHCP
message exchange. The elapsed time is measured from the time at which
the client sent the first message in the message exchange, and the
elapsed-time field is set to 0 in the first message in the message
exchange. Servers and Relay Agents use the data value in this option
as input to policy controlling how a server responds to a client
message. For example, the elapsed time option allows a secondary DHCP
server to respond to a request when a primary server has not answered
in a reasonable time. The elapsed time value is an unsigned, 16 bit
integer. The client uses the value 0xffff to represent any elapsed
time values greater than the largest time value that can be
represented in the Elapsed Time option.The Relay Message option carries a DHCP message in a Relay-forward
or Relay-reply message.The format of the Relay Message option is:OPTION_RELAY_MSG (9)Length of DHCP-relay-messageIn 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 messageThe Authentication option carries authentication information to
authenticate the identity and contents of DHCP messages. The use of
the Authentication option is described in . The delayed authentication protocol,
defined in , has been obsoleted by this
document, due to lack of usage. The format of the Authentication
option is:OPTION_AUTH (11).11 + length of authentication
information field.The authentication protocol used in this
authentication option.The algorithm used in the
authentication protocol.The replay detection method used in this
authentication option.The replay detection information
for the RDM.The authentication
information, as specified by the protocol and algorithm used in
this authentication option.The server sends this option to a client to indicate to the client
that it is allowed to unicast messages to the server. The format of
the Server Unicast option is:OPTION_UNICAST (12).16.The IP address to which the client
should send messages delivered using unicast.The server specifies the IPv6 address to which the client is to
send unicast messages in the server-address field. When a client
receives this option, where permissible and appropriate, the client
sends messages directly to the server using the IPv6 address specified
in the server-address field of the option.When the server sends a Unicast option to the client, some messages
from the client will not be relayed by Relay Agents, and will not
include Relay Agent options from the Relay Agents. Therefore, a server
should only send a Unicast option to a client when Relay Agents are
not sending Relay Agent options. A DHCP server rejects any messages
sent inappropriately using unicast to ensure that messages are relayed
by Relay Agents when Relay Agent options are in use.Details about when the client may send messages to the server using
unicast are in .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:OPTION_STATUS_CODE (13).2 + length of status-message.The numeric code for the status
encoded in this option.A UTF-8 encoded text string
suitable for display to an end user, which MUST NOT be
null-terminated.A Status Code option may appear in the options field of a DHCP
message and/or in the options field of another option. If the Status
Code option does not appear in a message in which the option could
appear, the status of the message is assumed to be Success.The status-codes values previously defined by and are:NameCodeDescriptionSuccess0Success.UnspecFail1Failure, reason unspecified; this status code is sent by either a
client or a server to indicate a failure not explicitly specified in
this document.NoAddrsAvail2Server has no addresses available to assign to the IA(s).NoBinding3Client record (binding) unavailable.NotOnLink4The prefix for the address is not appropriate for the link to
which the client is attached.UseMulticast5Sent 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.NoPrefixAvail6Delegating router has no prefixes available to assign to the
IAPD(s).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:OPTION_RAPID_COMMIT (14).0.A client MAY include this option in a Solicit message if the client
is prepared to perform the Solicit-Reply message exchange described in
.A server MUST include this option in a Reply message sent in
response to a Solicit message when completing the Solicit-Reply
message exchange.DISCUSSION:Each server that responds with a Reply to a Solicit that
includes a Rapid Commit option will commit the assigned addresses
in the Reply message to the client, and will not receive any
confirmation that the client has received the Reply message.
Therefore, if more than one server responds to a Solicit that
includes a Rapid Commit option, some servers will commit addresses
that are not actually used by the client.The problem of unused addresses can be minimized, for example,
by designing the DHCP service so that only one server responds to
the Solicit or by using relatively short lifetimes for assigned
addresses, or the DHCP client initiatively releases unused
addresses using the Release message.The User Class option is used by a client to identify the type or
category of user or applications it represents.The format of the User Class option is:OPTION_USER_CLASS (15).Length of user class data field.The user classes carried by the
client.The information contained in the data area of this option is
contained in one or more opaque fields that represent the user class
or classes of which the client is a member. A server selects
configuration information for the client based on the classes
identified in this option. For example, the User Class option can be
used to configure all clients of people in the accounting department
with a different printer than clients of people in the marketing
department. The user class information carried in this option MUST be
configurable on the client.The data area of the user class option MUST contain one or more
instances of user class data. Each instance of the user class data is
formatted as follows:The user-class-len is two octets long and specifies the length of
the opaque user class data in network byte order.A server interprets the classes identified in this option according
to its configuration to select the appropriate configuration
information for the client. A server may use only those user classes
that it is configured to interpret in selecting configuration
information for a client and ignore any other user classes. In
response to a message containing a User Class option, a server
includes a User Class option containing those classes that were
successfully interpreted by the server, so that the client can be
informed of the classes interpreted by the server.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:OPTION_VENDOR_CLASS (16).4 + length of vendor class data
field.The vendor's registered
Enterprise Number as registered with IANA .The hardware configuration of
the host on which the client is running.The vendor-class-data is composed of a series of separate items,
each of which describes some characteristic of the client's hardware
configuration. Examples of vendor-class-data instances might include
the version of the operating system the client is running or the
amount of memory installed on the client.Each instance of the vendor-class-data is formatted as follows:The vendor-class-len is two octets long and specifies the length of
the opaque vendor class data in network byte order.Servers and clients MUST NOT include more than one instance of
OPTION_VENDOR_CLASS with the same Enterprise Number. Each instance of
OPTION_VENDOR_CLASS can carry multiple sub-options.This option is used by clients and servers to exchange
vendor-specific information.The format of the Vendor-specific Information option is:OPTION_VENDOR_OPTS (17).4 + length of option-data field.The vendor's registered
Enterprise Number as registered with IANA .An opaque object, interpreted by
vendor-specific code on the clients and servers.The definition of the information carried in this option is vendor
specific. The vendor is indicated in the enterprise-number field. Use
of vendor-specific information allows enhanced operation, utilizing
additional features in a vendor's DHCP implementation. A DHCP client
that does not receive requested vendor-specific information will still
configure the host device's IPv6 stack to be functional.The encapsulated vendor-specific options field MUST be encoded as a
sequence of code/length/value fields of identical format to the DHCP
options field. The option codes are defined by the vendor identified
in the enterprise-number field and are not managed by IANA. Each of
the encapsulated options is formatted as follows:The code for the encapsulated
option.An unsigned integer giving the length
of the option-data field in this encapsulated option in
octets.The data area for the encapsulated
option.Multiple instances of the Vendor-specific Information option may
appear in a DHCP message. Each instance of the option is interpreted
according to the option codes defined by the vendor identified by the
Enterprise Number in that option. Servers and clients MUST NOT send
more than one instance of Vendor-specific Information option with the
same Enterprise Number. Each instance of Vendor-specific Information
option MAY contain multiple encapsulated options.A client that is interested in receiving a Vendor-specific
Information Option:MUST specify the Vendor-specific Information
Option in an Option Request Option.MAY specify an associated Vendor Class Option.MAY specify the Vendor-specific Information Option
with any data.Severs only return the Vendor-specific Information Options if
specified in Option Request Options from clients and:MAY use the Enterprise Numbers in the associated
Vendor Class Options to restrict the set of Enterprise Numbers in
the Vendor-specific Information Options returned.MAY return all configured Vendor-specific
Information Options.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.The relay agent MAY send the Interface-id option to identify the
interface on which the client message was received. If a relay agent
receives a Relay-reply message with an Interface-id option, the relay
agent relays the message to the client through the interface
identified by the option.The format of the Interface ID option is:OPTION_INTERFACE_ID (18).Length of interface-id field.An opaque value of arbitrary length
generated by the relay agent to identify one of the relay agent's
interfaces.The server MUST copy the Interface-Id option from the Relay-forward
message into the Relay-reply message the server sends to the relay
agent in response to the Relay-forward message. This option MUST NOT
appear in any message except a Relay-forward or Relay-reply
message.Servers MAY use the Interface-ID for parameter assignment policies.
The Interface-ID SHOULD be considered an opaque value, with policies
based on exact match only; that is, the Interface-ID SHOULD NOT be
internally parsed by the server. The Interface-ID value for an
interface SHOULD be stable and remain unchanged, for example, after
the relay agent is restarted; if the Interface-ID changes, a server
will not be able to use it reliably in parameter assignment
policies.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:OPTION_RECONF_MSG (19).1.5 for Renew message, 6 for Rebind, 11
for Information-request message.The Reconfigure Message option can only appear in a Reconfigure
message.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:OPTION_RECONF_ACCEPT (20).0.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.OPTION_IA_PD (25).12 + length of IA_PD-options
field.The unique identifier for this IA_PD; the
IAID must be unique among the identifiers for all of this
requesting router's IA_PDs.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.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.Options associated with this
IA_PD.The IA_PD-options field encapsulates those options that are
specific to this IA_PD. For example, all of the IA_PD Prefix Options
carrying the prefixes associated with this IA_PD are in the
IA_PD-options field.An IA_PD option may only appear in the options area of a DHCP
message. A DHCP message may contain multiple IA_PD options.The status of any operations involving this IA_PD is indicated in a
Status Code option in the IA_PD-options field.Note that an IA_PD has no explicit "lifetime" or "lease length" of
its own. When the valid lifetimes of all of the prefixes in a IA_PD
have expired, the IA_PD can be considered as having expired. T1 and T2
are included to give delegating routers explicit control over when a
requesting router should contact the delegating router about a
specific IA_PD.In a message sent by a requesting router to a delegating router,
the T1 and T2 fields SHOULD be set to 0. The delegating router MUST
ignore any values in these fields in messages received from a
requesting router.In a message sent by a delegating router to a requesting router,
the delegating router MUST use the values in the T1 and T2 fields for
the T1 and T2 parameters, unless those values in those fields are 0.
The values in the T1 and T2 fields are the number of seconds until T1
and T2.The 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. The requesting router MUST
follow the rules defined in .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.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.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.OPTION_IAPREFIX (26).25 + length of IAprefix-options
field.The recommended preferred
lifetime for the IPv6 prefix in the option, expressed in units of
seconds. A value of 0xFFFFFFFF represents infinity.The valid lifetime for the IPv6
prefix in the option, expressed in units of seconds. A value of
0xFFFFFFFF represents infinity.Length for this prefix in bits.An IPv6 prefix.Options associated with this
prefix.In a message sent by a requesting router to a delegating router,
the preferred and valid lifetime fields SHOULD be set to 0. The server
MUST ignore any received values in these lifetime fields.A requesting router may set the IPv6 prefix field to zero and a
given value in the prefix-length field to indicate a preference for
the size of the prefix to be delegated.In a message sent by a delegating router the preferred and valid
lifetimes should be set to the values of AdvPreferredLifetime and
AdvValidLifetime as specified in section 6.2.1, "Router Configuration
Variables" of , unless administratively
configured.A requesting router discards any prefixes for which the preferred
lifetime is greater than the valid lifetime. A delegating router
ignores the lifetimes set by the requesting router if the preferred
lifetime is greater than the valid lifetime and ignores the values for
T1 and T2 set by the requesting router if those values are greater
than the preferred lifetime.The values in the preferred and valid lifetimes are the number of
seconds remaining for each lifetime.An IA_PD Prefix option may appear only in an IA_PD option. More
than one IA_PD Prefix Option can appear in a single IA_PD option.The status of any operations involving this IA_PD Prefix option is
indicated in a Status Code option in the IAprefix-options field.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 . One use for the SOL_MAX_RT option is to
set a longer value for SOL_MAX_RT, which reduces the Solicit traffic
from a client that has not received a response to its Solicit
messages.The format of the SOL_MAX_RT option is:OPTION_SOL_MAX_RT (82).4.Overriding value for SOL_MAX_RT
in seconds; MUST be in range: 60 <= "value" <= 86400 (1
day).A DHCP client MUST include the SOL_MAX_RT option code in any Option
Request option (see ) it sends.The DHCP server MAY include the SOL_MAX_RT option in any response
it sends to a client that has included the SOL_MAX_RT option code in
an Option Request option. The SOL_MAX_RT option is sent in the main
body of the message to client, not as an encapsulated option in, e.g.,
an IA_NA, IA_TA, or IA_PD option.A DHCP client MUST ignore any SOL_MAX_RT option values that are
less than 60 or more than 86400.If a DHCP client receives a message containing a SOL_MAX_RT option
that has a valid value for SOL_MAX_RT, the client MUST set its
internal SOL_MAX_RT parameter to the value contained in the SOL_MAX_RT
option. This value of SOL_MAX_RT is then used by the retransmission
mechanism defined in and .Updated SOL_MAX_RT value applies only to the network interface on
which the client received SOL_MAX_RT option.A DHCP server sends the INF_MAX_RT option to a client to override
the default value of INF_MAX_RT. The value of INF_MAX_RT in the option
replaces the default value defined in . 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.The format of the INF_MAX_RT option is:OPTION_INF_MAX_RT (83).4.Overriding value for INF_MAX_RT
in seconds; MUST be in range: 60 <= "value" <= 86400 (1
day).A DHCP client MUST include the INF_MAX_RT option code in any Option
Request option (see ) it sends.The DHCP server MAY include the INF_MAX_RT option in any response
it sends to a client that has included the INF_MAX_RT option code in
an Option Request option. The INF_MAX_RT option is sent in the main
body of the message to client, not as an encapsulated option in, e.g.,
an IA_NA, IA_TA, or IA_PD option.A DHCP client MUST ignore any INF_MAX_RT option values that are
less than 60 or more than 86400.If a DHCP client receives a message containing an INF_MAX_RT option
that has a valid value for INF_MAX_RT, the client MUST set its
internal INF_MAX_RT parameter to the value contained in the INF_MAX_RT
option. This value of INF_MAX_RT is then used by the retransmission
mechanism defined in and .Updated INF_MAX_RT value applies only to the network interface on
which the client received INF_MAX_RT option.A client running in stateless mode requests this option. The server
includes this option in its response to specify an upper bound for how
long a client should wait before refreshing the information. Clients
that support stateless mode MUST support this option. This option is
listed here for completeteness. For complete reference, see .This section discusses security considerations that are not related
to privacy. For dedicated privacy discussion, see .The threat to DHCP is inherently an insider threat (assuming a
properly configured network where DHCP 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.Use of manually configured preshared keys for IPsec between relay
agents and servers does not defend against replayed DHCP messages.
Replayed messages can represent a DOS attack through exhaustion of
processing resources, but not through mis-configuration or exhaustion of
other resources such as assignable addresses.One attack specific to a DHCP client is the establishment of a
malicious server with the intent of providing incorrect configuration
information to the client. The motivation for doing so may be to mount a
"man in the middle" attack that causes the client to communicate with a
malicious server instead of a valid server for some service such as DNS
or NTP. The malicious server may also mount a denial of service attack
through misconfiguration of the client that causes all network
communication from the client to fail.A malicious DHCP server might cause a client to set its SOL_MAX_RT
and INF_MAX_RT parameters to an unreasonably high value with the
SOL_MAX_RT and INF_MAX_RT options, which may cause an undue delay in a
client completing its DHCP protocol transaction in the case no other
valid response is received. Assuming the client also receives a response
from a valid DHCP server, large values for SOL_MAX_RT and INF_MAX_RT
will not have any effect.There is another threat to DHCP clients from mistakenly or
accidentally configured DHCP servers that answer DHCP client requests
with unintentionally incorrect configuration parameters.A DHCP client may also be subject to attack through the receipt of a
Reconfigure message from a malicious server that causes the client to
obtain incorrect configuration information from that server. Note that
although a client sends its response (Renew or Information-request
message) through a relay agent and, therefore, that response will only
be received by servers to which DHCP messages are relayed, a malicious
server could send a Reconfigure message to a client, followed (after an
appropriate delay) by a Reply message that would be accepted by the
client. Thus, a malicious server that is not on the network path between
the client and the server may still be able to mount a Reconfigure
attack on a client. The use of transaction IDs that are
cryptographically sound and cannot easily be predicted will also reduce
the probability that such an attack will be successful.Many of these rogue server attacks can be mitigated by making use of
the mechanism described in .The threat specific to a DHCP server is an invalid client
masquerading as a valid client. The motivation for this may be for theft
of service, or to circumvent auditing for any number of nefarious
purposes.The threat common to both the client and the server is the resource
"denial of service" (DoS) attack. These attacks typically involve the
exhaustion of available addresses, or the exhaustion of CPU or network
bandwidth, and are present anytime there is a shared resource.In the case where relay agents add additional options to Relay
Forward messages, the messages exchanged between relay agents and
servers may be used to mount a "man in the middle" or denial of service
attack.This threat model does not consider the privacy of the contents of
DHCP messages to be important. DHCP is not used to exchange
authentication or configuration information that must be kept secret
from other networks nodes.Because of the opportunity for attack through the Reconfigure
message, a DHCP client MUST discard any Reconfigure message that does
not include authentication or that does not pass the validation process
for the authentication protocol.The Reconfigure Key protocol described in 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.Communication between a server and a relay agent, and communication
between relay agents, can be secured through the use of IPsec, as
described in . The use of manual
configuration and installation of static keys are acceptable in this
instance because relay agents and the server will belong to the same
administrative domain and the relay agents will require other specific
configuration (for example, configuration of the DHCP server address) as
well as the IPsec configuration.A rogue delegating router can issue bogus prefixes to a requesting
router. This may cause denial of service due to unreachability.A malicious requesting router may be able to mount a denial of
service attack by repeated requests for delegated prefixes that exhaust
the delegating router's available prefixes.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 DHCP messages. The details of using IPsec
for DHCP are under development. For point to point
links, where one trusts that there is no man in the middle, or one
trusts layer two authentication, IPsec may not be necessary. Networks configured with delegated prefixes should be configured to
preclude intentional or inadvertent inappropriate advertisement of these
prefixes.This section focuses on the server considerations. For extended
discussion about privacy considerations for the client, see . It particular, Section 3
of said document discuss various identifiers that could be misused to
track the client. Section 4 discusses existing mechanisms that may have
an impact on client's privacy. Finally, Section 5 discusses potential
attack vectors. For recommendations how to address or mitigate those
issues, see .This specification does not define any allocation strategies.
Implementers are expected to develop their own algorithm for the server
to choose a resource out of the available pool. Several possible
allocation strategies are mentioned in Section 4.3 of . Please keep in mind that
this list is not exhaustive and there are certainly possible other
strategies. Here are some observations for the implementer to
consider.Assigning addresses using some kind of sequential algorithm
(prefix::1, prefix::2, prefix::3,...) is fast, but greatly facilitate
scanning of the network. Also, it makes any attacks that require
guessing the next address much easier to conduct.Deriving the IID (Interface Identifier) part of the addresses from
the link layer address of the client exposes information about the
client hardware and enables tracking the client across multiple subnets.
Also, since the address will likely be used to access remote services,
this tracking can be conducted remotely.This document does not define any new DHCP name spaces or
definitions.IANA is requested to update the
http://www.iana.org/assignments/dhcpv6-parameters/dhcpv6-parameters.xhtml
page to add a reference to this document for definitions previously
created by , , and .IANA is requested to add a column to the DHCPv6 Option table at
http://www.iana.org/assignments/dhcpv6-parameters/dhcpv6-parameters.xhtml
to indicate which Options are allowed to appear in the ORO option. See Section 20.7.IANA is requested to update the
http://www.iana.org/assignments/bootp-dhcp-parameters/bootp-dhcp-parameters.xhtml#authentication-protocol-id
page to add an "Obsolete" annotation into the "DHCPv6 Delayed
Authentication" entity in the "Authentication Suboption (value 8) -
Protocol identifier values" registry, and
https://www.iana.org/assignments/auth-namespaces/auth-namespaces.xhtml
page to add an "Obsolete" annotation into the "Delayed Authentication"
entity in the "Protocol Name Space Values" registry.The publication of this document does not change the
assignment rules for new values for message types, option codes,
DUID types or status codes.The list of assigned values used in DHCPv6 is available at
http://www.iana.org/assignments/dhcpv6-parameters/dhcpv6-parameters.xmlNote to IANA: is this the right, long term link? I noticed
there are two similar ones ending with .xhtml and .xml. Please
update the link above if necessary.This specification is mostly a corrected and cleaned up version
of the original specification, , along with
numerous additions from later RFCs. However, there is a small number of
mechanisms that didn't get much traction, were not widely deployed,
underspecified or had other operational issues. Those mechanisms are now
considered deprecated. Legacy implementations MAY support them, but
implementations conformant to this document MUST NOT rely on them.The following mechanism are now obsolete:Delayed Authentication. This mechanism was underspecified and had
significant operational burden. As a result, after 10 years its adoption
was extremely limited at best.Lifetime hints sent by a client. Client used to be allowed to send
lifetime values as hints. This mechanism was not widely implemented and
there were known misimplementations that sent remaining lifetimes rather
than total lifetimes. That in turn was sometimes misunderstood by the
servers as a request for ever decreasing lease lifetimes, which caused
issues when values started approaching zero.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.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 and Christian Huitema. With
special thanks to Ralph Droms for answering many questions related to
the original RFC 3315 work.The following acknowledgements are from the original RFC 3315 and RFC
3633:Thanks to the DHC Working Group and the members of the IETF for their
time and input into the specification. In particular, thanks also for
the consistent input, ideas, and review by (in alphabetical order)
Bernard Aboba, Bill Arbaugh, Thirumalesh Bhat, Steve Bellovin, A. K.
Vijayabhaskar, Brian Carpenter, Matt Crawford, Steve Deering, Francis
Dupont, Dave Forster, Brian Haberman, Richard Hussong, Tatuya Jinmei,
Kim Kinnear, Fredrik Lindholm, Tony Lindstrom, Josh Littlefield, Gerald
Maguire, Jack McCann, Shin Miyakawa, Thomas Narten, Erik Nordmark, Jarno
Rajahalme, Yakov Rekhter, Pekka Savola, Mark Stapp, Matt Thomas, Sue
Thomson, Tatuya Jinmei, Bernie Volz, Trevor Warwick, Phil Wells and
Toshi Yamasaki.Thanks to Steve Deering and Bob Hinden, who have consistently taken
the time to discuss the more complex parts of the IPv6
specifications.And, thanks to Steve Deering for pointing out at IETF 51 in London
that the DHCPv6 specification has the highest revision number of any
Internet Draft.Private Enterprise Numbers registry
http://www.iana.org/assignments/enterprise-numbersIANATR-187 - IPv6 for PPP Broadband AccessBroadband ForumNote: This appendix should be removed by the RFC-Editor when preparing
the document for publication.Incorporated RFC3315 errata (ids: 294, 1373, 2928, 1815, 3577,
2509, 295).Partially incorporated RFC3315 errata id 2472 (place other IA
options if NoAddrsAvail is sent in Advertise).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.Added DUID-UUID and reference to RFC6355. Ticket #54.Specified a minimum length for the DUID in section "9.1. DUID
Contents". Ticket #39.Removed the use of term "sub-options" from section "19.1.1.
Creation and Transmission of Reconfigure Messages". Ticket #40.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.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.Merged RFC7083, "Modification to Default Values of SOL_MAX_RT and
INF_MAX_RT", into this document. Ticket #51.Incorporated RFC3315 errata (id 2471), into section 17.1.3.
Ticket #25.Added text that relay agents MUST NOT modify the relayed message
to section 20.1.2. Ticket #57.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.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.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.Clarified that: there should be no more than 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.Clarified relay agent definition. Ticket #12.Changed REL_MAX_RC and DEC_MAX_RC defaults from 5 to 4 and added
retry to parameter description. Ticket #84.Clarify handling process for Vendor-specific Information Option
and Vendor Class Option. Ticket #20.Replace "monotonic" with "strictly monotonic" in Section 21.3.
Ticket #11.Incorporate everything of RFC 6644, except for Security
Considerations Section, which has already covered in a more
abstracted way. Tickets #55 & #56.Clarify the server behavior process when a client violates
Delayed Authentication Protocol, in Section 21.4. Ticket #90.Updated titles of sections 19.4.2. and 19.4.4. to include Rebind
messages.Applied many of the review comments from a review done by Fred
Templin in August 2006. Ticket #14.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.Changed WG to DHC on the first page header, added keywords.Loosened requirements for DUID-EN, so that DUID type can be used
for virtual machines. Ticket #16.Clarified that IA may contain other resources than just address.
Ticket #93.Clarified that most options are singletons (i.e. can appear only
once). Ticket #83.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).Clarified that encapsulated options must be requested using
top-level ORO (ticket #38).Clarified that configuration for interface X should be requested
over interface X (ticket #48).CONFIRM is now an optional message (MUST send Confirm eased to
SHOULD) (ticket #120).Added reference to RFC7227: DHCPv6 Option Guidelines (ticket
#121).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.Addressed ticket #115 - don't use DHCPv6 for DHCPv4
configuration.Revised IANA Considerations based on ticket #117.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).Merged Section 12 from RFC3633 (ticket #107).Clarified behavior for unknown messages (RFC7283), ticket
#58.Addressed tickets #123 and #126, and clarified that the client
SHOULD abandon its bindings when restarts the server
solicitation.Clarified link-address field usage, ticket #73.Clarified that retransmitting at client's discretion (t1,t2=0)
does not mean immediate transmission (ticket #71).Merged section 4.4. of RFC7550 (stateful-issues). This includes
new Renew and Rebind processing by the server, i.e. a client may
request allocation of new addresses/prefixes during Renew and
Rebind. This addresses tickets #62 and #63.Merged section 4.1 and 4.2 of RFC7550 (stateful-issues). This
addresses tickets #59 and #60.Added normative reference to RFC7550 and to obsoleted list. Also
added terse text of Abstract and section 1.0 to indicate what this
document is about.Merged section 4.6 of RFC7550 (stateful-issues). This addresses
ticket #85.Clarified that the document assumes single provisioning domain.
This resolves ticket #66.Removed the Delayed Auth Protocol. This resolves ticket #86.Added text the text suggesting to not send all-zero
address/prefix unless the client wishes to hint the lifetimes and/or
prefix lengths. This resolves ticket #82.Cleaned up Confirm text regarding rebooting client an stable
storage.Updated server processing section to clarify that server unicast
check can be based on current configuration of unicast setting so
server is not required to remember what it sent. This resolves
ticket #130.Removed references to lifetime hints from the client; only
IAPREFIX prefix-length hints are now allowed. Servers will ignore
any lifetime hints; clients should set lifetime to 0. This resolves
ticket #148. Also, removed T1/T2 hints from clients to servers -
while not explicitly discussed, seems to make sense? And, fixed some
of the message processing text to include PD, not just addresses
(though I think Marcin will eventually replace much of this text?
Plus a few other minor edits.Clarified that the server may return different addresses in the
Reply than requested by the client in the Request message. Also
clarified that the server must not include addresses that it will
not assign. This resolves ticket #69.Introduction updated, including relation to previous RFCs (ticket
#136).Added section with deprecated mechanisms (ticket #149).Combined text for prefix delegation and address assignment in
sections 18 and 19. Also, introduced a term "lease" replacing
"allocable resources". This resolves ticket #146.Reorganized text about Reply processing on the client side
(ticket #140).Revised the "Creation and Transmission of Release Messages"
section to clarify what a client must do before initiating a Release
(ticket #151).Privacy considerations added (ticket #145).Abstract updated. Ticket #133.Removed references to the text that server was allowed to cache
its replies. Ticket #80.Merged sections 17, 18 and 19 into a single section describing
client and server behaviors. Ticket #142.Added text about single session for multiple IA option types.
Ticket #160.Moved additional text from RFC3633 section 12.1. Ticket #102.Addressed minor addition to text as per ticket 131 and also ticket #61.Clarified MUST perform DAD, excepting exceptions listed in RFC4862 Section
5.4. Ticket #153.Removed the requirement for the server to send Reconfigure Accept
in Reply messages, also clarified why it's useful in Advertise. Ticket
#154.Explicitly require Elapsed Time option to be placed in messages
sent by a client. Ticket #159.Update section 14 - explained that Elapsed Time option (and possibly
other options) must be updated prior to resending the message. Also
included "retransmission" in the DHCP terminology. Ticket #157.Added text explaining that the client should stop using an option
if it's not being sent by the server. Ticket #150.Added reference to RFC4242 (Information Refresh Time
Option). Ticket #161.Updated ORO Option to list Options that MUST NOT be included. Also added to that IANA
Consider should keep track of which options are allowed in ORO. Ticket #81.Updated Creation and Transmission of Advertise message so that the only options
in the ORO will be included in the Advertise unless configured otherwise. Ticket #81.Information Refresh Time Option is now mandatory for clients that
support stateless mode. Added reference to RFC4242. Ticket #161.Note: This appendix should be removed by the RFC-Editor when preparing
the document for publication.Incorporated RFC3633 errata (ids: 248, 1880, 2468, 2469, 2470,
3736)The following table indicates with a "*" the options are allowed in
each DHCP message type:NOTE:Only included in Information-request messages that are sent in
response to a Reconfigure (see ).The following table indicates with a "*" where options can appear in
the options field of other options:Note: "Relay Forw" / "Relay Reply" options appear in the options
field of the message but may only appear in these messages.