Network Working Group R. Droms
Internet-Draft Cisco Systems
Expires: April 24, 2003 October 24, 2002
A Guide to Implementing Stateless DHCPv6 Service
draft-droms-dhcpv6-stateless-guide-01.txt
Status of this Memo
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.
This Internet-Draft will expire on April 24, 2003.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
Stateless DHCPv6 service is used by hosts to obtain configuration
information such as the addresses of DNS servers that does not
require the maintenance of any dynamic state for individual clients.
A host that uses stateless DHCP must have obtained its IPv6 addresses
through some other mechanism, typically stateless address
autoconfiguration. This document is a guide to the protocol messages
and options that must be implemented to provide stateless DHCPv6
service.
1. Introduction
Hosts that have obtained IPv6 addresses through some other mechanism
Droms Expires April 24, 2003 [Page 1]
Internet-Draft Stateless DHCPv6 Implementation Guide October 2002
can use stateless DHCPv6 to obtain other configuration information
such as a list of DNS server or NTP servers. A stateless DHCPv6
server provides only configuration information to hosts and does not
perform any address assignment. Such a server is called "stateless"
because it need not maintain any dynamic state for individual
clients.
While the DHCPv6 specification [3] defines more than 10 protocol
messages and 20 options, only a subset of those messages and options
are required for stateless DHCPv6 service. This document gives
guidelines about which messages and options are required for
stateless DHCPv6 service. The intended use of the document is to
guide the efficient and complete implementation of clients and
servers that use stateless DHCPv6 service.
The operation of relay agents is the same for stateless and stateful
DHCPv6 service. The operation of relay agents is described in the
DHCPv6 specification.
Section 4 of this document lists the sections of the DHCPv6 document
that an implementor should read for an overview of the DHCPv6
specification and the basic requirements of a DHCPv6 service.
Section 5 lists the specific messages and options that are
specifically required for stateless DHCPv6 service. Section 6
describes how stateless and stateful DHCPv6 servers interact to
provide service to clients that require address assignment and
clients that require only stateless service.
2. Terminology
Throughout this document, "DHCP" refers to DHCP for IPv6.
This document uses the terminology defined in RFC2460 [1], the DHCP
specification, the DHCP DNS configuration options specification [4]
and the DHCP NTP configuration options specification [5]..
"Stateless DHCP" refers to the use of DHCP to provide configuration
information to clients that does not require the server to maintain
dynamic state about the DHCP clients.
3. Overview
This document assumes that a host using stateless DHCP configuration
is not using DHCP for address assignment, and that a host has
determined at least a link-local address as described in section 5.3
of RFC2461 [2]
To obtain configuration parameters through stateless DHCP, a host
Droms Expires April 24, 2003 [Page 2]
Internet-Draft Stateless DHCPv6 Implementation Guide October 2002
uses the DHCP Information-request message. DHCP servers respond to
the host's message with a Reply message that carries the DNS
configuration parameters. The Reply message from the server can
carry configuration information such as a list of DNS servers and NTP
servers.
4. Basic Requirements for Implementation of DHCP
Several sections of the DHCP specification [3] provide background
information or define parts of the specification that are common to
all implementations:
1-4 - give an introduction to DHCPv6 and an overview of DHCP
message flows
5 - defines constants used throughout the protocol specification
6, 7 - illustrates the format of DHCP messages
8 - describes the representation of Domain Names
9 - defines the "DHCP unique identifier" (DUID) used to identify
DHCP participants
13-16 - describe DHCP message transmission, retransmission and
validation
21 - describes authentication for DHCP
5. Implementation of stateless DHCP
The client indicates that it is requesting configuration information
by sending an Information-request message that includes an Option
Request option specifying the options that it wishes to receive from
the DHCP server. For example, if the client is attempting to obtain
DNS configuration information, it includes either or both of the DNS
configuration options in the Information-request message. The server
determines the appropriate configuration parameters for the client
based on its configuration policies and responds with a Reply message
containing the requested parameters. In this example, the server
would respond with DNS configuration parameters.
Use of the Client DUID option and the Server DUID option are not
required for stateless DHCP service. However, it can be beneficial
for the client to include a client DUID option, because the server
administrator may want to customize the server's response on a per-
client basis, and this requires that the client identify itself.
Droms Expires April 24, 2003 [Page 3]
Internet-Draft Stateless DHCPv6 Implementation Guide October 2002
5.1 Messages required for stateless DHCP
Clients and servers implement the following messages for stateless
DHCP service; the section numbers in this list refer to the DHCPv6
specification:
Information-request: sent by a DHCP client to a server to request DNS
configuration parameters (sections 18.1.5 and 18.2.5)
Reply: sent by a DHCP server to a client containing the
DNS configuration parameters (sections 18.1.6 and 18.2.8)
In addition, servers and relay agents implement the following
messages for stateless DHCP service:
Relay-forward: Sent by a DHCP relay agent to carry the client message
to a server (section 15.13)
Relay-reply: Sent by a DHCP server to carry a response message to
the relay agent (section 15.14)
5.2 Options required for stateless DHCP service
Clients and servers implement the following options for stateless
DHCP service; the section numbers in this list refer to the DHCPv6
specification:
Option Request: specifies the configuration information that the
client is requesting from the server (section 22.7)
Status Code: used to indicate completion status or other status
information (section 22.13)
Servers and relay agents implement the following options for
stateless DHCP service; the section numbers in this list refer to the
DHCPv6 specification:
Client message: Sent by a DHCP relay agent in a Relay-forward message
to carry the client message to a server (section 20)
Server message: Sent by a DHCP server in a Relay-reply message to
carry a response message to the relay agent (section 20)
Interface-ID: Sent by the DHCP relay agent and returned by the
server to identify the interface to use to forward a message to
the client (section 22.18)
Droms Expires April 24, 2003 [Page 4]
Internet-Draft Stateless DHCPv6 Implementation Guide October 2002
5.3 Options used for configuration information
Clients and servers use the following options to pass configuration
information to clients:
DNS Server: specifies the DNS servers the client uses for name
resolution; see "DNS Configuration options for DHCPv6"
DNS search list: specifies the domain names to be searched during
name resolution; see "DNS Configuration options for DHCPv6"
NTP Servers: specifies the NTP servers the client uses for
synchronizing its clock; see "Time Configuration Options for
DHCPv6"
5.4 Other options used in stateless DHCP
Clients and servers may implement the following options for stateless
DHCP service; the section numbers in this list refer to the DHCPv6
specification [3]:
Preference: Sent by a DHCP server to indicate the preference
level for the server (section 22.8)
Elapsed time: Sent by a DHCP client to indicate the time since the
client began the DHCP configuration process (section 22.9)
User Class: Sent by a DHCP client to give additional information
to the server for selecting configuration parameters for the
client (section 22.15)
Vendor Class: Sent by a DHCP client to give additional information
about the client vendor and hardware to the server for selecting
configuration parameters for the client (section 22.16)
Vendor-specific Information: Sent by a DHCP server to pass
information to clients in options defined by vendors (section
22.17)
Client DUID: Sent by a DHCP client to identify itself (section
22.2). Clients are not required to send this option; servers
never send this option
Authentication: Used to provide authentication of DHCP messages
(section 21)
Droms Expires April 24, 2003 [Page 5]
Internet-Draft Stateless DHCPv6 Implementation Guide October 2002
6. Interaction with DHCP for Address Assignment
In some networks, there may be both clients that are using stateless
address autoconfiguration and DHCP for DNS configuration and clients
that are using DHCP for stateful address configuration. Depending on
the deployment and configuration of relay agents, DHCP servers that
are intended only for stateless configuration may receive messages
from clients that are performing stateful address configuration.
A DHCP server that is only able to provide stateless configuration
information through an Information-request/Reply message exchange
discards any other DHCP messages it receives. Specifically, the
server discards any messages other than Information-Request or Relay-
forward it receives, and the server does not participate in any
stateful address configuration messages exchanges. If there are
other DHCP servers that are configured to provide stateful address
assignment, one of those servers will provide the address assignment.
7. Acknowledgments
Ted Lemon, Bernie Volz and Jim Bound reviewed this document and
contributed editorial suggestions.
References
[1] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
[2] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for
IP Version 6 (IPv6)", RFC 2461, December 1998.
[3] Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R.
Droms (ed.), "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", draft-ietf-dhc-dhcpv6-27 (work in progress), October
2002.
[4] Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R.
Droms, "DNS Configuration options for DHCPv6", draft-ietf-dhc-
dhcpv6-opt-dnsconfig-01 (work in progress), October 2002.
[5] Vijayabhaskar, A., "Time Configuration Options for DHCPv6",
draft-ietf-dhc-dhcpv6-opt-timeconfig-00 (work in progress),
February 2002.
[6] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
November 1998.
Droms Expires April 24, 2003 [Page 6]
Internet-Draft Stateless DHCPv6 Implementation Guide October 2002
Author's Address
Ralph Droms
Cisco Systems
300 Apollo Drive
Chelmsford, MA 01824
USA
Phone: +1 978 497 4733
EMail: rdroms@cisco.com
Droms Expires April 24, 2003 [Page 7]
Internet-Draft Stateless DHCPv6 Implementation Guide October 2002
Full Copyright Statement
Copyright (C) The Internet Society (2002). 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.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Droms Expires April 24, 2003 [Page 8]