4. Terminology
This section preserves the RFC text for DHCPv6, including message exchanges, relay behavior, DUIDs, IA_NA, IA_TA, IA_PD, DHCP options, RKAP authentication, IANA registries, normative requirements, and appendix option-appearance matrices.
Original RFC Text
4. Terminology
This section defines terminology specific to IPv6 and DHCP used in
this document.
4.1. IPv6 Terminology
IPv6 terminology from [RFC8200], [RFC4291], and [RFC4862] relevant to
this specification is included below.
address
An IP-layer identifier for an interface or a set of interfaces.
GUA
Global unicast address (see [RFC4291]).
host
Any node that is not a router.
IP
Internet Protocol Version 6 (IPv6). The terms "IPv4" and "IPv6"
are used only in contexts where it is necessary to avoid
ambiguity.
interface
A node's attachment to a link.
link
A communication facility or medium over which nodes can
communicate at the link layer, i.e., the layer immediately below
IP. Examples are Ethernet (simple or bridged); Point-to-Point
Protocol (PPP) and PPP over Ethernet (PPPoE) links; and Internet-
layer (or higher) "tunnels", such as tunnels over IPv4 or IPv6
itself.
link-layer identifier
A link-layer identifier for an interface -- for example, IEEE 802
addresses for Ethernet or Token Ring network interfaces.
link-local address
An IPv6 address having a link-only scope, indicated by having the
prefix (fe80::/10), that can be used to reach neighboring nodes
attached to the same link. Every IPv6 interface on which DHCPv6
can reasonably be useful has a link-local address.
multicast address
An identifier for a set of interfaces (typically belonging to
different nodes). A packet sent to a multicast address is
delivered to all interfaces identified by that address.
neighbor
A node attached to the same link.
node
A device that implements IP.
packet
An IP header plus payload.
prefix
The initial bits of an address, or a set of IP addresses that
share the same initial bits.
prefix length
The number of bits in a prefix.
router
A node that forwards IP packets not explicitly addressed to
itself.
ULA
Unique local address (see [RFC4193]).
unicast address
An identifier for a single interface. A packet sent to a unicast
address is delivered to the interface identified by that address.
4.2. DHCP Terminology
Terminology specific to DHCP can be found below.
appropriate to the link
An address is "appropriate to the link" when the address is
consistent with the DHCP server's knowledge of the network
topology, prefix assignment, and address assignment policies.
binding
A binding (or client binding) is a group of server data records
containing the information the server has about the addresses or
delegated prefixes in an Identity Association (IA) or
configuration information explicitly assigned to the client.
Configuration information that has been returned to a client
through a policy, such as 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 lease in the IA --
for example, address or delegated prefix). A binding containing
configuration information for a client is indexed by <DUID>. See
below for definitions of DUID, IA, and IAID.
configuration parameter
An element of the configuration information set on the server and
delivered to the client using DHCP. Such parameters may be used
to carry information to be used by a node to configure its network
subsystem and enable communication on a link or internetwork, for
example.
container option
An option that encapsulates other options (for example, the IA_NA
option (see Section 21.4) may contain IA Address options (see
Section 21.6)).
DHCP
Dynamic Host Configuration Protocol for IPv6. The terms "DHCPv4"
and "DHCPv6" are used only in contexts where it is necessary to
avoid ambiguity.
DHCP client
Also referred to as "client". A node that initiates requests on a
link to obtain configuration parameters from one or more DHCP
servers.
DHCP domain
A set of links managed by DHCP and operated by a single
administrative entity.
DHCP relay agent
Also referred to as "relay agent". A node that acts as an
intermediary to deliver DHCP messages between clients and servers.
In certain configurations, there may be more than one relay agent
between clients and servers, so a relay agent may send DHCP
messages to another relay agent.
DHCP server
This document condenses this term to "server". A node that
responds to requests from clients. It may or may not be on the
same link as the client(s).
DUID
A DHCP Unique Identifier for a DHCP participant. Each DHCP client
and server has exactly one DUID. See Section 11 for details of
the ways in which a DUID may be constructed.
encapsulated option
A DHCP option that is usually only contained in another option.
For example, the IA Address option is contained in IA_NA options
(see Section 21.6 and Section 21.4, respectively). See Section 9
of [RFC7227] for a more complete definition.
IA
Identity Association: a collection of leases assigned to a client.
Each IA has an associated IAID (see below). 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 lease; for example, an
identity association for non-temporary addresses (IA_NA) holds
addresses, and an 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. This document defines three IA
types: IA_NA, IA_TA (obsoleted), and IA_PD. Another IA type
(IA_LL) was defined in [RFC8947] and more may be defined.
IA option(s)
In this document, one or more IA_NA, IA_TA (obsoleted), and/or
IA_PD options. Another IA type (IA_LL) was defined in [RFC8947]
and more may be defined.
IAID
Identity Association Identifier: an identifier for an IA, chosen
by the client. Each IA has an IAID, which is chosen to be unique
among IAIDs for IAs of a specific type that belong to that client.
IA_NA
Identity Association for Non-temporary Addresses: an IA that
carries assigned addresses. See Section 21.4 for details on the
IA_NA option.
IA_PD
Identity Association for Prefix Delegation: an IA that carries
delegated prefixes. See Section 21.21 for details on the IA_PD
option.
IA_TA
Identity Association for Temporary Addresses: an IA that carries
temporary addresses (see [RFC8981]). This option is obsoleted by
this document. See [RFC8415] for details.
lease
A contract by which the server grants the use of an address or
delegated prefix to the client for a specified period of time.
message
A unit of data carried as the payload of a UDP datagram, exchanged
among DHCP servers, relay agents, and clients.
Reconfigure key
A key supplied to a client by a server. Used to provide security
for Reconfigure messages (see Section 20.4 for use cases for the
reconfigure key).
relaying
A DHCP relay agent relays DHCP messages between DHCP participants.
retransmission
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.
RKAP
The Reconfiguration Key Authentication Protocol (see
Section 20.4).
singleton option
An option that is allowed to appear only once as a top-level
option or at any encapsulation level. Most options are
singletons.
T1
The time interval after which the client is expected to contact
the server that did the assignment to extend (renew) the lifetimes
of the addresses assigned (via IA_NA option(s)) and/or prefixes
delegated (via IA_PD option(s)) to the client. T1 is expressed as
an absolute value in messages (in seconds), is conveyed within IA
containers (currently the IA_NA and IA_PD options), and is
interpreted as a time interval since the message's reception. The
value stored in the T1 field in IA options is referred to as the
T1 value. The actual time when the timer expires is referred to
as the T1 time.
T2
The time interval after which the client is expected to contact
any available server to extend (rebind) the lifetimes of the
addresses assigned (via IA_NA option(s)) and/or prefixes delegated
(via IA_PD option(s)) to the client. T2 is expressed as an
absolute value in messages (in seconds), is conveyed within IA
containers (currently the IA_NA and IA_PD options), and is
interpreted as a time interval since the message's reception. The
value stored in the T2 field in IA options is referred to as the
T2 value. The actual time when the timer expires is referred to
as the T2 time.
top-level option
An option conveyed in a DHCP message directly, i.e., not
encapsulated in any other option, as described in Section 9 of
[RFC7227].
transaction ID
An opaque value used to match responses with replies initiated by
either a client or a server.