Internet Engineering Task Force J. Bound
INTERNET DRAFT Nokia
DHC Working Group M. Carney
Obsoletes: draft-ietf-dhc-dhcpv6-18.txt Sun Microsystems, Inc
C. Perkins
Nokia Research Center
R. Droms(ed.)
Cisco Systems
15 April 2001
Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
draft-ietf-dhc-dhcpv6-18.txt
Status of This Memo
This document is a submission by the Dynamic Host Configuration
Working Group of the Internet Engineering Task Force (IETF). Comments
should be submitted to the dhcp-v6@bucknell.edu mailing list.
Distribution of this memo is unlimited.
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at
any time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at:
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at:
http://www.ietf.org/shadow.html.
Abstract
The Dynamic Host Configuration Protocol for IPv6 (DHCP) enables
DHCP servers to pass configuration parameters such as IPv6 network
addresses to IPv6 nodes. It offers the capability of automatic
allocation of reusable network addresses and additional configuration
flexibility. This protocol is a stateful counterpart to "IPv6
Stateless Address Autoconfiguration" [13], and can be used separately
or concurrently with the latter to obtain configuration parameters.
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Contents
Status of This Memo i
Abstract i
1. Introduction 1
2. Requirements 1
3. Background 1
4. Design Goals 3
5. Non-Goals 3
6. Terminology 4
6.1. IPv6 Terminology . . . . . . . . . . . . . . . . . . . . 4
6.2. DHCP Terminology . . . . . . . . . . . . . . . . . . . . 5
7. DHCP Constants 6
7.1. Multicast Addresses . . . . . . . . . . . . . . . . . . . 7
7.2. UDP ports . . . . . . . . . . . . . . . . . . . . . . . . 7
7.3. DHCP message types . . . . . . . . . . . . . . . . . . . 7
7.4. Error Values . . . . . . . . . . . . . . . . . . . . . . 9
7.4.1. Generic Error Values . . . . . . . . . . . . . . 9
7.4.2. Server-specific Error Values . . . . . . . . . . 9
7.5. Configuration Variables . . . . . . . . . . . . . . . . . 10
8. Overview 10
8.1. How does a node know to use DHCP? . . . . . . . . . . . . 10
8.2. What if the client and server(s) are on different links? 10
8.3. How does a client request configuration parameters from
servers? . . . . . . . . . . . . . . . . . . . . . . . 11
8.4. How do clients and servers identify and manage addresses? 12
8.5. Can a client release its assigned addresses before the lease
expires? . . . . . . . . . . . . . . . . . . . . . . . 12
8.6. What if the client determines one or more of its assigned
addresses are already being used by another client? . 12
8.7. How are clients notified of server configuration changes? 12
9. Message Formats 13
9.1. DHCP Solicit Message Format . . . . . . . . . . . . . . . 13
9.2. DHCP Advertise Message Format . . . . . . . . . . . . . . 14
9.3. DHCP Request Message Format . . . . . . . . . . . . . . . 14
9.4. DHCP Confirm Message Format . . . . . . . . . . . . . . . 15
9.5. DHCP Renew Message Format . . . . . . . . . . . . . . . . 15
9.6. DHCP Rebind Message Format . . . . . . . . . . . . . . . 15
9.7. DHCP Reply Message Format . . . . . . . . . . . . . . . . 16
9.8. DHCP Release Message Format . . . . . . . . . . . . . . . 16
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9.9. DHCP Decline Message Format . . . . . . . . . . . . . . . 17
9.10. DHCP Reconfigure-init Message Format . . . . . . . . . . 17
10. Relay messages 17
10.1. Relay-forward message . . . . . . . . . . . . . . . . . . 18
10.2. Relay-reply message . . . . . . . . . . . . . . . . . . . 18
11. Identity association 19
12. DHCP Server Solicitation 19
12.1. Solicit Message Validation . . . . . . . . . . . . . . . 19
12.2. Advertise Message Validation . . . . . . . . . . . . . . 19
12.3. Client Behavior . . . . . . . . . . . . . . . . . . . . . 19
12.3.1. Creation and sending of the Solicit message . . . 20
12.3.2. Time out and retransmission of Solicit Messages . 20
12.3.3. Receipt of Advertise messages . . . . . . . . . . 20
12.4. Server Behavior . . . . . . . . . . . . . . . . . . . . . 21
12.4.1. Receipt of Solicit messages . . . . . . . . . . . 21
12.4.2. Creation and sending of Advertise messages . . . 21
13. DHCP Client-Initiated Configuration Exchange 22
13.1. Client Message Validation . . . . . . . . . . . . . . . . 23
13.2. Server Message Validation . . . . . . . . . . . . . . . . 23
13.3. Client Behavior . . . . . . . . . . . . . . . . . . . . . 24
13.3.1. Creation and sending of Request messages . . . . 24
13.3.2. Creation and sending of Confirm messages . . . . 25
13.3.3. Creation and sending of Renew messages . . . . . 26
13.3.4. Creation and sending of Rebind messages . . . . . 27
13.3.5. Receipt of Reply message in response to a Reply,
Confirm, Renew or Rebind message . . . . . 28
13.3.6. Creation and sending of Release messages . . . . 30
13.3.7. Time out and retransmission of Release Messages . 30
13.3.8. Creation and sending of Decline messages . . . . 30
13.3.9. Time out and retransmission of Decline Messages . 31
13.3.10. Receipt of Reply message in response to a Release
message . . . . . . . . . . . . . . . . . 31
13.4. Server Behavior . . . . . . . . . . . . . . . . . . . . . 31
13.4.1. Receipt of Request messages . . . . . . . . . . . 32
13.4.2. Receipt of Confirm messages . . . . . . . . . . . 32
13.4.3. Receipt of Renew messages . . . . . . . . . . . . 33
13.4.4. Receipt of Rebind messages . . . . . . . . . . . 34
13.4.5. Receipt of Release messages . . . . . . . . . . . 35
13.4.6. Sending of Reply messages . . . . . . . . . . . . 35
14. DHCP Server-Initiated Configuration Exchange 36
14.1. Reconfigure-init Message Validation . . . . . . . . . . . 36
14.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 36
14.2.1. Creation and sending of Reconfigure-init messages 36
14.2.2. Time out and retransmission of unicast
Reconfigure-init messages . . . . . . . . 37
14.2.3. Time out and retransmission of multicast
Reconfigure-init messages . . . . . . . . 38
14.2.4. Receipt of Request messages . . . . . . . . . . . 38
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14.3. Client Behavior . . . . . . . . . . . . . . . . . . . . . 38
14.3.1. Receipt of Reconfigure-init messages . . . . . . 38
14.3.2. Creation and sending of Request messages . . . . 38
14.3.3. Time out and retransmission of Request messages . 39
14.3.4. Receipt of Reply messages . . . . . . . . . . . . 39
15. Relay Behavior 39
15.1. Relaying of client messages . . . . . . . . . . . . . . . 39
15.2. Relaying of server messages . . . . . . . . . . . . . . . 40
16. DHCP options 40
16.1. Format of DHCP options . . . . . . . . . . . . . . . . . 40
16.2. Identity association option . . . . . . . . . . . . . . . 41
16.3. Option request option . . . . . . . . . . . . . . . . . . 43
16.4. Client message option . . . . . . . . . . . . . . . . . . 43
16.5. Server message option . . . . . . . . . . . . . . . . . . 44
16.6. Retransmission parameter option . . . . . . . . . . . . . 44
16.7. Reconfigure-delay option . . . . . . . . . . . . . . . . 44
16.8. DSTM Global IPv4 Address Option . . . . . . . . . . . . . 45
16.9. Authentication option . . . . . . . . . . . . . . . . . . 46
17. DHCP Client Implementor Notes 46
17.1. Primary Interface . . . . . . . . . . . . . . . . . . . . 46
17.2. Advertise Message and Configuration Parameter Caching . . 46
17.3. Time out and retransmission variables . . . . . . . . . . 47
17.4. Server Preference . . . . . . . . . . . . . . . . . . . . 47
18. DHCP Server Implementor Notes 47
18.1. Client Bindings . . . . . . . . . . . . . . . . . . . . . 47
18.2. Reconfigure-init Considerations . . . . . . . . . . . . . 47
18.2.1. Reliable transmission of multicast Reconfigure-init
messages . . . . . . . . . . . . . . . . . 48
18.3. Server Preference . . . . . . . . . . . . . . . . . . . . 48
18.4. Request Message Transaction-ID Cache . . . . . . . . . . 48
19. DHCP Relay Implementor Notes 48
20. Open Issues for Working Group Discussion 49
20.1. Authentication . . . . . . . . . . . . . . . . . . . . . 49
20.2. Identification of IAs by servers . . . . . . . . . . . . 49
20.3. DHCP-DNS interaction . . . . . . . . . . . . . . . . . . 49
20.4. Temporary addresses . . . . . . . . . . . . . . . . . . . 49
20.5. Use of term "agent" . . . . . . . . . . . . . . . . . . . 49
20.6. Client behavior when response to Rebind is not received . 49
20.7. Additional options . . . . . . . . . . . . . . . . . . . 50
20.8. Operational parameters . . . . . . . . . . . . . . . . . 50
21. Security 50
22. Year 2000 considerations 50
23. IANA Considerations 50
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24. Acknowledgments 51
A. Comparison between DHCPv4 and DHCPv6 51
B. Full Copyright Statement 53
C. Changes in this draft 53
C.1. New messages for confirming addresses and extending the lease
on an IA . . . . . . . . . . . . . . . . . . . . . . . 54
C.2. New message formats . . . . . . . . . . . . . . . . . . . 54
C.3. Renamed Server-forward message . . . . . . . . . . . . . 54
C.4. Clarified relay forwarding of messages . . . . . . . . . 54
C.5. Addresses and options in Advertise messages . . . . . . . 54
C.6. Clarification of IA option format . . . . . . . . . . . . 54
C.7. Specification of transaction ID in Solicit message . . . 54
C.8. Edits to definitions . . . . . . . . . . . . . . . . . . 55
C.9. Relay agent messages . . . . . . . . . . . . . . . . . . 55
C.10. Relay agent behavior . . . . . . . . . . . . . . . . . . 55
C.11. Transmission of all client messages through relays . . . 55
C.12. Reconfigure-init messages . . . . . . . . . . . . . . . . 55
C.13. Ordering of sections . . . . . . . . . . . . . . . . . . 55
C.14. DSTM option . . . . . . . . . . . . . . . . . . . . . . . 55
C.15. Message and option numbering . . . . . . . . . . . . . . 55
C.16. Inclusion of IAs in Solicit message by client . . . . . . 56
C.17. Clarification of destination of client messages . . . . . 56
C.18. Clarification of client use of Confirm messages . . . . . 56
Chair's Address 58
Author's Address 58
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1. Introduction
This document describes DHCP for IPv6 (DHCP), a UDP [12]
client/server protocol designed to reduce the cost of management
of IPv6 nodes in environments where network managers require more
control over the allocation of IPv6 addresses and configuration
of network stack parameters than that offered by "IPv6 Stateless
Autoconfiguration" [13]. DHCP is a stateful counterpart to
stateless autoconfiguration. Note that both stateful and stateless
autoconfiguration can be used concurrently in the same environment,
leveraging the strengths of both mechanisms in order to reduce the
cost of ownership and management of network nodes.
DHCP reduces the cost of ownership by centralizing the management
of network resources such as IP addresses, routing information, OS
installation information, directory service information, and other
such information on a few DHCP servers, rather than distributing such
information in local configuration files among each network node.
DHCP is designed to be easily extended to carry new configuration
parameters through the addition of new DHCP "options" defined to
carry this information.
Those readers familiar with DHCP for IPv4 [6] will find DHCP for IPv6
provides a superset of features, and benefits from the additional
features of IPv6 and freedom from BOOTP [4]-backward compatibility
constraints. For more information about the differences between DHCP
for IPv6 and DHCP for IPv4, see Appendix A.
2. Requirements
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in [2].
This document also makes use of internal conceptual variables
to describe protocol behavior and external variables that an
implementation must allow system administrators to change. The
specific variable names, how their values change, and how their
settings influence protocol behavior are provided to demonstrate
protocol behavior. An implementation is not required to have them in
the exact form described here, so long as its external behavior is
consistent with that described in this document.
3. Background
Related work in IPv6 that would best serve an implementor to study
is the IPv6 Specification [5], the IPv6 Addressing Architecture [7],
IPv6 Stateless Address Autoconfiguration [13], IPv6 Neighbor
Discovery Processing [10], and Dynamic Updates to DNS [15]. These
specifications enable DHCP to build upon the IPv6 work to provide
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both robust stateful autoconfiguration and autoregistration of DNS
Host Names.
The IPv6 Specification provides the base architecture and design of
IPv6. A key point for DHCP implementors to understand is that IPv6
requires that every link in the Internet have an MTU of 1280 octets
or greater (in IPv4 the requirement is 68 octets). This means that
a UDP packet of 536 octets will always pass through an internetwork
(less 40 octets for the IPv6 header), as long as there are no IP
options prior to the UDP header in the packet. But, IPv6 does not
support fragmentation at routers, so that fragmentation takes place
end-to-end between hosts. If a DHCP implementation needs to send a
packet greater than 1500 octets it can either fragment the UDP packet
into fragments of 1500 octets or less, or use Path MTU Discovery [8]
to determine the size of the packet that will traverse a network
path.
DHCP clients use Path MTU discovery when they have an address of
sufficient scope to reach the DHCP server. If a DHCP client does not
have such an address, that client MUST fragment its packets if the
resultant message size is greater than the minimum 1280 octets.
Path MTU Discovery for IPv6 is supported for both UDP and TCP and
can cause end-to-end fragmentation when the PMTU changes for a
destination.
The IPv6 Addressing Architecture specification [7] defines the
address scope that can be used in an IPv6 implementation, and the
various configuration architecture guidelines for network designers
of the IPv6 address space. Two advantages of IPv6 are that support
for multicast is required, and nodes can create link-local addresses
during initialization. This means that a client can immediately use
its link-local address and a well-known multicast address to begin
communications to discover neighbors on the link. For instance, a
client can send a Solicit message and locate a server or relay.
IPv6 Stateless Address Autoconfiguration [13] (Addrconf) specifies
procedures by which a node may autoconfigure addresses based on
router advertisements [10], 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 addrconf is a design
requirement of DHCP (see Section 4).
IPv6 Neighbor Discovery [10] is the node discovery protocol in IPv6
which replaces and enhances functions of ARP [11]. To understand
IPv6 and Addrconf it is strongly recommended that implementors
understand IPv6 Neighbor Discovery.
Dynamic Updates to DNS [15] 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
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not only support autoconfiguration, but also autoregistration in
IPv6.
4. Design Goals
- DHCP is a mechanism rather than a policy. Network administrators
set their administrative policies through the configuration
parameters they place upon the DHCP servers in the DHCP domain
they're managing. DHCP is simply used to deliver parameters
according to that policy to each of the DHCP clients within the
domain.
- DHCP is compatible with IPv6 stateless autoconf [13].
- DHCP does not require manual configuration of network parameters
on DHCP clients, except in cases where such configuration is
needed for security reasons. A node configuring itself using
DHCP should require no user intervention.
- DHCP does not require a server on each link. To allow for scale
and economy, DHCP must work across DHCP relays.
- DHCP coexists with statically configured, non-participating nodes
and with existing network protocol implementations.
- DHCP clients can operate on a link without IPv6 routers present.
- DHCP will provide the ability to renumber network(s) when
required by network administrators [3].
- A DHCP client can make multiple, different requests for
configuration parameters when necessary from one or more DHCP
servers at any time.
- DHCP will contain the appropriate time out and retransmission
mechanisms to efficiently operate in environments with high
latency and low bandwidth characteristics.
5. Non-Goals
This specification explicitly does not cover the following:
- Specification of a DHCP server to server protocol.
- How a DHCP server stores its DHCP data.
- How to manage a DHCP domain or DHCP server.
- How a DHCP relay is configured or what sort of information it may
log.
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6. Terminology
6.1. IPv6 Terminology
IPv6 terminology relevant to this specification from the IPv6
Protocol [5], IPv6 Addressing Architecture [7], and IPv6 Stateless
Address Autoconfiguration [13] is included below.
address An IP layer identifier for an interface or
a set of interfaces.
unicast address An identifier for a single interface.
A packet sent to a unicast address is
delivered to the interface identified by
that address.
multicast address An identifier for a set of interfaces
(typically belonging to different nodes).
A packet sent to a multicast address is
delivered to all interfaces identified by
that address.
host Any node that is not a router.
IP Internet Protocol Version 6 (IPv6). The
terms IPv4 and IPv6 are used only in
contexts where it is necessary to avoid
ambiguity.
interface A node's attachment to a link.
link A communication facility or medium over
which nodes can communicate at the link
layer, i.e., the layer immediately below
IP. Examples are Ethernet (simple or
bridged); Token Ring; PPP links, X.25,
Frame Relay, or ATM networks; and Internet
(or higher) layer "tunnels", such as
tunnels over IPv4 or IPv6 itself.
link-layer identifier A link-layer identifier for an interface.
Examples include IEEE 802 addresses for
Ethernet or Token Ring network interfaces,
and E.164 addresses for ISDN links.
link-local address An IP address having link-only
scope, indicated by having the prefix
(FE80::0000/64), that can be used to reach
neighboring nodes attached to the same
link. Every interface has a link-local
address.
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message A unit of data carried in a packet,
exchanged between DHCP agents and clients.
neighbor A node attached to the same link.
node A device that implements IP.
packet An IP header plus payload.
prefix The initial bits of an address, or a set
of IP address that share the same initial
bits.
prefix length The number of bits in a prefix.
router A node that forwards IP packets not
explicitly addressed to itself.
6.2. DHCP Terminology
Terminology specific to DHCP can be found below.
abort status A status value returned to the
application that has invoked a DHCP
client operation, indicating anything
other than success.
agent address The address of a neighboring DHCP Agent
on the same link as the DHCP client.
binding A binding (or, client binding) is a
group of server data records containing
the server's information about the
addresses in an IA and any other
configuration information assigned to
the client. A binding is indexed by the
tuple <prefix, DUID>, where the 'prefix'
is a prefix assigned to the link to
which the client is attached and 'DUID'
is the DUID from the IA in the binding.
DISCUSSION:
The indexing of an IA by <prefix,
DUID> is still under discussion.
DHCP Dynamic Host Configuration Protocol
for IPv6. The terms DHCPv4 and DHCPv6
are used only in contexts where it is
necessary to avoid ambiguity.
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configuration parameter An element of the configuration
information set on the server and
delivered to the client using DHCP.
Such parameters may be used to carry
information to be used by a node to
configure its network subsystem and
enable communication on a link or
internetwork, for example.
DHCP client (or client) A node that initiates requests on a link
to obtain configuration parameters from
one or more DHCP servers.
DHCP domain A set of links managed by DHCP and
operated by a single administrative
entity.
DHCP server (or server) A server is a node that responds to
requests from clients, and may or
may not be on the same link as the
client(s).
DHCP relay (or relay) A node that acts as an intermediary to
deliver DHCP messages between clients
and servers, and is on the same link as
a client.
DHCP agent (or agent) Either a DHCP server on the same link as
a client, or a DHCP relay.
DUID A DHCP unique identifier for a client.
DISCUSSION:
Rules for choosing a DUID are TBD.
Identity association (IA) A collection of addresses assigned to
a client. Each IA has an associated
DUID. An IA may have 0 or more addresses
associated with it.
transaction-ID An unsigned integer to match responses
with replies initiated either by a
client or server.
7. DHCP Constants
This section describes various program and networking constants used
by DHCP.
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7.1. Multicast Addresses
DHCP makes use of the following multicast addresses:
All DHCP Agents address: FF02::1:2 This link-scoped multicast
address is used by clients to communicate with the
on-link agent(s) when they do not know those agents'
link-local address(es). All agents (servers and
relays) are members of this multicast group.
All DHCP Servers address: FF05::1:3 This site-scoped multicast
address is used by clients or relays to communicate
with server(s), either because they want to send
messages to all servers or because they do not know
the server(s) unicast address(es). Note that in order
for a client to use this address, it must have an
address of sufficient scope to be reachable by the
server(s). All servers within the site are members of
this multicast group.
DISCUSSION:
Is there a requirement for a site-scoped "All DHCP Clients"
multicast address, to be used as the default in sending
Reconfigure messages.
7.2. UDP ports
DHCP uses the following destination UDP [12] port numbers. While
source ports MAY be arbitrary, client implementations SHOULD permit
their specification through a local configuration parameter to
facilitate the use of DHCP through firewalls.
546 Client port. Used by servers as the destination port
for messages sent to clients and relays. Used by relay
agents as the destination port for messages sent to
clients.
547 Agent port. Used as the destination port by clients
for messages sent to agents. Used as the destination
port by relays for messages sent to servers.
7.3. DHCP message types
DHCP defines the following message types. More detail on these
message types can be found in Section 9. Message types 0 and
TBD--255 are reserved and MUST be silently ignored. The message code
for each message type is shown with the message name.
SOLICIT (1) The DHCP Solicit (or Solicit) message is used by
clients to locate servers.
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ADVERTISE (2) The DHCP Advertise (or Advertise) message is used
by servers responding to Solicits.
REQUEST (3) The DHCP Request (or Request) message is used by
clients to request configuration parameters from
servers.
CONFIRM (4) The DHCP Confirm (or Confirm) message is used by
clients to confirm that the addresses assigned
to an IA and the lifetimes for those addresses,
as well as the current configuration parameters
assigned by the server to the client are still
valid.
RENEW (5) The DHCP Renew (or Renew) message is used by
clients to obtain the addresses assigned to an IA
and the lifetimes for those addresses, as well as
the current configuration parameters assigned by
the server to the client. A client sends a Renew
message to the server that originally assigned the
IA when the lease on an IA is about to expire.
REBIND (6) The DHCP Rebind (or Rebind) message is used by
clients to obtain the addresses assigned to an IA
and the lifetimes for those addresses, as well
as the current configuration parameters assigned
by the server to the client. A clients sends a
Rebind message to all available DHCP servers when
the lease on an IA is about to expire.
REPLY (7) The DHCP Reply (or Reply) message is used by
servers responding to Request, Confirm, Renew,
Rebind, Release and Decline messages. In the case
of responding to a Request, Confirm, Renew or
Rebind message, the Reply contains configuration
parameters destined for the client.
RELEASE (8) The DHCP Release (or Release) message is used by
clients to return one or more IP addresses to
servers.
DECLINE (9) The DHCP Decline (or Decline) message is used by
clients to indicate that the client has determined
that one or more addresses in an IA are already in
use on the link to which the client is connected.
RECONFIG (10) The DHCP Reconfigure-init (or Reconfigure-init)
message is sent by server(s) to inform
client(s) that the server(s) has new or updated
configuration parameters, and that the client(s)
are to initiate a Request/Reply transaction with
the server(s) in order to receive the updated
information.
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RELAY-FORW (11) The DHCP Relay-forward (or Relay-forward) message
is used by relays to forward client messages to
servers. The client message is encapsulated in an
option in the Relay-forward message.
RELAY-REPL (12) The DHCP Relay-reply (or Relay-reply) message
is used by servers to send messages to clients
through a relay. The server encapsulates the
client message as an option in the Relay-reply
message, which the relay extracts and forwards to
the client.
7.4. Error Values
This section describes error values exchanged between DHCP
implementations.
7.4.1. Generic Error Values
The following symbolic names are used between client and server
implementations to convey error conditions. The following table
contains the actual numeric values for each name. Note that the
numeric values do not start at 1, nor are they consecutive. The
errors are organized in logical groups.
_______________________________________________________________
|Error_Name___|Error_ID|_Description_________________________|_
|Success______|00______|_Success_____________________________|_
|UnspecFail___|16______|_Failure,_reason_unspecified_________|_
|AuthFailed___|17______|_Authentication_failed_or_nonexistent|_
|PoorlyFormed_|18______|_Poorly_formed_message_______________|_
|Unavail______|19______|_Addresses_unavailable_______________|_
7.4.2. Server-specific Error Values
The following symbolic names are used by server implementations to
convey error conditions to clients. The following table contains the
actual numeric values for each name.
_______________________________________________________________
|Error_Name____|Error_ID|_Description________________________|_
|NoBinding_____|20______|_Client_record_(binding)_unavailable|_
|ConfNoMatch___|21______|_Client_record_Confirm_not_match_IA_|_
|RenwNoMatch___|22______|_Client_record_Renew_not_match_IA___|_
|RebdNoMatch___|23______|_Client_record_Rebind_not_match_IA__|_
|InvalidSource_|24______|_Invalid_Client_IP_address__________|_
|NoServer______|25______|_Relay_cannot_find_Server_Address___|_
|ICMPError_____|64______|_Server_unreachable_(ICMP_error)____|_
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7.5. Configuration Variables
This section presents a table of client and server configuration
variables and the default or initial values for these variables. The
client-specific variables MAY be configured on the server and MAY be
delivered to the client through the "DHCP Retransmission Parameter
Option" in a Reply message.
_________________________________________________________________________
|Parameter__________|Default|_Description______________________________|_
|MIN_SOL_DELAY______|1______|_MIN_(secs)_to_delay_1st_mesg_____________|_
|MAX_SOL_DELAY______|5______|_MAX_(secs)_to_delay_1st_mesg_____________|_
|ADV_MSG_TIMEOUT____|500____|_SOL_Retrans_timer_(msecs)________________|_
|ADV_MSG_MAX________|30_____|_MAX_timer_value_(secs)___________________|_
|SOL_MAX_ATTEMPTS___|-1_____|_MAX_attempts_(-1_=_infinite)_____________|_
|REP_MSG_TIMEOUT____|250____|_Retrans_timer_(msecs)_for_Reply__________|_
|QRY_MSG_ATTEMPTS___|10_____|_MAX_Request/Confirm/Renew/Rebind_attempts|_
|REL_MSG_ATTEMPTS___|5______|_MAX_Release/Decline_attempts_____________|_
|RECREP_MSG_TIMEOUT_|2000___|_Retrans_timer_(msecs)____________________|_
|REC_MSG_ATTEMPTS___|10_____|_Reconfigure_attempts_____________________|_
|REC_REP_MIN________|5______|_Minimum_pause_interval_(secs)____________|_
|REC_REP_MAX________|7200___|_Maximum_pause_interval_(secs)____________|_
|REC_THRESHOLD______|100____|_%_of_required_clients____________________|_
|SRVR_PREF_WAIT_____|2______|_Advertise_Collect_timer_(secs)___________|_
8. Overview
This section provides a general overview of the interaction between
the functional entities of DHCP. The overview is organized as a
series of questions and answers. Details of DHCP such as message
formats and retransmissions can be found in later sections of this
document.
8.1. How does a node know to use DHCP?
An unconfigured node determines that it is to use DHCP for
configuration of an interface by detecting the presence (or absence)
of routers on the link. If router(s) are present, the node examines
router advertisements to determine if DHCP should be used to
configure the interface. If there are no routers present, then
the node MUST use DHCP to configure the interface. Detail on
this process can be found in neighbor discovery [10] and stateless
autoconfiguration [13].
8.2. What if the client and server(s) are on different links?
Use of DHCP in such environments requires one or more DHCP relays
be set up on the client's link, because a client may only have a
link-local address. Relays receive messages from the client and
forward them to some set of servers within the DHCP domain. The
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client message is forwarded verbatim as an option in the message
from the relay to the server. A relay will include one of its own
addresses (of sufficient scope) from the interface on the same link
as the client, as well as the prefix length of that address, in its
message to the server. Servers receiving the forwarded traffic
use this information to aid in selecting configuration parameters
appropriate to the client's link.
Servers use relays to forward messages to clients. The message
intended for the client is carried as an option in the message to the
relay. The relay extracts the message from the optin and forwards it
to the client. Servers use the relay's address as the destination to
forward client-destined messages for final delivery by the relay.
Relays forward client messages to servers using some combination
of the All DHCP Servers site-local multicast address, some other
(perhaps a combination) of site-local multicast addresses set up
within the DHCP domain to include the servers in that domain, or a
list of unicast addresses for servers. The network administrator
makes relay configuration decisions based upon the topological
requirements (scope) of the DHCP domain they are managing. Note
that if the DHCP domain spans more than the site-local scope, then
the relays MUST be configured with global addresses for the client's
link so as to be reachable by servers outside the relays' site-local
environment.
8.3. How does a client request configuration parameters from servers?
To request configuration parameters, the client forms a Request
message, and sends it to the server either directly (the server is
on the same link as the client) or indirectly (through the on-link
relay). The client MAY include a Option Request Option 16.3 (ORO)
along with other options to request specific information from the
server. Note that the client MAY form multiple Request messages
and send each of them to different servers to request potentially
different information (perhaps based upon what was advertised) in
order to satisfy its needs. As a client's needs may change over time
(perhaps based upon an application's requirements), the client may
form additional Request messages to request additional information as
it is needed.
The server(s) respond with Reply messages containing the requested
configuration parameters, which can include status information
regarding the information requested by the client. The Reply MAY
also include additional information, such as a reconfiguration event
multicast group for the client to join to monitor reconfiguration
events, as described in section 8.7.
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8.4. How do clients and servers identify and manage addresses?
Servers and clients manage addresses in groups called "identity
associations." Each identity associations is identified using a
unique identifier. An identity association may contain one or
more IPv6 addresses. DHCP servers assign addresses to identity
associations. DHCP clients use the addresses in an identity
association to configure interfaces. There is always at least one
identity association per interface that a client wishes to configure.
Each address in an IA has its own preferred and valid lifetime. Over
time, the server may change the characteristics of the addresses in
an IA; for example, by changing the preferred or valid lifetime for
an address in the IA. The server may also add or delete addresses
from an IA; for example, deleting old addresses and adding new
addresses to renumber a client. A client can request the current
list of addresses assigned to an IA from a server through an exchange
of protocol messages.
8.5. Can a client release its assigned addresses before the lease
expires?
A client forms a Release message, including options identifying
the IA to be released. The client sends the Release to the server
which assigned the addresses to the client initially. If that
server cannot be reached after a certain number of attempts (see
section 7.5), the client can abandon the Release attempt. In this
case, the address(es) in the IA will be reclaimed by the server(s)
when the lifetimes on the addresses expire.
8.6. What if the client determines one or more of its assigned addresses
are already being used by another client?
If the client determines through a mechanism like Duplicate Address
Detection [13] that the address it was assigned by the server is
already in use by another client, the client will form a Decline
message, including the option carrying the in-use address. The
option's status field MUST be set to the value reflecting the "in
use" status of the address.
8.7. How are clients notified of server configuration changes?
There are two possibilities. Either the clients discover the new
information when they revisit the server(s) to request additional
configuration information/extend the lifetime on an address. or
through a server-initiated event known as a reconfigure event.
The reconfiguration feature of DHCP offers network administrators
the opportunity to update configuration information on DHCP clients
whenever necessary. To signal the need for client reconfiguration,
the server will unicast a Reconfigure-init message to each
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client individually. The server may use multicast to signal the
reconfiguration to multiple clients simultaneously. (Note that
there is no mechanism defined in the protocol to guarantee that
every client actually performs a reconfiguration in response to a
multicast reconfigure-init message.) A Reconfigure-init is a trigger
which will cause the client(s) to initiate a standard Request/Reply
exchange with the server in order to acquire the new or updated
addresses.
9. Message Formats
Each DHCP message has an identical fixed format header; some messages
also allow a variable format area for options. Not all fields in
the header are used in every message. In this section, every field
is described for every message and fields that are not used in a
message are marked as "unused". All unused fields in a message MUST
be transmitted as zeroes and ignored by the receiver of the message.
The DHCP message header:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | preference | transaction-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| client-link-local-address |
| (16 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| server-address |
| (16 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. options .
| (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
9.1. DHCP Solicit Message Format
msg-type SOLICIT
preference (unused) MUST be 0
transaction-ID An unsigned integer generated by the
client used to identify this Solicit
message.
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client-link-local-address The link-local address of the
interface for which the client is
using DHCP.
server-address (unused) MUST be 0
options See section 16.
9.2. DHCP Advertise Message Format
msg-type ADVERTISE
preference An unsigned integer indicating a
server's willingness to provide
service to the client.
transaction-ID An unsigned integer used to identify
this Advertise message. Copied from
the client's Solicit message.
client-link-local-address The IP link-local address of the
client interface from which the client
issued the Solicit message.
server-address The IP address of the server that
generated this message. If the DHCP
domain crosses site boundaries, then
this address MUST be globally-scoped.
options See section 16.
9.3. DHCP Request Message Format
msg-type REQUEST
preference (unused) MUST be 0
transaction-ID An unsigned integer generated by the
client used to identify this Request
message.
client-link-local-address The link-local address of the client
interface from which the client will
issue the Request message.
server-address The IP address of the server to which
the this message is directed, copied
from an Advertise message.
options See section 16.
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9.4. DHCP Confirm Message Format
msg-type CONFIRM
preference (unused) MUST be 0
transaction-ID An unsigned integer generated by the
client used to identify this Confirm
message.
client-link-local-address The link-local address of the client
interface from which the client will
issue the Confirm message.
server-address MUST be zero.
options See section 16.
9.5. DHCP Renew Message Format
msg-type RENEW
preference (unused) MUST be 0
transaction-ID An unsigned integer generated by the
client used to identify this Renew
message.
client-link-local-address The link-local address of the client
interface from which the client will
issue the Renew message.
server-address The IP address of the server to which
this Renew message is directed, which
MUST be the address of the server from
which the IAs in this message were
originally assigned.
options See section 16.
9.6. DHCP Rebind Message Format
msg-type REBIND
preference (unused) MUST be 0
transaction-ID An unsigned integer generated by the
client used to identify this Rebind
message.
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client-link-local-address The link-local address of the client
interface from which the client will
issue the Rebind message.
server-address MUST be zero.
options See section 16.
9.7. DHCP Reply Message Format
msg-type REPLY
preference An unsigned integer indicating a
server's willingness to provide
service to the client.
transaction-ID An unsigned integer used to identify
this Reply message. Copied from the
client's Request, Confirm, Renew or
Rebind message.
client-link-local-address The link-local address of the
interface for which the client is
using DHCP.
server-address The IP address of the server.
If the DHCP domain crosses site
boundaries, then this address MUST be
globally-scoped.
options See section 16.
9.8. DHCP Release Message Format
msg-type RELEASE
preference (unused) MUST be 0
transaction-ID An unsigned integer generated by the
client used to identify this Release
message.
client-link-local-address The client's link-local address for
the interface from which the client
will send the Release message.
server-address The IP address of the server that
assigned the IA.
options See section 16.
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9.9. DHCP Decline Message Format
msg-type DECLINE
preference (unused) MUST be 0
transaction-ID An unsigned integer generated by the
client used to identify this Decline
message.
client-link-local-address The client's link-local address for
the interface from which the client
will send the Decline message.
server-address The IP address of the server that
assigned the addresses.
options See section 16.
9.10. DHCP Reconfigure-init Message Format
preference (unused) MUST be 0
transaction-ID An unsigned integer generated
by the server to identify this
Reconfigure-init message
client-link-local-address (unused) MUST be 0
server-address The IP address of the DHCP server
issuing the Reconfigure-init message.
MUST be of sufficient scope to be
reachable by all clients.
options See section 16.
10. Relay messages
Relay agents exchange messages with servers to forward messages
between clients and servers that are not connected to the same link.
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10.1. Relay-forward message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | prefix length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
| relay-address |
| |
| |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| options (variable number and length) .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
msg-type RELAY-FORW
prefix-length The length of the prefix in the address in the
"relay-address" field.
relay-address An address assigned to the interface through which
the message from the client was received.
options MUST include a "Client message option"; see
section 16.4.
10.2. Relay-reply message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | prefix length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
| relay-address |
| |
| |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| options (variable number and length) .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
msg-type RELAY-REPL
prefix-length The length of the prefix in the address in the
"relay-address" field.
relay-address An address identifying the interface through which
the message from the server should be forwarded;
copied from the "client-forward" message.
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options MUST include a "Server message option"; see
section 16.5.
11. Identity association
An "identity-association" (IA) is a construct through which a server
and a client can identify, group and manage IPv6 addresses. Each IA
consists of a DUID and a list of associated IPv6 addresses (the list
may be empty). A client associates an IA with one of its interfaces
and uses the IA to obtain IPv6 addresses for that interface from a
server.
See section 16.2 for the representation of an IA in a DHCP message.
12. DHCP Server Solicitation
This section describes how a client locates servers. The behavior
of client and server implementations is discussed, along with the
messages they use.
12.1. Solicit Message Validation
Clients MUST silently discard any received Solicit messages.
Agents MUST silently discard any received Solicit messages if the
"client-link-local-address" field does not contain a valid link-local
address.
12.2. Advertise Message Validation
Servers MUST discard any received Advertise messages.
Clients MUST discard any Advertise messages that meet any of the
following criteria:
o The "Transaction-ID" field value does not match the value the
client used in its Solicit message.
o The "client-link-local-address" field value does not match the
link-local address of the interface upon which the client sent
the Solicit message.
12.3. Client Behavior
Clients use the Solicit message to discover DHCP servers configured
to serve addresses on the link to which the client is attached.
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12.3.1. Creation and sending of the Solicit message
The client sets the "msg-type" field to SOLICIT, and places the
link-local address of the interface it wishes to configure in the
"client-link-local-address" field.
The client generates a transaction ID inserts this value in the
"transaction-ID" field.
The client MUST include options for any IAs to which the client is
expecting to have the server assign addresses. Because the client
does not have any IAs with addresses when sending a Solicit message,
all of the IAs MUST be empty. The client MAY include an Option
Request Option in the Solicit message. The client MUST NOT include
any other options except those specifically allowed as defined by
specific options.
The client sends the Solicit message to the All DHCP Agents
multicast address, destination port 547. The source port selection
can be arbitrary, although it SHOULD be possible using a client
configuration facility to set a specific source port value.
12.3.2. Time out and retransmission of Solicit Messages
The client's first Solicit message on the interface MUST be delayed
by a random amount of time between the interval of MIN_SOL_DELAY and
MAX_SOL_DELAY. This random delay desynchronizes clients which start
at the same time (e.g., after a power outage).
The client waits ADV_MSG_TIMEOUT, collecting Advertise messages.
If no Advertise messages are received, the client retransmits
the Solicit, and doubles the ADV_MSG_TIMEOUT value. This process
continues until either one or more Advertise messages are received or
ADV_MSG_TIMEOUT reaches the ADV_MSG_MAX value. Thereafter, Solicits
are retransmitted every ADV_MSG_MAX until SOL_MAX_ATTEMPTS have been
made, at which time the client stops trying to DHCP configure the
interface. An event external to DHCP is required to restart the DHCP
configuration process.
Default and initial values for MIN_SOL_DELAY, MAX_SOL_DELAY,
ADV_MSG_TIMEOUT, AND ADV_MSG_MAX are documented in section 7.5.
12.3.3. Receipt of Advertise messages
Upon receipt of one or more validated Advertise messages, the client
selects one or more Advertise messages based upon the following
criteria.
- Those Advertise messages with the highest server preference
value (see section 17.4) are preferred over all other Advertise
messages.
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- Within a group of Advertise messages with the same server
preference value, a client MAY select those servers whose
Advertise messages advertise information of interest to
the client. For example, one server may be advertising the
availability of IP addresses which have an address scope of
interest to the client.
Once a client has selected Advertise message(s), the client will
typically store information about each server, such as server
preference value, addresses advertised, when the advertisement was
received, and so on. Depending on the requirements of the client's
invoking user, the client MAY initiate a configuration exchange with
the server(s) immediately, or MAY defer this exchange until later.
If the client needs to select an alternate server in the case that a
chosen server does not respond, the client chooses the server with
the next highest preference value.
The client MAY choose a less-preferred server if that server has a
better set of advertised parameters, such as the available addresses
advertised in IAs.
12.4. Server Behavior
For this discussion, the server is assumed to have been configured in
an implementation specific manner. This configuration is assumed to
contain all network topology information for the DHCP domain, as well
as any necessary authentication information.
12.4.1. Receipt of Solicit messages
If the server receives a Solicit message, the client must be on the
same link as the server. If the server receives a Relay-forward
message containing a Solicit message, the client must be on the
link to which the prefix identified by the "relay-address" and
"prefix-length" fields in the Relay-forward message is assigned.
The server records the "relay-address" field from the Relay-forward
message and extracts the solicit message from the "client-message"
option.
If administrative policy permits the server to respond to a client on
that link, the server will generate and send an Advertise message to
the client.
12.4.2. Creation and sending of Advertise messages
The server sets the "msg-type" field to ADVERTISE and copies the
values of the following fields from the client's Solicit to the
Advertise message:
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o transaction-ID
o client-link-local-address
The server places one of its IP addresses (determined through
administrator setting) in the "server-address" field of the Advertise
message. The server sets the "preference" field according to its
configuration information. See section 18.3 for a description of
server preference.
The server MUST include options to the Advertise message containing
any addresses that would be assigned to IAs contained in the Solicit
message from the client. The server MAY include other options the
server will return to the client in a subsequent Reply message.
The information in these options will be used by the client in the
selection of a server if the client receives more than one Advertise
message.
If the Solicit message was received in a Relay-forward message, the
server constructs a Relay-reply message with the Advertise message in
the payload of a "server-message" option. The server unicasts the
Relay-reply message to the address in the "relay-address" field from
the Relay-forward message.
If the Solicit message was received directly by the server, the
server unicasts the Advertise message directly to the client using
the "client-link-local-address" field value as the destination
address. The Advertise message MUST be unicast through the interface
on which the Solicit message was received.
13. DHCP Client-Initiated Configuration Exchange
A client initiates a message exchange with a server or servers to
acquire or update configuration information of interest. The client
may initiate the configuration exchange as part of the operating
system configuration process or when requested to do so by the
application layer.
The client uses the following messages to initiate a configuration
event with a server or servers:
Request Obtain initial configuration information (from a server
identified in a previously received Advertise message)
when the client has no assigned addresses
Confirm Confirm the validity of assigned addresses and other
configuration changes through the server from which the
configuration information was obtained when the client's
assigned addresses may not be valid; for example, when
the client reboots or loses its connection to a link
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Renew Extend the lease on an IA through the server that
originally assigned the IA
Rebind Extend the lease on an IA through any server willing to
extend the lease
A client uses the Release/Reply message exchange to indicate to the
DHCP server that the client will no longer be using the addresses in
the released IA.
A client uses the Decline/Reply message exchange to indicate to the
DHCP server that the client has detected that one or more addresses
assigned by the server is already in use on the client's link.
13.1. Client Message Validation
Clients MUST silently discard any received client messages (Request,
Confirm, Renew, Rebind, Release or Decline messages).
Agents MUST discard any received client messages in which the
"client-link-local-address" field does not contain a valid link-local
address.
Servers MUST discard any received client messages in which the
"options" field contains an authentication option, and the server
cannot successfully authenticate the client.
Servers MUST discard any received Request, Renew, Release or Decline
message in which the "server-address" field value does not match any
of the server's addresses.
13.2. Server Message Validation
Servers MUST silently discard any received server messages (Reply or
Reconfigure-init messages).
Clients MUST discard any server messages that meet any of the
following criteria:
o The "transaction-ID" field value in the server message does
not match the value the client used in its Request or Release
message.
o The "client-link-local-address" field value in the server message
does not match the link-local address of the interface from which
the client sent in its Request, Confirm, Renew, Rebind, Release
or Decline message.
o The server message contains an authentication option, and the
client's attempt to authenticate the message fails.
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Relays MUST discard any Relay-reply message in which the
"client-link-local-address" in the encapsulated Reply message does
not contain a valid link-local address.
13.3. Client Behavior
A client will use Request, Confirm, Renew and Rebind messages to
acquire and confirm the validity of configuration information. A
client may initiate such an exchange automatically in order to
acquire the necessary network parameters to communicate with nodes
off-link. The client uses the server address information from
previous Advertise message(s) for use in constructing Request and
Renew message(s). Note that a client may request configuration
information from one or more servers at any time.
A client uses the Release message in the management of IAs when
the client has been instructed to release the IA prior to the IA
expiration time since it is no longer needed.
A client uses the Decline message when the client has determined
through DAD or some other method that one or more of the addresses
assigned by the server in the IA is already in use by a different
client.
13.3.1. Creation and sending of Request messages
If a client has no valid IPv6 addresses of sufficient scope to
communicate with a DHCP server, it may send a Request message to
obtain new addresses. The client includes one or more IAs in the
Request message, to which the server assigns new addresses. The
server then returns IA(s) to the client in a Reply message.
The client sets the "msg-type" field to REQUEST, and places
the link-local address of the interface it wishes to acquire
configuration information for in the "client-link-local-address"
field.
The client generates a transaction ID inserts this value in the
"transaction-ID" field.
The client places the address of the destination server in the
"server-address" field.
The client adds any appropriate options, including one or more IA
options (if the client is requesting that the server assign it some
network addresses). The list of addresses in each included IA MUST
be empty.
The client sends the Request message to the All DHCP Agents
multicast address, destination port 547. The source port selection
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can be arbitrary, although it SHOULD be possible using a client
configuration facility to set a specific source port value.
The server will respond to the Request message with a Reply
message. If no Reply message is received within REP_MSG_TIMEOUT
milliseconds, the client retransmits the Request with the same
transaction-ID, and doubles the REP_MSG_TIMEOUT value, and waits
again. The client continues this process until a Reply is received
or REQUEST_MSG_ATTEMPTS unsuccessful attempts have been made, at
which time the client MUST abort the configuration attempt. The
client SHOULD report the abort status to the application layer.
Default and initial values for REP_MSG_TIMEOUT and REQ_MSG_ATTEMPTS
are documented in section 7.5.
13.3.2. Creation and sending of Confirm messages
Whenever a client may have moved to a new link, its IPv6 addresses
may no longer be valid. Examples of times when a client may have
moved to a new link include:
o The client reboots
o The client is physically disconnected from a wired connection
o The client returns from sleep mode
o The client using a wireless technology changes cells
In any situation when a client may have moved to a new link, the
client MUST initiate a Confirm/Reply message exchange. The client
includes any IAs, along with the addresses associated with those IAs,
in its Confirm message. The server will indicate the acceptability
of the addresses with the status in the IA it returns to the client.
DISCUSSION:
This section used to allow servers to change the addresses
in an IA. Without some additional mechanism, servers
responding to Confirm messages can't change safely
change the addresses in IAs (although they can change
the lifetimes), because servers may send back different
addresses.
The client sets the "msg-type" field to CONFIRM, and places
the link-local address of the interface it wishes to acquire
configuration information for in the "client-link-local-address"
field.
The client generates a transaction ID inserts this value in the
"transaction-ID" field.
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The client sets the "server-address" field to 0.
The client adds any appropriate options, including one or more IA
options (if the client is requesting that the server confirm the
validity of some network addresses). If the client does include
any IA options, it MUST include the list of addresses the client
currently has associated with that IA.
The client sends the Confirm message to the All DHCP Agents
multicast address, destination port 547. The source port selection
can be arbitrary, although it SHOULD be possible using a client
configuration facility to set a specific source port value.
Servers will respond to the Confirm message with a Reply message. If
no Confirm message is received within REP_MSG_TIMEOUT milliseconds,
the client retransmits the Confirm with the same transaction-ID,
and doubles the REP_MSG_TIMEOUT value, and waits again. The client
continues this process until a Reply is received or QRY_MSG_ATTEMPTS
unsuccessful attempts have been made, at which time the client MUST
abort the configuration attempt. The client SHOULD report the abort
status to the application layer.
Default and initial values for REP_MSG_TIMEOUT and QRY_MSG_ATTEMPTS
are documented in section 7.5.
If the client receives no response to its Confirm message, it MAY
restart the configuration process by locating a DHCP server with an
Advertise message and sending a Request to that server, as described
in section 13.3.1.
13.3.3. Creation and sending of Renew messages
IPv6 addresses assigned to a client through an IA use the same
preferred and valid lifetimes as IPv6 addresses obtained through
stateless autoconfiguration. The server assigns preferred and valid
lifetimes to the IPv6 addresses it assigns to an IA. To extend those
lifetimes, the client sends a Request to the server containing an
"IA option" for the IA and its associated addresses. The server
determines new lifetimes for the addresses in the IA according to
the server's administrative configuration. The server may also add
new addresses to the IA. The server remove addresses from the IA by
setting the preferred and valid lifetimes of those addresses to zero.
The server controls the time at which the client contacts the server
to extend the lifetimes on assigned addresses through the T1 and
T2 parameters assigned to an IA. If the server does not assign an
explicit value to T1 or T2 for an IA, T1 defaults to 0.5 times the
shortest preferred lifetime of any address assigned to the IA and
T2 defaults to 0.875 times the shortest preferred lifetime of any
address assigned to the IA.
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At time T1 for an IA, the client initiates a Request/Reply message
exchange to extend the lifetimes on any addresses in the IA. The
client includes an IA option with all addresses currently assigned to
the IA in its Request message. The client multicasts this Request
message to the All DHCP Agents multicast address.
The client sets the "msg-type" field to RENEW, and places
the link-local address of the interface it wishes to acquire
configuration information for in the "client-link-local-address"
field.
The client generates a transaction ID inserts this value in the
"transaction-ID" field.
The client places the address of the destination server in the
"server-address" field.
The client adds any appropriate options, including one or more IA
options (if the client is requesting that the server extend the lease
on some IAs; note that the client may check the status of other
configuration parameters without asking for lease extensions). If
the client does include any IA options, it MUST include the list of
addresses the client currently has associated with that IA.
The client sends the Renew message to the All DHCP Agents multicast
address, destination port 547. The source port selection can
be arbitrary, although it SHOULD be possible using a client
configuration facility to set a specific source port value.
The server will respond to the Renew message with a Reply message.
If no Reply message is received within REP_MSG_TIMEOUT milliseconds,
the client retransmits the Renew with the same transaction-ID, and
doubles the REP_MSG_TIMEOUT value, and waits again. The client
continues this process until a Reply is received or until time T2 is
reached (see section 13.3.4).
Default and initial values for REP_MSG_TIMEOUT are documented in
section 7.5.
13.3.4. Creation and sending of Rebind messages
At time T2 for an IA (which will only be reached if the server to
which the Renew message was sent at time T1 has not responded),
the client initiates a Rebind/Reply message exchange. The client
includes an IA option with all addresses currently assigned to the IA
in its Rebind message. The client multicasts this message to the All
DHCP Agents multicast address.
The client sets the "msg-type" field to REBIND, and places
the link-local address of the interface it wishes to acquire
configuration information for in the "client-link-local-address"
field.
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The client generates a transaction ID inserts this value in the
"transaction-ID" field.
The client sets the "server-address" field to 0.
The client adds any appropriate options, including one or more IA
options. If the client does include any IA options (if the client is
requesting that the server extend the lease on some IAs; note that
the client may check the status of other configuration parameters
without asking for lease extensions), it MUST include the list of
addresses the client currently has associated with that IA.
The client sends the Rebind message to the All DHCP Agents multicast
address, destination port 547. The source port selection can
be arbitrary, although it SHOULD be possible using a client
configuration facility to set a specific source port value.
The server will respond to the Rebind message with a Reply message.
If no Reply message is received within REP_MSG_TIMEOUT milliseconds,
the client retransmits the Rebind with the same transaction-ID, and
doubles the REP_MSG_TIMEOUT value, and waits again. The client
continues this process until a Reply is received.
Default and initial values for REP_MSG_TIMEOUT are documented in
section 7.5.
DISCUSSION:
The client has several alternatives to choose from if it
receives no response to its Rebind message.
- When the lease on the IA expires, the client may choose
to use a Solicit message to locate a new DHCP server and
send a Request for the expired IA to the new server
- Some addresses in the IA may have lifetimes that extend
beyond the lease of the IA, so the client may choose
to continue to use those addresses; once all of the
addresses have expired, the client may choose to locate
a new DHCP server
- The client may have other addresses in other IAs, so the
client may choose to discard the expired IA and use the
addresses in the other IAs
13.3.5. Receipt of Reply message in response to a Reply, Confirm, Renew
or Rebind message
Upon the receipt of a valid Reply message in response to a
Request, Confirm, Renew or Rebind message, the client extracts the
configuration information contained in the Reply. If the "status"
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field contains a non-zero value, the client reports the error status
to the application layer.
The client records the T1 and T2 times for each IA in the Reply
message. The client records any addresses included with IAs in
the Reply message. The client updates the preferred and valid
lifetimes for the addresses in the IA from the lifetime information
in the IA option. The client leaves any addresses that the client
has associated with the IA that are not included in the IA option
unchanged.
Management of the specific configuration information is detailed in
the definition of each option, in section 16.
When the client receives an Unavail error status in an IA from the
server for a Request message the client will have to find a new
server to create an IA.
When the client receives a NoBinding error status in an IA from the
server for a Confirm message the client can assume it needs to send a
Request to reestablish an IA with the server.
When the client receives a Conf_NoMatch error status in an IA from
the server for a Confirm message the client can send a Renew message
to the server to extend the lease for the addresses.
When the client receives a NoBinding error status in an IA from the
server for a Renew message the client can assume it needs to send a
Request to reestablish an IA with the server.
When the client receives a Renw_NoMatch error status in an IA from
the server for a Renew message the client can assume it needs to send
a Request to reestablish an IA with the server.
When the client receives an Unavail error status in an IA from the
server for a Renew message the client can assume it needs to send a
Request to reestablish an IA with the server.
When the client receives a NoBinding error status in an IA from the
server for a Rebind message the client can assume it needs to send a
Request to reestablish an IA with the server or try another server.
When the client receives a Rebd_NoMatch error status in an IA from
the server for a Rebind message the client can assume it needs to
send a Request to reestablish an IA with the server or try another
server.
When the client receives an Unavail error status in an IA from the
server for a Rebind message the client can assume it needs to send a
Request to reestablish an IA with the server or try another server.
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13.3.6. Creation and sending of Release messages
The client sets the "msg-type" field to RELEASE, and places the
link-local address of the interface associated with the configuration
information it wishes to release in the "client-link-local-address"
field.
The client generates a transaction ID and places this value in the
"transaction-ID" field.
The client places the IP address of the server that allocated the
address(es) in the "server-address" field.
The client includes options containing the IAs it is releasing in the
"options" field. The addresses to be released MUST be included in
the IAs. The appropriate "status" field in the options MUST be set
to indicate the reason for the release.
If the client is configured to use authentication, the client
generates the appropriate authentication option, and adds this option
to the "options" field. Note that the authentication option MUST be
the last option in the "options" field. See section 16.9 for more
details about the authentication option.
The client send the Release message to the All DHCP Agents multicast
address.
13.3.7. Time out and retransmission of Release Messages
If no Reply message is received within REP_MSG_TIMEOUT milliseconds,
the client retransmits the Release, doubles the REP_MSG_TIMEOUT
value, and waits again. The client continues this process until a
Reply is received or REL_MSG_ATTEMPTS unsuccessful attempts have been
made, at which time the client SHOULD abort the release attempt.
The client SHOULD return the abort status to the application, if an
application initiated the release.
Default and initial values for REP_MSG_TIMEOUT and REL_MSG_ATTEMPTS
are documented in section 7.5.
Note that if the client fails to release the IA, the addresses
assigned to the IA will be reclaimed by the server when the lease
associated with it expires.
13.3.8. Creation and sending of Decline messages
The client sets the "msg-type" field to DECLINE, and places the
link-local address of the interface associated with the configuration
information it wishes to decline in the "client-link-local-address"
field.
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The client generates a transaction ID and places this value in the
"transaction-ID" field.
The client places the IP address of the server that allocated the
address(es) in the "server-address" field.
The client includes options containing the IAs it is declining in the
"options" field. The addresses to be released MUST be included in
the IAs. The appropriate "status" field in the options MUST be set
to indicate the reason for declining the address.
If the client is configured to use authentication, the client
generates the appropriate authentication option, and adds this option
to the "options" field. Note that the authentication option MUST be
the last option in the "options" field. See section 16.9 for more
details about the authentication option.
The client send the Decline message to the All DHCP Agents multicast
address.
13.3.9. Time out and retransmission of Decline Messages
If no Reply message is received within REP_MSG_TIMEOUT milliseconds,
the client retransmits the Decline, doubles the REP_MSG_TIMEOUT
value, and waits again. The client continues this process until a
Reply is received or REL_MSG_ATTEMPTS unsuccessful attempts have
been made, at which time the client SHOULD abort the attempt to
decline the address. The client SHOULD return the abort status to
the application, if an application initiated the release.
Default and initial values for REP_MSG_TIMEOUT and REL_MSG_ATTEMPTS
are documented in section 7.5.
13.3.10. Receipt of Reply message in response to a Release message
Upon receipt of a valid Reply message, the client can consider the
Release event successful, and SHOULD return the successful status to
the application layer, if an application initiated the release.
13.4. Server Behavior
For this discussion, the Server is assumed to have been configured in
an implementation specific manner with configuration of interest to
clients.
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13.4.1. Receipt of Request messages
Upon the receipt of a valid Request message from a client the server
can respond to, (implementation-specific administrative policy
satisfied) the server scans the options field.
The server then constructs a Reply message and sends it to the
client.
The server SHOULD process each option for the client in an
implementation-specific manner. The server MUST construct a Reply
message containing the following values:
msg-type REPLY
preference Enter the servers preference to
provide services to the client.
transaction-ID Enter the transaction-ID from the
Request message.
client-link-local address Enter the client-link-local address
from the Request message.
server address Enter the IP address of the server.
When the server receives a Request and IA option is included the
client is requesting the configuration of a new IA by the server.
The server MUST take the clients IA and associate a binding for
that client in an implementation-specific manner within the servers
configuration parameter database for DHCP clients.
If the server cannot provide addresses to the client it SHOULD send
back an empty IA to the client with the status field set to Unavail.
If the server can provide addresses to the client it MUST send back
the IA to the client with all fields entered and a status of Success,
and add the IA as a new client binding.
The server adds options to the Reply message for any other
configuration information to be assigned to the client.
13.4.2. Receipt of Confirm messages
Upon the receipt of a valid Confirm message from a client the server
can respond to, (implementation-specific administrative policy
satisfied) the server scans the options field.
The server then constructs a Reply message and sends it to the
client.
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The server SHOULD process each option for the client in an
implementation-specific manner. The server MUST construct a Reply
message containing the following values:
msg-type REPLY
preference Enter the servers preference to
provide services to the client.
transaction-ID Enter the transaction-ID from the
Confirm message.
client-link-local address Enter the client-link-local address
from the Confirm message.
server address Enter the server's address.
When the server receives a Confirm and an IA option is included the
client is requesting confirmation that the addresses in the IA are
valid. The server SHOULD locate the clients binding and verify the
information in the IA from the client matches the information stored
for that client.
If the server cannot find a client entry for this IA the server
SHOULD return an empty IA with status set to NoBinding.
If the server finds that the information for the client does not
match what is in the servers records for that client the server
should send back an empty IA with status set to Conf_NoMatch.
If the server finds a match to the Confirm then the server should
send back the IA to the client with status set to success.
13.4.3. Receipt of Renew messages
Upon the receipt of a valid Renew message from a client the server
can respond to, (implementation-specific administrative policy
satisfied) the server scans the options field.
The server then constructs a Reply message and sends it to the
client.
The server SHOULD process each option for the client in an
implementation-specific manner. The server MUST construct a Reply
message containing the following values:
msg-type REPLY
preference Enter the servers preference to
provide services to the client.
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transaction-ID Enter the transaction-ID from the
Confirm message.
client-link-local address Enter the client-link-local address
from the Confirm message.
server address Enter the server's address.
When the server receives a Renew and IA option from a client it
SHOULD locate the clients binding and verify the information in the
IA from the client matches the information stored for that client.
If the server cannot find a client entry for this IA the server
SHOULD return an empty IA with status set to NoBinding.
If the server finds that the addresses in the IA for the client do
not match the clients binding the server should return an empty IA
with status set to Renw_NoMatch.
If the server cannot Renew addresses for the client it SHOULD send
back an empty IA to the client with the status field set to Unavail.
If the server finds the addresses in the IA for the client then the
server SHOULD send back the IA to the client with new lease times
and T1/T2 times if the default is not being used, and set status to
Success.
13.4.4. Receipt of Rebind messages
Upon the receipt of a valid Rebind message from a client the server
can respond to, (implementation-specific administrative policy
satisfied) the server scans the options field.
The server then constructs a Reply message and sends it to the
client.
The server SHOULD process each option for the client in an
implementation-specific manner. The server MUST construct a Reply
message containing the following values:
msg-type REPLY
preference Enter the servers preference to
provide services to the client.
transaction-ID Enter the transaction-ID from the
Confirm message.
client-link-local address Enter the client-link-local address
from the Confirm message.
server address Enter the server's address.
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When the server receives a Rebind and IA option from a client it
SHOULD locate the clients binding and verify the information in the
IA from the client matches the information stored for that client.
If the server cannot find a client entry for this IA the server
SHOULD return an empty IA with status set to NoBinding.
If the server finds that the addresses in the IA for the client do
not match the clients binding the server should return an empty IA
with status set to Rebd_NoMatch.
If the server cannot Rebind addresses for the client it SHOULD send
back an empty IA to the client with the status field set to Unavail.
If the server finds the addresses in the IA for the client then the
server SHOULD send back the IA to the client with new lease times
and T1/T2 times if the default is not being used, and set status to
Success.
13.4.5. Receipt of Release messages
Upon the receipt of a valid Release message, the server examines the
IAs and the addresses in the IAs for validity. If the IAs in the
message are in a binding for the client and the addresses in the IAs
have been assigned by the server to those IA, the server deletes
the addresses from the IAs and makes the addresses available for
assignment to other clients.
The server then generates a Reply message. If all of the IAs were
valid and the addresses successfully released,, the server sets the
"status" field to "Success". If any of the IAs were invalid or if
any of the addresses were not successfully released, the server
releases none of the addresses in the message and sets the "status"
field to "NoBinding"(section 7.4).
DISCUSSION:
What is the behavior of the server relative to a "partially
released" IA; i.e., an IA for which some but not all
addresses are released?
Can a client send an empty IA to release all addresses in
the IA?
If the IA becomes empty - all addresses are released - can
the server discard any record of the IA?
13.4.6. Sending of Reply messages
If the Request, Confirm, Renew, Rebind or Release message from
the client was originally received by the server, the server
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unicasts the Reply message to the link-local address in the
"client-link-local-address" field.
If the message was originally received in a Forward-request or
Forward-release message from a relay, the server places the Reply
message in the options field of a Response-reply message and unicasts
the message to the relay's address from the original message.
14. DHCP Server-Initiated Configuration Exchange
A server initiates a configuration exchange to force DHCP clients
to obtain new addresses and other configuration information. For
example, an administrator may use a server-initiated configuration
exchange when links in the DHCP domain are to be renumbered. Other
examples include changes in the location of directory servers,
addition of new services such as printing, and availability of new
software (system or application).
14.1. Reconfigure-init Message Validation
Agents MUST silently discard any received Reconfigure-init messages.
Clients MUST discard any Reconfigure-init messages that do
not contain an authentication option or that fail the client's
authentication check.
Clients MUST discard any Reconfigure-init messages that contain a
transaction-ID that matches the transaction-ID in a Reconfigure-init
message previously received from the same DHCP server.
14.2. Server Behavior
A server sends a Reconfigure-init message to trigger a client to
initiate immediately a Request/Reply message exchange with the
server. A server may unicast a Reconfigure-init message directly
to a single client or use multicast to deliver a Reconfigure-init
message to multiple clients.
14.2.1. Creation and sending of Reconfigure-init messages
The server sets the "msg-type" field to RECONFIG. The server
generates a transaction-ID and inserts it in the "transaction-ID"
field. The server places its address (of appropriate scope) in the
"server-address" field.
The server MAY include an ORO option to inform the client of what
information has been changed or new information that has been added.
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The server MUST include an authentication option with the appropriate
settings and add that option as the last option in the "options"
field of the Reconfigure-init message.
The server MAY include a Reconfigure-delay option in a
Reconfigure-init message to be unicast to a client, and MUST
include a Reconfigure-delay option in a Reconfigure-init message to
be multicast to a group of clients.
The server MUST NOT include any other options in the Reconfigure-init
except as specifically allowed in the definition of individual
options.
The server may either unicast the Reconfigure-init message to one
client or multicast the message to one or more Reconfigure Multicast
Addresses previously sent as options to the clients. The server
may unicast Reconfigure-init messages to more than one client
concurrently; for example, to reliably reconfigure all clients, the
server will unicast a Reconfigure-init message to each client.
If the server unicasts to one or more clients, it waits for a Request
message from those clients confirming that it has received the
Reconfigure-init and are thus initiating a Request/Reply transaction
with the server. The server can determine that a Request message is
in response to a Reconfigure-init because the transaction-ID in the
Request will be the same value as was used in the Reconfigure-init
message.
If the server multicasts the Reconfigure-init message, it must use
some TBD authentication mechanism that can authenticate the server to
multiple clients. There is no reliability mechanism for multicast
Reconfigure-init messages. A server might use multicast in the
case where it does not have a list of its clients; for example, a
server that distributes configuration information to clients using
stateless autoconfiguration might not keep a list of clients it has
communicated with.
DISCUSSION:
Authentication of multicast reconfigure-init is still an
open issue.
See section 18.2 for recommendations on the use of multicast
and unicast Reconfigure-init messages for reliable client
reconfiguration.
14.2.2. Time out and retransmission of unicast Reconfigure-init messages
If the server does not receive a Request message from the client
in RECREP_MSG_TIMEOUT milliseconds, the server retransmits
the Reconfigure-init message, doubles the RECREP_MSG_TIMEOUT
value and waits again. The server continues this process until
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REC_MSG_ATTEMPTS unsuccessful attempts have been made, at which point
the server SHOULD abort the reconfigure process.
Default and initial values for RECREP_MSG_TIMEOUT and
REC_MSG_ATTEMPTS are documented in section 7.5.
14.2.3. Time out and retransmission of multicast Reconfigure-init
messages
After the server transmits the initial Reconfigure-init message,
the server waits RECREP_MSG_TIMEOUT milliseconds. The server
then retransmits the Reconfigure-init message, doubles the
RECREP_MSG_TIMEOUT value and waits again. The server repeats this
process until a total of REC_MSG_ATTEMPTS Reconfigure-init messages
have been transmitted.
Default and initial values for RECREP_MSG_TIMEOUT and
REC_MSG_ATTEMPTS are documented in section 7.5.
14.2.4. Receipt of Request messages
The server generates and sends Reply message(s) to the client as
described in section 13.4.6, including in the "option" field new
values for configuration parameters.
14.3. Client Behavior
A client MUST always monitor UDP port 546 for Reconfigure-init
messages on interfaces upon which it has acquired DHCP parameters.
Since the results of a reconfiguration event may affect application
layer programs, the client SHOULD log these events, and MAY notify
these programs of the change through an implementation-specific
interface.
14.3.1. Receipt of Reconfigure-init messages
Upon receipt of a valid Reconfigure-init message, the client
initiates a Request/Reply transaction with the server.
14.3.2. Creation and sending of Request messages
When responding to a Reconfigure-init, the client creates and
sends the Request message in exactly the same manner as outlined in
section 13.3.1 with the following differences:
transaction-ID The client copies the
transaction-ID from the
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Reconfigure-init message into the
Request message.
IAs The client includes IA options
containing the addresses the client
currently has assigned to those IAs
for the interface through which
the Reconfigure-init message was
received.
Pause before sending Request The client pauses before sending
the Request for a random value
within the range REC_REP_MIN and
REC_REP_MAX seconds. This delay
helps reduce the load on the
server generated by processing
large numbers of triggered
Request messages from a multicast
Reconfigure-init message.
14.3.3. Time out and retransmission of Request messages
The client uses the same variables and retransmission algorithm as it
does with Request messages generated as part of a client-initiated
configuration exchange. See section 13.3.1 for details.
14.3.4. Receipt of Reply messages
Upon the receipt of a valid Reply message, the client extracts the
contents of the "option" field, and sets (or resets) configuration
parameters appropriately. The client records and updates the
lifetimes for any addresses specified in IAs in the Reply message.
If the configuration parameters changed were requested by the
application layer, the client notifies the application layer of the
changes using an implementation-specific interface.
15. Relay Behavior
For this discussion, the Relay may be configured to use a list of
server destination addresses, which may include unicast addresses,
the All DHCP Servers multicast address, or other multicast addresses
selected by the network administrator. If the Relay has not been
explicitly configured, it will use the All DHCP Servers multicast
address as the default.
15.1. Relaying of client messages
When a Relay receives a valid client message, it constructs
a Relay-forward message. The relay places an address from
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the interface on which the client message was received in the
"relay-address" field and the prefix length for that address in the
"prefix-length" field. This address will be used by the server to
identify the link to which the client is connected and will be used
by the relay to forward the Advertise message from the server back to
the client.
The relay constructs a "client-message" option 16.4 that contains
the entire message from the client in the data field of the
option. The relay places the "relay-message" option along with any
"relay-specific" options in the options field of the Relay-forward
message. The Relay then sends the Relay-forward message to the list
of server destination addresses that it has been configured with.
15.2. Relaying of server messages
When the relay receives a Relay-reply message, it extracts the server
message from the "server-message" option and forwards the message
to the address in the client-link-local-address field in the server
message. The relay forwards the server message through the interface
identified in the "relay-address" field in the Relay-reply message.
16. DHCP options
Options are used to carry additional information and parameters
in DHCP messages. Every option shares a common base format, as
described in section 16.1.
this document describes the DHCP options defined as part of the base
DHCP specification. Other options may be defined in the future in a
separate document.
16.1. Format of DHCP options
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-code | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-data |
| (option-len octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code An unsigned integer identifying the specific option
type carried in this option.
option-len An unsigned integer giving the length of the data in
this option in octets.
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option-data The data for the option; the format of this data
depends on the definition of the option.
16.2. Identity association option
The identity association option is used to carry an identity
association, the parameters associated with the IA and the addresses
assigned to the IA.
The format of the IA option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION IA | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IA DUID |
| (8 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IA status | num-addrs | addr status | prefix length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 address |
| (16 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| preferred lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| valid lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| addr status | prefix length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| IPv6 address |
| (16 octets) |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | preferred lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| pref. lifetime (cont.) | valid lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| valid lifetime (cont.) | IPv6 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_IA (1)
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option-len Variable; equal to 18 + num-addrs*25
IA DUID The unique identifier for this IA; chosen by the client
T1 The time at which the client contacts the server from
which the addresses in the IA were obtained to extend
the lifetimes of the addresses assigned to the IA.
T2 The time at which the client contacts any available
server to extend the lifetimes of the addresses assigned
to the IA.
IA status Status of the IA in this option.
num-addrs An unsigned integer giving the number of addresses
carried in this IA option (MAY be zero).
addr status Status of this address.
prefix length Prefix length for this address.
IPv6 address An IPv6 address assigned to this IA.
preferred lifetime The preferred lifetime for the associated IPv6
address.
valid lifetime The valid lifetime for the associated IPv6 address.
The "IPv6 address", "preferred lifetime" and "valid lifetime" fields
are repeated for each address in the IA option (as determined by the
"num-addrs" field).
DISCUSSION:
The details of the format and the selection of an IA's DUID
are TBD.
Note that an IA has no explicit "lifetime" or "lease length" of
its own. When the lifetimes of all of the addresses in an IA have
expired, the IA can be considered as having expired. T1 and T2
are included to give servers explicit control over when a client
recontacts the server about a specific IA.
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16.3. Option request option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_ORO | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| requested-option-code-1 | requested-option-code-2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_ORO (2)
option-len Variable; equal to twice the number of option codes
carried in this option.
option-data A list of the option codes for the options requested
in this option.
16.4. Client message option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_CLIENT_MSG | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DHCP client message |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_CLIENT_MSG (3)
option-len Variable; equal to the length of the forwarded DHCP
client message.
option-data The message received from the client; forwarded
verbatim to the server.
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16.5. Server message option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_SERVER_MSG | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DHCP server message |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_SERVER_MSG (4)
option-len Variable; equal to the length of the forwarded DHCP
server message.
option-data The message received from the server; forwarded
verbatim to the client.
16.6. Retransmission parameter option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_RETRANS_PARM | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-data |
| (option-len octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_RETRANS_PARM (5)
option-len An unsigned integer giving the length of the data in
this option in octets.
option-data TBD - The details of the operational parameters to be
set in the client
16.7. Reconfigure-delay option
The Reconfigure-delay option specifies the amount of time a client
should delay before sending a Request message in response to a
Reconfigure-init message.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_RECONF_DELAY | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| minimum delay time (msec) | maximum delay time (msec) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_RECONF_DELAY (6)
option-len An unsigned integer giving the length of the data in
this option in octets.
minimum delay time An unsigned integer giving the minimum delay
time in milliseconds
maximum delay time An unsigned integer giving the maximum delay
time in milliseconds
The client chooses a random number between the minimum delay time and
the maximum delay time and delays that number of milliseconds before
sending its Request message.
16.8. DSTM Global IPv4 Address Option
The DSTM Global IPv4 Address Option informs a client or server that
the Identity Association Option (IA) following this option will
contain an IPv4-Mapped IPv6 Address [7] in the case of a Client
receiving the option, or is a Request for an IPv4-Mapped IPv6 Address
from a client in the case of a DHCPv6 Server receiving the option.
The option can also provide an IPv6 address to be used as the Tunnel
Endpoint (TEP) to encapsulate an IPv4 packet within IPv6.
This option can be used with the Request, Reply, and Reconfigure-Init
Messages for cases where a server wants to assign to clients
IPv4-Mapped IPv6 Addresses, thru the Option Request Option (ORO).
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_DSTM | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tunnel End Point (TEP) |
| (If Present) |
| (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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option code OPTION_DSTM (7)
option length Variable: 0 or 16
tunnel end point IPv6 Address if Present
A DSTM IPv4 Global Address Option MUST only apply to the IA following
this option.
16.9. Authentication option
The authentication option is TBD.
17. DHCP Client Implementor Notes
This section provides helpful information for the client implementor
regarding their implementations. The text described here is not part
of the protocol, but rather a discussion of implementation features
we feel the implementor should consider during implementation.
17.1. Primary Interface
Since configuration parameters acquired through DHCP can be
interface-specific or more general, the client implementor SHOULD
provide a mechanism by which the client implementation can be
configured to specify which interface is the primary interface. The
client SHOULD always query the DHCP data associated with the primary
interface for non-interface specific configuration parameters. An
implementation MAY implement a list of interfaces which would be
scanned in order to satisfy the general request. In either case, the
first interface scanned is considered the primary interface.
By allowing the specification of a primary interface, the client
implementor identifies which interface is authoritative for
non-interface specific parameters, which prevents configuration
information ambiguity within the client implementation.
17.2. Advertise Message and Configuration Parameter Caching
If the hardware the client is running on permits it, the implementor
SHOULD provide a cache for Advertise messages and a cache of
configuration parameters received through DHCP. Providing these
caches prevents unnecessary DHCP traffic and the subsequent load
this generates on the servers. The implementor SHOULD provide a
configuration knob for setting the amount of time the cache(s) are
valid.
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17.3. Time out and retransmission variables
Note that the client time out and retransmission variables outlined
in section 7.5 can be configured on the server and sent to the client
through the use of the "DHCP Retransmission Parameter Option", which
is documented in section 16.6. A client implementation SHOULD be
able to reset these variables using the values from this option.
17.4. Server Preference
A client MUST wait for SRVR_PREF_WAIT seconds after sending a DHCP
Solicit message to collect Advertise messages and compare their
preferences (see section 18.3), unless it receives an Advertise
message with a preference of 255. If the client receives an
Advertise message with a preference of 255, then the client MAY act
immediately on that Advertise without waiting for any more additional
Advertise messages.
18. DHCP Server Implementor Notes
This section provides helpful information for the server implementor.
18.1. Client Bindings
A server implementation MUST use the IA's DUID and the prefix
specification from which the client sent its Request message(s) as an
index for finding configuration parameters assigned to the client.
While it isn't critical to keep track of the other parameters
assigned to a client, the server MUST keep track of the addresses it
has assigned to an IA.
The server should periodically scan its bindings for addresses whose
leases have expired. When the server finds expired addresses, it
MUST delete the assignment of those addresses, thereby making these
addresses available to other clients.
The client bindings MUST be stored in non-volatile storage.
The server implementation should provide policy knobs to control
whether or not the lifetimes on assigned addresses are renewable, and
by how long.
18.2. Reconfigure-init Considerations
A server implementation MUST provide an interface to the
administrator for initiating reconfigure-init events.
A server implementation may provide a mechanism for allowing the
specification of how many clients comprise a reconfigure multicast
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group. This enables the administrator to control the processing load
impact of the multicast of a Reconfigure-init message.
18.2.1. Reliable transmission of multicast Reconfigure-init messages
Because clients will ignore Reconfigure-init messages with the
same transaction-ID, a server can retransmit a Reconfigure-init
message (using the same transaction-ID) without causing any
client to reply more than once. A server SHOULD retransmit a
multicast Reconfigure-init message several times to maximize the
probability that all clients in the multicast group have received the
Reconfigure-init message.
If a server does not receive a Reply message from some clients in a
multicast group, the server MAY choose to unicast a Reconfigure-init
message to those clients. Because the clients may have received the
multicast Reconfigure-init messages while the server did not receive
the clients' Reply messages, the server SHOULD use a different
transaction-ID in the unicast Reconfigure-init messages to trigger
the client to reconfigure.
18.3. Server Preference
The server implementation SHOULD allow the setting of a server
preference value by the administrator. The server preference
variable is an unsigned single octet value (0--255), with the lowest
preference being 0 and the highest 255. Clients will choose higher
preference servers over those with lower preference values. If you
don't choose to implement this feature in your server, you MUST set
the server preference field to 0 in the Advertise messages generated
by your server.
18.4. Request Message Transaction-ID Cache
In order to improve performance, a server implementation MAY include
an in memory transaction-ID cache. This cache is indexed by client
binding and transaction-ID, and enables the server to quickly
determine whether a Request is a retransmission or a new Request
without the cost of a database lookup. If an implementor chooses to
implement this cache, then they SHOULD provide a configuration knob
to tune the lifetime of the cache entries.
19. DHCP Relay Implementor Notes
A relay implementation SHOULD allow the specification of a list of
destination addresses for forwarded messages. This list MAY contain
any mixture of unicast addresses and multicast addresses.
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If a relay receives an ICMP message in response to a DHCP message it
has forwarded, it SHOULD log this event.
20. Open Issues for Working Group Discussion
This section contains some items for discussion by the working group.
20.1. Authentication
Authentication is not discussed in this document. Authentication
will be modeled on DHCPv4 authentication. Authentication of
multicast Reconfigure-init messages is a special problem.
20.2. Identification of IAs by servers
Do servers identify an IA just by its DUID or by <prefix, DUID>? If
just by DUID, are DUIDs guaranteed unique (within the DHCP universe)?
If so, how is that guarantee implemented?
20.3. DHCP-DNS interaction
Interaction among DHCP servers, clients and DNS servers is not
discussed in this document.
20.4. Temporary addresses
How does DHCPv6 interact with temporary addresses? If the server
assigns temporary addresses (e.g., addresses with short lifetimes),
how can a client application choose an temporary address as a source
address in preference to a non-temporary address?
20.5. Use of term "agent"
The term "agent", taken to mean "relay agent or server", may be
confusing. "relay agent or server" might be clearer.
20.6. Client behavior when response to Rebind is not received
Section 13.3.4 describes several plausible ways in which a client
might respond when it does not receive a Reply to a Rebind message.
The acceptable client behaviors need to be defined and described
in 13.3.4.
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20.7. Additional options
Which additional options should be included in this base spec
document?
20.8. Operational parameters
Should servers have an option to set operational parameters -
retransmission timeouts, number of retries - in clients?
21. Security
This document references an "authentication option" which is TBD.
DISCUSSION:
Based on the discussion of security issues at the 8/31/00
design team teleconference and subsequent DHC WG mailing
list discussion, DHCPv6 will use the security model from
DHCPv4, as described in draft-ietf-dhc-authentication-16.txt
(which is soon to be an RFC).
22. Year 2000 considerations
Since all times are relative to the current time of the transaction,
there is no problem within the DHCPv6 protocol related to any
hardcoded dates or two-digit representation of the current year.
23. IANA Considerations
This document defines message types TBD to be received by UDP at port
numbers 546 and 547. Additional message types may be defined in the
future.
Section 7.1 lists several multicast addresses used by DHCP.
This document also defines several status codes that are to be
returned with the Reply message (see section 9.7). The non-zero
values for these status codes which are currently specified are shown
in the table in section 7.4.
There is a DHCPv6 option described in section 16.6, which allows
clients and servers to exchange values for some of the timing
and retransmission parameters defined in section 7.5. Adding new
parameters in the future would require extending the values by which
the parameters are indicated in the DHCP option. Since there needs
to be a list kept, the default values for each parameter should also
be stored as part of the list.
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All of these protocol elements may be specified to assume new values
at some point in the future. New values should be approved by the
process of IETF Consensus [9].
24. Acknowledgments
Thanks to the DHC Working Group for their time and input into the
specification. Ralph Droms and Thomas Narten have had a major
role in shaping the continued improvement of the protocol by their
careful reviews. Many thanks to Matt Crawford, Erik Nordmark, Gerald
Maguire, and Mike Carney for their studied review as part of the
Last Call process. Thanks also for the consistent input, ideas, and
review by (in alphabetical order) Brian Carpenter, Jack McCann, Yakov
Rekhter, Matt Thomas, Sue Thomson, and Phil Wells.
Thanks to Steve Deering and Bob Hinden, who have consistently
taken the time to discuss the more complex parts of the IPv6
specifications.
A. Comparison between DHCPv4 and DHCPv6
This appendix is provided for readers who will find it useful to see
a model and architecture comparison between DHCPv4 [6, 1] and DHCPv6.
There are three key reasons for the differences:
o IPv6 inherently supports a new model and architecture for
communications and autoconfiguration of addresses.
o DHCPv6 benefits from the new IPv6 features.
o New features were added to support the expected evolution and
the existence of more complicated Internet network service
requirements.
IPv6 Architecture/Model Changes:
o The link-local address permits a node to have an address
immediately when the node boots, which means all clients have a
source IP address at all times to locate an on-link server or
relay.
o The need for BOOTP compatibility and the broadcast flag have been
removed.
o Multicast and address scoping in IPv6 permit the design of
discovery packets that would inherently define their range by the
multicast address for the function required.
o Stateful autoconfiguration has to coexist and integrate with
stateless autoconfiguration supporting Duplicate Address
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Detection and the two IPv6 lifetimes, to facilitate the dynamic
renumbering of addresses and the management of those addresses.
o Multiple addresses per interface are inherently supported in
IPv6.
o Some DHCPv4 options are unnecessary now because the configuration
parameters are either obtained through IPv6 Neighbor Discovery or
the Service Location protocol [14].
DHCPv6 Architecture/Model Changes:
o The message type is the first octet in the packet.
o IPv6 Address allocations are now handled in a message option as
opposed to the message header.
o Client/Server bindings are now mandatory and take advantage of
the client's link-local address to always permit communications
either directly from an on-link server, or from a off-link server
through an on-link relay.
o Servers are discovered by a client Solicit, followed by a server
Advertise message
o The client will know if the server is on-link or off-link.
o The on-link relay may locate off-link server addresses from
system configuration or by the use of a site-wide multicast
packet.
o ACKs and NAKs are not used.
o The server assumes the client receives its responses unless it
receives a retransmission of the same client request. This
permits recovery in the case where the network has faulted.
o Clients can issue multiple, unrelated Request messages to the
same or different servers.
o The function of DHCPINFORM is inherent in the new packet design;
a client can request configuration parameters other than IPv6
addresses in the optional option headers.
o Clients MUST listen to their UDP port for the new Reconfigure
message from servers.
o New options have been defined.
With the changes just enumerated, we can support new user features,
including
o Configuration of Dynamic Updates to DNS
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o Address deprecation, for dynamic renumbering.
o Relays can be preconfigured with server addresses, or use of
multicast.
o Authentication
o Clients can ask for multiple IP addresses.
o Addresses can be reclaimed using the Reconfigure-init message.
o Integration between stateless and stateful address
autoconfiguration.
o Enabling relays to locate off-link servers.
B. Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However,
this document itself may not be modified in any way, such as by
removing the copyright notice or references to the Internet Society
or other Internet organizations, except as needed for the purpose
of developing Internet standards in which case the procedures
for copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
C. Changes in this draft
This section describes the changes between this version of the DHCPv6
specification and draft-ietf-dhc-dhcpv6-16.txt.
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C.1. New messages for confirming addresses and extending the lease on an
IA
Four new messages, DHCP Confirm, DHCP Renew, DHCP Rebind and DHCP
Decline, have been added and are described in section 13. Client
behavior - when and how to send these new messages - and server
behavior - how to respond to each - has been defined. The message
type codes for these messages have been added to section 7.3.
C.2. New message formats
Section 9 has been restructured to include only one copy of the DHCP
message header, because now all the messages have the same header
format. Descriptions of the use of header fields in the Confirm,
Renew, Rebind and Decline messages have been added to 9.
C.3. Renamed Server-forward message
Section 10.2 has been renamed "relay-reply" for consistency with the
rest of the document
C.4. Clarified relay forwarding of messages
Added text to sections on relay behavior to clarify encapsulation and
decapsulation of client messages in Relay-forward and Relay-reply
messages.
C.5. Addresses and options in Advertise messages
Modified section 12.4.2 so that servers include addresses to be
assigned and other options in Advertise messages. Also added text to
section 12.3.1 to disallow option values (except as noted in option
definitions) in Solicit messages.
C.6. Clarification of IA option format
Changed the label of the prefix length field in an IA option to
"prefix length" in the option format diagram, and moved the prefix
before the address for consistency with relay messages and other IPv6
protocols.
C.7. Specification of transaction ID in Solicit message
Add text (which was missing) to specify the insertion of a
transaction ID in Solicit messages.
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C.8. Edits to definitions
Some of the definitions in section 6 have been edited for clarity.
C.9. Relay agent messages
The formats of relay agent messages are now described in a separate
section, 10.
C.10. Relay agent behavior
The behavior of relay agents for all client and server messages is
now described in a single section, 15.
C.11. Transmission of all client messages through relays
All client messages are now multicast to the All Agents multicast
address and forwarded by relays as appropriate.
C.12. Reconfigure-init messages
Client behavior in response to a Reconfigure-init messages has
been extended to accommodate receipt of multiple copies of a
Reconfigure-init message due to duplicate messages or retransmission.
Server use of multicast Reconfigure-init has been specified.
Hints about use of multicast and unicast for reliable reconfiguration
have been added to server implementor's hints.
C.13. Ordering of sections
Several sections have been re-ordered for clarity.
C.14. DSTM option
The DSTM option has been added (section 16.8).
C.15. Message and option numbering
(In rev -18) Replaced TBD for message and option code numbering with
names and temporary values.
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C.16. Inclusion of IAs in Solicit message by client
Added text to section 12.3.1 explaining that clients include empty
IA(s) in a Solicit message and to section 12.3.3 explaining that
server advertises addresses in client IAs.
C.17. Clarification of destination of client messages
Added text to section 13 clarifying the destination (specific server
or any available server) of client messages
C.18. Clarification of client use of Confirm messages
Changed text in section 13.3.2 to correctly describe behavior of
clients in response to Replay messages from servers.
References
[1] S. Alexander and R. Droms. DHCP Options and BOOTP Vendor
Extensions. Request for Comments (Draft Standard) 2132,
Internet Engineering Task Force, March 1997.
[2] S. Bradner. Key words for use in RFCs to Indicate Requirement
Levels. Request for Comments (Best Current Practice) 2119,
Internet Engineering Task Force, March 1997.
[3] S. Bradner and A. Mankin. The Recommendation for the IP Next
Generation Protocol. Request for Comments (Proposed Standard)
1752, Internet Engineering Task Force, January 1995.
[4] W. J. Croft and J. Gilmore. Bootstrap Protocol. Request for
Comments 951, Internet Engineering Task Force, September 1985.
[5] S. Deering and R. Hinden. Internet Protocol, Version 6 (IPv6)
Specification. Request for Comments (Draft Standard) 2460,
Internet Engineering Task Force, December 1998.
[6] R. Droms. Dynamic Host Configuration Protocol. Request for
Comments (Draft Standard) 2131, Internet Engineering Task Force,
March 1997.
[7] R. Hinden and S. Deering. IP Version 6 Addressing Architecture.
Request for Comments (Proposed Standard) 2373, Internet
Engineering Task Force, July 1998.
[8] J. McCann, S. Deering, and J. Mogul. Path MTU Discovery for
IP version 6. Request for Comments (Proposed Standard) 1981,
Internet Engineering Task Force, August 1996.
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[9] T. Narten and H. Alvestrand. Guidelines for Writing an IANA
Considerations Section in RFCs. Request for Comments (Best
Current Practice) 2434, Internet Engineering Task Force, October
1998.
[10] T. Narten, E. Nordmark, and W. Simpson. Neighbor Discovery for
IP Version 6 (IPv6). Request for Comments (Draft Standard)
2461, Internet Engineering Task Force, December 1998.
[11] D. C. Plummer. Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet address
for transmission on Ethernet hardware. Request for Comments
(Standard) 826, Internet Engineering Task Force, November 1982.
[12] J. Postel. User Datagram Protocol. Request for Comments
(Standard) 768, Internet Engineering Task Force, August 1980.
[13] S. Thomson and T. Narten. IPv6 Stateless Address
Autoconfiguration. Request for Comments (Draft Standard) 2462,
Internet Engineering Task Force, December 1998.
[14] J. Veizades, E. Guttman, C. Perkins, and S. Kaplan. Service
Location Protocol. Request for Comments (Proposed Standard)
2165, Internet Engineering Task Force, June 1997.
[15] P. Vixie, Ed., S. Thomson, Y. Rekhter, and J. Bound. Dynamic
Updates in the Domain Name System (DNS UPDATE). Request for
Comments (Proposed Standard) 2136, Internet Engineering Task
Force, April 1997.
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Chair's Address
The working group can be contacted via the current chair:
Ralph Droms
Cisco Systems
300 Apollo Drive
Chelmsford, MA 01824
Phone: (978) 244-4733
E-mail: rdroms@cisco.com
Author's Address
Questions about this memo can be directed to:
Jim Bound
Nokia Networks
5 Wayside Road
Burlington, MA 01803
USA
Phone: +1-781-492-6010
Email: jim.bound@nokia.com
Mike Carney
Sun Microsystems, Inc
Mail Stop: UMPK17-202
901 San Antonio Road
Palo Alto, CA 94303-4900
USA
Phone: +1-650-786-4171
Email: mwc@eng.sun.com
Charles E. Perkins
Communications Systems Lab
Nokia Research Center
313 Fairchild Drive
Mountain View, California 94043
USA
Phone: +1-650 625-2986
EMail: charliep@iprg.nokia.com
Fax: +1 650 625-2502
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